Electronic engineering of amorphous Fe–Co–S sites in hetero-nanoframes for oxygen evolution and flexible Al–air batteries

Abstract

The electrochemical oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are key electrochemical processes in metal–air batteries and water splitting devices. Aluminium–air batteries, as an important type of metal–air battery, have been considered to be promising power candidates for flexible electronics. Here, we describe electronically engineered amorphous Fe–Co–S sites embedded in Prussian blue analogue (FeCoS_x-PBA) hetero-nanoframes. The experimental results and DFT calculations reveal the critical role of the introduced FeCoS_x layer to PBA, which enhances the electron transfer and alleviates the overbinding effect of OH* during the OER. The FeCoS_x-PBA hybrid system supplies an optimized electronic structure for the alkaline OER, which is also confirmed by the much-lowered overpotential (266 mV at 10 mA cm⁻²) for the alkaline OER. Furthermore, a flexible Al–air battery based on an FeCoS_x-PBA cathode catalyst exhibits a high peak power density (58.3 mW cm⁻²) and energy density (1483 W h kg_Al⁻¹), and outstanding stability for more than 50 h of operation under bending or stretching conditions, demonstrating its potential in the practical application of flexible electronic devices. Our results may provide a new strategy of modulating the electronic structure of air electrode catalysts to efficiently promote the reactivity of alkaline OER and Al–air battery processes.