Mechanism Of Hydrogen Evolution Reaction Research Articles

Gold as an efficient hydrogen isotope separation catalyst in proton exchange membrane water electrolysis

The development of proton exchange membrane water electrolysis (PEMWE) offers an updating potential for electrolytic hydrogen isotope separation. However, it has a significantly lower separation factor than the traditional alkaline water electrolysis. In this study, we propose gold as a promising cathodic catalyst for efficient hydrogen isotope separation in PEMWE. Au/C has a protium-to-deuterium (H/D) separation factor of 7.47 in PEMWE, about twice that of Pt/C. In addition, the full cell's electrochemical performance is comparable to that of its Pt/C counterpart. The separation mechanism in PEMWE is explained by the transitional hydrogen evolution reaction mechanism from Heyrovsky to Tafel for Pt and the unchangeable Volmer mechanism for Au. The high separation factor for Au is also calculated by the H/D zero-point vibrational energy difference between transition state and reaction state through a simple density functional theory calculation. This work offers an effective strategy to improve hydrogen isotope separation efficiency in PEMWE.

Dissociation of Pyridinethiolate Ligands during Hydrogen Evolution Reactions of Ni-Based Catalysts: Evidence from X-ray Absorption Spectroscopy.

The protonation of several Ni-centered pyridine-2-thiolate photocatalysts for hydrogen evolution is investigated using X-ray absorption spectroscopy (XAS). While protonation of the pyridinethiolate ligand was previously thought to result in partial dechelation from the metal at the pyridyl N site, we instead observe complete dissociation of the protonated ligand and replacement by solvent molecules. A combination of Ni K-edge and S K-edge XAS of the catalyst Ni(bpy)(pyS)2 (bpy = 2,2′-bipyridine; pyS = pyridine-2-thiolate) identifies the structure of the fully protonated catalyst as a solvated [Ni(bpy)(DMF)4]2+ (DMF = dimethylformamide) complex and the dissociated ligands as the N-protonated 2-thiopyridone (pyS-H). This surprising result is further supported by UV–vis absorption spectroscopy and DFT calculations and is demonstrated for additional catalyst structures and solvent environments using a combination of XAS and UV–vis spectroscopy. Following protonation, electrochemical measurements indicate that the solvated Ni bipyridine complex acts as the primary electron-accepting species during photocatalysis, resulting in separate protonated ligand and reduced Ni species. The role of ligand dissociation is considered in the larger context of the hydrogen evolution reaction (HER) mechanism. As neither the pyS-H ligand nor the Ni bipyridine complex acts as an efficient HER catalyst alone, the critical role of ligand coordination is highlighted. This suggests that shifting the equilibrium toward bound species by addition of excess protonated ligand (2-thiopyridone) may improve the performance of pyridinethiolate-containing catalysts.

Ligand-Centered Hydrogen Evolution with Ni(II) and Pd(II)DMTH.

In this study, we report a pair of electrocatalysts for the hydrogen evolution reaction (HER) based on the noninnocent ligand diacetyl-2-(4-methyl-3-thiosemicarbazone)-3-(2-pyridinehydrazone) (H2DMTH, H2L1). The neutral complexes NiL1 and PdL1 were synthesized and characterized by spectroscopic and electrochemical methods. The complexes contain a non-coordinating, basic hydrazino nitrogen that is protonated during the HER. The pKa of this nitrogen was determined by spectrophotometric titration in acetonitrile to be 12.71 for NiL1 and 13.03 for PdL1. Cyclic voltammograms of both NiL1 and PdL1 in acetonitrile exhibit diffusion-controlled, reversible ligand-centered events at -1.83 and -1.79 V (vs ferrocenium/ferrocene) for NiL1 and PdL1, respectively. A quasi-reversible, ligand-centered event is observed at -2.43 and -2.34 V for NiL1 and PdL1, respectively. The HER activity in acetonitrile was evaluated using a series of neutral and cationic acids for each catalyst. Kinetic isotope effect (KIE) studies suggest that the precatalytic event observed is associated with a proton-coupled electron transfer step. The highest turnover frequency values observed were 6150 s-1 at an overpotential of 0.74 V for NiL1 and 8280 s-1 at an overpotential of 0.44 V for PdL1. Density functional theory (DFT) computations suggest both complexes follow a ligand-centered HER mechanism where the metals remain in the +2 oxidation state.

