Dirhodium(II,II)/NiO Photocathode for Photoelectrocatalytic Hydrogen Evolution with Red Light

Abstract

A new Rh2(II,II) dimer has been synthesized and anchored onto a NiO photocathode. The dirhodium complex acts as both the sensitizer to inject holes into NiO and as catalyst for the production of hydrogen. The single-molecule design circumvents limitations of the conventional multicomponent approach with separate sensitizer and catalyst, thus simplifying the hydrogen production pathway and reducing energy losses associated with additional intermolecular charge transfer steps. The Rh2(II,II) complex absorbs strongly from the ultraviolet throughout the visible range and tails into the near-IR to ∼800 nm, permitting absorption of a significantly greater portion of the solar irradiance as compared to traditional dyes used in dye-sensitized solar cells and photoelectrosynthesis cells. The irradiation of the Rh2–NiO photoelectrode with 655 nm light (53 mW cm–2) results in a photocurrent that reaches 52 μA cm–2 at −0.2 V vs Ag/AgCl in the presence of p-toluenesulfonic acid (0.1 M), with Faradaic efficiencies of H2 production up to 85 ± 5% after 2.5 h without photoelectrode degradation. This work presents the first single-molecule photocatalyst, acting as both the light absorber and catalytic center on NiO, able to generate hydrogen from acidic solutions with red light when anchored to a p-type semiconductor, providing a promising new system for solar fuel production.

Unraveling the Mechanisms of Beneficial Cu-Doping of NiO-Based Photocathodes

“…The electronic energy levels and chemical stability make NiO a promising p-type semiconductor for application in dye-sensitized photocathodes . Despite the numerous strategies investigated, with particular focus on the design of new dyes and catalysts, improving the performance of NiO-based photocathodes remains a challenge. − Light-induced ultrafast hole injection from the dye into NiO should be followed by electron transfer from the dye to the catalyst, enabling the catalytic reduction reaction and restoring the light-absorbing capability of the dye. However, the photocathode performance is in general limited by fast charge recombination from NiO back to the dye radical anion, occurring normally even prior to the vital electron transfer step from the dye to the catalyst .…”

Red Light-Based Dual Photoredox Strategy Resembling the Z-Scheme of Natural Photosynthesis

“…The combination of [Cu(dap) 2 ] + and DCA complements and expands the known photochemical applications of these two individual components when used separately. 68 , 77 , 83 , 89 , 117 , 159 − 167 Red light-driven applications play important roles in other important contexts, for example, hydrogen production, 47 , 48 , 168 , 169 medical applications, 158 , 169 − 173 and polymerizations. 174 − 178 Now, red light as well as multiphoton excitation-based mechanisms seem to become of increasing interest for synthetic organic photoredox chemistry, 50 , 126 , 179 − 181 and we hope the insights gained from our work will be useful in that greater context.…”

Understanding Ir(III) Photocatalyst Structure–Activity Relationships: A Highly Parallelized Study of Light-Driven Metal Reduction Processes

“…Light absorption rapidly generates exceptionally reactive excited state species capable of converting photons into chemical energy for solar energy conversion, organic transformations, micropollutant degradation, CO 2 reduction, and photodynamic therapy applications while circumventing the need for harsh reaction conditions or reagents. − Following the example of nature, photochemical reactions can be initiated through absorption of visible light by a transition metal complex acting as a photocatalyst (PC). After Franck–Condon absorption upon illumination, internal conversion (IC) and, in some cases, intersystem crossing (ISC) results in the lowest energy excited state configuration (PC*).…”