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

• Published in: ACS applied engineering materials 2024-08, Vol.2 (8), p.2190-2200
• Main Authors: Clark, Michael D., Schmidt, Zachery A., Lapp, Gregory J., Dierolf, Hannah R., Liwosz, Kacie, Watson, David F.
• Format: Article
• Language: English
• ISSN: 2771-9545; 2771-9545
• DOI: 10.1021/acsaenm.4c00368

We prepared dye-sensitized photocathodes (DSPs) by attaching a phosphonic acid-functionalized selenorhodamine dye (3-SeP) to delafossite CuAlO2 thin films. The dye 3-SeP adsorbed to CuAlO2 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 CuAlO2 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/CuAlO2-on-FTO electrodes, consistent with a mechanism in which holes are transferred from photoexcited 3-SeP to CuAlO2. In linear sweep voltammetry measurements under chopped white-light illumination, 3-SeP/CuAlO2-on-FTO electrodes exhibited 7-to-8-fold greater reductive photocurrents than unfunctionalized CuAlO2-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/CuAlO2-on-FTO electrodes, in conjunction with a Co­(III) reduction cocatalyst and triethanolamine as a sacrificial electron donor, reduced H+ to H2 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.