Step Of Hydrogen Evolution Reaction Research Articles

Rationally designing of Co-WS2 catalysts with optimized electronic structure to enhance hydrogen evolution reaction

Designing and developing cost-effective, high-performance catalysts for hydrogen evolution reaction (HER) is crucial for advancing hydrogen production technology. Tungsten-based sulfides (WSx) exhibit great potential as efficient HER catalysts, however, the activity is limited by the larger energy required for water dissociation under alkaline conditions. Herein, we adopt a top-down strategy to construct heterostructure Co-WS2 nanofiber catalysts. The experimental results and theoretical simulations unveil that the work functions-induced built-in electric field at the interface of Co-WS2 catalysts facilitates the electron transfer from Co to WS2, significantly reducing water dissociation energy and optimizing the Gibbs free energy of the entire reaction step for HER. Besides, the self-supported catalysts of Co-WS2 nanoparticles confining 1D nanofibers exhibit an increased number of active sites. As expected, the heterostructure Co-WS2 catalysts exhibit remarkable HER activity with an overpotential of 113 mV to reach 10 mA cm−2 and stability with 30 h catalyzing at 23 mA cm−2. This work can provide an avenue for designing highly efficient catalysts applicable to the field of energy storage and conversion.

Ultralow-Pt-loading assisted by reconstruction of cobalt molybdate nanoarrays for enhanced hydrogen evolution reaction

The utilization of Pt nanoparticles as catalysts in hydrogen evolution reaction (HER) is a widely adopted strategy for hydrogen production. Nonetheless, the reduction of Pt usage costs and enhancement of its durability are crucial factors that need to be addressed in order to facilitate the commercialization of these catalysts. In this study, Pt–Co(OH)2@CoMoO4/NF has been developed and synthesized on nickel foam (NF) through the implementation of hydrothermal and electrodeposition techniques. Cobalt molybdate is subjected to surface reconstruction of the precatalyst by anion etching under electrodeposition conditions to form hydroxides nanosheets, and the ultra-low content of Pt nanoparticles (0.25 wt%) was uniformly dispersed on the CoMoO4 nanoarrays and Co(OH)2 nanosheets subsequently. Detailed experimental characterization showed that low Pt loading promoted charge transfer, accelerated the Heyrovsky step of HER, and surface reconstruction increased oxygen vacancies. Pt–Co(OH)2@CoMoO4/NF exhibited an overpotential of 100 mV at current densities of 100 mA cm−2, while lasting this current density for a duration of 100 h. At higher current densities, the electrocatalytic activity of Pt–Co(OH)2@CoMoO4/NF surpassed that of the commercially accessible 20 wt% Pt/C. Our work offers a viable approach towards designing efficient electrocatalysts for hydrogen production base on platinum.

Revealing the role of Sn in NiSn for enhancing hydrogen evolution performance by density functional theory

Doping Sn into transition metal Ni can gain an enhanced hydrogen evolution performance. Optimizing H binding free energy (ΔGH) is considered as the main function of Sn. However, the detailed action mechanism of Sn in NiSn catalyst is still ambiguous. Herein, the functional role of Sn in NiSn was systematically inspected using density functional theory (DFT) method. The difference site Ni of Ni slab was replaced by Sn to build NiSn with the difference distribution of Sn. The calculations about the barrier of H2O dissociation and ΔGH show that surface Ni in NiSn is the main active site for catalyzing the hydrogen evolution reaction (HER) and the distribution of Sn in NiSn alloy directly decides the main role of Sn in promoting HER. Only replacing surface Ni with Sn, the main role of Sn is to reduce the adsorption of H and promote the H desorption step of HER. When Sn locates at sub-surface or surface and sub-surface Sn exist simultaneously, ΔGH on NiSn has no reduction and accelerating the H2O dissociation is the main function of Sn.

