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

Abstract

• Physicochemical parameters affecting the photochemical water oxidation activity. • (NH 4 ) 2 CO 3 used to influence preferential crystal growth along (0 4 0) facets. • Mathematical model to estimate more accurately the O 2 production rate. • Morphology optimization of BiVO 4 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 O 2 and H 2 using appropriate catalysts. In this work BiVO 4 was evaluated as a candidate material for carrying out the water oxidation or O 2 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 O 2 production activity. A bubbling reaction system and a recently developed mathematical model were used to estimate more accurately the O 2 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 O 2 production activity of BiVO 4 samples, whereas exposure of (0 4 0) was only a secondary parameter. Finally, it was observed that the sacrificial reagent utilized (AgNO 3 ) 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).