Electrocatalytic potentials of biochars derived from Dioscorea bulbifera peel for hydrogen evolution reactions- experimental and tight binding quantum chemical study.

Amorphous Molybdenum Sulfide Deposited Graphene Liquid Crystalline Fiber for Hydrogen Evolution Reaction Catalysis

A new Ag(I) complex with the chemical composition, [Ag4(BBP)2(H2ebidc)]·4H2O (BBP = 1,3-bis(1H-benzimidazol-2-yl)propane, H6ebidc = 2,2’-(ethane-1,2-diyl)bis(1H-imidazole-4,5-dicarboxylic acid), was successfully synthesized by hydrothermal method and characterized by X-ray single crystal diffraction, elemental analysis, and infrared and ultraviolet spectroscopy. Crystallographic analysis revealed that the Ag(I) complex has a tetranuclear ring cluster structure, which are connected by π…π (d = 3.641 Å) interactions to form a one-dimensional supramolecular structure. The performance of electrocatalytic hydrogen evolution reaction (HER) of Ag(I) complex-modified carbon paste electrode (1-CPE) and bare electrode (sCPE) were investigated. In 0.5 M H2SO4 with current density of 10 mA·cm−2, compared to sCPE, 1-CPE exhibited excellent electrocatalytic performance, with a positive shift of the overpotential (η10) by 478 mV and a reduction of the Tafel slope (b) by 95 mV·dec−1. The Nyquist plot of 1-CPE at −0.65 V has significantly smaller semicircle diameter in the high frequency region than sCPE, which indicated that it possessed less charge transfer resistance at the electrode surface as HER catalyst. The 1-CPE exhibited better electrocatalytic performance than the sCPE, presumably because the presence of Ag(I) complex improved the electrocatalytic performance of HER. This further confirms the potential value of Ag(I) complex as electrochemical materials.

Anion-Modulated Platinum for High-Performance Multifunctional Electrocatalysis toward HER, HOR, and ORR.

The increasing energy demand, driven by industrialization and global population growth, has increased the focus on developing clean and sustainable energy sources [1]. Hydrogen (H2) has emerged as a promising alternative to carbon-based fuels due to its low cost, higher calorific value, and absence of pollution emissions [2]. Electrochemical water splitting has recently gained prominence as a highly attractive technique for efficient hydrogen production [3]. Therefore, the development of efficient and cost-effective catalysts for the hydrogen evolution reaction (HER) is crucial for advancing energy conversion and storage technologies [2]. The layered double hydroxides (LDHs) have emerged as promising non-noble metal catalysts for HER due to their unique composition and structural features, making them efficient and stable catalysts [4]. Indeed, copper (Cu)-based materials exhibit high electrical conductivity, the CuFe-LDH has been reported as an interesting electrocatalyst since iron (Fe) can enhance the reactivity in the HER process [5]. Likewise, cobalt (Co)-based catalysts emerge as potential alternatives to noble-metal catalysts in water-splitting applications, attributed to the high redox potential of Co species, cost-effectiveness, and stability in both acidic and basic environments [6]. Moreover, in binary LDHs, introducing a third metal ion has been shown to change the electronic structure and improve conductivity; hence, providing more active sites and facilitating a fast electron transfer process [7]. However, the LDHs as electrocatalysts are limited by their poor electronic conductivity and tendency for agglomeration. On the other hand, graphene (G), a single layer of carbon atoms arranged in a hexagonal lattice, serves as an excellent supporting matrix for LDHs due to its exceptional electronic conductivity and high surface area, facilitating efficient electron transfer during the water-splitting reaction [8]. Therefore, in this work, CoCuFe-LDH composites were synthesised and grown on graphene through a cost-effective and straightforward one-step hydrothermal process. Experiments were conducted to assess the electrocatalytic properties of the trimetallic CoCuFe-LDH/G and its binary counterparts to investigate how each component affected the electrochemical performance and HER activity. The onset potential and Tafel slope were selected as the basis for characterising the catalytic performance of the materials. The linear sweep voltammetry (LSV) curves of CoCuFe-LDH/G composites for HER are shown in Figure 1. It can be observed that the trimetallic Co[1.5]Cu[3]Fe[3]-LDH/G[10] shows the lowest onset potential at -0.39 V with a Tafel slope of 76.58 mV dec-1, compared to its binary counterparts. While CuFe-LDH/G shows the highest onset potential (-0.52 V) and Tafel slope (115.56 mVdec-1), indicating that Co plays an important role in the HER performance. Furthermore, the trimetallic composite demonstrated favourable electronic properties, with a charge transfer resistance (RCT) of 486.6 Ω, and exhibited good stability without significant loss of catalytic activity over 24 h. Therefore, this study provides a facile and efficient strategy to design a trimetallic LDH electrocatalyst combined with graphene, demonstrating that the conductive nanoflake structure established by graphene provides a sufficient electron supply to the composite during the electrocatalytic process, enhancing the HER activity.

