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 CO 2 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 CO 2 to methanol and formate with Faradaic efficiencies similar to those of the corresponding ANHs at Pt electrodes. 1,2-Dihydrophenanthridine furthermore exhibits improved CO 2 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 CO 2 reduction.