Capacitive-flow hybrid systems: electrochemical solutions for clean energy and climate applications

In order to mitigate the effects of climate change, the European Green Deal established ambitious objectives to reduce CO₂ emissions. Achieving these goals requires a radical transformation of energy production, harvesting, and storage. From this perspective, electrochemical energy storage systems (EESSs) play a crucial role in the transition, as they enable the storage of variable and intermittent energy derived from renewable sources. Redox Flow Batteries (RFBs) and Supercapacitors (SCs) represent two categories of EESSs that differ significantly in energy and power performance, although they share considerable design flexibility. The integration of RFBs and SCs creates an innovative Hybrid Energy Storage System (HESS) that allows various configurations suitable for multiple applications. Hence, this study investigates different multidisciplinary approaches to integrate the Flow Technology with the Capacitive one by exploring three levels of integration: System integration, where two systems operate in parallel; Material integration, which enables the exploitation of materials designed for supercapacitive applications within flow systems; and Functional integration, which aims to design a dual-function device. In detail, at the System level, it examines the passive integration of a Vanadium Redox Flow Battery with a Supercapacitor and the coupling of a Supercapacitor with a piezoelectric generator, combining experimental analysis, numerical and semi-empirical modelling, and sustainability assessment. At the Material level, it contributes to the upscaling of a Semi-Solid Lithium–Air Flow Battery by developing carbon-based slurries suitable for flow configurations and eliminating critical components. At the functional level, it explores a flow supercapacitor for CO₂ capture via Supercapacitive Swing Adsorption, thereby integrating energy storage and gas capture within a single device.