A homogeneous rhenium(I) electrocatalyst possessing hydroxy and ammonio groups in the second coordination sphere is reported for the reduction of carbon dioxide (CO2) to carbon monoxide, wherein the former and latter groups induce a high local concentration of protons and local coulombic interactions with a metallocarboxylate reaction intermediate, respectively. In a comparison with precedent catalysts possessing single functional groups in the spheres, we found that the catalyst exhibits a concerted improvement over these single functional groups in the efficiencies of catalysis, based on experimental standard electrode potentials for the reduction in aqueous N,N-dimethyl-formamide or acetonitrile solutions and the equilibrium potentials depending on the catalytic systems.