HER Electrocatalysts Research Articles

Nickel Nanowire Arrays with Preferential Orientation for Boosting Hydrogen Evolution Reaction Capability

Nickel nanowire arrays with preferential growth of (111), (200) and (220) lattice planes were prepared via a modified template-assisted electrodeposition method respectively. As a HER electrocatalyst, (220) preferred orientation nickel nanowire arrays exhibited higher catalytic activity and stability in alkaline solution, and the hydrogen evolution overpotential was as low as 128 mV at the current density of 10 mA · cm−2. The performance is attributed to the higher surface energy of the (220) lattice plane of nickel nanowire arrays as the exposed surface and more active sites participate in HER process, which is beneficial to charge transfer and decrease of activation energy of reactions. Simultaneously, the activation energy of exposed surface evaluated directly by calculating with First-principles correspond to the trend of the experimental results, catalytic activity (220) > (200)> (111) lattice plane in the hydrogen evolution process. The strategy of using crystal anisotropy to improve catalytic performance can be extended to the synthesis of other nanocrystals with higher activity and high-energy surface catalysts.

Interface engineering of Ag-Ni3S2 heterostructures toward efficient alkaline hydrogen evolution.

Exploring Earth-abundant transition-metal-based electrocatalysts with high performance toward the alkaline hydrogen evolution reaction (HER) is crucial for sustainable hydrogen production. Ni3S2 has been recently identified as a promising HER catalyst, but it has unfavorable water dissociation and hydrogen adsorption characteristics. Here, we report Ag-decorated Ni3S2 nanosheet arrays grown on Ni Foam (NF) (Ag-Ni3S2/NF) as efficient heterostructure electrocatalysts for the HER in alkaline media. The catalyst only requires a low overpotential of 89 mV at 10 mA cm-2, as well as sustaining long-term durability for 15 h. The experimental analysis, in combination with density functional theory calculation, demonstrates that the electronic coupling at the interface between Ni3S2 and Ag results in enhanced electronic conductivity and optimized hydrogen adsorption and water adsorption/dissociation free energies. This work not only develops a highly efficient catalyst toward the HER, but also sheds light on the structure-activity relationship of the heterostructure catalyst on an atomic scale.

Spontaneous deposition of Ir nanoparticles on 2D siloxene as a high-performance HER electrocatalyst with ultra-low Ir loading.

Herein, 2D siloxene terminated by surface functional groups of Si-H and Si-OH is demonstrated to be an effective support for the spontaneous deposition of iridium nanoparticles (Ir NPs) to promote HER electrocatalysis. With ultra-low Ir loading, the obtained Ir NPs/siloxene electrocatalyst shows superior electrocatalytic activity toward the HER.

The coupling of experiments with density functional theory in the studies of the electrochemical hydrogen evolution reaction

This article discusses the power of coupling experiments with DFT in obtaining insights into the fundamentals of HER, Qincluding explaining experimental results and revealing reaction mechanisms and facilitating the development of new HER electrocatalysts.

MoC based Mott–Schottky electrocatalyst for boosting the hydrogen evolution reaction performance

Searching for promising HER electrocatalysts is an urgent task for the practical application of hydrogen production by water electrolysis.

Preparation of Ni–P–La alloy as a novel electrocatalysts for hydrogen evolution reaction

Ternary Ni–P–La alloy was synthesized by the co-electrodeposition method on the copper substrate. The energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used for characterization of the synthesized alloy. The electrochemical performance of the novel alloy was investigated based on electrochemical data obtained from steady-state polarization, Tafel curves, linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) in alkaline solution and at ambient temperature. The results showed that the microstructural properties play a vital purpose in determining the electrocatalytic activity of the novel alloys. Also, the HER on investigated alloys was performed via the Volmer-Heyrovsky mechanism and Volmer step as RDS in this work. Ni–P–La catalyst was specified by ƞ250 = −139.0 mV, b = −93.0 mV dec−1, and jo = −181.0 μA cm−2. The results revealed that the Ni–P–La catalysts have a high potential for HER electrocatalysts in 1M NaOH solution.

Improving Electrochemical Hydrogen Evolution of Ag@CN Nanocomposites by Synergistic Effects with α-Rich Proteins.

