Electrocatalysis, which can store electrical energy from renewable sources like solar and wind in chemical bonds, is an attractive solution to activating abundant small molecule precursors. Heterogeneous electrocatalysts are relatively scalable and easy to separate from product solutions, but there are challenges to improving activity and selectivity because of the difficulty of quantifying and optimizing specific active sites. Conversely, molecular electrocatalysts are comparatively easy to isolate and quantify, and present well-defined active sites, often resulting in higher selectivity for specific reduction products. The advantages of molecular characterization methods in identifying relevant intermediates also means that synthetic tools can be brought to bear for iterative optimization through catalyst design. However, molecular catalysts are generally less active and do not commonly produce highly reduced species like methane or methanol and have low activity for O2 reduction to H2O. New strategies to improve the selectivity and activity of molecular electrocatalysts for reduced products from small molecules like O2 and CO2 are required. Co-catalysts are molecules that show greater activity and selectivity for a chemical transformation when combined than as individual components. Stahl and co-workers have shown that if p-hydroquinone is included with Co(salophen), which normally generates H2O2 during the electrocatalytic reduction of O2 (2H+/2e– product), the combined system becomes selective for H2O (4H+/4e– product). In this case, the p-hydroquinone co-catalyst has no intrinsic activity, but can reduce intermediate Co superoxo and peroxo species by 2H+/2e– to improve selectivity for H2O; any p-benzoquinone produced during the reaction is electrochemically recycled back to p-hydroquinone. Inspired by this, we are investigating the use of electron–proton transfer (EPT) mediators in the context of electrocatalytic O2 and CO2 reduction by molecular transition metal complexes.

Improving the activity and selectivity of catalytic CO2 and O2 reduction by inorganic complexes using mediators

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.