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.