Surface Design Strategy of Catalysts for Water Electrolysis.

Hydrogen, a new energy carrier that can replace traditional fossil fuels, is seen as one of the most promising clean energy sources. The use of renewable electricity to drive hydrogen production has very broad prospects for addressing energy and environmental problems. Therefore, many researchers favor electrolytic water due to its green and low-cost advantages. The electrolytic water reaction comprises the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Understanding the OER and HER mechanisms in acidic and alkaline processes contributes to further studying the design of surface regulation of electrolytic water catalysts. The OER and HER catalysts are mainly reviewed for defects, doping, alloying, surface reconstruction, crystal surface structure, and heterostructures. Besides, recent catalysts for overall water splitting are also reviewed. Finally, this review paves the way to the rational design and synthesis of new materials for highly efficient electrocatalysis.

Dianion Induced Electron Delocalization of Trifunctional Electrocatalysts for Rechargeable Zn–Air Batteries and Self‐Powered Water Splitting

AbstractThe development of low‐cost multifunctional electrocatalysts with high activity for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) is critical for the advancement of sophisticated energy conversion and storage devices. Herein, a trifunctional Ni(S0.51Se0.49)2@NC catalyst is designed and fabricated using a dianionic regulation strategy. Synchrotron radiation X‐ray absorption spectroscopy and density functional theory calculations reveal that simultaneous sulfidation and selenization can induce the electronic delocalization of Ni(S0.51Se0.49)2 active sites to enhance the adsorption of *OOH/*OH intermediate for ORR/OER and H* intermediate for HER. The OER and HER mechanisms are revealed by in situ Raman spectroscopy. The Ni(S0.51Se0.49)2@NC exhibits trifunctional catalytic activity for the HER (111 mV at 10 mA cm−2), OER (320 mV at 10 mA cm−2), and ORR (half‐wave potential of 0.83 V). The rechargeable zinc–air batteries (ZABs) exhibit an open‐circuit voltage of 1.46 V, a specific capacity of 799.1 mAh g−1, and excellent stability for 1000 cycles. The water electrolytic cell using Ni(S0.51Se0.49)2@NC electrodes delivers a current density of 10 mA cm−2 at a cell voltage of 1.59 V, and it can be powered using the constructed ZABs. These findings contribute to developing low‐cost and efficient non‐noble metal multifunctional catalysts.

Facile hydrothermal synthesis of rare earth phosphate for boosting hydrogen evolution reaction

The water electrolysis process has attracted great attention due to the production of high energy density pure hydrogen. However, the involved cell reactions in this process such as hydrogen and oxygen evolution reactions are kinetically sluggish and demands high input energy to accelerate the rate of these reactions. Therefore, the development and application of efficient electrocatalyst is essential for hydrogen evolution reaction (HER) as well as oxygen evolution reaction (OER). In the present work, we have successfully synthesized two rare earth phosphates through the hydrothermal route and used as a catalysts towards HER in an acidic medium. The rare earth phosphate PrPO 4 exhibits better catalytic activity than YPO 4 catalyst. The overpotential of PrPO 4 , YPO 4 and standard Pt/C were found as 147, 484.3 and 58 mV vs. reversible hydrogen electrode, respectively, to reach current density 10 mA·cm −2 and corresponding Tafel slopes were found as 107.58, 118.73 and 80.89 mV decade −1 , respectively in 0.5 M H 2 SO 4 . The catalytic activity of PrPO 4 (472.83 mA·cm −2 ) overcome standard Pt/C (179.60 mA·cm −2 ) at high overpotential 450 mV vs. reversible hydrogen electrode. The prepared PrPO 4 shows efficient electrocatalytic activity towards HER in acidic medium because it possess high BET surface area, large ECSA value and small charge transfer resistance than YPO 4 . • Hydrothermal synthesis of rare earth phosphates and explored HER performance. • As prepared PrPO 4 exhibits good catalytic activity towards HER in 0.5 M H 2 SO 4 . • The overpotential 147 mV to get 10 mA·cm −2 and Tafel slope 107.58 mV decade −1 . • The efficient PrPO 4 followed Volmer-Heyrovsky mechanism for HER.

