This work is focused on the combination of two building-blocks,nanocrystalline TiO_2 particles and polyaniline conductive films(PAni).The preparation of new nanostructured composite materials,displaying electron-and proton-conductive properties,to be used for the fabrication of new and superior energy storage devices was envisaged.The semiconducting TiO_2 nanoparticles were obtained by means of a hydrothermal route.The PAni films were prepared on glassy carbon electrodes by electrochemical polymerization,under potential dynamic conditions.After characterization by X-ray diffraction,transmission electron microscopy or scanning electron microscopy and electrochemical techniques,the nanocrystalline particles were immobilized in the polymer matrix.The incorporation of the TiO_2 was achieved using two distinct approaches:during the polymer growth or by deposition over previously prepared PAni films.The results demonstrate that the PAni morphology depends on the experimental conditions used during the polymer growth.After TiO_2 immobilization,the best electrochemical response was obtained for the nanocomposite structure produced through the TiO_2 incorporation after the PAni film synthesis.The modified electrodes were structurally and morphologically characterized and their electro-catalytic activity towards the hydrogen evolution reaction was analyzed.A new electrochemical performance related with the oxidation of molecular hydrogen entrapped in the PAni-TiO_2 matrix was observed for the modified electrode after TiO_2 incorporation.This behavior can be directly associated with the synergetic combination of the TiO_2 and PAni,and is dependent on the amount of the semiconductor. This work is focused on the combination of two building-blocks, nanocrystalline TiO 2 particles and polyaniline conductive films (PAni). The preparation of new nanostructured composite materials, displaying electron-and proton-conductive properties, to be used for the fabrication of new and superior energy storage devices was envisaged.The semiconducting TiO_2 nanoparticles were obtained by means of a hydrothermal route. The PAni films were prepared on glassy carbon electrodes by electrochemical polymerization, under potential dynamic conditions. After characterization by X-ray diffraction, transmission electron microscopy or scanning electron microscopy and electrochemical techniques, the nanocrystalline particles were immobilized in the polymer matrix. The incorporation of the TiO 2 was achieved using two distinct approaches: during the polymer growth or by deposition over previously prepared PAni films. on the experimental conditions us ed during the polymer growth. After TiO 2 immobilization, the best electrochemical response was obtained for the nanocomposite structure produced through the TiO 2 incorporation after the PA ni film synthesis. the modified electrodes were structurally and morphologically characterized and their electro-catalytic activity towards the hydrogen evolution reaction was analyzed. A new electrochemical performance related with the oxidation of molecular hydrogen entrapped in the PAni-TiO 2 matrix was observed for the modified electrode after TiO 2 incorporation. This behavior can be directly associated with the synergetic combination of the TiO 2 and PAni, and is dependent on the amount of the semiconductor.