XPS-CHARACTERIZATION OF HYDROGEN-EVOLVING PLATINUM-COATED P-SILICON PHOTOELECTRODES

To study the morphology of the Pt system on p-Si for hydrogen-evolving photoelectrodes and consequently their related activity in detail, Pt is deposited on monocrystalline silicon by physical vapour deposition (PVD) methods and a photo-assisted electrochemical technique. X-ray p hotoelectron spectroscopy (XPS) is used as an analytical tool to revea l atomic concentration and chemical binding states of species in the s ystem. Reactions and intermixing of the matrix elements are deduced fr om depth profiles. Correlation to current density-potential (i-U) char acteristics reveal that only ultra-thin Pt submonolayers formed by PVD processes or microscopic islands formed by the electrochemical deposi tion process affect the hydrogen evolution reaction at the photocathod es. XPS analyses are also employed to characterize the degradation mec hanisms of the photocathode during long-term operation in various elec trolytes. Soluble silicates are formed on photocathodes operating in a lkaline electrolyte, which led to a degradation due to ablation of Pt islands via the corrosion of silicon from the edge of the Pt islands.