How “Rust” Could Possibly Help to Power Fuel Cells

How “Rust” Could Possibly Help to Power Fuel Cells

The global push for clean energy has brought technologies like fuel cells to the forefront of innovation. Fuel cells use the reaction of hydrogen and oxygen to transform chemical energy to electric power with water being the only product. To enable this, catalysts are required. The standard catalyst – platinum – is both expensive and rare. For this reason, scientists worldwide work on cost-effective alternative as for instance so called iron nitrogen carbon (FeNC) catalysts. While they reach required activity, their durability is often insufficient, while the exact origin of degradation is debated. For years, the prevailing theory was that the catalytic activity is mainly attributed to FeN4 moieties.

A recent study by the Collaborative Research Centre (CRC) 1487 Iron, upgraded! at TU Darmstadt challenges long-held beliefs about FeNC catalysts.

By combining advanced microscopy with real-time analysis, the research team from the Max Planck Institute for Chemical Energy Conversion, the TU Darmstadt and the Fritz-Haber Institute discovered very small iron oxide moieties that are reversibly “redox-active.” This observation was rather unexpected, as bulky iron oxide is known to dissolve under the relevant application conditions.

Rather than being mere degradation products, the findings suggest that specific iron oxide moieties in FeNC catalysts may be dynamic components that might eventually even actively participate in the catalyst's activity.

A Breath of Air Rearranges the Iron Atoms

One of the study's most striking findings is the extreme environmental sensitivity of these materials. When freshly prepared in a nitrogen-filled atmosphere, the material primarily contains iron as isolated atoms and tiny “atomic clusters” (i.e. a few atoms, ACs) distributed throughout the carbon matrix.

In stark contrast, once the material is exposed to air, the iron atoms migrate and clump together to form iron oxide nanoparticles (NPs).

The Importance of In Situ Analysis

A key lesson from this research is that to truly understand a catalyst, the catalyst must be studied “in action” (in situ). Only then, researchers can identify the dynamic nature of involved species. With the design of the experiment, the authors were also able to identify a partial leaching of iron from the catalyst. However, even taking this into account, the reversibility of the redox switching was confirmed by combing two very powerful techniques: electron paramagnetic resonance (EPR) spectroscopy and Mössbauer spectroscopy.

A New Path Forward

This research fundamentally reframes the discussion around iron oxides in FeNC catalysts. The discovery of their redox active and reversible nature suggests a possible, but previously unconsidered contribution to the catalysis.

This could on the one hand indicate that such sites might be at the origin of the fast degradation under harsher fuel cell conditions. On the other hand, rather than a problem to be eliminated, their functions must be understood and could possibly being optimized to enable a more stable performance.

The path to a platinum-free future could thus be paved by a fundamentally better understanding of iron oxide moieties, thereby paving the way to truly affordable, clean energy.

Other Information

This work was financially supported by the Deutsche Forschungsgemeinschaft (DFG) via the CRC 1487 Iron, upgraded!.

Publication:

Authors: Kaltum Abdiaziz, Lingmei Ni, Derya Demirbas, Hendrik Haak, Edward Reijerse, Pascal Theis, Wulyu Jiang, Sonia Chabbra, Thomas Lunkenbein, Ulrike I. Kramm, and Alexander Schnegg

Title: Reversibly Redox-Active Iron Oxide Structures in FeNC Catalysts Identified by Microscopy and Spectroelectrochemical EPR and Mössbauer Methods

In: Journal of the American Chemical Society 2026 148 (4), 3995-4007

DOI: 10.1021/jacs.5c12396

https://pubs.acs.org/doi/10.1021/jacs.5c12396?ref=pdf

Scientific contact:

• Alexander Schnegg

Max Planck Institute for Chemical

Energy Conversion, Mülheim an der Ruhr 45470, Germany;

Email: alexander.schnegg@cec.mpg.de

• Ulrike I. Kramm

Catalysts and Electrocatalysts Group,

Department of Chemistry, Technical University Darmstadt,

Darmstadt 64287, Germany;

Email: ulrike.kramm@tu-darmstadt.de