Polymeric Unimolecular CO Dehydrogenase Mimic with both Inner and Outer Spheres for Enhanced Photocatalytic CO2 Reduction in Aqueous Solution.

ABSTRACT

Inspired by carbon monoxide dehydrogenase (CODH), mimicking its inner and outer spheres is a promising strategy in CO2 reduction catalyst design. However, artificial CODH-like catalysts are generally limited to the inner sphere effect and only applicable in organic solvents or for electrocatalysis. Herein, an aqueous CODH mimic with both inner and outer spheres for photocatalysis is reported. In this polymeric unimolecular catalyst, the inner sphere is composed of cobalt porphyrin with four appended amido groups and the outer sphere consists of four poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) arms. Upon visible light irradiation (λ >420 nm), the as-prepared catalyst exhibits a turnover number (TONCO ) of 1731.2 in the reduction of CO2 into CO, which is comparable to most reported molecular catalysts in aqueous solution. The mechanism studies indicate that, in this water-dispersible and structurally well-defined CODH mimic, the cobalt porphyrin core serves as the catalysis center and the amido groups function as hydrogen-bonding pillars helping to stabilize the CO2 adduct intermediate, whereas the PDMAEMA shell renders both water solubility and a CO2 reservoir through reversibly capturing of CO2 . The present work has clarified the significance of coordination sphere effects for improving the aqueous photocatalytic CO2 reduction performance of CODH mimics.