Salt-Templated Nanoarchitectonics of CoSe2-NC Nanosheets as an Efficient Bifunctional Oxygen Electrocatalyst for Water Splitting

Recently, the extensive research of efficient bifunctional electrocatalysts (oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)) on water splitting has drawn increasing attention. Herein, a salt-template strategy is prepared to synthesize nitrogen-doped carbon nanosheets encapsulated with dispersed CoSe₂ nanoparticles (CoSe₂-NC NSs), while the thickness of CoSe₂-NC NSs is only about 3.6 nm. Profiting from the ultrathin morphology, large surface area, and promising electrical conductivity, the CoSe₂-NC NSs exhibited excellent electrocatalytic of 10 mA·cm⁻² current density at small overpotentials of 247 mV for OER and 75 mV for HER. Not only does the nitrogen-doped carbon matrix effectively avoid self-aggregation of CoSe₂ nanoparticles, but it also prevents the corrosion of CoSe₂ from electrolytes and shows favorable durability after long-term stability tests. Furthermore, an overall water-splitting system delivers a current density of 10 mA·cm⁻² at a voltage of 1.54 V with resultants being both the cathode and anode catalyst in alkaline solutions. This work provides a new way to synthesize efficient and nonprecious bifunctional electrocatalysts for water splitting.     

MOF nanosheet array-derived NiS with Co,N-doped carbon layer: A highly efficient oxygen evolution electrocatalyst

The development of the hydrogen industry from electrolytic water is confined in great measure to the slow kinetics of oxygen evolution reaction (OER), which means the rational design of a stabilized and efficient OER electrode is the key. The construction of easily accessible hydroxide ion (OH^?) adsorption sites can effectively accelerate the kinetics of the OER. Herein, the NiS/CoNC electrocatalysts, which can effectively adsorb OH^? and exhibited excellent OER performance in an alkaline environment, were obtained by pyrolysis and sulfidation of NiCo-MOF nanosheets on nickel foam (NF). In particular, the optimized NiS/CoNC electrocatalyst achieved an overpotential of 46/106 mV at 10/100 mA cm^?2 and Tafel slope of 57.41 mV dec^?1, which is superior to most reported materials. The outstanding function of OER results from the NiOOH/CoOOH active component generated by surface reconstruction after activation of the NiS/CoNC catalyst and the excellent charge transfer capability of the NiS component. This work offers a scheme to construct the electrocatalysts derived from MOF with excellent OER performance.     

Oxygen-deficient MoOx/Ni3S2 heterostructure grown on nickel foam as efficient and durable self-supported electrocatalysts for hydrogen evolution reaction

High-performance and ultra-durable electrocatalysts are vital for hydrogen evolution reaction (HER) during water splitting. Herein, by one-pot solvothermal method, MoO_x/Ni₃S₂ spheres comprising Ni₃S₂ nanoparticles inside and oxygen-deficient amorphous MoO_x outside in situ grow on Ni foam (NF), to assembly the heterostructure composites of MoO_x/Ni₃S₂/NF. By adjusting volume ratio of the solvents of ethanol to water, the optimized MoO_x/Ni₃S₂/NF-11 exhibits the best HER performance, requiring an extremely low overpotential of 76 mV to achieve the current density of 10 mA∙cm^‒2 (η₁₀ = 76 mV) and an ultra-small Tafel slope of 46 mV∙dec^‒1 in 0.5 mol∙L^‒1 H₂SO₄. More importantly, the catalyst shows prominent high catalytic stability for HER (> 100 h). The acid-resistant MoO_x wraps the inside Ni₃S₂/NF to ensure the high stability of the catalyst under acidic conditions. Density functional theory calculations confirm that the existing oxygen vacancy and MoO_x/Ni₃S₂ heterostructure are both beneficial to the reduced Gibbs free energy of hydrogen adsorption (|∆G_H*|) over Mo sites, which act as main active sites. The heterostructure effectively decreases the formation energy of O vacancy, leading to surface reconstruction of the catalyst, further improving HER performance. The MoO_x/Ni₃S₂/NF is promising to serve as a highly effective and durable electrocatalyst toward HER.     

