Dynamics and Photochemical H₂ Evolution of Dye–NiO Photocathodes with a Biomimetic FeFe-Catalyst

High Resolution Image Download MS PowerPoint Slide Mesoporous NiO films were cosensitized with a coumarin 343 dye and a proton reduction catalyst of the [Fe 2 (CO) 6 (bdt)] (bdt = benzene-1,2-dithiolate) family. Femtosecond ultraviolet–visible transient absorption experiments directly demonstrated subpicosecond hole injection into NiO from excited dyes followed by rapid ( t 50% ∼ 6 ps) reduction of the catalyst on the surface with a ∼70% yield. The reduced catalyst was long-lived (2 μs to 20 ms), which may allow protonation and a second reduction step of the catalyst to occur. A photoelectrochemical device based on this photocathode produced H 2 with a Faradaic efficiency of ∼50%. Fourier transform infrared spectroscopy and gas chromatography experiments demonstrated that the observed device deterioration with time was mainly due to catalyst degradation and desorption from the NiO surface. The insights gained from these mechanistic studies, regarding development of dye–catalyst cosensitized photocathodes, are discussed.