Fabrication of Bendable BiVO4-Based Photoelectrodes for Efficient Photoelectrochemical Water Splitting

Abstract

Unlike planar photoelectrodes, bendable and malleable photoelectrodes extend their application to mechanical flexibility beyond conventional rigid structures, which have garnered new attention in the field of photoelectrochemical water splitting. A bendable metal (Hastelloy), which has both bendability and compatibility with various oxide layers, allows high-temperature processes for crystallization; therefore, it is far superior as a substrate than a conventional flexible polymer. Besides, a flexible-yttria stabilized zirconia (FYSZ) has a highly stable thermal resistance and chemical compatibility enough to deposit oxide layers through the high thermal process such as pulsed laser deposition (PLD). In this thesis, we fabricate bendable BiVO4 crystalline thin films on the metal substrates by employing template layers (SrRuO3/SrTiO3) to reduce the structural misfits between BiVO4 and the substrate, and on the flexible oxide substrate. For the thin films on the metal substrate, the crystallinities were verified through X-ray diffraction and transmission electron microscopy, and photocatalytic performances were examined. The crystallinity of BiVO4 was significantly improved by utilizing similar lattice constants and affinities between BiVO4 and the oxide template layers. We also formed a type-II heterojunction by adding a WO3 layer which complements the charge separation and charge transfer as a photoanode. The photocurrent densities of tensile-bent BiVO4/WO3 thin films with a bending radius of 10 mm are comparable to those of pristine BiVO4/WO3 thin films in various aqueous electrolytes. Moreover, photostability tests showed that the tensile-bent crystalline photoanodes retained 90% of their initial photocurrent density after 24 h, which proved their exceptional durability. Then, we applied same the strategy to the FYSZ substrate by inserting the WO layer through optimization of its thickness. Our work demonstrates that the bendable photoelectrodes with crystallinity hold great potential in terms of device a structure for solar-driven water splitting.