Hierarchical CoP3/NiMoO4 heterostructures on Ni foam as an efficient bifunctional electrocatalyst for overall water splitting

Controllable synthesis strategies of the cost-effective and high-active non-noble metal bifunctional electrocatalysts for overall water splitting are imperatively required. Herein, the hierarchical heterostructure CoP₃/NiMoO₄ nanosheets on Ni foam (CoP₃/NiMoO₄–NF) are synthesized by hydrothermal, annealing and phosphorization treatment. The synergistic effect between CoP₃ and NiMoO₄ remarkably promotes the HER intrinsic activity. Moreover, the Ni foam promotes the vertical growth of well-aligned nanosheet arrays, which expose more active sites for HER and OER. The CoP₃/NiMoO₄–NF-2 (Co/Mo = 1/1) electrocatalyst reveals a low overpotential of 92 mV for HER and 347 mV for OER at 10 mA cm⁻² in 1.0 M KOH. Especially, the CoP₃/NiMoO₄–NF-2 exhibits exceptional performance for overall water splitting which presents a low cell voltage of 1.57 V at 10 mA cm⁻², and outstanding durability which could maintain over 12 h. The design strategy and controllable synthesis of the hierarchical heterostructure bifunctional electrocatalyst will be beneficial for efficient overall water splitting.     

富氧空位Co3O4纳米线的制备及其电解水性能研究

在室温下利用NaBH₄溶液还原Co₃O₄纳米线获得富含氧空位（V_O）的三维自支撑纳米线阵列用作全水解电催化剂,其中NaBH₄处理10 min的Co₃O₄/NF在碱性介质中对析氧反应（OER）和析氢反应（HER）表现出很高的活性,在10 mA·cm^-2电流密度下分别仅需240和132 mV的过电位。V_O-Co₃O₄/NF同时作为阴极和阳极电催化剂时,在10 mA·cm^-2下电解水槽电压仅为1.63 V,其耐久性可达60 h以上。该工作为富含氧空位结构的过渡金属氧化物双功能电催化剂的制备提供了新的方法和思路。     

Engineering oxygen vacancy-rich Co3O4 nanowire as high-efficiency and durable bifunctional electrocatalyst for overall alkaline water splitting

A novel kind of vacancy-rich nanowire arrays were prepared by reducing rough Co₃O₄ nanowires with NaBH₄ solution on 3D nickel foam at room temperature for overall water splitting. Co₃O₄/NF treated by NaBH₄ for 10 min was highly active for oxygen evolution reaction (OER) and simultaneously efficient for hydrogen evolution reaction (HER) with the need of the overpotentials of 240 and 132 mV to drive 10 mA·cm^-2 in alkaline media, respectively. Furthermore, the electrocatalysts as both cathode and anode in a two-electrode system presented excellent durability for over 60 h at 10 mA·cm^-2, maintaining the cell voltage of merely 1.63 V. This work provides new methods and ideas for the preparation of transition metal oxide bifunctional electrocatalysts rich in oxygen vacancies.     

Hierarchical FeC/MnO2 composite with in-situ grown CNTs as an advanced trifunctional catalyst for water splitting and Metal−Air batteries

