Molecular Transition Metal Oxide Electrocatalysts for the Reversible Carbon Dioxide-Carbon Monoxide Transformation

Abstract

Carbon monoxide dehydrogenase (CODH) enzymes are active for the reversible CO oxidation-CO₂ reduction reaction and are of interest in the context of CO₂ abatement and carbon-neutral solar fuels. Bioinspired by the active-site composition of the CODHs, polyoxometalates triply substituted with first-row transition metals were modularly synthesized. The polyanions, in short, {SiM₃ W₉ } and {SiM'₂ M''W₉ }, M, M', M''=Cu^II , Ni^II , Fe^III are shown to be electrocatalysts for reversible CO oxidation-CO₂ reduction. A catalytic Tafel plot showed that {SiCu₃ W₉ } was the most reactive for CO₂ reduction, and electrolysis reactions yielded significant amounts of CO with 98 % faradaic efficiency. In contrast, Fe-Ni compounds such as {SiFeNi₂ W₉ } preferably catalyzed the oxidation of CO to CO₂ similar to what is observed for the [NiFe]-CODH enzyme. Compositional control of the heterometal complexes, now and in the future, leads to control of reactivity and selectivity for CO₂ electrocatalytic reduction.

Keywords: CO oxidation; CO2 reduction; d-block metals; electrocatalysis; polyoxometalates.