A graphitic carbon nitride nanostructure has been successfully functionalized by incorporation of different silver contents and subsequent modification with an α-rich protein, namely hemoglobin. Mechanochemistry has been employed, as an efficient and sustainable procedure, for the incorporation of the protein. A complete characterization analysis has been performed following a multitechnique approach. Particularly, XPS data exhibited considerable differences in the C 1s region for the Hb/xAg@CN, ensuring the successful protein anchorage on the surface of the graphitic carbon nitride-based materials. The as-synthesized nanomaterials delivered impressive performance toward hydrogen evolution reactions with an overpotential of 79 mV at a current density of 10 mA/cm2 for Hb/20Ag@CN nanohybrids, which is comparable with the most efficient HER electrocatalysts reported in the literature. The outstanding HER properties were associated with the unique synergistic interactions, quantitatively measured, between AgNPs, Hb tertiary architecture, and the graphitic carbon nitride networks.

Ultrathin and porous Mo-doped Ni nanosheet arrays as high-efficient electrocatalysts for hydrogen evolution reaction

High-active and low-cost electrocatalysts is crucial in obtaining clean hydrogen energy via water splitting. Nickel (Ni) is an attractive alternative to the noble metal electrocatalysts for alkaline HER. However, in high concentration alkaline media, it suffers from severe corrosion and deactivation. To solve this problem an ultrathin and porous Ni nanosheet were fabricated with Molybdenum (Mo) doping by hydrogen reduction of NiMoO4-Ni(OH)2 nanosheets to fine-tune the morphology and HER activity. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) demonstrate that the introduced Mo does not only help to control the morphology but also greatly boosts the HER activity of Ni due to the strong interaction between Mo and Ni. The enhanced HER performance is attested by the overpotential of 91 mV at 10 mA cm−2, low Tafel slope of 62 mV dec−1 and good stability, which is much superior to that of recently reported non-noble metal-based HER electrocatalysts. This study present Ni catalyst as a promising catalyst for the industrial production of H2.

Ultrathin WS2 nanosheets vertically aligned on TiO2 nanobelts as efficient alkaline hydrogen evolution electrocatalyst

Highly efficient and durable non-noble metal-based hydrogen evolution electrocatalysts are critical to advance the production of hydrogen energy via alkaline water electrolysis. Herein, we prepared a novel TiO2@WS2 hybrid via a facile and scalable two-step hydrothermal strategy combined with selective etching. Benefited from acid-etched TiO2 nanobelts with rough surface as substrate, ultrathin WS2 nanosheets nucleated and vertically grew into few layers in the confined configuration with more exposed active edges. Furthermore, the partial incorporation of oxygen in WS2 inherited from the remaining O–W bonds of tungsten precursor enhanced the electrical conductivity of the hybrid. Therefore, TiO2@WS2 hybrid was proved to be efficient and durable electrocatalyst for hydrogen evolution in alkaline medium. Upon optimal conditions, the hybrid only required a small onset overpotential of 95 mV and a low overpotential of 142 mV at 10 mA cm−2, superior to pristine WS2 and TiO2. In addition, better cycling stability during the alkaline HER process was also obtained, indicating its capability in future practical application. The synthesis strategy presents a cost-effective approach to produce efficient WS2-based HER electrocatalyst for electrochemical water splitting.

Zinc oxide functionalized molybdenum disulfide heterostructures as efficient electrocatalysts for hydrogen evolution reaction

Technology urges to replace the state-of-the-art catalysts such as platinum with low cost, earth abundant and durable electrocatalysts for efficient hydrogen evolution (HER) reaction which is going to become the major sustainable production of energy in future. Herein, we present the heterostructure based MoS2.ZnO (MZO) heterostructures for successful electrochemical water splitting process. For HER, the prepared MoS2.ZnO nanocomposites show the over potential as low as 239 mV at cathodic current density 10 mAcm−2 with an exchange current density of 3.2 μAcm−2. A Tafel slope of about 62 mV per decade suggested to have the Volmer-Heyrovsky mechanism for the HER process with MoS2.ZnO nanocomposite as the catalyst. The small Tafel slope indicates a promising electrocatalyst for HER in practical application. The strong interface formation at the MoS2.ZnO heterostructure facilitates higher catalytic activity and excellent cycling stability. The heterostructure formation based on semiconductor two dimensional (2D) transition metal dichalcogenides (TMDC) open up new avenues for effective manipulation of HER catalysts.

