Hydrogen Evolution Reaction Properties Research Articles

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.

Ultrathin and porous CoP nanosheets as an efficient electrocatalyst for boosting hydrogen evolution behavior at a broad range of pH

Designing highly-efficient, stable and low-cost catalysts for electrocatalytic hydrogen evolution reaction (HER) plays an important role in renewable energy conversion technology. The particularly ultrathin and porous 2D architecture can provide plentiful activation sites, short delivery channels to improve reaction kinetic and promote HER procedure. High-performance transition metal phosphide (CoP) combined with unique and holey 2D ultrathin nanosheet structure is prepared by successively hydrothermal reaction, oxidation and phosphorization techniques, which presents remarkable stability and electrocatalytic HER properties in a wide pH range. The thickness and pore dimension of ultrathin and porous CoP nanosheets are ∼15 and 3–17 nm. The optimized CoP nanosheets only require 60, 128, 90 mV overpotentials to drive the current density of 10 mA cm−2 in acidic, neutral and alkaline environment, respectively, much better than those of oxide counterpart and the previously reported transition metal-based electrocatalysts. Moreover, the small Tafel slopes of porous CoP nanosheets are 54, 69.9 and 62.9 mV dec−1 in acidic, neutral and alkaline media. CoP nanosheets also exhibit high conductivity, large Cdl, and long-term stability for 20 h in pH-universal electrolyte.

Designed bifunctional flower-like structural molybdenum disulfide doped with Ag atoms for clean energy and contaminant detection

An efficient bifunctional material still remains a stupendous challenge for the use of Surface-enhanced Raman scattering (SERS) substrate and hydrogen evolution reaction (HER) electrocatalysts and suffer from cost issues. In this study, heteroatom Ag doping instead of Ag compound MoS2 has been used to activate the inert plane of MoS2 and improve charge transfer, modulating the SERS and HER properties of MoS2. As SERS substrate, Ag doped MoS2 can be widely used for the rapid detection of organic dyes (MG, CV, R6G), pesticides (endosulfan and dipterex), and endocrine disrupter Bisphenol A and biological macromolecules bilirubin. Meanwhile, the HER activity of the MoS2 is remarkably boosted by introducing Ag atoms. The low overpotentials of pure MoS2 is 524 mV, while the low overpotentials of the Ag doped MoS2 can be reach 54 mV in alkaline electrolytes. Tafel slope, electrochemically active surface area (ECSA), Turnover frequency (TOF) and the normalized ECSA were analyzed to reveal the real reason for the increasing in electrocatalytic activity. As-synthesized Ag doped MoS2 shows highly efficient hydrogen evolution. This work synthesized low-cost bifunctional materials Ag doped MoS2 not only provides a guidance for MoS2-base SERS substrate design but also facilitates cope with the growing demand for clean energy.

Discrepancy of alkaline/neutral hydrogen evolution activity from NiCoSe2/NC and Co–NiSe/NC derived from in-situ thermal and solution processing selenizations of ZIF-67

Constructing cobalt-based selenide catalyst with accessible active site and superior charge transfer capability by simultaneous tailoring chemical component and structure through the feasible strategy is the key to display improved hydrogen evolution reaction (HER) activity. Herein, the bimetal NiCoSe2/nitrogen-doped carbon (NC) with novel flake structure (NiCoSe2/NC/NF) and particle-like cobalt-doped NiSe/NC (Co–NiSe/NC/NF) were synthesized by the in-situ thermal and solution processing selenizations of ZIF-67/NF, respectively. The intrinsic catalytic activity of NiCoSe2, the further accelerated charge-transfer capability originated from the fresh NC and two-dimensional layer structure, and mutually reinforcing kinetics from the closely integrated NiCoSe2 nanoparticles and NC plate endow NiCoSe2/NC/NF with 141 and 284 mV to reach 10 mA cm−2 under alkaline and neutral electrolytes, respectively, accompanying with Tafel slope of 109 and 206 mV dec−1, which were obviously higher than that of the HER properties of Co–NiSe/NC/NF (η10 = 179 mV and Tafel slope of 127 mV dec−1 at alkaline condition, η10 = 301 mV and Tafel slope of 235 mV dec−1 at neutral condition). Meanwhile, the NiCoSe2/NC/NF and Co–NiSe/NC/NF were exhibited well electrochemical stability under alkaline/neutral conditions. This study offers practicable strategy for intuitive comparing the influence of selenization procedures on the whole alkaline/neutral HER activity of cobalt-based catalysts.

