The carbon dioxide reduction reaction (CO 2 RR) presents the opportunity to consume CO 2 and produce desirable products. However, the alkaline conditions required for productive CO 2 RR result in the bulk of input CO 2 being lost to bicarbonate and carbonate. This loss imposes a 25% limit on the conversion of CO 2 to multicarbon (C 2+ ) products for systems that use anions as the charge carrierand overcoming this limit is a challenge of singular importance to the field. Here, we find that cation exchange membranes (CEMs) do not provide the required locally alkaline conditions, and bipolar membranes (BPMs) are unstable, delaminating at the membrane−membrane interface. We develop a permeable CO 2 regeneration layer (PCRL) that provides an alkaline environment at the CO 2 RR catalyst surface and enables local CO 2 regeneration. With the PCRL strategy, CO 2 crossover is limited to 15% of the amount of CO 2 converted into products, in all cases. Low crossover and low flow rate combine to enable a single pass CO 2 conversion of 85% (at 100 mA/cm 2 ), with a C 2+ faradaic efficiency and full cell voltage comparable to the anion-conducting membrane electrode assembly.
Electrochemical
CO2 reduction can convert waste emissions
into dense liquid fuels compatible with existing energy infrastructure.
High-rate electrocatalytic conversion of CO2 to ethanol
has been achieved in membrane electrode assembly (MEA) electrolyzers;
however, ethanol produced at the cathode is transported, via electroosmotic
drag and diffusion, to the anode, where it is diluted and may be oxidized.
The ethanol concentrations that result on both the cathodic and anodic
sides are too low to justify the energetic and financial cost of downstream
separation. Here, we present a porous catalyst adlayer that facilitates
the evaporation of ethanol into the cathode gas stream and reduces
the water transport, leading to a recoverable stream of concentrated
ethanol. The adlayer is comprised of ethylcellulose-bonded carbon
nanoparticles and forms a porous, electrically conductive network
on the surface of the copper catalyst that slows the transport of
water to the gas channel. We achieve the direct production of an ethanol
stream of 12.4 wt %, competitive with the concentration of current
industrial ethanol production processes.
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