Electrochemical Reduction of CO2 to CO or Ethylene: Status of Electrocatalysis and Technoeconomic Insights

One strategy to reduce anthropogenic CO2 emissions is the use of CO2 as a feedstock for the production of useful chemicals such as formic acid, carbon monoxide, ethylene, ethanol, or methanol via the electrochemical reduction of CO2. Over the past decade, significant advances have been made in the development of electrocatalysts for the efficient and selective conversion of CO2 to some of the aforementioned products. Scale up and commercialization activities are already ongoing for the conversion of CO2 to formic acid or CO. These electrolysis processes have the promise to be executed in a cost effective and sustainable manner, especially if otherwise-wasted renewable energy (produced in excess of grid demand) is used. This presentation will summarize our efforts to perform electrolysis of CO2 to CO at high efficiency and selectivity using Ag, Au, and N-doped carbon based catalysts. Furthermore it will cover our recent advances in developing ever more active and especially selective catalysts for the production of ethylene and ethanol. Many researchers are pursuing Cu-based catalysts for this task. While reasonable conversion rates can be achieved (overall current densities exceeding 100 mA/cm2), the main challenge has been achieving selectivity for the desired products of ethylene and ethanol. We have developed Cu-based catalysts that produce 70-80% ethylene and ethanol, at a combined rate exceeding 170 mA/cm2. The presentation will also include an analysis of economic feasibility for the production of ethylene and ethanol from CO2, which highlights the importance of low electrical energy cost (as expected) as well as the need for high energy efficiency (low cell potential, low overpotentials) in the electrolysis process itself. This insight has led us to explore alternative reactions to the oxygen evolution reaction on the anode which typically represents >85% of the energy needs to drive a CO2 electrolysis process. For example performing the electro-oxidation of glycerol, a large byproduct of biomass conversion, can reduce the overall energy needs by 50%.