Tuning the Photoelectrocatalytic Hydrogen Evolution of Pt-Decorated Silicon Photocathodes by the Temperature and Time of Electroless Pt Deposition

The electroless deposition of Pt nanoparticles (NPs) on hydrogen-terminated silicon (H–Si) surfaces is studied as a function of the temperature and the immersion time. It is demonstrated that isolated Pt structures can be produced at all investigated temperatures (between 22 and 75 °C) for short deposition times, typically within 1–10 min if the temperature is 45 °C or less than 5 min at 75 °C. For longer times, dendritic metal structures start to grow, ultimately leading to highly rough interconnected Pt networks. Upon increasing the temperature from 22 to 75 °C and for an immersion time of 5 min, the average size of the observed Pt NPs monotonously increases from 120 to 250 nm, and their number density calculated using scanning electron microscopy decreases from (4.5 ± 1.0) × 10 8 to (2.0 ± 0.5) × 10 8 Pt NPs cm –2 . The impact of both the morphology and the distribution of the Pt NPs on the photoelectrocatalytic activity of the resulting metallized photocathodes is then analyzed. Pt deposited at 45 °C for 5 min yields photocathodes with the best electrocatalytic activity for the hydrogen evolution reaction. Under illumination at 33 mW cm –2, this optimized photoelectrode shows a fill factor of 45%, an efficiency (η) of 9.7%, and a short-circuit current density (| J sc |) at 0 V versus a reversible hydrogen electrode of 15.5 mA cm –2 .