Active Sites For Hydrogen Evolution Reaction Research Articles

Synergistic Pt doping and phase conversion engineering in two-dimensional MoS2 for efficient hydrogen evolution

Molybdenum disulphide (MoS2) is proven to be a promising catalyst for hydrogen evolution reaction (HER), but the HER performance of reported MoS2-based catalysts is still limited by its poor conductivity and low density of active sites. Herein, a Pt-doped MoS2 ([email protected]2) catalyst is synthesized by a potential-cycling method, which introduces the Pt dopant into the MoS2 lattice and achieves partial 2H to 1T phase conversion of MoS2 simultaneously. Benefitting from the optimized geometric and electronic structure of MoS2, the [email protected]2 exhibits a low overpotential of 88.43 mV at 10 mA cm−2, which is decreased by two-thirds as compared to that of the pristine MoS2. A comprehensive study reveals the position and the contribution of Pt atom in electronic structure modulation of MoS2. Theoretical calculations further reveal that the S atom adjacent to the Pt in MoS2 acts as the most active site for HER, and possesses a small hydrogen adsorption free energy (∆GH*) of ~ 0.04 eV, similar to the benchmark Pt catalyst. This study opens up a new avenue for designing MoS2 and other transition metal dichalcogenide-based electrocatalysts with enhanced HER performance, as well as providing in-depth understanding on the HER mechanism in external metal-activated MoS2 catalyst.

Hydrogen production from methanol reforming electrolysis at NiO nanosheets supported Pt nanoparticles

In this work, ultrathin NiO nanosheets (NS) supported Pt nanoparticles (NP) nanohybrids (termed as Pt-NP/NiO-NS) are synthesized by cyanogel-NaBH4 method, in-situ reduction and calcination treatment, in which the thickness of Pt-NP/NiO-NS nanohybrids is only 1.8 nm and their specific surface area is as large as 171.5 m2 g−1. The Pt-NP/NiO-NS nanohybrids can efficiently act as a versatile electrocatalyst for both methanol oxidation reaction (MOR) and hydrogen evolution reaction (HER) in alkaline environment. At Pt-NP/NiO-NS nanohybrids, only a 57 mV overpotential is required to obtain a current density of 10 mA cm−2 for HER. The MOR current at Pt-NP/NiO-NS nanohybrids can achieve 179.9 mA cm−2 at 1.45 V potential, which is 15.9 times bigger than that at NiO-NS. The excellent electrocatalytic activity and durability of Pt-NP/NiO-NS nanohybrids can be ascribed to the morphology feature of NiO-NS and synergistic effect between Pt-NP and NiO-NS. The uniformly dispersed Pt-NP at NiO-NS can serve as active sites for HER. Meanwhile, Pt-NP can modify the electronic property of NiO-NS, and boost the formation of active NiIIIOOH species. Consequently, a symmetric Pt-NP/NiO-NS||Pt-NP/NiO-NS methanol electrolyzer only requires 1.39 V electrolysis voltage for hydrogen production at cathode, accompanying with the production of value-added potassium formate at anode.

Effects of structural changes on the enhanced hydrogen evolution reaction for Pd NPs @ 2H-MoS2 studied by in-Situ Raman spectroscopy

We investigated the effects of structural evolution on the enhanced Hydrogen Evolution Reaction (HER) for Pd nanoparticles (NPs) @ 2H-MoS2 studying by a modified in-Situ electrochemical Raman spectroscopy. This novel technique dramatically reduces the influence of air bubbles on the electrode surface for Raman signal detecting. The in-Situ Raman results reveal that the terminal S-S is the true HER active sites. Pd NPs can promote the appearance of terminal S-S bonds earlier, make some bands shifting dramatically, make or break some chemical bonds of MoS2, which may relate to the enhanced HER.

