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

Proton conducting gel electrolytes based on a network of various polymer matrices such as methyl methacrylate (MMA) and glycidyl methacrylate (GMA) containing perdeuterated H3PO4 have been synthesized using: propylene carbonate (PC), dimethylformamide (DMF) and dimethylacetamide (DMA) as entrapped solvents. These systems have ionic conductivities as high as 10(-4) S cm (-1) at ambient temperatures. The operating range of these electrolytes is from 220 to 370 It. In an attempt to understand their structure and dynamic properties, we report P-31 (I = 1/2) spectroscopic and self-diffusion coefficient (D) measurements of mobile phosphorus species for these materials at room temperature, using pulsed field-gradient Hahn spin-echo techniques. The P-31 NMR signal in some systems was found to have multiple peaks indicating the presence of o-phosphoric acid, charged dissociated species, and condensed phosphates. It is estimated that condensed phosphates comprise up to 40% of the phosphate species in GMA based electrolytes. As expected 31P diffusion coefficients of the different phosphate species present are determined to be dependent on the size of the moving phosphate species. (C) 2001 Elsevier Science Ltd. All rights reserved.