The Marriage of Hydrazone‐Linked Covalent Organic Frameworks and MXene Enables Efficient Electrocatalytic Hydrogen Evolution

Electrochemical water splitting is long regarded as a green and feasible pathway to realize the scalable hydrogen production, while the overall hydrogen evolution reaction (HER) efficiency is largely dependent on the electrocatalytic ability of the cathode catalysts. Herein, the in situ growth of hydrazone‐linked covalent organic framework (COF‐42) nanocrystals with a unique nanoflower‐shaped morphology on 2D ultrathin Ti3C2Tx MXene nanosheets (COF/Ti3C2Tx) is achieved through a convenient and robust stereoassembly strategy. Strikingly, the marriage of COF‐42 and Ti3C2Tx nanosheets not only offers multiscale porous channels for the fast transportation of electrolyte and electrons, but also enables the full exposure and activation of numerous catalytically active centers. As a consequence, the optimized COF/Ti3C2Tx nanoarchitecture displays exceptional HER properties in terms of a very low onset potential of 19 mV, a small Tafel slope of 50 mV dec−1 as well as reliable long‐term durability, which are comparable to those of commercial Pt/C catalyst. Density functional theory calculations further disclose that the rational combination of COF‐42 with Ti3C2Tx provides more diversified active positions with appropriate ΔGH values, thus leading to a boosted hydrogen generation rate.

Cobalt-doped WSe2@conducting polymer nanostructures as bifunctional electrocatalysts for overall water splitting

Designing of high-performance, low-cost, and nonprecious metal-based bifunctional electrocatalysts is highly significant for the development of water splitting process and expanding the practical application of green hydrogen production. Transition metal dichalcogenides (TMDs) with intrinsic physical and chemical properties have been considered potential catalytic materials for electrode fabrication. However, it has remained challenging to develop TMD catalysts that have bifunctional properties for overall water splitting. Herein, WSe2, as a typical representative of TMDs, was utilized to design electrocatalysts using polypyrrole (PPy) or polyaniline (PANI) as a conducting polymer (CP) and cobalt doping. A facile hydrothermal preparation of WSe2 in the presence of CP enabled the construction of cobalt-doped WSe2@CP electrocatalysts. Morphological analysis indicated that the CP played an important role as a conductive template to enhance the distribution of WSe2 nanosheets, leading to higher surface area. In addition, cobalt doping led to the formation of defect structures and boosted the electrocatalytic activities of the catalysts for oxygen evolution reaction (OER). Owing to the increased electrochemical surface area and defect structures, the cobalt-doped WSe2@CP nanostructures exhibited enhanced electrochemical properties for hydrogen evolution reaction (HER) and OER in an alkaline medium. The cobalt-doped WSe2@PANI modified glassy carbon electrode (GCE) exhibited overpotentials down to 308 and 360 mV at a current density of 10 mA cm−2 for the HER and OER, respectively. Furthermore, the cobalt-doped WSe2@CP electrocatalysts demonstrated long-term stability and continuous cycling. More importantly, the Co–WSe2@PANI electrolyzer required cell voltage of 1.87 V at a current density of 10 mA cm−2 for overall water splitting process. This work provides new findings for designing efficient bifunctional electrocatalysts utilizing TMD materials and conducting polymers.

