Insight into the Superior Photoactive Electrochemical Performances of NiCo2S4 for Efficient Bifunctional Catalyst Towards Oer/ORR in Rechargeable Zn-Air Batteries

Abstract

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are considered to be a fundamental basis of many energy conversion and storage technologies. Many studies have been devoted to developing high active ORR and OER bifunctional electrocatalysts to improve the efficiency of Zinc-air batteries (ZABs)[1]. However, the possibility of using free solar energy in ORR/OER electrocatalysts to enhance the efficiency of ZABs has not yet been recognized. Herein, we report a photoactive bifunctional catalyst of spinel-type NiCo2S4 (NCS) urchin-like structure with rich mesopores and direct band gap energies of ca. 1.4 and 2.4 eV which is good agreement with computational calculation. The NCS catalyst exhibits high catalytic activities for both OER (ɳ=338 mV at 10 mA cm-2) and ORR (ɳ=475 mV at E1/2), comparable to that of the state-of-the-art counterparts (e.g., Pt/C for ORR, RuO2 for OER). Under light illumination, the p-type photoactive NCS catalyst can absorb visible light, generating photogenerated holes and photoelectrons via the photoelectric effect for direct conversion of photoenergy into electric energy with increasing kinetic charge transfer process and provides ca. 10% and 18.5% lower OER and ORR overpotential than those under the dark condition. In addition, the as-fabricated zinc-air battery with the photoactive NCS as cathode exhibits the decrease in voltage gap from 0.82 to 0.60 V with an increase in round-trip efficiency from 59.2% to 68.8% after exposed to visible light. The zinc-air battery with a reversible redox reaction for simultaneous conversion of chemical and photoenergy into electric energy could open a new pathway for the utilization of a single energy conversion and storage device. Figure 1. The schematic of photocatalytic Zn-Air-Batteries with NiCo2S4 cathode. Keywords: Zn-air batteries, photoactive catalyst, Nickel cobalt sulfide.