Boosting CO 2 -to-CO evolution using a bimetallic diketopyrrolopyrrole tethered rhenium bipyridine catalyst

• Published in: Catalysis science & technology Vol. 12; no. 21; pp. 6427 - 6436
• Main Authors: Carr, Cody R., Koenig, Josh D. B., Grant, Michael J., Piers, Warren E., Welch, Gregory C.
• Format: Journal Article
• Language: English
• Published: 31.10.2022
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/D2CY01453J

The use of homogeneous electro- and photo-catalysis involving molecular catalysts offers valuable insight into reaction mechanisms as it relates to the structure–function of these tunable systems. However, supported molecular catalysts ( i.e. , hybrid electrodes) are multiplexed and not fully understood with regards to specific support–catalyst interactions. Even so, it still remains that catalyst activity for CO 2 electroreduction can be tuned by modifying specific functional groups to achieve performance enhancement. Herein, a series of derivatized [Re(bpy)(CO) 3 Cl] catalysts were prepared with molecular structures having variability in both the number of Re-centers and π-conjugated diketopyrrolopyrrole (DPP) units. While tethering [Re(bpy)(CO) 3 Cl] to the DPP unit had a negligible effect on molecular electro- and photo-catalyst properties in organic solvent, the DPP chromophore enabled facile coupling of two [Re(bpy)(CO) 3 Cl] moieties. As a homogeneous species, the bimetallic system effectively doubles the rate of CO 2 -to-CO conversion in the reaction–diffusion layer achieving a TOF CO = 1000 s −1 and FEco% = 98% for up to 6 hours of electrolysis as the two catalytic centers act independently. Immobilization onto carbon hybrid electrodes was found to evolve H 2 , where the ratio of CO : H 2 produced during electrolysis depended on both the molecular structure of the catalyst and the additive(s) to the carbon surface used to suppress the hydrogen evolution reaction (HER). Introducing a commercial DPP-based polymer and/or colloid imprinted carbons (CICs) into carbon paper favours CO evolution from the catalyst by suppressing the HER at carbon and by dispersing the molecular catalyst across a larger more wettable surface to mitigate mass transport limitations. Once again, the bimetallic catalyst has the highest activity in comparison to the monometallic analogues, with a selectivity (FEco% = 53%), activity (TOF = 39 h −1 ), and longevity (active for up to 5 hours) for CO 2 -to-CO evolution from aqueous electrolyte.