Hierarchically three-level Ni3(VO4)2@NiCo2O4 nanostructure based on nickel foam towards highly efficient alkaline hydrogen evolution

Recent Progress of Transition Metal Compounds as Electrocatalysts for Electrocatalytic Water Splitting

Hydrogen has enormous commercial potential as a secondary energy source because of its high calorific value, clean combustion byproducts, and multiple production methods. Electrocatalytic water splitting is a viable alternative to the conventional methane steam reforming technique, as it operates under mild conditions, produces high-quality hydrogen, and has a sustainable production process that requires less energy. Electrocatalysts composed of precious metals like Pt, Au, Ru, and Ag are commonly used in the investigation of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Nevertheless, their limited availability and expensive cost restrict practical use. In contrast, electrocatalysts that do not contain precious metals are readily available, cost-effective, environmentally friendly, and possess electrocatalytic performance equal to that of noble metals. However, considerable research effort must be devoted to create cost-effective and high-performing catalysts. This article provides a comprehensive examination of the reaction mechanism involved in electrocatalytic water splitting in both acidic and basic environments. Additionally, recent breakthroughs in catalysts for both the hydrogen evolution and oxygen evolution reactions are also discussed. The structure-activity relationship of the catalyst was deep-going discussed, together with the prospects of current obstacles and potential for electrocatalytic water splitting, aiming at provide valuable perspectives for the advancement of economical and efficient electrocatalysts on an industrial scale.

Heterostructured mixed metal oxide electrocatalyst for the hydrogen evolution reaction

The hydrogen evolution reaction (HER) has attracted considerable attention lately because of the high energy density and environmental friendliness of hydrogen energy. However, lack of efficient electrocatalysts and high price hinder its wide application. Compared to a single-phase metal oxide catalyst, mixed metal oxide (MMO) electrocatalysts emerge as a potential HER catalyst, especially providing heterostructured interfaces that can efficiently overcome the activation barrier for the hydrogen evolution reaction. In this mini-review, several design strategies for the synergistic effect of the MMO catalyst on the HER are summarized. In particular, metal oxide/metal oxide and metal/metal oxide interfaces are explained with fundamental mechanistic insights. Finally, existing challenges and future perspectives for the HER are discussed.

Sulfur doping enhanced desorption of intermediates on NiCoP for efficient alkaline hydrogen evolution

Electrocatalysts with high catalytic activity, high stability and low cost are critical to the hydrogen evolution reaction (HER). In this paper, sulfur(S)-doped NiCoP nanowire arrays on a carbon fiber paper skeleton (S-NiCoP NW/CFP) are prepared, and it is demonstrated that the electrocatalytic properties of NiCoP in alkaline solution could be well improved by sulfur doping. In 1.0 M KOH, only an overpotential of 172 mV (vs. RHE) at 100 mA cm-2 is required for S doped NiCoP nanowires on CFP, and the turnover frequency (TOF) is 1.71 times that of NiCoP at an overpotential of 100 mV, indicating its superior intrinsic activity. Density functional theory (DFT) calculations show that S doping could lower the center of the d-band, and thus weaken the interaction between NiCoP and the intermediates. This leads to an optimized hydrogen adsorption Gibbs free energy (ΔGH*) and faster desorption of OH*. This study offers a promising way to design and optimize electrocatalysts for the HER in alkaline solution.

3D Metallic Ti@Ni0.85 Se with Triple Hierarchy as High-Efficiency Electrocatalyst for Overall Water Splitting

In this study, Ti@Ni_0.85 Se electrodes with a triple hierarchy architecture were designed, and their applications in electrocatalytic water splitting were studied. The 3D electrode is comprised of three types of structures including the bottom square Ti mesh structure as the conductive substrate, a vertical and uniform Ni_0.85 Se nanosheet arrays structure in the intermediate section, and the topmost Ni_0.85 Se flower structure. This triple hierarchy architecture is binder-free, conductive, and has a particular feature of enlarged surface areas, exposing more active sites, promoting mass- and charge-transfer, and accelerating dissipation of gases generated during water electrolysis. Moreover, DFT calculations confirmed that the Ni_0.85 Se possesses metallic character, which further promotes the charge transfer of the electrocatalyst. Benefiting from this special structure and metallic character, the electrode displays a superior activity of 10 mA cm^-2 at 120 mV hydrogen evolution reaction overpotential and 30 mA cm^-2 at 270 mV oxygen evolution reaction overpotential. By using this electrode as a bifunctional electrocatalyst, an alkali electrolyzer affords a water splitting current of 10 mA cm^-2 at a cell voltage of 1.66 V.

Controllable design of double metal oxide (NiCo2O4)-modified CdS for efficient photocatalytic hydrogen production

In the present study, we have successfully synthesized a kind of high-efficiency NiCo₂O₄/CdS composite photocatalyst using the hydrothermal method and high-temperature calcination.