Volmer Heyrovsky Research Articles

Enhanced Electrocatalytic Activity of Mo-Doped NiFe Layered Double Hydroxide Nanosheet Arrays for the Hydrogen Evolution Reaction

NiFeMo layered double hydroxide (NiFeMo-LDH) nanosheet array structures in situ grown on Ni foam were rationally designed and fabricated by a convenient and green hydrothermal strategy. The systematic characterization proved that NixFe1Mo1-LDH/NF (x = 4, 6, 8, 10) composites grew on the surface of Ni foam as vertically interlaced LDH nanosheets. The electrochemical results showed that all composites possessed high electrocatalytic activity, and Ni6Fe1Mo1-LDH/NF exhibited the best hydrogen evolution reaction (HER) performance. Furthermore, the nanosheet array structure with the best active metal molar ratio was in situ grown on reduced graphene oxide (rGO) uniformly modified Ni foam (∼210 nm × 20 nm) with an overpotential of 90 mV at 10 cm–2 in an alkaline solution, which was superior to most non-noble metal-based catalysts. Experimental results and density functional theory with the Hubbard U (DFT + U) calculations confirmed that the active site for H adsorption changed from the Fe site to the Mo site after Mo doping in NiFe-LDH, which reduced the water dissociation energy barrier and the subsequent proton adsorption energy barrier and adjusted the electronic structure of Fe and Ni sites, thereby greatly promoting the whole Volmer–Heyrovsky process under alkaline conditions and improving the HER performance. The synergistic coupling of NiFeMo-LDH nanosheets with rGO enhanced conductivity and electrochemical performance. The growth of NiFeMo-LDH on rGO/NF facilitated the formation of bubbles and significantly improved electrochemical stability. The present electronic regulation strategies using metal doping can be extended to synthesize other types of transition metal composite catalysts and used for the development of renewable and friendly energy devices.

Surface oxygen vacancy defects induced CoTiO3-x perovskite nanostructures for highly efficient catalytic activity from acidic and seawater electrolysis

Efficient electrocatalysts have great demand for improved hydrogen evolution (HE) from natural seawater splitting. In this work, a new type of oxygen (O2) vacancies and Ti3+ defective perovskite nanostructures (DPNSs) of D-CoTiO3-x were prepared by using eco-friendly sonochemical assisted laser irradiation technique (SCA-LIT) for the first time. These DPNSs were thoroughly characterized, and HE activity was evaluated to determine their electrocatalytic potential and efficiency improvement. The existence of abundantly available active sites in the prepared D-CoTiO3-x electrocatalyst composed of defective D-TiO2-x was confirmed through various physicochemical measurements. The designed DPNSs-based working electrode exhibited excellent electrochemical performance due to its low over-potential (0.352 V), reduced Tafel slope (94.7 mV/dec), high double layer capacitance (235.3 µF/cm2), large electrochemically active surface area (6.72 cm2) and exceptional long-term stability. The attained improvement in the HE efficiency was ascribed to the induced synergistic strong metal-support interaction (SMSI) effect of the surface O2 vacancies and Ti3+ defects in DPNSs that yielded high conductivity, high exposure of abundant active sites, wide active surface area, improved kinetics, and fast charge transport. Furthermore, Volmer-Heyrovsky (V-H) reaction mechanism was responsible for the generation of hydrogen (H2) by the proposed DPNSs-based electrode. In addition to the natural seawater, the D-CoTiO3-x DPNSs outperformed in terms of the electrocatalytic hydrogen activity and stability. Thus, our systematic approach for the fabrication of surface O2 vacancy and Ti3+ defect engineering DPNSs-based electrodes to produce H2 from natural seawater splitting may be beneficial for green energy generation, solving future environmental problems and energy demand crises.

