Electrochemical Reduction of Carbon Dioxide to Methanol in the Presence of Benzannulated Dihydropyridine Additives

Dihydropyridines (DHPs) have been postulated as active intermediates in the pyridine-mediated electrochemical conversion of CO2 to methanol; however, the ability of isolated DHPs to facilitate methanol production in a fashion similar to that of their parent aromatic N-heterocycles (ANHs) has not been tested. Here, we use bulk electrolysis to show that 1,2- and 1,4-DHPs (1,2-dihydrophenanthridine and 9,10-dihydroacridine) can mediate the substoichiometric electrochemical reduction of CO2 to methanol and formate with Faradaic efficiencies similar to those of the corresponding ANHs at Pt electrodes. 1,2-Dihydrophenanthridine furthermore exhibits improved CO2 reduction activity compared to its parent ANH (phenanthridine) at glassy carbon electrodes. These results provide the first experimental evidence for the participation of DHPs as additives in electrochemical CO2 reduction.