Charge redistribution and extraction in photocatalytically synthesized Au-ZnO nanohybrids

ZnO is a promising catalyst for hydrogen and oxygen production due to the position of the conduction and valence bands. Nevertheless, there are some limitations to the efficiency due to its n-type character. Once in contact with the electrolyte, an extraction barrier for electrons is formed. The purpose of this work was to create an extraction site for electrons by synthesizing small pyramidally shaped ZnO nanocrystals (similar to 10 nm), which consist of a predefined site for the growth of a gold particle at the tip. Photoelectrochemical deposition of gold on ZnO was performed to yield the hybrid structure. Photoluminescence (PL) studies of the relative change of intensities of band gap versus defect state relaxation showed electron transfer from the conduction band of ZnO to Au. Using cyclic voltammetry, Au-mediated charge extraction from Au-ZnO hybrids was demonstrated, which circumvents the electron extraction barrier in ZnO. Thus, this work demonstrates the nanoscale design of hybrid structures for photocatalytic applications.