Quantitative evaluation of synergistic effects for Pt nanoparticles embedded in N-enriched carbon matrix as an efficient and durable catalyst for the hydrogen evolution reaction and their PEMWE performance

The N-enriched carbon matrix (NCS) exerts an important role in HER process. Yet, the quantitative research of such co-catalyst is quite limited, which definitely deserves our deeply investigation. Herein, we report the Pt nanoparticles embedded in N-enriched carbon matrix (Pt-NCS) with low Pt loading, which as a HER electrocatalyst in acidic electrolyte. Notably, the electrochemical tests show that the optimal Pt-NCS exhibits the low overpotential of 22.0 mV at a current density of 10 mA cm−2, which is lower thant that of Pt-carbon matrix (Pt-CS) (41.0 mV) and 20 wt% Pt/C (27.0 mV). It is worth noting that the addition of g-C3N4 into Pt-CS enhanced the exchange current density and a turnover frequency by 7.98 and 8.12 folds, respectively. The remarkable performance of these catalysts was evaluated with synergistic factors, which may be up to 5.55 for the optimal catalyst. More significantly, the optimal Pt-NCS also displays good stability and offers a superior performance in PEMWE. The outstanding HER performance may be attributed to the N-enriched carbon matrix, which supply large electrochemically active surface area and fast charge transfer. This research provides an effective strategy to prepare highly efficient and stable catalysts for electrochemical catalysis.

Strongly coupled Mo2C and Ni nanoparticles with in-situ formed interfaces encapsulated by porous carbon nanofibers for efficient hydrogen evolution reaction under alkaline conditions

Herein, strongly coupled Mo2C and Ni nanoparticles with in-situ formed interfaces encapsulated by porous carbon nanofibers (Ni-Mo2C-CNF) have been rationally fabricated via pyrolyzing electrospinning polyvinyl alcohol fibers containing hydrothermally obtained NiMoO4 under Ar atmosphere and applied as high-performance and stable electrocatalyst for HER in alkaline electrolytes. Powered by NiMoO4 as homologous bimetallic precursor, the Ni-Mo2C-CNF possesses numerous in-situ formed Ni-Mo2C interfaces, which facilitates the synergistic effect between Ni and Mo2C, improving the conductivity and thus boosting the electrocatalytic performance towards HER. In the meantime, the porous carbon nanofibers with well encapsulated Ni-Mo2C active components stacks, constituting conductive network, which promotes the mass transport, electron transfer, active sites exposure and electrocatalytic stability. As a result, the Ni-Mo2C-CNF features prominently in HER, as it demands a low overpotential of 196 mV but is able to stably yield the current density of 10 mA cm−2 with a small Tafel plot of 54.7 mV dec−1. The method demonstrated in our work to synthesize bimetallic heterostructured materials will offer valuable inspiration to construct promising non-precious electrocatalysts for diverse vital renewable energy applications.

Advanced Co3O4–CuO nano-composite based electrocatalyst for efficient hydrogen evolution reaction in alkaline media

In this study, we incorporate a copper impurity into (Co3O4) nanowires precursor that turn them into an active catalyst for the hydrogen evolution reaction in 1M KOH. The XRD and XPS results are in good agreement and confirmed the formation of Co3O4–CuO nano-composite by wet chemical method. To date, the performance of hydrogen evolution reaction in alkaline for the composite catalyst is comparable or superior to cobalt oxide based HER electro-catalysts. The HER catalyst exhibits the lowest Tafel slope of 65 mVdec−1 for the cobalt-based catalysts in alkaline media. A current density of 10 mA/cm2 is achieved at a potential of 0.288 V vs reversible hydrogen electrode (RHE). The mixed transition metal oxide Co3O4–CuO based HER electro-catalyst is highly stable and durable. The EIS results demonstrates that HER is highly favorable on the Co3O4–CuO due to the relatively small charge transfer resistance (173.20 Ohm) and higher capacitance values (1.97 mF).

