Designing Co-Pi Modified One-Dimensional n-p TiO2/ZnCo2O4 Nanoheterostructure Photoanode with Reduced Electron-Hole Pair Recombination and Excellent Photoconversion Efficiency (>3%)

The poor visible light absorption, defect-mediated charge carrier recombination, slow water oxidation kinetics, and charge transportation limit the performance of TiO2 photoelectrodes for water oxidation. In order to tackle these issues, here a one-dimensional photoanode is designed by electrodepositing a p-ZnCo2O4 nanolayer on n-TiO2 nanotubes surface and finally electrochemically coupling the TiO2/ZnCo2O4 surface with an ultrathin layer of the cobalt phosphate (Co-Pi) catalyst nanoparticles. These typical TiO2/ZnCo2O4@Co-Pi nanoheterostructures exhibit a remarkably enhanced visible light driven photoelectrochemical property with applied bias photoconversion efficiency (ABPE) similar to 3% at 0.2 V vs NHE. The TiO2/ZnCo2O4@Co-Pi nanoheterostructures also show enhanced visible light absorption with large photocurrent density similar to 440% higher than that of the TiO2 nanotubes electrode at 1.2 V vs Ag/AgCl and significantly low onset potential for water oxidation. Studies on the transient photocurrent and flat-band potential demonstrate the remarkable improvement in the photogenerated charge carrier separation or reduced recombination because of the favorable band alignment at the heterointerface. The Co-Pi catalyst further boosts the water oxidation reaction by reducing electronhole pair recombination through the suppression of the surface trap states. Moreover, Co-Pi also serves as a hole-acceptor layer, improving the charge-transfer kinetics for an enhanced photoelectrochemical performance.