The electrochemical CO2 reduction reaction (CO2RR) attracts a lot of attention as a promising strategy for the conversion of waste CO2 to value-added products. The molecular catalysts with redox-active ligands have shown great activity to reduce CO2 selectively to single products. Moreover, the activity and selectivity of the catalysts can be tuned by modifying the ligand structures. In this presentation, we report our recent studies investigating CO2RR in acetonitrile using a series of Co complexes with the redox-active bis(pyridylmonoimine) ligands (Fig.1a, [Co(BPMI)]: [Co(LL)], [Co(LcycL)], [Co(LCH2L)] and [Co(LCH2CH2L)]). In particular, we show that Co(BPMI) reduces CO2 to formate in acetonitrile solutions with low acid concentrations but shows poor stability upon catalytic turnover. However, the addition of a proton source dramatically enhances the catalyst activity and stability (Fig. 1b), decreasing the rate of turnover-dependent decomposition and increasing the Faradaic efficiency for CO generation. In the presence of 11 M water in acetonitrile, [Co(LL)] reduces CO2 to CO with 100% Faradaic efficiency at -2.15 V vs. Fc/Fc+. Investigations into catalytic activity as a function of ligand structure show that more flexible ligands ([Co(LcycL)], [Co(LCH2L)] and [Co(LCH2CH2L)]) reduce CO2 with less negative onset potentials, but also decreased overall activity. Further electrochemical studies and DFT calculations are used to propose changes in the catalytic mechanism as a function of ligand rigidity and planarity. These studies provide mechanistic insight into a new class of cobalt complexes that show promising activity for electrocatalytic CO2 reduction.

Electrocatalytic CO2 reduction by cobalt nis(pyridylmonoimine) complexes: Effects of ligand structure on catalytic activity

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.