High phase purity of stable 1T-phase Co-doped WS2 for full pH hydrogen evolution reaction in water and seawater

Metallic 1T phase transition metal dichloride (TMDs) shows excellent catalytic activity for the hydrogen evolution reaction (HER), but stabilization of 1T phase TMDs is still challenging. Herein, the Finke-type POMs K10[Co4(H2O)2(PW9O34)2] [Co4(PW9)2] was used for the first time as a precursor to obtaining size ∼ 4 nm, highly dispersed 1T-WS2 in the hollow mesoporous carbon sphere (HMCS) by the effect of confinement, named 1T-CoWS/HMCS. 1T-WS2 was obtained based on the natural Co-W atomic interface of POMs and further enhanced dispersion at the molecular and nano scales. 1T-CoWS/HMCS only requires ultralow overpotential with high electrocatalytic surface area and robust stability in water and seawater. According to DFT calculations, the Co-S-edge site of 1T-CoWS significantly reduced the rate-limiting step of HER as the predominant active site. This work provides a worthy reference for the synthesis of high-quality metastable TMDs.

Size effect of ruthenium nanoparticles on water cracking properties with different crystal planes for boosting electrocatalytic hydrogen evolution

Small size ruthenium (Ru) nanoparticles have shown remarkable potential for electrocatalytic hydrogen evolution reaction (HER). Nevertheless, the complicated preparation and relatively low activity of small size Ru nanoparticles are two key challenges. In this work, carbon nanotubes supported Ru nanoparticles catalysts (cnts@NC-Ru t °C) with different sizes were prepared via using the combination of L-3,4-dihydroxyphenylalanine (l-dopa) self-polymerization oxidation reaction and different high temperature annealing to study the variation of particle activity with size. Electrochemical test results showed that the optimized cnts@NC-Ru 700 °C catalyst exhibited a very low overpotential at 10 mA/cm2 (21 mV) and tafel slope of 34.93 mV/dec when the mass loading of precious metal per unit area was merely 12.11 μg/cm2 that surpassed most recently reported high-performance Ru based catalyst. The results of density functional theory (DFT) calculation showed that small Ru nanoparticles had abundant active sites, and the H2O dissociation on small Ru nanoparticles (110) surface is quite easy than other surfaces, while (111) surface of small Ru nanoparticles is beneficial for Tafel step of HER. The synergy between (110) and (111) surfaces on the Ru cluster contributes to its outstanding HER performance. This study provides a novel design idea in promoting the preparation method and uncovering the reason of high activity of small size Ru nanoparticles.

Interfacial Engineering of Copper-Nickel Selenide Nanodendrites for Enhanced Overall Water Splitting in Alkali Condition.

Fabricating heterogeneous interfaces is an effective approach to improve the intrinsic activity of noble-metal-free catalysts for water splitting. Herein, 3D copper-nickel selenide (CuNi@NiSe) nanodendrites with abundant heterointerfaces are constructed by a precise multi-step wet chemistry method. Notably, CuNi@NiSe only needs 293 and 41mV at 10mA cm-2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. Moreover, the assembled CuNi@NiSe system just requires 2.2V at 1000mA cm-2 in anion exchange membrane (AEM) electrolyzer, which is 2.0 times better than Pt/C//IrO2 . Mechanism studies reveal Cu defects on the Cu2-x Se surface boost the electron transfer between Cu atoms and Se atoms of Ni3 Se4 via Cu2-x Se/Ni3 Se4 interface, largely lowering the reaction barrier of rate-determining step for HER. Besides, the intrinsic activity of Ni atoms for in situ generated NiOOH is largely enhanced during OER because of the electron-modulating effect of Se atoms at Ni3 Se4 /NiOOH interface. The unique 3D structure also promotes the mass transfer during catalysis process. This work emphasizes the essential role of interfacial engineering for practical water splitting.

