Nickel-Cobalt Diselenide 3D Mesoporous Nanosheet Networks Supported on Ni Foam: An All-pH Highly Efficient Integrated Electrocatalyst for Hydrogen Evolution

Transferable Active Centers of Strongly Coupled MoS2@Sulfur and Molybdenum Co-doped g-C3N4 Heterostructure Electrocatalysts for Boosting Hydrogen Evolution Reaction in Both Acidic and Alkaline Media

Designing an excellent acidic and alkaline general-purpose hydrogen evolution electrocatalyst plays an important role in promoting the development of the energy field. Here, a feasible strategy is reported to use the strongly coupled MoS₂@sulfur and molybdenum co-doped g-C₃N₄ (MoS₂@Mo-S-C₃N₄) heterostructure with transferable active centers for catalytic reactions in acidic and alkaline media. Research studies have shown that the unsaturated S site at the edge of MoS₂ and the active N atom on the Mo-S-C₃N₄ substrate are, respectively, the active centers of acidic and alkaline hydrogen evolution reaction. Specifically, Mo-S-C₃N₄ is regarded as a synergistic catalyst for the active species MoS₂ in acidic hydrogen evolution, while MoS₂ acts as a co-catalyst when the alkaline active species are transferred to Mo-S-C₃N₄. The coordination of the electrons between the interfaces achieves a synergistic balance, which provides the optimal sites for the adsorption of the reactants. Such an electrocatalyst exhibits overpotentials of 193 and 290 mV at 10 mA cm^-2 in 0.5 M H₂SO₄ and 1 M KOH, respectively, which was better than numerous previous reports. This research provides an outstanding avenue to realize multifunctional electrocatalysts.

Layered double hydroxide derived bimetallic nickel–iron selenide as an active electrocatalyst for nitrogen fixation under ambient conditions

NiFe–LDH derived nickel–iron selenide can cause an NRR positive process due to the exposure of N₂ adsorption sites resulting from the lattice distortion related to the Jahn–Teller effect after selenization.

Iron and nitrogen Co-doped CoSe2 nanosheet arrays for robust electrocatalytic water oxidation

Fe–N–CoSe₂ electrocatalysts with good OER performance and long-term durability were synthesized using an anion and cation co-doping strategy.

Excessive Se on RuSe2 nanocrystals to accelerate water dissociation for the enhanced electrocatalytic hydrogen evolution reaction

Selenium-enriched RuSe2 (RuxSe) nanocrystals as electrocatalysts for the HER in basic media have been synthesized via a facile hydrothermal method followed by a calcination process. The catalytic activity of the obtained RuxSe nanocrystals is greatly dependent on calcination temperatures. The nanocrystals obtained at 400 °C (RuxSe-400) demonstrate the highest HER activity with a low overpotential of 45 mV to deliver a current density of 10 mA cm-2 and a small Tafel slope of 31.4 mV dec-1. The enhanced catalytic HER performance of RuxSe-400 could be attributed to the excessive Se on the RuSe2 nanocrystal surface. Density functional theory (DFT) calculations reveal that the excessive Se would lower the energy barrier for water dissociation and lessen the dependence on the Ru sites for OH* adsorption but have a negligible effect on hydrogen adsorption energy, leading to an accelerated HER process. Furthermore, the excessive Se on the nanocrystal surface further endows the catalyst with promoted charge-transfer kinetics, ensuring a more efficient catalytic reaction. The strategy herein for the design of highly efficient HER catalysts by engineering the separation of different intermediate (H* and OH*) adsorption sites is expected to be extended to other electrocatalysts for high-efficiency energy conversion.

CoP and Ni2P implanted in a hollow porous N-doped carbon polyhedron for pH universal hydrogen evolution reaction and alkaline overall water splitting

Developing low-cost and highly active bifunctional electrocatalysts for water splitting is very important but still remains a challenge. Herein, a novel bifunctional electrocatalyst composed of CoP and Ni2P nanoparticles implanted in a hollow porous N-doped carbon polyhedron (CoP/Ni2P@HPNCP) is synthesized by carbonization of Co/Ni-layered double hydroxide@zeolitic imidazolate framework-67 (Co/Ni-LDH@ZIF-67) followed by an oxidation and phosphorization strategy. The introduction of LDH can not only promote the formation of a hollow porous structure to supply more active sites, but also generate the CoP/Ni2P nanoheterostructure to afford extra active sites and modulate the electronic structure of the catalyst. As a result, CoP/Ni2P@HPNCP exhibits excellent pH universal hydrogen evolution reaction activity and alkaline oxygen evolution reaction activity. Furthermore, the electrolytic cell assembled from bifunctional CoP/Ni2P@HPNCP requires a cell voltage of 1.59 V in 1.0 M KOH at 10 mA cm-2, revealing its potential as a high performance bifunctional electrocatalyst.