In high demand is developing trifunctional electrocatalysts to simultaneously drive hydrogen evolution reaction (HER) and oxygen evolution/reduction reaction (OER/ORR) for metal-air batteries and water splitting. Here we develop the carbon nanotubes (CNTs)-grafted FeC/MnO₂ nanocomposite catalyst by carbonizing FeMn metal-organic frameworks. The synergistic effect between FeC and MnO₂ dominantly contributes the ORR, OER, and HER. The transition metal-mediated growth of CNTs by an in-situ catalysis mechanism enables high electrical conductivity, abundant active sites, as well as efficient reaction pathways. The optimized chemical composite and unique hierarchical structure endow the FeC/MnO₂ with low overpotentials for multiply electrochemical reactions. Consequently, the composite catalyst successfully serves as the bifunctional electrode for water splitting with a voltage of 1.66 V at 10 mA cm^?2 as well as the cathode for all-solid-state metal-air battery with Pt/C-comparable performance. The advanced transition metal composite presented in this work provides the guidance for rationally developing trifunctional electrocatalysts for efficient integrated energy conversion systems.     

Fabrication of Co doped MoS2 nanosheets with enlarged interlayer spacing as efficient and pH-Universal bifunctional electrocatalyst for overall water splitting

Exploring inexpensive and active bifunctional electrocatalysts to produce hydrogen and oxygen from water at all pHs is highly desirable. Herein, we report a facile one-step method to prepare vertically aligned Co doped MoS₂ nanosheets with extended interlayer distance on carbon cloth (Co–MoS₂@CC) for full hydrolysis in both alkaline and acidic medium. Co–MoS₂@CC exhibits long-term durability with overpotentials of 56.6 mV and 130 mV for hydrogen generation and 242 mV and 201 mV for oxygen production at 10 mA cm^?2 in basic and acidic conditions, respectively. Moreover, we achieve low voltages of 1.585 V and 1.55 V in basic and acidic conditions respectively for the overall water splitting. We assume that such excellent property of Co–MoS₂@CC may be ascribed to the uncovering of more active sites and high porosity resulted from Co doping, which boosts the conductivity and thus reduces MoS₂ hydrogen adsorption free energy in HER, as well as benefits to catalytic active sites in OER. This one-step doping approach opens up new ways to regulate the intrinsic catalytic activity to catalyze total hydrolysis at all PHs.     

电解海水催化剂的设计与改性

电解海水是一种可再生、可持续、低成本且节约淡水资源的氢气生产方案。因此,针对天然海水或盐水电解质的析氢反应（HER）和析氧反应（OER）,设计开发高效、稳定的电催化剂具有良好的应用前景。为了深入了解海水电解所面临的现状和挑战,本文对电催化分解海水催化剂的设计思路与改性方法进行了系统的回顾和总结。首先详细讨论了电解海水中析氢反应、析氧反应、析氯反应的基本原理。随后对最近报道的在海水中能够稳定运行的HER和OER电催化剂进行了汇总和分析。针对阴极催化剂,分别概述了高效贵金属基电催化剂和低成本过渡金属基电催化剂。针对阳极催化剂,主要讨论了取得较大进展的镍基催化剂,随后对镍基之外的其他电催化剂进行对比补充。文章最后对电解海水催化剂目前所面临的挑战和发展方向进行了总结和展望,基于现有分析认为,在未来的研究中需要进一步探索新型电解海水催化剂的种类和结构,开发更高效稳定的阴极和具有更高OER选择性的阳极电催化剂,以满足分解海水电催化剂工业化应用的要求。     

全pH范围下MoS2/Ni3S2/NF的高效电催化析氢行为

在全pH（0~14）范围下设计开发低廉、高活性的析氢电催化剂对新能源开发和利用具有重要实际意义。通过简单的溶剂热法在镍网（NF）上原位构筑了纳米线结构MoS2/Ni3S2/NF电催化剂，该催化剂在全PH范围下表现出优异的析氢（HER）活性。电化学测试结果表明，使用41 mg四硫代钼酸铵制得的MoS2/Ni3S2/NF-41电极,在电流密度10 mA/cm2时，其在碱性（1 moL/L KOH，pH=14）、中性（0.5 moL/L PBS，pH=7）和酸性（0.5 moL/L H2SO4，pH=0）介质中HER过电位分别为87、113和195 mV，并相应表现出较低的Tafel斜率。另外，SEM、TEM、EDX、XPS等表征手段表明该催化剂具有良好的结构稳定性。本研究为过渡金属硫化物在全pH环境下高效析氢提供了新途径。     

