Selenorhodamine-Sensitized CuAlO₂ Photocathodes That Reduce Protons to Hydrogen under Visible Illumination

Abstract

We prepared dye-sensitized photocathodes (DSPs) by attaching a phosphonic acid-functionalized selenorhodamine dye (3-SeP) to delafossite CuAlO 2 thin films. The dye 3-SeP adsorbed to CuAlO 2 as a mixture of monomeric and H-aggregated dyes, broadening the dye's absorption profile and enhancing the absorption of visible light. Upon exposure to solvent, 3-SeP persisted on CuAlO 2 to a much greater extent than analogous selenorhodamines either bearing a terminal carboxylic acid group or lacking a surface-anchoring group. Transient photovoltage measurements revealed a long-lived positive shift of the Fermi level of 3-SeP/CuAlO 2 -on-FTO electrodes, consistent with a mechanism in which holes are transferred from photoexcited 3-SeP to CuAlO 2 . In linear sweep voltammetry measurements under chopped white-light illumination, 3-SeP/CuAlO 2 -on-FTO electrodes exhibited 7to-8-fold greater reductive photocurrents than unfunctionalized CuAlO 2 -on-FTO electrodes, revealing that excited-state hole transfer and the resulting separation of photogenerated holes from electrons could be exploited to promote reduction and oxidation half reactions. In prolonged-illumination chronocoulometry experiments, 3-SeP/CuAlO 2 -on-FTO electrodes, in conjunction with a Co(III) reduction cocatalyst and triethanolamine as a sacrificial electron donor, reduced H + to H 2 with Faradaic efficiency of 43 ± 27%. Our results highlight the potential of selenorhodamine-sensitized Cu(I) delafossites as DSPs for redox photocatalysis and the production of solar fuels.