Enhanced electrocatalytic HER performance of non-noble metal nickel by introduction of divanadium trioxide

Vanadium Oxide: Phase Diagrams, Structures, Synthesis, and Applications

Vanadium oxides with multioxidation states and various crystalline structures offer unique electrical, optical, optoelectronic and magnetic properties, which could be manipulated for various applications. For the past 30 years, significant efforts have been made to study the fundamental science and explore the potential for vanadium oxide materials in ion batteries, water splitting, smart windows, supercapacitors, sensors, and so on. This review focuses on the most recent progress in synthesis methods and applications of some thermodynamically stable and metastable vanadium oxides, including but not limited to V₂O₃, V₃O₅, VO₂, V₃O₇, V₂O₅, V₂O₂, V₆O₁₃, and V₄O₉. We begin with a tutorial on the phase diagram of the V-O system. The second part is a detailed review covering the crystal structure, the synthesis protocols, and the applications of each vanadium oxide, especially in batteries, catalysts, smart windows, and supercapacitors. We conclude with a brief perspective on how material and device improvements can address current deficiencies. This comprehensive review could accelerate the development of novel vanadium oxide structures in related applications.

Maximized Schottky Effect: The Ultrafine V2 O3 /Ni Heterojunctions Repeatedly Arranging on Monolayer Nanosheets for Efficient and Stable Water-to-Hydrogen Conversion

The Mott-Schottky heterojunction formed at the interface of ultrafine metallic Ni and semiconducting V₂ O₃ nanoparticles is constructed, and the heterojunctions are "knitted" into the tulle-like monolayer nanosheets on nickel foam (NF). The greatly reduced particle sizes of both Ni and V₂ O₃ on the Mott-Schottky heterojunction highly enhance the number of Schottky heterojunctions per unit area of the materials. Moreover, arranging the heterojunctions into the monolayer nanosheets makes the heterojunctions repeat and expose to the electrolyte sufficiently. The Schottky heterojunctions are like countless self-powered charge transfer workstations embedded in the tulle-like monolayer nanosheets, promoting maximum of the materials to participate into the electron transfer and become catalytic active sites. In addition, the tulle-like monolayer nanosheet structure can assist in pumping liquid phase electrolyte to the surface of catalysts, owing to the capillary force. The V₂ O₃ /Ni/NF Mott-Schottky catalyst exhibits excellent hydrogen evolution reaction (HER) performance with a low η₁₀ of 54 mV and needs -107 mV to get the current density of -100 mA cm^-2 . Furthermore, V₂ O₃ /Ni/NF Schottky electrocatalyst exhibits excellent urea oxidation reaction activity: 1.40, 1.51, and 1.61 V versus reversible hydrogen electrode (RHE) voltage are required to reach a current density of 100, 500, and 1000 mA cm^-2 , respectively.

Molybdenum Nitride Electrocatalysts for Hydrogen Evolution More Efficient than Platinum/Carbon: Mo2N/CeO2@Nickel Foam

To produce hydrogen economically by electrolysis of water, one needs to develop a non-precious-metal catalyst that is as efficient as platinum metal. Here, we prepare such a catalyst by growing a layer of Mo₂N over a layer of CeO₂ deposited on nickel foam (NF) [hereafter, Mo₂N /CeO₂@NF] and show that the activity of this self-supported catalyst for hydrogen evolution in 1.0 M KOH is more efficient than that of the Pt/C electrode, achieving a current density of 10 mA/cm² at a fairly low overpotential of 26 mV. Furthermore, after a long-time electrochemical stability test for 24 h at a fixed current density, the overpotential needed to attain a current density of 10 mA/cm² is increased only by 6 mV, implying the huge potential of this method to prepare a super HER activity electrode for water splitting.

Porous nickel electrodes with controlled texture for the hydrogen evolution reaction and sodium borohydride electrooxidation

Porous Ni electrodes with different textures were successfully fabricated by electrodeposition in the presence of NH₄Cl and (NH₄)₂SO₄. Moreover, we studied the effect of texture on porous nickel electrodes for HER and NaBH₄ electrooxidation.