TiO2 nanorods based self-supported electrode of 1T/2H MoS2 nanosheets decorated by Ag nano-particles for efficient hydrogen evolution reaction

Molybdenum disulfide (MoS2) has shown significant promise as an economic hydrogen evolution reaction (HER) catalyst for hydrogen generation, but its catalytic performance is still lower than noble metal-based catalysists. Herein, a silver nanoparticles (Ag NPs)-decorated 1T/2H phase layered MoS2 electrocatalyst grown on titanium dioxide nanorod arrays (Ag NPs/1T(2H) MoS2/TNRs) was prepared through acid-tunable ammonium ion intercalation. Taking advantage of MoS2 layered structure and crystal phase controllability, as-prepared Ag NPs/1T(2H) MoS2/TNRs exhibited ultrahigh HER activity. As-proposed strategy combines facile hydrogen desorption (Ag NPs) with efficient hydrogen adsorption (1T/2H MoS2) effectively circumventes the kinetic limitation of hydrogen desorption by 1T/2H MoS2. The as-prepared Ag NPs/1T(2H) MoS2/TNRs electrocatalyst exhibited excellent HER activity in 0.5 mol/L H2SO4 with low overpotential (118 mV vs. reversible hydrogen electrode (RHE)) and small Tafel slope (38.61 mV/dec). The overpotential exhibts no obvious attenuation after 10 h of constant current flow. First-principles calculation demonstrates that as-prepared 1T/2H MoS2 exhibit a large capacity to store protons. These protons can be subsequently transferred to Ag NPs, which significantly increases the hydrogen coverage on the surface of Ag NPs in HER process and thus change the rate-determining step of HER on Ag NPs from water dissociation to hydrogen recombination. This study provides a unique strategy to improve the catalytic activity and stability for MoS2-based electrocatalyst.

Significantly Stabilizing Hydrogen Evolution Reaction Induced by Nb-Doping Pt/Co(OH)2 Nanosheets.

High stability and efficiency of electrocatalysts are crucial for hydrogen evolution reaction (HER) toward water splitting in an alkaline media. Herein, a novel nano-Pt/Nb-doped Co(OH)2 (Pt/NbCo(OH)2 ) nanosheet is designed and synthesized using water-bath treatment and solvothermal reduction approaches. With nano-Pt uniformly anchored onto NbCo(OH)2 nanosheet, the synthesized Pt/NbCo(OH)2 shows outstanding electrocatalytic performances for alkaline HER, achieving a high stability for at least 33 h, a high mass activity of 0.65mA µg-1 Pt, and a good catalytic activity with a low overpotential of 112mV at 10mA cm-2 . Both experimental and theoretical results prove that Nb-doping significantly optimizes the hydrogen adsorption free energy to accelerate the Heyrovsky step for HER, and boosts the adsorption of H2 O, which further enhances the water activation. This study provides a new design methodology for the Nb-doped electrocatalysts in an alkaline HER field by facile and green way.

Improving the Catalytic Performance of the Hydrogen Evolution Reaction of α-MoB2 via Rational Doping by Transition Metal Elements.

Abundant transition metal borides are emerging as promising electrochemical hydrogen evolution reaction (HER) catalysts which have a potential to substitute noble metals. Those containing graphene-like (flat) boron layers, such as α-MoB2, are particularly promising and their performance can be further enhanced via doping by the second metal. In order to understand intrinsic effect of doping and rationalize selection of dopants, we employ density functional theory (DFT) calculations to study substitutional doping of α-MoB2 by transition metals as a route towards systematic improvement of intrinsic catalytic activity towards HER. We calculated thermodynamic stability of various transition metal elements to select metals which form a stable ternary phase with α-MoB2 . We inspected surface stability of dopants and assessed catalytic activity of doped surface through hydrogen binding free energy at various hydrogen coverages. We calculated the reaction barriers and pathways for the Tafel step of HER for the most promising dopants. The results highlight iron as the best dopant, simultaneously lowering the reaction barrier of the Tafel step while having suitable thermodynamic stability within MoB2 lattice.

