Hybrid all-Fe redox flow batteries: Coupling theory and experiment

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Reliable electrical energy storage devices are required in order to implement more of the highly fluctuating renewable energy sources into our electrical supply grid. To make this energy transition process also sustainable, it is important to use energy storage devices that rely on earth-abundant and non-toxic materials. Iron (Fe) fulfils these criteria and can be used in all-Fe redox flow batteries (IRFB), thereby providing a promising sustainable alternative to lithium-ion batteries and vanadium redox flow batteries. However, many critical challenges across length scales need to be overcome to enable this technology. At the nanoscale, smart interface designs are needed to inhibit the parasitic hydrogen evolution reaction. At the microscale, porous 3D-structured electrodes must facilitate reversible Fe plating and stripping inside the pores. At the macroscale, suitable rebalancing systems must handle hydrogen evolution, while carefully chosen operating conditions are required to mitigate capacity loss due to undesired plating/stripping of Fe. Unfortunately, those obstacles cannot be tackled independent of each other, but must be considered simultaneously. The goal of this project is to establish a comprehensive mechanistic understanding of the IRFB by using a joint theoretical and experimental approach across scales. Only by coupling experiment and theory in a multiscale approach, it will be possible to assess, understand, and rationally improve this complex system. From the theoretical side we will combine continuum and molecular models. With length scales from plating and stripping processes on the molecular scale up to operating conditions at system scale, we will cover the relevant processes by applying and advancing multiscale modelling techniques. On the experimental side we will modify surface properties by introducing defect sites into planar model surfaces, integrate the knowledge gained into 3D porous electrode samples, and test their properties under realistic operating conditions on the system level. Theory and experiment will be coupled by establishing parameterization and validation cycles to arrive at reliable and concise recommendations for interface, electrode and system design.