Development of membrane diagnostics and novel porous materials for next generation redox flow batteries
On February 21, 2023, Rémy Jacquemond successfully defended his PhD thesis entitled 'Development of membrane diagnostics and novel porous materials for next generation redox flow batteries'
Currently, the human economy heavily relies on the use of fossil carbon sources to produce the energy needed to sustain our global economy. An alternative route to decarbonize human activities is to shift towards renewable energy sources (solar, wind, hydropower, etc). However, matching the energy production of renewables with the currently adopted grid system is a challenge due to intermittency of renewables. To this end large-scale energy storage systems stand out as a viable option to act as a compatibilizer between the intermittent renewable energy production and the variable needs of the grid users. Redox Flow Batteries (RFBs) are a promising candidate to electrochemically store energy from mid- to long-duration owing to their flexible design where power can be scaled independently from energy. To this day, RFBs are still not cost-competitive compared to Lithium-ion batteries and a possible strategy to address this relies on the optimization of the system performance. This work focuses on two major improvement strategies: understanding and optimizing some of the performance-defining components and developing new characterization techniques to gain more insights into material properties – RFB performance relationships.
The first two experimental chapters of this thesis cover the synthesis of a new type of porous electrode microstructure, deviating from the state-of-the-art fibrous electrodes which were repurposed from other electrochemical technologies and often showed unoptimized performance for RFB applications. Non-Solvent Induced Phase Separation (NIPS) was used to prepare electrodes with multimodal porosities composed of assemblies of large finger-like macrovoids surrounded by interconnected microvoids. The microstructural features, hydraulic permeability and RFB performance of the newly prepared electrodes were characterized. It was found that experimental parameters efficiently controlled the microstructure of the NIPS electrodes, resulting in an increased design space (hydraulic permeability vs electrochemically active surface area). Finally, NIPS electrodes showed improved performance in iron and vanadium electrolytes compared to fibrous standards. This finding was attributed to reduced charge transfer and mass transfer overpotentials and motivates future work to optimize NIPS electrode preparation and explore alternative NIPS methods.
The last three experimental chapters of this work describe the development of tailor made analytical tools for RFBs to raise the current understanding of material-function-performance relationship. First, two methods are described to study membrane transport phenomena and ion exchange capacity (IEC) in non-aqueous electrolytes by means of microelectrode analysis and quantitative 19F-Nuclear Magnetic Resonance (19F q-NMR), respectively. The microelectrode sensor was successfully placed in the electrolyte tank and membrane crossover rates, state of charge and migration effects were determined. 19F q-NMR show that a partial IEC utilization when complex ions are exchanged (i.e., PF6- and BF4-). Finally, a neutron radiography methodology was developed and used to study operando mass transport phenomena in organic RFBs. For the first time time-of-flight neutron energy selection was used to deconvolute concentration maps of active species and supporting salt. The method was employed to unveil the effect of the membrane type on internal concentration distribution.
Rémy Jacquemond defended his thesis 'Development of membrane diagnostics and novel porous materials for next generation redox flow batteries' on Tuesday, February 21st, 2023. He was supervised by prof.dr.ir. Kitty Nijmeijer and dr. Toni Forner-Cuenca