Iron porphyrin flanked by viologen redox units for persistent carbon dioxide reduction in the presence of oxygen.

The electrocatalytic reduction of CO2 to energy-rich forms such as CO or hydrocarbons is typically realized with pure CO2. This is primarily to exclude O2, which is a far better oxidant and a major competitor upon reduction of the CO2/O2 feed gas. Furthermore, the presence of O2 can deactivate the catalytic material and reduce its effectiveness for CO2 reduction. To confront this major challenge, different strategies are being pursued. We utilize a molecular design approach by adjoining to a known catalyst a redox active module that can competitively divert the deleterious O2 activity. We tailored an iron porphyrin, a prominent catalyst for CO2 reduction, flanked by viologen units known for their efficient O2 reduction. Electrochemical studies on the homogeneous phase of the pre-catalyst, the iron(iii)-μ-oxo form, show the independent activity of both modules. When heterogenized with carbon nanotubes on a carbon paper electrode, we found that the catalyst could sustain the aerobic (5% O2) reduction of CO2 to CO with a faradaic efficiency of 62%, while the activity of the unmodified iron porphyrin fell to 18% under the same experimental conditions.