P-doping optimized d-band center position in MoO2 with enhanced oxygen reduction reaction and oxygen evolution reaction activities for rechargeable Zn-air battery

Abstract

Zn-air battery is considered as a prospective energy conversion and storage device, which achieves charge/discharge with oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). For Zn-air battery, bifunctional electrocatalyst with high efficiency is extremely important. MoO2 exhibits both ORR and OER activities. But the performance requires further enhancement when employed in Zn-air battery. To achieve this goal, P-doped MoO2 (P–MoO2) is synthesized. Theoretical calculation implies P-doping elevates d-band center, which strengthens interaction between MoO2 and relevant oxygen species during ORR/OER. This donates P–MoO2 excellent ORR/OER activities. In ORR, its half-wave potential reaches 0.78 V. In OER, to acquire 10 mA cm−2, P–MoO2 only consumes 280 mV. P–MoO2 shows good stability in ORR/OER. Zn-air battery is assembled with P–MoO2 as cathode material. Its open circuit voltage and power density reach 1.46 V, 121.9 mW cm−2. In Zn-air battery, specific capacitance and energy density achieve 838.7 mAh·g−1Zn, 927.8 Wh·kg−1Zn at 10 mA cm−2. The work not only offers a feasible method to improve performance of MoO2 in Zn-air battery, but also implies the origin of enhanced ORR/OER activities after P-doping.