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

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. © 2022 The Royal Society of Chemistry.