Characterization of perdeuterated H3PO4-doped nonaqueous gel electrolytes using P-31 nuclear magnetic resonance spectroscopy

Proton conducting gel electrolytes based on a network of various polymer ma trices such as methyl methacrylate (MMA) and glycidyl methacrylate (GMA) co ntaining perdeuterated H3PO4 have been synthesized using: propylene carbona te (PC), dimethylformamide (DMF) and dimethylacetamide (DMA) as entrapped s olvents. These systems have ionic conductivities as high as 10(-4) S cm (-1 ) at ambient temperatures. The operating range of these electrolytes is fro m 220 to 370 It. In an attempt to understand their structure and dynamic pr operties, we report P-31 (I = 1/2) spectroscopic and self-diffusion coeffic ient (D) measurements of mobile phosphorus species for these materials at r oom temperature, using pulsed field-gradient Hahn spin-echo techniques. The P-31 NMR signal in some systems was found to have multiple peaks indicatin g the presence of o-phosphoric acid, charged dissociated species, and conde nsed phosphates. It is estimated that condensed phosphates comprise up to 4 0% of the phosphate species in GMA based electrolytes. As expected 31P diff usion coefficients of the different phosphate species present are determine d to be dependent on the size of the moving phosphate species. (C) 2001 Els evier Science Ltd. All rights reserved.