Open AccessCCS ChemistryRESEARCH ARTICLE25 May 2022Controlled Growth Interface of Charge Transfer Salts of Nickel-7,7,8,8-Tetracyanoquinodimethane on Surface of Graphdiyne Yuxin Liu, Yang Gao, Feng He, Yurui Xue and Yuliang Li Yuxin Liu Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 University of Chinese Academy of Sciences, Beijing 100049 , Yang Gao Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 University of Chinese Academy of Sciences, Beijing 100049 , Feng He Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 University of Chinese Academy of Sciences, Beijing 100049 , Yurui Xue *Corresponding authors: E-mail Address: [email protected]; E-mail Address: [email protected] Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 Science Center for Material Creation and Energy Conversion, School of Chemistry and Chemical Engineering, Institute of Frontier and Interdisciplinary Science, Shandong University, Jinan 250100 and Yuliang Li *Corresponding authors: E-mail Address: [email protected]; E-mail Address: [email protected] Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 University of Chinese Academy of Sciences, Beijing 100049 https://doi.org/10.31635/ccschem.022.202202005 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Here we report an in situ assembly growth method that controls the growth of NiTCNQ on the surface of graphdiyne (GDY). The catalytic system of donor–acceptor–donor (GDY/TCNQ/Ni) structure with multiple charge transfer (CT) was achieved by controlling the growth of NiTCNQ on the surface of GDY. Significantly, a controlled double layer interface of GDY/TCNQ/Ni was formed. This system implemented simultaneously the two elements we expected (1) an incomplete CT, and (2) the infinite distribution of active sites originating from highly asymmetric surface charge distribution. The high conductivity and typical semiconductor characteristics of the catalyst endows it with high catalytic activity. We found that an electrolytic cell consisting of the CT salt as a catalyst provided a 1.40 V ultra-small cell voltage up to 10 mA cm−2 and the outer GDY film effectively prevented the corrosion of the catalyst. Our study is the first to introduce CT complexes to a novel catalytic material platform for high selectivity of catalysts, and undoubtedly demonstrates the high selectivity, stability, and activity of such catalytic systems, which provides a new space for the development of novel conceptual catalysts. Download figure Download PowerPoint Introduction The sustainable hydrogen (H2) production through electrocatalytic overall water splitting (OWS) provides a promising method to overcome the global energy crisis and environmental problems, which is of great significance for industrial and scientific progress.1,2 In terms of hydrogen conversion, precious metal-based materials (e.g., Ru or Ir-based materials for the oxygen evolution reaction (OER); Pt-based materials for the hydrogen evolution reaction (HER)) remain the benchmark catalysts with high catalytic performances, but they are not suitable for large-scale commercialization due to their high cost, low abundance, and insufficient stability. At present, the high cost of precious metals has seriously restricted the development of this field. Transition metal-based materials, such as metal hydroxides, oxides, nitrides, phosphides, carbides, and sulfides, have been extensively studied for anodic OER and cathodic HER.3–6 However, the low catalytic activity of these systems results in sluggish kinetics of OER and HER. In addition, there is no stability advantage of these catalysts. Furthermore, to meet the requirement of industrial alkaline water splitting for hydrogen production, the catalysts should produce large current densities at low cell voltages (e.g., ∼200–400 mA cm−2 at 1.8–2.4 V) and be synthesized from earth-abundant elements to minimize the H2 production cost.7–10 Therefore, to develop catalysts with excellent comprehensive performance, we need to find a new way to produce electrocatalysts with low cost, high activity, and high stability. The unique and excellent structures and properties of graphdiyne (GDY) has triggered extensive investigations on its fundamental properties and potential applications in various research fields, such as catalysis, energy conversion and storage, optical and electrical devices, and so on.11–26 As a new sp- and sp2-cohybridized two-dimensional carbon material, GDY shows large porous structure, high intrinsic activity, excellent electron transfer ability, high electronic conductivity, and high stability.27–29 GDY is an ideal carbon material for synthesizing high-performance catalysts with determined structures and abundant active sites, and provides the opportunities for clearly understanding the relationship of structure and performance. GDY can be grown on arbitrary substrates at low temperatures and ambient pressures, which protects the parent structure and the active site structure from destruction and generates new active sites. 7,7,8,8-Tetracyanoquinodimethane (TCNQ) is a well-known electron acceptor with high electron affinity, which easily reacts with metal atoms to form charge transfer (CT) complexes with high conductivity, high carrier density, and special electron transport properties.30 Metal-TCNQs show excellent electrical and optical properties, and unique and adjustable electron and high CT ability. CT complexes where the CT amount is not an integer is called incomplete CT; it is different from traditional inorganic complexes with an integer CT. Because of their high conductivity and semiconductor characteristics, they have attracted more and more interest in many research fields.31–34 However, until now, research on CT complexes mainly focused on controlled growth, photoelectric devices. and semiconductor properties, while basic and applied research in the field of catalysis remain silent. Recently, we took NiTCNQ–GDY as an example and explored the basis and application of NiTCNQ–GDY as an emerging catalyst in hydrogen energy conversion. In addition, we deeply understand the GDY plays the key role in the generation of efficient catalysts, and find its introduction overcomes important issues such as solvent corrosion, structural instability caused by light or electricity, and poor conductivity.35,36 In this work, we report the successful synthesis of a donor–acceptor–donor (GDY/TCNQ/–Ni) structure with multiple CT by in situ growing GDY layers on the surface of NiTCNQ nanowires (GDY–NiTCNQ). Experimental results demonstrated the incomplete CT and the infinite distribution of active sites originating from highly asymmetric surface charge distribution endow the catalyst with high conductivity, typical semiconductor characteristics, high catalytic activity, and excellent intrinsic properties. These unique and fascinating properties endow GDY–NiTCNQ with excellent catalytic activities toward OER, HER, and OWS. For instance, GDY–NiTCNQ exhibited small overpotentials of 218 and 61 mV at 10 mA cm−2 for OER and HER in 1.0 M KOH. When used as an electrolytic cell, it can drive 10 mA cm−2 at a low cell voltage of 1.40 V. This work provides a new direction toward the development of cost-effective and high-performance electrocatalysts. Experimental Methods Material TCNQ was purchased from Tokyo Chemical Industry (TCI, Shanghai, China). Acetonitrile and methanol were obtained from Concord Technology (Tianjin) Co., Ltd. Nickel foams (NFs) were treated with dilute hydrochloric acid, rinsed with deionized water, and dried with N2 flow before use. Deionized water was purified with a Millipore system. All chemicals were analytical grade and used without further purification unless otherwise specified. Preparation of NiTCNQ in acetonitrile A piece of freshly pretreated nickel film (3 cm × 1.5 cm) was immersed in 10 mM TCNQ acetonitrile solution for 10 min followed by the addition of 3% deionized water at room temperature. After reaction for 6 h, the material was removed from the solution, washed carefully with acetonitrile and water, and dried under the protection of N2. Preparation of GDY on NiTCNQ (GDY–NiTCNQ) A piece of NiTCNQ was immersed in 50 mL acetone solution of hexaethynylbenzene (HEB) at 50 °C under Ar atmosphere protected from light. After reaction for 12 h, the resulting GDY–NiTCNQ was washed with acetone, deionized water, and acetone, followed by drying at 50 °C in a vacuum oven. Characterization The morphology of the material was characterized by scanning electron microscopy (SEM; Hitachi, S 4800; Institute of Chemistry, Chinese Academy of Sciences), transmission electron microscopy (TEM, a JEOL JEM-2100F field-emission high-resolution transmission electron microscope at an accelerating voltage of 200 kV; Institute of Chemistry, Chinese Academy of Sciences), and high-resolution TEM (HRTEM). The energy-dispersive spectroscopy (EDS) mapping analysis was also obtained to characterize the elemental composition of the samples. X-ray diffraction (XRD) measurements were carried out on a PANalytical high-resolution XRD system (EMPYREAN) using Cu Kα radiation (λ = 1.540598 mm). X-ray photoelectron spectroscopy (XPS) was performed on a Thermo Scientific ECSALab 250Xi instrument with monochromatic Al Kα X-ray radiation (Institute of Chemistry, Chinese Academy of Sciences). Electrochemical measurements All electrochemical tests were carried out using an electrochemical workstation (CHI 760E) through a typical three-electrode system, in which the as-prepared samples, graphite rods, and saturated calomel electrode were used as the working electrode, the counter electrode, and the reference electrode, respectively. All the electrolytes used in the experiments were bubbled with Ar for 2 h before use. Linear sweep voltammetry (LSV) measurements were carried out at a scan rate of 2 mV s−1 in 1.0 M KOH solution. Cyclic voltammetry (CV) measurements were carried out at a scan rate of 100 mV s−1. Electrochemical impedance spectroscopy (EIS) was obtained at the frequency range of 100 KHz to 0.1 Hz with a sampling rate of 12 points per decade, and the data obtained was fitted. All potentials were converted to the reversible hydrogen electrode (RHE) according to ERHE = ESCE + E0SCE + 0.059 × pH. X-ray absorption fine structure measurements The X-ray absorption fine structure (XAFS) spectra (Ni K-edge) were collected at 1W1B station in Beijing Synchrotron Radiation Facility (BSRF). The storage rings of BSRF were operated at 2.5 GeV with an average current of 250 mA. Using a Si(111) double-crystal monochromator, the data collection was carried out in transmission/fluorescence mode using an ionization chamber. All spectra were collected in ambient conditions. XAFS analysis and results The acquired extended XAFS (EXAFS) data were processed according to the standard procedures using the ATHENA module implemented in the IFEFFIT software packages. The k3-weighted EXAFS spectra were obtained by subtracting the post-edge background from the overall absorption and then normalizing with respect to the edge-jump step. Subsequently, k3-weighted χ(k) data of Ni K-edge were Fourier transformed to real (R) space using a Hanning windows (dk = 1.0 Å−1) to separate the EXAFS contributions from different coordination shells. To obtain the quantitative structural parameters around central atoms, least–squares curve parameter fitting was performed using the ARTEMIS module of the IFEFFIT software packages. Results and Discussion As shown in Figures 1a and 1b, a two-step in situ growth strategy was used to selectively synthesize the GDY–NiTCNQ catalysts with D–A–D (GDY/TCNQ/Ni) structure, including the first in situ growth of NiTCNQ nanorods and the subsequent growth of the GDY film on the outer layer of the NiTCNQ nanorods that leads to the formation of GDY–NiTCNQ nanowires. Typically, with the dropwise addition of water into the acetonitrile solution of TCNQ, the Ni ions released from the substrate and then interacted with TCNQ forming the A–D (TCNQ–Ni) structure. The NiTCNQ assembled into highly ordered NiTCNQ-nanorods array on the surface of NF.37 The NiTCNQ was then immersed into the acetone solution, after which the HEB precursor was added to grow GDY films on the NiTCNQ surface with the morphology gradually changing from nanorod to nanowire. During this process, the D–A–D (GDY/TCNQ/Ni) structure was formed. Figure 1 | Schematic representation of the controlled synthesis