Fluid distribution and pore wettability of monolithic carbon xerogels measured by 1H NMR relaxation
The pore wettability of two types of carbon xerogels exhibiting micro- and mesopores with different sizes was investigated using 1H NMR relaxation. These nanomaterials are great candidates as active material for gas diffusion electrodes in mobile energy storage devices. The distribution of fluids in these electrodes is a critical parameter determining the electrode performance. Using 1H NMR relaxation information about the wettability of micro- as well as mesopores is determined simultaneously. Two important solvents for electrolytes, water and dimethyl sulfoxide (DMSO), were studied for different filling states inside the porous structure. While for water no discrimination between micro- and mesopores could be achieved because of its fast exchange rate between the pores, the measurements with DMSO allow for discriminating between solvent in micro- and mesopores. Thus, the wettability of DMSO in both pore regimes was determined by calculating the surface relaxation strength. It turned out that the wettability of the porous structure is dependent on the differences in the pore sizes between micro- and mesopores. At low filling states both pore regimes compete for the remaining fluid leading to a nonuniform distribution. The pores with the better wettability keep the complete surface in contact with the bulk fluid.
Institute for Applied and Physical Chemistry and Center for Environmental Research and Sustainable Technology, University Bremen