Breakthrough in Energy Storage: The Journey of Aytac Yilmaz
15 November 2024

He had a dream: creating something that makes a real impact on the planet. With his fast-growing startup in iron-air battery technology for renewable energy storage, Aytac Yilmaz seems to be doing just that. “The Faculty of Impact helped us take the step from academic research to the real world and fast-tracked our progress dramatically.

Aytac Yilmaz (1998) earned his PhD in Materials Science at TU Delft, where he focused on developing innovative methods to store energy. Even then, he believed his work on iron-air battery technology could pave the way for a major shift in large-scale renewable energy storage—and by the looks of it, he was right.

Iron-Air Batteries: A Simple but Powerful Concept

After completing his PhD, Yilmaz stayed at TU Delft as a postdoctoral researcher, diving deeper into the challenge of creating cost-effective energy storage. His team developed a sustainable technology using rust as a medium for energy retention. The concept was straightforward yet impactful: by discharging the battery, iron would transform into rust while absorbing oxygen from the air. When charged, the rust would convert back into iron, releasing the stored energy as the battery “breathed out” oxygen.

“Our solution is sustainable and scalable,” Yilmaz explains. “We wanted to store large amounts of renewable energy from sources like wind and solar, making it available at all times rather than relying on fossil fuels when nature isn’t cooperating.”

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Strike when the iron is hot: why Ore Energy believes in bringing back iron-air batteries
Perhaps not a silver bullet, but one of iron, is to play a pivotal part in the energy transition. Delft start-up Ore Energy hopes to decarbonize the energy grid with long-term energy storage, using a surprisingly old form of technology: iron-air batteries. Founder Aytac Yilmaz explains why now’s the time for this technology to flourish.

By Jochen Meischke • April 24, 2025

Aytac, iron-air batteries are almost antique knowledge, originally invented in the 1960s. What made you decide to revive this technology?

‘It’s true — iron-air batteries have been around since 1968, originally explored for electric vehicles. But the timing back then wasn’t right. The world wasn’t focused on decarbonization the way it is today. For decades, this technology was basically collecting dust. But with growing interest in renewable energies, so did interest in battery technology. The research group at TU Delft that I was part of were looking into the fundamentals of this technology. It seemed the right time to bring iron-air batteries back.’

How are iron-air batteries different from other types of batteries?

‘Our battery uses iron and water to rust and de-rust iron metal. This reversible process of oxidation creates a specific type of rust on iron, that, when the iron is charged with electricity, returns the rust to its iron form. At the same time the battery breathes in and out the oxygen from ambient air. This makes them cheap, because we can use materials that are abundant and everywhere: iron, water and air. We don’t need rare earth minerals or critical materials. They are also very safe: They are non-flammable, making them far safer than many existing battery types like lithium-ion.


What drives you to revive this technology with Ore Energy?

‘We’re facing a paradox: we have access to more renewable energy than ever, but often not at the right time. The grid is overwhelmed during peak solar or wind production, and underpowered when the sun isn’t shining or the wind isn’t blowing. That imbalance leads to curtailment, congestion, and lost potential. At Ore Energy, we’re driven by the belief that with the right storage solution — one that’s clean, scalable, and local — we can finally unlock the full power of renewables.’

What is it exactly that iron-air batteries have to offer?

‘Two things: long duration and low cost. Iron-air batteries can store energy for up to 100 hours, far beyond the capabilities of typical lithium-ion systems. That makes them ideal for bridging multi-day gaps in renewable supply. And because our materials are cheap and widely available, we can deliver this performance at a price point that makes real grid-scale storage viable. This kind of breakthrough is essential if we’re serious about replacing fossil fuels.

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