Combining Cd0.6Zn 0.4S with Cu-doped MoS2 to boost hydrogen production

In this paper, Cu-doped MoS2 (Cu-MoS2) acting as an efficient co-catalyst was successfully attached to the surface of Cd0.6Zn0.4S via the solvothermal method to formed a unique Schottky structure. Cu-MoS2/Cd0.6Zn0.4S (6499.66 μmol/g/h) showed a greatly enhanced photocatalytic hydrogen production yield that was 73.47 times higher than those of pure CdS (88.47 μmol/g/h). Better light absorption, a remarkable photo-generated charge separation and transfer capacity, and greater availability of HER active sites were observed in Cu-MoS2/Cd0.6Zn0.4S. In all, combining with efficient co-catalyst is a promising method for providing photocatalytic hydrogen evolution reaction (HER) sites and promoting interfacial charge separation and transfer for improved photocatalytic hydrogen production.

Molybdenum Tungsten Disulfide with a Large Number of Sulfur Vacancies and Electronic Unoccupied States on Silicon Micropillars for Solar Hydrogen Evolution.

Hydrogen energy is a promising alternative for fossil fuels because of its high energy density and carbon-free emission. Si is an ideal light absorber used in solar water splitting to produce H2 gas because of its small band gap, appropriate conduction band position, and high theoretical photocurrent. However, the overpotential required to drive the photoelectrochemical (PEC) hydrogen evolution reaction (HER) on bare Si electrodes is severely high owing to its sluggish kinetics. Herein, a molybdenum tungsten disulfide (MoS2-WS2) composite decorated on a Si photoabsorber is used as a cocatalyst to accelerate HER kinetics and enhance PEC performance. This MoS2-WS2 hybrid showed superior catalytic activity compared with pristine MoS2 or WS2. The optimal MoS2-WS2/Si electrode delivered a photocurrent of -25.9 mA/cm2 at 0 V (vs reversible hydrogen electrode). X-ray absorption spectroscopy demonstrated that MoS2-WS2 possessed a high hole concentration of unoccupied electronic states in the MoS2 component, which could promote to accept large amounts of carriers from the Si photoabsorber. Moreover, a large number of sulfur vacancies are generated in the MoS2 constituent of this hybrid cocatalyst. These sulfur defects served as HER active sites to boost the catalytic efficiency. Besides, the TiO2-protective MoS2-WS2/Si photocathode maintained a current density of -15.0 mA/cm2 after 16 h of the photocatalytic stability measurement.

In-Operando Insights on the Hydrogen Evolution Reaction Activity and Stability of Non-Noble Metal Electrocatalysts for Water Electrolysis

Market penetration of proton exchange membrane water electrolysers (PEMWE) as energy conversion technologies in a renewable energy sector would imply, given the 2.3$/Kg H2 production cost aimed by the DoE,1 a drastic decrease in total noble metal electrocatalyst loading. For the state-of-the-art hydrogen evolution reaction (HER) catalyst, platinum, recent targets suggest this limit to be 0.05mgPt/cm2.2 In some applications, like direct photoelectrochemical water splitting, application of any amount of noble metal as a co-catalyst cannot be tolerated at all. Thus, given increasing scarcity of platinum, alternative materials based on earth-abundant non-noble metals represent a significant interest as promising HER catalysts. Among them, transition metal dichalcogenides such as molybdenum disulfide (MoS2) have provided excellent performances, particularly in their cluster-based allotropic structure [Mo3S13]2-.3 Whilst the role of sulfide atoms in the Mo-terminated edges as HER active sites in crystalline MoS2 is well-established, the HER mechanism of [Mo3S13]-based materials is still under debate. Preceded by an electrochemical activation step, operando spectroscopic studies ascribed the active sites to the electrochemically-cleaved S2 2-,4 but other reports have suggested undercoordinated Mo sites to be responsible for the HER activity.5 To date, no study has evaluated the in operando activity and stability of [Mo3S13]-based materials, shown to be intimately dependent on the electrochemical conditioning and electrolyte pH.6 This work devotes to the simultaneous detection of Mo and S species under HER operating conditions in pristine and anchored [Mo3S13]2- clusters to nitrogen-doped carbon nanotubes, by use of our dedicated on-line inductively-coupled plasma mass spectrometry (on-line ICP-MS). Our findings demonstrate, contrary to previous understanding, that the electrochemical activation step is mostly related to Mo dissolution rather than S loss, which is one order of magnitude lower. After such activation, Mo dissolution is significantly mitigated, whereas S dissolution is still observed, with magnitudes dependent on the anchoring material. The overarching picture obtained by such study enabled to shed light on the HER activation mechanism, and demonstrate that the stabilities of these materials are comparable to some Ir-based catalysts. The aforementioned results provide further guidelines to implement non-noble HER metal electrocatalysts in PEMWE.

