Coupling Interface Construction of Ni(OH)2/MoS2 Composite Electrode for Efficient Alkaline Oxygen Evolution Reaction

The transition metal-based catalysts have excellent electrochemical oxygen evolution reaction catalytic activity in alkaline electrolytes, attracting a significant number of researchers’ attention. Herein, we used two-step hydrothermal and solvothermal methods to prepare a Ni(OH)2/MoS2/NF electrocatalyst. The electrocatalyst displayed outstanding OER activity in 1.0 M KOH electrolyte with lower overpotential (296 mV at 50 mA·cm−2) and remarkable durability. Comprehensive analysis shows that reinforcement of the catalytic function is due to the synergistic effect between Ni(OH)2 and MoS2, which can provide more highly active sites for the catalyst. This also provides a reliable strategy for the application of heterogeneous interface engineering in energy catalysis.

Self-supported CoMoO4/NiFe-LDH core-shell nanorods grown on nickel foam for enhanced electrocatalysis of oxygen evolution

Developing high-performance catalysts is an effective strategy for speeding up the oxygen evolution reaction (OER) and increasing production efficiency. Here, a core-shell electrocatalyst consisting of CoMoO₄ nanorods grown in situ on nickel foam substrate covered by nickel-iron layered double hydroxide (NiFe-LDH) via electrodeposition was demonstrated (CoMoO₄/NiFe-LDH@NF). Experimental investigations revealed that self-supporting and binder-free electrodes ensured that the catalysts exposed an abundance of active sites, faster electron transfer, and excellent long-cycle stability. The NiFe-LDH shell with a crystalline-amorphous dual structure served as an accurate active material, lowering the energy barrier and contributing more catalytic sites for water oxidation. Furthermore, the core CoMoO₄ nanorods not only effectively avoided the accumulation of NiFe-LDH to increase the electrochemically active area but also acted as a highway for electrons from the active site to the substrate to promote the OER kinetics. Specifically, CoMoO₄/NiFe-LDH@NF exhibited lower overpotential (180 mV at 10 mA cm^-2) and smaller Tafel slope (34 mV dec^-1) than pure CoMoO₄@NF and NiFe-LDH@NF, revealing its excellent catalytic performance and fast intrinsic reaction kinetics. In addition, CoMoO₄/NiFe-LDH@NF exhibited long-term stability of more than 20 h at 50 mA cm^-2, further demonstrating its potential for practical applications. These findings pointed to a potential option for building innovative OER catalysts.

Controlled synthesis of P-Co3O4@NiCo-LDH/NF nanoarrays as binder-free electrodes for water splitting

The design and development of robust and environmentally friendly electrocatalytic materials are of great significance to the hydrogen production industry for the electrolysis of water. A series of P-Co₃O₄@NiCo-LDH/NF materials was firstly successfully synthesized by a hydrothermal method, high temperature calcination and an electrochemical deposition approach when sodium hypophosphite was used as the source of P and Ni(NO₃)₂·6H₂O as the source of nickel and introduced cobalt at the same time. The structure, composition, morphology and electrochemical performance of the P-Co₃O₄@NiCo-LDH/NF electrocatalytic material were determined by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and electrochemical performance testing. It is worth noting that the P-Co₃O₄@NiCo-LDH-2/NF material presents excellent hydrogen evolution reaction performance in 1 M KOH alkaline solution. It only needs an overpotential of 181 mV to drive a current density of 100 mA cm^-2, which is one of the best catalytic activities reported so far. The experimental results and theoretical calculations demonstrate that the electrocatalytic activity of the P-Co₃O₄@NiCo-LDH-2/NF material is attributed to the faster electron transfer rate, exposure of more active sites, optimal water adsorption energy and better electrical conductivity.

