Photocatalytic hydrogen evolution on the hetero-system polypyrrol/TiO2 under visible light

The semiconducting properties of the hetero-system polypyrrol(PPy)/TiO2 are investigated for the first time to assess its photo catalytic hydrogen evolution under visible light. The hetero-system PPy/TiO2 is stable up to similar to 345 K, with a weight loss accounting for similar to 1.2%. The Xray diffraction shows mixed phases with the rutile TiO2 variety. Optical transitions at 0.42 and 3.01 eV, directly allowed, are determined for PPy and TiO2 respectively. The p-type conductivity of PPy is evidenced from the Mott-Schottky plot; In neutral solution, a flat band potential of 0.11 V-SCE and a holes density of 4.57 x 1021 cm(-3) are obtained. The electrochemical impedance spectroscopy, measured over a wide frequency range (1 mHz-10(5) Hz), reveals the contribution of the bulk and grain boundaries with a constant phase element (CPE). The energetic diagram predicts the electron injection from PPy into TiO2 and the best photoactivity is achieved at pH similar to 7. A hydrogen liberation rate of 1.15 mmolh(-1) (g catalyst)(-1) and a quantum efficiency of 0.17% under full light (29 mW cm(-2)) are determined in presence S2O32-. The photoactivity is completely restored during the second cycle, indicating a zero deactivation effect. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.