Carbon monoxide dehydrogenase (CODH) enzymes are active for the reversible CO oxidation-CO 2 reduction reaction and are of interest in the context of CO 2 abatement and carbon-neutral solar fuels.B ioinspired by the active-site composition of the CODHs,polyoxometalates triply substituted with first-rowt ransition metals were modularly synthesized.T he polyanions,i ns hort, {SiM 3 W 9 }a nd {SiM' 2 M''W 9 }, M, M',M '' = Cu II ,N i II ,F e III are shown to be electrocatalysts for reversible CO oxidation-CO 2 reduction. A catalytic Tafel plot showed that {SiCu 3 W 9 }w as the most reactive for CO 2 reduction, and electrolysis reactions yielded significant amounts of CO with 98 %f aradaic efficiency.I n contrast, Fe-Ni compounds such as {SiFeNi 2 W 9 }p referably catalyzedt he oxidation of CO to CO 2 similar to what is observed for the [NiFe]-CODH enzyme.C ompositional control of the heterometal complexes,now and in the future,leads to control of reactivity and selectivity for CO 2 electrocatalytic reduction.