MnCo_2O_4 Nanofibers as Efficient Photo-electrocatalyst for Oxygen Evolution Reaction and Oxygen Reduction Reaction

摘要

The development of catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are attracted enormous interest for improving the performance of Zn-air batteries (ZABs). However, the use of cation-substituted spinel cobaltite XCo_2O_4 (X = Fe, Co, Ni, and Mn) as photo-electrocatalysts for OER/ORR in ZABs has not yet been reported. The XCo_2O_4 materials were synthesized by using an electrospinning method followed by a calcination process at 700°C. Among these XCo_2O_4 catalysts, the NiCo_2O_4 exhibits the superior performance for both OER (η = 300 mV at 10 mA/cm~2) and ORR (η = 460 mV at E_(1/2)). It mainly attributes to the narrowest band gap energy at 1.50 eV which corresponds to the ratios of X~(2+)/X~(3+) and Co~(2+)/Co~(3+) that investigates by the UV-vis spectroscopy, Mott-Schottky plots, and XPS analysis. Under the exposure of light, the NiCo_2O_4 provides the lower in overpotential of OER and ORR around 10% - 30% due to the occurring of electron(e~-) - hole (NiCo_2O_4~+) separation from absorbing the photon energy. Both of e~- and NiCo_2O_4~+ can accelerate the ORR and OER, which is confirmed by in-situ XAS under the light and dark conditions. Finally, the as-fabricated artificial ZAB cell by using NiCo_2O_4 as a photo-electrocatalyst presents the superb ZAB performance.