Interplay between transition-metal dopants and sulfur vacancies in MoS2 electrocatalyst

We investigate the effect of single-atom doping on the hydrogen evolution reaction (HER) activity of MoS2 using first-principles calculations. In Ru-doped MoS2 that was recently suggested as a promising HER catalyst, we show that sulfur vacancy (VS) prefers to form defect complexes with Ru substituting for Mo (RuMo). We examine hydrogen adsorption free energy at various potential active sites, which underlines that VS in the defect complex can serve as important active centers for HER. We also examine various transition-metal (TM) dopants for MoS2. The results show that several TMs such as Sn, Tc, Ir, Rh, Ru, Re, Os, Pd, and Pt can be used as dopants to promote the HER process on MoS2. By uncovering the active sites for HER in single-atom doped MoS2 as well as suggesting several promising dopants, this work will open the way to developing novel 2D catalysts for HER.

Modification of the ultrasonication derived-g-C3N4 nanosheets/quantum dots by MoS2 nanostructures to improve electrocatalytic hydrogen evolution reaction

In this work, graphitic carbon nitride (g-C3N4) nanosheets/quantum dots (NS/QD) was prepared using a simple and low-cost procedure. By two steps exfoliation in a bath and tip sonicator, the g-C3N4 (NS/QD) was produced from bulk g-C3N4. To improve electrocatalytic hydrogen evolution reaction (HER), the g-C3N4 (NS/QD) were modified by the MoS2 nanostructures. Nanocomposite of the g-C3N4 (NS/QD) with MoS2 nanostructures was deposited on a flexible, conductive and three dimensional carbon cloth by a facile and binder-free electrophoretic technique. This electrode exhibited a Tafel slope of 88 mV/dec and an overpotential of 0.28 V vs RHE at −2 mA/cm2, lower than that of the g-C3N4, and good stability after 1000 cycles and 100 days for HER. The enhanced electrocatalytic performance was attributed to the MoS2 and g-C3N4 nanostructures on three dimensional carbon cloth, leading to high surface area and more number of the exposed active sites for HER. This heterostructure improved charge transport, proton adsorption and hydrogen evolution on the electrode. This work proposes cost-effective, stable and three dimensional g-C3N4 based electrode for hydrogen evolution reaction.

Temperature differentiated synthesis of hierarchically structured N,S-Doped carbon nanotubes/graphene hybrids as efficient electrocatalyst for hydrogen evolution reaction

The development of carbon-based catalysts with excellent activity for hydrogen evolution reaction (HER) is highly desirable but still remains a significant challenge. Chemical doping and morphology engineering are paramount to enhance their catalytic performance toward HER. Herein, we present a novel and effective strategy to synthesize heteroatoms-doped three-dimensional (3D) carbon nanotubes/graphene hierarchical architecture (N,S-CNTs/N,S-G) on layered double oxide substrates, in which the N,S-doped CNTs are in-situ grown on both sides of N,S-doped graphene, by two differentiated chemical vapor deposition (CVD) processes. The high concentrations of N and S dopants (up to 6.5 at.%) provide sufficient catalytic active sites for HER, while the CNTs seamlessly grafted on graphene ensure the excellent electric conductivity of N,S-CNTs/N,S-G hybrids. Consequently, the 3D N,S-CNTs/N,S-G composites display superior electrocatalytic activity for HER with an onset potential of 62 mV vs. RHE (achieve current density of 1 mA cm−2) and a small overpotential of 126 mV at 10 mA cm−2, which outperforms most of reported chemical doped carbon-based composites. The synthetic strategy facilitates the fabrication of other heteroatoms-doped 3D electrochemical catalysts.

