Facile Synthesis of Self-Assembled Cobalt Oxide Supported on Iron Oxide as the Novel Electrocatalyst for Enhanced Electrochemical Water Electrolysis

Abstract

We report, for the first time, a facile, scalable, and cost-effective method for the synthesis of high-performance and monodispersed hexagonally shaped cobalt oxide platelets supported on iron oxides (Fe3O4 and α-Fe2O3) as the electrocatalyst systems for water electrolysis. The Fe3O4 was synthesized in the absence of an inert environment and organic solvent, using a modified coprecipitation procedure. Fe3O4 nanoparticles of average size 15 nm served as the best catalyst support for Co3O4, in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). A current density of 10 mA/cm2 was achieved, at −0.36 and 1.64 V for the HER and OER [versus reversible hydrogen electrode (RHE)], respectively, for the Co3O4/Fe3O4 system, in 0.1 M KOH with low total catalyst loading of 250 μg/cm2 (or 100 μgCo3O4/cm2). Compared to those using the same total loading of unsupported Co3O4 catalyst, the overpotentials of Co3O4/Fe3O4 catalyst decreased by 0.22 and 0.06 V for the HER and OER, respectively. Despite low nonprecious metal loading, the Co3O4/Fe3O4 system showed high OER kinetics with low Tafel slope of 63 mV/dec. Chronoamperometry tests performed, at 1.62 and −0.30 V for the OER and HER, respectively, on the Co3O4/Fe3O4 catalyst demonstrated extremely stable OER over a period of 8 h. FESEM images of Co3O4/Fe3O4 revealed that the Co3O4 platelets were self-assembled into edge-on orientation on the Fe3O4 support. This largely accounted for the high catalytic activities observed because of the large total exposed surface area of Co3O4/Fe3O4 for catalytic reactions, in addition to electrochemical and morphological effects. Despite negating the need for specially tailored morphologies, Co3O4/Fe3O4 demonstrated enhanced electrochemical performance and stability. This may serve as a cost-effective route to the large-scale commercialization of electrolyzers and fuel cells via facile synthesis of nonprecious metal oxides as the catalyst–support system for enhanced electrochemical water electrolysis.