(Digital Presentation) Cathodic Exfoliation of Few-Layer Tellurium As Electrocatalyst Support for Hydrogen Evolution

Few-layer tellurium represents the two-dimensional (2D) form of tellurium crystal with the majority of the Te atoms exposed on its surface. Recent studies demonstrated that 2D Te has good environmental stability and high charge carrier mobility, making it suitable electrocatalyst support to host active sites and assist electron transfer between the electrode and the sites [1]. Yet, its mass production for electrocatalysis application remains challenging.In this study, we present a simple cathodic exfoliation method to exfoliate commercially available Te crystal directly into few-layer tellurium with exceptionally high yield [2] (see Figure 1A). Using alkaline aqueous electrolyte (1.0 M KOH), Te nanosheets with the thickness of 7~10 nm and lateral size of 1~4 µm were produced at an applied potential of −0.42 V (vs. RHE). Combining in situ Raman spectroscopy and ex situcharacterization results, we were able to reveal the exfoliation mechanism, where the in situ generated ditelluride (Te2 2−) anions on the nanosheets played the critical role of separating nanosheets from the bulk crystal (see Figure 1B).At the presence of transition metal ions in the electrolyte, such as Pt2+ and Ni2+, simultaneous surface doping of Te nanosheets was enabled by the interaction between Te2 2− anions and metal ions, producing Pt/Ni-doped Te with tunable doping level. Such doped nanosheets exhibited high stability and hydrogen evolution reaction (HER) activity. Particularly at high potential, Pt-doped Te nanosheets outperformed both polycrystalline Pt and commercial Pt/C catalysts (see Figure 1C). We suggested a collaborative hydrogen production mechanism via Volmer–Heyrovsky pathway to justify such unusual activity. In short, at HER conditions, the surface Te atoms of Pt-doped Te nanosheets are reduced to Te2 2− anions. Such species can help attract protons and assist their transfer to adjacent Pt atoms, where the protons are reduced to form hydrogen (see Figure 1D). Figure 1 (A) Experimental setup and photos of the electrochemical exfoliation of Te crystal; (B) Exfoliation mechanism; (C) HER performance and relative energy of Pt-doped Te with various doping levels; (D) Collaborative HER mechanism. Reference: Shi, Z.; Cao, R.; Khan, K.; Tareen, A. K.; Liu, X.; Liang, W.; Zhang, Y.; Ma, C.; Guo, Z.; Luo, X.; Zhang, H., Nano-Micro Lett. 2020, 12 (1), 99. Zheng, W.; Li, Y.; Liu, M.; Lee, L. Y. S., Small 2021, 17 (18), e2007768. Figure 1

Alkali metal cations change the hydrogen evolution reaction mechanisms at Pt electrodes in alkaline media

The effects of seemingly inert alkali metal (AM) cations on the electrocatalytic activity of electrode materials towards reactions essential for energy provision have become the emphasis of substantial research efforts in recent years. The hydrogen and oxygen evolution reactions during alkaline water electrolysis and the oxygen electro-reduction taking place in fuel cells are of particular importance. There is no universal theory explaining all the details of the AM cation effect in electrocatalysis. For example, it remains unclear how “spectator” AM-cations can change the kinetics of electrocatalytic reactions often more significantly than the modifications of the electrode structure and composition. This situation originates partly from a lack of systematic experimental and theoretical studies of this phenomenon. The present work exploits impedance spectroscopy to investigate the influence of the AM cations on the mechanism of the hydrogen evolution reaction at Pt microelectrodes. The activity follows the trend: Li + ≥Na + >K + >Cs + , where the highest activity corresponds to 0.1 ​M LiOH electrolytes at low overpotentials. We demonstrate that the nature of the AM cations also changes the relative contribution of the Volmer–Heyrovsky and Volmer–Tafel mechanisms to the overall reaction, with the former being more important for LiOH electrolytes. Our density functional theory-based thermodynamics and molecular dynamics calculations support these findings.

Cobalt Incorporated Graphitic Carbon Nitride as a Bifunctional Catalyst for Electrochemical Water-Splitting Reactions in Acidic Media.

