Sacrificial ZnO nanorods drive N and O dual-doped carbon towards trifunctional electrocatalysts for Zn–air batteries and self-powered water splitting devices

Integrated energy systems (IES) have attracted increasing attention in recent years. Zn–air battery powered water splitting devices require the development of highly active and durable trifunctional electrocatalysts for the oxygen evolution, oxygen reduction, and hydrogen evolution reactions (OER/ORR/HER). However, engineering rational nano-scaled designs and achieving the required synergy are major challenges due to the lack/weak control of synthesis processes. Herein, ZIF-67 regular polyhedra were fabricated for the first time to incorporate single ZnO nanorods. Thereafter, pyrolysis sacrificed the nanorods and stimulated intriguing modifications on the ZnONR@ZIF-67-derived CoOx@N, O-doped hierarchical carbon (CoOx@NOC), not only from the outside-in, but also from the inside out. Consequently, an outstanding enhancement in OER/ORR/HER trifunctional activity was achieved. The CoOx@NOC based Zn–air battery showed a small initial charge–discharge voltage gap of 92 mV at 10 mA cm−2 and a high specific capacity and maximum power density of 757.39 mA h gZn−1 and 141.65 mW cm−2, respectively. A CoOx@NOC-based all-solid-state Zn–air battery (SS ZAB) was fabricated, which showed a high open circuit potential of 1.49 V. Two SS ZABs in series drove an overall water splitting system, which showed an intriguingly low potential of 1.51 V at 10 mA cm−2, surpassing most reported electrocatalysts. Thus, the excellent performance of CoOx@NOC implies its great potential to compete with noble metal electrocatalysts.