Sensitivity Enhancements in Lithium Titanates by Incipient Wetness Impregnation DNP NMR

Abstract

Solid-state NMR spectroscopy is a widely used method for investigating structural and electronic properties of inorganic materials, but its use is often limited by low sensitivity. Here, we show how solvent-generated dynamic nuclear polarization can be used to efficiently hyperpolarize the surface and bulk of lithium-containing inorganic materials, through impregnation with a radical-containing solution and transfer of hyperpolarization to lithium nuclei in the materials. This is demonstrated on two lithium titanates, Li2TiO3 and Li4Ti5O12, resulting in improved sensitivity of both 7Li and 6Li NMR spectra of the compounds. We also show that hyperpolarization is relayed from the surface toward the bulk for both 7Li and 6Li and demonstrate an overall gain in sensitivity of a factor '90 for the bulk spectrum of 6Li in Li4Ti5O12. The method can in principle be applied to increase sensitivity in the surface and bulk spectra of other inorganic lithium oxides.