Photocatalytic Membrane for Hydrogen Evolution: Directed Electron and Hole Transfer across Pt–AgInS2–Nafion

A photocatalytically active membrane, designed by embedding AgInS2 semiconductor nanoparticles and a Pt cocatalyst, facilitates a "vectorial" flow of photogenerated electrons and holes in opposite directions. The fabricated Pt–AgInS2–Nafion membrane, when inserted in an H-cell containing 50% ethanol (AgInS2 side) and water (pH = 4, Pt side), produced H2 under visible light irradiation. Photogenerated electrons reduced H+ at the Pt surface to produce H2, while oxidation of ethanol with holes at AgInS2 also produced H2. Back electron transfer at the Pt surface and surface defects within AgInS2 were responsible for the lower H2 yield in the reduction compartment. Remediation of the AgInS2 film with mercaptopropionic acid increased the yield 5–10 times by overcoming the loss of charge carriers at the defect sites. The feasibility of carrying out selective reduction and oxidation processes by directing the flow of charge carriers highlights the usefulness of photocatalytic membranes in solar fuel generation.