Synthesis of Co2-xNixO2 (0 < x < 1.0) hexagonal nanostructures as efficient bifunctional electrocatalysts for overall water splitting

Designing low-cost and high-performance bifunctional electrocatalysts towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is vitally important for water splitting. Herein, we synthesize Co2-xNixO2 (0 < x < 1.0) hexagonal nanosheets with different Co/Ni molar ratios via a facile coprecipitation process followed by calcination under an Ar atmosphere. Changing the Co/Ni molar ratios of the Co2-xNixO2 products is found to have a momentous influence on the microstructures, specific surface areas and electrocatalytic performances. At a Co/Ni molar ratio of 0.6, the Co1.4Ni0.6O2 nanosheet exhibits the largest specific surface area of 60.63 m2 g-1, the best OER with an onset overpotential of 278.5 mV, and HER of 72.8 mV as a bifunctional electrocatalyst. Meanwhile, the minimum Tafel slope is 113.6 mV dec-1 for OER and 77.4 mV dec-1 for HER. The Co1.4Ni0.6O2 nanosheet has excellent OER and HER activity at 0.1 mg cm-2 trace loading. Moreover, we construct an overall water splitting cell using the Co1.4Ni0.6O2 bifunctional electrocatalyst in a two-electrode system to further demonstrate the practical application, which needs a cell voltage of 1.75 V at a current density of 10 mA cm-2 and exhibits great long-term stability. These results provide an efficient strategy for the rational design of Co-based oxides towards bifunctional overall water electrocatalysts.

Fe doped Ni5P4 nanosheet arrays with rich P vacancies via phase transformation for efficient overall water splitting

Proper vacancy engineering is considered as a promising strategy to improve intrinsic activity, but it is challenging to construct rich vacancies by a simple strategy. Herein, Fe doped Ni₅P₄ nanosheet arrays with rich P vacancies are developed via a facile phase transformation strategy. Based on systematic investigations, we have demonstrated that an optimized surface electronic structure, abundant active sites and improved charge transport capability can be effectively achieved by vacancy engineering. Consequently, Fe doped Ni₅P₄ with rich vacancies show remarkable catalytic performances with 94.5 mV for the hydrogen evolution reaction (HER) and 217.3 mV for the oxygen evolution reaction (OER) at 10 mA cm^-2, respectively, as well as good durability. When directly employed as working electrodes, the as-obtained Fe doped Ni₅P₄ with rich vacancies can attain 10 mA cm^-2 at a low voltage of 1.59 V. This work demonstrates a feasible strategy for rationally fabricating electrocatalysts with rich vacancies via a simple phase transformation.

Engineering coordination polymer-derived one-dimensional porous S-doped Co3O4 nanorods with rich oxygen vacancies as high-performance electrode materials for hybrid supercapacitors

1D porous S-doped Co₃O₄ nanorods with rich oxygen vacancies and enhanced energy storage capability were engineered by a coordination polymer-engaged strategy.

Bi-functional Mo and P co-doped ZnCo-LDH nanosheets as high performance electrocatalysts for boosting overall water splitting

To rationally construct electrode structures with high activity is very significant for bi-functionalization conversion systems.

Simple synthesis of a vacancy-rich NiO 2D/3D dendritic self-supported electrode for efficient overall water splitting

Hydrogen production by water electrolysis is a common strategy for the development of renewable energy. However, meeting the industrial requirement for high efficiency and low cost is difficult to achieve with the existing methods. Herein, a novel and simple synthesis route for a dendritic self-supported electrode consisting of oxygen vacancy-rich NiO embedded within ultrathin 2D/3D nanostructures (NiO-Vo@2D/3D NS@DSE) for overall water splitting is developed for the first time. Based on the simple compound synthesis by jet electrodeposition and in situ acid etching, 2D nanosheets adhering uniformly to 3D nanospheres are successfully obtained on the dendritic self-supported skeleton surface. The experiments and density functional calculations illustrate that this electrode integrates the advantages including numerous active sites, intrinsic catalytic activity, good electrical conductivity, and outstanding reaction kinetic performance. Moreover, NiO-Vo@2D/3D NS@DSE shows excellent oxygen evolution reaction and hydrogen evolution reaction activities in 1 M KOH with overpotentials of 230 and 51 mV at 10 mA cm^-2, respectively. Additionally, the electrode, as an alkali-electrolyzer, displays a potential of 1.51 V at 10 mA cm^-2 with favorable stability that is superior to that of IrO₂@nickel foam (NF)//Pt/C@NF (1.62 V). Surprisingly, the cost of NiO-Vo@2D/3D NS@DSE is ≈1/120 of the price of noble electrocatalysts with the same mass. This research opens up a new pathway for the design of bifunctional electrocatalysts.