Visible-light-driven photo-enhanced zinc–air batteries using synergistic effect of different types of MnO2 nanostructures

Abstract

Crystalline phases along with the morphology of any semiconducting material are the key factors that govern photocatalytic properties. Herein, we have prepared a composite of α- and δ-MnO₂ with distinct crystallographic orientation and phases. The bandgap of the composite (α + δ)-MnO₂ lies in the range of visible light. Similarly, MnO₂ is well known for its energy storage capability. Photocatalytic and energy storage processes can be combined in a single device to achieve higher energy storage efficiency. The focus of our study is to investigate the synergy between two crystallographic phases of MnO₂ and its influence on electrochemical and photoelectrochemical energy conversion and storage properties. The prepared composite, with the advantage of tunnel structure of the rod-shaped α-MnO₂, as well as the layered structure of 2D δ-MnO₂ with high surface area, was found to induce positive effects and superior electrochemical storage properties. The prepared composite produced favorable results for the Zn–air battery application, which showed approximately 2 and 4 times higher power density than the δ-MnO₂ and α-MnO₂, respectively. Moreover, to illustrate the practical applicability of the composite, a rechargeable solid-state Zn–air battery was fabricated to power a light-emitting diode. A photo-enhanced Zn–air battery using the composite MnO₂ electrode was also fabricated to explore the photoactivity and concurrent effect on the storage property of the composite material. The visible-light-driven Zn–air battery exhibited significant improvement in the bifunctional oxygen electrode activity by 7.20% in the presence of light as compared to that in dark. The battery also exhibits lowering of the potential difference for charging and discharging by 7.62% and 29.89% enhancement in the round-trip efficiency, indicating the positive role of light illumination on the battery performance.