Active Sites For Hydrogen Evolution Reaction Research Articles

MoS2-CuCo2S4 nanosheets with a honeycomb structure formed on Ni foam: An efficient electrocatalyst for hydrogen evolution reaction

The physical, chemical, and electrocatalytic properties of conventional single-component electrocatalysts developed for the hydrogen evolution reaction (HER) no longer match the needs of many commercial applications. This necessitates for the creation of more sophisticated and effective electrocatalysts for the HER. In this study, MoS2-CuCo2S4 was loaded onto NF using a simple two-step hydrothermal method. In the resultant NF/MoS2-CuCo2S4 material, CuCo2S4 offers a lot of active sites to support vertically arranged MoS2 nanosheets, thereby decreasing their agglomeration. Moreover, the heterogeneous structure formed between CuCo2S4 and MoS2 facilitates charge transfer and exposes the active sites for HER, further improving the electrochemical hydrogen evolution performance of the heterostructured electrocatalyst. In a 1.0 M KOH solution, the synthesized NF/MoS2-CuCo2S4 nanosheet catalyst has outstanding electrocatalytic efficacy, with an overpotential as low as 67 mV at a current density of 10 mA·cm−2.

In Situ Reconstruction to Surface Sulfide Adsorbed Metal Scaffold for Enhanced Electrocatalytic Hydrogen Evolution Activity

AbstractTransition‐metal‐based compounds have been intensively explored as efficient electrocatalysts for hydrogen evolution reaction (HER). Feasible reconstruction to the real active sites, which is yet to be identified, endows the promotion of HER activity. Here, it is reported that the incoming S coordinates and anion vacancies prompt the structural reconstruction of S‐doped Co3O4 on carbon cloth (S‐Co3O4/CC) during HER. A list of in situ studies reveals that the real active sites for HER are the “metallic surface‐adparticles” system embracing metallic Co scaffold and the dilute coverage of S coordinated Coδ+. Reaction mechanism exploration illustrates that interfacial perimeters between the coverage of Co3S4 moieties and metallic Co considerably facilitate the adsorption of H*, improve the kinetics of water dissociation, and consequently promote HER activity. The exemplified sulfide‐mediated topotactic transformation strategy is extended to the preparation of S, Fe codoped Ni(OH)2 (S‐NiFe/CC) as a bifunctional electrocatalyst. The assembled anion exchange membrane water electrolyzer achieves a current density of 1.0 A cm−2 at 1.72 V, showing excellent capability in catalyzing overall water splitting at ampere level. This study, showing a feasible strategy that enables the facile reconstruction to identify active sites, would inspire the development of efficient electrocatalysts for HER and other electrochemical hydrogenation reaction.

Rational design of MoS2@M (M=Sn, Cu, Ni, Co) hybrid nanostructures for enhanced electrocatalytic hydrogen evolution reaction

MoS2 has attracted attraction in electrocatalytic hydrogen evolution reaction (HER). The low electrical conductivity and limited exposure of active sites hindered the electrocatalytic efficiency of MoS2. In this paper, we design MoS2@M (M = Sn, Cu, Ni, Co) hybrid nanostructures by growing MoS2 nanosheets on the surface of M (M = Sn, Cu, Ni, Co) nanowires. Due to the high conductivity of metal nanowires and the increased HER active sites, the MoS2@M (M = Sn, Cu, Ni, Co) hybrid nanostructures show a superior HER efficiency. In alkaline media, the MoS2@M (M = Sn, Cu, Ni, Co) hybrid nanostructures exhibit the low overpotential of 130–172 mV at the current density of 10 mA/cm2 and a small Tafel slope of 61–86 mV/dec. In addition, the MoS2@M (M = Sn, Cu, Ni, Co) hybrid nanostructures also possess excellent electrocatalytic durability. This work provides an efficient way to achieve highly efficient MoS2 based electrocatalysts for water splitting.

