(67d) COx Electrochemical Reduction with Additive Molecules Towards Longer Chain Products

Conventional production of carbon-based fuels and chemicals contributes significantly to greenhouse gas emissions and climate change, increasing the urgency to develop mitigation or capture technologies. Electrochemical carbon dioxide/monoxide reduction (CO_xRR) is a promising alternative route for production of carbon-based fuels and chemicals; it requires mild electrolyzer operating conditions, integrates well with renewable energy sources, and enables flexibility of possible product selectivity. Engineering tunable systems is necessary to ensure critical chemicals and fuels are produced according to their relative demand. Although products with one or two carbons can be formed with reasonable selectivity on copper (Cu), tunability must be improved to enable production of longer carbon chain molecules.

Ethylene acts as a chain initiator itself as well as a source of C₁ monomer species which promote chain propagation and can potentially improve CO_xRR tunability as in Fischer-Tropsch (Krishna 1992). A custom cell was designed to perform CO_xRR experiments with ability to control flow rates of CO_x and ethylene separately. Preliminary data suggests that ethylene increases the amount of methane, ethane, and propane formed and generates higher current compared to baseline CO_xRR with only CO₂, both on Cu and in 0.1M potassium bicarbonate (Fig. 1). Longer chain products also begin forming at lower absolute potentials than that of the baseline. Gaseous and liquid products are analyzed as a function of CO_x and ethylene flow rates, applied potential, and reaction environment.

Considering other possible additives, biofuel production generates byproducts like oxalates, acetaldehydes, and glyoxylic acids. These bioprivileged molecules can be repurposed and added to CO_xRR feedstreams to act as chain propagators (Shanks 2017). Co-electroreduction of CO_x and oxalate are investigated for novel product distributions as a function of electrolyte concentration and pH. Both additive strategies ultimately inform the viability of CO₂RR as a greener pathway to carbon-based fuels and chemicals.