CO2 Electrochemical Reduction to Hydrocarbon Fuels on Carbon-Supported Copper Nanoparticles: Support Effect

Previously, we reported activity and selectivity of Cu nanoparticles towards CO₂ electroreduction to hydrocarbon fuels (CH₄ and C₂H₄) on three different supports (Vulcan Carbon (VC), Ketjenblack (KB) and singled walled carbon nanotubes (SWCNT))¹. We found that carbon materials not only serve as inert supports, but are actively involved in electrochemical CO₂ reduction likely due to hydrogen spillover from the support to the surface of Cu nanoparticles.  Here we explore the effect of carbon support on the product distribution in CO₂ electroreduction reaction in more detail expanding the number of nanostructered supports to reduced graphene oxide (rGO), and onion-like carbon (OLC)³.  These five carbon materials (VC, KB, SWCNT, rGO and OLC) have different surface area, electronic conductivity, morphology, and inherent size.

Cu nanoparticles of 15-25 nm diameters on different carbon supports were synthesized by the reduction of CuCl₂ using NaBH₄ in aqueous ethylene glycol solution (20% v/v). X-Ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were used for nanoparticles ex-situ analysis. The catalytic activities and selectivity of supported Cu nanoparticles towards CO₂ electrochemical reduction to hydrocarbon fuels were evaluated using a sealed rotating disk electrode (RDE) setup connected to a gas chromatograph¹.

Cu nanoparticles supported on VC and OLC exhibited higher catalytic activity vs other catalysts towards CH₄ and C₂H₄ generation, respectively, between -1.4 and -1.6 V (vs Ag/AgCl reference electrode). At a more negative potential of -1.6 V, all five Cu catalysts promoted generation of both CH₄ and C₂H₄, with the higher selectivity in terms of Faradaic efficiencies towards C₂H₄ formation. The C₂H₄/CH₄  ratio increased by almost an order of magnitude in the following order: Cu/VC (2.6:1) <Cu/KB (4.5:1) < Cu/SWNT (5.8:1) < Cu/GPO (10.8:1)< Cu/OLC (33:1). Cu/OLC showed both the lowest onset potential and the greatest selectivity towards C₂H₄ formation. 

This presentation will discuss the reasoning behind the different catalytic activity and selectivity of supported Cu nanoparticles in catalyzing the CO₂ electrochemical reduction reaction.

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[2] P. V. Kamat, J. Phys. Chem. Lett. 1 (2010), 520.

[3] J. K. McDonoug, Y Gogotsi, Interface,   22 (2013), 61.