Boosting Efficient Alkaline Hydrogen Evolution Reaction of CoFe-Layered Double Hydroxides Nanosheets via Co-Coordination Mechanism of W-Doping and Oxygen Defect Engineering.

While surface defects and heteroatom doping exhibit promising potential in augmenting the electrocatalytic hydrogen evolution reaction (HER), their performance remains unable to rival that of the costly Pt-based catalysts. Yet, the concurrent modification of catalysts by integrating both approaches stands as a promising strategy to effectively address the aforementioned limitation. In this work, tungsten dopants are introduced into self-supported CoFe-layered double hydroxides (LDH) on nickel foam using a hydrothermal method, and oxygen vacancies (Ov) are further introduced through calcination. The analysis results demonstrated that tungsten doping reduces the Ov formation energy of CoFeW-LDH. The Ov acted as oxophilic sites, facilitating water adsorption and dissociation, and reducing the barrier for cleaving HO─H bonds from 0.64 to 0.14eV. Additionally, Ov regulated the electronic structure of CoFeW-LDH to endow optimized hydrogen binding ability on tungsten atoms, thereby accelerating alkaline Volmer and Heyrovsky reaction kinetics. Specifically, the abundance of Ov induced a transition of tungsten from a six-coordinated to highly active four-coordinated structure, which becomes the active site for HER. Consequently, an ultra-low overpotential of 41mV at 10 mAcm-2 , and a low Tafel slope of 35mVdec-1 are achieved. These findings offer crucial insights for the design of efficient HER electrocatalysts.

Fe−N bonds induced highly efficient Fe3O4/g-C3N4 heterojunction for electrocatalytic hydrogen evolution

Fe-based catalysts with the merits of the most abundant reserves in the crust, cheapest, and low toxicity, show significant superiorities to noble-metal catalysts for electrocatalytic water splitting. Fe3O4 as a member of Fe-based catalysts has been widely used for oxygen evolution reaction (OER). However, it is rarely applied for Hydrogen evolution reaction (HER) owing to the lack of inherent active sites for hydrogen absorption. Fe−N coordination bonds can act as active sites for electrocatalytic performance. Therefore, we reasonably designed and constructed Fe3O4/g-C3N4 heterojunction, where abundant Fe−N bonds acting as HER active sites were formed with the aid of rich Pyridine N of g-C3N4. Activity characterization result indicates the optimized 50%-Fe3O4/g-C3N4 heterojunction exhibits excellent HER performance with a low overpotential of 160 mV at 10 mA cm−2, a low Tafel slope of 77.18 mV dec−1, and outstanding cycle stability. Density functional theory (DFT) calculation demonstrates that the enhanced electrocatalytic performance stems from the Fe−N bonding interaction, which endows 50%-Fe3O4/g-C3N4 with lower water dissociation barrier and a moderate Gibbs free energy of hydrogen adsorption (ΔGH*) in comparison with pristine Fe3O4 and g-C3N4.

Dense r-Ru/FeCoP heterointerfaces induced by a defect-assisted strategy for ultrastable alkaline overall water splitting.

Simplifying the anchoring process of Ru nanoparticles (NPs) and activating their bifunctional activity are challenges in the construction of Ru-based catalysts. In this work, FeCoP nanosheets anchored by Ru NPs (r-Ru/FeCoP) were innovatively synthesized using an oxygen defect-assisted-gas-phase phosphorization strategy. Surprisingly, the η100 values of r-Ru/FeCoP in the alkaline hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) processes were 0.8 and 0.58 times those of Pt/C and RuO2, respectively. Notably, the rich Ru NPs as HER active sites on r-Ru/FeCoP enhanced the conductivity of the catalyst and promoted the reaction kinetics for HER, while the metal atoms on the FeCoP nanosheets served as OER active sites to accelerate the desorption of O2. The synergy between the two promoted the improvement of overall water splitting efficiency. Overall, this work provides a new approach for the development of low-cost bifunctional catalysts with high Ru utilization.