多孔普鲁士蓝类似物的合成及电催化析氧性能

采用一种简单易行的共沉淀法合成了前驱体镍铁普鲁士蓝类似物NiFe-PBA（NF）,然后通过溶剂热处理获得了镍铁普鲁士蓝纳米多孔材料（NFP）。通过XRD、SEM、TEM、XPS、BET及电化学方法对所得材料进行了结构表征和析氧性能测试。结果表明,NFP相对于前驱体NF,电化学比表面积增大、催化活性位点增多,电催化析氧反应（OER）性能显著提高。在浓度1 mol/L KOH水溶液中,达到10 mA/cm2电流密度时,NFP所需过电位仅为260 mV,比NF（320 mV）前驱体低18.75%,也优于大多数已报道的非贵金属催化剂和商用贵金属催化剂,显示出良好的应用前景。     

Tuning the electronic structure of NiCoP arrays through V doping for pH-universal hydrogen evolution reaction electrocatalyst

The exploration of cost-effective, high-performance, and stable electrocatalysts for the hydrogen evolution reaction (HER) over wide pH range (0–14) is of paramount importance for future renewable energy conversion technologies. Regulation of electronic structure through doping vanadium atoms is a feasible construction strategy to enhance catalytic activities, electron transfer capability, and stability of the HER electrode. Herein, V-doped NiCoP nanosheets on carbon fiber paper (CFP) (denoted as V_x-NiCoP/CFP) were constructed by doping V modulation on NiCoP nanosheets on CFP and used for pH-universal HER. Benefiting from the abundant catalytic sites and optimized hydrogen binding thermodynamics, the resultant V₁₅-NiCoP/CFP demonstrates a significantly improved HER catalytic activity, requiring overpotentials of 46.5, 52.4, and 85.3 mV to reach a current density of 10 mA·cm^–2 in 1 mol·L^–1 KOH, 0.5 mol·L^–1 H₂SO₄, and 1 mol·L^–1 phosphate buffer solution (PBS) electrolytes, respectively. This proposed cation-doping strategy provides a new inspiration to rationally enhance or design new-type nonprecious metal-based, highly efficient, and pH-universal electrocatalysts for various energy conversion systems.     

一步水热法制备高效析氧3D花球阵列Co9S8/MoS2@TM催化电极

以四水合钼酸铵、六水合硝酸钴和硫脲为原料,采用一步水热法在钛网(TM)上原位构筑了不同阵列结构Co9S8/MoS2@TM催化电极.通过改变原料中钴、钼、硫的物质的量之比来调控Co9S8/MoS2@TM电极的结构.采用SEM、XRD和XPS对Co9S8/MoS2@TM进行物相分析和形貌表征,并在1 mol/L KOH电解...     

Low-temperature synthesized amorphous quasi-high-entropy carbonate electrocatalyst with superior surface self-optimization for efficient water oxidation

Anionic High-entropy materials have seldom been reported as a new library of water oxidation electrocatalysts owing to great difficulty in uniformly distributing multiple elements with different physicochemical properties and harsh synthesis conditions. Herein, a series of amorphous quasi-high-entropy carbonates for the first time is prepared via a facile low-temperature hydrothermal route. The optimized CoCrFeMnMoCO₃ with hydrothermal treatment of 6 h can serve as a promising oxygen evolution reaction (OER) electrocatalyst for water splitting on account of amorphous structure rendering more exposed active sites, superior synergistic effect realizing surface component self-optimization, high-valence ferritic species (Fe^(3+δ)+) providing high catalytic activity and high-entropy stabilization guaranteeing long-term OER performance, thus exhibiting the low overpotentials of 302 and 355 mV at the current densities of 10 and 100 mA cm⁻², respectively, the small Tafel slope of 36.7 mV dec⁻¹, and excellent durability longer than 38 h, dramatically exceeding its corresponding crystalline counterpart and benchmark RuO₂ catalyst, as well as yielding the current density of 10 mA cm⁻² with impressive low voltage of 1.56 V while used as bifunctional electrocatalyst for overall water splitting. This study lights a broad avenue to design other anionic high-entropy materials as promising OER catalysts.     

