Reversible Electron Storage in an All-Vanadium Photoelectrochemical Storage Cell: Synergy between Vanadium Redox and Hybrid Photocatalyst

Abstract

Colossal solar energy conversion and storage studies using photoelectrochemical cells (PECs) have been undertaken in the past four decades; however, how to efficiently utilize solar energy despite the intermittent nature of sunlight still remains a challenge. In this paper, a WO3/TiO2 hybrid photoelectrode was coupled with our newly developed all-vanadium photoelectrochemical cell (PEC) with the aim of implementing photoelectrochemical solar energy conversion and storage. Zero-resistance ammetry (ZRA) and electrochemical impedance spectroscopy (EIS) were employed to study the photoelectrochemical response of this system in the conversion and storage of solar energy both under illumination and in the dark. The preliminary results proved the feasibility of this approach to store/release solar energy, even under dark conditions and showed that hydrogen tungsten bronze was responsible for the storage and release of photogenerated electrons from the semiconductor. The results also indicated an important synergy between electron storage and the all-vanadium electrolytes, which potentially offers great reversibility, high-capacity electron storage, and significant improvement in the photocurrent. To better understand the observed photoelectrochemical and electrochemical impedance behavior of our system, a model that unfolds the WO3 electron storage mechanism and photogenerated charge carrier pathways in the all-vanadium PEC is proposed.