A heterogeneous catalyst made of well-defined Co3O4 hexagonal platelets with varied exposed facets is coupled with [Ru(bpy)(3)]Cl-2 photosensitizers to effectively and efficiently reduce CO2 under visible-light irradiation. Systematic investigation based on both experiment and theory discloses that the exposed {112} facets are crucial for activating CO2 molecules, giving rise to significant enhancement of photocatalytic CO2 reduction efficiency.