CeO2 as an “electron pump” to boost the performance of Co4N in electrocatalytic hydrogen evolution, oxygen evolution and biomass oxidation valorization

Developing multifunctional electrocatalysts with excellent hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and 5-hydroxymethylfurfural oxidation reaction (HMFOR) activities will contribute to "carbon neutrality". Here, CeO2 is introduced into the Co4N system as an "electron pump" to attract electrons to transfer from Co4N to CeO2. The interface electronic structure optimization enables Co4N@CeO2 to exhibit excellent HER, OER, and HMFOR performance. Specifically, to deliver 10 mA cm−2 current density, (1) it only requires low overpotentials of 49 and 263 mV for HER and OER in 1.0 M KOH, respectively; (2) it merely needs an ultra-low potential of 1.22 VRHE for HMFOR in 1.0 M KOH + 300 mM HMF, which is 273 mV lower than the required potential in 1.0 M KOH. Theoretical calculation results show that the introduction of CeO2 effectively reduces the barriers for potential-determining steps of HER and OER, and optimizes OH- adsorption to promote the HMFOR process.

Reversible hydrogen spillover in Ru-WO3-x enhances hydrogen evolution activity in neutral pH water splitting

Noble metal electrocatalysts (e.g., Pt, Ru, etc.) suffer from sluggish kinetics of water dissociation for the electrochemical reduction of water to molecular hydrogen in alkaline and neutral pH environments. Herein, we found that an integration of Ru nanoparticles (NPs) on oxygen-deficient WO3-x manifested a 24.0-fold increase in hydrogen evolution reaction (HER) activity compared with commercial Ru/C electrocatalyst in neutral electrolyte. Oxygen-deficient WO3-x is shown to possess large capacity for storing protons, which could be transferred to the Ru NPs under cathodic potential. This significantly increases the hydrogen coverage on the surface of Ru NPs in HER and thus changes the rate-determining step of HER on Ru from water dissociation to hydrogen recombination.

In situ precipitated NiCo nanoparticles synergize with metaborate to promote hydrogen evolution and couple with urea oxidation to reduce overall water splitting potential

A novel NiCo nanoparticles anchored on Ni(Co)(BO2)2 are constructed via a simple redox reaction of NiCo LDH (layered double hydroxide) with NaBH4 which method avoids the Ni foam deformation caused by high temperature reduction or pyrolysis. The experimental and DFT (density functional theory) investigation reveal metaborate (Ni(Co)(BO2)2) exhibits a stronger water adsorption capacity than that conventional metal LDH, which is conducive to the occurrence of hydrogen adsorption in the next step, while NiCo (ΔGH* is closer to 0) is a more suitable hydrogen reaction site than Ni or Co, this synergistic effect of the two substances greatly promotes Volmer step for HER (hydrogen evolution reaction), thereby fundamentally improving HER. The existence of Co0 helps to generate more Ni0, and Co plays an electronic auxiliary role. The Ni0(Co0)-Ni(Co)(BO2)2/NF catalyst possesses small charge transfer resistance, large electrochemical surface area and good hydrophilicity. The Ni0(Co0)-Ni(Co)(BO2)2/NF catalyst exhibits a great application prospect with an overpotential of only 25 mV at a current density of 10 mA cm−2. Even at a large current density of 100 mA cm−2, the overpotential is 107 mV. At a current density of 10 mA cm−2, the voltages of OER (oxygen evolution reaction) and UOR (urea oxidation reaction) are 1.561 V (vs. RHE) and 1.353 V, respectively. Using Ni0(Co0)-Ni(Co)(BO2)2/NF as a bifunctional catalyst for HER and UOR, only 1.47 V can drive a current density of 10 mA cm−2. It is shown that the catalyst will greatly reduce energy consumption and decompose urea when coupling HER and UOR.