High‐Throughput Designed and Laser‐Etched NiFeCrVTi High‐Entropy Alloys with High Catalytic Activities and Corrosion Resistance for Hydrogen Evolution in Seawater

AbstractElectrocatalytic hydrogen evolution from seawater through wind or solar energy is a cost‐effective way to produce green hydrogen fuel. However, the lack of highly active and anti‐corrosive electrocatalysts in seawater severely hinders the industrial application. Herein, a novel Ni1.1FeCr0.4V0.3Ti0.3 high‐entropy alloy (HEA) is designed through high throughput computing and prepared via powder metallurgy with the surface treated by laser etching under different laser power. The laser‐etched NiFeCrVTi high‐entropy alloys exhibit a unique periodically ordered structure with multiple active centers and high porosity. The Ni‐HEA‐30 displays remarkable hydrogen evolution reaction (HER) performance with an overpotential of 55.9 mV and a Tafel slope of 47.3 mV dec−1 in seawater. Density functional theory (DFT) calculations are applied to identify the real active sites for HER on the HEA surface as the key factor for both proton and intermediate transformation, which also reveals that the Cr atom promotes the adsorption energy of water molecules, and the modulation of the electronic structure plays a crucial role in optimizing the hydrogen binding capabilities of the Ni atoms within the alloy. Additionally, the electrocatalyst displays high corrosion resistance in seawater, contributing to the good durability for hydrogen production. This work uncovers a new paradigm to develop novel electrocatalysts with superior reaction activity in seawater.

Tailoring the morphology of Mo2S3/MoP2 composite thin films via aerosol assisted chemical vapor deposition for enhanced hydrogen evolution reaction performance

In this study, we report on the fabrication of Mo2S3/MoP2 composite thin films using a single-step aerosol assisted chemical vapor deposition method from a single-source precursor solution of [(ƞ5-Cp)Mo(CO)2(S2P(SC6H4Me)2)] (1). Deposition times of 20, 30, and 40 min were used to obtain thin films with different morphologies. Our investigation found that the 30-minute thin film, which had a widely distributed grainy morphology, exhibited the highest electrocatalytic performance for hydrogen evolution reaction (HER) as determined by linear sweep voltammetry studies. This film required the lowest applied potential of 250 mV to generate a current density of 10 mAcm−2 with a low charge transport resistance of 715 Ω, despite having the lowest charge donor density of 5.52 × 1019 cm−3. We found that the unique morphology of this thin film enhanced electron mobility, resulting in superior HER performance with a Tafel slope of ∼123 mVdec−1 and a higher current charge density of 0.408 mAcm−2 due to increased active sites for HER. The Mo2S3/MoP2 heterostructure exhibited favourable band gaps of ∼2.2 and ∼2.7 eV, respectively, resulting in a synergistic effect that allowed for effective electron transfer. Our study concludes that different deposition durations produced composite thin films with altered morphologies that exhibit dissimilar electrochemical kinetics in HER.

Constructing a Functionalized Electrocatalyst of a Transition Metal Chalcogenide on Accordion-Like MXene to Boost the Hydrogen Evolution Reaction.

MXenes exhibit unique layered structures and excellent electrical conductivity, and their multiple surface termination groups are favorable for hosting impressive performance for electrochemical reactions. Therefore, a two-dimensional (2D) layered MXene-based catalyst may become a novel high-efficiency electrocatalyst to replace traditional noble metal electrocatalysts. In this work, a transition metal chalcogenide (MoS2/CuS) and MXene are combined to prepare a 2D electrocatalyst (MoS2/CuS/MXene) for the hydrogen evolution reaction (HER). MXene exhibited a large specific surface area in the shape of an accordion, which was very beneficial for the growth of nanomaterials. CuS/MXene promoted electron transfer and improved the exposed active site for HER. The exposed MoS2 edges exhibited a high chemical adsorption capacity, which is conducive to HER. Electrochemical tests reveal that the MoS2/CuS/MXene electrocatalyst can reduce the charge transfer resistance toward the HER and increase active sites for HER, leading to enhancing the catalytic performance. The MoS2/CuS/MXene electrocatalyst affords an efficient HER with a low overpotential (115 mV@10 mA cm-2). This work offers a new idea to create layered transition metal chalcogenide- and MXene-based electrocatalysts for HER.