The kinetics of cathodic hydrogen evolution on titanium disilicide in a sulphuric acid solution

The kinetics and mechanism of hydrogen evolution reaction on the TiSi2 electrode in x M H2SO4 + (0.5 – x) M Na2SO4 (x = 0.5; 0.35; 0.20; 0.05) solutions were studied using the methods of polarisation and impedance measurements. The cathodic polarisation curves of TiSi2 were characterised by a Tafel section with a slope of 0.116–0.120 V at E ranging from –0.30 to –0.48 V (SHE). The value of hydrogen evolution overpotential at i = 1 A/cm2 for TiSi2 was 0.90–0.96 V. The kinetic parameters of the hydrogen evolution reaction on silicide were close to the theoretical values for the slow stage of charge transfer. Based on the measurements of the differential capacitance of the TiSi2 electrode (at f = 10 kHz), depending on the cathodic polarisation and acidity of the electrolyte, it was concluded that a thin dielectric film of silicon dioxide (Si + 2H2O →SiO2 + 4H+ + 4e–) was present on the surface of the silicide. The film was not reduced with low cathodic polarisations. The impedance spectra of the TiSi2 electrode at the potentials of the Tafel region were capacitive semicircles with a misplaced centre. The impedance spectra were described by an equivalent electrical circuit, the Faraday impedance of which consisted of a series-connected charge transfer resistance R1 and a parallel R2C2 chain corresponding to the adsorption of atomic hydrogen on the electrode surface. The impedance of the double layer capacitance was modelled using the constant phase element CPE1. The χ2 criterion for the circuit was (1.3-3.7)·10-4 (when using data modulus weighting), the sum of square deviations was (1.5–4.1)·10–2, and the error in the determination of the values of circuit parameters did not exceed 10 %.The experimental values of the slopes of lg R1,E-, lg R2,E-, and lg C2,E-dependences were close to the theoretical values of the slopes for the discharge-electrochemical desorption mechanism, in which both stages were irreversible and the transfer coefficients of the stages were not equal, when the Langmuir isotherm for adsorbed atomic hydrogen was fulfilled. The reaction of absorption of hydrogen with the kinetic control proceeded at the same time as the hydrogen evolution reaction.

Metalloporphyrins as Catalytic Models for Studying Hydrogen and Oxygen Evolution and Oxygen Reduction Reactions.

The hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) are involved in biological and artificial energy conversions. H-H and O-O bond formation/cleavage are essential steps in these reactions. In nature, intermediates involved in the H-H and O-O bond formation/cleavage are highly reactive and short-lived, making their identification and investigation difficult. In artificial catalysis, the realization of these reactions at considerable rates and close to their thermodynamic reaction equilibria remains a challenge. Therefore, the elucidation of the reaction mechanisms and structure-function relationships is of fundamental significance to understand these reactions and to develop catalysts.This Account describes our recent investigations on catalytic HER, OER, and ORR with metalloporphyrins and derivatives. Metalloporphyrins are used in nature for light harvesting, energy conversion, electron transfer, O2 activation, and peroxide degradation. Synthetic metal porphyrin complexes are shown to be active for these reactions. We focused on exploring metalloporphyrins to study reaction mechanisms and structure-function relationships because they have stable and tunable structures and characteristic spectroscopic properties.For HER, we identified three H-H bond formation mechanisms and established the correlation between these processes and metal hydride electronic structures. Importantly, we provided direct experimental evidence for the bimetallic homolytic H-H bond formation mechanism by using sterically bulky porphyrins. Homolytic HER has been long proposed but rarely verified because the coupling of active hydride intermediates occurs spontaneously and quickly, making their detection challenging. By blocking the bimolecular mechanism through steric effects, we stabilized and characterized the NiIII-H intermediate and verified homolytic HER by comparing the reaction behaviors of Ni porphyrins with and without steric effects. We therefore provided an unprecedented example to control homolytic versus heterolytic HER mechanisms through tuning steric effects of molecular catalysts.For the OER, the water nucleophilic attack (WNA) on high-valent terminal Mn-oxo has been proposed for the O-O bond formation in natural and artificial water oxidation. By using Mn tris(pentafluorophenyl)corrole, we identified MnV(O) and MnIV-peroxo intermediates in chemical and electrochemical OER and provided direct experimental evidence for the Mn-based WNA mechanism. Moreover, we demonstrated several catalyst design strategies to enhance the WNA rate, including the pioneering use of protective axial ligands. By studying Cu porphyrins, we proposed a bimolecular coupling mechanism between two metal-hydroxide radicals to form O-O bonds. Note that late-transition metals do not likely form terminal metal-oxo/oxyl.For the ORR, we presented several strategies to improve activity and selectivity, including providing rapid electron transfer, using electron-donating axial ligands, introducing hydrogen-bonding interactions, constructing dinuclear cooperation, and employing porphyrin-support domino catalysis. Importantly, we used Co porphyrin atropisomers to realize both two-electron and four-electron ORR, representing an unparalleled example to control ORR selectivity by tuning only steric effects without modifying molecular and/or electronic structures.Lastly, we developed several strategies to graft metalloporphyrins on various electrode materials through different covalent bonds. The molecular-engineered materials exhibit boosted electrocatalytic performance, highlighting promising applications of molecular electrocatalysis. Taken together, this Account demonstrates the benefits of exploring metalloporphyrins for the HER, OER, and ORR. The knowledge learned herein is valuable for the development of porphyrin-based catalysts and also other molecular and material catalysts for small molecule activation reactions.

