Elucidation of important parameters of BiVO4 responsible for photo-catalytic O2 evolution and insights about the rate of the catalytic process

• Physicochemical parameters affecting the photochemical water oxidation activity.
• (NH4)2CO3 used to influence preferential crystal growth along (0 4 0) facets.
• Mathematical model to estimate more accurately the O2 production rate.
• Morphology optimization of BiVO4 to produce a highly active photocatalyst.

There is an increasing attention in the development of solar fuels due to its potential advantages over current renewable and non-renewable technologies. Solar fuels can be effectively produced by the photocatalytic spitting of water into O2 and H2 using appropriate catalysts. In this work BiVO4 was evaluated as a candidate material for carrying out the water oxidation or O2 evolution half reaction, considered as the limiting step for overall water splitting. In particular, the morphology optimization of this material was targeted as a first approach to produce a highly active photocatalyst. Therefore, a series of hydrothermal samples were prepared and different synthesis parameters were investigated (pH and synthesis time), in order to understand the morphology changes and the resultant differences in O2 production activity. A bubbling reaction system and a recently developed mathematical model were used to estimate more accurately the O2 production rate versus time in every single test performed. The main outcomes of this work indicate that the synthesis procedure utilized here was effective for the preparation of highly organized leaf-like powders with preferential growth towards the (0 4 0) facet when pH 10 and 12 h were used. In addition, we found that crystallite size was the main parameter controlling the O2 production activity of BiVO4 samples, whereas exposure of (0 4 0) was only a secondary parameter. Finally, it was observed that the sacrificial reagent utilized (AgNO3) had a larger impact in the deactivation of samples with a larger exposure of (0 4 0) facet (pH 10, 12 h) as compared to the sample without preferential growth (pH 0).

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