Urea-bridging synthesis of nitrogen-doped carbon tube supported single metallic atoms as bifunctional oxygen electrocatalyst for zinc-air battery

Single atom (SA) catalysts have recently emerged as promising candidates to substitute noble metals catalysts. Herein, a urea-bridge method has been exploited to fabricate stable metallic single atom dispersed on nitrogen-doped carbon tubes. The preparation involved a facile pyrolysis of ellagic acid (EA)-metal coordination compound mediated through the usage of urea. During the synthesis process, urea acted as a bridge to drive the formation of hollow carbon tube as well as to provide N sites to immobilize SA in a space-confined environment. The active SA sites together with the accessibility and rapid mass transport from the hollow substrate endowed the obtained EA-SAs (e.g. EA-Co-900, EA-Ni-900) outstanding performances in oxygen reduction/evolution reactions. Furthermore, EA-Co-900 showed a high power density (e.g. 73 mW cm(-2), at 65 mA cm(-2)) and excellent durability of 110 h at 20 mA cm(-2) when assembled into rechargeable zinc-air batteries.