Robust Electrocatalytic CO₂ Reduction in Acid Enabled by “Molecularly Charged” Cobalt Phthalocyanine: A Profound Understanding from Electric Double Layer

Abstract

Electrocatalytic CO₂ reduction (eCO₂R) in acid holds promise in renewable electricity-powered CO₂ utilization with high efficiency, but the hydrogen evolution reaction (HER) often prevails and results in a low eCO₂R selectivity. Here, using cobalt phthalocyanine/Ketjen black (CoPc/KB) as the model catalysts, we systematically study the effect of active site density, operational current density, and hydrated cations on the acidic eCO₂R selectivity and decipher it through the componential dynamics of electric double layer (EDL). The optimal CoPc-4/KB demonstrates a near-unity CO Faradaic efficiency from 50 to 400 mA cm^-2 and superb operational stability (>120 h) at 100 mA cm^-2. Aided by <i>in situ</i> Raman and infrared spectroscopies, we reveal that the proper cations establish an electrostatic shield for mitigating bulk H⁺ penetration and mediate the interfacial water structure for suppressing HER. This study should elicit further profound thinking on robust eCO₂R system design from the perspective of multiphasic and dynamic EDL.