Non-noble metal-based bifunctional electrocatalysts may be a promising new resource for electrocatalytic water-splitting devices. In this work, transition metal (cobalt)-incorporated graphitic carbon nitride was synthesized and fabricated in electrodes for use as bifunctional catalysts. The optimum catalytic activity of this bifunctional material for the hydrogen evolution reaction (HER), which benefitted at a cobalt content of 10.6 wt%, was promoted by the highest surface area and conductivity. The activity achieved a minimum overpotential of ~85 mV at 10 mA/cm2 and a Tafel slope of 44.2 mV/dec in an acidic electrolyte. These values of the HER were close to those of a benchmark catalyst (platinum on carbon paper electrode). Moreover, the kinetics evaluation at the optimum catalyst ensured the catalyst flows (Volmer–Heyrovsky mechanism), indicating that the adsorption step is rate-determining for the HER. The activity for the oxygen evolution reaction (OER) indicated an overpotential of ~530 mV at 10 mAcm−2 and a Tafel slope of 193.3 mV/dec, which were slightly less or nearly the same as those of the benchmark catalyst. Stability tests using long-term potential cycles confirmed the high durability of the catalyst for both HER and OER. Moreover, the optimal bifunctional catalyst achieved a current density of 10 mAcm−2 at a cell voltage of 1.84 V, which was slightly less than that of the benchmark catalyst (1.98 V). Thus, this research reveals that the present bifunctional, non-noble metallic electrocatalyst is adequate for use as a water-splitting technology in acidic media.

Effect of sodium dodecyl sulfate surfactant concentrations on the novel strontium copper oxide nanostructures for enriching hydrogen evolution reaction electrochemical activity in alkaline solution

Nowadays, hydrogen evolution reaction (HER) has gained more attention than the oxygen evolution reaction (OER) in water-splitting. The OER, which involves a four-electron process, is more complex whereas the HER, which involves a two-electron process, is more easy. Hydrogen is one of the promising and efficient energy carriers for renewable and sustainable energy yield. In this work, we have successfully prepared a low-cost electrocatalyst of strontium copper oxide (SCO) through a simple co-precipitation method, followed by an annealing process. The X-ray diffraction is consistent with an orthorhombic structure of SCO. The different modes of vibrations containing Cu, Sr, and O bonds were identified by using the Raman and Fourier transform infrared spectra. The scanning electron microscopy images confirmed that the introduction of sodium dodecyl sulfate (SDS) surfactant allowed to control the size and morphology of the prepared material. Electrochemical measurements indicated that 2 wt% SDS-assisted SCO material exhibited excellent HER performance and high stability. It achieved 166 mV to deliver 10 mA/cm2 and attained the low 124 mV/dec Tafel slope value, indicating that hydrogen evolution reaction followed the Volmer–Heyrovsky mechanism. Compared to the pure and 1 wt% SDS-SCO, 2 wt% SDS-SCO material exhibited a high electrochemically active surface area (ECSA) of 19.3 cm2 and showed a low 0.33 Ω charge-transfer resistance, indicating the presence of supplementary active sites and enhanced electrical conductivity than the reference electrocatalysts. Hence, this work could be considered as a successful approach in exploring the performance of alkaline-based metal oxides in electrochemical hydrogen evolution reactions.

One-step galvanostatic electrodeposition of Ni-Se-Dy film on Ni foam for hydrogen evolution reaction in alkaline solution

Efficient, stable, and environmentally friendly electrocatalysts urgently need to be explored for hydrogen evolution reaction (HER). A novel and facile nickel–selenium–dysprosium (Ni–Se–Dy) electrocatalyst was synthesized on Ni foam via simple and feasible one–step galvanostatic electrodeposition. The prepared Ni–Se–Dy electrodes showed excellent HER activity in alkaline medium with low overpotential values of 72 and 173 mV to deliver the current density values of 10 and 50 mA·cm−2. Tafel slope value (119.72 mV·dec−1) for Ni–Se–Dy electrode in 1.0 M KOH indicated that the Ni–Se–Dy catalyst followed a Volmer–Heyrovsky mechanism, and the rate–determining step of this reaction was a Volmer step. Electrochemical test and scanning electron microscopy results showed that the excellent HER performance of Ni–Se–Dy electrode can be attributed to surface morphology, better intrinsic activity, and high conductivity.

Circumventing the OCl versus OOH scaling relation in the chlorine evolution reaction: Beyond dimensionally stable anodes

The development of selective electrocatalysts for the chlorine evolution reaction (CER) is majorly restrained by a scaling relation between the OCl and OOH adsorbates, rendering that active CER catalysts are also reasonably active in the competing oxygen evolution reaction (OER). While theory predicts that the OCl versus OOH scaling relation can be circumvented as soon as the elementary reaction steps in the CER comprise the Cl rather than the OCl adsorbate, it was demonstrated recently that PtN 4 sites embedded in a carbon nanotube follow this theoretical prediction. Advanced experimental analyses illustrate that the PtN 4 sites also reveal a different reaction kinetics compared to the industrial benchmark of dimensionally stable anodes (DSA). A reverse Volmer–Heyrovsky mechanism was identified, in which the rate-determining Volmer step for small overpotentials is followed by the kinetically limiting Heyrovsky step for larger overpotentials. Since the PtN 4 sites excel DSA in terms of activity and chlorine selectivity, we suggest the Cl intermediate as well as the reverse Volmer–Heyrovsky mechanism as the design criteria for the development of next-generation electrode materials beyond DSA.

