Abstract _AIChE_XNie_03/14/14

DFT Studies on Facet Dependence of CO2 Electroreduction Path and Selectivity

Xiaowa Nie1, Wenjia Luo1, Michael J. Janik2, and Aravind Asthagiri1

1William G. Lowrie Department of Chemical & Biomolecular Engineering, The Ohio State

University, Columbus, Ohio 43210, USA

2Department of Chemical Engineering, Pennsylvania State University, University Park, PA 16802, USA

Electrocatalytic reduction of carbon dioxide (CO2) is a potential candidate process to utilize the renewable sources (hydro, solar, or wind) for energy storage and synthetic fuel production. However, the complexity of the electrochemical environment and inability to control the product selectivity and lower the overpotential are significant barriers for the application and development of this technology in CO2 utilization and conversion. Electrokinetic experiments reveal that Cu facet plays an important role in impacting CO2 reduction selectivity and applied potential. We used density functional theory (DFT) to examine the elementary thermochemistry and kinetics of CO2 electroreduction on various Cu facets. Computational results uncover an obvious facet dependence of CO2 reduction path and selectivity.
Cu facet shows selective preference for the key hydrogenation intermediates between
hydroxymethylidyne (COH*) and formyl (CHO*). Cu(111) predicts a favorable COH* intermediate through which methane and ethylene are produced at the same electrode potential. COH* reduction to C* step has a highest kinetic barrier which determines the reduction rate and potential requirement. The selective preference of COH* than CHO* results in the favorability of methane and ethylene production over methanol on Cu(111). On Cu(100), formation of CHO* is preferred and ethylene formation goes through C-C coupling of CHO* and further reduction of the C2 species. C-OH bond dissociation steps in C2 species conversion have significant barriers. Surface coverage and competitive adsorption of key species such as H* and CO* potentially impact the reaction rate and catalytic selectivity. At relatively high overpotentials, CHO* would go through C-C coupling to form C2 intermediates rather than reduce to methanol through C1 species involving CH2O* and
CH3O* as observed experimentally.

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