Beyond Butler-Volmer equation for CO2 electro-reduction on Cu-based gas diffusion electrodes

We present a methodology for modelling gas diffusion electrodes with Cu-based catalysts. The applicability of the Butler Volmer equation (B-Ve) based on Tafel analysis is limited to single electron transfer reactions which are not typical of CO2 reduction reactions on Cu catalysts. We developed a method that involves linking the nanoscale effects encapsulated in a detailed calibrated microkinetic model (MKM) on Cu(100) electrodes to a mass transport model (MTM) on a low surface area, flooded agglomerate electrode. The MKM carries richer kinetic information of most reaction pathways described in contemporary literature for Cu(100). Polynomial equations are used to bridge kinetic and transport models without the need for excessive complexity. Our results show that using regression modelling, the microkinetic information at the microscopic level of the catalyst can be successfully linked with the macroscopic electrode models. We observe how mass transport parameters such as CO2 concentration, pH, and applied voltage, interacts with microkinetic information of the catalyst, influencing the reaction pathways and current densities of key products methane, ethylene, ethanol, and hydrogen. Although the model explores the medium to high voltage regimes, the methodology can address the oversimplification of CO2 reduction (CO2RR) kinetics and hydrogen evolution reaction (HER) for observed multiple kinetic regimes if comprehensive microkinetic models are integrated. It also serves as a foundational work for further experimental endeavours for the development of comprehensive microkinetic models. The holistic approach carried out in this work allows for the optimization of both reaction rates and mass transport, paving the way for rational optimisation of electrode designs and their scaling towards commercialization.