BESSY II: Influence of protons on water molecules
The spectral fingerprints of water molecules could be studied at BESSY II. The result: the electronic structure of the three innermost water molecules in an H7O3+ complex is drastically changed by the proton. In addition, the first hydrate shell of five other water molecules around this inner complex also changes, which the proton perceives via its long-range electric field. © MBI
How hydrogen ions or protons interact with their aqueous environment has great practical relevance, whether in fuel cell technology or in the life sciences. Now, a large international consortium at the X-ray source BESSY II has investigated this question experimentally in detail and discovered new phenomena. For example, the presence of a proton changes the electronic structure of the three innermost water molecules, but also has an effect via a long-range field on a hydrate shell of five other water molecules.
Excess protons in water are complex quantum objects with strong interactions with the dynamic hydrogen bond network of the liquid. These interactions are surprisingly difficult to study. Yet so-called proton hydration plays a central role in energy transport in hydrogen fuel cells and in signal transduction in transmembrane proteins. While the geometries and stoichiometries have been extensively studied both in experiments and in theory, the electronic structure of these specific hydrated proton complexes remains a mystery.
A large collaboration of groups from the Max Born Institute, the University of Hamburg, Stockholm University, Ben Gurion University and Uppsala University has now gained new insights into the electronic structure of hydrated proton complexes in solution.
Using the novel flatjet technology, they performed X-ray spectroscopic measurements at BESSY II and combined them with infrared spectral analysis and calculations. This allowed them to distinguish between two main effects: Local orbital interactions determine the covalent bond between the proton and neighbouring water molecules, while orbital energy shifts measure the strength of the proton's extended electric field.
The results suggest a general hierarchy for proton hydration: the proton interacts with three water molecules and forms an H7O3+ complex. The hydrate shell of this complex is influenced by the electric field of the positive charge of the proton.
The new research findings have direct implications for understanding proton hydration from protons in aqueous solution to proton complexes in fuel cells to water structure hydration pockets of proton channels in transmembrane proteins.
Full text of the MBI-Press release >
- Cool vaccines in rural Kenya: solar solution has been awarded by UNIn May 2026, Tabitha Awuor Amollo is spending some weeks as a guest scientist at HZB, analysing perovskite thin films at BESSY II. The Kenyan physicist from Egerton University, Nairobi, was recently recognised for her achievements in research and teaching. For the development of a solar-powered refrigeration system for use in rural health centres, she has been awarded the 2026 Organization for Women in Science for the Developing World (OWSD)-Elsevier Foundation Award. An interview on exceptional projects and daily struggles of a scientist. Questions were asked by Antonia Rötger.
- BESSY II: How intrinsic oxygen shortens the lifespan of solid-state batteriesAlthough solid-state batteries (SSBs) demonstrate high performance and are intrinsically safe, their capacity currently declines rapidly. A team from the TU Wien, Humboldt-University Berlin and HZB has now analysed a TiS₂|Li₃YCl₆ solid-state half-cell in operando at BESSY II using a special sample environment that allows for non-destructive investigation under real operating conditions. Data obtained by combination of soft and hard X-ray photoelectron spectroscopy (XPS and HAXPES) revealed a new degradation mechanism that had not previously been identified in solid-state batteries. They have gained some surprising insights, particularly regarding the harmful role played by intrinsic oxygen. This study provides valuable information for improving design and handling of such batteries.
- Spintronics at BESSY II: Real-time analysis of magnetic bilayer systemsSpintronic devices enable data processing with significantly lower energy consumption. They are based on the interaction between ferromagnetic and antiferromagnetic layers. Now, a team from Freie Universität Berlin, HZB and Uppsala University has succeeded in tracking, for each layer separately, how the magnetic order changes after a short laser pulse has excited the system. They were also able to identify the main cause of the loss of antiferromagnetic order in the oxide layer: the excitation is transported from the hot electrons in the ferromagnetic metal to the spins in the antiferromagnet.