Oxygen Evolving Photocatalyst Development

Abstract

This chapter details the development and understanding of the extremely efficient photocatalyst, Ag 3 PO 4 . Due to the lack of literature which followed on from the initial investigation (by Yi et al.) exploring the photooxidation of water, it was envisaged that the preparation method was difficult to replicate [1]. This was indeed the case, as results show there was considerable differences in oxygen evolution from water between samples synthesised using different phosphate precursor sources (PO 4 − ), and different solvents. A method was established to fabricate a silver phosphate sample which had a similar roughly spherical morphology, and exhibited a photooxidative ability analogous to that published, using ethanol, AgNO 3 , and Na 2 HPO 4 . Most notably, when the phosphate precursor was changed to H 3 PO 4 , and using a large volume of ethanol was used, it was possible to slow the growth of Ag 3 PO 4 crystals, and retain low index facets, resulting in the production of novel {111} terminated tetrahedral Ag 3 PO 4 crystals. By changing the concentration of H 3 PO 4 , and thus changing the reaction kinetics, it is possible to monitor the growth mechanism of Ag 3 PO 4 crystals from tetrapods to tetrahedrons.Ag 3 PO 4 tetrahedrons demonstrate considerably higher oxygen evolution activity in comparison to roughly spherical particles, and other low index facets. DFT calculations were used to model the surface energy, and the hole mass of Ag 3 PO 4 in different directions. It is concluded that a combination of high surface energy and low hole mass on Ag 3 PO 4 {111} surfaces result in extremely high oxygen evolution from water, with an internal quantum yield of 98 % [2]. IntroductionWater photolysis for H 2 fuel synthesis has the potential to solve both increasing demand of renewable energy and climate change caused by CO 2 emissions. However the search for a solitary low cost semiconductor which has a band gap suitable for an efficient, neutral water splitting reaction under ambient conditions has been met with little success. Nature, however, demonstrates an