TiO2-coated window for facilitated gas evolution in PEC solar water splitting

Abstract

Photoelectrochemical (PEC) cells for water splitting generally have a transparent front window for the sunlight to reach the surface of the photoelectrode or tandem photoelectrode. The overall efficiency of a PEC system for solar hydrogen production is strongly affected by the evolved gases that get trapped in the front window. This negative effect is clearly observed when the PEC cells are placed in tilted positions to maximize light harvesting. Titanium dioxide coatings become superhydrophilic when exposed to UV light, facilitating the gas bubbles to slip up. The present study focuses on the development of a thin TiO₂ coating to minimize the adhesion of the evolved bubbles in the front window of PEC cells, thereby maximizing its transparency. Highly transparent, crack-free, and stable thin films of TiO₂ were prepared by spin coating followed by sintering at 465 °C for 45 min. A water contact angle (WCA) of 0° was obtained after irradiating the surface of the sample for 30 min with UV-light (365 nm, 2 W m⁻²), confirming the superhydrophilic behaviour. The irradiance loss during the evolution of H₂/O₂ was assessed using a silicon PV cell; the cell, tilted at 45° and equipped with a TiO₂-coated glass window, showed ca. 10% higher irradiance as compared to the uncoated glass window cell for both hydrogen and oxygen evolutions, whereas no significant differences were observed when the cells were vertically placed.