Bendable BiVO4-Based Photoanodes on a Metal Substrate Realized through Template Engineering for Photoelectrochemical Water Splitting.

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. In this study, 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. 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 film 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. Our work demonstrates that the bendable photoelectrodes with crystallinity hold great potential in terms of device structure for solar-driven water splitting.

Micro-Structural Properties of YBa2Cu3O(7-x)/ZnO Nanorods on SrTiO3.

We examined the local structural and the interfacial properties of YBa2Cu3O(7-x) (YBCO)/ZnO nanorods on SrTiO3 (STO) substrates using various measurements. Vertically aligned ZnO nanorods were synthesized on STO substrates using a catalyst-free metal-organic chemical vapor deposition. YBCO films were deposited ex-situ on the ZnO nanorods/STO templates using a DC magnetron sputtering deposition. X-ray diffraction revealed that the YBCO films were crystallized along their c-axes on the ZnO nanorods/STO templates. Transmission electron microscopy measurements demonstrated that YBCO filled the space between ZnO nanorods and that both interfaces of YBCO/ZnO nanorods and ZnO nanorods/STO were quite clean with no disorder. Polarization-dependent extended X-ray absorption fine structure measurements at the Cu K edge showed extra disorder in the CuO2 planes of YBCO/ZnO nanorods/STO, compared with that of YBCO/STO. The superconductivity transition temperature (T(c)) of YBCO/ZnO nanorods/STO was approximately 50 K whereas that of YBCO/STO was 93 K. The decrease of T(c) of YBCO/ZnO nanorods/STO was ascribed to the structural disorder of CuO2 planes as well as grain boundaries in the YBCO films.