Cobalt phthalocyanine promoted copper catalysts toward enhanced electro reduction of CO2 to C2: synergistic catalysis or tandem catalysis?

The activity and selectivity of electrocatalytic CO2 reduction reaction (CO2RR) to C2 products on metal catalysts can be regulated by molecular surfactants. However, the mechanism behind it remains elusive and debatable. Herein, copper nanowires (Cu NWs) were fabricated and decorated with cobalt phthalocyanine (CoPc). The electronic interaction between the Cu NWs, CoPc, CO2 and CO2RR intermediates were explored by density functional theory (DFT) calculations. It was found that the selectivity and activity of CO2RR towards C2 products on Cu NWs were considerably enhanced from 35.2% to 69.9% by surface decoration of CoPc. DFT calculations revealed that CO2RR can proceed in the interphase between Cu substrate and CoPc, and the CO2RR intermediates could synergistically bond with both Cu and Co metal centre in CuNWs-CoPc, which favours the adsorption of CO2, CO and CO2RR intermediates, thus reducing the free energy for CO-CO coupling towards C2 products. The synergistic interaction was further extended to phthalocyanine (Pc) and other metal phthalocyanine derivatives (MPc), where a relatively weaker synergistic interaction of CO intermediates with MPc and Cu substrate and only a slight enhancement of CO2RR towards C2 products were observed. This study demonstrates a synergistic catalysis pathway for CO2RR, a novel perspective in interpreting the role of CoPc in enhancing the activity and selectivity of CO2RR on Cu NWs, in contrast to the conventional tandem catalysis mechanism.