Nanostructural dependence of hydrogen production in silicon photocathodes

Hydrogen production from solar power energy is an important energy and environmental issue. Silicon (Si) has been widely studied as a photocathode for hydrogen production from water splitting. In this study, the electrochemical behavior of a Si photocathode for water splitting is highly dependent on its nanostructure. The optimum nanostructure of a Si photocathode exhibits an enhanced photocurrent and a lower overpotential compared to the planar bulk Si. The limiting current density of nanostructured Si is 1.58 times greater than that of the planar structure for p-type Si/aqueous electrolyte solution. Nanostructured Si without any catalyst notably produced a current density of −10.65 mA cm−2 under Air Mass 1.5 Global conditions with a light intensity of 100 mW cm−2 at the reversible potential vs. reversible hydrogen electrode, which is about 43 times higher than that of the untreated Si structure. The solar-to-hydrogen conversion efficiency of the optimized Si nanowire without depositing any catalyst has reached up to about 70% of the efficiency of planar Si decorated with Pt. This significant enhancement achieved in this study emphasizes the importance of a controlled nanostructure in the development of highly efficient photoelectrochemical devices for hydrogen production.