Abstract
Synergistically designing porous nanostructures and appropriate band alignment for TiO2 heterophase junctions is key to efficient charge transfer, which is crucial in enhancing photoelectrochemical (PEC) water splitting for hydrogen production. Here, we investigate the efficiency of PEC water oxidation in anatase–rutile TiO2 nanostructured heterophase junctions that present the type-II band alignment. We specifically prove the importance of a phase alignment in heterophase junction for effective charge separation. The TiO2 heterophase junctions were prepared by transferring TiO2 nanotube (TNT) arrays onto FTO substrate with the help of a TiO2 nanoparticle (TNP) glue layer. The PEC characterization reveals that the rutile (R)-TNT/anatase (A)-TNP heterophase junction has a higher photocurrent density than those of A-TNT/R-TNP junction and anatase or rutile single phase, corresponding to twofold enhanced efficiency. This type-II band alignment of R-TNT/A-TNP for water oxidation, in which photogenerated electrons (holes) will flow from rutile (anatase) to anatase (rutile), enables to facilitate efficient electron-hole separation as well as lower the effective bandgap of heterophase junctions. This work provides insight into the functional role of heterophase junction for boosting the PEC performances of TiO2 nanostructures.
Highlights
Semiconductor nanostructure-based photoelectrochemical (PEC) or photocatalytic (PC) water splitting is an emerging technology in energy conversion, benefiting from its possible high efficiency.The diverse one-dimensional (1D) nanostructures of a semiconductor have been extensively explored for heterogeneous photocatalysis and heterostructure-based PEC photoelectrodes [1,2,3]
We developed TiO2-based heterophase junctions that have a larger specific surface area provided by nanostructures with high porosity and long aspect ratio; further, they exhibit an efficient charge transfer/separation offered by a favorable band alignment toward highly efficient PC
We developed TiO2 -based heterophase junctions that have a larger specific surface area provided by nanostructures with high porosity and long aspect ratio; further, they exhibit an efficient charge transfer/separation offered by a favorable band alignment toward highly efficient PC water oxidation
Summary
Semiconductor nanostructure-based photoelectrochemical (PEC) or photocatalytic (PC) water splitting is an emerging technology in energy conversion, benefiting from its possible high efficiency. The higher PEC performance mainly results from significantly lowering the effective bandgap of composite materials and facilitating efficient charge carrier separation due to a type-II band alignment of phase junctions. PC activity of anatase–rutile TiO2 composite nanoparticles is still impeded by the small specific surface area and limited surface active sites In this respect, developing TiO2 -based heterophase junctions that have the larger specific surface area provided by nanostructures with high porosity and long aspect ratio and an efficient charge transfer/separation offered by a favorable band alignment would provide a feasible route toward highly efficient PEC water oxidation. The R-TNT/A-TNP junction exhibited superior PEC performance, which is one order than that of R-TNP and two times higher than A-TNP Such enhanced PEC or PC properties are responsible for the efficient charge separation due to optimal band alignment and the enhanced surface catalytic activity due to 1D nanostructured TNT with a hierarchical porous structure
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