Heterogeneous Cu incorporated into Ni6Fe2-LDH/rGO induces spin exchange interaction to enhance alkaline hydrogen evolution

The efficiency of hydrogen evolution reaction (HER) takes an important influence on electrochemical water electrolysis, yet it still delivers sluggish kinetics mainly due to the high kinetic energy barriers. Herein, Cu1Ni5Fe2-Layered double hydroxides/reduced graphene oxide (denoted as Cu1Ni5Fe2-LDHs/rGO) with heterogeneous Cu atoms incorporated into Ni6Fe2-LDHs/rGO is constructed through a hydrothermal method and doping strategy in this works, wherein the subtle lattice distortion is availably regulated and optimized by Cu2+ Jahn-Teller effect, offering more active sites for HER. As benefits of the subtle lattice distortion and the spin exchange interaction, Cu1Ni5Fe2-LDHs/rGO displays ferromagnetism at room temperature and shows superior alkaline HER properties with a relatively low overpotentials of 50 mV at 10 mA cm−2 in 1.0 M KOH. The low Tafel slope of 38 mV dec−1 implies Cu1Ni5Fe2-LDHs/rGO owns an ultra-fast HER kinetic. This study can offer a new strategy to construct high efficient HER catalysts based on transition metal NiFe-LDHs.

Modulation of active site environment in an embedded CuOx@TiO2 photocatalyst for enhanced hydrogen evolution and CO2 reduction

Cocatalyst act as the active site usually plays an important role in both photocatalytic hydrogen evolution reaction (HER) and carbon dioxide reduction reaction (CO2RR). As the size, distribution, location, contact behavior with semiconductor etc. show significant effects for the activity. In this work, the active site environment (aggregation state of the active site of the cocatalyst) was modulated by locating the different amounts of CuOx nanoparticles (NPs) into the porous TiO2 (CuOx@TiO2), which was achieved by calcination of Cu@MIL-125 as the precursor. The composition, morphology, and chemical state of the catalyst were analyzed by a series of characterization methods. The results showed that the embedded CuOx NPs exhibited obviously better dispersion than the externally supported ones, especially at the high loading amount. Cu NPs totally transformed to CuO at the lower loading amount, while it transformed to CuOx with partial Cu (I) species existence at the higher loading amount. Photocatalytic reactions showed that the activity of CuOx@TiO2 was ∼ twice that of the traditional outside loading catalyst CuOx/TiO2 in both HER and CO2RR. The high HER activity was obtained at relatively lower loading capacity (0.200 wt%∼0.500 wt%), while CO2RR was the advantageous reaction at higher loading capacity (5.000∼15.000 wt%). Apparently, CuOx@TiO2 offered a quite different active site environment for the two type of reactions. The embedded structure can provide highly dispersed single active sites for HER at lower loading capacity, while it facilitates the formation of multi-electron environment under irradiation for CO2RR at higher loading capacity. The construction of an appropriate active center environment determines the occurrence of high-efficiency photocatalytic reactions.

Towards Higher NH3 Faradaic Efficiency: Selective-Poisoning of HER Active Sites by Co-Feeding CO in NO Electroreduction.

