Effect of nanostructured carbon support on copper electrocatalytic activity toward CO2 electroreduction to hydrocarbon fuels

Abstract The effect of support on electrocatalytic activity of Cu nanoparticles (NPs) towards CO 2 electroreduction to hydrocarbon fuels (CH 4 and C 2 H 4 ) is investigated for three types of nanostructured carbons: single wall carbon nanotubes (SWNT), reduced graphene oxide (RGO) and onion-like carbon (OLC). Cu/SWNT, Cu/RGO and Cu/OLC composite catalysts are synthesized and characterized by X-ray diffraction analysis, transmission electron microscopy and electrochemical surface area measurements. Electrocatalytic activities of the synthesized materials, as measured in an electrochemical cell connected to a gas chromatograph, are compared to that of Cu NPs supported on Vulcan carbon. All four catalysts demonstrate higher activity towards C 2 H 4 generation vs CH 4 , with production of the latter mostly suppressed on Cu NPs supported on nanostructured substrates. Onset potentials for C 2 H 4 vs CH 4 generation demonstrate 200 mV positive shifts for Cu/SWNT, Cu/RGO, and Cu/OLC catalysts. The Cu/OLC catalyst is found to be superior to the other two nanostructured catalysts in terms of stability, activity and selectivity towards C 2 H 4 generation. Its faradaic efficiency reached 60% at −1.8 V vs Ag/AgCl. The enhanced stability and activity of the Cu/OLC catalyst can be attributed to the unique catalyst design, wherein a shell of OLC surrounds the Cu NPs. Such a configuration enables the outer layer to act as a filter that protects the Cu surface from adsorption of undesirable species, enhances its electrocatalytic performance, and improves its viability in CO 2 electroreduction reaction. The enhanced selectivity of the Cu/OLC catalyst towards the C 2 H 4 production is most likely related to the enhanced electrocatalytic activity of the OLC support towards the CO 2 electroreduction to CO. Higher CO surface concentration from CO 2 electroreduction on the OLC support, rather than a greater number of available sites for CO dimerization, likely originated this behavior. CO molecules generate on surfaces of OLCs, dimerize on Cu NP (100) planes, and, subsequently, yield additional C 2 H 4 molecules. Both the reduction of the CO 2 to CO on the surface of OLCs and reduction of “extra” CO molecules to C 2 H 4 on the surface of Cu NPs are expected to lead to an increase in the local pH, which is also beneficial for the C 2 H 4 production.