Exploring complex pore structure in multi-scale porous materials by combining advanced NMR cryoporometry and NMR relaxometry

• Applicant: Professor Dr. Rustem Valiullin
• Subject Area: Analytical Chemistry ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545661271

There is an increased interest in the recent years for heterogenous, multi-scale porous materials. With pore sizes ranging from nanometers up to tens of micrometers, they are found in many systems such as natural clay formations used for diffusion barriers, in artificial hierarchical systems exploited in heterogeneous catalysis or in battery electrodes. Complex pore architecture renders explorations of their structural properties and establishing structure-transport relationships extremely difficult. In many of these materials, the routinely used approaches, such as mercury injection or gas sorption, may fail. Thus, the former one is destructive, not suitable for soft materials and is only sensitive to pore throats. The latter method, which benefited from major advancements in the past decades, is limited to the micro- and mesopore range in carefully dried materials. NMR cryoporometry (NMRC) is known for its capability of determining pore size distributions (PSD) in wetted and soft materials in a broad range including macropores, but is not commonly applied irrespective of several advantageous features. Its limited use is mostly caused by the lack of advanced methodology, by far less developed as compared to gas sorption, and instrumental costs. It is the goal of this project to show that NMRC can bring comparable or even higher level of structural insight compared to other methods by profiting from recent advancements in this field and by exploiting the unique power of NMR allowing to combine cryoporometry with NMR relaxation measurements. Most of the experiments will be performed on low-field and low-cost instruments. The project has the following objectives: (i) To extend the NMRC capabilities by introducing a library of standard liquids with supplementary melting and freezing kernels for accurate structure determination, these shall be compatible with a larger variety of porous media and have a potential to increase significantly of the measurable PSD range (brine, octamethylcyclotetrasiloxane, ionic liquids); This will be done using an original approach, the serially connected model, recently developed; (ii) To lay down approaches for extracting topological information such as connectivity from the melting-freezing cycles complemented by scanning (freezing after partial melting) experiments and by designing 2D NMR experiments for correlating nuclear magnetic relaxation with solid-liquid equilibria; (iii) To develop the NMR relaxation filters for NMRC applicable under the conditions when conventionally-used transversal relaxation filter cannot be applied. The latter situation is typical for industrially-relevant porous materials, such as battery electrodes.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Cooperation Partner: Professor Dr. Marc Fleury