Advances in ferroelectric and piezoelectric photocatalysts with oxygen vacancy

Photocatalysis technology including hydrogen evolution from water splitting, CO₂ reduction and N₂ conversion to ammonia emerges as a significant approach for energy crisis and environmental pollution. For these conventional semiconductors such as TiO₂, ZnO, WO₃, CdS and g-C₃N₄, however, inefficient photoabsorption, rapid recombination of photogenerated carriers, and inadequate surface reactive sites hamper the photoinduced activity and stability. Defect engineering, especially oxygen vacancy, has recently drawn the attention of a number of investigators primarily in connection with its feasibility of regulatability, identifiability and effectiveness. A series of ferroelectric and piezoelectric semiconductors, with internal electric field generated by the polarization, are considered an excellent candidate for replacement of conventional semiconductors, because the observed charge separation ability of those is far from theoretical expectation. With the boost of oxygen vacancy, polarization behavior can be effectively regulated to further improve photocatalytic performance. Related studies based on the above background are the current hotspot of photocatalysis; this paper reviews the latest research progress of ferroelectric and piezoelectric photocatalysts with oxygen vacancy. Starting from the generation of oxygen vacancies, five preparation strategy including ion doping, thermal treatment, chemical reduction, ultraviolet irradiation, and plasma etching are introduced; advanced characterization are summarized in classification of spectroscopy, energy spectrum, electron microscopy, density function theory and in situ techniques. Secondly, the mechanism of oxygen vacancy regulated polarization and their synergistic photocatalytic reactions are reviewed and summarized. Finally, an overview on the prospect of advanced photocatalytic engineering concerned to oxygen vacancies involved ferroelectric and piezoelectric photocatalysts is proposed.

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