In this study, electrochemical reduction of carbon dioxide (CO2) is carried out on tandem electrodes consisting of Ag- and Cu-based nanoparticles and a proton-permeable membrane to selectively produce ethylene (C2H4) with Faradaic efficiencies up to 80%. We demonstrate that the origin of this high selectivity arises from the tandem architecture utilized. In particular, CO2 is first reduced to CO on Ag, and the CO is subsequently reduced to C2H4 on the surface of the Cu-based nanoparticles. CO2 reduction products were quantified, and experiments were carried out as a function of voltage, the membrane overlayer thickness, and the oxidation state of Cu in the nanoparticles. Together, these results lay a framework for the selective production of value-added products from CO2 reduction using membrane-modified tandem electrocatalysis.

In this manuscript, we fabricate copolymer blends of polyvinylidene fluoride (PVDF) and Nafion as overlayers on Zn and brass substrates to create electrodes for the CO 2 reduction reaction with enhanced selectivity. By varying the blend composition, the rates of proton transfer and polymer stabilization of reaction intermediates are modulated. C 2 H 4 was obtained with a Faradaic efficiency of 74.1% at −0.89 V vs RHE using 52 wt % PVDF in Nafion on top of a brass electrode. Synergy among Cu, Zn, Nafion, and PVDF allows for this high yield of C 2 H 4 . Additionally, Zn and brass electrodes modified with a Nafion overlayer in a mixed acetonitrile−water electrolyte, which contain a lower proton concentration than aqueous electrolytes, produce 60% CH 3 OH and 65% C 2 H 4 , respectively. These results enable us to develop a mechanistic framework that explains CO 2 reduction catalyst selectivity in terms of proton transfer rates and the stability of reaction intermediates. In particular, we demonstrate that slowing proton transfer to the electrode results in more CO−CO coupling and that brass stabilizes a *C 2 O 2 − intermediate to generate C 2 H 4 . As a whole, these findings will aid the CO 2 reduction community in developing next-generation catalysts with improved selectivity.

Bimetallic Cu materials are promising CO2 reduction electrocatalysts for the formation of valuable multicarbon products. We describe membrane-modified Ag-Cu electrocatalysts that convert CO2 to C2 products with high selectivity. While...