route to the catalytic system of donor–acceptor–donor (GDY/TCNQ/Ni) structures through in situ growth of (a) NiTCNQ nanorods and (b) GDY–NiTCNQ. Download figure Download PowerPoint Figure 2a shows that the color of the samples changed from gray for NF to dark green for NiTCNQ and black for GDY–NiTCNQ during the synthetic process. SEM images clearly show that the smooth surface of 3D NF (Figures 2b–2d) was covered by a film of NiTCNQ nanorods (average diameter, ∼210 nm; Figures 2e–2h). As shown in Supporting Information Figure S1, the NiTCNQ has a flat surface and a fringe lattice spacing of 0.254 nm. The electrostatic potential (ESP) of NiTCNQ (Figure 2h) confirms the interactions between Ni ions and TCNQ with evident CT from Ni to TCNQ, which also demonstrates the formation of the A–D structure. With the growing of GDY on the NiTCNQ surface, the morphology of the nanorods of NiTCNQ changed to nanowires for GDY–NiTCNQ (Figures 2i–2l). As revealed by HRTEM images (Figures 2l and 2m), an obvious shell layer was observed outside of the NiTCNQ core, confirming the successful growth of GDY on the surface of NiTCNQ (Figure 2m). GDY–NiTCNQ exhibits a rough and porous surface, which is beneficial for enlarging the active surface area and the number of active sites. The lattice spacing of the core structure of GDY–NiTCNQ is 0.254 nm ( Supporting Information Figure S2), in accordance with the NiTCNQ, indicating the structure of NiTCNQ was well maintained during the GDY growth process. Scanning TEM (STEM) and EDS mapping images (Figures 2n–2q and Supporting Information Table S1) confirm the presence of carbon, nitrogen, and nickel elements in the GDY–NiTCNQ sample without any impurities. Ni and N are densely distributed in the inner space and sparsely distributed in the edge, and C is evenly distributed throughout the whole material. These results demonstrated the formation of the double layer interface of GDY/TCNQ/Ni, and the GDY film on the outer layer can effectively prevent the catalyst corrosion, which guarantees the long-term stability of the catalyst. Figure 2 | Morphological characterizations of GDY–NiTCNQ and NiTCNQ. (a) Photographs of (i) NF, (ii) NiTCNQ, and (iii) GDY–NiTCNQ. SEM images of (b–d) NF, (e–g) NiTCNQ, and (i–k) GDY–NiTCNQ samples. (h) Electrostatic potential of NiTCNQ. TEM images of (l and m) GDY–NiTCNQ. Elemental mapping images (n–p) of C, Ni, and N atoms in the GDY–NiTCNQ. Download figure Download PowerPoint XRD and XPS measurements were performed to characterize the compositions and structures of the samples. As shown in Figure 3a, the intensity of the peaks for GDY–NiTCNQ decreased as compared with that of NiTCNQ, which might be due to the growth of GDY on NiTCNQ. The XPS survey spectra confirm the presence of Ni, C, and N elements in accordance with the EDS result ( Supporting Information Figures S3 and S4). Compared with pure NiTCNQ (Figure 3b), the C 1s XPS spectra of GDY–NiTCNQ shifted to higher binding energies (BE) by 0.75 eV, revealing the CT from GDY to NiTCNQ. The appearance of an sp-C peak in the C 1s spectra of GDY–NiTCNQ (Figure 3c) indicates the successful growth of GDY on NiTCNQ. Moreover, an independent new peak at 291.96 eV originating from the π–π* shakeup satellite implies the interactions between NiTCNQ and GDY.7 In the Ni 2p region (Figure 3d), the peaks for GDY–NiTCNQ decreased by 1.23 eV as compared with that of NiTCNQ ( Supporting Information Figure S5), revealing the remarkable CT between NiTCNQ and GDY. For GDY–NiTCNQ, the peaks for Ni2+ 2p3/2 and Ni2+ 2p1/2 appear at 856.39 and 873.72 eV, and Ni3+ 2p3/2 and Ni3+ 2p1/2 appear at 858.30 and 875.58 eV, respectively, indicating the presence of the mixed valence states of nickel species. The N 1s (Figure 3e) and O 1s (Figure 3f) peaks of GDY–NiTCNQ located at higher BE than those of pristine NiTCNQ further reveal the presence of electron-transfer in the GDY–NiTCNQ sample.38,39 The Raman ( Supporting Information Figure S6) and Fourier transform infrared (FTIR) ( Supporting Information Figure S7) measurements of the GDY layer were conducted. As shown in Supporting Information Figure S6, pure NiTCNQ spectra features several sharp characteristic peaks. GDY–NiTCNQ exhibits characteristic peaks corresponding to the D-band, G-band, and the vibration of conjugated diine links (2189.8 and 1926.2 cm−1), while the characteristic peaks of NiTCNQ diminished. Moreover, as shown in Supporting Information Figure S7, the FTIR shows the characteristic peak corresponding to GDY, as compared with that of pure NiTCNQ. These results demonstrated the successful growth of GDY on the surface of NiTCNQ. Figure 3 | Structural characterization of GDY–NiTCNQ. (a) XRD spectra of NiTCNQ and GDY-NiTCNQ. XPS spectra for GDY–NiTCNQ and NiTCNQ of (b and c) C 1s, (d) Ni 2p, (e) N 1s, and (f) O 1s. The inset figure in (b) represents the deformation charge density of NiTCNQ. (g) The normalized Co K-edge XANES spectra and (h) the first derivative XANES of GDY–NiTCNQ along with the references. (i) EXAFS spectra of GDY–NiTCNQ at the Co K-edge. Download figure Download PowerPoint Ni K-edge X-ray absorption near-edge structure (XANES) for the samples was performed. Figure 3g shows that the GDY–NiTCNQ exhibits the higher edge energy position than those of NiCl2 and NiO, suggesting the average valence state of nickel in GDY–NiTCNQ is larger than Ni2+. This also implies the mixed valence state of nickel in GDY–NiTCNQ (Figure 3h). The Fourier transforms of the Ni K-edge EXAFS spectrum of GDY–NiTCNQ exhibited a dominant peak at 1.6 Å, which could be assigned to the nearest shell coordination of the Ni–N bond (Figure 3i). The weak peak at 2.5 Å might be attributed to the aggregation of a small number of nickel atoms. The fitted Ni–N coordination number for GDY–NiTCNQ was 4.9 with an average Ni–N bond distance of 2.05 Å ( Supporting Information Table S2), smaller than that of hexa-coordinated NiTCNQ,40 which might be ascribed to the strong interactions between the GDY and NiTCNQ species. The obviously enhanced CT ability at the double layer interfaces of GDY/TCNQ/Ni was expected to endow the catalyst with incomplete CT and the infinite distribution of active sites originating from highly asymmetric surface charge distribution. The significantly increased number of active sites would further accelerate CT and lower energy barriers of the reaction. These are all beneficial to improve the catalytic activity of the catalysts. The OER catalytic performances of the samples were studied using a three-electrode system by testing LSV in O2-saturated 1.0 M KOH solution at the scan rate of 2 mV s−1. All polarization curves were corrected by the iR-compensation. NiTCNQ, NF, and RuO2 were also tested in the same conditions for reference. As shown in Figure 4a, the anodic peak appearing in the range of 1.3–1.4 V versus RHE referred to the nickel oxidation from Ni(II) to Ni(III), and the following peak represented the OER catalytic activity. GDY–NiTCNQ showed the best OER activity with the smallest overpotential of 218 mV at 10 mA cm−2 compared with pure NiTCNQ (343 mV) and commercial RuO2 (282 mV). Moreover, GDY–NiTCNQ exhibited a lower of mV than NiTCNQ mV NF mV and RuO2 mV indicating it the reaction kinetics for OER evolution (Figure For further of the OER activity, the frequency was At the overpotential of GDY–NiTCNQ a higher of s−1 than NiTCNQ NF and of the electrocatalysts ( Supporting Information Table Figure | OER and HER (a) curves of NiTCNQ, NF and RuO2 for OER at the scan rate of 2 mV s−1. (b) of the samples for curves of GDY–NiTCNQ obtained before and after OER (d) O 1s XPS spectra of GDY–NiTCNQ after OER (e) Ni 2p XPS spectra and (f) the of Ni2+ of GDY–NiTCNQ obtained after OER (g) curves of NiTCNQ, NF, and for HER at the scan rate of 2 mV s−1. (h) of the materials for HER. (i) curves of GDY–NiTCNQ obtained before and after HER O 1s XPS Ni 2p XPS and the of Ni2+ in GDY–NiTCNQ samples. Download figure Download PowerPoint stability of the catalyst is of great significance for As shown in Supporting Information Figure GDY–NiTCNQ maintained its catalytic activity for h under at mA revealing its long-term stability ( Supporting Information Figure GDY–NiTCNQ also a in catalytic activity during the tests for (Figure The of the GDY–NiTCNQ catalysts after the stability characterized by SEM ( Supporting Information Figure and TEM ( Supporting Information Figure showed no and the nanorod morphology was well the high stability of the as-prepared catalysts. situ XPS tests were on GDY–NiTCNQ to the structural evolution during the The O 1s XPS spectra showed two new peaks at and eV lattice oxygen in metal after the tests (Figure was also found that the position of the Ni 2p peak shifted to lower BE and the of the Ni2+ increased gradually during the catalysis (Figures and the of Ni2+ at these results confirm the generation of the was with the of Ni2+ in OER which a key role in the oxygen The HER catalytic activity of GDY–NiTCNQ was further tested in 1.0 M KOH solution. Figure shows the LSV curves of GDY–NiTCNQ exhibited a small overpotential of 61 mV at 10 mA which was smaller than NiTCNQ mV) and NF and to the catalyst mV). The corresponding of GDY–NiTCNQ, NiTCNQ, NF, and were and mV (Figure The for GDY–NiTCNQ, NiTCNQ, and NF were and respectively, at the overpotential of 100 All results the obvious of HER activity. Moreover, there was a in current density after indicating the high stability (Figure The of the GDY–NiTCNQ catalysts after the HER tests ( Supporting Information Figure for Supporting Information Figure for were well the high stability of the as-prepared catalysts. To reveal the of the catalytic activity, the in situ XPS measurements were conducted. As shown in Figure new peaks corresponding to the were observed at eV in the O 1s XPS spectra as compared with the as-prepared catalysts. The of Ni2+ decreased as the HER (Figures and the of state of nickel which might be the of of HER activity. For the further of the activity of GDY–NiTCNQ, were to the CT The parameters obtained were fitted with solution CT and absorption to the (Figure GDY–NiTCNQ exhibited the of and compared with NiTCNQ = = and NF = = which the conductivity and transfer process. The electrochemical active surface area was also through layer under various scan of (Figure and Supporting Information Figure GDY–NiTCNQ showed a larger of cm−2 than NiTCNQ and NF indicating the larger surface area and higher surface assigned to the introduction of GDY. on OER and HER performance, GDY–NiTCNQ was used as and in a for OWS. The catalytic system exhibited high with a low cell voltage of 1.40 V to 10 mA lower compared with those V) (Figure and the catalysts, including [email protected] V at 10 mA [email V at 10 mA V at 10 mA and so on (Figure and Supporting Information Table S4). During the of H2 and were from the and (Figure The catalytic in in basic demonstrates the promising in applications of GDY–NiTCNQ. Figure | Electrochemical properties and performance. (a) of samples in 1.0 M KOH solution. for and the fitting is (b) The at V of scan for samples. of the (d) activities of GDY–NiTCNQ and electrocatalysts. (e) The water in a working Download figure Download PowerPoint We report an in situ assembly growth method that controls the growth of NiTCNQ on the surface of GDY, to the formation of a unique D–A–D (GDY/TCNQ/Ni) structure with multiple CT. In such catalytic systems, the amount of CT between and acceptor is that incomplete CT between and surface charge distribution the number of active sites and intrinsic activity of the catalytic system, a new for the activity of the catalytic system through incomplete CT between the The results show that the by incomplete CT demonstrates excellent electrical conductivity and typical semiconductor characteristics, to the high catalytic activity of such a catalytic system in OER, HER, and OWS. We found that an electrolytic cell consisting of the CT salt as a catalyst provided a 1.40 V ultra-small cell voltage up to 10 mA is that the outer GDY film effectively prevented the corrosion of the which is to its long-term stability. This work provides a new way to selectively novel catalysts with high selectivity, activity, and stability. Supporting Information Supporting Information is the for the of Figure and Table of is no of interest to Information This research was by a from the and of the Science of and and the of the Chinese Academy of

