Nanoscale structure turns peat into a powerful candidate for sustainable fuel cells

Electrochemists Rutha Jäger of the University of Tartu and Eneli Härk of the Helmholtz-Zentrum Berlin mapped the atomic structure of this iron-nitrogen-carbon catalyst, demonstrating how it might compete with costly precious metals in fuel cell technology. The article “Small-Angle X-ray Scattering Monitoring of Porosity Evolution in Iron–Nitrogen–Carbon Electrocatalysts” was published in ACS Nano, a ranked in the top 5 in the Nanoscience & Nanotechnology and the Multidisciplinary Materials Science.
Fuel cells, which convert the chemical energy of hydrogen directly into electricity, producing only water as a byproduct, are emerging as a key technology for a climate-neutral energy system. However, the main obstacle is the high cost of electrocatalysts, which are usually based on the precious metal platinum. Researchers are currently exploring catalyst options using common metals rather than precious ones, which could dramatically lower expenses without sacrificing performance. However, these catalysts have a key limitation: the oxygen reaction occurs slowly through multiple stages and can generate hydrogen peroxide as a byproduct along the way, causing harm to fuel cell parts.
Carbon Structures Like an Anthill
Rutha Jäger, Associate Professor in Physical and Electrochemistry at the University of Tartu, described their research approach. The team investigated five iron-nitrogen-carbon catalysts produced under different conditions, each using well-decomposed Estonian peat as the precursor material. The key question driving their investigation was why materials derived from nearly identical precursors exhibited vastly different levels of activity and selectivity.
According to Dr. Jäger, carbon-based materials display extraordinary variation in structure. High-performing fuel cell catalysts require extensive porosity, creating an interconnected maze of passages analogous to an anthill's tunnel architecture. These channels allow hydrogen and oxygen molecules to travel toward catalytically active sites for water formation, with the resulting water departing via the same pathways. Variables like pore size and wall dimensions may either promote or limit the material's catalytic activity and selectivity.
Tracing the Optimal Carbon Networks
Dr. Eneli Härk, an electrochemist from Helmholtz-Zentrum Berlin, and her team utilized (anomalous) small-angle scattering techniques (ASAXS/SAXS) at the BESSY II third-generation synchrotron radiation facility, working alongside specialists from the German National Institute for Metrology (PTB). This small-angle X-ray scattering method delivers precise, quantitative insights into pore curvature and the relationship between pore dimensions and wall thickness - characteristics that are notoriously challenging to measure. Dr. Härk explained that the researchers mapped essential structural features of the catalysts, including hierarchical porosity, structural irregularities, and the spacing between active sites nested within the pores. By examining catalysts across the entire spectrum from micropores to macropores, they uncovered the characteristics of the otherwise hidden nanostructure.
From Structure to Performance
The investigation pinpointed 13 structural parameters, including porosity, structural irregularities, and pore curvature, and follow-up oxygen reduction reaction experiments allowed the researchers to connect these structural characteristics with catalytic effectiveness. Revisiting the anthill comparison: small-angle scattering creates a comprehensive blueprint of the anthill's architecture, while electrochemical testing reveals how molecules, like "ants," navigate through its tunnels. A significant discovery was that oxygen reduction to water works most efficiently when pore curvature reaches a minimum of three nanometers, which helps prevent the unwanted generation of hydrogen peroxide.
Bridging Structure and Sustainability
While researchers previously understood the connection between electrochemical performance and multi-level porosity, Dr. Eneli Härk and Dr. Rutha Jäger's ASAXS-based investigation now illuminates the specific structural details that govern these reactions, creating fresh opportunities for catalyst innovation. Equally significant, the team emphasized, is the practical pathway from peat bog to fuel cell: well-decomposed peat serves as an effective source for producing eco-friendly, non-precious metal carbon catalysts. According to Dr. Härk and Dr. Jäger, Estonia's abundant peat reserves thus offer considerable potential as a feedstock for advanced functional materials.

ACS Nano 2025, 19, 46, 40072–40084 https://doi.org/10.1021/acsnano.5c14955