Domain-engineered BiFeO3 thin-film photoanodes for highly enhanced ferroelectric solar water splitting
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In photoelectrochemical (PEC) water splitting, charge separation and collection by the electric field in the photoactive material are the most important factors for improved conversion efficiency. Hence, ferroelectric oxides, in which electrons are the majority carriers, are considered promising photoanode materials because their high built-in potential, provided by their spontaneous polarization, can significantly enhance the separation and drift of photogenerated carriers. In this regard, the PEC properties of BiFeO3 thin-film photoanodes with different crystallographic orientations and consequent ferroelectric domain structures are investigated. As the crystallographic orientation changes from (001)pc via (110)pc to (111)pc, the ferroelastic domains in epitaxial BiFeO3 thin films become mono-variant and the spontaneous polarization levels increase to 110 μC/cm2. Consequently, the photocurrent density at 0 V vs. Ag/AgCl increases approximately 5.3-fold and the onset potential decreases by 0.180 V in the downward polarization state. It is further demonstrated that ferroelectric switching in the (111)pc BiFeO3 thin-film photoanode leads to an approximate change of 8,000% in the photocurrent density and a 0.330 V shift in the onset potential. This study strongly suggests that domain-engineered ferroelectric materials can be used as effective charge separation and collection layers for efficient solar water-splitting photoanodes.
KeywordsBiFeO3 ferroelectric photoelectrochemical domain orientation pulsed laser deposition
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The authors gratefully acknowledge the financial support from the Basic Science Research Program (No. NRF-2014R1A1A2053552) and the Future Material Discovery Program (No. NRF-2016M3D1A1027666) through the National Research Foundation of Korea, and the International Energy Joint R&D Program through the Korea Institute of Energy Technology Evaluation and Planning (No. 20168510011350), and by the GIST (Gwangju Institute of Science and Technology) Research Institute (GRI) Project through a grant provided by GIST in 2016.
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