Revisiting Reaction Kinetics of CO Electroreduction to C₂₊ Products in a Flow Electrolyzer

Abstract

The identification of the rate-determining step (RDS) in the electrochemical CO/CO 2 reduction to multi-carbon (C 2+ ) products has been complicated by the deficiency of rigorous reaction kinetic data. This work describes an experimental analysis of the key reaction steps by exploring the effect of CO partial pressure on the activity of C 2+ products. With the aid of a flow electrolyzer integrated with a gas diffusion electrode, the distinct reaction orders of CO and reaction mechanisms in forming different C 2+ products were determined. Specifically, *CO dimerization is identified as the RDS for ethylene and ethanol production, as evidenced by the gradual transition of measured CO reaction order from second to zero as CO partial pressure increases from 0.05 to 1 atm. The formation of npropanol is suggested to proceed via the *CO trimerization mechanism. The acetate generation mechanism might involve a critical step of *CO hydrogenation before C−C coupling. Kinetic studies reveal that product-specific active sites are responsible for activity and selectivity toward specific C 2+ products over oxide-derived copper.

Nickel as Electrocatalyst for CO(2) Reduction: Effect of Temperature, Potential, Partial Pressure, and Electrolyte Composition

“…For the electrochemical Fischer–Tropsch like mechanism of CO 2 RR, the CO 2 activation is an additional step that could be rate-limiting. For CO 2 to CO, it is generally assumed that the first electron transfer to activate CO 2 is the RDS, − while for C2+ formation on copper, the CO dimerization is generally considered the RDS. − Both steps are highly sensitive to catalyst structure − and local electrolyte composition, i.e. cation concentration and identity. − From the data in Figure , we suggest that the CO 2 dissociation is not the RDS for the formation of hydrocarbons on Ni as the activities for the CO 2 RR are higher than for the CORR.…”