Comparative life cycle assessment on electrochemical CO2 reduction products, as compared to thermochemical CO2 reduction and incumbent processes.

The economic viability of carbon dioxide electroreduction (CO2R) relies on improved performance accompanied by scalable system design. Membranes are commonly used for the separation of reduction and oxidation products as well as to provide a suitable micro‐environment for CO2R. Commercial membranes often address only one of the key challenges in CO2R: either they offer a suitable micro‐environment for CO2R (e.g., anion exchange membrane) or suppress carbonate cross‐over (e.g., cation exchange membrane and bipolar membrane). This work presents a cation‐infused ultrathin (≈3 µm) solid polymer electrolyte (CISPE) that concomitantly addresses both challenges via a bidirectional ion transport mechanism and suppressed cathode flooding. This directly‐deposited CISPE (that substitutes the commonly used pre‐made membrane) enables record high full‐cell energy efficiency of 28% at 100 mA cm−2 for one‐step CO2 electrolysis to ethylene (C2H4) with ≈110 h of stable operation. This translates into a record low energy cost of 290 GJ per ton C2H4 for the end‐to‐end process (i.e., CO2 capture and electroreduction, carbonate regeneration, CO2 separation from anode and cathode streams) in a membrane electrode assembly CO2R. The present work offers a versatile design paradigm for functional polymer electrolytes, opening the door to stable, and efficient electrolysis of high‐value feedstock chemicals and fuels using low‐cost catalysts.

Industrial activities lead to a substantial share of current anthropogenic CO 2 emissions and are some of the most challenging to abate. Direct utilization of industrial flue gases to produce fuels or value-added chemicals is challenging due to the presence of impurities and low concentrations of CO 2 . Herein, we demonstrate a rational assembly of a permselective gas diffusion electrode (PGDE) for direct CO 2 conversion from quasi flue gas (i.e., 10−15% CO 2 , 4% O 2 , and N 2 balance at 100% relative humidity). The electrode design consists of a metal−organic framework (MOF) based mixed matrix membrane (MMM) that enables the selective permeation of CO 2 to a silver electrocatalyst. The MOF is CALF-20, notable for the ability to physisorb CO 2 in wet gas streams. Applying this approach, we convert N 2 -diluted CO 2 streams to CO at a faradaic efficiency of 95% compared to 58% for the nonmodified counterpart electrode with MMM. The PGDE retained its electrochemical performance when introducing O 2 by preventing ∼84% loss of current toward parasitic oxygen reduction reaction (ORR) and reported 30 mA cm −2 CO partial current density. Further, wetting the gas stream showed a negligible effect on the MOF and the electrochemical performance. Using our PDGE, we report nearly constant CO selectivity over 19 h in a membrane electrode assembly electrolyzer. This approach offers the potential for direct utilization of low-concentration CO 2 while avoiding the economic and environmental costs of obtaining purified CO 2 feedstocks.

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<p>Development of electrochemical pathways to convert CO₂ into fuels and feedstock is rapidly progressing over the past decade. Here we present a comparative cradle-to-gate life cycle assessment (LCA) of one and two-step electrochemical conversion of CO₂to eight major value-added products; wherein we consider CO₂ capture, conversion and product separation in our process model. We measure the carbon intensity (i.e., global warming impact) of one and two-step electrochemical routes with its counterparts – thermochemical CO₂ utilization and fossil-fuel based conventional synthesis routes for those same products. Despite inevitable carbonate formation in one-step CO₂ electrolysis, this analysis reveals one-step electrosynthesis would be equally compelling (through the lens of climate benefits) as compared to two-step route. This analysis further reveals that the carbon intensity of electrosynthesis products is due to significant energy requirement for the conversion (70-80% for gas products) and product separation (40-85% for liquid products) phases. Electrochemical route is highly sensitive to the electricity emission factor and is compelling only when coupled with electricity with low emission intensity (<0.25 kg CO₂e/kWh). As the technology advances, we identify the near-term products that would provide climate benefits over fossil-based routes, including syngas, ethylene and n-propanol. We further identify technological goals required for electrochemical route to be competitive, notably achieving liquid product concentration >20 wt%. It is our hope that this analysis will guide the CO₂ electrosynthesis community to target achieving these technological goals, such that when coupled with low-carbon electricity, electrochemical route would bring climate benefits in near future. </p>