Regulating the tip effect on urchin-like N-NiCoP/NF as high-performance electrocatalyst for hydrogen evolution reaction

Transition metal phosphides (TMPs) have emerged as highly promising electrocatalysts for the hydrogen evolution reaction (HER) due to their earth-abundance reserves, rich electrochemical active sites and high stability. Herein, to cope with the inert atoms on the basal plane and sluggish electrochemical kinetics, we propose a novel strategy involving the in-situ conversion of urchin-like NiCo-LDH into a nitrogen-doped NiCoP electrocatalyst on nickel foam (N-NiCoP/NF) via a hydrothermal-phosphorylation approach. In this structure, NiCoP nanoneedles are assembled into a tip-rich urchin-like structure on NF substrates, delivering abundant mismatched active sites for capturing catalytic intermediates, accelerating charge transport and constructing an optimized heterogeneous interface. Additionally, heterogeneous N-atom doping can further regulate the charge distribution of NiCoP needles, and significantly contribute to enhancing the electrocatalytic performance for HER. Benefitting from the synergistic effect of the abundant active sites provided by tip-rich NiCoP nano-urchin, electronic modulation by heterogeneous N-species and optimized interfacial coupling, the N-NiCoP/NF electrocatalyst displays low overpotentials of 75 mV and obtains 10 mA cm−2 in alkaline electrolyte without significant decrease even after 5000 cycles, indicating high catalytic activity and stability. This study provides a low-cost and controlled approach for developing novel heteroatom-doped TMPs for HER applications.The various properties of the materials surprisingly demonstrate that our diatomic codoping strategy prepared by facile hydrothermal phosphatization with annealing can effectively enhance the HER properties of the materials. The unique morphology possessed by the material provides advantages such as active sites and accelerated charge transport that can further enhance the catalytic performance of the material, which is further formalized by our DFT calculations. Our theoretical and experimental studies provide a good case for the development of simple and low-cost electrocatalytic materials.

Dodecylation of molybdenum disulfide and its electrochemical properties for hydrogen evolution reaction

Functionalization of MoS2 was achieved by treatment in a strongly reducing sodium naphthalene solution. Dodecyl was grafted onto MoS2 nanosheets using alkyl sulphates as electrophiles to obtain dodecylated MoS2 without affecting the MoS2 crystalline structure. Superior electrocatalytic properties are obtained for dodecylated MoS2. The polarisation curve of this nanomaterial remained constant even after 1000 consecutive cycles. This route provides a new pathway for covalent functionalization of MoS2 and might find a variety of applications, such as electrocatalysts.

Enhancing the catalytic hydrogen evolution reaction (HER) of the defective borophene@Pt/Pd/MoS2 heterojunction

Borophene (B) is a promising two dimensional (2D) material because of the excellent carrier mobility, large specific surface area and very light mass. However, many problems (overactive borophene chemistry and difficulty) have limited it's further applications. To improve the catalytic hydrogen evolution reaction properties, here, we apply ab-initio calculations to study the structural stability of two defective borophene (χ3 and β12)/MoS2 heterojunction as a hydrogen evolution reaction (HER) catalyst. In particular, we further explore the influence noble metals (Pt and Pd) on the catalytic properties of borophene(χ3 and β12)/MoS2 heterojunction. The calculated results show that the involvement of MoS2 not only improves the structural stability of the defective borophene@MoS2 but also further improves the catalytic ability of the borophene@MoS2. In particular, the calculated hydrogen adsorption Gibbs free energy (ΔG) of the χ3/MoS2-III heterojunction is only −0.0004 eV, which is an ideal catalyst for HER. Furthermore, the calculated Gibbs free energy (ΔG) of borophene (β12)/Pd@MoS2-II is 0.0007 eV because of the strong localized hybridization between Pd and the borophene (β12)/MoS2-II. Therefore, we believe that the Pd-doping can effectively improve the catalytic properties of the borophene (β12)/Pd@MoS2 as a hydrogen evolution reaction (HER) catalyst.

