Silicon sub-oxides as driving force for efficient light-enhanced hydrogen generation on silicon nanowires
in: Materials Today (2020)
We report efficient light-stimulated hydrogen generation from top-down produced highly doped n-type silicon nanowires (SiNWs) decorated with silver nanoparticles (AgNPs) in an oxygen-containing medium under white light irradiation. We observed that SiNWs with AgNPs generate at least 2.5 times more hydrogen than SiNWs without AgNPs. Our results, based on vibrational, UV/VIS, and X-ray spectroscopy studies, strongly suggest that the sidewalls of the SiNWs are covered by silicon sub-oxides (SiOx, x = 1.3–1.7), by up to a thickness of 120 nm, with wide bandgap semiconductor properties that are similar to those of titanium dioxide and remain stable during hydrogen evolution in an oxygen-containing medium for at least 3 h of irradiation. For the first time, an electronic structure model of the SiNWs, based on atomic and electronic structure synchrotron studies, was used to estimate the band gap. We found that the increase in the silicon band gap is related to the energetically beneficial position of the valence band in nanostructured silicon, which renders these promising structures for efficient photocatalysis.