Using photoelectrochemical (PEC) water splitting to produce green hydrogen from solar energy is a potentially practical approach. Unfortunately, the slow water oxidation reaction and very low charge separation efficiency of contemporary PEC systems make them unsuitable for practical applications.
The Formed Built-In Electric Field and Polarized-Induced Electric Field at the Interface of Heterojunction to Promote Carrier Separation. Image Credit: Green Energy & Environment
Achieving effective charge spatial separation is the primary hurdle in the efficient conversion of solar energy into hydrogen. One of the most promising techniques for spatial charge separation is heterojunction engineering; nevertheless, because of energy band matching or the structural and interfacial compatibility of various semiconductors, heterojunction’s carrier separation efficiency is still restricted.
In the meantime, it has been demonstrated that it is possible to create p-n homojunction by precisely regulating dopants or defects in semiconductors; nonetheless, the phenomena that neutralize the interfacial electric field during the transfer process by rapidly accumulating carriers is essentially insignificant.
In order to get beyond the charge separation and transfer limitation of p-n junctions, a group of researchers from the School of Chemical Engineering and Technology at Tianjin University created a novel n-TiO2/BaTiO3/p-TiO2 heterojunction that couples with piezoelectric effect and p-n junctions.
In our designed heterojunction, the ferroelectric BaTiO3 layer is between n-TiO2 with oxygen vacancies and p-TiO2 with titanium vacancies. Consequently, the TBT3 achieves a prominent photocurrent density which is 2.4- and 1.5-times higher than TiO2 and TiO2–BaTiO3 heterojunction, respectively.
Minhua Ai, Study Lead Author. School of Chemical Engineering and Technology, Tianjin University
Notably, based on thorough characterizations of charge carrier behaviors in such a multi-heterojunction, a stable polarized electric field generated in ferroelectric BaTiO3 can further govern built-in electric fields. This is driven by mechanical deformation.
Additionally, piezoelectric enhancement of PEC performance (2.84 times better than TiO2 at 1.23 V vs RHE) is achieved by n- TiO2/ BaTiO3/p- TiO2 heterojunction.
Based on the coupling with piezoelectric effect and p-n junctions, our work provides a piezoelectric polarisation strategy for modulating the built-in electric field of heterojunction for charge separation enhancement.
Lun Pan, Senior and Corresponding Author, School of Chemical Engineering and Technology, Tianjin University
Journal Reference
Ai, M., et.al., (2023). Piezoelectric-enhanced n-TiO2/BaTiO3/p-TiO2heterojunction for highly efficient photo electrocatalysis. Green Energy & Environment. doi.org/10.1016/j.gee.2023.12.001.