Electrocatalytic performance of carbon dots/palladium nanoparticles composite towards hydrogen evolution reaction in acid medium

The construction of cost-effective new generation electrocatalysts as an alternative to price metal-based electrocatalysts is of great importance for unitized reversible fuel cell (URFC) technology. In this study, indium incorporated graphite-based electrocatalysts (InGs) were prepared by electrochemical synthesis methods and their effects on the hydrogen evolution reaction (HER) activity in the electrolyzer mode of the URFC system were investigated. The electrochemical HER performance of the electrocatalysts were compared using the linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). This study provides encouraging findings for indium embedded graphite-based electrocatalysts for URFC, and InG1-coded electrocatalyst has also demonstrated better performance. Keywords: Electrochemical synthesis, Cyclic voltammetry, Indium-graphite, Hydrogen evolution reaction, Unitized reversible fuel cell Introduction Hydrogen is a key solution to climate change in achieving a world net-zero emissions by 2050. The URFC systems that combine electrolyzer (EC) and fuel cell (FC) mode into a single electrochemical device known as hydrogen production technology EC mode. URFCs are a compact new generation energy storage and conversion technology because of their relatively low cost, lightweight, user- and eco-friendly features. In the long term, URFCs have great potential among the energy conversion technologies in terms of efficient use of renewable energy sources 1,2. Noble metal-based electrocatalysts such as Pt, Ir, IrO2, Pt-IrO2-RuO2 etc. are widely used in the URFC systems. However, the high price and availability of these metals is a considerable drawback in terms of commercial sustainability for URFC 3. The development of new generation metal-based electrocatalysts as noble metal alternatives plays a key role for these systems.Herein, we propose electrochemically synthesized precious metal-free indium incorporated graphite-based electrocatalysts to analyze their performance on hydrogen production in electrolyser mode of URFC system. Materials And Methods A pencil graphite rod was utilized as both the working and counter electrodes, and Ag/AgCl (in 3.0 M KCl) as the reference electrode in the electrocatalyst synthesis. With the aim of synthesizing different functionality In modified graphite-based electrocatalysts wereobtained by the cyclic voltammetric method in indium acetate containing electrolyte solution at the various potential ranges under ambient condition, and synthesized electrocatalysts called as InG1, and InG2. The comparison of the electrochemical synthesis methods, chronoamperometry was used to electrodeposition indium on graphite substrate, and prepared electrocatalyst named as InG3. After the synthesis process, each electrocatalyst was rinsed with deionized water and dried at room temperature4.HER activities of the electrocatalysts were explored by LSV in 1.0 M KOH alkaline medium at a scan rate of 5 mV s−1. EIS was employed to analyze the electrocatalytic activity of the electrocatalysts for HER. Results and Discussion In this study, we have suggested an alternative approach for the electrochemical synthesis of indium incorporated graphite-based electrocatalysts, were studied for their effect on the electrochemical HER behaviors in an alkaline solution for URFC. LSV results demonstrated that incorporating of indium into graphite-based materials enhanced HER activity, which is probably the result of increased indium functionality and more active sites on the graphite substrate. Fig. 1 LSV curves of InGs for HER at a scan rate of 5 mVs−1 in 1.0 M KOHThe experimental results have shown that various synthesis methods and electrochemical synthesis parameters may lead to chemical and physical differences in the obtained electrocatalyst structure. Conclusion In this paper, the InG-based electrocatalaysts with various functional properties were electrochemically prepared in one-step and their hydrogen evolution performances for the electrolyzer mode of URFC were examined by LSV and EIS. The results of this research indicate that InGs as electrocatalysts appear to be promising candidates for URFC systems. Acknowledgment This study is supported by the Scientific and Technological Research Council of Türkiye (TUBITAK), 2219-International Postdoctoral Research Fellowship Program. References I. Dincer, Int J Hydrogen Energy, 48, 16143–16147 (2023).Z. Pu et al., Appl Energy, 283 (2021).T. Sadhasivam et al., Int J Hydrogen Energy, 43, 18169–18184 (2018).H. Gursu, M. Gencten, and Y. Sahin, J Electrochem Soc, 168, 060504 (2021). Figure 1

