Dynamic Photoelectrochemical Device Using an Electrolyte-Permeable NiOx/SiO2/Si Photocathode with an Open-Circuit Potential of 0.75 V

As a thermodynamic driving force obtained from sunlight, the open-circuit potential (OCP) in photo-electrochemical cells is typically limited by the photovoltage (V-ph). In this work, we establish that the OCP can exceed the value of V-ph when an electrolyte-permeable NiOx thin film is employed as an electrocatalyst in a Si photocathode. The built-in potential developed at the NiOx/Si junction is adjusted in situ according to the progress of the NiOx hydration for the hydrogen evolution reaction (HER). As a result of decoupling of the OCP from V-ph, a high OCP value of 0.75 V (vs reversible hydrogen electrode) is obtained after 1 h operation of HER in an alkaline electrolyte (pH = 14), thus outperforming the highest value (0.64 V) reported to date with conventional Si photoelectrodes.