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[Display omitted] • Surface selenation strategy is performed on metal cocatalysts for enhanced CO 2 -to-CH 3 OH conversion. • Stacked photocatalysts with metal core sandwiched between semiconductor and selenated shell are fabricated. • Metal core accelerates the migration of photoelectrons from semiconductor to selenated shell. • Selenated shell decreases the energy barriers for CH 3 OH production and inhibits the side H 2 evolution. Solar-driven reduction of CO 2 and H 2 O to methanol is highly desirable owing to multiple advantages of green and renewable liquid fuels, whose efficiency and selectivity are restricted by sluggish charge kinetics and unfavorable surface reaction dynamics in conversional semiconductor photocatalysts. This study proposes a surface selenation strategy on metal cocatalysts to improve the photocatalytic performance in CO 2 -to-CH 3 OH conversion. Electron microscopy observation shows the formation of a stacked structure with crystalline Rh core sandwiched between semiconductor substrate and amorphous selenated Rh (RhSe) shell after the treatment. The combination of experimental characterizations with theoretical simulations reveals that Rh core smoothens the migration of photoelectrons from light-harvesting semiconductor to RhSe shell, while the selenation of Rh shell not only reduces the rate-limiting barriers required for CH 3 OH production, but also inhibits the occurrence of side H 2 evolution. Enabled by such a design, significantly enhanced photocatalytic activities (41.2 μmol g cat -1 h-1) and selectivties (91.2%) in CH 3 OH generation are achieved by the Rh@RhSe semi-core-shell cocatalysts, 12.7 and 6.4 times as high as that of pristine Rh, respectively. Moreover, the generalized strategy can be extended to other metal cocatalysts for improved CO 2 -to-CH 3 OH transformation, which opens a new avenue for powering the future with liquid sunshine. [ABSTRACT FROM AUTHOR]