Iron and Manganese Codoped Cobalt Tungstates Co_{1–(<i>x</i>+<i>y</i>)}Fe<i>_x</i>Mn<i>_y</i>WO₄ as Efficient Photoelectrocatalysts for Oxygen Evolution Reaction

Abstract

Photoelectrocatalysts are robust materials for the production of energy through different ways such as water splitting. Narrow optical band gaps and high overpotentials are limiting the development of photoelectrocatalysts. In this study, a series of Co_{1-(<i>x</i>+<i>y</i>)}Fe <i>_x</i> Mn <i>_y</i> WO₄ solid solutions of cobalt tungstate codoped with iron and manganese have been synthesized hydrothermally. The synthesized solid solutions have been characterized by powder XRD, UV-visible spectra, cyclic voltammetry (CV), and linear sweep voltammetry (LSV). They all crystallize in a wolframite-type monoclinic crystal system with space group <i>P</i>2/<i>c</i>. Doping of iron and manganese leads to narrowing of the optical band gap of Co_{1-(<i>x</i>+<i>y</i>)}Fe <i>_x</i> Mn <i>_y</i> WO₄ from 2.60 to 2.04 eV. The electrocatalytic activity toward oxygen evolution reaction of all of the samples has been evaluated through LSV measurements. It is found that the sample named C5, which is codoped with manganese and iron, has the lowest onset potential and needs the lowest overpotential to attain the targeted 5 mA cm^-2 and standard 10 mA cm^-2 current densities as compared with all other synthesized samples. This study shows that the synthesized tungstates can be good candidates for the photoelectrocatalytic oxygen evolution reaction.