Electrochemical proton insertion modulates the hydrogen evolution reaction on tungsten oxides.

The development of new electrocatalysts for the hydrogen evolution reaction (HER) could reduce the dependence on Pt and other rare metals and enable large-scale production of hydrogen with near-zero carbon emissions. Mechanistic insight into the electrocatalytic activity of a material helps to accelerate the development of new electrocatalysts. Alternative electrocatalyst materials such as transition metal oxides and sulfides can undergo insertion reactions that change their properties. Recent reports indicate that the presence of inserted ions can influence the electrocatalytic activity. Here, we utilized a materials chemistry approach to understand the role of proton insertion in the HER activity of the layered tungsten oxide hydrates (WO3·xH2O, x = 1, 2). We synthesized a series of tungsten oxide hydrates along with an octylamine-pillared tungsten oxide (OA-WO3). We used cyclic voltammetry to study the electrochemical reactivity of each material and performed ex situ x-ray diffraction and Raman spectroscopy to understand bulk and surface structural changes during electrochemical cycling. We show an inverse relationship between the degree of proton insertion and HER overpotential in tungsten oxides: the lack of proton insertion leads to a high overpotential for the HER. We discuss three hypotheses for how proton insertion leads to the HER activity in WO3·xH2O: (1) proton insertion changes the electronic band structure of WO3·xH2O, (2) the presence of bulk protons can influence ΔGH,ads at the surface sites, and (3) the inserted protons may participate in the HER mechanism on WO3·xH2O. Overall, this work shows the critical role of proton insertion in enabling the high HER activity in tungsten oxides.

Constructing heterostructure of CeO2/WS2 to enhance catalytic activity and stability toward hydrogen generation

Transition metal disulfides (TMD) are considered as promising catalysts for hydrogen evolution reaction (HER) due to their unique structural and electronic properties. However, as a representative, the tungsten disulfide (WS 2 ) shows an insufficient HER performance and is still needed to be further improved. Herein, we report the synthesis of CeO 2 -modified WS 2 nanosheets with abundant heterostructures on carbon cloth (CeO 2 /WS 2 /CC) as an efficient self-supported integral electrode for HER. Experimental results and theoretical calculations imply that the intimate electronic interaction between CeO 2 and WS 2 promotes the production of more oxygen vacancies in CeO 2 to regulate the electronic structure of WS 2 , endowing extra active sites, high electron transfer efficiency, and downshifted d-band center of W, which can lead to thermoneutral hydrogen adsorption Gibbs free energies (ΔG H* ) and thus boosts HER. The optimized CeO 2 /WS 2 /CC electrode displays an improved HER performance with an overpotential of 128 mV at 10 mA cm −2 in 0.5 M H 2 SO 4 aqueous solution, 87 mV smaller than that of the WS 2 /CC electrode. Meanwhile, it also could maintain a 20 h of stable HER activity. Our work provides an effective approach to achieve various hybrid catalysts of rare earth compounds-transition metal compounds with highly active sites for superior electrocatalysis. • A monolithic CeO 2 /WS 2 /CC electrode with heterostructure of CeO 2 /WS 2 is fabricated. • The hybrid CeO 2 /WS 2 nanosheets structure is beneficial to exposing more active sites. • The electronic interaction between WS 2 and CeO 2 results in a superior HER activity. • The mechanism of HER over CeO 2 /WS 2 /CC electrode is clarified by DFT calculations.

