Towards Electrode Design for Redox Flow Batteries By Using a 3D Pore-Scale Lattice Boltzmann Model: Experimental Validation and the Role of Porous Electrode Structure

Abstract

Redox flow batteries (RFBs) have emerged as a promising technology for large-scale storage of intermittent power generated from renewable energy sources due to its advantages such as scalability, decoupling of energy and power, and high energy efficiency. However, to make it technologically and economically viable, advancement is needed to improve the performance (i.e. power and energy density) and reduce cost. The porous structure of electrodes in RFBs plays a critical role on performance, but the exact role remains poorly understood. In this paper, we report our efforts in understanding the fundamental mechanisms in redox flow battery electrodes and electrode design using computational modelling, which is important for improving the performance. A three-dimensional (3D) pore scale lattice Boltzmann model has been developed at University of Surrey to simulate the transport mechanisms of gases, liquid electrolyte flow, species and charge in the porous electrodes of RFBs. An electrochemical model based on the Butler-Volmer equation is used to provide species and charge coupling at the interface of active electrode materials and electrolyte. We apply this model first to simulate a vanadium based RFB and demonstrate that this model is able to capture the multiphase flow phenomenon and predict the local concentration for different species, over-potential and current density profiles under charge/discharge conditions[1]. To prove the validity of the developed LBM model, the simulated electrochemical performance are compared with the experimental measurement, based on the same electrode structures[2]. 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[2]. The three electrodes show very different pore size distribution and specific surface area, which result in significant differences in battery performance. From the simulation result, the electrode based on Carbon Cloth shows better performance comparing with other two electrodes, which is consistent with the experimental results[2]. Moreover, the developed model is used to investigate the effect of wetting area in electrode on the performance of redox flow battery. It is found that the electrochemical performance is reduced with air bubbles trapped inside the electrode[1]. The above studies confirm that the developed 3D pore scale lattice Boltzmann model can be used as a design tool to optimize the electrode structure of redox flow batteries. Acknowledgement The authors gratefully acknowledge the financial support for this work by the UK Engineering and Physical Sciences Research Council (EPSRC) projects [grant number EP/K036548/2] and [grant number EP/R021554/1]; and the EU FP7 IPACTS [grant number 268696]; [1] Duo Zhang, Qiong Cai, Oluwadamilola O. Taiwo, Vladimir Yufit, Nigel P Brandon, Sai Gu (2018) 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 pp. 1806-1819 [2] Duo Zhang, Qiong Cai, Oluwadamilola O. Taiwo, Vladimir Yufit, Nigel P Brandon, Sai Gu (2018) Understanding the role of porous electrodes in redox flow batteries by an experimentally validated 3D pore-scale lattice Boltzmann model, Journal of Power Sources, submitted.