Catalytic Oxidation of Methane to Oxygenated Products: Recent Advancements and Prospects for Electrocatalytic and Photocatalytic Conversion at Low Temperatures

Methane is an important fossil fuel and widely available on the earth's crust. It is a greenhouse gas that has more severe warming effect than CO2. Unfortunately, the emission of methane into the atmosphere has long been ignored and considered as a trivial matter. Therefore, emphatic effort must be put into decreasing the concentration of methane in the atmosphere of the earth. At the same time, the conversion of less valuable methane into value-added chemicals is of significant importance in the chemical and pharmaceutical industries. Although, the transformation of methane to valuable chemicals and fuels is considered the "holy grail," the low intrinsic reactivity of its C-H bonds is still a major challenge. This review discusses the advancements in the electrocatalytic and photocatalytic oxidation of methane at low temperatures with products containing oxygen atom(s). Additionally, the future research direction is noted that may be adopted for methane oxidation via electrocatalysis and photocatalysis at low temperatures.

V-Doped CoP Nanosheet Arrays as Highly Efficient Electrocatalysts for Hydrogen Evolution Reaction in Both Acidic and Alkaline Solutions

It is of significant necessity to explore inexpensive and high-active electrocatalysts toward hydrogen evolution reaction (HER) in both acidic and basic media. In this work, V-doped CoP nanosheet arrays supported on the carbon cloth (V-CoP/CC) are fabricated though a facile water-bath/phosphorization method. The nanoarray structure on the three-dimensional self-supporting electrode can provide a large electrochemical active surface area with more exposed active sites to accelerate the reaction kinetics. Furthermore, V doping is able to tune the electronic properties and thus enhance the intrinsic catalytic activity of CoP. Consequently, the V-CoP/CC electrode exhibits excellent electrocatalytic activities toward HER in both 0.5 M H₂SO₄ and 1 M KOH solutions with small overpotentials of 88 and 98 mV at a current density of 10 mA cm⁻², respectively. The present work will offer a feasible way to tailor the catalytic activity by hetero-atoms doping toward HER.

3D Hydrangea Macrophylla-like Nickel-Vanadium Metal-Organic Frameworks Formed by Self-Assembly of Ultrathin 2D Nanosheets for Overall Water Splitting

The development of highly efficient and low-cost bifunctional noble metal-free electrocatalysts for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is an effective strategy for improving efficiency. Herein, novel three-dimensional (3D) bimetallic metal-organic frameworks containing Ni and V with adjustable stoichiometry were synthesized on nickel foam successfully. Notably, Ni2V-MOFs@NF only require rather low overpotentials of 244 and 89 mV for the OER and HER, respectively, and expedites overall water splitting with 1.55 V at 10 mA cm^-2 with robust durability during the 80 h test. The high efficiency of the novel obtained electrocatalysts should be attributed to the particular morphological design of the two-dimensional (2D) ultrathin nanosheets self-assembling into a 3D nanoflower and the electronic structure regulation resulting from the synergetic interaction between nickel and vanadium. Subsequent theoretical calculations reveal the following conclusions: (I) the exceptional electronic conductivity of Ni2V-MOFs shows enhanced optimization as a result of electronic structure reconstruction, (II) the energy barrier reduction of the rate-limiting step is responsible for the enhanced dynamics of Ni2V-MOFs for the OER, and (III) the facilitation of the adsorption of H⁺ and H₂O plays a key role in progressing the HER catalytic activity of Ni2V-MOFs.

Mulberry-Inspired Nickel-Niobium Phosphide on Plasma-Defect-Engineered Carbon Support for High-Performance Hydrogen Evolution

Bimetallic phosphate electrocatalysts on carbon-cloth support are among the most promising industry-relevant solutions for electrocatalytic hydrogen production. To address the persistent issue of hetero-phase interfacing on carbon support while ensuring high activity and stability, a low-cost, high-performance hydrogen evolution reaction (HER) electrocatalyst is developed. Bi-phase Ni₁₂ P₅ -Ni₄ Nb₅ P₄ nanocrystals with rich heterointerfaces and phase edges are successfully fabricated on carbon cloth (CC), which is enabled by intentional defect creation by atmospheric pressure dielectric barrier discharge (DBD) plasma (PCC). The obtained Ni₁₂ P₅ -Ni₄ Nb₅ P₄ /PCC electrocatalyst exhibits excellent HER performance, heralded by the low overpotentials of 81 and 287 mV for delivering current densities of 10 (j₁₀ ) and 500 (j₅₀₀ ) mA cm^-2 , respectively. Meanwhile, the Ni₁₂ P₅ -Ni₄ Nb₅ P₄ /PCC maintains spectacular catalytic activity at high current density region (>j₆₁₅ ), which outperformed the industry-relevant benchmark Pt/C/PCC catalyst. The catalyst grown on the plasma-treated support shows remarkably longer operation and ultra-stable electrocatalytic characteristics over 100 h continuous operation. Ab initio numerical simulations reveal that Ni atoms exposed in the heterointerfaces act as the main catalytically active centers for HER.

