Photofuel cell comprising titanium oxide and bismuth oxychloride (BiO1−xCl1−y) photocatalysts that uses acidic water as a fuel

Abstract

Solar cells and fuel cells have been extensively investigated. However, the need for sustainability, durability, and an electromotive force greater than 1.5 V per cell has not yet been fully realized. Herein, a photofuel cell (PFC) comprising two photocatalysts TiO₂ and BiOCl that uses acidic water as a fuel is described. The PFC is designed such that water can be regenerated from the photogenerated O₂ in the cell, and the electromotive force is as high as the difference between the conduction band minimum of TiO₂ and the valence band maximum of BiOCl (theoretical: 2.75 V, experimental: 1.76 V). The photocurrents were in accordance with a kinetic model based on the combination of the excited electron concentration at TiO₂ and the hole concentration at BiOCl. The reaction between the surface sites of O and/or Cl-deficient BiO_1−xCl_1−y species formed by ultraviolet-visible light irradiation with O₂ was in situ monitored using Bi L₃-edge extended X-ray absorption fine structure and X-ray photoelectron spectroscopy supported by Raman and UV-visible spectroscopy and could be involved in the cathodic O₂ photoreduction in the PFC. Furthermore, amorphous-like BiO_1−xCl species were observed on the surface of the BiOCl crystallites in high-resolution transmission electron microscopy. Importantly, this PFC that comprises TiO₂ and BiOCl is sustainable, recyclable, and has a series resistance that can be controlled by adjusting the BiOCl particle size, and exhibits a more efficient charge flow because of band bending than that of a previously reported PFC based on the rectification of the Schottky barrier.