Chemical Engineering Seminar

A promising approach to store energy is the use of excess electricity to drive the production of fuels and chemicals in electrochemical reactors. The lack of understanding of the relation between transport phenomena (e.g. mass, heat, charge), intrinsic kinetics and electrocatalytic performance is currently limiting the scale-up of electrocatalytic technologies particularly for transformations where transport phenomena play a role in determining product selectivity and production rate. In this presentation, I will discuss our approach of combining reactors design, multi-scale modeling and dimensionless analysis to understand and decouple mass, charge and heat transfer effects from intrinsic electrode kinetics particularly for transformations that involve dissolved gas substrates (i.e. H2, O2, CO2, CO, CH4, N2) and diluted protons in near neutral pH.

In this talk, the development of a multi-scale first-principles reaction-transport model is presented 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, bulk electrolyte concentration, and catalyst porosity are rationalized by introducing dimensionless numbers that reduce complexity and capture relative timescales for mesoscopic and microscopic dynamics of electrocatalytic reactions on copper electrodes of any porosity. 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. The reaction-transport model presented here should enable the rational design of CO2 electrolyzers.