Peculiar reactions between interstitial compounds of transition metals and hydrogen peroxide and characterization of resultant materials

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It has been found that some tungsten oxide clusters like peroxo-oxalato-polytungstate formed by a reaction of tungsten carbide with hydrogen peroxide show high proton conductivity. In this fiscal year have studied a methodology to incorporate such a cluster into an organic matrix to enhance chemical stability, and evaluated nanohybrid materials thus obtained as a proton conductive solid electrolyte membrane.We obtained a homogeneous solution of a peroxotungstate complex by reacting tungsten trioxide monohydrate with hydrogen peroxide at 40℃ for 24 h. A carboxylic acid such as oxalic, malonic or dimethylmalonic acid was added to the solution at the ratio of 0.25-4.0 to tungsten atom, to yield a chelated complex. This solution was added to a methanol solution of alchoxysillilated poly (ethyleneoxide)-600 and polymerized at 60℃ by a sol-gel process. A homogeneous and transparent membrane was formed.Proton conductivity of those membranes was measured in the temperature range of 25-160℃ under suturated water vapor pressure by the ac impedance method. Conductivity of a typical membrane at 80℃ was 1.4x10^<-2> Scm-1, which was 10 times higher that that of a composite membrane fabricated by simply blending PEO and tungsten trioxide dihydrate as an inorganic high proton conductor. This means that tungstate clusters dispersed at a nano-level homogeneity throughout the PEO-matrix form a percolation path for fast proton transport. Such a situation was also confirmed by vibration spectra and X-ray diffraction. Although conductivity fell with raising temperature above 100℃, it remained at a level of 10^<-4> Scm^<-1> in the range of 140-160℃. Bulky ligands such as dimethylmalonate tended to suppress conductivity fall at high temperature.