Anthropogenic carbon dioxide (CO₂) emissions from fossil fuel based power stations could be lessened by addition of carbon capture and utilization technology to separate CO₂ from the flue gas and either sequester the greenhouse gas or transform it into a useful product. Of particular interest, are energy efficient CO₂ electroreactors that employ excess electricity from intermittent renewable sources (i.e. wind, solar) to drive the electrochemical reduction of carbon dioxide, thus transferring electrical energy into chemical bonds of carbon neutral fuels. Multiple studies have been performed on bulk metals to evaluate their electrochemical activity and product selectivity for CO₂ conversion ^1–3. Group 11 metals, namely gold, silver, and copper, have demonstrated success reducing carbon dioxide without succumbing to large amounts of hydrogen evolution. Modifications to these metals such as nanostructuring^4,5 and straining⁶ have improved performance but only minimal attention has been given towards developing bimetallic catalysts for carbon dioxide reduction⁷. However, bimetallic catalysts, specifically platinum alloys, have been successfully employed to drive sluggish complex electrode reactions (e.g., methanol oxidation reaction, oxygen reduction reactions) not only enhancing catalytic properties^8,9 but also enabling reduced catalyst loadings and cheaper materials^10,11.

Here, we investigate bimetallic gold-copper nanotubes as electrocatalysts for the carbon dioxide reduction reaction, with particular focus on the role of alloying on catalyst activity and selectivity.  We also note that such structures may eventually provide lower cost alternatives to current state-of-the-art materials.  Prior work by Kim et al. showed that bimetallic surfaces, specifically Cu and Au, exhibit binding strengths conducive to carbon dioxide reduction and varying the electrocatalyst composition tunes the stabilization of key reactive intermediates⁷. Building on this fundamental study and current trends in CO₂ reduction literature, we seek to design nanotubular Au-Cu alloys via galvanic replacement on copper nanowires.  Specifically, we study the role of synthesis conditions on the electrochemical and physical properties of the Au-Cu nanotubes and how these properties impact electron efficiency, product generation rate, and product distribution.  Figures 1 and 2 show exemplar electrochemical data, to quantify catalyst performance, and microscopy characterization data, to verify the existence of a single bimetallic particle.  Based on these analytical studies, promising alloys are integrated into a small-scale CO₂ electroreactor to evaluate complete cell performance and durability analysis.

Acknowledgments

We gratefully acknowledge the financial support of the Massachusetts Institute of Technology Energy Initiative and the Kuwait – MIT Center for Natural Resources and the Environment. The assistance of Dr. Kyler Carroll, Mr. Jarrod Milshtein, and Mr. John Barton is much appreciated.

References

1.         Kuhl, K. P. et al. J. Am. Chem. Soc. 136, 14107–14113 (2014).

2.         Azuma, M. et al. J. Electrochem. Soc. 137, 1772–1778 (1990).

3.         Hori, Y. in Modern Aspects of Electrochemistry (eds. Vayenas, C. G., White, R. E. & Gamboa-Aldeco, M. E.) 89–189 (Springer New York, 2008).

4.         Zhu, W. et al. J. Am. Chem. Soc. 136, 16132–16135 (2014).

5.         Manthiram, K., Beberwyck, B. J. & Alivisatos, A. P. Meet. Abstr. MA2015-01, 1522–1522 (2015).

6.         Li, C. W., Ciston, J. & Kanan, M. W. Nature 508, 504–507 (2014).

7.         Kim, D., Resasco, J., Yu, Y., Asiri, A. M. & Yang, P. Nat. Commun. 5, 4948 (2014).

8.         Liu, L. et al. J. Phys. Chem. C 116, 23453–23464 (2012).

9.         Zhang, J. et al. Angew. Chem. Int. Ed. 44, 2132–2135 (2005).

10.       Stamenkovic, V. R. et al. Nat. Mater. 6, 241–247 (2007).

11.       Marković, N. M., Schmidt, T. J., Stamenković, V. & Ross, P. N. Fuel Cells 1, 105–116 (2001).