Open AccessCCS ChemistryRESEARCH ARTICLE1 Oct 2021Synergistic Effect of Platinum Single Atoms and Nanoclusters Boosting Electrocatalytic Hydrogen Evolution Yihui Zhu†, Pengfei Tian†, Hongliang Jiang, Jingren Mu, Lu Meng, Xiaozhi Su, Yu Wang, Yunxiang Lin, Yihua Zhu, Li Song and Chunzhong Li Yihui Zhu† Key Laboratory for Ultrafine Materials of Ministry of Education, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237 Shanghai Engineering Research Center of Hierarchical Nanomaterials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 , Pengfei Tian† Key Laboratory for Ultrafine Materials of Ministry of Education, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237 , Hongliang Jiang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory for Ultrafine Materials of Ministry of Education, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237 , Jingren Mu Shanghai Engineering Research Center of Hierarchical Nanomaterials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 , Lu Meng Shanghai Engineering Research Center of Hierarchical Nanomaterials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 , Xiaozhi Su Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210 , Yu Wang Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210 , Yunxiang Lin National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029 , Yihua Zhu Shanghai Engineering Research Center of Hierarchical Nanomaterials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 , Li Song National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029 and Chunzhong Li *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory for Ultrafine Materials of Ministry of Education, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237 Shanghai Engineering Research Center of Hierarchical Nanomaterials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 https://doi.org/10.31635/ccschem.020.202000497 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Maximizing atomic utilization of precious metal-based catalysts is of great significance in heterogeneous catalysis, also becoming a useful strategy to develop efficient electrocatalysts for hydrogen evolution reaction (HER). Although the dispersion of platinum (Pt) as single atoms (SAs) has increasingly been used in the design of HER electrocatalysts, it is still controversial if the SAs possess higher reactivity relative to the nanoparticles with identical atom loading. Here, by virtue of computational studies, we find that atomic step-rich Pt clusters and defective graphene (DG)-loaded Pt SAs are beneficial to water dissociation and hydrogen coupling, respectively, predicting that decent activity and high atomic utilization for alkaline HER electrocatalysis will be exhibited on the structure that integrates both Pt SAs and nanoclusters onto the DG matrix (PtSA/NC-DG). We experimentally synthesize the PtSA/NC-DG catalyst for alkaline HER. The optimized PtSA/NC-DG delivers an overpotential of 41 mV at a current density of 10 mA cm−2 and mass activity of 5.4 mA μgpt−1 at the overpotential of 100 mV. The mass activity is nearly 6 and 10 times higher than that of its Pt SA counterpart and commercial Pt/C catalyst. This work deepens the knowledge of the synergistic effect of single atoms and nanoclusters for alkaline HER electrocatalysis. Download figure Download PowerPoint Introduction Hydrogen production enabled by electrocatalytic methods represents an attractive approach to utilize renewable electricity from intermittent energy, such as solar, wind energy, geothermal power, and so forth.1–5 Although nonprecious materials based on earth's abundant resources have achieved substantial development,6–8 platinum (Pt) is still the benchmark catalyst for the electrocatalytic hydrogen evolution reaction (HER) in terms of low overpotentials and high mass activities.9–11 The electrocatalytic hydrogen production in alkaline electrolytes offers more benign conditions compared with that of acid media.12 More importantly, alkaline water splitting into hydrogen allows the application of active catalysts based on earth-abundant transition metals for anodic oxygen evolution reaction.1,6 However, the catalytic activity of Pt in alkaline media is nearly two to three orders of magnitude slower than that in acid media due to the high-energy barrier of water dissociation.13 In terms of cost efficiency, it is highly desirable to reduce the Pt amount to the greatest extent, while maintaining or even improving catalytic activities.14–17 In recent years, decreasing the size of catalytically active species in atomic dispersion, also referred to as single atoms (SAs), has attracted considerable attention thanks to their high atomic utilization and unique physicochemical properties.18–21 However, the catalytic nature remains highly controversial, especially since it is not clear how the SA sites achieve the splitting and recombination of chemical bonds.22,23 For instance, the hydrogen evolution process in alkaline media commonly consists of water dissociation and hydrogen coupling, a typical Volmer step (H2O + e− → H* + OH−) and Heyrovsky step (H2O + H* + e− → H2 + OH−) or Tafel step (H* + H* → H2).13 The structure with dual active components, typically a metal/oxide interfacial structure,24 has generally been adopted to optimize the water dissociation and hydrogen coupling simultaneously, boosting alkaline water electrolysis to produce hydrogen. To date, various attempts have successfully been made to obtain efficient low-Pt catalysts for acid HER electrocatalysis, but it has been determined that neither the Pt SAs nor nanoparticles deliver satisfactory performance in alkaline media.25–27 Developing efficient Pt-based catalysts with ultimate atomic utilization for alkaline HER electrocatalysis remains a severe challenge.28–31 Here, we demonstrate both theoretically and experimentally that the synergistic function from the integration of defective graphene (DG)-supported Pt SAs and nanoclusters (named as PtSA/NC-DG) boosted electrocatalytic hydrogen evolution in alkaline media. In alkaline HER, given typical elementary steps of the water dissociation and hydrogen coupling, we employed density functional theory (DFT) calculations to compute the two steps onto Pt(111), Pt(211), Pt38 cluster, and DG-supported Pt SA models. It was revealed that the Pt nanoclusters and SAs helped water dissociation and hydrogen coupling, respectively. Therefore, the coexistence of Pt SAs and nanoclusters on the DG matrix would decouple the optimization of the two steps, integrally delivering superior hydrogen evolution. We experimentally synthesized the PtSA/NC-DG and DG-supported Pt SAs (named as PtSA-DG). The electrocatalytic performance of the PtSA/NC-DG outperformed that of PtSA-DG and commercial Pt/C catalysts, verifying the synergistic effect of Pt SAs and nanoclusters for alkaline HER electrocatalysis. Experimental Methods Synthesis of DG About 20.00 g urea was dispersed uniformly in its crucible. Then the powder was calcined in a muffle furnace at 550 °C for 4 h, and the heating rate was controlled at 5 °C min−1. The temperature was reduced to 300 °C at 10 °C min−1, and then naturally cooled to obtain carbon nitride (C3N4). About 5.00 g of the prepared C3N4 and 4.50 g (C6H12O6 > 99 %) glucose were dispersed in mortar, the mixture was uniformly mixed, and then it was placed in a tube furnace at 1000 °C for 2 h under an argon atmosphere. The heating rate was controlled at 5 °C min−1. The temperature was reduced to 300 °C at 10 °C min−1, followed by natural cooling to obtain nitrogen-doped DG. Synthesis of PtSA-DG and PtSA/NC-DG In a typical preparation of Pt SAs loaded on the graphene matrix, 0.05 g of the DG was dispersed in 60.00 mL ultrapure water and sonicated for 30 min. Then 2.00 mL aqueous solution of chloroplatinic acid hexahydrate (2 mg mL−1) was added into the suspension and stirred for 12 h. The mixture was placed in an oil bath at 80 °C. It was collected by centrifuging, washing, and then drying at 75 °C for 6 h. The dark powdered sample, namely PtSA-DG, was obtained. The PtSA-DG was placed into a quartz tube and heated to 400 °C at a rate of 5 °C min−1 under a flow of gas mixture of argon and hydrogen (volume ratio = 9∶1). After 2 h of pyrolysis, the PtSA/NC-DG-400 was collected. By adjusting the annealing temperature (200 and 600 °C), the PtSA/NC-DG-X (X = 200 or 600) was also obtained. Other related experimental methods are available in the Supporting Information. Results and Discussion Structural investigation by DFT calculation The water dissociation and hydrogen coupling results on established models are shown in Figure 1 and Supporting Information Table S1. It was found that the energy barrier of water dissociation (EH2O) on a typical Pt(111) surface was estimated as 0.98 eV, and the hydrogen-binding energy (ΔGH*) was −0.20 eV, in keeping with previously published theoretical data.32,33 The results indicated the low ,activity of large size Pt crystals for alkaline HER electrocatalysis. When reducing the Pt size for the usage decrease, in addition to the thermodynamically stable Pt(111) surface, a high-index facet is increasingly exposed. Therefore, a typical high-index Pt(211) surface covered by atomic steps was here introduced.10 As shown in Figures 1a and 1b, the EH2O on the Pt(211) surface was 0.65 eV. On the contrary, the ΔGH* (−0.40 eV) on the Pt(211) surface was extremely negative (Figures 1c and 1d). The results suggested that the atomic steps can accelerate water dissociation to supply H*, but hamper the H* combination into H2. It can reasonably be anticipated that atom-assembled nanoclusters with rich atomic steps can further facilitate the water dissociation, but severely hinder the hydrogen coupling. The computational EH2O and ΔGH* on typical Pt38 clusters were 0.59 and −0.60 eV, respectively, verifying that only the presence of nanoclusters can not efficiently accomplish the water splitting into H2 (Figures 1b and 1d). In view of the ultimate in atomic utilization efficiency, Pt SAs anchored in suitable support naturally come to mind. Here, a nitrogen-doped defective carbon matrix for the anchoring of Pt SAs was considered, thanks to high structural feasibility and electronic conductivity as well as rich surface chemistry.34 Here, typical four-coordination structure is investigated in consideration of the high structure stability.10,32 It was determined that all simulated Pt-CxNy structures (x + y = 4) displayed large EH2O (Figure 1b), revealing the inferior water dissociation process. And moderate |ΔGH*| was exhibited on most of the Pt-CxNy structures, including Pt-C1N3, Pt-C2N2, and Pt-C4 (Figure 1d), thereby benefitting the hydrogen coupling process on these structures. Combined with the aim of atomic utilization maximization, these theoretical results predicted that decent activity and high atomic utilization of alkaline HER electrocatalysis would be exhibited on the structure that integrates both Pt SAs and nanoclusters onto proper nitrogen-doped defective carbon support. In the integrated structure, Pt clusters can accelerate water dissociation to supply adsorbed H atoms onto Pt clusters. The migration of H atoms from Pt clusters to the graphene support and then to the SAs can be carried out through hydrogen spillover.35–37 The DG as the substrate of Pt clusters receives excess H* from the spillover. Most of Pt-CxNy structures are beneficial to the hydrogen coupling process. Figure 1 | Structural investigation by DFT calculation. (a and c) The adsorption configurations of H2O and H on Pt(111), Pt(211), Pt38, and Pt-CxNy (x + y = 4), respectively. The dark blue, gray, blue, red, and white spheres are Pt, C, N, O, and H atoms, respectively. (b) Reaction energy diagram of water dissociation on Pt(111), Pt(211), Pt38, and Pt-CxNy (x + y = 4). (d) Free-energy barriers for HER on Pt(111), Pt(211), Pt38, and Pt-CxNy (x + y = 4). Download figure Download PowerPoint Synthesis and characterization of DG-supported Pt catalysts The nitrogen-doped DG selected for the loading of Pt species was obtained by the pyrolysis of the physical mixture of glucose and carbon nitride ( Supporting Information Figures S1 and S2). Transmission electron microscopy (TEM) images showed typical graphene nanosheets with a high degree of structural wrinkle38 ( Supporting Information Figure S3). The graphene displayed rich porosity and suitable pyridinic- or pyrrolic-nitrogen defects ( Supporting Information Figures S4 and S5), which were beneficial to the anchoring of metal species.39–41 The Pt SAs were anchored onto the DG matrix by a one-step electroless deposition to obtain the PtSA-DG with 3.89 wt % Pt loading.22,23 Aberration-corrected high-angle annular dark-field scanning TEM (HAADF-STEM) images showed the Pt species of the PtSA-DG were atomically dispersed onto the DG support20–22 (Figure 2a and Supporting Information Figure S6). Subjected to thermal treatment at a different temperature, the PtSA-DG was transformed into the PtSA/NC-DG-X (X = 200, 400, or 600 °C). In the thermal treatment, a part of the Pt SAs owing to its unsaturated coordination structure and low binding energy with CN matrix (Pt-CxNy, x + y < 4) were readily aggregated into Pt clusters.10,42 The Pt species in PtSA/NC-DG-X (X = 200, 400, or 600 °C ) dispersed as Pt nanoclusters with a similar average diameter ( Supporting Information Figure S7). Unless otherwise specified, the PtSA/NC-DG was the one obtained by heat treatment in 400 °C. From the HAADF-STEM images (Figure 2b and Supporting Information Figure S8), it was determined for the PtSA/NC-DG that both atom-assembled nanoclusters and SAs were dispersed onto the DG matrix. The energy-dispersive X-ray spectroscopy (EDS) mapping element further evidenced the coexistence of SAs and nanoclusters onto the nitrogen-doped carbon substrate (Figure 2c). X-ray diffraction (XRD) patterns (Figure 2d and Supporting Information S9) also revealed the presence and absence of crystalline Pt species in the PtSA/NC-DG and PtSA-DG, respectively. Figure 2 | Morphology and structure characterizations of PtSA-DG and PtSA/NC-DG. (a) High magnification HAADF-STEM image of PtSA-DG. (b) Gradually magnified HAADF-STEM images of PtSA/NC-DG. (c) Elemental mapping of PtSA/NC-DG. (d) XRD patterns of PtSA-DG and PtSA/NC-DG. Download figure Download PowerPoint X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS) measurements were carried out to identify the electronic and geometric structure of Pt species in the PtSA-DG and PtSA/NC-DG-X catalysts. The high-resolution Cl 2p XPS spectra showed the complete removal of chlorine ( Supporting Information Figure S10), suggesting the absence of Pt-Cl coordination in the obtained catalysts. The normalized X-ray absorption near-edge structure (XANES) spectra showed that white-line intensity of all the PtSA-DG and PtSA/NC-DG-X catalysts was located among PtO2 and Pt foil, demonstrating the existence of positively charged Pt species in these catalysts (Figure 3a).42 Furthermore, the decreased white-line intensity of PtSA/NC-DG-X catalysts indicated the enriching of Pt0 species with the increase of annealing temperature, which was also evidenced by high-resolution Pt 4f XPS spectra23 ( Supporting Information Figure S11). The coordination environments of Pt species were disclosed by k3-weighted extended XAFS (EXAFS). From Figure 3b and Supporting Information Figure S12, it was clearly found that only the dominant peak of Pt-C/N/O coordination was observed for the PtSA-DG catalyst, confirming the atomic dispersion of Pt species.22 For the PtSA/NC-DG-X catalysts, in addition to the peak from Pt-C/N/O contribution, those peaks close to the Pt–Pt coordination were also observed, evidencing the coexistence of Pt SAs and nanoclusters,10 in line with the above HAADF-STEM results. To more directly discriminate the coordination environment of PtSA-DG and PtSA/NC-DG catalysts, an EXAFS wavelet transform (WT) was performed (Figure 3c).43 For the PtSA-DG catalyst, only one intensity maximum region close to that of PtO2 was displayed, confirming the mononuclear centers of Pt species. Two maximum-intensity regions aligned with that of PtO2 and Pt foil were observed for the PtSA/NC-DG catalyst, strongly evidencing the presence of Pt-C/N/O and Pt–Pt coordination. Combining these spectroscopic results with the above microscopic observation, it was demonstrated that the PtSA-DG and PtSA/NC-DG were successfully constructed. Figure 3 | Spectroscopic identifications of PtSA-DG and PtSA/NC-DG-X. (a) Normalized XANES spectra and local enlargement at the Pt L3 edge. (b) k3-weighted R space Fourier-transformed spectra from the XANES. (c) WT for the EXAFS spectra. Download figure Download PowerPoint HER performance of different carbon-loaded Pt catalysts The high-performance catalytic activities of the PtSA/NC-DG for alkaline HER were verified in a typical three-electrode cell filled by 1 M KOH. First, from the polarization curves of PtSA/NC-DG-X catalysts ( Supporting Information Figure S13), the PtSA/NC-DG obtained at 400 °C was reactivity-optimized, probably due to the suitable ratio of Pt SAs and nanoclusters.32 The optimized PtSA/NC-DG achieved an overpotential (η) of 41 mV at a current density of 10 mA cm−2, significantly surpassing that of the PtSA-DG and commercial 20 wt % Pt/C catalysts (Figure 4a and Supporting Information Figure S14). The comparison of mass activities for precious metal-based catalysts is of great importance.9,44 Thus, the mass activities of PtSA-DG, PtSA/NC-DG, and commercial Pt/C were calculated based on the Pt loading at the electrode. The PtSA/NC-DG delivered significantly higher mass activity than the PtSA-DG and commercial Pt/C (Figure 4b and Supporting Information Figure S15). In particular, the mass activity of PtSA/NC-DG was as high as 5.40 mA μgpt−1 at 100 mV, which was nearly 6 and 10 times higher than that of PtSA-DG (0.83 mA μgpt−1) and commercial Pt/C (0.52 mA μgpt−1). In addition, the calculated turnover frequency (TOF) also demonstrated the remarkable activity of the PtSA/NC-DG ( Supporting Information Figure S16). From Supporting Information Figure S17, the Tafel slope of PtSA/NC-DG (40 mV dec−1) was close to that of commercial Pt/C, and was lower than that of PtSA-DG, following the Volmer–Tafel mechanism.28,45 Moreover, the exchange current density of PtSA/NC-DG was 1.25 mA cm−2 (Figure 4c), which is nearly seven and two times larger than that of PtSA-DG and commercial Pt/C, indicating rapid reaction kinetics of the PtSA/NC-DG. To further compare the intrinsic activity, the electrochemically active surface area (ECSA) was evaluated ( Supporting Information Figure S18). The ECSA-normalized mass activity of the PtSA/NC-DG at 100 mV was still five times higher than that of the PtSA-DG ( Supporting Information Figure S19), demonstrating superior intrinsic activity. To rule out the possible influence of particle size, exposed surface and the metal–support interaction, we prepared the Pt nanoclusters supported on high-surface-area carbon black support (PtNC-BP2000-400) with similar Pt loading according to previous studies.10 The PtNC-BP2000-400 without Pt SAs displayed a similar size of Pt clusters with PtSA/NC-DG ( Supporting Information Figure S20), which was also confirmed by high-resolution Pt 4f XPS spectra ( Supporting Information Figure S21). The metal–support interaction result from particle size could also be excluded. Then, we compared their electrocatalytic activity and stability. The PtSA/NC-DG catalyst displayed a lower overpotential and superior stability than PtNC-BP2000-400 ( Supporting Information Figure S22). The negligible overpotential increase after accelerated degradation test evidenced the long-term stability of PtSA-DG and PtSA/NC-DG, probably thanks to the confinement effect of the defective carbon matrix (Figure 4d and Supporting Information Figures S23 and S24).22,46 HAADF-STEM images of PtSA/NC-DG after 10,000 cycles further confirmed that PtSA/NC-DG is only slight larger than that of slight larger than that of the pristine PtSA/NC-DG ( Supporting Information Figure S25). N 1s and Pt 4f high-resolution XPS spectrum of PtSA/NC-DG further demonstrated the outstanding structural stability of PtSA/NC-DG catalyst ( Supporting Information Figures S26 and S27). The PtSA/NC-DG compared with that of PtSA-DG, PtNC-BP2000-400, commercial Pt/C as well as other Pt-based catalysts ( Supporting Information Table S2) displayed higher activity, verified the above theoretical synergistic effect of Pt SAs and nanoclusters boosting water splitting into hydrogen. Figure 4 | Electrochemical characterization. All data are IR-corrected. (a) LSV curves of PtSA-DG, PtSA/NC-DG, and commercial Pt/C in 1 M KOH. (b) Mass activities of PtSA-DG, PtSA/NC-DG, and commercial Pt/C at an overpotential of 50 and 100 mV. (c) Exchange current density of PtSA-DG, PtSA/NC-DG, and commercial Pt/C. (d) LSV curves of PtSA/NC-DG recorded initially and after 10,000 potential cycles. IR, infrared; LSV, linear sweep voltammetry. Download figure Download PowerPoint Conclusion Combining the DFT simulation and experimental verification, we have reported a highly efficient PtSA/NC-DG electrocatalyst for alkaline HER by the integration of Pt nanoclusters and SAs onto DG matrix. In the integrated structure, the Pt nanoclusters promote water dissociation into *H and *OH, and the Pt SAs facilitate the H–H coupling into gaseous hydrogen. Consequently, despite low Pt loading in the PtSA/NC-DG catalyst, the electrocatalytic performance toward alkaline HER is substantially better than that of the Pt SA counterpart and commercial Pt/C catalyst with 20 wt % Pt. The notion presented in this work will provide some guidance for the design of noble metal-based heterogeneous catalysts approaching the ultimate in atomic utilization efficiency. Supporting Information Supporting Information is available. Conflict of Interest There is no conflict of interest to report. Funding Information This work was supported by the National Natural Science Foundation of China (nos. 21838003, 91834301, and 21978278), the Shanghai Scientific and Technological Innovation Project (nos. 18JC1410500 and 19JC1410400), and the Fundamental Research Funds for the Central Universities (no. 222201718002). Acknowledgments The authors thank Shanghai Synchrotron Radiation Facility (BL14W1, SSRF).