Facile synthesis of novel molybdenum disulfide decorated banana peel porous carbon electrode for hydrogen evolution reaction

Hydrogen is one of the cleanest renewable and environmentally friendly energy resource that can be generated through water splitting. However, hydrogen evolution occurs at high overpotential, and efficient hydrogen evolution catalysts are desired to replace state-of-the-art catalysts such as platinum. In the present work, a novel molybdenum disulfide decorated banana peel porous carbon (MoS2@BPPC) catalyst has been developed using banana peel carbon and molybdenum disulfide (MoS2) for hydrogen evolution reaction (HER). Banana peel porous carbon (BPPC) was initially synthesized from the banana peel (biowaste) by a simple carbonization method. Subsequently, 20 wt% of bare MoS2 was distributed on the pristine BPPC matrix using the dry-impregnation method. The resulting MoS2@BPPC composites were systematically investigated to determine the morphology and structure. Finally, using a three-electrode cell system, pristine BPPC, bare MoS2, and MoS2@BPPC composite were used as HER electrocatalysts. The developed MoS2@BPPC composite showed greater HER activity and possessed excellent stability in the acid solution, including an overpotential of 150 mV at a current density of −10 mA cm−2, and a Tafel slope of 51 mV dec−1. This Tafel study suggests that the HER takes place by Volmer–Heyrovsky mechanism with a rate-determining Heyrovsky step. The excellent electrochemical performance of MoS2@BPPC composite for HER can be ascribed to its unique porous nanoarchitecture. Further, due to the synergetic effect between MoS2 and porous carbon. The HER activity using the MoS2@BPPC electrode advises that the prepared catalyst may hold great promise for practical applications.

Designing Novel Co2FeV2O8 Microsticks with Prompted Multiple Electrochemical Performances for an Asymmetric Solid-State Supercapacitor and the Hydrogen Evolution Reaction

This article reports the preparation of novel Co2FeV2O8 microsticks by the solvothermal route for multiple electrochemical applications such as a solid-state asymmetric supercapacitor and hydrogen evolution reactions. The prepared microstick’s physical and chemical characterizations have been performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS) to ensure the phase purity and morphology of the material. Co2FeV2O8 microsticks exhibit a specific capacity of 261 C g–1 at 1 A g–1 with excellent capacity retention after 10,000 cycles. Furthermore, the charge-storage contributions of the capacitive and diffusion-controlled process were estimated using Dunn’s approach, and the estimation of accumulated external and internal surface charges was done using Trassati’s approach. For practical applications, a solid-state asymmetric supercapacitor device has been fabricated, which exhibits excellent electrochemical energy storage performance such as an attractive specific capacity (352 C g–1), high capacitance retention for 10,000 cycles, and huge specific energy and power outcomes (60 Wh kg–1 at 900 W kg–1). Along with the energy storage performance, the prepared Co2FeV2O8 exhibits excellent electrochemical energy conversion performance for the hydrogen evolution reactions. The electrode exhibits a low overpotential (188 mV) to generate the current density of 20 mA cm–2 in 1 M KOH, and also displays excellent stability at −1.3 V for 24 h. It is concluded that the HER of CFVO can be conducted through the Volmer–Heyrovsky mechanism with a Tafel slope of 97 mV dec–1.

