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 FE_CO 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.

Keywords

charge-switchable ligand / cobalt phthalocyanine / electrochemical CO ₂ reduction reaction / MEA test

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