Au/TiO2 Photo(electro)catalysis: The Role of the Au Cocatalyst in Photoelectrochemical Water Splitting and Photocatalytic H2 Evolution

Photoelectrochemical water oxidation and photocatalytic H-2 evolution on planar nanocrystalline Au/TiO2 catalyst film electrodes were studied by combined electrochemistry and online mass spectrometry, allowing for the detection and quantification of the volatile reaction products O-2 and H-2, and thus, by comparison with the photocurrent, to determine selectivities and to map out contributions from side reactions. The catalysts were prepared by a photodeposition method and deposited on conductive glass substrates, and measurements were performed under defined mass transport conditions in a photoelectrochemical thin-layer flow cell. The role of Au nanopartides as cocatalysts in these reactions was explored by varying the Au loading and the light intensity, respectively. On the basis of these data, it is demonstrated that the Au nanopartides affect the above reactions in different ways, by (i) catalyzing the recombination of photogenerated holes and electrons as well as parasitic side reactions (O-2 reduction) in the photoelectrochemical water oxidation reaction, by (ii) affecting the selectivity in that reaction, and by (iii) improving the separation of photogenerated electrons and holes by catalyzing the reaction with sacrificial agents such as methanol, thus enhancing the photocatalytic H-2 evolution reaction.