The use of molybdenum disulfide (MoS 2 ) as a non‐noble metal electrocatalyst for the hydrogen evolution reaction (HER) has gained significant attention due to its affordability and the ease of modifying factors such as voltage, current, duration, and the composition and concentration of the electrolyte solution using electrodeposition techniques. To increase the number of active sites on the surface of MoS 2 , fine nanoscale tailoring of the crystalline phase is necessary. This can be accomplished using electrochemical phase formation. In this study, four types of MoS 2 nanoparticles are successfully electrodeposited on copper foil substrates using a mixture of Na 2 MoO 4 and Na 2 S electrolytes, namely fine nodular MoS 2 (FNMoS 2 ), small sheet MoS 2 (SSMoS 2 ), highly porous MoS 2 (HPMoS 2 ), and low porous MoS 2 (LPMoS 2 ), with nanoparticles of FNMoS 2 , SSMoS 2 , HPMoS 2 , and LPMoS 2 being produced at potentials of −0.9, −1.0, −1.1, and −1.2, respectively. The electrochemical performance of these nanoparticles on HER is carefully investigated using techniques such as high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), and energy dispersive spectroscopy. Linear sweep voltammetry, Tafel plot analysis, and electrochemical impedance spectroscopy are used to study the electrocatalytic performance of HER in a 0.5 M KOH electrolyte. HPMoS 2 electrodeposited at −1.1 V for 200 s had a HER current density of 10 mA cm −2 at η = −270 mV and a Tafel slope (vs RHE) of 35.8 mV/dec, lower than that of FNMoS 2 , SSMoS 2 , and LPMoS 2 . These results have significant implications for the development of low cost, affordable, and environmentally friendly electrochemical methods of producing hydrogen, and pave the way for further research in this field.