Direct electroreduction of nitric oxide offers a promising avenue to produce valuable chemicals, such as ammonia, which is an essential chemical to produce fertilizers. Direct ammonia synthesis from NO in a polymer electrolyte membrane (PEM) electrolyzer is advantageous for its continuous operation and excellent mass transport characteristics. However, at a high current density, the faradaic efficiency of NO electroreduction reaction is limited by the competing hydrogen evolution reaction (HER). Herein, we report a CO-mediated selective poisoning strategy to enhance the faradaic efficiency (FE) towards ammonia by suppressing the HER. In the presence of only NO at the cathode, Pt/C and Pd/C catalysts showed a lower FE towards NH3 than to H2 due to the dominating HER. Cu/C catalyst showed a 78 % FE towards NH3 at 2.0 V due to the stronger binding affinity to NO* compared to H*. By co-feeding CO, the FE of Cu/C catalyst towards NH3 was improved by 12 %. More strikingly, for Pd/C, the FE towards NH3 was enhanced by 95 % with CO co-feeding, by effectively suppressing HER. This is attributed to the change of the favorable surface coverage resulting from the selective and competitive binding of CO* to H* binding sites, thereby improving NH3 selectivity.

Construction of multiple heterogeneous interfaces boosting alkaline hydrogen evolution

Alkaline hydrogen evolution reaction (HER) is suppressed by the water dissociation, leading to more sluggish kinetics than acidic HER. Developing multifunction catalysts via constructing heterogeneous interfaces is a feasible tactic to accelerate the alkaline HER. Herein, NiO coupled with Ni and MoxN (NMN) nanorods were prepared via a hydro-thermal synthesis combined with a thermal decomposition under ammonia atmosphere. The low crystalline NMN nanorods are rich in heterointerfaces, and have sufficient high active sites for HER. The synergistic effect between NiO and Ni-MoxN promotes the water dissociation the hydrogen adsorption, and the charge transfer, contributing to excellent alkaline HER activity. The overpotential on NMN is only 36 and 150 mV for the current density of 10 and 300 mA cm−2, respectively, and the Tafel slope is 48 mV/dec, demonstrating a superior performance for alkaline HER, which is even comparable to the commercial electrocatalysts.

NiS/Cd0.6 Zn0.4 S Schottky Junction Bifunctional Photocatalyst for Sunlight-Driven Highly Selective Catalytic Oxidation of Vanillyl Alcohol Towards Vanillin Coupled with Hydrogen Evolution Reaction.

Selective oxidation of biomass-based molecules to high-value chemicals in conjunction with hydrogen evolution reaction (HER)is an innovative photocatalysis strategy. The key challenge is to design bifunctional photocatalysts with suitable band structures, which can achieve highly efficient generation of high-valuechemicals and hydrogen. Herein, NiS/Cd0.6 Zn0.4 S Schottky junction bifunctional catalysts are constructed for sunlight-driven catalytic vanillyl alcohol (VAL) selective oxidation towards vanillin (VN) coupling HER. At optimal conditions, the 8% NiS/Cd0.6 Zn0.4 S photocatalyst achieves high activity of VN production (3.75mmol g-1 h-1 ) and HER (3.84mmol g-1 h-1 ). It also exhibits remarkable VAL conversion (66.9%), VN yield (52.1%), and selectivity (77.8%). The photocatalytic oxidation of VAL proceeds a carbon-centered radical mechanism via the cleavage of αC-H bond. Experimental results and theoretical calculations show that NiS with metallic properties enhances the electron transfer capability. Importantly, a Ni-S-Cd "electron bridge" formed at the interface of NiS/Cd0.6 Zn0.4 S further improves the separation/transfer of electrone/h+ pairs and also furnishes HER active sites due to its smaller the |ΔGH* | value, thereby resulting in a remarkably HER activity. This work sheds new light on the selective catalytic oxidation VAL to VN coupling HER, with a new pathway towards achieving its efficient HER efficiency.

