Sensitivity Enhancements in Lithium Titanates by Incipient Wetness Impregnation DNP NMR

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 Li-7 and Li-6 NMR spectra of the compounds. We also show that hyperpolarization is relayed from the surface toward the bulk for both Li-7 and Li-6 and demonstrate an overall gain in sensitivity of a factor similar to 90 for the bulk spectrum of Li-6 in Li4Ti5O12. The method can in principle be applied to increase sensitivity in the surface and bulk spectra of other inorganic lithium oxides.