Hybrid Ni2P/CoP Nanosheets as Efficient and Robust Electrocatalysts for Domestic Wastewater Splitting

The development of low‐cost, robust and efficient non‐noble metal electrocatalysts is still a pursuit for the hydrogen evolution reaction (HER). Herein, a self‐standing electrocatalyst, Ni2P/CoP nanosheet, was fabricated directly on three‐dimensional Ni foams by two facile steps, which illustrated both high activity and stability for HER in different electrolytes. Benefiting from the porous structures of nanosheets with large specific surface area and the hybrid Ni2P/CoP, the as‐prepared electrocatalyst presented remarkable HER with overpotentials of 65.2 and 87.8 mV to reach a current density of −10 mA cm−2 in neutral and alkaline media, respectively. Density function theory calculations revealed a lower activation energy of water dissociation and efficient HER steps of hybrid Ni2P/CoP nanosheets compared with mono CoP. The self‐standing electrocatalyst maintained excellent chemical stability. Additionally, the HER process in domestic wastewater was realized with more impressive performance by using Ni2P/CoP nanosheets compared with commercial Pt/C. Hydrogen was continuously generated for 20 h in mildly alkaline dishwashing wastewater. This work provides a feasible way to fabricate non‐noble metal and self‐standing hybrid bimetallic phosphides for HER in neutral and alkaline media, showing great potential for efficient hydrogen production by re‐utilizing wastewater resources.

Early Transition-Metal-Based Binary Oxide/Nitride for Efficient Electrocatalytic Hydrogen Evolution from Saline Water in Different pH Environments.

Using abundant seawater can reduce reliance on freshwater resources for hydrogen production from electrocatalytic water splitting. However, seawater has detrimental effects on the stability and activity of the hydrogen evolution reaction (HER) electrocatalysts under different pH conditions. In this work, we report the synthesis of binary metallic core-sheath nitride@oxynitride electrocatalysts [Ni(ETM)]δ+-[O-N]δ-, where ETM is an early transition metal V or Cr. Using NiVN on a nickel foam (NF) substrate, we demonstrate an HER overpotential as low as 32 mV at -10 mA cm-2 in saline water (0.6 M NaCl). The results represent an advancement in saline water HER performance of earth-abundant electrocatalysts, especially under near-neutral pH range (i.e., pH 6-8). Doping ETMs in nickel oxynitrides accelerates the typically rate-determining H2O dissociation step for HER and suppresses chloride deactivation of the catalyst in neutral-pH saline water. Heterointerface synergism occurs through H2O adsorption and dissociation at interfacial oxide character, while adsorbed H* proceeds via Heyrovsky or Tafel step on the nitride character. This electrocatalyst showed stable performance under a constant current density of -50 mA cm-2 for 50 h followed by additional 50 h at -100 mA cm-2 in a neutral saline electrolyte (1 M PB + 0.6 M NaCl). Contrarily, under the same conditions, Pt/C@NF exhibited significantly low performance after a mere 4 h at -50 mA cm-2. The low Tafel slope of 25 mV dec-1 indicated that the reaction is Tafel limited, unlike commercial Pt/C, which is Heyrovsky limited. We close by discussing general principles concerning surface charge delocalization for the design of HER electrocatalysts in pH saline environments.

Dual-cation-doped MoS2 nanosheets accelerating tandem alkaline hydrogen evolution reaction

Molybdenum disulfide (MoS2) nanosheets are promising candidates as earth-abundant and low-cost catalyst for hydrogen evolution reaction (HER). Nevertheless, compared with the benchmark Pt/C catalyst, the application of MoS2 nanosheets is limited to its relatively low catalytic activity, especially in alkaline environments. Here, we developed a dual-cation doping strategy to improve the alkaline HER performance of MoS2 nanosheets. The designed Ni, Co co-doped MoS2 nanosheets can promote the tandem HER steps simultaneously, thus leading to a much enhanced catalytic activity in alkaline solution. Density functional theory calculations revealed the individual roles of Ni and Co dopants in the catalytic process. The doped Ni is uncovered to be the active site for the initial water-cleaving step, while the Co dopant is conducive to the H desorbing by regulating the electronic structure of neighboring edge-S in MoS2. The synergistic effect resulted by the dual-cation doping thus facilitates the tandem HER steps, providing an effective route to raise the catalytic performance of MoS2 materials in alkaline solution.

