Efficient photoelectrochemical water oxidation over cobalt-phosphate (Co-Pi) catalyst modified BiVO4/1D-WO3 heterojunction electrodes.

We report the design, synthesis and photoelectrochemical characterization of cobalt phosphate (Co-Pi) oxygen evolution catalyst modified heterojunction photoelectrodes consisting of one-dimensional WO3 nanorods (1D-WO3) and highly porous BiVO4 layers. The 1D-WO3 nanorods were prepared by the decomposition of the tetrabutylammonium decatungstate precursor in the presence of poly(ethylene glycol) as a binding agent. The porous BiVO4 layers were spray deposited using a surfactant assisted metal-organic decomposition method. The Co-Pi oxygen evolution catalyst was deposited onto the BiVO4/1D-WO3/FTO heterojunction electrode using a photoassisted electrodeposition method. The Co-Pi catalyst modified heterojunction electrodes exhibited a sustained enhancement in the photocurrent compared to the unmodified BiVO4/1D-WO3/FTO heterojunction electrodes. The improved photoelectrochemical properties profited from the enhanced charge carrier separation achieved through the integration of highly porous BiVO4 layers on top of 1D-WO3 nanorods and from the superior kinetics due to the presence of the Co-Pi oxygen evolution catalyst on top of BiVO4/1D-WO3/FTO heterojunction electrodes.

BiVO(4)/CuWO(4) heterojunction photoanodes for efficient solar driven water oxidation.

BiVO(4)/CuWO(4) heterojunction electrodes were prepared using spray deposition of a highly porous bismuth vanadate film onto the surface of an electrodeposited three dimensional network connected copper tungstate. Bilayer BiVO(4)/CuWO(4)/fluorine doped tin oxide glass (FTO) electrodes demonstrated higher photocurrent magnitudes than either with BiVO(4)/FTO or CuWO(4)/FTO electrodes in 1.0 M Na(2)SO(4) electrolyte buffered at pH 7. The photocurrent is enhanced by the formation of the heterojunction that aids charge carrier collection brought about by the band edge offsets. When the pH 7 buffered electrolytes contained 1.0 M bicarbonate is employed instead of 1.0 M sulfate, the charge transfer resistance was decreased. This led to nearly 1.8 times the photocurrent density at 1.0 V vs. Ag/AgCl. The photocurrent was stable over 24 hours in bicarbonate electrolyte.

Light induced water oxidation on cobalt-phosphate (Co-Pi) catalyst modified semi-transparent, porous SiO2-BiVO4 electrodes.

A facile and simple procedure for the synthesis of semi-transparent and porous SiO2-BiVO4 electrodes is reported. The method involves a surfactant assisted metal-organic decomposition at 500 °C. An earth abundant oxygen evolution catalyst (OEC), cobalt phosphate (Co-Pi), has been used to modify the SiO2-BiVO4 electrode by electrodeposition (ED) and photoassisted electrodeposition (PED) methods. Modified electrodes by these two methods have been examined for light induced water oxidation and compared to the unmodified SiO2-BiVO4 electrodes by various photoelectrochemical techniques. The PED method was a more effective method of OEC preparation than the ED method as evidenced by an increased photocurrent magnitude during photocurrent-potential (I-V) characterizations. Electrode surfaces catalyzed by PED exhibited a very large cathodic shift (∼420 mV) in the onset potential for water oxidation. The chopped-light I-V measurements performed at different intervals over 24-hour extended testing under illumination and applied bias conditions show a fair photostability for PED Co-Pi modified SiO2-BiVO4.