Introduction

Electrochemical reduction of CO_$2$ has attracted researchers’ attention as it has the potential to utilize the abundant greenhouse gas in the Earth’s atmosphere and store intermittent energy from solar panels and wind turbines in chemical bonds. A commercially viable catalyst for CO2 electroreduction should meet the cost-effective requirement while possessing high efficiency and selectivity. Experimental studies showed that Copper (Cu) can catalyze direct electrochemical reduction of CO2 to hydrocarbons in an aqueous bicarbonate solution with a high current density. Some Studies also showed there was a surface evolution of Cu surface under the reducing potential.

Challenges

• The underlying mechanism remains elusive due to multistep kinetic pathways.
• Improved kinetic models are needed to consider various complexites of surface reactions at solid/electrolyte interfaces.
• Mechanisms of CO2 reduction can be better studied with more understanding of Cu surface evolution.

Computational Methods

• Zacros: a theoretical KMC package[1]
• Lattice configuration: Cu(100) surface
• DFT calculated energetics of reaction steps

• Adsorbate-adsorbate interactions can be included.

• Kimocs: an atomistic KMC package[2]
• Configuration: Cu(100) cube on surface
• Neural networks combined to calculate energy barriers

Kinetic Modeling of Surface Reactions

• Mean-field approximation doesn’t consider adsorbate-adsorbate interactions.
• Dynamic evolution of the system can be retrieved while using KMC simulations.

Reaction Network toward C2 species

C2 Kinetics from Experiment and Modeling

• KMC captures the trend of experimental CV curve.
• It shows some differences compared to mean field approximation.

Surface Configuration from KMC

• With applied potential at -0.5 V vs RHE
• COads dominates the surface.
• The surface has a small amount of Hads and H2Oads.

Surface Evolution of Cu(100) cube

Surface evolution of Cu(100) cube from 0 to 1.5 microseconds.

Site population of for atoms at different positions (bulk, edge, and terrace).

• Cu (100) cube collapsed as time advanced.
• Bulk atoms decreased first then increased since moving to the subtrate.
• Terrace atoms decreased while edge atoms increased since more terrace atoms formed edges.

Conclusions

• By considering adsorbate-adsorbate interactions, KMC model can better understand the mechanism of CO2 reduction.
• By employing artificial neural networks, the diffusion processes can be better simulated to help understanding the evolution of Cu surface.

References

• Stamatakis, Michail, and Dionisios G. Vlachos. 2011. “A Graph-Theoretical Kinetic Monte Carlo Framework for on-Lattice Chemical Kinetics.” The Journal of Chemical Physics 134 (21): 214115.
• V Jansson, E Baibuz, and F Djurabekova. “Long-term stability of Cu surface nanotips.” Nanotechnology, 27(26):265708, 2016, arXiv:1508.06870.
• Goodpaster, J. D., Bell, A. T. & Head-Gordon, M. “Identification of Possible Pathways for C–C Bond Formation during Electrochemical Reduction of CO2: New Theoretical Insights from an Improved Electrochemical Model.” J. Phys. Chem. Lett. 7, 1471–1477 (2016).
• Peterson, A. A., Abild-Pedersen, F., Studt, F., Rossmeisl, J. & Nørskov, J. K. “How copper catalyzes the electroreduction of carbon dioxide into hydrocarbon fuels.” Energy Environ. Sci. 3, 1311–1315 (2010).
• Garza, Alejandro J., Alexis T. Bell, and Martin Head-Gordon. 2018. “Mechanism of CO2 Reduction at Copper Surfaces: Pathways to C2 Products.” ACS Catalysis 8 (2): 1490–99.

Tianyou Mou

Chemical Engineer and Data Scientist

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