Nanoconfinement promotes CO electroreduction to methanol on a molecular catalyst.

Confining catalysis within a nanospace can effectively regulate intermediate configurations and product distributions. Here, we demonstrate the inner cavity of carbon nanotubes (CNTs) as a nanoreactor to promote the electrochemical conversion of CO to methanol (CHOH). Cobalt phthalocyanine (CoPc) molecules are rationally incorporated into CNTs of varying diameters, exhibiting different CHOH selectivities. CoPc confined within the CNTs is more prone to CHOH production, whereas CoPc located on the exterior primarily facilitates CO formation. Operando spectroelectrochemical measurements and theoretical calculations demonstrate that the nanoconfined environment effectively accumulates CO as an intermediate, introduces structural deformation in CoPc molecules, enhances *CO adsorption on Co sites, and consequently improves CHOH production. This work underscores the significance of local microenvironment in electrocatalysis and presents an approach to enhancing deep-reduction product selectivity in molecular catalysts through nanoconfinement.