Efficient Electrochemical Water Splitting with PdSn4 Dirac Nodal Arc Semimetal

Recently, several researchers have claimed the existence of superior catalytic activity associated with topological materials belonging to the class of Dirac/Weyl semimetals, owing to the high electron conductivity and charge carrier mobility in these topological materials. By means of X-ray photoelectron spectroscopy, electrocatalytic tests, and density functional theory, we have investigated the chemical reactivity (chemisorption of ambient gases), ambient stability, and catalytic properties of PdSn4, a topological semimetal showing Dirac node arcs. We find a Tafel slope of 83 mV in the hydrogen evolution reaction (HER) dec–1 with an overpotential of 50 mV, with performances resembling those of pure Pd, regardless of its limited amount in the alloy, with a subsequent reduction in the cost of raw materials by ∼80%. Remarkably, the PdSn4-based electrode shows superior robustness to CO compared to pure Pd and Pt and high stability in water media, although the PdSn4 surface is prone to oxidation with the formation of a sub-nanometric SnO2 skin. Moreover, we also assessed the significance of the role of topological electronic states in the observed catalytic properties. Actually, the peculiar atomic structure of oxidized PdSn4 enables the migration of hydrogen atoms through the Sn–O layer with a barrier comparable with the energy cost of the Heyrovsky step of HER over Pt(111) in acidic media (0.1 eV). On the other hand, the topological properties play a minor role, if existing, contrarily to the recent reports overestimating their contribution in catalytic properties.

Modulation of Volmer step for efficient alkaline water splitting implemented by titanium oxide promoting surface reconstruction of cobalt carbonate hydroxide

The sluggish water dissociation (Volmer step) is a rate-limiting step slowing down alkaline hydrogen evolution reaction (HER), and therefore hinders the efficient industrial production of clean hydrogen resource. In this work, we report that the Volmer step can be facilitated by in-situ surface reconstruction on a composite between cobalt carbonate hydroxide and titanium oxide (TiO 2 @CoCH), and the resultant activated structure turns to be a highly efficient electrocatalyst for alkaline HER. Experimental characterization and density functional theory calculation evidence that under HER potential the smooth TiO 2 @CoCH surface is roughened and Co interstitial defects in TiO 2 are formed, which are energetically favorable for Volmer step. The activated composite exhibits an overpotential of 99 ± 6 mV for a current density of 20 mA cm −2 and 187 ± 21 mV for 100 mA cm −2 , suggesting that TiO 2 @CoCH is one of promising non-precious metal electrocatalysts for HER in alkaline media. • The combination of two inert component resulted in a highly active electrocatalyst for alkaline hydrogen evolution reaction. • Titanium oxide promoted the surface reconstruction of cobalt carbonate hydroxide during hydrogen evolution reaction. • The Volmer step of hydrogen evolution reaction was significantly promoted after surface reconstruction. • The surface reconstruction of cobalt carbonate hydroxide during hydrogen evolution reaction was evidenced.