Variation of dithiolate bridges in carbon nanotube-attached diiron chelate compounds for electrocatalytic hydrogen evolution reaction

In an effort to explore the effect of dithiolate bridges on the electrochemical hydrogen evolution reaction (HER) performances of hydrogenase-inspired catalysts under fully aqueous condition, three new diphosphine-chelate diiron molecular compounds [Fe2(μ-xdt)(CO)4(k2-(Ph2PCH2)2N(CH2CH2OH)] (labeled as 1xdt, xdt = (SCH2)2X, X = NPh (adt) vs. O (odt) vs. CH2 (pdt)) with various dithiolate bridges (i.e., xdt) were prepared and then are covalently attached onto carbon nanotubes (CNTs) to fabricate biomimetic CNT-attached hybrid catalysts labeling as CNT-f-1xdt. The intact structures of target catalysts CNT-f-1xdt have been evidenced through Raman, X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). Further, the electrochemical HER properties and stabilities of CNT-f-1xdt loaded onto glassy carbon electrode (GC) are studied and compared in 0.05 M phosphate buffer solution (PBS, pH of 7.4) as neutral aqueous medium by using CV, linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry. In comparison with homologues CNT-f-1odt or CNT-f-1pdt containing odt or pdt bridges, the hybrid catalyst CNT-f-1adt bearing an adt bridge is found to have the better electrocatalytic HER activity and similar stability in 0.05 M PBS. This work is significant to develop a promising generation of CNT-attached electrode materials engineered with diiron-based molecular HER catalysts for water splitting into H2.

Ultrasmall CoSe2 Nanoparticles Grown on MoS2 Nanofilms: A New Catalyst for Hydrogen Evolution Reaction

Non‐noble‐metal‐based and earth‐abundant electrocatalysts have been extensively investigated for the hydrogen evolution reaction (HER). However, they still suffer from large Tafel slopes and high overpotentials, resulting in inferior HER catalytic activity. Herein, a novel, cost‐effective, and electrochemically stable catalyst is presented by growing ultrasmall CoSe2 nanoparticles on MoS2 nanofilms using a facile hydrothermal method. The CoSe2/MoS2 hybrid catalyst shows superior catalytic activity in HER to both CoSe2 or MoS2 alone and their physical mixture. With the Tafel slope as small as 37.8 mV dec−1, the CoSe2/MoS2 shows excellent catalytic properties for HER in an acidic solution. The promising performance can be attributed to the synergistic effect of CoSe2 nanoparticles and MoS2 nanofilms. In addition, the catalytic activity of the CoSe2/MoS2 catalyst is almost unchanged after 1000 cyclic voltammetric sweeps, indicating its long‐term durability under acidic conditions.

Boosted water electrolysis capability of NixCoyP via charge redistribution and surface activation

Water electrolysis for efficiently generating hydrogen is a key chemistry to realize the hydrogen economy. Transition metal phosphides (TMPs) have become promising catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline conditions. But their widespread application is still limited due to the intermediates’ adsorption/desorption energy to be improved and the rare analysis of activation. Herein, we demonstrate a bifunctional catalyst, bimetallic phosphide (NixCoyP) supported by Ni foam (NF), towards HER and OER. X-ray photoelectron spectra demonstrate that the synergy between nickel and cobalt regulates the electron redistribution around active sites, which optimizes reaction intermediates’ adsorption/desorption kinetics on active sites. Post-stability analysis further reveals the surface activation phenomenon, that NixCoyP can transform into hydroxides for HER and oxyhydroxides for OER. Such behaviors allow the surface of catalysts to form new heterostructures with reorganized electronic structures to sustain the low voltage of water electrolysis and excellent stability. Density functional theory analysis proves that the NiCoP/M-OH heterostructure significantly enhances the HER properties through the optimized adsorption/desorption capacities for H* intermediates. Remarkably, this catalyst exhibits an outstanding overall water electrolysis performance.

