Efficient paired electrolysis for CO and acrolein coproduction

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Efficient paired electrolysis for CO and acrolein coproduction
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The carbon dioxide electroreduction reaction (CO2RR) powered by renewable electricity offers a promising route to generate valuable chemicals and fuels.1 However, current CO2RR systems – typically relying on cathodic CO2RR coupled with the anodic oxygen evolution reaction (OER) – suffer from high full-cell voltages, limited CO2 utilization, and, in cases, carbonate formation due to the use of alkaline/neutral media.2-8 Each of these leads to energy penalties when considering the overall system.

 CO2RR in acidic media addresses the CO2 loss issue resulting from carbonate formation and crossover in alkaline/neutral media during reaction.9-12 However, hydrogen evolution reaction (HER) under acidic media is kinetically favored relative to CO2RR, leading to low selectivity towards carbon-based products in CO2RR.6,9,10 Thus, to achieve high CO2 utilization efficiency practically, one must suppress HER and promote Faradaic efficiency (FE) to desired products in acidic CO2RR.

 As noted above, CO2RR systems today typically rely on OER on the anode, which has a standard potential of 1.23 V vs. the reversible hydrogen electrode.14 Replacing OER with another anodic reaction that requires a lower thermodynamic potential offers to decrease the full-cell voltage and thus the electricity consumption of CO2RR system. It also provides a means to electroproduce economically valuable products at the anode.

 Here we report an efficient electrocatalysis system with low energy consumption: cathodic CO2-to-CO in acidic media coupled to anodic allyl alcohol oxidation reaction (AOR) to acrolein (a precursor in the manufacture of acrylic acid), where the cathode chamber and anode chamber are separated by the cation exchange membrane (CEM). In this design, using acidic catholyte and CEM circumvents the CO2 loss arising from the carbonate formation and crossover of carbonate ions from the cathode to anode (Figure 1a below).

 In cathodic CO2RR, we lever the K+ strategy reported previously,11 and achieve a CO FE of (96 ± 1)% on an Ag cathode prepared by sputtering a layer of Ag on a carbon-based gas diffusion layer. In anodic AOR, through anode catalyst screening and reaction condition optimization, we achieve an acrolein FE of (85 ± 1)% on a Pt anode at a current density of 100 mA cm2. We reach a CO2 single pass utilization (SPU) of 84% in this CO2RR-AOR system, fully a 6× improvement compared to the best values reported in prior acidic CO2RR-to-CO studies above 100 mA cm2.7,8,11,15,16 At 100 mA cm2, the average full-cell voltage of this paired electrolysis system is 3.2 V during 10 h operation, and the energy consumption for producing 1 kg of CO is 44 MJ; these represent a decrease in voltage of 0.7 V and a reduction of 1.6× in energy consumption relative to the most energy-efficient prior reported acidic ambient-temperature CO2-to-CO studies (Figure 1b).

 This thus points to strategies for CO2RR systems with lowered energy consumption.

 If you are interested in our work, you may find the full paper here: https://www.nature.com/articles/s41893-024-01363-1

Figure 1. a, Schematic of a paired electrolysis system consisting of CO2-to-CO at cathode and allyl alcohol-to-acrolein at anode. b, Comparison of product selectivities at cathode and anode, full-cell potential, CO2 SPU, and energy consumption in this work with those of state-of-the-art CO2-to-CO ambient-temperature electrolysis systems.

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Chemical Engineering
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Electrocatalysis
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