Synthesis and Characterization of a Photosensitive Interface for Hydrogen Generation: Chemically Modified p-Type Semiconducting Silicon Photocathodes

p-Si photocathodes functionalized first with an N,N′-dialkyl-4,4′-bipyridinium redox reagent, (PQ2+/+·)surf, and then with a Pt precursor, PtCl6 2-, give significant efficiency (up to 5%) for photoelectrochemical H2generation with 632.8-nm light. Naked p-Si photocathodes give nearly zero efficiency, owing to poor H2evolution kinetics that are improved by the (PQ2+/+·)surf/Pt modification. The mechanism of H2evolution from p-Si/(PQ2+/+·)surf/Pt is first photoexcitation of electrons to the conduction band of Si followed by (PQ2+)surf→ (PQ+·)surfreduction. The dispersion of Pt then catalyzes H2O reduction to give H2and regeneration of (PQ2+)surf. The overall energy conversion efficiency rivals the best direct optical to chemical conversion systems reported to date.