Robust Electrocatalytic CO 2 Reduction in Acid Enabled by "Molecularly Charged" Cobalt Phthalocyanine: A Profound Understanding from Electric Double Layer.

Electrocatalytic CO 2 reduction (eCO 2 R) in acid holds promise in renewable electricity-powered CO 2 utilization with high efficiency, but the hydrogen evolution reaction (HER) often prevails and results in a low eCO 2 R 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 eCO 2 R 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 in situ 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 eCO 2 R system design from the perspective of multiphasic and dynamic EDL.