Green fabrication of nanostructured Ni(OH)2/Ni/Carbon felt electrodes with water-containing deep eutectic solvent for enhanced water electrolysis performance

To produce green hydrogen, the development of high-performance, environmentally friendly, and cost-effective electrocatalysts for efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is imperative. This study explores the potential application of water-containing deep eutectic solvents (DESs) in the synthesis of nanostructured electrocatalysts for water electrolysis. Ni(OH)2/Ni/carbon felt (CF) composite electrodes are developed via one-step electrodeposition in a water-containing choline chloride/urea DES as a green reaction medium. Heterostructured Ni(OH)2/Ni nanosheets are formed and uniformly deposited on the CF substrate with the addition of 10 wt% water to DES (CU10W), which increases active sites for HER and OER. The initial confinement of water molecules by the DES is found to be crucial in forming the hierarchical structure of the electrocatalysts. Notably, the CU10W electrode exhibits excellent bifunctional activity toward HER and OER, with reduced overpotentials of 192 and 564 mV, respectively, at 100 mA cm−2. This renders the CU10W electrode-based electrolysis system stable with a reduced cell voltage of 1.69 V and a high Faradaic efficiency of over 99% for the HER. The augmented electrochemical active surface area and reduced charge transfer resistance of the CU10W electrode account for the improved HER/OER performance associated with the special hierarchical Ni(OH)2/Ni nanostructure.

Modulation of electronic density states of carbon atom via multifaceted Cu doped Co2P particle for robust and efficient electrocatalytic hydrogen evolution reaction in aqueous acidic medium

Development of Pt free catalyst for hydrogen evolution reaction (HER) having both superb efficiency and sound stability is a key challenge in the field of alternate fuel production. Herein, we have reported Cu doped multifaceted Co2P particles incorporated on expanded graphite synthesized via solvothermal method, and studied its catalytic activity. The composite catalyzes the evolution of H2 efficiently with a potential value 81 mV to achieve the benchmark current density of 10 mA cm-2 and a Tafel slope value of 113 mV dec‑1 coupled with a remarkable long-term stability for 21.6 h. Our experimental analysis provides strong evidence that the multifaceted Cu doped Co2P could work in concert with carbon atoms of the expanded graphite (EG) that leads in the changing of the energy states of nearby carbon atoms of the metal phosphide particle which is also in well agreement of our theoretical calculation. The lower contact electrical resistance of EG have significant impact in endowing fast electron transfer to the catalytic active sites and the aid of catalytic performance. The specific morphology of the catalyst hints at increased surface area and overall exposed active sites to bestow the catalytic performance. The study suggests that the energetically modulated carbon atoms can act as a fine active site for HER.

Creating Dual Active Sites in Conductive Metal‐Organic Frameworks for Efficient Water Splitting

AbstractThe achievement of bifunctional metal‐organic frameworks (MOFs) remains a huge challenge due to their lack of dual active sites. Herein, dual sites in the Co‐catecholate (Co‐CAT) are created through Ru, Ir, or Rh doping for overall water splitting. Among them, RuCo‐CAT exhibits excellent bifunctional activities, outperforming benchmarked Pt/C for the hydrogen evolution reaction (HER) and RuO2 for the oxygen evolution reaction (OER). The theoretical calculations demonstrate that the doped Ru atoms with optimal absorption energy for the hydrogen intermediate and the Co centers with a reduced energy barrier for the rate‐determining step are the active sites for HER and OER, respectively. Furthermore, the incorporation of Ru atoms can improve the electrical conductivity and capacity of water adsorption of Co‐CAT greatly, synergistically improving the bifunctional activity. This strategy for engineering dual active sites offers novel insights into designing bifunctional MOFs for overall water splitting.

