The solvation environment of molecularly dispersed cobalt phthalocyanine determines methanol selectivity during electrocatalytic CO2 reduction

Abstract

Heterogenized molecular electrocatalysts are a promising group of materials that can electrocatalytically convert waste molecules into higher-value products. However, how the dispersion state of molecules affects the catalytic process is not well understood. Using cobalt phthalocyanine (CoPc) dispersed on carbon nanotubes (CNTs) as a model system, here we show that increasing the direct interaction of the molecular catalyst with cations notably enhances the CO2 reduction reaction. Specifically, molecularly dispersed CoPc on CNTs yields an eightfold increase in methanol selectivity compared with aggregated CoPc on CNTs. In situ spectroscopic studies confirm the presence of two intermediates located at different positions of the double layer. Density functional theory calculations further reveal that CoPc molecules inside the Stern layer are active for methanol production due to the direct interaction with cations. Similar enhancement effects are also observed for other reactions, showing that dispersing molecular catalysts into monomeric states is a general design parameter. Heterogenized molecular catalysts provide a means to add well-defined active sites to electrode surfaces. Here, using cobalt phthalocyanine on carbon nanotubes in cation-mediated CO2 reduction, the mechanism of molecular dispersion and its impact on rate and product selectivity are revealed.