Nanoarchitectonics with Fe-doping on the optical and electrocatalytic properties of ZnO prepared by the malonate coprecipitation route: Application in the hydrogen evolution reaction

Abstract

Producing green hydrogen through water electrolysis in alkaline media using a suitable, eco-friendly, and inexpensive electrocatalyst is an effective approach to address the current energy problem. Transition metal oxides like ZnO are promising alternatives to noble metal-based electrocatalysts. However, their electrocatalytic properties are less reported due to their low performance. Doping is a proven strategy to enhance the functional properties of metal oxides, and the effectiveness of doping strongly depends on the synthesis route. In this work, Fe-doped ZnO (FexZn(1-x)O, x = 0, 0.06, 0.07, 0.11) was successfully synthesized via the pyrolysis of Fe-doped Zn malonate precursors obtained by the coprecipitation method. Results from a set of instrumental techniques revealed that the main phase formed is ZnO nanoparticles, with iron substituting zinc in the structure. UV–Visible diffuse reflectance results demonstrated that the optical band gap gradually decreases from 3.09 eV to 2.52 eV upon increases of iron content. The optimal amount of iron in ZnO exhibited an overpotential of 448 mV at 10 mA cm−2 (lower than that of pure ZnO and Fe2O3) and a small Tafel slope of 70 mV dec−1. The observed enhancement in electrocatalytic performance can be attributed to the generation of more active sites due to the optimal amount of iron in the matrix of the ZnO parent structure.