Molybdenum carbonyl complexes as HER electrocatalysts

Four cyclopentadienyl and allylic molybdenum carbonyl complexes have been prepared and tested as proton reduction electrocatalysts using trifluoroacetic acid as the proton source in acetonitrile. Cyclic voltammetry studies showed that these complexes are able to function as moderate electrocatalysts with overpotentials of about 0.9 V and catalytic efficiency of up to 60%. The average turnover number and turnover frequency for each of the molybdenum catalyst measured over a five-hour period have been calcualted to be in the range of 16–24 and 3.2 h−1 to 5.4 h−1 respectively for 1 mM catalyst and 20 acid equivalent. A mechanism to account for the proton reduction process is also proposed based on the electrochemical and spectroscopic measurements.

Boron-Doped Carbon nanoparticles supported palladium as an efficient hydrogen evolution electrode in PEM water electrolysis

Boron doped Carbon Nanoparticles (B-CNPs) with various boron doping percentages have been successfully synthesized by chemical vapor deposition (CVD) method in the presence of ferrocene and boric acid, further the same was used as a support material for Palladium (Pd) catalyst. The synthesized Pd/B-CNPs with various amounts of palladium (5-30 wt%) were used as a hydrogen evolution electrode in PEM water electrolysis for hydrogen production. The Pd/B-CNPs surface morphological studies and electrochemical performances have been investigated by FE-SEM, EDS, TEM, ICP, XRD, XPS and Cyclic Voltammetry methods. The membrane electrode assemblies (MEAs) have been fabricated using synthesized Pd/B-CNPs and its performance studied in single cell PEM water electrolyser at various experimental conditions. The synthesized 30 wt% Pd/B3-CNPs (B-doping 6.68 at%) results have shown competitive electrochemical performance (1 A cm−2 with 2.04 V at 80 °C) and stability. Therefore the synthesized 30 wt% Pd/B3-CNPs can be used as a promising alternative for Pt based electrocatalysts for HER in PEM cells.

Cover Feature: High‐Current‐Density HER Electrocatalysts: Graphene‐like Boron Layer and Tungsten as Key Ingredients in Metal Diborides (ChemSusChem 16/2019)

Cover Feature: High‐Current‐Density HER Electrocatalysts: Graphene‐like Boron Layer and Tungsten as Key Ingredients in Metal Diborides (ChemSusChem 16/2019)

Ni-Co-Mo-O nanosheets decorated with NiCo nanoparticles as advanced electrocatalysts for highly efficient hydrogen evolution

The development of efficient and durable HER electrocatalysts is urgently required to enhance the efficiency of water splitting. Here we report the Ni-Co-Mo-O nanosheets decorated with NiCo nanoparticles supported on NF (NF/NiCoMoO-H2) as efficient HER electrocatalysts in alkaline media. The introduction of oxygen vacancies and multiple metal ions (Ni-Co-Mo-O nanosheets) accelerates water dissociation, while metal atoms (NiCo nanoparticles) promote the adsorption and association of hydrogen intermediates into H2 molecules. The efficiently synergistic effect between Ni-Co-Mo-O nanosheets and NiCo nanoparticles results in the NF/NiCoMoO-H2 with a low overpotential of 15 mV at 10 mA cm−2 and Tafel slope of 33.1 mV dec−1. More importantly, the water–alkali electrolyzer using NF/NiCoMoO-H2 as cathode and NF/NiFe-LDH as anode shows a low voltage of 1.44 V at 10 mA cm−2 and remarkable stability. Owing to the controllable fabrication process and excellent HER performance, the NF/NiCoMoO-H2 is a promising electrocatalyst for the practical water splitting.

Molecular and Material Engineering of Photocathodes Derivatized with Polyoxometalate-Supported {Mo3S4} HER Catalysts.