Template-assisted Fabrication of O-doped CoP Microflowers with Optimal Electronic Modulation for Electrochemical Hydrogen Evolution.

Exploring efficient, affordable and stable electrocatalyst toward hydrogen evolution reaction (HER) is of great scientific significance for the practical implementation of the water splitting. The heteroatom doping represents a serviceable strategy to further elevate the catalytic performance for a transition metal-based electrocatalyst because of the electronic regulation effect. Herein, a reliable self-sacrificial template-engaged approach is proposed to synthesize O-doped CoP (denoted as O-CoP) microflowers, which simultaneously considers the regualtion of electronic configuration via anion doping and sufficient exposure of active sites via nanostructure engineering. The suitable O incorporation content in CoP matrix could tremendously modify the electronic configuration, accelerate the charge transfer, promote the exposure of active sites, strengthen the electrical conductivity, and adjust the adsorption state of H*. Consequently, the optimized O-CoP microflowers with optimal O concentration display a remarkable HER property with a small overpotential of 125 mV to afford a current density of 10 mA cm-2 , a low Tafel slope of 68 mV dec-1 and long-term durability for 32 h under alkaline electrolyte, manifesting a considerable potential application for hydrogen production at large scale. The integration of anion incorporation and architecture engineering in this work will bring in a depth insight for the design of low-cost and effective electrocatalysts in energy conversion and storage systems.

Nanoarchitectonic Ni-doped edge dislocation defect-rich MoS2 boosting catalytic activity in electrochemical hydrogen production

The world is moving towards a more sustainable future, and hydrogen is emerging as a key player in this transition. Hydrogen production through the use of electrocatalysts is becoming increasingly popular as a sustainable and efficient method. Herein, we report the monodisperse nickel (Ni) nanoparticles incorporated molybdenum disulfide (MoS2) (Ni/MoS2) electrocatalyst synthesized via a hydrothermal method, followed by an annealing process. It is found that the edge dislocations which are topological defects that occur when a crystal lattice has an extra plane of atoms. These defects can drastically affect the chemical properties and electronic structure of materials, which can improve their electrocatalytic performance. However, defect-rich electrocatalysts for hydrogen evolution reaction (HER) is becoming more popular nowadays. It is not yet clear how the active sites of the edge dislocations of MoS2 affect the catalytic properties of hydrogen evolution. The most promising electrocatalyst without precious metals is considered to be metallic MoS2 (1T phase), which exhibits Pt-like HER performance in alkaline media. One of the expected functions of MoS2 is to act as a conductive support with relatively large surface area for more catalytically active and highly dispersed Ni species. The 1T-MoS2 exhibits remarkable catalytic properties for HER due to the abundance of active sites connected by edge dislocations. Compared with pristine MoS2, the edge dislocation defect-rich Ni/MoS2 shows the outstanding HER activity, delivering a current density of 10 mA cm−2 at an overpotential of only 89 mV with a lower Tafel slope of 59 mV dec−1. Additionally, chronopotential analysis is performed at a constant current density of 10 mA cm−2 for 30 h with minimal loss in overpotential, which demonstrates an extremely potential and stable HER catalyst.

Heteroatom inducing local geometrical configuration transformation of metallic oxygen clusters in metal hydroxide-organic frameworks with optimized hydrogen evolution performance

Various heteroatom doped metal organic frameworks (MOFs) and MOFs derived materials with high activity are designed as electrochemical water splitting catalysts. However, local geometrical configuration transformation or local structure distortion on account of heteroatom doping are usually neglected. Herein, this work firstly investigated local structure transformation of metallic oxygen clusters to β-Ni(OH)2-like geometrical configuration (edge-shared octahedrons) in heteroatom (Ru, Cr, Sn and Ce) doped nickel based metal hydroxide-organic frameworks (MHOFs). The transformation process, atomic/electronic structure and composition are investigated via spectroscopy methods such as X-ray absorption structure spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. Hereinto, Ru doped Ni-MHOFs with high local geometrical configuration transformation as a representative one was deeply studied to reveal hydrogen evolution reaction properties. Density functional theory calculations provided a deep understanding of the effect of organic linker defect on local structure and descriptor of p-band center of O. This work provides a sight into local structural transformation in heteroatom doped MHOFs and proposes a novel strategy to modulate structural microenvironment of MOFs materials towards electrochemical applications.

