CO2 Electroreduction to Hydrocarbon Fuels on Carbon-Supported Copper Nanoparticles: Particle Size Effect

Activity of Cu catalysts towards CO₂ electroreduction is found to be strongly dependent on the Cu surface structure [1-3]. Hori [1] demonstrated that Cu(100) facets favored C₂H₄ production, while Cu(111) favored CH₄ production during CO₂ electrolysis in electrochemical cells. High-index crystal facets such as Cu(311), Cu(511) and Cu(711) were found to be more active towards  generation of C₂ and C₃ compounds. Previously, we reported that product distribution can be inverted by switching from smooth Cu films to carbon-supported Cu nanoparticles. The product distribution was dominated by CH₄ over C₂H₄ for smooth Cu films, while the reverse order was observed for carbon-supported Cu nanoparticles.  A similar trend was reported by Norskov’s  group [3] for unsupported 50-100 nm Cu nanoparticles. The higher activity of nanoparticles towards C₂H₄ generation was attributed to a larger amount of under-coordinated sites, such as corners, edges and defects on the surface of nanoparticles compared to a smooth Pt surface. 

Here we report particle size effect for CO₂ electroreduction to hydrocarbon fuels on Vulcan Carbon (VC)-supported Cu nanoparticles. Cu nanoparticles of 5, 12 and 27 nm diameter on carbon supports were synthesized by the reduction of Cu(acac)₂ in a mixture of oleylamine and hexane by LiBEt₃H .

 X-Ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were used for nanoparticles ex-situ analysis. Pb underpotential deposition was used for in-situ evaluation of the electrochemical surface area (ECSA) of Cu nanoparticles [4].

The activity of the Cu nanoparticles towards CO₂ electroreduction to hydrocarbon fuels was evaluated using a sealed RDE setup connected to a GC. Thin films of three Cu/VC catalysts were deposited on the surface of custom-made 7 mm glassy carbon disks (Pine Instruments, Inc), following a well-established in the PEMFC community protocol [5]. GC sampling from the electrochemical cell was performed at 5, 25, 45 and 65 min from the beginning of each experiment, while holding the electrode potential at -1.2, -1.4, -1.6, -1.8, -2 and -2.2 V vs. Ag/AgCl reference electrode. 

Our preliminary results show that the ratio of C₂H₄ to CH₄ increases with a decrease in the Cu particle size. 

This presentation will discuss different aspects of CO₂ electroreduction reaction on Cu nanoparticles.

Acknowledgements

OAB is grateful to the Office of Naval Research for financial support of this project.

References

[1] Y. Hori, Electrochemical CO2 reduction on metal electrodes, in: C.e.a. Vayenas (Ed.) Modern Aspects of Electrochemistry, vol. 42, Springer, New York, 2008.

[2] M.R. Goncalves, A. Gomes, J. Condeco, T.R.C. Fernandes, T. Pardal, C.A.C. Sequeira, J.B. Branco, Electrochimica Acta, 102 (2013) 388.

[3] W. Tang, A.A. Peterson, A.S. Varela, Z.P. Jovanov, L. Bech, W.J. Durand, S. Dahl, J.K. Norskov, I. Chorkendorff, Physical Chemistry Chemical Physics, 14 (2012) 76.

[4] S. Trasatti, O.A. Petrii, Pure and Applied Chemistry, 63 (1991) 711.

[5] H.A. Gasteiger, S.S. Kocha, B. Sompalli, F.T. Wagner, Appl. Catal. B-Environ., 56 (2005) 9.