The HORTA project (High-performing Organic Redox flow bATteries) pioneers a new generation of long-duration energy storage (LDES) based on safe, sustainable, and fully metal-free organic redox flow batteries. As industry and the electricity grid shift toward large shares of wind and solar power, storage systems capable of delivering energy for many hours become essential. HORTA addresses this need by developing a high-performance non-aqueous organic redox flow battery technology that can be produced locally, avoids critical raw materials, and offers the flexibility and durability required for industrial energy-intensive applications in Flanders and across Europe.

Over four years, HORTA will develop the complete technology stack needed to bring organic flow batteries to TRL 4. This includes (1) discovering and engineering next-generation redox-active organic molecules with high stability, solubility, and voltages above 2 V; (2) designing advanced electrodes and membrane–electrode assemblies to improve kinetics, reduce resistances, and support efficient cycling; (3) developing membranes that combine high ionic conductivity with minimal crossover; and (4) integrating all components into an optimized prototype cell operated under realistic flow, current, and lifetime conditions. The project will also assess economic viability, sustainability, and system-level performance to guide future industrial adoption.

HORTA combines the complementary expertise of four leading Flemish research groups at the following universities:

• VITO, project coordinator, leading materials development, membrane research, and system integration;

• KU Leuven, contributing expertise in organic molecule design, synthesis routes, and computational screening;

• VUB, advancing multiscale modeling to understand degradation, ion transport, and limiting processes;

• University of Antwerp, specializing in electrochemical engineering, flow-field and stack design, and prototype testing.

Together, these partners aim to create a robust, scalable, and cost-competitive energy-storage technology that can strengthen industrial resilience, reduce renewable curtailment, and accelerate the transition toward a carbon-neutral energy system. The innovations developed in HORTA will lay the scientific and technological foundation for future industrial demonstrations and a European value chain for sustainable long-duration energy storage.