Trifunctional electrocatalysts based on feather-like NiCoP 3D architecture for hydrogen evolution,oxygen evolution,and urea oxidation reactions

Finding efficient and versatile catalysts that can both produce clean energy H₂ and treat wastewater is an important matter to solve energy shortages and wastewater pollution. Herein, a feather-like NiCoP supported on NF was synthesized via the two-step hydrothermal-phosphorization process. NiCoP/NF requires only overpotentials of 44 and 203 mV to reach 10 mA cm^?2 for HER and OER in 1 M KOH, respectively. Besides, NiCoP/NF requires only 1.13 V (vs RHE) to achieve 10 mA cm^?2 in 1 M KOH containing 0.33 M urea. DFT calculation shows that NiCoP exhibits enhanced DOS in the Fermi level attachment, which promotes charge transfer. Subsequently, the trifunctional NiCoP/NF, for overall water splitting, requires a lower potential of 1.48 V to gain 10 mA cm^?2 in 1 M KOH. For urea electrolysis, NiCoP/NF requires just 1.36 V to drive 10 mA cm^?2 in 1 M KOH with 0.33 M urea. This work provides extraordinary insights into electrolytic hydrogen production and wastewater treatment through simple preparative methods. The performance of the prepared catalyst is at a high level in non-noble metal.     

Metal oxide/carbon nanosheet arrays derivative of stacked metal organic frameworks for triggering oxygen evolution reaction

Numerous clean energy systems rely on the oxygen evolution process (OER), which takes place during water splitting reaction. For this purpose, transition-metal oxides have garnered considerable attentions as a prominent OER electrocatalysts. In present study, we fabricate the nanosheet arrays of metal oxide/carbon (MOx/C; M = Fe, Ag, and Mn) fabricated via hydrothermal route. As templates, this approach employs the covered 2-dimensional (2D) metal-organic frameworks (2D-MOFs), and these MOx/C arrays made from 2D MOFs exhibit significant electrocatalytic activity and durability. Among all, Ag₂O/C showed the overpotentials of 270 mV at a current density (j) of 10 mA cm^?2, while the tafel slope is 45 mV dec^?1, that is lower than other metal oxide-based catalysts like MnO/C, and Fe₂O₃/C. It also shows 48 h high stability due to the conductive nature, larger surface area and the presence of carbon cage for easy transfer of electrons. The conceptual framework and synthetic strategy employed in this study can be applied to create more multi-metal oxide anchoring Ag₂O carbon matrix-based electrocatalysts that are extremely efficient, affordable, and perform significantly better in OER and other future applications.     

Enhanced oxygen evolution reaction performance of synergistic effect of TiO2/Ti3C2/FeNi LDH

The introduction of high-efficiency electrocatalysts can improve the efficiency of oxygen evolution reaction (OER). However, the synergistic effect of elcetrocatalyst and cocatalyst is rarely studied. In this paper, by combining FeNi layered double hydroxide (LDH) electrocatalyst with a two-dimensional (2D) Ti₃C₂ co-catalyst on TiO₂ photocatalyst, the OER performance of TiO₂/Ti₃C₂/FeNi LDH is greatly improved due to the synergistic coupling effect. The microstructure, electrochemical performance and oxygen generation mechanism of TiO₂/Ti₃C₂/FeNi LDH are investigated in this paper. The results showed that the vertical array of FeNi LDH nanosheets created many nanoscale channels for reaction intermediates, enabling them to enter the most active sites on the surface. More importantly, the addition of Ti₃C₂ with high conductivity greatly effectively improved the charge separation and transfer between TiO₂ and FeNi LDH. Therefore, the required over-potential for current density 100 mA/cm² was only 633 mV for TiO₂/2 Ti₃C₂/FeNi LDH. Meanwhile, Tafel slope was as low as 30 mV/dec with good stability. This work provides a reference for using Ti₃C₂ as a new type of co-catalyst material to obtain an efficient, stable and economical OER reaction catalyst.     

