The proton highway: Taking a closer look at materials for hydrogen processing

Hydrogen is a sustainable energy carrier. "Green" hydrogen, meaning hydrogen produced with renewable energy, can be used for energy storage and as a fuel. To make its production and use more efficient, sustainable, and cost-effective, new materials are needed. For example, the membranes used in fuel cells and electrolysers play a key role in determining how efficiently these devices function. Such membranes are often made from special ceramics.

Exactly how the behavior of hydrogen ions - protons - in ceramic membranes relates to their material structure is not yet fully understood. In a project funded by the Swiss National Science Foundation (SNSF), Empa researchers led by Artur Braun, group leader in the Laboratory for High Performance Ceramics, are collaborating with international partners to investigate this question.

Braun and his team have been studying ceramic proton conductors for 20 years. Good proton conductors must meet two key requirements: They must absorb as many protons as possible, and the protons should be able to move as freely as possible within the material. However, these two properties are often at odds with each other: Optimizing one usually compromises the other.

Rugged terrain instead of a smooth ride

"You can imagine the ceramic membrane as a landscape crisscrossed by roads. The protons move along these roads like cars," Braun explains. The more cars on the roads, the more traffic slows down. "A multi-lane proton highway where charges flow unimpeded in both directions would be the ideal scenario," he explains. However, the proton membranes currently in use are more like rough mountain slopes, with protons laboriously making their way along narrow paths.

Unlike the landscapes all around us, the crystal lattices of ceramic membranes are dynamic - they change. In a previous study, Braun's team was able to show that proton conductivity in highly conductive ceramics does not always remain constant but oscillates between low and particularly high values. "It is as if the mountains and valleys suddenly level out. For a brief moment, the protons have a clear path," explains Braun. The Empa team was also able to show that proton transport in ceramic conductors is closely coupled to lattice vibrations of the crystal lattice - and that protons embedded in the lattice can themselves alter its vibrations.

Looking into the lattice

To better understand this effect in their current project, the researchers are not focusing on a good proton conductor, but on a rather poor one instead. Although lanthanum cerium oxide (LCO) can accommodate many protons, it does not conduct them further. "If a poor proton conductor can be compared to a traffic jam, LCO is a full-blown gridlock," says Braun.

However, this apparent disadvantage offers the researchers a unique opportunity to investigate the effects of the material's structure on proton conductivity. In addition to high-resolution crystallographic structure determination using neutrons at the Paul Scherrer Institute (PSI), the team is using new methods at major research facilities in the U.S. and Japan to precisely measure the vibrations of the crystal lattices and experimentally verify the theoretical models. "If we understand the scientific fundamentals of proton conductivity, we can ideally determine how future ceramics can become better proton conductors, thereby enabling more efficient membranes for fuel cells and electrolysers," explains the physicist.

To the press release

Literature

A Braun, A Rulev, N Nagasawa, H Wang, H Bendikov, V Pomjakushin, M Kunz, Y Yoda, Q Chen, SP Cramer: How Proton Incorporation Reshapes Lattice Dynamics in BaSnO3-type Proton Conductors; Advanced Science (2026); doi: 10.1002/advs.76065

A Rulev, N Nagasawa, H Wang, V Pomjakushin, M Kunz, Y Yoda, SP Cramer, Q Chen, A Braun: Strong Proton-Phonon Coupling Drives Fast Ion Transport in Perovskites; Advanced Science (2025); doi: 10.1002/advs.202507261

A Braun, Q Chen: Experimental neutron scattering evidence for proton polaron in hydrated metal oxide proton conductors; Nature Communications (2017); doi: 10.1038/ncomms15830

Further information

Dr. Artur Braun
High Performance Ceramics
Phone +41 58 765 48 50
[email protected]