The electrocatalytic reduction of CO₂to industrial chemicals and fuels is a promising pathway to sustainable electrical energy storage and to an artificial carbon cycle, but is currently hindered by the low energy efficiency and low activity displayed by traditional electrode materials. In order to overcome these challenges, we have explored how catalyst nanostructure and oxidation state can be used to control the activity and selectivity of the reaction.

      Using the inverse micelle synthesis method, nanoparticles (NPs) with well-defined size and interparticle distance supported on glassy carbon electrodes were prepared and tested as catalysts for CO₂ electroreduction. Previously, we have reported the dramatic effect of the size of these NPs size on activity and selectivity for Cu¹ and Au² NPs. Here, we will show that interparticle distance is also a critical parameter for controlling reactivity.³ For largely spaced NPs, we find that selectivity to CO is enhanced, since this reaction intermediate is less likely to readsorb on neighboring NPs after formation. Large NPs which are highly spaced have slightly higher hydrocarbon selectivity than smaller NPs, since there is more chance for the intermediates to readsorb on the same particle. On the contrary, for closely spaced NPs we find that hydrocarbon selectivity is enhanced, since the re-adsorption of reaction intermediates on neighboring NPs can facilitate the multi-step pathway required for hydrocarbon production. These results are also corroborated by theoretical diffusion calculations. This study addresses previously unexplored aspects of how product selectivity can be controlled using mesoscale transport processes during CO₂ electroreduction. In addition, it shows that IP distance is a critical design parameter to consider when developing improved NP catalysts for CO₂electroreduction.

      Another critical parameter for selectivity control in nanostructured electrocatalysts is the oxidation state. We will discuss new oxide-derived metal catalysts that can reduce CO₂ with lowered overpotential and improved hydrocarbon selectivity. We will also discuss critical insights into the catalyst reaction mechanism which were unraveled using structural and chemical information on the sample during the reaction using operando X-ray absorption fine structure spectroscopy.

References

1) R. Reske, H. Mistry, F. Behafarid, B. Roldan Cuenya, P. Strasser, J. Am. Chem. Soc. (2014) 136: 6978-6986.

2) H. Mistry, R. Reske, Z. Zeng, Z. Zhao, J. Greeley, P. Strasser, B. Roldan Cuenya, J. Am. Chem. Soc. (2014) 136: 16473-16476.

3) H. Mistry, F. Behafarid, R. Reske, A. S. Varela, P. Strasser, B. Roldan Cuenya, ACS Catal. (2015), DOI: 10.1021/acscatal.5b02202.