Molecular engineering of efficient HER catalysts is an attractive approach for controlling the spatial environment of specific building units selected for their intrinsic functionality required within the multistep HER process. As the {Mo3S4} core derived as various coordination complexes has been identified as one as the most promising MoSx-based HER electrocatalysts, we demonstrate that the covalent association between the {Mo3S4} core and the redox-active macrocyclic {P8W48} polyoxometalate (POM) produces a striking synergistic effect featured by high HER performance. Various experiments carried out in homogeneous conditions showed that this synergistic effect arises from the direct connection between the {Mo3S4} cluster and the toroidal {P8W48} units featured by a stoichiometry that can be tuned from two to four {Mo3S4} cores per {P8W48} unit. In addition, we report that this effect is preserved within heterogeneous photoelectrochemical devices where the {Mo3S4}-{P8W48} (thio-POM) assembly was used as cocatalyst (cocat) onto a microstructured p-type silicon. Using a drop-casting procedure to immobilize cocat onto the silicon interface led to high initial HER performance under simulated sunlight, achieving a photocurrent density of 10 mA cm-2 at +0.13 V vs RHE. Furthermore, electrostatic incorporation of the thio-POM anion cocat into a poly(3,4-ethylenedioxythiophene) (PEDOT) film is demonstrated to be efficient and straightforward to durably retain the cocat at the interface of a micropyramidal silicon (SimPy) photocathode. The thio-POM/PEDOT-modified photocathode is able to produce H2 under 1 Sun illumination at a rate of ca. 100 μmol cm-2 h-1 at 0 V vs RHE, highlighting the excellent performance of this photoelectrochemical system.

Insights into electrodeposition and catalytic activity of MoS2 for hydrogen evolution reaction electrocatalysis

MoS2-x films were electrodeposited cathodically onto copper rod substrates from a solution, containing MoS42− as the common Mo and S ion precursor. The catalyst loading was varied by adjusting electrodeposition conditions – applied potential and deposition time. A typical set of HER electrocatalyst experiments (polarization, Tafel slope analysis) carried out in 0.5 M H2SO4 was applied on the deposited MoS2-x films. Analysis of surface morphology (SEM) and chemical composition (EDS) were also performed. Electrochemical impedance spectroscopy in the same acidic media was used to evaluate the catalyst-solution interface and the interfacial kinetics (by calculating double layer capacitance and charge transfer resistance), as well as characterize the hydrogen adsorption process (adsorption capacitance and resistance). A linear correlation between electrodeposition time and double layer capacitance was observed. However, the charge transfer resistance was found to decrease until it plateaued at longer deposition times. The MoS2-x film, deposited for 7200 s at −1.0 V (vs. Ag/AgCl), reached 10 mA cm−2 HER current at −0.18 V (vs. RHE), and represented the best result of this study. Electrochemical impedance spectroscopy (EIS) was further applied to evaluate the subtle changes in the MoS2-x films’ semiconductor properties after HER stability tests (at −40 mA cm−2), and to estimate the number of active sites on the material. EIS, in comparison to cyclic voltammetry or roughness factor calculations, is a completely non-destructive method that can be applied to accurately assess the system under investigation.

A facile one-pot synthesis of microspherical-shaped CoS2/CNT composite as Pt-free electrocatalyst for efficient hydrogen evolution reaction

Hydrogen evolution reaction has been recognized as a green technology in the field of electrochemical energy conversion and storage devices. Nevertheless, it is necessary task to finding an economical and effective electrocatalysts for HER. Among the different HER catalysts, the cobalt disulfide (CoS2) showed an excellent HER activity owing to its low cost, easy to synthesize and good stability. Hence, in this work, we prepared a series of CoS2/CNT composites with different contents CNT from 4 to 12 wt% by a simple one-step hydrothermal method to investigate the influence of CNT on HER activity of CoS2. The structural and morphological properties of the obtained samples were analyzed through XRD, SEM, HR-TEM, and XPS. The SEM images of CoS2/CNT composite showed the spherical-shaped CoS2 covered by the CNT nanostructure. In addition, the electrochemical tests were carried out using 0.5 M H2SO4 solution in order to assess their HER activity. The attained electrochemical results showed that the CoS2/CNT composite with 8% CNT offers an outstanding HER activity with the smallest overpotential of 155 mV at 10 mA cm−2 and lowest Tafel slope of 59 mV dec−1 when compared with other composites. Also, the optimized CoS2/CNT composite provided excellent stability in the acidic medium after 1000 cycles. Therefore, the as-synthesized CoS2/CNT composite will be an efficient, low-cost and Pt-free electrocatalyst for HER application.