The preparation of metal oxides on a conductive substrate has been an important issue for improving photoelectrochemical water splitting efficiency. In this work, a facile synthetic process is reported for single-crystalline WO3 microplates with variable thicknesses grown directly on a fluorine-doped tin oxide substrate followed by an annealing procedure. The WO3 microplate electrode showed an improved photocurrent under 1 sun irradiation (1.9 mA/cm2 at 0.6 V vs Ag/AgCl, 100 mW/cm2) for water oxidation, including a significant enhancement in the visible light region compared to either a nanoparticle or a bulk film electrode. The enhanced water oxidation activity originates from both the single crystallinity with an optimum thickness and the oxygen-deficient characteristic of the WO3 microplates. To improve the photochemical stability, FeOOH electrocatalysts were deposited on the surfaces of the WO3 microplates. The resulting WO3/FeOOH composite electrode showed enhanced stability for water oxidation reactions.

A well-defined WO 3 /Bi 2 S 3 composite comprised of single-crystalline Bi 2 S 3 nanowire (Bi 2 S 3 NW) layers on top of the WO 3 nanoparticles (WO 3 NP) was synthesized via an in situ hydrothermal reaction. The single-crystalline Bi 2 S 3 nanowires were uniformly grown on the surface of the WO 3 nanoparticle layer. This in situ hydrothermal process is also a general route for the synthesis of well-aligned Bi 2 S 3 nanowires on various metal oxide substrates, such as TiO 2 , BiVO 4 , and ZnO. Compared to the sole Bi 2 S 3 electrode, the resulting WO 3 NP/Bi 2 S 3 NW composite showed enhanced photoelectrochemical activity. The origin of this enhanced activity is mainly attributed to the enhancement of charge separation on the Bi 2 S 3 layer, due to the effective photogenerated electron transfer from the Bi 2 S 3 conduction band to that of WO 3 . Furthermore, the single-crystalline longitudinal structure of the Bi 2 S 3 nanowires can provide a direct electrical pathway through a single domain of nanowires.

A pinhole-free BiVO4 electrode was successfully synthesized using an ultrasonic-assisted synthetic method on a conductive substrate. The pinhole-free BiVO4 electrode showed highly improved photoelectrochemical activity for both sulfite oxidation and water oxidation. The blocking recombination processes were examined to clarify the enhanced photoelectrochemical performances.

The addition of water initiates the phase transition of hexagonal CoO to Co(OH) nanocrystals. Inducing the phase transition of h-CoO on various substrates results in efficient chemical bonding between Co(OH) and the substrate. The efficient deposition of Co(OH) is widely applicable for electrochemical and photoelectrochemical water oxidation reactions.