Structural and photoelectrochemical characterization of MWCNT-TiO2 matrices sensitized with Bi2S3

Structural and photoelectrochemical characterization of multiwall carbon nanotubes–titanium oxide (MWCNT-TiO2) matrices, sensitized with bismuth sulfide (Bi2S3), are presented as a function of MWCNT-TiO2 annealing temperature and Bi2S3 deposition time. Random matrices of multiwall carbon nanotubes were grown on stainless steel substrates by spray pyrolysis and then functionalized with a thin layer of TiO2. Air annealing modifies the morphology and C/TiO2 ratio in the hybrid materials, from MWCNT-TiO2 core and shell structures at 400 °C to carbon-doped TiO2 (C-TiO2) at 550 °C. Both matrices increase the amount of Bi2S3 deposited by the chemical bath, but the best photoelectrochemical performance is observed in electrodes based on C-TiO2. Electrodes based on core–shell structures of MWCNT-TiO2 show large capacitive currents that interfere with photocurrent generation, demonstrating the storage potential of MWCNT and the critical role of MWCNT/TiO2 ratio for photoelectrochemical applications. Regardless of the superior properties of C-TiO2 photoanodes, the power conversion efficiency of Bi2S3-sensitized C-TiO2 is limited by the appearance of an electron collection barrier at the substrate/film interface.