Organic ligand-facilitated in situ exsolution of CoFe alloys over Ba0.5Sr0.5Co0.8Fe0.2O3−δ perovskite toward enhanced oxygen electrocatalysis for rechargeable Zn-air batteries

Abstract

Cobalt-based perovskites are promising electrocatalysts for the oxygen evolution/reduction reaction (OER/ORR), while their surface modification with nanoparticles may further improve the performance. In the past, in situ exsolution of a metal (alloy) over a perovskite surface promoted by a H₂ atmosphere has been widely applied in developing nanoparticle modified anode materials for solid oxide fuel cells. However, it is a big challenge to apply this strategy for synthesizing cobalt-rich perovskite oxides for oxygen electrocatalysis due to their poor phase stability under a highly reducing atmosphere. Here, we report another strategy of organic ligand-facilitated in situ exsolution under a N₂ atmosphere for developing CoFe nanoalloys over Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) perovskite as an air electrode for zinc-air batteries (ZABs). The BSCF–CoFe interface, newly generated oxygen vacancies and Co–N–C porous networks provide conduction pathways for oxygen ions and electrons, leading to the enhanced electrochemical bi-functional performance. BSCF/CoFe offers OER activity, while Co–N–C and CoFe contribute to the ORR activity. Interestingly, the exsolved CoFe alloy also considerably promotes the ORR selectivity, leading to a 4e⁻ pathway. Consequently, ZABs integrated with the bi-functional electrocatalyst exhibit a favourable potential gap of 0.835 V at a discharge/charge current density of 5 mA cm⁻², and the cell operates stably without obvious degradation for over 250 h.