Unveiling active sites by structural tailoring of two‐dimensional niobium disulfide for improved electrocatalytic hydrogen evolution reaction

Here we report, unveiling the active sites for improved electrocatalytic hydrogen evolution reaction (HER) by structural tailoring of Niobium Disulfide (NbS2). NbS2 synthesized by chemical vapor deposition method, structural deformation is carried out by post-argon plasma and annealing treatment. Plasma-treated (P.T) NbS2 exhibits layer-by-layer stacked (≈250 nm) long and (≈200 nm) wide flakes, which show more edge sites and demonstrates low hydrogen evolution activity. Annealed NbS2 flakes are enlarged in size (≈1 μm) having more surface area which shows additional active basal plane sites and demonstrate remarkable HER performance at 10 mA cm−2. As the thickness of NbS2 is reduced, more basal planes are exposed hence improved HER activity was achieved. This enhanced electrocatalytic change demonstrates that the basal planes are the main active sites for HER in NbS.

Self-supporting hierarchically micro/nano-porous Ni3P-Co2P-based film with high hydrophilicity for efficient hydrogen production

Designing efficient and stable non-precious metal HER (hydrogen evolution reaction) electrocatalysts with high large current density adaptability is significant for industrial application of hydrogen production by water electrolysis. Herein, a facile strategy was developed to construct a multi-phase Ni3P-Co2P-(Ni-Co) film with self-supporting hierarchically micro/nano-porous structure by using bubble template method electrodeposition of self-supporting micro-porous NiCoP film, oxygen-free annealing for phase separation producing Ni3P-Ni-Co2P-Co structure, and acid etching for constructing surface nano-porous structure. The effective active sites for HER was significantly increased due to the hierarchically micro/nano-porous structure, which not only enlarged the surface roughness, but enhanced the bubble detachment by improving the hydrophilicity. Meanwhile, the HER electrolysis durability was improved benefiting from the Ni3P-Co2P phases with high corrosion resistance (especially in acid solution) and the self-supporting film structure without binder. Consequently, the NiCoP-OA-AE film exhibited high HER catalytic performance, which delivered a current density of 10 mA cm−2 at a low overpotential of 42.9 and 39.7 mV in 1 M KOH and 0.5 M H2SO4, respectively. It also possessed high long-term electrolysis durability, and the cell voltage of water electrolysis using self-supporting porous NiCoP-OA-AE||IrO2-Ta2O5 electrolyzer at 500 mA cm−2 for 250 h in 0.5 M H2SO4 is only 2.9 V.

Ni–Fe nanocubes embedded with Pt nanoparticles for hydrogen and oxygen evolution reactions

Electrochemical water-splitting is widely regarded as one of the essential strategies to produce hydrogen energy, while Metal-organic frameworks (MOFs) materials are used to prepare electrochemical catalysts because of its controllable morphology and low cost. Herein, a series of trimetallic porous Pt-inlaid Ni–Fe nanocubes (NCs) are developed with bifunctions of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In the process of prepare the electrochemical catalysts, Pt nanoparticles are uniformly embedded in the Fe–Ni PBA cube structure, and ascorbic acid is employed as a reducing agent to reduce Pt2+ to Pt nanoparticles. In this work, the cubic structure of Fe–Ni PBA is maintained and the noble metal Pt nanoparticles are embedded. Remarkably, the formation of PBA cubes, Pt inlay and reduction are completed in one step, and Pt nanoparticles are embedded by a simple method for the first time. By employing acid etching method, a porous structure is formed on the PBA cube, which increases the exposed area of the catalyst and provides more active sites for HER and OER. Due to the porous structure, highly electrochemical active surface area and the embedded of highly dispersed Pt nanoparticles, the porous 0.6 Ni–Fe–Pt nanocubes (NCs) exhibits excellently electrocatalytic performance and durable stability to HER and OER. In this work, for HER and OER, the Tafel slopes are 81 and 65 mV dec−1, the overpotential η at the current density of 10 mA cm−2 are 463 and 333 mV, and the onset potential are 0.444 and 1.548 V, respectively. And after a 12-h i-t test and 1000 cycles of cyclic voltammetry (CV), it maintained high stability and durability. This work opens up a new preparation method for noble metal embedded MOF materials and provided a new idea for the preparation of carbon nanocomposites based on MOF.

