Enhanced plasmon-mediated photo-assisted hydrogen evolution on silicon by interfacial modification

Abstract

The superior catalytic activity of Pt towards proton reduction suggests application of Pt also in device architectures where hydrogen is produced by light-generated charge carriers. Large optical absorption cross sections of Pt nanoparticles, however, turn the attention to potential substitutes for Pt such as Au with more advantageous optical properties. In order to approach a functional Si/Au photocathode for hydrogen evolution, we report here on modifications of the Si–Au interface which result in improvements of charge transfer kinetics and optical properties of the device. After current-less deposition of Au nanoparticles onto silicon, these improvements are realized by chemical oxide exchange reactions at the Si/SiO_2/Au interface, i.e., dynamic etching of SiO_2 and re-oxidation of Si in NH_4F (40%). A chemical reaction route for the reformation of the SiO_2 layer in the presence of Au and the aqueous NH_4F solution is discussed. Simultaneous to the modification of the Si/SiO_2 interface, small Au nanoparticles form larger clusters with enhanced effective scattering cross sections. Thereby, improved electronic interface properties and enhanced forward scattering of light increase the saturation photocurrent density by about 9% from 32 to 35 mA cm^(−2). Improved stability of the device in acidic electrolytes, near the thermodynamic potential for evolution of hydrogen, is furthermore discussed.