In Situ Exsolution of Ba3(VO4)2 Nanoparticles on a V-Doped BaCoO3-δ Perovskite Oxide with Enhanced Activity for Electrocatalytic Hydrogen Evolution.

The successful preparation of a perovskite-based heterostructure is important for broadening the applications of perovskites in the field of electrocatalysis, especially in a hydrogen evolution reaction (HER). Nevertheless, the limited active sites of perovskites severely hindered the HER properties. Herein, an in situ exsolution method was used to construct a nanocomposite based on V-doped BaCoO3-δ decorated with Ba3(VO4)2 (BVCO19) for alkaline HER. The exsolved Ba3(VO4)2 can induce more Co4+ ions on BaCoO3-δ, which serves as active sites for the release of H2. Meanwhile, by regulating the valency of V and Co species, the catalyst can reach a charge balance by generating more oxygen vacancies, which greatly facilitates the adsorption and dissociation of H2O molecules. The synergistic effect between the oxygen vacancies and high-valence Co4+ leads to an enhanced HER performance of BVCO19. The as-obtained catalyst delivers a low overpotential of 194 mV at 10 mA cm-2 as well as impressive stability for 100 h in alkaline media, which outperforms pristine BaCoO3-δ and most of the nonprecious-based perovskite oxides. This work provides new insights into the preparation of perovskite-based heterostructure for boosting HER.

3D nanostructured nickel film supported to a conducting polymer as an electrocatalyst with exceptional properties for hydrogen evolution reaction

A two-layer system was applied to a nickel substrate for use as the electrocatalyst of the hydrogen evolution reaction (HER) in a phosphate buffer solution. It was comprised of a three-dimensional (3D) porous underlayer of nickel nanoparticles with a size of less than 35 nm, followed by an electrodeposited top layer of poly (aniline-co-pyrrole). The underlayer and top coating were both synthesized by applying a constant potential to a three-electrode system. The catalyst characterization was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectrometry. The electrocatalytic activity of the fabricated electrodes was measured by linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry. The electrode exhibited an overpotential of 520 mV at a current density of 10 mA cm−2, comparable to 530 mV of platinum. Furthermore, the Tafel slope of the electrode was 90 mV dec−1, almost equal to that of platinum. This exceptional performance was explained by the synergistic interaction between 3D-Ni and poly (aniline-co-pyrrole) layers. Such a synergism was demonstrated by the fact that the resulting electrode lacked substantial catalytic activity when each of these two layers was deposited on the substrate alone. The Nyquist diagrams revealed that the 3D-Ni film resulted in minimal charge transfer resistance, allowing fast kinetics of HER. The coupling of this property with the ability of the polymer to adsorb H+ ions led to the high electrocatalytic activity of the proposed electrode. This electrode performed better than platinum, which was a promising result. This indicated that a lower voltage input was required to generate hydrogen gas using the prepared electrode.

