Cobalt-N4 macrocyclic complexes for heterogeneous electrocatalysis of the CO2 reduction reaction

Metal-N4 (M-N4) macrocyclic complexes are interesting electrocatalysts due to their well-defined structures and rich molecular tuning. Among them, metal phthalocyanines have been widely studied for the carbon dioxide reduction reaction (CO2RR) in heterogeneous systems and demonstrated good electrocatalytic performance. However, other complexes like metal corroles and metal porphyrins are much less explored, and often show inferior performances. In this study, three cobalt macrocyclic complexes, cobalt phthalocyanine, cobalt meso-tetraphenylporphyrin, and cobalt meso-triphenylcorrole (CoPc, CoTPP and CoTPC) are investigated in heterogeneous electrocatalysis of CO2RR. Although CoPc/carbon nanotube (CNT) hybrid exhibits high electrocatalytic activity, CNT hybridization does not work for CoTPC and CoTPP that hold weak interactions with CNTs. By the drop-dry method with a high molecular loading of 5.4 × 10–7 mol cm–2, CoTPC and CoTPP could deliver appreciable electrode activities. Poly(4-vinylpyridine) (PVP) introduction is further demonstrated as a facile method to afford enhanced activities for CoTPP at low molecular loadings through enhancing molecule-substrate interactions. The partial current density of carbon monoxide for CoTPP+CNT/PVP is around 8 times higher than the sample without PVP at –0.67 V versus reversible hydrogen electrode. This work provides solutions to enhance the electrode activities of molecular electrocatalysts with weak substrate interactions in heterogeneous systems.