NiCo2 O4 -Based Nanosheets with Uniform 4 nm Mesopores for Excellent Zn-Air Battery Performance

Herein, a strategy is reported for the fabrication of NiCo₂ O₄ -based mesoporous nanosheets (PNSs) with tunable cobalt valence states and oxygen vacancies. The optimized NiCo_2.148 O₄ PNSs with an average Co valence state of 2.3 and uniform 4 nm nanopores present excellent catalytic performance with an ultralow overpotential of 190 mV at a current density of 10 mA cm^-2 and long-term stability (700 h) for the oxygen evolution reaction (OER) in alkaline media. Furthermore, Zn-air batteries built using the NiCo_2.148 O₄ PNSs present a high power and energy density of 83 mW cm^-2 and 910 Wh kg^-1 , respectively. Moreover, a portable battery box with NiCo_2.148 O₄ PNSs as the air cathode presents long-term stability for 120 h under low temperatures in the range of 0 to -35 °C. Density functional theory calculations reveal that the prominent electron exchange and transfer activity of the electrocatalyst is attributed to the surface lower-coordinated Co-sites in the porous region presenting a merging 3d-e_g -t_2g band, which overlaps with the Fermi level of the Zn-air battery system. This favors the adsorption of the *OH, and stabilized *O radicals are reached, toward competitively lower overpotential, demonstrating a generalized key for optimally boosting overall OER performance.

Electrochemical Synthesis of Mesoporous Architectured Ru Films Using Supramolecular Templates

The electrochemical synthesis of mesoporous ruthenium (Ru) films using sacrificial self-assembled block polymer micelles templates, and its electrochemical surface oxidation to RuO_x is described. Unlike standard methods such as thermal oxidation, the electrochemical oxidation method described here retains the mesoporous structure. Ru oxide materials serve as high-performance supercapacitor electrodes due to their excellent pseudocapacitive behavior. The mesoporous architectured film shows superior specific capacitance (467 F g^-1_Ru ) versus a nonporous Ru/RuO_x electrode (28 F g^-1_Ru ) that is prepared via the same method but omitting the pore-directing polymer. Ultrahigh surface area materials will play an essential role in increasing the capacitance of this class of energy storage devices because the pseudocapacitive redox reaction occurs on the surface of electrodes.

Single-Crystalline Mo-Nanowire-Mediated Directional Growth of High-Index-Faceted MoNi Electrocatalyst for Ultralong-Term Alkaline Hydrogen Evolution

As appealing alternatives to noble-metal-based electrocatalysts for catalyzing hydrogen evolution reaction (HER) in alkali electrolyzers, earth-abundant MoNi-based catalysts have attracted intensive attention. Unfortunately, the exploration of MoNi-based electrocatalysts with superior intrinsic activity and ultralong-term stability still remains a grand challenge. Here, ultralong high-index faceted Mo@MoNi core-shell nanowires were topochemically synthesized through the thermal reduction of Mo@NiMoO₄ core-shell nanowires, where single-crystalline Mo support facilitates the topological transformation of NiMoO₄ into high-index faceted MoNi. When the as-achieved Mo@MoNi core-shell nanowire film serve as a free-standing cathode in alkaline solutions, it exhibit a remarkably decreased HER overpotential of 18 mV at 10 mA cm^-2 and a Tafel slope of ∼33 mV dec^-1, which are much lower than those for the state-of-the-art earth-abundant electrocatalysts and even commercial Pt/C. Experimental and theoretical investigations reveal that the exposed high-index (331) facets of MoNi can considerably reduce the energy barriers of initial water dissociation and subsequent hydrogen combination steps, which synergistically accelerates the sluggish alkaline HER kinetics. Significantly, after a 70-day HER operation, the overpotential of Mo@MoNi electrocatalysts at 10 mA cm^-2 decreases by only 4 mV. Therefore, this work sheds a bright light on the rational design of high-performance HER electrocatalysts and their practical utilization for alkaline electrolyzers.

