(Invited) Enhanced Photoelectrocatalytic Activity for Splitting Water Based on Heterostructured TiO2 Nanotube Arrays

Photoelectrocatalytic water splitting is widely recognized as one of the most promising strategies to large-scale production of hydrogen for renewable energy. To further enhance the photoelectrocatalytic efficiency, severalheterostructures based on TiO2 nanotube arrays were developed in this work. (1) TiO2 nanotube arrays (TNTAs) were decorated with NiO nanoparticles via a sequential chemical bath deposition (CBD) approach to yield NiO@TNTA photoanodes. It demonstrated that the incident-photon-to-current-conversion efficiency (IPCE) and hydrogen production rate of the optimized NiO@TNTA reached 62.8% and 37.8 μmol.h-1.cm-2, respectively, approximately 5.0 times higher than pure TNTAs, which was attributed primarily to the efficient separation of photogenerated charge carriers at the p–n junction of p-type NiO and n-type TiO2. (2) CuxZn1-xIn2S4 ultrathin nanosheets on TiO2 nanotube arrays (CZIS@TNTAs) was successfully synthesized by solvothermal reaction. It found that the CuxZn1-xIn2S4 ultrathin nanosheets on TNTAs significantly enhanced visible light absorption and and a near 8.0-fold increase in photoelectrocatalytic hydrogen production rate was achieved compared to that of the blank TNTAs. The superior photoelectrocatalytic activity of CZIS@TNTAs heterostructured composite electrode was mainly due to enhanced light absorption and separation of photo-generated charges, and facilitating electron transport along the 1D TiO2 structure. (3) TiO2 nanotube arrays (TNTAs) sensitized by palladium quantum dots (Pd QDs) by a modified hydrothermal reaction. When Pd@TNTA nanocomposites were used as both photoanode and cathode in water splitting, the photon-to-current conversion efficiency of nearly 100% atλ=330 nm and a greatly promoted photocatalytic hydrogen production rate of 592 μmol·h−1·cm−2 under 320 mW·cm−2 irradiation were achieved. The synergy between nanotubular structures of TiO2 and uniformly dispersed Pd QDs on TiO2 facilitated the charge transfer from TiO2 nanotubes to Pd QDs and the high activity of Pd QDs catalytic center, thereby leading to high-efficiency photoelectrocatalytic hydrogen generation.