Rust to riches: Swiss iron reactors store hydrogen 10x cheaper, safer, longer

Researchers at the ETH Zurich have devised a novel way to use abundantly available iron to store hydrogen. In three stainless steel walled containers, just six millimeters thick walls, the researchers demonstrated hydrogen storage of 10 megawatt hours (MWh) for months without losing storage capacity.

Energy storage and retrieval happens thanks to the commonly occurring process of iron rusting, a principle also used in iron-air batteries.

In a bid to reduce its dependence on fossil fuels, the Swiss government plans to use solar energy to source 40 percent of its energy needs by 2050.  The problem with solar energy, especially in Switzerland, is that there is too much of it in summer and too little in winter when energy demand shoots up.

To overcome this shortcoming, the government plans to use energy from wind and hydro farms but also gas-fired plants when required. Researchers at ETH Zurich, however, have a better idea and think hydrogen could meet this need.

Hydrogen gas can be made by splitting water using solar energy during summer months and used as a clean fuel in winter. But, storing this highly volatile and flammable gas over long periods is energy-intensive and comes with many risks. The safer and much cheaper solution is to store it as rust.

19th-century technology

Led by Wendelin Stark, a professor of functional materials, ETH Zurich researchers use the steam-iron process, known since the 19th century, to store hydrogen in iron. The flammable gas is pumped into a stainless steel reactor, where iron ore is maintained at 752 Fahrenheit (400 degrees Celsius).

At these temperatures, hydrogen extracts oxygen from iron oxide or rust, making water and iron. This is much like charging a battery, where energy is stored in water and iron and can be retained for months without major losses.

In winter months, when energy demand is high, researchers can run hot steam into these reactors. This reverses the process, forming rust and releasing hydrogen gas. The hydrogen can be used to generate electricity in a fuel cell or even burned as fuel to move a turbine.

Inexpensive storage option

The greatest advantage of this storage option is that it is easy to execute and inexpensive. The materials used in the process do not need any preprocessing, and they can be easily scaled anywhere in the world without pumping up market prices of iron.

Onsite storage capacities can be increased by simply adding more reactors, and the material can be recycled through charge-discharge cycles for years without requiring replacement. ETH researchers have built three such reactors as a pilot facility at the Hönggerberg campus to demonstrate the technology.

The facility can store 10 MWh of hydrogen, which, when converted back, could yield 4-6 MWh of energy. The technology’s drawback is that it loses up to 60 percent of energy in the conversion steps.

However, the researchers are keen to test the technology at a larger scale and plan to store 4 gigawatt hours (GWh) in reactors with a volume of 2,000 cubic meters. Such a facility could meet one-fifth of the campus’ winter energy requirements using energy trapped in the summer months.

The “advantages” make the tech an estimated “ten times cheaper than existing methods,” says the research.

“This plant could replace a small reservoir in the Alps as a seasonal energy storage facility. To put that in perspective, it equates to around one-tenth of the capacity of the Nate de Drance pumped storage power plant,” Stark added in a press release.

The research findings were also published in the journal Sustainable Energy and Fuels .