Redox behavior of iridium octaethylporphycene and electrocatalytic hydrogen evolution

The electrochemical properties of [Formula: see text]-octaethylporphycene iridium complex (Ir-OEPo) were determined. Based on the electro-spectro measurement results, the reduction of Ir-OEPo did not occur at the central metal but at the ligand, while the reduction of [Formula: see text]-octaethylporphyrin iridium complex (Ir-OEPor) occurred at the central iridium. A catalytic current was observed during the cyclic voltammetry (CV) measurements with trifluoroacetic acid (TFA) under a reductive condition, indicating the catalytic reactivity of Ir-OEPo for the hydrogen evolution reaction (HER). By constant potential electrolysis, hydrogen gas was detected by gas chromatography (GC) and the catalytic reactivity of Ir-OEPo was confirmed. The HER mechanism via ligand reduction of macrocyclic aromatic complexes could be one of the concepts for the development of new catalysts.

In Situ Studies of Hydrogen Evolution Kinetics on Pure Titanium Surface: The Effects of Pre-Reduction and Dissolved Oxygen

The apparent cathodic current on the Ti surface in acidic solution is composed of three reactions: the reductions of the oxide film, H+, and O2. However, classical electrochemical tests usually provide coupled multi-reaction currents. Furthermore, dissolved oxygen makes in situ measurements significant due to the thermodynamic instability of Ti. In this study, the effects of pre-reduction and dissolved oxygen on hydrogen evolution reaction (HER) kinetics on the Ti surface were investigated by electrochemical and composition characterizations. The HER current was quantitatively separated from the apparent cathodic current from Ti, including the reductions of the oxide film, H+, and O2 by scanning electrochemical microscopy. The HER transfer coefficient and standard rate constant for Ti spontaneously passivated in air (P-Ti) are both 0.48/4.9 × 10–12 cm/s in aerated and O2-saturated solutions, while those for Ti activated by electro-reduction (EA-Ti) are 0.25/3.6 × 10–7 cm/s and 0.25/3.1 × 10–7 cm/s, respectively. The variable HER behavior is caused by the changes in the film electronic structure and composition except for the competition reduction between O2 and H+ as indicated by Mott–Schottky and surface-enhanced Raman spectroscopy. The deviation from 0.5 in the transfer coefficient implies that the Tafel slope and HER mechanism should be analyzed with caution.

Кинетические параметры процесса получения молекулярного водорода в присутствии акридина и его производных

In order to study in more detail the mechanism of hydrogen evolution reaction, knowledge of which is ne- cessary for the practical implementation of existing ideas and developments in the field of modern electrocatalysis and hydrogen energy in general, the electrocatalytic properties of acridine and its derivatives in the presence of acids of var- ious natures were studied. The obtained electrochemical data made it possible to calculate the kinetic parameters of these systems, as well as to reveal the dependence of the rate constant of the limiting stage of the hydrogen generation process on the рКа of the acids used. The results of the work will make it possible to treat with greater understanding the creation of «molecular platforms» based on organic compounds, as well as improving the efficiency of the catalytic process and varying the available parameters.

Unveiling the mechanism of high-performance hydrogen evolution reaction on noble-metal-free (113)-faceted Ni3C: ab initio calculations.

