Nanocrystalline Boron-Doped Diamond as a Corrosion Resistant Anode for Water Oxidation via Si Photoelectrodes.

Due to its high sensitivity to corrosion, the use of Si in direct photoelectrochemical water splitting systems that convert solar energy into chemical fuels has been greatly limited. Therefore, the development of low-cost materials resistant to corrosion under oxidizing conditions is an important goal towards a suitable protection of otherwise unstable semiconductors used in photoelectrochemical cells. Here we report on the development of a protective coating based on thin and electrically conductive nanocrystalline boron-doped diamond (BDD) layers. We found that BDD layers protect the underlying Si photoelectrodes over a wide pH range (1-14) in aqueous electrolyte solutions. BDD layer maintains an efficient charge carrier transfer from the underlying silicon to the electrolyte solution. Si|BDD photoelectrodes show no sign of performance degradation after a continuous photoelectrochemical treatment in neutral, acidic and basic electrolytes. Deposition of cobalt phosphate (CoPi) oxygen evolution catalyst onto the BDD layer significantly reduces the overpotential for water oxidation, demonstrating the ability of BDD layers to substitute transparent conductive oxide coatings such as indium tin oxide (ITO) and fluorine-doped tin oxide (FTO) frequently used as protective layers in Si photoelectrodes.