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| Home > Publications database > Magnetic Resonance Techniques to Study Porous Electrodes and Electrode Surfaces |
| Conference Presentation (After Call) | FZJ-2020-02962 |
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2020
Abstract: Nuclear Magnetic Resonance (NMR) is a unique analytical tool to study molecular properties of various materials indestructively. Observable parameters include chemical structure, molecular motion, diffusion and various exchange processes. Moreover, these parameters may be resolved spatially over a region of interest with a resolution up to 50 µm employing Magnetic Resonance Imaging (MRI). Fundamental elements in MR techniques are magnetic fields and radio frequency irradiation.Thus, NMR is an attractive tool to study chemical processes in and at porous electrodes. Such electrodes are employed to convert electrical energy to chemical energy. A detailed understanding of the processes occurring during electrolysis is key to a rational approach in efficiency optimization.However, electrically conductive materials pose additional challenges in NMR: i) NMR measurements need to be performed at particular frequencies and the resonance mode of the sensor coil must be adjusted accordingly. Introduction of conductive samples in the sensor coil strongly shift its resonance mode and often render commercial probes untunable. Thus, custom probe head designs offering a large tuning range are needed. ii) Radio frequency eddy currents in conductive materials distort the exciting field.iii) The radio frequency response from the sample is distorted in the same way as the exciting field.This talk provides an introduction into NMR on electrically conductive samples. The effect of mode shifts upon sample change and its implications are discussed. Using different model systems, distortions in the exciting radio frequency field are visualized. The strength of these distortions is analyzed with respect to material type and thickness. It is shown that thin metal layers neither significantly perturb qualitative information in NMR spectra, nor relaxometric or diffusometric information. It is shown that radio frequency field distortion can be advantageous as an additional spectroscopic dimension, although most often regarded as a nuisance in literature.
Keyword(s): Chemical Reactions and Advanced Materials (1st) ; Energy (1st) ; Instrument and Method Development (1st) ; Chemistry (2nd) ; Instrument and Method Development (2nd)
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