(176g) Kinetic Modeling of Electrocatalysis in Electrolytic Media Using Dimensional Analysis: Bridging Electrocatalytic Systems of Different Mass Transport Characteristics

The development of high-performance catalysts and devices for the electrified activation and transformation of small molecules such as CO₂, CO, CH₄, NO₃^-/NO₂^- and H₂O into fuels and chemicals calls for a profound understanding of the processes occurring at multiple scales in liquid media. In studying the kinetics of small molecule activation on the electrode surface, it is essential to distinguish transport-limited kinetics from true surface kinetics since rates of these reactions are not only dependent on the intrinsic catalytic activity itself, but are highly affected by the local environment near the electrode surface deviating from the bulk electrolytic condition. In this talk, we demonstrate dimensionless characterization of electrocatalytic systems involving multi-scale transport phenomena from external mass transfer of gas phase reactants across electrolyte and the pore diffusion followed by the transformation into intermediates and products, and their transport into the bulk media. Such analyses using dimensionless quantities (e.g., Reynolds, Schmidt, Sherwood and Damköhler numbers) can standardize mass transport characteristics of various cell designs used across different labs and readily translate mass transfer effects on electrochemical processes of different scales. We have also investigated the contribution of diffusion inside porous electrocatalysts through nano-structuring of the electrodes, and this effect of the concentration polarization is quantified using the Thiele modulus that is dependent on the concentration overpotential and the effectiveness factor for pore utilization of reactants and intermediates. Through computational fluid dynamics modeling, we have identified a unique feature of back mixing near the electrode surface caused by Eddy vortices in turbulent hydrodynamics which has led to the assumption of continuous stirred tank reactor type of mixing volume at the reaction front. Here, the residence times of reactants and intermediates inside such volume are critical descriptors expressed using dimensionless numbers and determine the conversion and selectivity of reactions involving complex further reduction/oxidation.