Biomass-based Hierarchical Porous ORR and OER Bifunctional Catalysts with Strong Stability for Zn-Air Batteries

Although the Zn-air battery has many advantages, its short practical life hinders its development. Many solutions have been proposed and extensively studied. In this paper, a cobalt-nitrogen co-doped hierarchical porous carbon-based bifunctional catalyst (Co/N-HPCs-800) is reported, using sustainable and low-cost sodium alginate (Na-Alg), a common seaweed extract, as a precursor to complex excess metal particles. The hydrogel network formed by the exchange of sodium ions with metal cation (Co2+) ions is the key to the controllable synthesis of highly dispersed metal atoms. Co/N-HPCs-800 shows excellent catalytic performance and durability in oxygen reduction reaction (E1/2 = 0.86 V) and oxygen evolution reaction (367 mV @ 10 mA cm–2). Importantly, we only attenuated the half-wave potential by 8 mV after more than 50,000 cycles. In addition, the Zn-air batteries (ZABs) using Co/N-HPCs-800 as a cathode exhibit a power density up to 159.67 mW cm–2 and a high specific capacity of 787.94 mA h g–1. This work opens up practical new strategies for synthesizing excess metal catalysts in low cost, effectively improving the service life of Zn-air batteries.