Remarkable improvements in the performance and stability of Si photoanodes adopting nanocrystalline NiOx electrocatalyst and stoichiometric SiO2 protection

Abstract Silicon photoanodes have been studied intensively for efficient photoelectrochemical (PEC)-mediated catalysis of the oxygen evolution reaction, but their performance and stability still need to be improved before they can be applied practically. Here, we demonstrate that the porous, nanocrystalline NiO x electrocatalyst integrated with a thermally-grown SiO 2 protection layer results in unexpectedly high PEC performances as well as long-term stability in Si photoanodes. The porous structure of NiO x and its large active area in contact to the electrolyte improves electrocatalytic activity and greatly reduces the kinetic overpotential required for charge transfer. In addition, the redox-active surface contributed by nanocrystalline nature of NiO x results in the accumulation of charges during the PEC reaction, predominantly affecting the interface energetics of NiO x /n-Si junctions. This feature enables a high open circuit potential of ~0.6 V even without p-n junctions. Stoichiometric SiO 2 affords strong electrochemical corrosion resistance during the PEC water oxidation in 1 M KOH electrolyte, in contrast to the wet chemical-grown, nonstoichiometric SiO x . The porous and nanocrystalline NiO x and stoichiometric SiO 2 incorporated in the n-Si photoanode ensures continuous operation for 100 h at high performance. These results can help inform a new way to design a high performance Si photoanodes with long-term stability.