Research Highlights

February 9, 2026

Researchers at Hamburg University of Technology and at Helmholtz-Zentrum Hereon have developed a new theoretical framework that explains a long-standing puzzle in hydrogen-solid interactions: why hydrogen uptake in metals can slow down dramatically near phase transformations, even when diffusion inside the material is extremely fast. The results have been published in Physical Review Letters.

Hydrogen absorption in solids is a key process in energy storage, electrochemical actuation, and adaptive materials. Hydrogen typically enters the crystal lattice as an interstitial solute. While the equilibrium thermodynamics of this phenomenon is well understood, theory struggles to explain why the kinetics of hydrogen uptake can slow down by orders of magnitude near critical points or phase transformations. Rationalizing the observation by conventional kinetic rate laws, based on the Butler-Volmer equation, faces multiple challenges. Ultimately, one touches on the question whether the established rate laws are inherently compatible with the principle of microscopic reversibility, a cornerstone of statistical mechanics.

The study in Physical Review Letters derives a physically consistent rate equation for hydrogen insertion. The theory describes each phase as an internally equilibrated, ergodic ensemble of particles, and it derives the insertion flux from the statistical-mechanics-based probability of finding the ensemble in a transition configuration. The insertion rate than naturally exhibits microscopic reversibility.

As a key result, the hydrogen chemical potentials in the two phases enter the rate law explicitly and separately, rather than only through their difference. This makes the theory naturally compatible with established equations of state for hydrides that undergo phase transformations. On that basis, the theory explains experimental observations, including the slow-down in hydrogen charging and the pronounced asymmetry of hydrogen uptake kinetics on different sides of a critical composition.

Beyond resolving a fundamental question in materials physics, the results are highly relevant to the Cluster of Excellence BlueMat: Water-Driven Materials. Hydrogen electrosorption from aqueous electrolytes is a prime example of how water-mediated chemical processes can actively control materials properties. Hydrogen insertion into nanoporous metals is known to induce strong changes in elastic moduli, enabling reversible switching between stiff and highly compliant states.

By identifying the kinetic bottleneck that governs hydrogen exchange near phase boundaries, the new framework provides a crucial link between hydrogen chemistry, phase stability, and mechanical response. This insight supports BlueMat’s overarching goal: to understand and exploit water-driven chemical processes as control parameters for designing adaptive, responsive materials.

The work was carried out as preparatory research within the context of the Cluster of Excellence BlueMat, funded by the Deutsche Forschungsgemeinschaft (DFG) under Germany’s Excellence Strategy.

Reference:

Rate Equation for the Transfer of Interstitials across Interfaces between Equilibrated Crystals
J. Weissmüller
Physical Review Letters 2026 Vol. 136 Issue 6 Pages 066201
DOI: 10.1103/kfpq-9dd1

A European research team involving Hamburg University of Technology (TUHH) and Deutsches Elektronen-Synchrotron DESY has developed a novel way for converting mechanical energy into electricity – by using water confined in nanometre-sized pores of silicon as the active working fluid.

In a study published in Nano Energy (Elsevier), scientists from CIC energiGUNE (Spain), the University of Ferrara(Italy), the Hamburg University of Technology (TUHH) and DESY(Germany), the University of Silesia in Katowice (Poland), and Riga Technical University (Latvia) — supported by the Cluster of Excellence “BlueMat – Water-Driven Materials” — demonstrate that the cyclic intrusion and extrusion of water in water-repellent nanoporous silicon monoliths can produce measurable electrical power.

Electricity generated by friction in tiny pores

The developed system, known as an Intrusion–Extrusion Triboelectric Nanogenerator (IE-TENG), uses pressure to repeatedly force water into and out of nanoscale pores. During this process, charge generation occurs at the interface between the solid and the liquid. This is a type of friction electricity that often occurs in everyday life. An example that everyone is familiar with: walking across a PVC carpet with shoes on. Electrons transfer from one body to another, accumulating a charge that is suddenly discharged when a third body is touched. For example, when touching a door handle, the charge flows away and you get a small electric shock. 

The achieved energy conversion efficiency of up to 9% ranks among the highest ever reported for solid–liquid nanogenerators. “Even pure water, when confined at the nanoscale, can enable energy conversion,” says Prof. Patrick Huber, spokesperson of the BlueMat – Water-Driven Materials Excellence Cluster at the Hamburg University of Technology (TUHH) and DESY. Dr. Luis Bartolomé (CIC energiGUNE) adds: “Combining nanoporous silicon with water enables an efficient, reproducible power source — without exotic materials, but just by using the most abundant semiconductor on earth, silicon, and the most abundant liquid, water.”

Materials design as the key

“A crucial step was the development of precisely engineered silicon structures that are simultaneously conductive, nanoporous, and hydrophobic,” explains Dr. Manuel Brinker from the Hamburg University of Technology. “This architecture allows us to control the motion of water inside the pores — making the energy conversion process both stable and scalable.”The technology paves the way for autonomous, maintenance-free sensor systems — for example in water detection, sports and health monitoring in smart garments, or haptic robotics, where touch or motion directly generates an electrical signal. “Water-driven materials mark the beginning of a new generation of self-sustaining technologies,” emphasize the corresponding authors Prof. Simone Meloni (University of Ferrara) and Dr. Yaroslav Grosu (CIC energiGUNE).

Reference:
L. Bartolomé et al., Triboelectrification during non-wetting liquids intrusion–extrusion in hydrophobic nanoporous silicon monoliths,
Nano Energy 146 (2025) 111488.
DOI: 10.1016/j.nanoen.2025.111488