Microrods-evolved WO3 nanospheres with enriched oxygen-vacancies anchored on dodecahedronal CoO(Co2+)@carbon as durable catalysts for oxygen reduction/evolution reactions

Abstract

Oxygen reduction/evolution reactions (ORR/OER) play the vital roles in energy-conversion devices, especially for Zn-air batteries (ZABs). However, it is always a challenge to explore a stable bifunctional catalyst. Here, WO3-anchored ZIF-67-derived CoO@graphitized carbon is wrapped by a thin carbon-layer to obtain CoO@GC/WO3@CL catalysts. The well-crystallized WO3 nanospheres are evolved from WO3 microrods via an intra-particle maturation. For ORR, the peak-potential of CoO@GC/WO3@CL-800 (800 ℃) (0.81 V vs. RHE) is higher than that of Pt/C (0.79 V). Synergies between WO3 (oxygen vacancies) and CoO (Co2+) improve mass/charge transfer to boost the 4e− pathway. For OER, CoO@GC/WO3@CL-800 has a lower overpotential (330 mV) than RuO2 (490 mV) at 10 mA cm−2. The O2 evolution rate can reach 0.125 mmol s−1 with a high Faraday efficiency of 96.7 %. Cooperation between CoOOH and oxygen vacancies promotes the H2O-oxidation to boost the O2-generation. A relatively low ΔE [Ej=10(OER)-E1/2(ORR)] of 0.72 V confirms the highly-stable ORR/OER activities of CoO@GC/WO3@CL-800, which obtains a higher power density (138 mW cm−2) than Pt/C + RuO2 cathode in primary ZABs. This study indicates a new direction to build a multilayer-structured ORR/OER catalyst by using ZIFs as templates.