The Photoactive Cation-Substituted Spinel Cobaltite XCo2O4 (X = Fe, Co, Ni, and Mn) Using As Air Cathodes in Zinc-Air Batteries

Abstract

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 XCo2O4 (X = Fe, Co, Ni, and Mn) as photo-electrocatalysts for OER/ORR in ZABs has not yet been reported. The XCo2O4 materials were synthesized by using an electrospinning method followed by a calcination process at 700oC. Among these XCo2O4 catalysts, the NiCo2O4 exhibits the superior performance for both OER (η = 300 mV at 10 mA/cm2) and ORR (η = 460 mV at E1 / 2). It mainly attributes to the narrowest band gap energy at 1.50 eV which corresponds to the ratios of X2 +/X3 + and Co2 +/Co3 + that investigates by the UV-vis spectroscopy, Mott-Schottky plots, and XPS analysis. Under the exposure of light, the NiCo2O4 provides the lower in overpotential of OER and ORR around 10% - 30% due to the occurring of electron(e-) – hole (NiCo2O4 +) separation from absorbing the photon energy. Both of e- and NiCo2O4 + 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 NiCo2O4 as a photo-electrocatalyst presents the superb ZAB performance. Figure 1