Water Interaction with Sputter-Deposited Nickel Oxide on n-Si Photoanode: Cryo Photoelectron Spectroscopy on Adsorbed Water in the Frozen Electrolyte Approach

The interaction of water with a magnetron-sputtered nickel oxide thin film on an n-type silicon photoanode is investigated in perspective to oxygen evolution. The substrate was exposed in-situ stepwise to gas phase water up to 10 L at liquid N2 temperature and analyzed via X-ray and UV photoelectron spectroscopy in the so called frozen electrolyte approach. Photoemission of the pristine NiOx layer shows the presence of stoichiometric NiO and Ni2O3 as well as of non-stoichiometric phases. In the monolayer range, molecular and dissociative adsorption is detected assigned to the NiO respective Ni2O3 phase. Initially, the emission of the molecular adsorbed water species interacting with NiO is found at 0.8 eV lower binding energies as compared to water related emission for higher coverages with binding energies commonly assigned to H2O-H2O interaction. In addition to the chemical analysis, the electronic structure of the n-Si/SiOx/NiOx/H2O photoanode is measured and discussed