<p indent="0mm">The use of fossil fuels has resulted in serious environmental and energy crises, necessitating urgent exploration of a sustainable and environment-friendly alternative energy source to achieve the strategic goals of carbon peaking and carbon neutrality. In this regard, hydrogen energy offers the advantages of high density, pollution-free production, and abundant raw materials, and it presents a solution to the energy crisis. Electrochemical water splitting is an effective method for producing hydrogen energy, the hydrogen evolution reaction (HER) occurring at the involved cathode exhibits high Faraday efficiency, progresses under mild conditions and yields hydrogen with high purity, rendering the method suitable for use in large-scale hydrogen production. The key to achieving an efficient HER is finding a suitable catalyst. Presently, platinum-based precious-metal catalysts deliver the best electrocatalytic HER performance. However, their high cost due to scarcity restricts their large-scale application. Consequently, nonprecious-metal catalysts with abundant reserves and excellent electrolytic HER performance are urgently desired. Compared with other nonprecious metals, Ni, as a transition metal, offers high abundance, low toxicity and excellent electronic properties. Further, the outer layer of a Ni atom has unpaired 3d electrons, which easily pair with the electron in the 1s orbital of a hydrogen atom to form Ni-H bonds during the HER. Ni exhibits considerable potential for catalytic application in the HER under alkaline conditions. Notably, Ni-based oxides, phosphates, sulfides, etc. show excellent electrocatalytic HER properties. Among them, NiO has recently garnered widespread research interest because of its simple preparation and low cost. For instance, researcher successfully synthesized a NiO/C nanocomposite electrocatalyst using eggshells as the carbon source. The synergistic effect between NiO and C effectively resulted in high electrocatalytic activity of the involved sample under alkaline conditions. Moreover, through oxygen vacancy regulation and cation exchange, researcher successfully prepared a NiO nanorod array electrocatalyst with abundant oxygen vacancies on a carbon fiber paper, the oxygen vacancies resulted in a substantially enhanced charge-transport performance of the involved NiO sample. Further, researcher prepared a NiO/Ni heterojunction electrocatalyst on carbon cloth through in situ surface reconstruction. The involved sample exhibited good hydrophilicity and abundant oxygen vacancies as well as excellent electrocatalytic HER activity and stability under alkaline conditions. However, because of the low conductivities and inappropriate adsorption strengths of H and H₂O on the sample surface, NiO exhibited slow HER kinetics in alkaline media, considerably hindering its large-scale application as an HER catalyst. To address this issue, in this research, three-dimensional self-supported V-doped NiO nanosheet arrays were designed and successfully fabricated for catalytic application in the HER under alkaline conditions. Experimental results show that V doping can effectively improve the electrocatalytic HER activity of NiO, with the catalyst exhibiting good stability. Moreover, a V:Ni molar ratio of 10% is found to result in the best electrocatalytic HER performance. Experimental tests and density functional theory calculations show that V doping optimizes the electronic structure of NiO, effectively improves its charge transport performance, and increases its electrochemically active area. In addition, through optimization of the d-band center of the catalyst, excessive proton binding is inhibited, and through enhancement of H₂O adsorption, the energy barriers involved in the rate-determining step (i.e., water dissociation) of the HER are reduced. Overall, owing to various synergistic effects between V and NiO, the electrocatalytic HER performance of NiO is notably promoted through V doping.

