CO2 Electroreduction to Hydrocarbon Fuels on Carbon-Supported Copper Nanoparticles: Particle Size Effect
Authors: Baturina Olga A , Lu Qin , Xin Le , Li Wenzhen , Brintlinger Todd , Epshteyn Albert 
Published: February 2020

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

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