Revisiting the Active Sites at the MoS2/H2O Interface via Grand-Canonical DFT: The Role of Water Dissociation.

MoS2 is a promising low-cost catalyst for the hydrogen evolution reaction (HER). However, the nature of the active sites remains a subject of debate. By taking the electrochemcal potential explicitly into account using grand-canonical density functional theory (DFT) in combination with the linearized Poisson-Boltzmann equation, we herein revisit the active sites of 2H-MoS2. In addition to the well-known catalytically active edge sites, also specific point defects on the otherwise inert basal plane provide highly active sites for HER. Given that HER takes place in water, we also assess the reactivity of these active sites with respect to H2O. The thermodynamics of proton reduction as a function of the electrochemical potential reveals that four edge sites and three basal plane defects feature thermodynamic overpotentials below 0.2 V. In contrast to current proposals, many of these active sites involve adsorbed OH. The results demonstrate that even though H2O and OH block "active" sites, HER can also occur on these "blocked" sites, reducing protons on surface OH/H2O entities. As a consequence, our results revise the active sites, highlighting the so far overlooked need to take the liquid component (H2O) of the functional interface into account when considering the stability and activity of the various active sites.

Enhancing hydrogen evolution activity of triangular PtPdCu nanodarts by phosphorus incorporation

The development of effective and stable catalysts for hydrogen evolution reaction (HER) is desired for hydrogen production. Herein, we report a facile solvothermal approach to fabricate P-doped triangular PtPdCu nanodarts (PtPdCu-P NDs) using trioctylphosphine as phosphorus dopant. The PtPdCu-P NDs with separated branches can provide high surface areas and sufficient active sites for HER. Moreover, the incorporation of phosphorus into alloys can tailor the electronic structure and the d-band electron density of metals, which is beneficial for adsorption of hydrogen intermediates. Additionally, the phosphorus doping can effectively inhibit the metal dissolution during the electrolysis. Therefore, the PtPdCu-P NDs achieve a very low overpotential of 12 mV at current density of 10 mA cm−2, rapid kinetics (Tafel slope: 29 mV dec-1) in 0.5 M H2SO4, superior to the undoped PtPdCu NDs. Moreover, the PtPdCu-P NDs also exhibit excellent stability, without obvious structure change and activity degradation after 10,000 cycles and 50-h electrolysis. This P-doping strategy is a universal approach to incorporate phosphorus into various nanomaterials without the change of the overall morphology, which holds a high potential in the water electrolysis.

Se-Rich MoSe2 Nanosheets and Their Superior Electrocatalytic Performance for Hydrogen Evolution Reaction.

Two-dimensional MoSe2 has emerged as a promising electrocatalyst for the hydrogen evolution reaction (HER), although its catalytic activity needs to be further improved. Herein, we report Se-rich MoSe2 nanosheets synthesized using a hydrothermal reaction, displaying much enhanced HER performance at the Se/Mo ratio of 2.3. The transition from the 2H to the 1T' phase occurred as Se/Mo exceeded 2. Structural analysis revealed the presence of Se adatoms as well as the formation of Se-Se bonding. Based on first-principles calculations, we propose two equally stable Se-rich structures. In the first one, excess Se atoms bridge two MoSe2 layers via the interlayer Se-Se bonds. In the second one, the Se atoms substitute for the Mo atoms, and extra Se atoms are added closest to the Mo-substituted Se. Calculation of Gibbs free energy along the reaction path indicates that the Se adatoms of the second model are the most active sites for HER.

