Fast annealing fabrication of porous CuWO4photoanode for charge transport in photoelectrochemical water oxidation.

Ternary-phase CuWO4oxide with an electronic band gap of 2.2-2.4 eV is a potential candidate photoanode material for photoelectrochemical (PEC) water splitting. Herein, we present an efficient method to prepare CuWO4film photoanode by combining hydrothermal method and hybrid microwave annealing (HMA) process. In comparison with conventional thermal annealing (CTA), HMA can achieve CuWO4thin film within minutes by using SiC susceptor. When the CuWO4photoanode is prepared by HMA, its PEC water oxidation performance improves from 0.21 to 0.29 mA cm-2at 1.23 VRHEcomparing with the one prepared by CTA. The origin of the enhanced photocurrent was investigated by means of complementary physical characterizations and PEC methods. The results demonstrated that the obtained HMA processed CuWO4photoanode not only exhibited intrinsic porous nanostructures but also abundant surface hydroxyl groups, which facilitated sufficient mass transport and the charge transfer. Our results highlight the application of HMA for the fast fabrication of porous film photo-electrodes without using sacrificial template.

Nanostructure-Preserved Hematite Thin Film for Efficient Solar Water Splitting.

High-temperature annealing above 700 °C improves the activity of photoelectrochemical water oxidation by hematite photoanodes by increasing its crystallinity. Yet, it brings severe agglomeration of nanostructured hematite thin films and deteriorates electrical conductivity of the transparent conducting oxide (TCO) substrate. We report here that the nanostructure of the hematite and the conductivity of TCO could be preserved, while the high crystallinity is attained, by hybrid microwave annealing (HMA) utilizing a graphite susceptor for efficient microwave absorption. Thus, the hematite thin-film photoanodes treated by HMA record 2 times higher water oxidation photocurrents compared to a conventional thermal-annealed photoanode. The enhanced performance can be attributed to the synergistic effect of a smaller feature size of nanostructure-preserved hematite and a good electrical conductivity of TCO. The method could be generally applied to the fabrication of efficient photoelectrodes with small feature sizes and high crystallinity, which have been mutually conflicting requirements with conventional thermal annealing processes.