In situ embedding of Mo2C/MoO3-x nanoparticles within a carbonized wood membrane as a self-supported pH-compatible cathode for efficient electrocatalytic H2 evolution

A rational design of active, stable, and pH-compatible electrocatalysts is crucial to produce high-purity H2via an electrocatalytic water splitting reaction. Herein, we report a carbonized wood membrane (CWM) embedded with Mo2C/MoO3-x nanoparticles (denoted as MCWM) as an efficient and stable self-supported H2 evolution cathode in both acidic and alkaline solutions. The CWM features a high surface area with numerous aligned and open channels and abundant porosity, greatly facilitating electrolyte transport and gas release. The in situ embedded Mo2C/MoO3-x nanoparticles are uniformly dispersed throughout the entire framework of the CWM, providing abundant active sites. These structural synergies endow the as-fabricated MCWM electrodes with excellent electrocatalytic H2 evolution activity, and the optimal MCWM electrode requires overpotentials of 187 and 275 mV to achieve a current density of 10 mA cm-2 in 0.5 M H2SO4 and 1.0 M KOH, respectively. Moreover, the MCWM electrode exhibits superior H2 evolution stability at a high current density of 80 mA cm-2 in both solutions with nearly 100% faradaic efficiencies. This work provides a promising nature-inspired strategy for the development of self-supported and pH-compatible electrodes for large-scale electrocatalytic H2 evolution reactions.

Ultrafine CoP/Co2P Nanorods Encapsulated in Janus/Twins-type Honeycomb 3D Nitrogen-Doped Carbon Nanosheets for Efficient Hydrogen Evolution

In this study, we report a Janus- or twins-type honeycomb 3D porous nitrogen-doped carbon (NC) nanosheet array encapsulating ultrafine CoP/Co₂P nanorods supported on Ti foil (CoP/Co₂P@NC/Ti) as a self-supported electrode for efficient hydrogen evolution. The synthesis and formation mechanism of 3D porous NC nanosheet array assembled into a honeycomb layer with ultrafine CoP/Co₂P single-crystal nanorods encapsulated is systematically presented. The CoP/Co₂P@NC/Ti electrode exhibits low overpotentials (η₁₀) of 31, 49, and 64 mV at a current density of −10 mA cm⁻² in 0.5 M H₂SO₄, 1.0 KOH, and 1.0 M PBS, respectively, exceeding the overwhelming majority of the documented transition metal phosphide-based electrocatalysts. Density functional theory calculation reveals that the superior electrocatalytic performance for hydrogen evolution reaction could be ascribed to the strong coupling effects of the reactive facets of CoP and Co₂P with the 3D porous NC nanosheet, making it exhibit a more thermo-neutral hydrogen adsorption free energy.

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A nitride-hydroxide cobalt is reported as precursor for CoP/Co₂P@NC/Ti electrode

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Janus- or twins-type morphology of CoP/Co₂P@NC/Ti electrode can be well controlled

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The Janus-type CoP/Co₂P@NC/Ti electrode exhibits very low overpotential for HER

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Coupling effects between CoP/Co₂P and NC matrix contributes to enhanced performance

NiSe2-anchored N, S-doped graphene/Ni foam as a free-standing bifunctional electrocatalyst for efficient water splitting

It is still challenging to develop non-precious free-standing bifunctional electrocatalysts with high efficiency for hydrogen and oxygen evolution reactions. Herein, for the first time, we present a novel hybrid electrocatalyst synthesized via a facile hydrothermal reaction, which is constructed from ultrafine NiSe2 nanoparticles/nanosheets homogeneously anchored on 3D graphene/nickel foam (NiSe2/3DSNG/NF). This hybrid delivers superior catalytic performances for hydrogen/oxygen evolution reactions and overall water splitting: it shows an ultra-small Tafel slope of 28.56 mV dec-1 for hydrogen evolution in acid, and a small Tafel slope of 42.77 mV dec-1 for the oxygen evolution reaction; particularly, in a two-electrode setup for water splitting, it requires an ultra-small potential of 1.59 V to obtain 10 mA cm-2 with nearly 100% faradaic efficiencies for H2 and O2. This study presents a new approach of catalyst design and fabrication to achieve highly efficient and low-cost water electrolysis.