In-Operando Insights on the Hydrogen Evolution Reaction Activity and Stability of Non-Noble Metal Electrocatalysts for Water Electrolysis

Market penetration of proton exchange membrane water electrolysers (PEMWE) as energy conversion technologies in a renewable energy sector would imply, given the 2.3$/Kg H2 production cost aimed by the DoE,1 a drastic decrease in total noble metal electrocatalyst loading. For the state-of-the-art hydrogen evolution reaction (HER) catalyst, platinum, recent targets suggest this limit to be 0.05mgPt/cm2.2 In some applications, like direct photoelectrochemical water splitting, application of any amount of noble metal as a co-catalyst cannot be tolerated at all. Thus, given increasing scarcity of platinum, alternative materials based on earth-abundant non-noble metals represent a significant interest as promising HER catalysts. Among them, transition metal dichalcogenides such as molybdenum disulfide (MoS2) have provided excellent performances, particularly in their cluster-based allotropic structure [Mo3S13]2-.3 Whilst the role of sulfide atoms in the Mo-terminated edges as HER active sites in crystalline MoS2 is well-established, the HER mechanism of [Mo3S13]-based materials is still under debate. Preceded by an electrochemical activation step, operando spectroscopic studies ascribed the active sites to the electrochemically-cleaved S2 2-,4 but other reports have suggested undercoordinated Mo sites to be responsible for the HER activity.5 To date, no study has evaluated the in operando activity and stability of [Mo3S13]-based materials, shown to be intimately dependent on the electrochemical conditioning and electrolyte pH.6 This work devotes to the simultaneous detection of Mo and S species under HER operating conditions in pristine and anchored [Mo3S13]2- clusters to nitrogen-doped carbon nanotubes, by use of our dedicated on-line inductively-coupled plasma mass spectrometry (on-line ICP-MS). Our findings demonstrate, contrary to previous understanding, that the electrochemical activation step is mostly related to Mo dissolution rather than S loss, which is one order of magnitude lower. After such activation, Mo dissolution is significantly mitigated, whereas S dissolution is still observed, with magnitudes dependent on the anchoring material. The overarching picture obtained by such study enabled to shed light on the HER activation mechanism, and demonstrate that the stabilities of these materials are comparable to some Ir-based catalysts. The aforementioned results provide further guidelines to implement non-noble HER metal electrocatalysts in PEMWE.

Co nanoparticles coupling induced high catalytic activity of nitrogen doped carbon towards hydrogen evolution reaction in acidic/alkaline solutions

The development of highly-efficient and noble-metal-free catalysts with low cost and high durability for hydrogen evolution reaction (HER) is of great importance to many energy-related technologies. This work reports that nitrogen-doped carbon coated Co nanoparticles encapsulated in bamboo-like nitrogen-doped carbon nanotubes (Co@NC/B-NCNTs), synthesized by a simple calcination of Co(NO3)2, melamine and P123, is a promising catalyst for HER in both acidic and alkaline solutions. In acidic solution, the Co@NC/B-NCNTs has the HER onset potential of ∼0 V and only needs an overpotential of 7 mV to drive the current density of 10 mA cm−2. Its HER catalytic activity is very close to that of Pt/C. In alkaline solution, its onset potential and overpotential to drive 10 mA cm−2 are 100 and 182 mV, respectively. Both the values are lower than those of many other catalysts reported. The DFT calculations show electronic coupling between Co nanoparticles and NC layer plays an important role in high catalytic activity of Co@NC/B-NCNTs. The Co nanoparticles can change the charge density distribution of the outer NC layer, affecting its properties for hydrogen adsorption and desorption. Additionally, the pyridinic N in the outer NC layer is calculated to be a promising active site for HER.

