Study of photoelectrochemical water splitting using composite films based on TiO2 nanoparticles and nitrogen or boron doped hollow carbon spheres as photoanodes

Novel composite films based on TiO2/hollow carbon spheres were used as photoanodes in photoelectrochemical water splitting studies. CVD grown pristine hollow carbon spheres (HCSs), N-doped HCSs (NHCSs) and B-doped HCSs (BHCSs) were used to prepare composites with TiO2 nanoparticles. The presence of B and N doping in these carbonaceous materials was confirmed by X-ray photoelectron spectroscopy (XPS). The composite films were characterized by X-ray diffraction, UV vis spectroscopy and electron microscopy techniques. In the photoelectrochemical studies, the influence of the addition of NHCSs or BHCSs in the TiO2 matrix was evaluated and compared with a pristine TiO2 film. The TiO2/NHCS (0.5 wt%) composite electrode exhibited a 2.4 increase in anodic current density compared to the pure TiO2 electrode; it also showed an enhanced incident photon to current efficiency (IPCE) and good photo electrochemical stability over time. The EIS analysis at open circuit conditions showed that the irradiated TiO2/NHCS electrode exhibited smaller resistance values (R-1 =43 Omega and R-2 =3.1 k Omega) than the irradiated TiO2/BHCS electrode (3.3 k Omega and 10 k Omega. From the experimental results, we propose a photocatalytic mechanism for the NHCS/TiO2 and BHCS/TiO2 composites as a photoanode. The presence of p-type BHCSs between the n-type TiO2 nanoparticles impairs the photocatalytic processes by the formation of a p-n diode with enhanced resistance and recombination. On the other hand, an appreciable enhancement of photocurrent density was achieved for the NHCS/TiO2 composite films due to a combination of their electronic properties, crack free compact film morphology and enhanced light absorption. (C) 2015 Elsevier B.V. All rights reserved.