Covalently Connected Nb4N5-xOx-MoS2 Heterocatalysts with Desired Electron Density to Boost Hydrogen Evolution

Rational design and controllable synthesis of efficient and robust electrocatalysts for hydrogen evolution reaction (HER) remain a critical challenge for the renewable energy economy. Herein, heterostructured Nb₄N_5-xO_x-MoS₂ (0 < x < 1) anchored on N-doped graphene (defined as Nb₄N_5-xO_x-MoS₂/NG) is synthesized by hydrothermal and chemical vapor deposition (CVD) approaches. During the CVD process, MoS₂ nanosheets are etched into small pieces and covalently interconnected with Nb₄N_5-xO_x to form fine Nb₄N_5-xO_x-MoS₂ heterostructures, which possess abundant interfaces and fully exposed edge active sites. The as-prepared Nb₄N_5-xO_x-MoS₂ heterostructures with Nb-(N,S)-Mo bridges provide desired electron density, which exhibit excellent chemisorption ability for both H and water, significantly improving the intrinsic HER activity. Meanwhile, the covalently connected Nb₄N_5-xO_x-MoS₂ heterostructures together with chemical coupling of Nb₄N_5-xO_x-MoS₂ and N-doped graphene improve the structural stability and ensure fast electron transfer in the Nb₄N_5-xO_x-MoS₂/NG nanocomposite, further supporting the H₂ generation and stability.

Intrinsic nature of photocatalysis by comparing with electrochemistry

Photocatalysis has been gathering much attention because of the unique applications of photoenergy for environmental cleaning and solar fuel production. Electron transfer (ET) at the solid-liquid interface, which initiates photocatalytic reactions, has been the subject of electrochemistry, and hence the reactions are often analyzed in terms of electrochemistry. However, how extensively the concept of electrochemistry can be incorporated has not been discussed so far. In this report, by comparing with electrochemistry, the intrinsic nature of photocatalysis is disclosed and the limitation of the use of the concept of electrochemistry was pointed out. The electric potential near the photocatalyst surface was calculated and visualized, showing a potential gradient similar to that at the electrode surface but localized near the positive hole. Since the frequency of the ET at the photocatalyst surface is limited by the photon absorption, the investigation of photocatalysis in terms of energy states and kinetics should be different from those for electrochemistry. Since semiconductor photocatalysts are not wired to the electric source, the estimation of energy band positions may be altered, which was actually discussed in terms of the band alignments of anatase and rutile TiO2 crystals.

ZnO-Templated Selenized and Phosphorized Cobalt-Nickel Oxide Microcubes as Rapid Alkaline Water Oxidation Electrocatalysts

Oxygen electrocatalysis is of remarkable significance for electrochemical energy storage and conversion technologies, together with fuel cells, metal-air batteries, and water splitting devices. Substituting noble metal-based electrocatalysts by decidedly effective and low-cost metal-based oxygen electrocatalysts is imperative for the commercial application of these technologies. Herein, a novel strategy is presented to fabricate selenized and phosphorized porous cobalt-nickel oxide microcubes by using a sacrificial ZnO spherical template and the resulting microcubes are employed as an oxygen evolution reaction (OER) electrocatalyst. The selenized samples manifest desirable and robust OER performance, with comparable overpotential at 10 mA cm^-2 (312 mV) as RuO₂ (308 mV) and better activity when the current reaches 13.7 mA cm^-2 . The phosphorized samples exhibit core-shell structure with low-crystalline oxides inside amorphous phosphides, which ensures superior activity than RuO₂ with the same overpotential (at 10 mA cm^-2 ) yet lower Tafel slope. Such a surface doping method possibly will provide inspiration for engineering electrocatalysts applied in water oxidation.

Recent advances in soft functional materials: preparation, functions and applications

Synthetic materials and biomaterials with elastic moduli lower than 10 MPa are generally considered as soft materials. Research studies on soft materials have been boosted due to their intriguing features such as light-weight, low modulus, stretchability, and a diverse range of functions including sensing, actuating, insulating and transporting. They are ideal materials for applications in smart textiles, flexible devices and wearable electronics. On the other hand, benefiting from the advances in materials science and chemistry, novel soft materials with tailored properties and functions could be prepared to fulfil the specific requirements. In this review, the current progress of soft materials, ranging from materials design, preparation and application are critically summarized based on three categories, namely gels, foams and elastomers. The chemical, physical and electrical properties and the applications are elaborated. This review aims to provide a comprehensive overview of soft materials to researchers in different disciplines.

Recent Advances in Non-Precious Transition Metal/Nitrogen-doped Carbon for Oxygen Reduction Electrocatalysts in PEMFCs

The proton exchange membrane fuel cells (PEMFCs) have been considered as promising future energy conversion devices, and have attracted immense scientific attention due to their high efficiency and environmental friendliness. Nevertheless, the practical application of PEMFCs has been seriously restricted by high cost, low earth abundance and the poor poisoning tolerance of the precious Pt-based oxygen reduction reaction (ORR) catalysts. Noble-metal-free transition metal/nitrogen-doped carbon (M–NxC) catalysts have been proven as one of the most promising substitutes for precious metal catalysts, due to their low costs and high catalytic performance. In this review, we summarize the development of M–NxC catalysts, including the previous non-pyrolyzed and pyrolyzed transition metal macrocyclic compounds, and recent developed M–NxC catalysts, among which the Fe–NxC and Co–NxC catalysts have gained our special attention. The possible catalytic active sites of M–NxC catalysts towards the ORR are also analyzed here. This review aims to provide some guidelines towards the design and structural regulation of non-precious M–NxC catalysts via identifying real active sites, and thus, enhancing their ORR electrocatalytic performance.

