31P and 1H NMR investigation of nanoparticulate lanthanum and cerium phosphates: Novel materials for PEM fuel cell membranes

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Shashi Vyas, svyas@lbl.gov1, Sam L. Wilcke2, Gabriel, A. Harley, gharley@lbl.gov3, Lindsey, A. Karpowich, lakarpowich@lbl.gov3, Rong Yu, ryu@lbl.gov1, Lutgard De Jonghe, dejonghe@lbl.gov4, and Jeffery A. Reimer, reimer@socrates.berkeley.edu5. (1) Materials Science Division, Lawrence Berkeley National Laboratory, Department of Chemical Engineering, 201 Gilman Hall, University of California, Berkeley, CA 94720-1460, (2) Department of Chemical Engineering, University of California, Berkeley, 201 Gilman Hall, University of California, Berkeley, CA 94720-1462, (3) Department of Material Science and Engineering, Materials Science Division, Lawrence Berkeley National Laboratory, University of California, 210 Hearst Memorial Mining Building, Bldg. 62- Rm 203, Berkeley, CA 94720, (4) Materials Science Division, Department of Materials Science and Engineering, Lawrence Berkeley National Laboratory, University of California, Building 62- Rm 245, 210 Hearst Memorial Mining Building, Rm. 324, Berkeley, CA 94720, (5) Materials Science Division, University of California, Lawrence Berkeley National Laboratory, Department of Chemical Engineering, Berkeley, CA 94720-1462
31P and 1H NMR is used to investigate structure and protonic mobility in pure and doped nanoparticulate lanthanum and cerium phosphates for potential use as fuel cell membranes in the temperature range of 200 400 oC. Nanoparticulate cerium and lanthanum phosphates are synthesized with varying strontium concentrations and polyphosphate modified intergranular regions. 31P NMR in undoped CePO4 results in three peaks, one from the crystalline bulk CePO4 and the other two due to 31P of amorphous or poorly crystallized intergranular phosphate phases. Variable temperature 1H NMR in these materials are used to characterize the proton dynamics, in particular the hopping rates and the activation energy for the motion. In particular, the site-specific proton kinetics and activation energies are probed by studying the hopping between spectrally resolved protonic sites in a high-resolution multi-dimensional 1H NMR experiment.