Efficient Co-MoS2 electrocatalyst for cathodic degradation of halogenated disinfection by-products in water sample

The development of non-noble metal electrocatalysts that are efficient and low-cost are being sought as alternatives to noble metals for electrochemical degradation of organic halides. In this study, Co-MoS2, a non-noble metal electrocatalyst, was synthesized and deposited on graphite felt (GF) via the hydrothermal approach. The functionalized graphite felt was used as a cathode electrode for reductive degradation of halogenated disinfection products from water samples. Five halogenated disinfection byproducts (DBPs), CHBr2Cl, C3H5Br2Cl, CHBr3, CHCl3, and CCl4 were selected as model compounds, and electro-reductive degradation by the electrode was evaluated. The batch experiments performed with an undivided electrolytic cell revealed that the Co-MoS2-GF electrode exhibited superior electrocatalytic degradation towards the DBPs compounds compared to other reported electrodes in literature. Co-MoS2-GF electrode displayed a current efficiency of ̴ 13% and degradation efficiency of more than 90% for each of the DBPs after 60 min of electrolysis. The enhanced catalytic activity of the Co-MoS2 was ascribed to the synergistic role of CoS /MoS2 towards the accelerated Volmer step of hydrogen evolution reaction (HER), which aided the production of surface-bound atomic hydrogen *H. Cyclic voltammetry and scavenging experiments clarify the formation of *H during Co-MoS2-GF catalyzed water reduction and show its contribution to DBPs degradation. The prepared Co-MoS2-GF electrode also displayed substantial stability and reusability potential even after ten cycles of recurring operation.

Enhancing hydrogen evolution reaction activity on cobalt oxide in alkaline electrolyte by doping inactive rare-earth metal

In order to reduce the energy consumption of hydrogen evolution reaction (HER), a series of lanthanum-doped cobalt oxide (x%La–Co3O4–T, where x% represents the La doping molar ratio and T represents the annealing temperature) electrocatalysts are successfully synthesized by a co-precipitation process, followed by annealing in air. Through X-ray diffraction (XRD) refinements, La3+ is doped into Co3O4 lattice, which decreases the crystallinity of Co3O4. It inhibits the aggregation and growth of Co3O4 grains. 2%La–Co3O4-350 is the optimized sample to show the lowest overpotential of 98 mV at 10 mA cm−2 with the corresponding Tafel slope of 72.8 mV dec−1 in 1 M KOH. Although La is an inactive rare-earth metal element for HER, it enhances the HER activity of Co3O4 efficiently. From further studies, the high HER catalytic activity of 2%La–Co3O4-350 can be owing to three aspects: (i) The highly dispersed and small-size Co3O4 nanoparticles caused by La doping own high specific surface area and electrochemically active surface area (ECSA), which benefits exposing more Co3+ active sites to electrolyte. (ii) La dopants make 2%La–Co3O4-350 own more oxygen vacancies that facilitating the water dissociation step of HER. (iii) La doping leads to improved conductivity and charge transfer efficiency of 2%La–Co3O4-350 during HER.

Electron density modulation of Fe1-xCoxP nanosheet arrays by iron incorporation for highly efficient water splitting

The good performance of base metal phosphides as alternative catalysts for hydrogen evolution has attracted great attention. However, phosphorus-hydrogen bonds (P-Hads) are easily formed on the surface of metal phosphides, which will severely inhibit hydrogen evolution reaction (HER). Herein, we propose a universal strategy to improve the HER activity of metal phosphides by modulating the surface electron densities. The iron modulated Fe0.29Co0.71P nanosheet arrays exhibit an overpotential of 74 mV at 10 mA cm−2 and a Tafel slope of 53.56 mV dec−1, which are close to the performance of noble metal catalysts in alkaline condition. The electronic interactions between cobalt and phosphorus are modulated after iron doping, resulting in more positively charged Co, which can promote adsorption and activation of H2O molecules and will weaken P-Hads bonds formed on the catalyst surfaces. Therefore, Fe0.29Co0.71P can optimize the adsorption and desorption of H atoms, and can promote both Volmer and Heyrovsky steps of HER. In addition, the electron density modulation of catalytic sites also improves the OER catalytic performance of Fe0.29Co0.71P. The overall water splitting electrolyzer assembled by Fe0.29Co0.71P/Ni-foam exhibits a lower cell voltage (1.59 V/10 mA cm−2), compared to that (1.61 V/10 mA cm−2) of the IrO2//Pt/C electrolyzer.