Ru nanoclusters coupling with hierarchical phosphorus and oxygen dual-doped carbon nanotube architectures for effective hydrogen evolution reaction

The construction of an effective catalyst for hydrogen evolution reaction (HER) is a top priority. Herein, we demonstrate ruthenium (Ru) nanoclusters coupled with phosphorus and oxygen dual-doped carbon nanotube (CNT) architecture (Ru-POCA). The increased hydrophilicity and negatively charged surface of CNTs can strongly trap Ru ions. The hierarchical structure is favorable of providing abundant pathways and exposing more active sites for HER. Due to the synergistic effect of the hierarchical structure and modified surface chemistry, Ru-POCA exhibits excellent catalytic HER activity. The overpotential is 22 and 40 mV with a Tafel slope of 28.0 and 27.1 mV dec−1 in 1 M KOH and 0.5 M H2SO4 at 10 mA cm−2. Moreover, Ru-POCA processes good catalytic stability in both acidic and alkaline electrolytes, while the boosted catalytic HER activity is fundamentally studied by density functional theory calculation. This work provides a rational approach to constructing hierarchically structured Ru-CNTs-based catalysts for hydrogen evolution reaction.

Synergistic Coupling of Hierarchical Heterostructured Ni3P/Ni/VN Microflower Electrocatalyst for Enhanced Hydrogen Evolution Reaction

AbstractThe exploration of economical and highly efficient electrocatalysts for hydrogen evolution reaction (HER) is paramount for the development of sustainable hydrogen economy. Herein, a novel three‐dimensional (3D) hierarchical microflower electrocatalyst comprised of N‐doped carbon‐armored Ni3P/Ni/VN heterogeneous nanoparticles (Ni3P/Ni/VN@NC) is developed by combining a hydrothermal method with in‐situ carbonization‐phosphating strategy. The unique robust hierarchical structure derived from 3D NiV layered double hydroxide (NiV‐LDH) skeleton as precursor provides multidimensional mass and charge transport channels as well as numerous active sites for HER, leading to the improved HER activity. More importantly, the possible electron transfer route of Ni3P→Ni→VN is demonstrated due to the charge pumping capability of VN during interfacial electron intercoupling among the tri‐component, which endows Ni3P/Ni/VN with the favorable absorption of hydrogen‐intermediates and thus upgraded HER kinetics over such heterostructure. The resulting Ni3P/Ni/VN@NC catalyst exhibits extremely low overpotentials of 81 mV and 134 mV to deliver a current density of 10 mA cm−2 without iR‐compensation in alkaline and acidic media, respectively, and maintains continuous operation for over 90 h. This work enlightens the rational design of hierarchical multi‐component heterostructured catalysts for efficient hydrogen production.

From the single-atom limit to the mixed-metal phase: finding the optimum condition for activating the basal plane of a FePSe3 monolayer towards HER.

Layered ternary transition metal tri-chalcogenides are some of the most promising candidates for hydrogen evolution reaction (HER) because of their ease of synthesis and affordability. However, majority of the materials in this category have HER active sites only at their edges, rendering a large portion of the catalyst useless. In this work, ways for activating the basal planes of one of these materials, namely, FePSe3, are explored. The effects of substitutional transition metal doping and external biaxial tensile strain on the HER activity of the basal plane of a FePSe3 monolayer are studied via first principles electronic structure calculations based on density functional theory. This study reveals that although the basal plane of the pristine material is inactive towards HER (value of H adsorption free energy, ΔGH* = 1.41 eV), 25% Zr, Mo, and Tc doping makes it more active (ΔGH* = 0.25, 0.22 and 0.13 eV, respectively). The effect of reducing the doping concentration, moving to the single-atom limit, on the catalytic activity is studied for Sc, Y, Zr, Mo, Tc and Rh dopants. For Tc, the mixed-metal phase FeTcP2Se6 is also studied. Among the unstrained materials, 25% Tc-doped FePSe3 gives the best result. Significant tunability of HER catalytic activity in the 6.25% Sc doped FePSe3 monolayer via strain engineering is also discovered. An external tensile strain of 5% reduces ΔGH* to ∼0 eV from 1.08 eV in the unstrained material, making this an attractive candidate for HER catalysis. The Volmer-Heyrovsky and Volmer-Tafel pathways are examined for some of the systems. A fascinating correlation between the electronic density of states and HER activity is also observed in most materials.