Inversed Cation Size Effects on Methanol Formations From CO ₂ Electroreduction by Immobilized Cobalt Phthalocyanine

ABSTRACT The electrocatalytic reduction of CO 2 to methanol offers a compelling pathway for sustainable fuel synthesis, wherein cations in the electric double layer (EDL) exert a substantial influence on catalytic performance. Although cation modulation of CO 2 ‐to‐CO conversion has been extensively documented, its influence on downstream reduction pathways toward CH 3 OH has received comparatively little attention. Using multiscale simulation, we establish that methanol synthesis over immobilized cobalt phthalocyanine (CoPc) is kinetically governed by the final proton transfer (*CH 2 OH + H 2 O → * + CH 3 OH + OH − ). The EDL environment substantially accelerates this rate‐determining step (RDS). Moreover, the activity exhibits a clear dependence on cation radius, following the trend Li + > Na + > K + > Cs + , with smaller cations systematically lowering the proton transfer barrier. This trend stems from the enhanced accessibility of smaller cations to the transition state, where Li + achieves tighter coordination than Cs + , conferring greater electrostatic stabilization and a correspondingly reduced barrier. Conversely, smaller cations attenuate the hydrogen‐bond network surrounding OH − , potentially impeding OH − transfer from the catalyst surface to the bulk electrolyte. These multifaceted cation effects underscore the complex interplay between kinetic promotion and mass transfer limitations in electrocatalytic systems.