Fabrication of a 3D self-supporting Ni–P/Ni2P/CC composite and its robust hydrogen evolution reaction properties in alkaline solution

The Ni–P/Ni₂P/CC composite exhibits excellent alkaline HER properties derived from Ni–P filling the sites on the CC not occupied by Ni₂P nanosheets.

Non-precious-metal catalysts for alkaline water electrolysis: operando characterizations, theoretical calculations, and recent advances

Advances of non-precious-metal catalysts for alkaline water electrolysis are reviewed, highlighting operando techniques and theoretical calculations in their development.

Self-Supported Transition-Metal-Based Electrocatalysts for Hydrogen and Oxygen Evolution

Electrochemical water splitting is a promising technology for sustainable conversion, storage, and transport of hydrogen energy. Searching for earth-abundant hydrogen/oxygen evolution reaction (HER/OER) electrocatalysts with high activity and durability to replace noble-metal-based catalysts plays paramount importance in the scalable application of water electrolysis. A freestanding electrode architecture is highly attractive as compared to the conventional coated powdery form because of enhanced kinetics and stability. Herein, recent progress in developing transition-metal-based HER/OER electrocatalytic materials is reviewed with selected examples of chalcogenides, phosphides, carbides, nitrides, alloys, phosphates, oxides, hydroxides, and oxyhydroxides. Focusing on self-supported electrodes, the latest advances in their structural design, controllable synthesis, mechanistic understanding, and strategies for performance enhancement are presented. Remaining challenges and future perspectives for the further development of self-supported electrocatalysts are also discussed.

Devisable POM/Ni Foam Composite: Precisely Control Synthesis toward Enhanced Hydrogen Evolution Reaction at High pH

Polyoxometalates (POMs) are promising catalysts for the electrochemical hydrogen production from water owing to their high intrinsic catalytic activity and chemical tunability. However, poor electrical conductivity and easy detachment of the POMs from the electrode cause significant challenges under operating condition. Herein, a simple one-step hydrothermal method is reported to synthesize a series of Dexter-Silverton POM/Ni foam composites (denoted as NiM-POM/Ni; M=Co, Zn, Mn), in which the stable linkage between the POM catalysts and the Ni foam electrodes lead to high activity for the hydrogen evolution reaction (HER). Among them, the highest HER performance can be observed in the NiCo-POM/Ni, featuring an overpotential of 64 mV (at 10 mA cm-2 , vs. reversible hydrogen electrode), and a Tafel slope of 75 mV dec-1 in 1.0 m aqueous KOH. Moreover, the NiCo-POM/Ni catalyst showed a high faradaic efficiency ≈97 % for HER. Post-catalytic of NiCo-POM/Ni analyses showed virtually no mechanical or chemical degradation. The findings propose a facile and inexpensive method to design stable and effective POM-based catalysts for HER in alkaline water electrolysis.

Amorphous Ruthenium-Sulfide with Isolated Catalytic Sites for Pt-Like Electrocatalytic Hydrogen Production Over Whole pH Range

Electrocatalytic hydrogen evolution reaction (HER) is an efficient way to generate hydrogen fuel for the storage of renewable energy. Currently, the widely used Pt-based catalysts suffer from high costs and limited electrochemical stability; therefore, developing an efficient alternative catalyst is very urgent. Herein, one pot hydrothermal synthesis is reported of amorphous ruthenium-sulfide (RuS_x ) nanoparticles (NPs) supported on sulfur-doped graphene oxide (GO). The as-obtained composite serves as a Pt-like HER electrocatalyst. Achieving a current density of -10 mA cm^-2 only requires a small overpotential (-31, -46, and -58 mV in acidic, neutral, and alkaline electrolyte, respectively) with high durability. The isolated Ru active site inducing Volmer-Heyrovsky mechanism in the RuS_x NPs is demonstrated by the Tafel analysis and X-ray absorption spectroscopy characterization. Theoretical simulation indicates the isolated Ru site exhibits Pt-like Gibbs free energy of hydrogen adsorption (-0.21 eV) therefore generating high intrinsic HER activity. Moreover, the strong bonding between the RuS_x and S-GO, as well as pH tolerance of RuS_x are believed to contribute to the high stability. This work shows a new insight for amorphous materials and provides alternative opportunities in designing advanced electrocatalysts with low-cost for HER in the hydrogen economy.

