Ion transport in energy materials

Specifically, NMR studies allow us not only to obtain diffusion coefficients but also to measure correlation functions and spectral densities of the ionic motion in a straightforward manner. Moreover, temperature-dependent analysis provides access to the energy landscape of the ion transport. We exploit these capabilities to determine, e.g., the mechanisms for the charge transport in glass-ceramics, which exhibit promisingly high ion conductivities. Our results show that broad distributions of activation energies govern the ion jumps in these materials. Thus, the ions have largely different jump rates. This fact needs to be considered in theoretical models of the charge transport in battery materials.

In fuel cells, hydrated polymer membranes, e.g., Nafion, serve not only to separate anode and cathode but also to enable the proton transport, which is crucial for the function. Despite intense research efforts, the mechanism for the proton transport in the polymer matrix is not fully understood to this day. In particular, it remains elusive in which way the absorbed water enhances the proton mobility. We study polymer membranes with different chemical composition and water content and use the isotope selectivity of NMR to determine both proton and oxygen diffusion coefficients. In this way, we tackle, e.g., the question whether the protons use the water molecules as vehicles.