Swiss start-up Unbound Potential builds membrane-free redox flow battery aimed at long-duration storage

The technology

Unbound Potential, a Zurich-based clean-tech start-up spun out of ETH Zurich (Swiss Federal Institute of Technology, 苏黎世联邦理工学院), is developing a membrane-free redox flow battery it says removes the costly, failure-prone ion-exchange membrane used in conventional flow stacks. The design reportedly uses two immiscible water-based electrolytes that exchange ions across an interface rather than through stacked membrane layers. Founders David Taylor (CEO) and Anetta Platek‑Mielczarek (CTO) — both with doctoral and postdoctoral experience at ETH Zurich — led the early prototyping work.

Why it matters

Flow batteries are attractive for long-duration, fixed storage because energy is stored in tanks and power and capacity scale independently. But membranes and stacked cell hardware have long been the bottleneck: expensive, fragile and hard to mass-produce. Unbound says removing the membrane cuts manufacturing complexity and cost, lowers internal resistance (reportedly improving ion-exchange efficiency to about 85%), reduces sealing surfaces by roughly 90% and trims the battery’s carbon footprint by about 30%. The cells are water‑based and non‑flammable, and the company claims lifetimes exceeding 20,000 cycles — promising for industrial sites, data centres and microgrids that need safe, calendar‑stable, long-duration storage.

Commercial traction and financing

It has been reported that Unbound is on Venturelab’s Swiss Innovation 100 list and that the company reached a commercial agreement with Amazon in October 2024 to supply its membrane‑free flow batteries to a European logistics site to raise on‑site renewable utilisation. It has also been reported that Unbound is in discussions with FlexBase about using the technology in a large European redox flow project and plans a pilot factory with a local partner by mid‑2026. The start‑up reportedly closed a pre‑seed round of €14.4 million — including €8 million in non‑dilutive funding and €6.4 million equity — led by Founderful, Kvanted and Zürcher Kantonalbank (ZKB), money earmarked for scale‑up and pilot deployments.

Context and outlook

The pitch comes as global demand for grid storage is set to surge and as lithium‑ion systems face limits on cycle life, cost and raw‑material concentration. Reducing reliance on mineral‑intensive cell chemistries is also a geopolitical objective: battery raw‑material processing and cell manufacturing are highly concentrated in China, and policymakers in Europe and North America are pushing for more resilient, locally scalable alternatives. Can a simpler, membrane‑free flow architecture make long‑duration storage cheap and modular enough to reach grid scale? The answer will depend on how laboratory performance translates into durable, low‑cost manufacture and whether pilots — now being reported across Europe — prove the chemistry and economics in real sites.