Electrochemical CO2 Reduction Mechanism on Copper: Relation between Mesoscopic Mass Transport and Intrinsic Kinetics

A multi-scale first-principles transport-reaction model is derived for the electrochemical reduction of CO2 to fuels and chemicals on polycrystalline copper electrodes. The model utilizes a continuous stirred-tank reactor (CSTR)-volume approximation that captures the relative timescales for mesoscale stochastic processes at the electrode/electrolyte interface that determine product selectivity. The model is built starting from a large experimental dataset obtained under a broad range of well-defined transport regimes in a gastight rotating cylinder electrode cell. Product distributions under different conditions of transport, applied potential, and bulk electrolyte concentration are rationalized by introducing dimensionless numbers that reduce complexity and capture relative timescales for mesoscopic and microscopic dynamics of electrocatalytic reactions on copper electrodes. This work demonstrates that one CO2 reduction mechanism can explain differences in selectivity reported for copper-based electrocatalysts when mass transport, concentration polarization effects, and primary and secondary current distributions are taken into account.