Is It Greener? Impact of Cathode Catalyst Performance on Life-Cycle Emissions of Producing Methanol By Electrocatalytic CO 2 Reduction

Direct electrocatalytic reduction of carbon dioxide (deCO 2 rr) is being developed as a route to energy-dense liquid transportation fuels for a low-emissions future. This technology would reduce net emissions from fuel combustion, because these would be fully offset by upstream capture of the CO 2 used to produce the fuel. However, it would produce some additional emissions from related processes, such as generating the process electricity and purifying the product stream. Although extensive basic-science catalysis research is underway in this area, the full life-cycle emissions of this technology platform have not been quantified. In this prospective technology analysis, we apply systematic life cycle assessment (LCA) to estimate the total life cycle emissions associated with producing methanol from low-temperature electrocatalytic reduction of CO 2 . This analysis framework (1) quantifies the emissions impact of using deCO 2 rr to provide drop-in liquid hydrocarbon fuels, and (2) provides catalyst performance targets (faradic efficiency, overpotential, and yield) for this technology to provide net emissions reductions. The framework provides a long-term emissions impact perspective to guide priorities in catalysis research for sustainability. The hypothetical reference case deCO 2 rr system in this analysis features a cathode electrocatalyst that reduces CO 2 to methanol with 15% faradaic efficiency, 0.8 V overpotential, and 25% conversion of CO 2 to product. Water is oxidized at the anode. The methanol production system is coupled to CO 2 capture from a coal-fired power plant. In a preliminary analysis of this integrated methanol-electricity system, the products (1 g MeOH plus 6.1 Wh of electricity) have a total emissions intensity of 3.8 g CO 2 . This is approximately half the emissions produced when using conventional processes to produce the same electricity (without carbon capture) and methanol (using a natural gas-based process). In addition, we quantify the emissions impact of improving the performance of the CO 2 reduction catalyst from present values. We identify technology performance thresholds for this renewable methanol process to provide a net emissions reduction compared to conventional processes. For instance, we estimate that using present-day CO 2 capture technology, the integrated electricity-methanol production system would provide a net reduction in emissions if the cathode catalyst has 20% faradaic efficiency and 20% molar conversio