In situ reconstruction of bimetallic heterojunctions encapsulated in N/P co-doped carbon nanotubes for long-life rechargeable zinc-air batteries

Abstract

Efficient and stable bifunctional electrocatalysts are crucial for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in high-performance rechargeable zinc-air batteries (ZABs). Despite significant advancements in non-noble metal-based catalysts over the past decades, the rational tuning of various active materials for efficient ORR and OER, along with the identification of genuine active sites, remains a formidable challenge. Encouraged by the development of in-situ characterization technologies, research on bifunctional catalysts for ZABs has gradually shifted to exploring the true active sites and investigating catalyst evolution and degradation, which is vital for further breakthroughs in bifunctional catalysts. In this study, we developed a facile method to encapsulate bimetallic heterojunction CoFe/CoFeP in N/P co-doped carbon nanotubes (CNTs) as a bifunctional catalyst for ZABs. This unique heterojunction structure prevents the dissolution and erosion of transition metals, enhances continuous electron transfer and mass transport, and effectively boosts the catalyst's bifunctional activity and stability. Importantly, ex-situ and in-situ techniques were employed to track the dynamic ORR and OER catalytic processes, capture the reconstructions of bifunctional catalysts, and reveal the real active sites. The CoFe/CoFeP@NPC catalyst exhibits superior bifunctional catalytic activity and stability, especially with a half-wave potential of 0.887 V for ORR and 1.55 V at 10 mA cm−2 for OER. Impressively, the assembled rechargeable ZABs demonstrate a high-power density (550 mW cm−2), a low charge-discharge voltage difference (0.7 V), and ultralong cycling for over 1600 h.