The process of solar water splitting and photocatalytic CO2 reduction is limited by water oxidation at the anode due to the sluggish oxygen evolution kinetics. Bismuth vanadate compounds (BVO) are promising for water oxidation. However, the relatively short diffusion length and surface recombination still limit the performance of BVO anodes. In this work, several strategies have been applied in order to increase strongly the photocurrent of BVO. The strategies can be distinguished by improving local charge separation, reducing distances for diffusion of photo-generated charge carriers to reactive sites, reducing surface recombination by passivation without losses of activity, optimizing absorption by control of light scattering and layer thickness of the photocatalyst and minimizing transport losses in the photocatalytic system. For this purpose, a passivated porous nanocomposite of monoclinic BiVO4 and monoclinic Bi4V2O11 has been developed and passivated with cobalt phosphate (Co-Pi). Photo-electrochemical measurements were carried out and a photocurrent density of bare BVO of 2.2±0.2 mA/cm2 at 1.23 V vs. RHE was achieved. To our knowledge, this is the highest value reached on bare BVO electrodes to date. The photocurrent density was further increased by 2.3 times after deposition of the Co-Pi. The monoclinic BiVO4 and monoclinic Bi4V2O11 were compared by density functional theory and electronic properties of BVO and BVO/Co-Pi were characterized by spectral- and transient dependent surface photovoltage and photocurrent measurements in air and aqueous electrolyte, respectively. The high photocurrent of BVO can be attributed to local charge separation on large areas due to the mixed phases of monoclinic BiVO4 and monoclinic Bi4V2O11. The enhancement of the photocurrent for BVO/Co-Pi is caused by improved surface passivation whereas the charge transfer from BVO into Co-Pi is not the rate limiting step. It seems that a barrier at the Co-Pi / electrolyte interface limits the charge transfer and therefore the OER.

Passivated porous m-BiVO4/m-Bi4V2O11 nanocomposite for highly efficient water oxidation

256th National Meeting (2018)

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