Abstract
This paper is a brief review of our recent research into novel uses for heteropoly compounds as precursors for thin films that can be used as catalysts and materials with good optical, conductive and other characteristics. In view of this, we have chosen thin film obtained with 12-tungsphosphoric acid on aluminum substrates. In all cases, a relatively new, microarc oxidation technique has been used to prepare oxide coatings on substrate surfaces. Advanced physicochemical methods, AFM and SEM-EDS, XRD, Raman and Micro-Raman, and luminescence spectroscopy, as the most powerful techniques, have been used for the characterization of new materials. Possible applications have been discussed as well.
Highlights
Polyoxometalates (POMs), having more than a hundred years of history, continue to attract the attention of researchers as catalysts, solid superionic proton conductors at room temperatures, applicable in different electrochemical devices, and as photochromic, biochemical and biomedical active materials [1,2,3,4,5,6,7]
Materials 2010, 3 proton electrolytes started with the study of Nakamura et al [3], who have found that heteropoly acids (HPAs), at room temperature, have proton conductivity between (100–1) × 10-3 S/cm
We have developed an ultrasonic spray pyrolysis (USP) method to obtain fine, spherical, nanostructured PWB particles starting with WPA, or metal-WPA salt solutions [44,45,46]
Summary
Polyoxometalates (POMs), having more than a hundred years of history, continue to attract the attention of researchers as catalysts, solid superionic proton conductors at room temperatures, applicable in different electrochemical devices, and as photochromic, biochemical and biomedical active materials [1,2,3,4,5,6,7]. Primary and secondary structures of HPCs define their high redox properties, polarity, surface charge distribution, electron and proton transfer/storage ability, high charges and high ionic weight of heteropoly anions, and explain their applications Drawbacks of these compounds are their sensitivity to environmental conditions, temperature and relative humidity. These disadvantages can be overcome by incorporation of the acid into various stable porous supports and formation of different composites [14,15,16,17] or by neutralization of the acid with large cations (K+, Rb+, Cs+, NH4+) to form porous insoluble salts, which are less sensitive to the ambient conditions [18,19,20,21,22] All these compounds exhibit high proton conductivity and can be used as solid electrolytes in fuel cells, or as catalysts due to their high specific surface areas. Based on our previous knowledge and experience, we have made an effort to improve the film characteristics for their better commercial exploitation, by using WPA as precursor
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