The spatial distribution of cobalt phthalocyanine and copper nanocubes controls the selectivity towards C-2 products in tandem electrocatalytic CO2 reduction

The coupling of CO-generating molecular catalysts with copper electrodes in tandem schemes is a promising strategy to boost the formation of multi-carbon products in the electrocatalytic reduction of CO2. While the spatial distribution of the two components is important, this aspect remains underexplored for molecular-based tandem systems. Herein, we address this knowledge gap by studying tandem catalysts comprising Co-phthalocyanine (CoPc) and Cu nanocubes (Cu-cub). In particular, we identify the importance of the relative spatial distribution of the two components on the performance of the tandem catalyst by preparing CoPc-Cu-cub/C, wherein the CoPc and Cu-cub share an interface, and CoPc-C/Cu-cub, wherein the CoPc is loaded first on carbon black (C) before mixing with the Cu-cub. The electrocatalytic measurements of these two catalysts show that the faradaic efficiency towards C-2 products almost doubles for the CoPc-Cu-cub/C, whereas it decreases by half for the CoPc-C/Cu-cub, compared to the Cu-cub/C. Our results highlight the importance of a direct contact between the CO-generating molecular catalyst and the Cu to promote C-C coupling, which hints at a surface transport mechanism of the CO intermediate between the two components of the tandem catalyst instead of a transfer via CO diffusion in the electrolyte followed by re-adsorption.