High-efficiency acidic CO2-to-CO conversion enabled by a pseudocapacitive cobalt-phthalocyanine polymer

Electrochemical CO 2 reduction (ECR) in acidic media presents a viable strategy to overcome carbonate formation and improve CO 2 utilization. However, the development of efficient cobalt-phthalocyanine (CoPc)-based catalysts for acidic ECR remains challenging due to competing hydrogen evolution. Here, we design a redox-active CoPc polymer (CoPc-PEDOT) via in-situ electropolymerization on carbon nanotube/carbon cloth electrodes, enabling dual p- and n-doping behavior and efficient charge transfer for multi-electron catalysis. In alkaline flow cells, CoPc-PEDOT achieves near-unity CO selectivity at high current densities. More importantly, under strongly acidic conditions (pH ∼1.6), it maintains >90% CO Faradaic efficiency across a wide operational range, surpassing most molecular catalysts. The ultrathin, well-dispersed polymer structure ensures long-term stability (>220 h) while mitigating agglomeration. This work demonstrates electropolymerized CoPc-PEDOT as a scalable and robust catalyst for efficient ECR in both alkaline and acidic environments, advancing practical CO 2 conversion technologies. During electrochemical CO 2 reduction, the intrinsic pseudocapacitive charge storage of the redox-active CoN 4 site progressively suppresses the hydrogen evolution reaction and steers the reduction pathway toward CO production. • Polymer electrocatalyst is prepared via In-situ electropolymerization. • Polymers of cobalt (II)-phthalocyanine shows high pseudocapacitance. • In alkaline flow cells, near-unity CO Faradaic efficiency is achieved in electrochemical CO 2 reduction. • It maintains exceptional selectivity and stability in electrochemical CO 2 reduction under strong acid.