One–step electrodeposition of Ni–Ce–Pr–Ho/NF as an efficient electrocatalyst for hydrogen evolution reaction in alkaline medium

Finding non-precious metal hydrogen evolution reaction (HER) electrocatalysts with high efficiency and low cost is a great challenge. A novel HER electrocatalyst of amorphous Nickel–Cerium–Praseodymium–Holmium coating supported on nickel foam (Ni–Ce–Pr–Ho/NF) was successfully synthesized through one-step galvanostatic electrodeposition. The Ni–Ce–Pr–Ho catalyst exhibited excellent electrocatalytic activity toward HER with a low overpotential of 78 mV at 10 mA cm−2 in 1 M KOH. The Tafel slope of Ni–Ce–Pr–Ho electrocatalyst (121.6 mV·dec−1) indicated that the hydrogen reaction mechanism for Ni–Ce–Pr–Ho electrocatalysts followed a typical Volmer–Heyrovsky step. The remarkable HER performance was attributed to Pr and Ho doping, which resulted in the development of an amorphous structure, satisfactory intrinsic activity, and high conductivity.

Investigation of Topological and Catalytic Properties of Gold Iodide Monolayer: A Density Functional Theory Study

Insulating bulk and conducting edge states makes 2D topological insulators (TI) a candidate quantum material with varied applications. 2D binary monolayers composed of group‐11 transition metals and halides with puckered structures have been recently explored for their photocatalytic and quantum cutting properties. However, such binary systems have not yet been explored for their topological properties. Herein, the topological and catalytic properties of one such binary compound, gold iodide (AuI) which belongs to P6 3/mmc [194] space group governed by a honeycomb lattice structure is explored. The nontrivial TI nature exists in a narrow window of strain from −2% to 4%. Within this region, by employing strain engineering technique the bandgap can be tuned to as high as 0.113 eV. The nontrivial character is further investigated by calculating the invariant, robust edge state spectra and slab band structures. The Gibbs free energy towards hydrogen evolution reaction is computed to assess the catalytic property of AuI. The Gibbs free energy was found to be −0.40 eV with Volmer–Heyrovsky as the preferred reaction mechanism. With this study, it is proposed AuI monolayer as a candidate material for prospective applications in the field of nanoelectronics and catalysis.

Ultrahigh Pt‐Mass‐Activity Hydrogen Evolution Catalyst Electrodeposited from Bulk Pt

AbstractMaximizing the Pt utilization is important for the widescale implementation of Pt‐based hydrogen evolution reaction (HER) electrocatalysts, owing to the scarcity of Pt. Here, three‐component heterostructured HER catalysts with ultrahigh Pt mass activity in which hollow PtCu alloy nanospheres are supported on an array of WO3 on Cu foam, are reported. It has been pointed out that the use of Pt counter electrode in a three‐electrode configuration in evaluating catalysts’ HER performances in acidic media carries the risk of contaminating the working electrode in previous reports. Here, the authors rationally utilize this “contaminating” to “activate” low‐HER‐activity materials, maximizing the Pt utilization. As a result, ultrahigh Pt mass activity is achieved, that is 1.35 and 10.86 A mg−1Pt at overpotentials of 20 and 100 mV, respectively, 27 and 13 times higher than those of commercial Pt/C catalysts, outperforming some state‐of‐the‐art Pt‐single‐atom catalysts. The hollow sphere structure and PtCu alloying increase the number and reactivity of active sites. Density function calculations and electrochemical experiments reveal that the synergy between WO3 and Pt is also responsible for the high HER activity where the hydrogen spillover effect triggers the Volmer–Heyrovsky mechanism and promotes the rapid removal of H* from Pt to re‐expose the active sites.

Incorporating Au11 nanoclusters on MoS2 nanosheet edges for promoting the hydrogen evolution reaction at the interface.

The electrocatalytic hydrogen evolution reaction (HER) holds grip as a promising strategy to obtain renewable energy resources in the form of clean fuel - hydrogen (H2). However, understanding the catalytic mechanism at the atomic level for sustainable and efficient production of hydrogen remains an arduous challenge. In this regard, atomically precise nanoclusters (NCs) with their molecule-like properties can be utilized for a better understanding of the mechanism at the catalytic interface, identification of active sites, and much more. Herein, we report a strategy to enhance the HER activity of the well-known electrocatalyst MoS2 by the incorporation of atomically precise gold nanoclusters, Au11(PPh3)7I3. Interestingly, Au11(PPh3)7I3 NCs were impregnated onto MoS2 nanosheets without protecting ligands as naked Au11 clusters which have increased atom efficiency. Different loadings of Au11(PPh3)7I3 nanoclusters on MoS2 nanosheets revealed the superior HER activity of 2% loading of the NCs. Theoretical calculations have shown that the nanocomposite has the optimum hydrogen adsorption energy that is crucial for efficient H2 production. Combined experimental and theoretical results provide the atomic-level understanding of the utilization of electrochemically dormant ligand-protected NCs to accelerate the HER activity of MoS2 nanosheets.

