Prussian Blue Analogue-Derived Metal Oxides as Electrocatalysts for Oxygen Evolution Reaction: Tailoring the Molar Ratio of Cobalt to Iron

The incorporation of iron into pristine transition metal oxides has been considered as an effective strategy to enhance the electrocatalytic activity toward oxygen evolution reaction (OER). However, the introduction of other transition metals in diverse catalytic systems using a precisely controllable method has remained a great challenge. In this study, a facile strategy is proposed by using Prussian blue analogues (PBAs) with tunable metal composition as a template to synthesize various Co–Fe molar ratios of spinel metal oxides. The iron–cobalt oxide (FeCo oxide) is successfully synthesized by utilizing thermal conversion of FeCo-based PBAs; the obtained oxide possessed a rough and porous structure with numerous interconnected granular nanoparticles formed in hollow multiple voids of each surface. In addition, the suitable iron contents occupying the octahedral sites in the spinel structure of FeCo oxide can further reduce the charge-transfer resistance and enhance the electrocatalytic activities toward OER. Benefiting from the unique structure and the chemical composition, the as-synthesized FeCo oxide shows an excellent OER activity with a low overpotential of 310 mV at 10 mA cm–2 and a good stability for at least 12 h of operation in alkaline solution. These results suggest that the electrocatalytic activities can be optimized by controllable metal composition of the PBA-derived metal oxides, which are the promising electrocatalysts for OER application.