Tuning of cationic distribution in “partially inversed” cobalt ferrite spinel nanocubes via a nitrogen-doped graphene oxide support for enhanced bifunctional oxygen electrocatalysis

Abstract

A strategy to improve the bifunctional oxygen electrocatalytic activity of cobalt ferrite spinel (CoFe₂O₄) nanocubes by a N-doped graphene oxide (NGO) support induced redistribution of cations at octahedral versus tetrahedral sites is presented. Moreover, a cost-effective and simple hydrothermal synthesis of CoFe₂O₄/NGO using an ammonia and hydrazine hydrate mixture as a nitrogen dopant cum reducing agent is reported. For the ORR, CoFe₂O₄/NGO shows a shift of the peak position by 230 mV to lower overpotential compared to bare CoFe₂O₄. Importantly, the overall oxygen electrocatalytic activity of CoFe₂O₄/NGO defined in terms of ΔE, the potential gap between E_1/2 for the ORR and the potential where the OER reaches 10 mA cm⁻², is the lowest to be reported for Co–Fe oxide-based catalysts. Raman, XPS, EXAFS, and XANES analyses of CoFe₂O₄/NGO reveal that N-doping induces defects in the GO-support, which alter not only the relative distribution of cations at octahedral and tetrahedral sites but also the electronic structure of the redox active building block, Co–O, leading to enhanced bifunctional oxygen electrocatalysis.