With the growing interest in sustainability in the Internet-of-Things (IoTs), the miniaturization of Solid Oxide Cells (SOC) would provide new and greener possibilities for powering portable electronic devices. Despite recent advancements in the development of micro-Solid Oxide Fuel Cells (µSOFCs), there are still several challenges that need to be addressed, such as improving the cells durability, stabilizing the electrodes, and enhancing electrode performance.

The coupling of the experimental and numerical methods is a very efficient way to investigate and optimize the material performance, the electrode microstructure, the cell architecture, or the device design. Experimental methods provide detailed information on the physical properties of a material such as the surface exchange coefficient, while numerical methods are used to simulate and predict the performance of the oxygen electrode under different conditions. Experimental methods are also used to validate the predictions of numerical simulations, and the results of simulations can be used to guide the design of new material microstructures. This leads to a more efficient use of resources and a faster development of new materials with desired properties.

Here, we implemented a 3D Finite Element Method (FEM) model representing a simplified nano-columnar microstructure. This study has been driven by the work of A. Stangl et al., which shows how the lanthanum-nickel oxide electrode performance can be increased by tuning the microstructure [1]. The numerical model developed includes the oxygen gas diffusion within the electrode pores; the oxygen adsorption, dissociation, and incorporation into the bulk material (all included as the “surface exchange” step); the ionic diffusion; and the charge transfer at the electrode/electrolyte interface. The 3D FEM model is solved in both stationary and dynamic modes to predict the Area Specific Resistance (ASR) and the impedance spectra.
The experimental work consisted of the deposition of praseodymium-substituted lanthanum nickelate layers on YSZ substrates by Pulsed-injection Metal-Organic Chemical Vapour Deposition, along with the structural, morphological and chemical characterization of the films, as well as their functional characterization. The oxygen electrode morphology was investigated by SEM and TEM, while the electrode performance was evaluated by Electrical Conduction Relaxation (ECR) and Electrical Impedance Spectroscopy (EIS). The praseodymium substitution aims to increase the electrode performance by improving the electronic conductivity. The results exhibit a clear relationship between the chemical composition of La_2-xPr_xNiO_4+d and its functional properties.

Finally, by combining the two approaches, we have been able to deepen our understanding of material-microstructure-performance relationships and suggest optimization guidelines to improve performance, in particular in fuel cell mode.

[1]       A. Stangl et al., “Tailored nano-columnar La2NiO4 cathodes for improved electrode performance,” J Mater Chem A Mater, vol. 10, pp. 2528–2540, 2022