To examine the reactivity of noble-metal-free Ni3C towards hydrogen evolution reaction (HER), we report a comprehensive first-principles density functional theory (DFT) study on the stability, geometric structure, electronic characteristics, and catalytic activity for HER on the Ni3C crystal (113) surfaces with different surface terminations, namely the C-rich and Ni-rich terminated surface of Ni3C (113). The results indicate that C-rich and some stoichiometric surfaces are thermodynamically stable. The bridge-site of C-rich Ni3C (113) is indispensable for HER because it not only displays improved electrocatalytic activity, but also possesses appropriate hydrogen adsorption energy, overpotential and robust stability. The ΔGH (0.02 eV) and overpotential obtained by C-rich Ni3C outperformed that obtained by Pt determined by computation (ΔGH = −0.07 eV). Thus, the bridge-sites of C-rich Ni3C (113) function as both excellent and stable active sites and adsorption/desorption sites. Increasing the density of active sites through doping or enlarging the surface area renders a prospective strategy to ameliorate the HER activity further. Overall, this study elucidates new insights into the surface properties of Ni3C for HER from water splitting and opens up a fascinating avenue to optimize the performance of solar energy conversion devices by synthesizing preferentially exposed catalyst facets.

Preparation of MoS2 spheres from Mo plate and elemental sulfur and the effect of sphericalization on electrochemical hydrogen evolution catalysis

The growth of MoS2 catalysts with a controlled morphology has been actively pursued to improve the electrocatalytic activity for hydrogen evolution reaction (HER) by modifying the shape of catalysts. However, it is questionable whether changes in morphological structure affect its intrinsic activity. Here we present a facile hydrothermal synthesis of amorphous MoSx spheres on Mo plates at 180 °C using elemental sulfur. Hydrolysis of elemental sulfur during the hydrothermal synthesis produces H2S and H2SO4 in hot water. Consequently, the surface of the Mo plate is sulfurized by H2S and dissolved by H2SO4 to form amorphous MoSx spheres with diameters in the range of 0.4–0.8 μm on the Mo plate. To investigate the effect of the sphericalization of crystalline MoS2 on its intrinsic activity for the HER, the amorphous MoSx spheres were annealed to form crystalline MoS2 spheres. The Tafel slopes of the amorphous MoSx (∼45 mV/dec) and crystalline MoS2 (∼103 mV/dec) spheres were similar to those of amorphous MoSx and crystalline MoS2 thin films, regardless of whether the shape of the catalyst was sphericalized or not. This reveals that the sphericalization cannot change the intrinsic activity and the HER mechanism on molybdenum sulfide.

Highly efficient hydrogen production via a zinc-carbon @ nickel system

Hydrogen energy is a promising energy carrier for powering electric vehicles lying in its dense energy and zero pollution. However, the problems of hydrogen production and control have yet to be resolved. Here we present a novel hydrogen production using zinc plate connected to carbon @ nickel electrode in the alkaline solution, where the device works through zinc oxidation at the anode and hydrogen evolution reaction at the cathode. The results demonstrate that the amount of hydrogen production with carbon @ nickel electrode can be improved 5 times higher than that of nickel electrode, and carbon @ nickel electrode can block zinc oxide adsorption upon nickel surface to keep hydrogen production stable. Moreover, hydrogen production is flexibly controlled by means of switching on/off connection between zinc electrode and carbon @ nickel electrode, facilitating to promote hydrogen application. Lastly, the mechanism of hydrogen evolution reaction is analyzed based on electrochemical characterization and density functional theory calculation, displaying that carbon @ nickel electrode can improve electron transfer ability for hydrogen evolution reaction.

Insight into enhanced hydrogen evolution of single-atom Cu1/TiO2 catalysts from first principles

Developing efficient catalysts of low-cost transition metals for hydrogen production is of great importance but remains a huge challenge. Motivated by the idea of engineering local atomic configuration, we propose to focus on single metal atom confined in the lattice oxygen environment, as a class of non-Pt catalysts for hydrogen production. By first principles calculations, we study the characteristics and mechanism of hydrogen evolution reaction of single-atom Cu supported on anatase TiO2 catalysts, Cu1/TiO2. Cu preferentially sits on the bridge-centre site between two 2-fold coordinated O atoms (O2c) on the surface. Cu and coordinated O2c function as copper oxide species (-Cu-O-) in the reaction. The reaction starts with two isolated H respectively positioned on Cu and O2c, proceeds with a transfer of H from O2c to Cu, and eventually forms a H2 molecule. The free energy profiles indicate that Cu1/TiO2 exhibits excellent hydrogen evolution activity even better than Pt and MoS2. This study not only shows that single-atom Cu1/TiO2 is an excellent hydrogen evolution catalyst, but also expands the understanding of oxide species in single-atom catalysis and proposes an engineering local atomic configuration strategy for optimizing the design of single-atom catalysts for enhanced hydrogen production.

