eNMR basics

eNMR is a unique NMR spectroscopic technique for the investigation of transport properties in electrolytes under the influence of an electric field. The electric field \(E\) induces a coherent drift velocity \(\nu\) of the investigated NMR-active nuclei, which is proportional to the electrophoretic mobility \(\mu\) of the investigated species.

\[\nu = \mu E\]

This coherent drift induces a phase shift \(\phi-\phi_0\) of the observed NMR resonance, which is directly proportional to the observation time \(\varDelta\), the magnetic field gradient pulse duration \(\delta\), the magnetic field gradient pulse strength \(G\), and the gyromagnetic ratio of the observed nucleus \(\gamma\).

\[\begin{split}\phi - \phi_0 = \gamma G \delta \varDelta \nu\\\end{split}\]

eNMR combines the spectroscopic selectivity with electrochemistry, enabling the determination of electrochemical transference numbers of a plethora of ionic species, which would otherwise not be possible. The determined transference numbers are sign sensitive contrary to transference number estimations from the self-Diffusion coefficient via the Nernst-Einstein equation. Furthermore, using eNMR, the correlated migration of uncharged molecules with ions can be observed observing the migration of e.g. complex lithium-oligoether cations, or the interaction of additives/co-solvents with ions in highly concentrated ionic systems.