The potential of tantalum as an efficient electrocatalyst for green hydrogen production

Worldwide, discovering a low-cost, highly active and durable electrocatalyst for green hydrogen production is an attractive research field for future renewable energy. Herein, we study the suitability of utilizing metallic Ta as promising electrocatalytic material for hydrogen creation from acidic solutions. The morphological structure and crystal lattice system, as well as the chemical composition and oxidation states of Ta are examined using scanning electron microscopy, X-ray diffraction analysis, and X-ray photoelectron spectroscopy, respectively. Hydrogen evolution reaction (HER) on Ta is investigated using cathodic polarization and electrochemical impedance techniques as a function of electrolyte concentration, applied potential, and temperature. Various kinetic parameters distinguishing catalytic activity of the process on Ta including Tafel slope, exchange current density, cathodic transfer coefficient, and HER rates are determined. At −1500 mV cathodic potential in 0.5 M H2SO4 solution, the results confirm well that, to reach a similar HER rate of say 100 mA cm-2, the overpotential on Ta cathode is found equal -520 mV, which is lower than the value of -940 mV attained on the platinum cathode, indicating high electrocatalytic activity of the HER on Ta surface. The obtained results also demonstrated that, for the hydrogen production process the overpotential greatly diminishes and its current density significantly improves with increasing either the electrolyte concentration or its temperature. Additionally, Tafel slope analysis and impedance parameters establish that HER proceeds by the Volmer–Heyrovsky mechanism. The outcome of this study reveals that the valve metal Ta is a sustainable, efficient, and promising cathode for green hydrogen generation fuel from sulphuric acid electrolytes.

Restructuring electronic structure via W doped 1T MoS2 for enhancing hydrogen evolution reaction

The intrinsic electronic structure on the surface of 1T MoS2 makes the non-optimal bonding strength with hydrogen atoms, which is the key factor that the catalytic performance cannot be improved. However, modifying surface electronic structure by doped exotic atom is an effective approach to optimal the bonding strength between hydrogen atoms and 1T MoS2. Herein, this work reports W doped 1T MoS2 with different concentrations by hydrothermal method. The results indicate that W-1T MoS2-15 exhibits excellent catalytic activity for hydrogen evolution reaction (HER), the catalytic activity is better than that of 2H MoS2 and pristine 1T MoS2, the lowest overpotential and tafel slope in acid electrolyte is 292 mV and 55.7 mV dec−1, respectively. Theoretical calculation results show that W-1T MoS2-2/9 has relatively much lower barrier than pristine 1T MoS2 both in Volmer reaction and Heyrovsky reaction. Therefore, W-1T MoS2-2/9 has a faster reaction kinetics for HER. In addition, introducing W atoms can trigger spontaneous electrons redistribution on the basal plane, optimize energy level, and reduce the Gibbs free energy. This study confirmed that doping of atom with similar physical and chemical properties can optimize electronic structure of 1T MoS2 on the basal plane, and effectively improve its electrocatalytic activity.

Reaction Mechanism and Strategy for Optimizing the Hydrogen Evolution Reaction on Single-Layer 1T' WSe2 and WTe2 Based on Grand Canonical Potential Kinetics.

Transition-metal dichalcogenides (TMDs) in the 1T' phase are known high-performance catalysts for hydrogen evolution reaction (HER). Many experimental and some theoretical studies report that vacant sites play an important role in the HER on the basal plane. To provide benchmark calculations for comparison directly with future experiments on TMDs to obtain a validated detailed understanding that can be used to optimize the performance and material, we apply a recently developed grand canonical potential kinetics (GCP-K) formulation to predict the HER at vacant sites on the basal plane of the 1T' structure of WSe2 and WTe2. The accuracy of GCP-K has recently been validated for single-crystal nanoparticles. Using the GCP-K formulation, we find that the transition-state structures and the concentrations of the four intermediates (0-3 H at the selenium or tellurium vacancy) change continuously as a function of the applied potential. The onset potential (at 10 mA/cm-2) is -0.53 V for WSe2 (experiment is -0.51 V) and -0.51 V for WTe2 (experiment is -0.57 V). We find multistep reaction mechanisms for H2 evolution from Volmer-Volmer-Tafel (VVT) to Volmer-Heyrovsky (VH) depending on the applied potential, leading to an unusual non-monotonic change in current density with the applied potential. For example, our detailed understanding of the reaction mechanism suggests a strategy to improve the catalytic performance significantly by alternating the applied potential periodically.

