Heterostructured CoO/3D-TiO2 nanorod arrays for photoelectrochemical water splitting hydrogen production

Homogeneous p-type cobalt (II) oxide (CoO) nanoparticles were successfully deposited on n-type three-dimensional branched TiO2 nanorod arrays (3D-TiO2) through photochemical deposition and thermal decomposition to form a novel CoO/3D-TiO2 p-n heterojunction nanocomposite. Due to the narrow band gap of CoO nanoparticles (similar to 2.4 eV), the as-synthesized CoO/3D-TiO2 exhibited an excellent visible light absorption. The amounts of deposited CoO nanoparticles obviously influence the hydrogen production rate in the photoelectrochemical (PEC) water splitting. The as-synthesized CoO/3D-TiO2-5 obtains the highest PEC hydrogen production rate of 0.54 mL h(-1) cm(-2) after five-time CoO deposition cycles (at a potential of 0.0 V vs Ag/AgCl). The photocurrent density of CoO/3D-TiO2-5 is 1.68 mA cm(-1), which is ca. 2.5 times greater than that of pure 3D-TiO2. The results showed that the formation of internal electrical-field between the CoO/3D-TiO2 heterojunction, which has a direction from n-type TiO2 to p-type CoO, facilitated the charge separation and transfer and resulted in a high efficiency and stable PEC activity.