Tuning Electrochemical Hydrogen-Evolution Activity of CoMoO₄ through Zn Incorporation

Abstract

Designing cheap, efficient, and durable electrocatalysts on three-dimensional (3D) substrates such as nickel foam (NF) for the hydrogen-evolution reaction (HER) is in high demand for the practical application of electrochemical water splitting. In this work, we adopted a simple one-step hydrothermal method to realize the incorporation of Zn into the lattice of CoMoO4 with various atomic concentrations—Co1-xZnxMoO4 (x = 0, 0.1, 0.3, 0.5, and 0.7). The morphological studies demonstrated that parent CoMoO4 consists of nanoflowers and nanorods. However, as the concentration of Zn increases within the host CoMoO4, the portion of nanoflowers decreases and simultaneously the portion of nanorods increases. Moreover, the substitution of Zn2+ in place of Co2+/Co3+ creates oxygen vacancies in the host structure, especially in the case of Co0.5Zn0.5MoO4, giving rise to lower charge-transfer resistance and a higher electrochemically active surface area. Therefore, among the prepared samples, Co0.5Zn0.5MoO4 on NF showed an improved HER performance, reaching 10 mA cm−2 at an overpotential as low as 204 mV in a 1.0 M KOH medium. Finally, the Co0.5Zn0.5MoO4 electrode exhibited robust long-term stability at an applied current density of 10 mA cm−2 for 20 h. The Faradaic efficiency determined by a gas chromatograph found that the hydrogen-production efficiency varied from 94% to 84%.

Keywords

• electrocatalysis
• hydrogen-evolution reaction
• transition metal oxides
• metal substitution