Ternary compound heterojunction from isomerism h-CdS/c-CdSe exhibits boosting photoelectrochemical and hydrogen evolution reaction properties

A novel h-CdS/c-CdSe ternary compound heterojunction catalyst CdSS is constructed from isomerism hexagonal CdS and cubic CdSe. The isomerism hexagonal CdS and cubic CdSe is the key factor to obtain the CdSS heterojunction, as compared, ternary compound CdSSe can only be prepared from isomorphic hexagonal CdS and hexagonal CdSe. Under different S:Se ratio, the main XRD peaks of CdSS displayed continuous shift between related CdS and CdSe peaks that confirms the S and Se atoms embedding CdSe and CdS lattice respectively to form atomic level ternary compound heterojunction. The photoelectrochemical and electrocatalytic results show that the CdSS catalysts have boosting properties. Under an optimal S:Se ratio, the photocurrent density of the CdSS reach 8.23 μA/cm2, which was 4.5 times that of original CdS (1.83 μA/cm2), 4.9 times of CdSe (1.67 μA/cm2) and 5.1 times of CdSSe (1.60 μA/cm2). The hydrogen evolution reaction Tafel slope of CdSS also declined 60% compared with CdS and 64% compared with CdSe. The electrocatalytic impedance and fluorescence spectra fully show that CdSS has lower internal resistance and low electron-hole recombination efficiency due to the atomic level heterojunction. The work develops a new strategy to construct high efficiency atomic level ternary compound heterojunction between isomerism homologous element compounds.

Phase Evolution on the Hydrogen Adsorption Kinetics of NiFe-Based Heterogeneous Catalysts for Efficient Water Electrolysis.

Transition metal layered double hydroxides, especially nickel-iron layered double hydroxide (NiFe-LDH)shows significant advancement as efficient oxygen evolution reaction (OER) electrocatalyst but also plays a momentous role as a precursor for NiFe-based hydrogen evolution reaction (HER) catalysts. Herein, a simple strategy for developing Ni-Fe-derivative electrocatalysts via phase evolution of NiFe-LDH under controllable annealing temperatures in an argon atmosphere is reported. The optimized catalyst annealed at 340 o C (denoted NiO/FeNi3 ) exhibits superior HER properties with an ultralow overpotential of 16 mV@10mA cm-2 . Density functional theory simulation and in situ Raman analyses reveal that the excellent HER properties of the NiO/FeNi3 can be attributed to the strong electronic interaction at the interface of the metallic FeNi3 and semiconducting NiO, which optimizes the H2 Oand Hadsorption energies for efficient HER and OER catalytic processes. This work will provide rational insights into the subsequent development of related HER electrocatalysts and other corresponding compounds via LDH-based precursors.

Prussian blue analog-derived nickel iron phosphide-reduced graphene oxide hybrid as an efficient catalyst for overall water electrolysis

Efficient and bifunctional nonprecious catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are essential for the production of green hydrogen via water electrolysis. Transition metal (Ni, Co, Fe, etc.) phosphides are frequently documented HER catalysts, whereas their bimetallic oxides are efficient OER catalysts, thus enabling bifunctional catalysis for water electrolysis via proper operation. Herein, phosphide-reduced graphene oxide (rGO) hybrids were prepared from graphene oxide (GO)-incorporated bimetal Prussian blue analog (PBA) precursors. The hybrids could experience partial surface oxidation to create oxide layers with OER activities, and the hybrids also possessed considerable HER properties, therefore enabling bifunctional catalytic features for water electrolysis. The typical NiFeP-rGO hybrid demonstrated an overpotential of 250 mV at 10 mA cm−2 and good durability for OER, as well as moderate HER catalytic features (overpotential of 165 mV at −10 mA cm−2 and acceptable catalytic stability). Due to the bifunctional catalytic features, the NiFeP-rGO-based symmetric water electrolyzer demonstrated a moderate input voltage and high faradaic efficiency (FE) for O2 and H2 production. The current work provides a feasible way to prepare OER and HER bifunctional catalysts by facile phosphorization of PBA-associated precursors and spontaneous surface oxidation. Given the oxidation/reduction bifunctional catalytic behaviors, phosphide-rGO hybrid catalysts have great potential for widespread application in fields beyond water electrolysis, such as electrochemical pollution abatement, sensors, energy devices and organic syntheses.