High‐Resolution Electrochemical Mapping of the Hydrogen Evolution Reaction on Transition‐Metal Dichalcogenide Nanosheets

AbstractHigh‐resolution scanning electrochemical cell microscopy (SECCM) is used to image and quantitatively analyze the hydrogen evolution reaction (HER) catalytically active sites of 1H‐MoS2 nanosheets, MoS2, and WS2 heteronanosheets. Using a 20 nm radius nanopipette and hopping mode scanning, the resolution of SECCM was beyond the optical microscopy limit and visualized a small triangular MoS2 nanosheet with a side length of ca. 130 nm. The electrochemical cell provides local cyclic voltammograms with a nanoscale spatial resolution for visualizing HER active sites as electrochemical images. The HER activity difference of edge, terrace, and heterojunction of MoS2 and WS2 were revealed. The SECCM imaging directly visualized the relationship of HER activity and number of MoS2 nanosheet layers and unveiled the heterogeneous aging state of MoS2 nanosheets. SECCM can be used for improving local HER activities by producing sulfur vacancies using electrochemical reaction at the selected region.

High Active and Durable Vanadium Sulfide Multilayer Structure Featuring Rich Hole Defects Constructed for Accelerated Hydrogen Evolution Reaction

VS2 nanomaterials with special morphology, exposed edges, defects have studied as an active and inexpensive electrocatalyst for hydrogen evolution reaction (HER). Here, we reported the fabrication of multilayer Waffle structured VS2 featuring rich hole defects (VS2 MLW). This structure shows excellent kinetic metrics for electrocatalytic HER, exhibiting a overpotential of 82 mV at the current density of −10 mA cm−2, a Tafel slope of 61 mV dec−1, and a long-term stability without any current fading. Its HER performance is much better than that of other V-based catalysts, and even comparable to that of commercial Pt/C. Through experimental and theoretical calculation, the outstanding electrocatalytic activity of the VS2 MLW is attributed to its special morphology and electronic structure. The hole defects in this structure provide larger electrochemical active area and more active sites for HER, more importantly, hole defects change the electron structure of catalyst and reduce the free energy of hydrogen adsorption, the optimized free energy consequently leading to the improved inherent catalytic activity of VS2 MLW. This work provides a new concept to design efficient HER catalyst by specific surface area and defect engineering.

Hierarchical Zn-Co-P nanoneedle arrays supported on three-dimensional framework as efficient electrocatalysts for hydrogen evolution reaction in alkaline condition

Currently, the numerous research efforts have focused on the development of efficient non-nobble-metal electrocatalysts toward electrochemical hydrogen evolution reaction (HER) for producing high-purity hydrogen, which has been recognized as a cost-effective and eco-friendly fuel to satisfy global energy demands in the future. Herein, an active HER electrocatalyst based on Zn-Co-P nanoneedle arrays growing directly on the surface of three-dimensional (3D) nickel foam (Zn-Co-P NNs/3D-NF) was successfully synthesized via the simple and low-cost methods. The combination of desired properties for electrocatalysts such as 3D hierarchical nanostructure containing large surface area and abundant electroactive sites for fast diffusion and mass transfer of reactant/electrolyte, highly physical stability for strongly catalytic durability along with the remarkable feature of 1D porous structure of Zn-Co-P NN providing richly active sites for HER resulted in a highly electrocatalytic activity. Interesting, in the introduction of Zn, the Zn-Co-P NNs/3D-NF provides rich edge sites and defects for exposing more active sides, leading to the great enhancing in active surface area, and thereby improving HER catalytic activity. The obtained Zn-Co-P NNs/3D-NF catalyst shown high electrocatalytic efficiency toward HER with the requirement of low overpotential of 138 mV and 210 mV to reach a current density of 10 and 50 mA cm−2 in alkaline media, respectively, together with rapid kinetic at a small Tafel slope of 81.9 mV dec−1. In addition to highly electrocatalytic performance, the Zn-Co-P NNs/3D-NF catalyst also shown the superior durability at −0.138 V, this allowed the production process of H2 to continually occur at least 12 h with retaining a constant current density of 10 mA cm−2. More importantly, our research offered an attractive approach to design non-noble-metal electrocatalysts in the requirement of cost-effectiveness, high catalytic activity, and strong stability for practical HER application.