MXene as a frame for 2D water films shows new properties
Cooling down the MXene with enclosed water (left) leads to the formation of amorphous ice clusters (right), significantly increasing the distance between the MXene layers and the formerly metallic MXene becomes a semiconductor. When heated, the clusters dissolve, the distance between the layers decreases and the sample becomes metallic again. © HZB
An international team led by Dr. Tristan Petit and Prof. Yury Gogotsi has investigated MXene with confined water and ions at BESSY II. In the MXene samples, a transition between localised ice clusters to quasi-two-dimensional water films was identified by increasing temperature. The team also discovered that the intercalated water structure drives a reversible transition from metallic to semiconducting behaviour of the MXene film. This could enable the development of novel devices or sensors based on MXenes.
Water still has unknown sides. When water is forced into two dimensions by enclosing it in appropriate materials, new properties, phase transitions, and structures emerge. MXenes as a class of materials offer a unique platform for exploring these types of phenomena: MXenes consist of transition metal carbides and nitrides with a layered structure whose surfaces can help them absorb water easily. The water forms an extremely thin film between the individual layers.
A team led by Dr Tristan Petit, HZB, and Yury Gogotsi, Drexel University, USA, has investigated a series of MXene samples containing enclosed water and different ions at BESSY II using various analytical methods.
X-ray structural analysis revealed the formation of amorphous ice clusters in the enclosed water, which increases the distance between the MXene layers. The previously metallic MXene film then becomes a semiconductor. “When heated above 300 K, the clusters dissolve again, restoring the distance between the layers and their metallic behaviour,” says Petit. This metal-semiconductor transition is therefore reversible, unless the water layer is removed. Further X-ray investigations using different techniques revealed unique characteristics in the water hydrogen bond networks.
‘In the next step, we need computer-aided modelling to improve our understanding of the formation of amorphous ice and its impact on electronic transport,’ says Katherine Mazzio, who is co-first author of the study. She concludes that MXene is ideal for investigating the phase changes of confined water, providing new insights into how water behaves at the nanoscale. The use of MXene as a material for energy storage and catalysis is already being discussed, and the role of confined water on the unique MXene properties for these applications is currently being investigated.
- Fascinating archaeological find becomes a source of knowledgeThe Bavarian State Office for the Preservation of Historical Monuments (BLfD) has sent a rare artefact from the Middle Bronze Age to Berlin for examination using cutting-edge, non-destructive methods. It is a 3,400-year-old bronze sword, unearthed during archaeological excavations in Nördlingen, Swabia, in 2023. Experts have been able to determine how the hilt and blade are connected, as well as how the rare and well-preserved decorations on the pommel were made. This has provided valuable insight into the craft techniques employed in southern Germany during the Bronze Age. The BLfD used 3D computed tomography and X-ray diffraction to analyse internal stresses at the Helmholtz-Zentrum Berlin (HZB), as well as X-ray fluorescence spectroscopy at a BESSY II beamline supervised by the Bundesanstalt für Materialforschung und -prüfung (BAM).
- MXene for energy storage: More versatile than expectedMXene materials are promising candidates for a new energy storage technology. However, the processes by which the charge storage takes place were not yet fully understood. A team at HZB has examined, for the first time, individual MXene flakes to explore these processes in detail. Using the in situ Scanning transmission X-ray microscope 'MYSTIIC' at BESSY II, the scientists mapped the chemical states of Titanium atoms on the MXene flake surfaces. The results revealed two distinct redox reactions, depending on the electrolyte. This lays the groundwork for understanding charge transfer processes at the nanoscale and provides a basis for future research aimed at optimising pseudocapacitive energy storage devices.
- Bernd Rech elected to the BR50 Board of DirectorsThe Scientific Director at Helmholt-Zentrum Berlin is the new face behind the "Natural Sciences" unit at Berlin Research 50 (BR50). Following the election in December 2025, the constituent meeting of the new BR50 Board of Directors took place on 22 January 2026.
Its members are Michael Hintermüller (Weierstrass Institute, WIAS), Noa K. Ha (German Centre for Integration and Migration Research, DeZIM), Volker Haucke (Leibniz Research Institute for Molecular Pharmacology, FMP), Uta Bielfeldt (German Rheumatism Research Centre Berlin, DRFZ) and Bernd Rech (HZB).