Cr-doped CoFe2O4 nanorod array modified by oxygen vacancy-rich cerium oxide as an efficient bifunctional total water splitting catalyst†

Abstract

Highly efficient and stable bifunctional electrocatalysts for total water splitting are crucial for the realization of large-scale hydrogen production. In this study, we successfully synthesized CeO_x-modified CoCr_yFe_2−yO₄ nanorod array structures on a nickel foam substrate via two-step hydrothermal method followed by calcination. It is demonstrated that Cr doping increases the electrical conductivity of the catalyst, which allows for a larger number of electrochemically accessible active sites at the catalyst terminals, thereby improving its activity. Modification of the CoCr_yFe_2−yO₄/NF surface with oxygen vacancy-rich CeO_x resulted in a highly efficient and stable bifunctional catalyst (CoCr_yFe_2−yO₄@CeO_x/NF), and the exceptional bifunctional activity and stability can be attributed to: (i) Cr doping and CeO_x modification induced a self-assembly transformation of the catalyst morphology from a nanosphere structure to a nanorod array structure, resulting in an increased specific surface area; (ii) the high conductivity especially in CoCr_0.6Fe_1.4O₄, allows electrochemical access to a greater number of active sites at the catalyst periphery; (iii) the introduction of abundant oxygen vacancies by CeO_x modification, which alters the electronic structure of CoCr_yFe_2−yO₄, leading to electron redistribution of Co, Cr and Fe, shifting them to higher oxidation states favorable for catalytic reactions. This promotes the formation of highly catalytically active metal oxyhydroxides on the CoCr_yFe_2−yO₄ surface during the OER process, thereby enhancing the catalytic efficiency.