(621eq) Theoretical Calculations of Electrochemical Reduction of CO2 at Cu and Cu-Au Nanoparticles

Theoretical calculations of Electrochemical Reduction of CO₂ at Cu and Cu−Au Nanoparticles

Javed Hussain¹, Egill Skúlason¹and Hannes Jónsson^1,2

¹Science Institute and Faculty of Physical Sciences, University of Iceland, Reykjavík, Iceland

²Department of Applied Physics, Aalto University, Espoo, Finland

Density functional theory (DFT) calculations have led to a deeper understanding of catalytic activity and thus helped develop better heterogeneous catalysts, a task that is vital for the design of processes with higher energy and atom efficiency in the chemical industry. By providing information about the factors controlling the reactivity, such as the energetics of molecule/surface interaction and the kinetics of elementary processes at solid surfaces, trends in the catalytic activity as the chemical composition of the catalyst is varied have been established and predictions made for new and improved catalysts. The field of nanoparticle catalysis is, however, very challenging since many different types of structures and active sites can be present, and the catalytic activity has in many cases been shown to be strongly dependent on size.

       In the future, fuels could be synthesized sustainably by electroreduction of CO₂ [1]. This would allow excess electricity produced from intermittent renewable sources to be stored in the form of chemical bonds. Such a process would require an active and selective catalyst. The electrochemical reduction of CO₂ is a promising way to recycle CO₂ by converting it to hydrocarbon
fuel. To date, copper is the best metal catalyst; however the overpotential to
achieve this reaction on Cu is excessively high [2-8]. It follows that the development
of a catalyst to efficiently catalyze the conversion with a low overpotential at a
reasonable current density is needed [9-12]. Many aspects of the molecular details of
the reaction are still unclear. However, the electrochemical reduction of CO₂ into hydrocarbons on Cu or into CO on gold-based nanoparticles has been demonstrated with improved reaction kinetics [13-14]. In this work, DFT calculations are applied to
investigate CO₂ electroreduction to CH₄ at sites that are characteristic of Cu and Cu-Au nanoparticles. Periodic models of edges as well as steps are used in the calculations to investigate the extent to which the catalytic performance of Cu can be improved by the formation of nanoparticles and by alloying with Au. The potential limiting elementary reaction (*CO to either *CHO/*COH) have been analyzed in particular.

       We find that the geometry of alloyed structures using periodic models are well correlated with those determined in global optimization method [15]. The results show that with replacement of 25% of the Cu atoms with Au atoms on the edge sites, a slightly lower overpotential compared to the Cu(111) surface is obtained.  However, the ration of H₂ formed would at the same time increase. The insights gained through this study may serve as a foundation for designing better carbon dioxide electrochemical reduction catalysts.

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