Electrocatalytic hydrogen production by bulk and nano Fe2O3 and carbon nanotube modified with Fe2O3

Interwoven CoSe2/CNTs hybrid as a highly efficient and stable electrocatalyst for hydrogen evolution reaction

Industrial stainless steel meshes for efficient electrocatalytic hydrogen evolution

Electrochemical hydrogen evolution reaction (HER) is an appealing strategy to utilize renewable electricity to produce green H2. Moreover, use of neutral-pH electrolyte such as water and seawater for the HER has long been desired for eco-friendly energy production that aligns with net zero emission goal. Herein, new heterogeneous catalysts were developed by dispersing an HER-active copper complex containing N4-Schiff base macrocycle (CuL) on carbonaceous materials, i. e. multi-walled carbon nanotube (CNT) and graphene oxide (GO), via non-covalent interaction and investigated their HER performance. It was found that CuL/GO exhibited higher HER activity than CuL/CNT, possibly due to its significantly larger amount of CuL immobilized onto GO. In addition, CuL/GO showed satisfactory HER performance in a neutral (pH 7) NaCl electrolyte solution. Notably, the performances of CuL/GO were boosted up when performed in natural seawater sample with the faradaic efficiency of 70 % and 3 times higher amount of H2 at -0.6 V vs reversible hydrogen electrode (RHE), in comparison to the HER in a NaCl electrolyte. Furthermore, it possessed a low overpotential of 139 mV at -10 mA/cm2. This demonstrated the potential use of CuL/GO as an effective HER catalyst in seawater for further sustainable development.

In this paper, novel cobalt-doped Ni0.85Se chalcogenides (Co xNi0.85- xSe, x = 0.05, 0.1, 0.2, 0.3, and 0.4) are successfully synthesized and studied as high active and stable electrocatalysts for hydrogen evolution reaction (HER) in electrolysis water splitting. The morphologies, structures, and composition of these as-prepared catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy. The electrochemical tests, such as linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry testing, are performed to evaluate these catalysts' HER catalytic performance including activity and stability. The results indicate that a suitable doping can result in synergetic effect for increasing the catalytic performance. Among different catalysts, Co0.1Ni0.75Se shows the highest HER performance. After introducing the reduced graphene oxide (rGO) into this catalyst as the support, the resulted Co0.1Ni0.75Se/rGO shows even better performance than unsupported Co0.1Ni0.75Se, which are confirmed by the reduction of HER overpotential of Co0.1Ni0.75Se/rGO to 103 mV compared to 153 mV of Co0.1Ni0.75Se at a current density of 10 mA/cm2, and the smaller Tafel slope (43 mV/dec) and kinetic resistance (21.34 Ω) than those of Co0.1Ni0.75Se (47 mV/dec, 30.23 Ω). Furthermore, the large electrochemical active surface area and high conductivity of such a Co0.1Ni0.75Se/rGO catalyst, induced by rGO introduction, are confirmed to be responsible for the high HER performance.