Enhanced H₂ Production of TiO₂/ZnO Nanowires Co-Using Solar and Mechanical Energy through Piezo-Photocatalytic Effect

Abstract

TiO2/ZnO nanowire arrays on stainless steel mesh for piezo-photocatalytic H2 production are synthesized via a two-step hydrothermal route. The photocatalytic H2 production efficiency under solar illumination can be enhanced by introducing mechanical vibration energy. As coutilizing the solar and mechanical energy (ultrasonic irradiation), the nanowires show high H2 production. The nanowire arrays also show excellent recyclability and stability. Additionally, this mesh-based structure can be retrieved easily from aqueous solution, which can meet the practical application demand. The working mechanism can be attributed to the piezo-photocatalytic effect, in which the piezoelectric field of bent ZnO nanowires and the built-in electric field of TiO2/ZnO heterostructures can efficiently separate the photogenerated electrons and holes for effectively producing H2. Present results provide a new strategy for developing photocatalytic H2 production techniques.

Enhanced Piezo‐Photoelectric Catalysis with Oriented Carrier Migration in Asymmetric Au−ZnO Nanorod Array

“…As shown in Figure a, ZnO nanorod array had an absorbance only in UV light region due to its large bandgap (≈3.3 eV). [ 36,37 ] In comparison, a shoulder LSPR peak at around 530 nm appeared after loading Au NPs onto the ZnO nanorods, for both Sy‐Au−ZnO and Asy‐Au−ZnO.…”

“…[ 31 ] However, ZnO as a n‐type semiconductor has a wide bandgap (≈3.3 eV) and rapid recombination of photon‐generated carriers. [ 32,33 ] Interestingly, wurtzite ZnO draws more attention because of its inherent piezotronic effect and piezo‐phototronic effect, [ 1,2,14,34–36 ] with the internal coupling of piezoelectric, semiconducting, and photonic properties. [ 37 ] When ZnO is subjected to an external mechanical force, a piezotronic potential (piezopotential) can be generated, [ 2 ] which could modulate the migration and separation of internal charge carriers, finally enhancing photocatalytic performance.…”

Coupling Piezocatalysis and Photocatalysis in Bi4NbO8X (X = Cl, Br) Polar Single Crystals

“…Singh and Khare demonstrated the enhanced water splitting activity of piezoelectric‐NaNbO 3 owing to the piezophototronic effect . Wang et al fabricated TiO 2 /ZnO nanowire to enhance H 2 production by piezo–photocatalytic effect . However, a thorough mechanism behind the piezo–photocatalytic behavior is not established by the very limited reports in this emerging area, while the piezo–photocatalytic ROS evolution initiated by piezoelectric semiconductors has never been touched so far.…”

The Role of Polarization in Photocatalysis

“…[35] As at ypical piezoelectric material, ZnO is employed to capture mechanical energy and provides ap iezoelectric polarization field in heterojunctions.In2016, Wang et al revealed the potential of piezotronics in photocatalysis on account of the research of polarization-induced interface band bending by assembling TiO 2 nanoparticles onto ZnO nanoplatelets. [36] Meanwhile,Hong et al reported the preparation of CuS/ZnO heterostructured nanowire arrays by vertically aligning them on stainless steel mesh using as imple two-step wet-chemical method (Figure 7a,b) [37] TheC uS/ ZnO nanocomposite displayed excellent piezo-photocatalytic performance for degrading MB (degradation ratio of % 100 %w ithin 20 min) under light and ultrasonic irradiation (Figure 7c), and is ascribed to the interfacial polarization field caused by ZnO nanowires.D riven by this polarization field, the photoinduced e À in the conduction band (CB) of CuS moved to that of ZnO,w hile the h + migrated from the valence band (VB) of ZnO to that of CuS.A s aconsequence,the photogenerated e À /h + pairs were separated at the interface of the CuS/ZnO nanowires,benefitting photocatalysis.A similar strategy is also applied in Ag/Ag 2 S-ZnO/ZnS branched heterostructures [38] and TiO 2 /ZnO nanowires, [39] and all depend on ZnO to provide apiezoelectric polarization field for promoting interface charge separation.…”