Do the Hydrogen Evolution Reaction and Oxygen Reduction Reaction Really Need To Be Suppressed in O₂-Tolerant CO₂...

This letter chooses DAE-BPy-CoPor [DAE, 1,2-bis(5'-formyl-2'-methylthien-3'-yl)cyclopentene; BPy, 2,2'-bipyridine-5,5'-dicarbaldehyde; and CoPor, two-dimensional cobalt porphyrin-based covalent organic framework] and Co-TAPP [10,15,20-tetrakis(4-aminophenyl)porphinatocobalt] as two model catalysts to investigate the effect of the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) in the O₂-tolerant CO₂ electroreduction reaction (CO₂RR). Both catalysts have been proven to have CO₂RR activity at a potential range from -0.60 to -1.10 V when CO₂ and O₂ are co-feeding (Zhu, H.-J.; Si, D.-H.; Guo, H.; Chen, Z.; Cao, R.; Huang, Y.-B. Oxygen-tolerant CO₂ electroreduction over covalent organic frameworks via photoswitching control oxygen passivation strategy. Nat. Commun. 2024, 15, 1479, DOI: 10.1038/s41467-024-45959-9). The calculated results by grand canonical density functional theory (GC-DFT) and microkinetic (MK) simulation show that the effect of HER could be categorized into two groups: (1) Positive *H formation energy: HER would have no effect on the turnover frequency (TOF) of the CO₂RR. (2) Negative *H formation energy: HER would also have no effect to the TOF of CO₂RR when the calculated limiting potential for HER is larger than that for CO₂RR. Otherwise, all active sites would be covered by *H and poisoned before CO₂RR can happen. The effect of ORR could be categorized into three types: (1) ORR would have no effect to the TOF of the CO₂RR when ORR happened with the CO₂RR at the same time. (2) ORR is suppressed; the active site is covered by an intermediate state (such as *OH); and the CO₂RR is also suppressed because of the poisoned active site. (3) ORR is suppressed; the active site is not covered; and the TOF of the CO₂RR is not affected.