Authors: Andrea Pizzato | Paolo Canu
Source: ECS Meeting Abstracts (article, 2025-11-24)
Field: Materials Science — Materials Chemistry

First-Principles Modeling of Ni-YSZ|YSZ|CGO|LSCF Cell Guiding Rational Electrodes Design Solid oxide fuel cells offer a clean and efficient alternative to conventional power generation based on fossil fuel combustion. However, their commercialization remains challenging due to various forms of polarization, primarily associated with the slow oxygen reduction reaction (ORR) rate. This study presents the development of a one-dimensional (1D) isothermal model for an electrolyte-supported solid oxide cell. The model incorporates mass balance equations for gaseous chemical species, adsorbed species and ions on electrode surfaces, and lattice species within the electrodes. It also accounts for charge and momentum conservation. At the electrodes, a microkinetic model describes species adsorption, electron transfer, and ion transfer processes for oxidation and reduction reactions. Percolation theory is employed to determine the microstructural and textural properties of the active layers, enabling the calculation of effective electrode properties. The model was developed using COMSOL Multiphysics® and validated against experimental data, including polarization curves for a Ni-YSZ|YSZ|CGO|LSCF cell tested at different temperatures (700°C to 900°C). This model bridges multiple scales, from the atomic scale, where elementary reaction steps are described, to the mesoscale, where the electrode is treated as a continuum percolating cluster, to the macroscale, which accounts for the cell’s current output at a given overvoltage. The cell’s performance was evaluated using hydrogen diluted in an inert gas, followed by an assessment of CO₂ addition to the fuel mixture. Model calibration and validation were performed using multiple datasets, and sensitivity analyses were conducted to evaluate parameter influence, identify limiting processes under different operating conditions, and assess the current output. Most kinetic parameters of the elementary reaction steps were fitted during calibration, while others were retrieved from the literature. This work aims to develop and calibrate the model based on experimental data obtained at the Department of Chemical Sciences of the University of Padua. The model can then be used to investigate the phenomena limiting the cell’s current output under various operating conditions, such as temperature, feed flow rate, composition, and applied voltage. Another application is the rational design of the Ni-YSZ|YSZ|CGO|LSCF cell, optimizing both electrode size and textural properties. Finally, the model can be adapted for other electrode materials and employed in the design of new mixed ionic-electronic conductor (MIEC) materials. Since a change in MIEC composition affects only the model parameters, while the governing equations remain unchanged, the model can be applied to new materials once their kinetic parameters are determined from symmetric cell experiments. The model effectively captures all forms of polarization, distinguishing between different regimes depending on temperature. The cell is kinetically limited near the open-circuit voltage (OCV) and diffusion-limited at high current densities. In the kinetic regime, the limiting elementary reaction was found to be temperature-dependent; however, it was consistently related to oxygen consumption, confirming ORR as the primary limiting process in overall cell performance and highlighting the need for more active cathode materials. The structural properties of electrodes significantly influence cell performance. Specifically, reducing the thickness and increasing the porosity of the LSCF cathode shifted concentration polarization to lower voltages, thereby improving performance. However, excessive porosity reduced particle contact, diminishing current output in the kinetic regime. Increasing pore formation by adding pore formers during electrode manufacturing mitigated diffusion limitations at high cell utilization but required careful balancing to maintain optimal performance and prevent mechanical failure of the electrodes. Additionally, the model assessed the impact of lattice species composition on cell performance. Increased LSCF doping enhanced ionic conductivity and reduced cell resistance, highlighting opportunities for electrode composition optimization. To reduce computational costs and evaluate the significance of various physical and electrochemical phenomena in the overall device performance, simplified models were developed. Three main sub-models were considered: (i) a model with simplified kinetics, where the semi-reaction mechanism was neglected and the ORR and HOR reactions were treated as single-step processes, omitting adsorption-related phenomena; (ii) a model neglecting gaseous species diffusion through the porous electrodes and the mobility of the oxygen vacancy/lattice oxygen pair in the MIEC material or ionic conductor; and (iii) a model replacing the complex Dusty Gas Model (DGM) with the simpler Stefan-Maxwell diffusion model in the kinetic regime. The results showed that a detailed anode microkinetic model was unnecessary in the diffusive regime, and replacing the DGM with the Stefan-Maxwell model provided a computationally efficient alternative without significant loss of accuracy Electrode ; Solid oxide fuel cell ; Isothermal process ; Polarization (electrochemistry) ; Hydrogen ; Oxide ; Limiting current ; Analytical Chemistry (journal) ; Inert Advancements in Solid Oxide Fuel Cells ; Electrocatalysts for Energy Conversion ; Chemical Looping and Thermochemical Processes