Composite of Cobalt-C3N4 on TiO2 Nanorod Arrays as Co-catalyst for Enhanced Photoelectrochemical Water Splitting

TiO2@Co-C3N4 nanorod arrays were prepared by drop coating and hydrothermal method. The Photoelectrochemical (PEC) performance of TiO2@Co-C3N4 nanorod arrays can be tuned by the amount of Co-C3N4 coated. When the amount of Co-C3N4 reached about 0.75 mu g/cm(2), the PEC performance of TiO2@Co-C3N4 reached the maximum. The results show that the photocurrent density of TiO2@Co-C3N4 nanorod array reaches 1.79 mA/cm(2) at 1.23 V-RHE, which is about 2.3 times of that from TiO2@g-C3N4. And the PEC device has good stability and the photocurrent density remains no decline after 10 hours of continuous operation. Co atoms coordinated with g-C3N4 could act as a co-catalyst for water oxidation, and a possible mechanism is proposed for water oxidation based on careful analysis of the detailed results. The holes photogenerated by excited electrons oxidize Co atoms from Co-II to Co-III and Co-IV, and then these high-valence cobalt species accelerate the kinetics of water oxidation. In addition, Co-C3N4 not only can promote the charge transfer but also improve the overall energy conversion efficiency of the PEC device.