Ternary VS2/ZnS/CdS hybrids as efficient electrocatalyst for hydrogen evolution reaction: Experimental and theoretical insights

Widely used precious metal (i.e., Pt, or Pd) electrocatalysts need to be replaced with other cost-effective and earth-abundant materials for economical water splitting applications. Recently, two-dimensional (2D) transition metal dichalcogenides (MoS2, VS2, WS2, etc.) have emerged as ideal electrocatalysts for the hydrogen evolution reaction (HER) due to their tunable physicochemical properties and rich catalytic active sites. In this regard, we propose a strategy to achieve improved HER performance of VS2 by fabricating a hybrid material with transition metal (Zn and Cd)-based sulfides. A facile hydrothermal approach is employed to prepare a VS2/ZnS/CdS hybrid catalyst that exhibits remarkable electrocatalytic performance for the HER in acidic media with a small overpotential of 86 mV at 10 mA/cm2 and a Tafel slope of 74.4 mV/dec. This inferred the Volmer–Heyrovsky mechanism with electrochemical desorption of hydrogen as the rate-limiting step. High performance is attributed to the abundance of catalytically active sites and the synergistic interactions between the materials. Theoretical calculations reveal that the VS2/ZnS/CdS hybrid shows favorable HER activity owing to its low hydrogen adsorption free energy of about 0.35 eV. We believe that this work on designing 2D VS2/ZnS/CdS will offer a new pathway to discover an efficient H2 generation electrocatalyst.

Unveiling the Mechanisms Ruling the Efficient Hydrogen Evolution Reaction with Mitrofanovite Pt3Te4.

By means of electrocatalytic tests, surface-science techniques and density functional theory, we unveil the physicochemical mechanisms ruling the electrocatalytic activity of recently discovered mitrofanovite (Pt3Te4) mineral. Mitrofanovite represents a very promising electrocatalyst candidate for energy-related applications, with a reduction of costs by 47% compared to pure Pt and superior robustness to CO poisoning. We show that Pt3Te4 is a weak topological metal with the invariant, exhibiting electrical conductivity (∼4 × 106 S/m) comparable with pure Pt. In hydrogen evolution reaction (HER), the electrode based on bulk Pt3Te4 shows a very small overpotential of 46 mV at 10 mA cm–2 and a Tafel slope of 36–49 mV dec–1 associated with the Volmer–Heyrovsky mechanism. The outstanding ambient stability of Pt3Te4 also provides durability of the electrode and long-term stability of its efficient catalytic performances.

Nitrogen Functionalization of CVD Grown Three-Dimensional Graphene Foam for Hydrogen Evolution Reactions in Alkaline Media.

Three-dimensional graphene foam (3D-GrFoam) is a highly porous structure and sustained lattice formed by graphene layers with sp2 and sp3 hybridized carbon. In this work, chemical vapor deposition (CVD)—grown 3D-GrFoam was nitrogen-doped and platinum functionalized using hydrothermal treatment with different reducing agents (i.e., urea, hydrazine, ammonia, and dihydrogen hexachloroplatinate (IV) hydrate, respectively). X-ray photoelectron spectroscopy (XPS) survey showed that the most electrochemically active nitrogen-doped sample (GrFoam3N) contained 1.8 at % of N, and it exhibited a 172 mV dec−1 Tafel plot associated with the Volmer–Heyrovsky hydrogen evolution (HER) mechanism in 0.1 M KOH. By the hydrothermal process, 0.2 at % of platinum was anchored to the graphene foam surface, and the resultant sample of GrFoamPt yielded a value of 80 mV dec−1 Tafel associated with the Volmer–Tafel HER mechanism. Furthermore, Raman and infrared spectroscopy analysis, as well as scanning electron microscopy (SEM) were carried out to understand the structure of the samples.