Metal-organic frameworks derived FeS2@CoS2 heterostructure for efficient and stable bifunctional electrocatalytic water splitting

The exploration of efficient metal-based bifunctional catalysts for electrochemical water splitting is a promising approach for large-scale applications. In this work, we constructed a FeS₂@CoS₂ heterostructure electrocatalyst by a facile solution-dipping and hydrothermal method. The optimum FeS₂@CoS₂ heterostructure showed notable oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performances, with overpotential values of 280 mV and 136 mV (10 mA cm⁻² current density), respectively. Additionally, the electrocatalyst exhibited a robust stability performance of 50 h at a current density of 10 mA cm⁻². The two-cell electrolyzer is assembled using FeS₂@CoS₂||FeS₂@CoS₂ and delivers a cell voltage of 1.62 V and 1.99 V at 10 and 50 mA cm⁻² current densities with excellent durability. The outstanding overall water-splitting activity of the obtained heterostructure can be attributed to effective electronic interactions, synergistic effects, and exposure of more reactive active sites in the electrocatalyst. This work presents a promising strategy for developing highly active and cost-effective metal sulfide-based bifunctional electrocatalysts for energy conversion technology.     

Highly active and stable synergistic Ir–IrO2 electro-catalyst for oxygen evolution reaction

The design of efficient and stable electrocatalysts is still crucial to realize oxygen evolution reaction (OER) in acid and corrosive environment. Inspired by the metal/metal oxides catalysts, we hydrothermally synthesized Ir–IrO₂ composites duly confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive spectrometer (EDS), X-ray absorption data, and transmission electron microscope results. A low onset over-potential of merely 234?mV and a Tafel slope of 53?mV?dec^?1 were obtained for the prepared catalyst Ir–IrO₂_0.5AF. In addition, Ir–IrO₂_0.5AF catalyst retained high activity for long time under constant potential polarization. The enhanced performance is attributed to the introduction of lower valence Ir as hydrogen acceptor: hydrogen transfers from –OOH intermediate in OER to adjacent H acceptor site, forming intermediate with relatively lower Gibbs free energy, and resulting in higher activity. The present study emphasizes on important role of the lower valence composition in launching H acceptors and providing wide opportunities toward rational designing of efficient and stable electro-catalysts.     

In situ coupling of lignin-derived carbon-encapsulated CoFe-CoxN heterojunction for oxygen evolution reaction

Exploring highly active and stable electrocatalysts for oxygen evolution reaction (OER) is crucial for developing water splitting and rechargeable metal-air batteries. In this study, a hybrid electrocatalyst of CoFe alloy and Co_xN heterojunction encapsulated and anchored in N-doped carbon support (CoFe-Co_xN@NC) was in situ coupled via the pyrolysis of a novel coordination polymer derived from lignin biomacromolecule. CoFe-Co_xN@NC exhibited outstanding OER activity with a low overpotential of 270 mV at 10 mA cm⁻² and stability with an increment of 20 mV, comparable to commercial Ir/C. DFT calculations showed that Co_xN and N-doped graphitic encapsulation can reduce the binding strength between *O and CoFe alloy, limit metal leaching and agglomeration, and improve electron transfer efficiency, considerably enhancing the OER activity and stability. In situ coupling approach for preparing alloy and nitride heterojunctions on N-doped lignin-derived carbon offers a promising and universal catalyst design for developing renewable energy conversion technologies.