Nickel-coated silicon photocathode for water splitting in alkaline electrolytes

Photoelectrochemical (PEC) water splitting is a promising approach to harvest and store solar energy [1]. Silicon has been widely investigated for PEC photoelectrodes due to its suitable band gap (1.12 eV) matching the solar spectrum [2]. Here we investigate employing nickel both as a catalyst and protecting layer of a p-type silicon photocathode for photoelectrochemical hydrogen evolution in basic electrolytes for the first time. The silicon photocathode was made by depositing 15 nm Ti on a p-type silicon wafer followed by 5 nm Ni. The photocathode afforded an onset potential of ∼0.3 V vs. the reversible hydrogen electrode (RHE) in alkaline solution (1 M KOH). The stability of the Ni/Ti/p-Si photocathode showed a 100 mV decay over 12 h in KOH, but the stability was significantly improved when the photocathode was operated in potassium borate buffer solution (pH ≈ 9.5). The electrode surface was found to remain intact after 12 h of continuous operation at a constant current density of 10 mA/cm2 in potassium borate buffer, suggesting that Ni affords good protection of Si based photocathodes in borate buffers.