Nitrogen-Doped Graphene-Encapsulated Nickel-Copper Alloy Nanoflower for Highly Efficient Electrochemical Hydrogen Evolution Reaction

Development of high-performance and low-cost nonprecious metal electrocatalysts is critical for eco-friendly hydrogen production through electrolysis. Herein, a novel nanoflower-like electrocatalyst comprising few-layer nitrogen-doped graphene-encapsulated nickel-copper alloy directly on a porous nitrogen-doped graphic carbon framework (denoted as Ni_x Cu_y @ NG-NC) is successfully synthesized using a facile and scalable method through calcinating the carbon, copper, and nickel hydroxy carbonate composite under inert atmosphere. The introduction of Cu can effectively modulate the morphologies and hydrogen evolution reaction (HER) performance. Moreover, the calcination temperature is an important factor to tune the thickness of graphene layers of the Ni_x Cu_y @ NG-NC composites and the associated electrocatalytic performance. Due to the collective effects including unique porous flowered architecture and the synergetic effect between the bimetallic alloy core and graphene shell, the Ni₃ Cu₁ @ NG-NC electrocatalyst obtained under optimized conditions exhibits highly efficient and ultrastable activity toward HER in harsh environments, i.e., a low overpotential of 122 mV to achieve a current density of 10 mA cm^-2 with a low Tafel slope of 84.2 mV dec^-1 in alkaline media, and a low overpotential of 95 mV to achieve a current density of 10 mA cm^-2 with a low Tafel slope of 77.1 mV dec^-1 in acidic electrolyte.

Hollow Nanotube Ru/Cu2+1 O Supported on Copper Foam as a Bifunctional Catalyst for Overall Water Splitting

Hydrogen energy is considered as one of the ideal clean energies for solving the energy shortage and environmental issues, and developing highly efficient electrocatalysts for overall water splitting to produce hydrogen is still a huge challenge. Herein, for the first time, Ru-doped Cu₂₊₁ O vertically arranged nanotube arrays in situ grown on Cu foam (Ru/Cu₂₊₁ O NT/CuF) are reported and further investigated for their catalytic properties for overall water splitting. The Ru/Cu₂₊₁ O NT/CuF presents ultrahigh catalytic activities for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline conditions, and it exhibits a small overpotential of 32 mV at 10 mA cm^-2 in the HER, and only needs 210 mV overpotential to achieve a current density of 10 mA cm^-2 in the OER. Importantly, the alkaline electrolyzer using Ru/Cu₂₊₁ O NT/CuF as a bifunctional electrocatalyst only needs 1.53 V voltage to deliver a current density of 10 mA cm^-2 , which is much lower than the benchmark of IrO₂ (+)/Pt(-) counterpart (1.64 V at 10 mA cm^-2 ). The excellent performance of the Ru/Cu₂₊₁ O NT/CuF catalyst is attributed to its high conductive substrate and special Ru-doped nanotube structure, which provides a high electrochemical active surface area and 3D gas diffusion channel.

Advanced Cu3Sn and Selenized Cu3Sn@Cu Foam as Electrocatalysts for Water Oxidation under Alkaline and Near-Neutral Conditions

Water electrolysis is a field growing rapidly to replace the limited fossil fuels for harvesting energy in future. In searching of non-noble and advanced electrocatalysts for the oxygen evolution reaction (OER), here we highlight a new and advanced catalyst, selenized Cu₃Sn@Cu foam, with overwhelming activity for OER under both alkaline (1 M KOH) and near-neutral (1 M NaHCO₃) conditions. The catalysts were prepared by a double hydrothermal treatment where Cu₃Sn is first formed which further underwent for second hydrothermal condition for selenization. For comparison, Cu₇Se₄@Cu foam was prepared by a hydrothermal treatment under the same protocol. The as-formed Cu₃Sn@Cu foam, selenized Cu₃Sn@Cu foam, and Cu₇Se₄@Cu foam were utilized as electrocatalysts and showed their potentiality in terms of activity and stability. In 1 M KOH, for attaining the benchmarking current density of 50 mA cm^-2, selenized Cu₃Sn@Cu foam required a low overpotential of 384 mV and increased charge transfer kinetics with a lower Tafel slope value of 177 mV/dec comparing Cu₃Sn@Cu foam, Cu₇Se₄@Cu foam, and pristine Cu foam. Furthermore, potentiostatic analysis (PSTAT) was carried out for 40 h for selenized Cu₃Sn@Cu foam and with minimum degradation in activity assured the long-term application for hydrogen generation. Similarly, under neutral condition selenized Cu₃Sn@Cu foam also delivered better activity trend at higher overpotentials in comparison with others. Therefore, the assistance of both Sn and Se in Cu foam ensured better activity and stability in comparison with only selenized Cu foam. With these possible outcomes, it can also be combined with other active, non-noble elements for enriched hydrogen generation in future.

