Abstract: The 3D microstructure of porous electrodes plays an important role in the performance of electrochemical energy devices including fuel cells, batteries and electrolysers. Computational models are useful as they can provide a direct link between microstructure properties and the complex transport phenomenon and electrochemical performance [1]. A three-dimensional (3D) pore-scale lattice Boltzmann modelling (LBM) framework has been developed at University of Surrey to simulate the transport mechanisms of gases, liquid electrolyte flow, species and charge in the porous electrodes [2-4], coupled with electrochemical reactions at the interface of electrode materials and electrolyte. In this talk we will demonstrate the applications of this modelling framework in proton exchange membrane fuel cells (PEMFCs), redox flow batteries (RFBs), and lithium ion batteries (LIBs).

The LBM model was firstly developed to simulate the gas-liquid two phase flow in the gas diffusion layer (GDL) of PEMFCs, with electrochemical reactions at the catalyst layer included [2]. The model can capture the flow pathways of water and predict the local concentration of oxygen and water within the GDL. The benefit of having a microporous layer is clearly shown, to facilitate the flow of water generated at the CL away, making more reaction sites available and improving the electrochemical performance [2].

The LBM model is also developed to simulate a vanadium based RFB. It is found that the electrochemical performance is reduced with air bubbles trapped inside the electrode [3]. To validate the model, the simulated pressure drop and electrochemical performance are compared against the experimental measurement based on the same electrode structures [4]. Three electrode structures (SGL paper, Freudenberg paper, Carbon Cloth) are reconstructed from X-ray computed tomography (CT). These electrodes are used in an organic aqueous RFB based on TEMPO. Excellent agreement is achieved between the simulated and experimentally measured electrochemical performance, indicating the validity of our model [4]. The effects of different porous structures on the performance are also investigated and discussed.

The 3D pore-scale LBM framework has been further modified and adapted to simulate LIB electrodes. The model is able to simulate the complex transport processes within real electrode geometries and predict electrochemical performance. Li distribution profiles within active materials and the liquid electrolyte are derived [5]. Furthermore, we demonstrate that the model can capture how Li distribution changes with charging/discharging time, and how different microstructures affects this process [5]. The model can be used to understand the impact of electrode microstructure on electrode performance, and lead to design principles for creating electrodes with optimal microstructure for LIBs applications.

Keywords: Porous electrodes, proton exchange membrane fuel cells, redox flow batteries, lithium ion batteries, 3D pore-scale lattice Boltzmann model

References:
[1] D. Zhang, A.Bertei, F.Tariq, N. P. Brandon, and Q. Cai Progress in 3D electrode microstructure modelling for fuel cells and batteries: Transport and electrochemical performance, Progress in Energy 1 (2019) 1-35. doi: 10.1088/2516-1083/ab38c7
[2] D.Zhang, Q.Cai, and S. Gu, Three-dimensional lattice-Boltzmann model for liquid water transport and oxygen diffusion in cathode of polymer electrolyte membrane fuel cell with electrochemical reaction, Electrochimica Acta 262 (2018) 282-296. doi: 10.1016/j.electacta.2017.12.189
[3] D. Zhang, Q. Cai, O. O. Taiwo, V. Yufit, N.P. Brandon, and S.Gu, The effect of wetting area in carbon paper electrode on the performance of vanadium redox flow batteries: A three-dimensional lattice Boltzmann study, Electrochimica Acta 283 (2018) 1806-1819. doi: 10.1016/j.electacta.2018.07.027
[4] D.Zhang, A. Forner-Cuenca, O.O. Taiwo, V.Yufit, F. R. Brushett, N. P. Brandon, S. Gu, and Q. Cai Understanding the role of porous electrodes in redox flow batteries by an experimentally validated 3D pore-scale lattice Boltzmann model, Journal of Power Sources 447 (2019) 227249. doi:10.1016/j.jpowsour.2019.227249
[5] D. Zhang, W. Liu, C. Wu, and Q. Cai, Three-dimensional lattice Boltzmann modelling of the electrode performance of lithium-ion batteries, under review.