Probing the Synergistic Effects of Mg on CO Reduction Reaction on CoPc by Electrochemical Scanning Tunneling Microscopy.

We report herein the electrochemical scanning tunneling microscopy (ECSTM) study on the synergistic effect of Mg in CO reduction reaction (CORR) catalyzed by cobalt phthalocyanine (CoPc). ECSTM measurement molecularly resolves the self-assembled CoPc monolayer on the Au(111) substrate. In the CO environment, high-contrast species are observed in the adlayer and assigned to the CO adsorption on CoPc. Furthermore, the contrast of the CO-bound complex is higher in Mg-containing electrolytes than in Mg-free electrolytes, indicating the formation of the CoPc-CO-Mg complex. The surface coverage of adsorbed CO is positively correlated with the Mg concentration as the additive in electrolytes up to a plateau of 30.8 ± 2.7% when (Mg) > 30 mM. The potential step experiment indicates the higher CO adsorption dynamics in Mg-containing electrolytes than without Mg. The rate constants of CO adsorption and dissociation in different electrolytes are extracted from the data fitting of statistical results from ECSTM experiments.