Ternary TiO2/Ni–Ni(OH)2/NiPi nanotube arrays with synergetic effect for enhanced photoelectrocatalytic H2-evolution

Dual co-catalysts have an essential effect on improving the photoelectrochemical (PEC) performance of semiconductor materials. In this study, Ni–Ni(OH)2 or/and Nikel phosphate (NiPi) nanocrystals co-catalysts were deposited on the surface of as-prepared TiO2 nanotube arrays (TNTAs) by a simple electrodeposition route for PEC hydrogen production. The TNTAs loading with Ni and NiPi bifunctional co-catalysts exhibited remarkably enhanced PEC performance, with about an 8.3-fold increase in the photocurrent; and an 11.7-fold improvement in H2 evolution rate in comparison to bare TNTAs. The constructed ternary TNTAs/Ni–Ni(OH)2/NiPi comprised the advantage of Ni–Ni(OH)2 and NiPi nanoparticles to enhance visible-light absorption and promote oxygen evolution reaction (OER) kinetics. The internal electric field is generated between supported p-type Ni(OH)2 and n-type TiO2 under light irradiation, which will drive holes to flow to Ni(OH)2 and oxidize it as the OER active layer. Also, the photo-generated holes remaining in the TiO2 valence band can migrate to NiPi co-catalysts to cause OER. Therefore, the photogenerated electron-hole pairs can be successfully separated under the synergetic influence of Ni–Ni(OH)2 and NiPi co-catalyst, leading to a superior PEC water splitting ability.