Design of NiCo2O4 nanoparticles decorated N, S co-doped reduced graphene oxide composites for electrochemical simultaneous detection of trace multiple heavy metal ions and hydrogen evolution reaction

It is anenormous challenge to explore multifunctional electrocatalysts for simultaneous detection of Cd(II), Cu(II), Hg(II) and hydrogen evolution reaction (HER). In this work, NiCo2O4 decoratedN,Sco-doped reduced grapheneoxide composites (NCO/N, S-rGO) are synthesized via hydrothermal followed calcination process. The synergetic effect, oxygen vacancies and hybridization of NCO/N, S-rGO improve its excellent electrocatalytic performance for simultaneous and individual detection of Cd(II), Cu(II), Hg(II) and HER activity. When NCO/N, S-rGO is acted as heavy metal ions (HMIs) electrochemical sensors, it exhibits the high sensitivity and low detection limit for Cd(II) with 2.38 μA μM−1 and 123 nM, Cu(II) with 10.90 μA μM−1 and 14.4 nM, as well as Hg(II) with 5.41 μA μM−1 and 67 nM. NCO/N, S-rGO has outstanding stability and anti-interference performance and has been successfully implemented in the actual water environment. Furthermore, NCO/N, S-rGO also exhibits HER activity with overpotential and Tafel slope of 107 mV and 71.35 mV dec-1, respectively. The electrochemical detection and HER activity mechanism of NCO/N, S-rGO are further investigated and demonstrated that the synergetic effect of NCO/N, S-rGO can improve its electronic microstructure and promote electrocatalytic performance. This work not only provides a simple method for the preparation of multifunctional electrocatalysts, but also enhances the comprehension of HMIs detection and HER mechanism.

Mechanism of sulfur vacancies and doping in 1 T'-MoS2 toward the evolution of hydrogen

Due to the high activity, MoS2 is promising in replacing Pt-based electrocatalysts in hydrogen evolution reaction (HER) applications. However, the poor conductivity and fewer activity sites of 2H-MoS2 impede its practical application. The overall performance of 1 T'-MoS2 still has gaps to those Pt-based electrocatalysts. Thus, in this work, methods of doping and introducing defects were attempted to further improve the HER performance of 1 T'-MoS2. Through first-principle methods, the mechanism of HER on 1 T'-MoS2 with dopants or defects was analyzed. We found that Ni doping can further optimize the HER performance of 1 T'-MoS2.

Modification of NiCo-S with Phytate for Enhanced Electrocatalytic Hydrogen Evolution Activity

Transition metal phosphides (TMP) are excellent non-precious metal electrocatalysts for hydrogen evolution reaction (HER). The generation of PO4 3− before and during the HER process may be inevitable due to the instability of TMP. To investigate the effect of PO4 3− on the HER catalytic activity of electrocatalysts in alkaline medium, NiCo-S nanotubes were modified with phytate (PHY) with six phosphate groups via adsorption. The successful modification was verified by zeta potential, FT-IR, element mapping, XPS, etc The NiCo-S/PHY displayed a higher HER activity than original NiCo-S. Under the optimum adsorption time (7 h), the overpotential at 10 mA cm−2 (η 10) of NiCo-S/PHY (173 mV) was only half that of the original NiCo-S (346 mV). The role of PO4 3− was discussed in detail. Moreover, this strategy was extended to NiCo-S grown directly on nickel foam (NiCo-S/NF) and the corresponding NiCo-S/PHY/NF also showed superior HER activity and good stability. This work provides a new strategy to improve the HER activity of electrocatalysts and also a novel perspective for the HER mechanism of TMP.