Potassium Hydroxide Mixed with Lithium Hydroxide: An Advanced Electrolyte for Oxygen Evolution Reaction

Photoelectrochemical (PEC) water splitting devices have attracted lots of interest in academia and industry as an environmentally friendly approach to generate clean hydrogen fuels. However, the stability of the PEC water splitting devices is still a huge challenge in this field. Herein, the effect of different alkaline electrolytes on 5 nm Ni/SiOX/n-Si/Ti photoanodes by PEC, chemical, and morphologic characterizations is studied. Although the photoanode at 1 m potassium hydroxide (KOH) (pH 14) shows low onset potential, it starts to decay after ≈141 h PEC tests due to the formation of pinholes. However, PEC tests in the mixture electrolyte of KOH and lithium hydroxide (LiOH) (pH 12.5) or the mixture electrolyte of K-borate and Li-borate (pH 9.5) show a stability of >264 h due to the presence of lithium ions. Compared with the measurement at pH 9.5 with the Li ions electrolyte, a 5 nm Ni/SiOX/n-Si/Ti photoanode tested at pH 12.5 shows a lower onset potential of 1.254 V versus that with the reversible hydrogen electrode (RHE) for water oxidation, indicating an overpotential of 0.024 V. The pH 12.5 solution made of KOH and LiOH can be an attractive electrolyte to enhance the activity and lifetime of silicon-based photoanodes for PEC water splitting devices.