Iron-Salen Complex and Co2+ Ion-Derived Cobalt-Iron Hydroxide/Carbon Nanohybrid as an Efficient Oxygen Evolution Electrocatalyst

Metal-salen complexes are widely used as catalysts in numerous fundamental organic transformation reactions. Here, CoFe hydroxide/carbon nanohybrid is reported as an efficient oxygen evolution electrocatalyst derived from the in situ formed molecular Fe-salen complexes and Co2+ ions at a low temperature of 160 °C. It has been evidenced that Fe-salen as a molecular precursor facilitates the confined-growth of metal hydroxides, while Co2+ plays a critical role in catalyzing the transformation of organic ligand into nanocarbons and constitutes an essential component for CoFe hydroxide. The resulting Co1.2Fe/C hybrid material requires an overpotential of 260 mV at a current density of 10 mA cm-2 with high durability. The high activity is contributed to uniform distribution of CoFe hydroxides on carbon layer and excellent electron conductivity caused by intimate contact between metal and nanocarbon. Given the diversity of molecular precursors, these results represent a promising approach to high-performance carbon-based water splitting catalysts.

Nucleation and growth mechanism of a nanosheet-structured NiCoSe2 layer prepared by electrodeposition

Ni-Co-Se layers have attracted a great deal of attention in the field of solar cells, electrocatalyst water splitting and supercapacitors. Electrodeposition is a simple, convenient and low-cost way to obtain Ni-Co-Se layers. However, until now, the electrochemical kinetics of the Ni-Co-Se system, including its growth and nucleation mechanisms, are still unclear. In present work a NiCoSe₂ layer with a nanosheet structure was electrodeposited in a chloride bath. The electrochemical mechanisms of the Ni-Co-Se system were also studied. It is noted that the electrochemical kinetics of Ni-Co-Se electrodeposition can be influenced by both temperature and electrode material; however, temperature does not change the progressive nucleation process and mixed controlled growth mechanism of Ni-Co-Se. The diffusion coefficient D and charge-transfer coefficient α of the Ni-Co-Se system were calculated. The values of D obtained by cyclic voltammogram and chromoamperometry are close to each other at both 20 and 50 °C, respectively, and increase with the increase of temperature. Moreover, the activation energy E _a was also calculated. Specially, a uniform 3D network-structure NiCoSe₂ layer was electrodeposited on ITO glass at -0.9 V and 40 ∼ 60 °C. The increased overpotential during deposition makes the NiCoSe₂ layer more easily gather together; however, there is no significant effect on the surface morphology of the NiCoSe₂ layer when the temperature is between 40 and 60 °C.

Evaluating DNA Derived and Hydrothermally Aided Cobalt Selenide Catalysts for Electrocatalytic Water Oxidation

Electrocatalysts with engaging oxygen evolution reaction (OER) activity with lesser overpotentials are highly desired to have increased cell efficiency. In this work, cobalt selenide catalysts were prepared utilizing both wet-chemical route (CoSe and CoSe-DNA) and hydrothermal route (Co_0.85Se-hyd). In wet-chemical route, cobalt selenide is prepared with DNA (CoSe-DNA) and without DNA (CoSe). The morphological results in the wet-chemical route had given a clear picture that, with the assistance of DNA, cobalt selenide had formed as nanochains with particle size below 5 nm, while it agglomerated in the absence of DNA. The morphology was nano networks in the hydrothermally assisted synthesis. These catalysts were analyzed for OER activity in 1 M KOH. The overpotentials required at a current density of 10 mA cm^-2 were 352, 382, and 383 mV for Co_0.85Se-hyd, CoSe, and CoSe-DNA catalysts, respectively. The Tafel slope value was lowest for Co_0.85Se-hyd (65 mV/dec) compared to CoSe-DNA (71 mV/dec) and CoSe (80 mV/dec). The chronoamperometry test was studied for 24 h at a potential of 394 mV for Co_0.85Se-hyd and was found to be stable with a smaller decrease in activity. From the OER study, it is clear that Co_0.85Se was found to be superior to others. This kind of related study can be useful to design the catalyst with increased efficiency by varying the method of preparation.