Charge-switchable ligand ameliorated cobalt polyphthalocyanine polymers for high-current-density electrocatalytic CO2 reduction

Abstract

Metallic phthalocyanines are promising electrocatalysts for CO2 reduction reaction (CO2RR). However, their catalytic activity and stability (especially under high potential) are still unsatisfactory. Herein, we synthesized a covalent organic polymer (COP-CoPc) by introducing charge-switchable viologen ligands into cobalt phthalocyanine (CoPc). The COP-CoPc exhibits great activity for CO2RR, including a high Faradaic efficiency over a wide potential window and the highest CO partial current density among all ligand-tuned phthalocyanine catalysts reported in the H-type cell. Particularly, COP-CoPc also shows great potential for practical applications, for example, a FECO of >95% is realized at a large current density of 150 mA/cm2 in a two-electrode membrane electrode assembly reactor. Ex situ and in situ X-ray absorption fine structure spectroscopy measurements and theory calculations reveal that when the charge-switchable viologen ligands switch to neutral-state ones, they can act as electron donors to enrich the electron density of Co centers in COP-CoPc and enhance the desorption of *CO, thus improving the CO selectivity. Moreover, the excellent reversible redox capability of viologen ligands and the increased Co–N bonding strength in the Co–N4 sites enable COP-CoPc to possess outstanding stability under elevated potentials and currents, enriching the knowledge of charge-switchable ligands tailored CO2RR performance.