Synthesis, characterization and properties of a melanin-like/vanadium pentoxide hybrid compound

An intercalated material has been prepared consisting of a regular alternation of organic/inorganic layers. The products were obtained by reacting 3,4-dihydroxyphenylalanine (dl-DOPA) with V2O5. nH(2)O gel, which underwent an oxidative polymerization/intercalation process, forming a dark blue metallic colored film. The films were characterized using thermogravimetric analysis, UV-VIS transmission spectroscopy, FTIR, EPR, X-ray diffraction, dc conductivity, and cyclic voltammetry. The X-ray diffractograms indicate that the lamellar structure of the V2O5 is preserved but that the interplanar spacing increases from 1.18 to 1.38 nm. The FTIR and EPR spectra confirm that the V2O5 structure is preserved; however the presence of melanin-like structures induces the reduction of V-V ions to V-IV. The increase in the interplanar spacing is observed to increase the stability and reproducibility of the electrochemical insertion/deinsertion of Li+. This increase in stability is also observed in the electrochromic properties of the film, which are fully reproducible even after > 60 oxidation-reduction cycles. The incorporation of melanin-like structures also affects the activation energy of the dc conductivity, which is reduced from 0.35 to 0.20 eV.