Ferroelectric materials hold great promise in the field of photocatalytic water splitting due to their spontaneous polarization that sets up an inherent internal field for the spatial separation of photogenerated charges. The ferroelectric polarization, however, is generally accompanied by some intrinsic defects, particularly oxygen vacancies, whose impact upon photocatalysis is far from being fully understood and modulated. Here, we have studied the role of oxygen vacancies over the photocatalytic behavior of single-domain PbTiO3 through a combination of theoretical and experimental viewpoints. Our results indicate that the oxygen vacancies in the negatively polarized facet (001) are active sites for water oxidation into O2, while the defect-free sites prefer H2O2 as the oxidation product. The apparent quantum yield at 435 nm for photocatalytic overall water splitting with PbTiO3/Rh/Cr2O3 is determined to be 0.025%, which is remarkable for single undoped metal oxide-based photocatalysts. Furthermore, the strong correlation among oxygen vacancies, polarization strength, and photocatalytic activity is properly reflected by charge separation conditions in the single-domain PbTiO3. This work clarifies the crucial role of oxygen vacancies during photocatalytic reactions of PbTiO3, which provides a useful guide to the design of efficient ferroelectric photocatalysts and their water redox reaction pathways.

Exploiting spontaneous polarization of ferroelectric materials to achieve high charge separation efficiency is an intriguing but challenging research topic in solar energy conversion. This work shows that loading high work function RuO2 cocatalyst on BiFeO3 (BFO) nanoparticles enhances the intrinsic ferroelectric polarization by efficient screening of charges to RuO2 via RuO2/BFO heterojunction. This leads to enhancement of the surface photovoltage of RuO2/BFO single nanoparticles nearly 3 times, the driving force for charge separation and transfer in photocatalytic reactions. Consequently, efficient photocatalytic water oxidation is achieved with quantum efficiency as high as 5.36 % at 560 nm, the highest activity reported so far for ferroelectric materials. This work demonstrates that, unlike low photocurrent density in film‐based ferroelectric devices, high photocatalytic activity could be achieved by regulating the ferroelectric spontaneous polarization using appropriate cocatalyst to enhance driving force for efficient separation and transfer of photogenerated charges in particulate ferroelectric semiconductor materials.

Ferroelectric (FE) resistive switching has attracted considerable interest as a promising candidate for applications in non‐volatile memory technology. In this work, via judiciously controlling the defect states of oxygen vacancy through Sm‐doping, the authors obtain multiple current jumps/discrete resistance states in the resistive switching memories based on a model FE BiFeO3 (BFO). These hitherto unreported current jumps are attributed to the space‐charge‐limited current correlated with electron trapping by oxygen vacancies in the BFO film. Concurrently, oxygen vacancies serve as the pinning centers for the FE domains, leading to the domain wall creep behavior. These results illustrate the strong interplay between the defect, resistive switching, and domain wall creep behavior in FE diodes, providing a new insight into the mechanism of FE resistive switching. Overall, the large on/off ratio of ≈5 × 105, multiple resistance states, and fast switching speed of ≈30 ns, promise their potential applications in multi‐level data storage memories.

Controlling the domain evolution is critical both for optimizing ferroelectric properties and for designing functional electronic devices. Here we report an approach of using the Schottky barrier formed at the metal/ferroelectric interface to tailor the self-polarization states of a model ferroelectric thin film heterostructure system SrRuO3/(Bi,Sm)­FeO3. Upon complementary investigations of the piezoresponse force microscopy, electric transport measurements, X-ray photoelectron/absorption spectra, and theoretical studies, we demonstrate that Sm doping changes the concentration and spatial distribution of oxygen vacancies with the tunable host Fermi level which modulates the SrRuO3/(Bi,Sm)­FeO3 Schottky barrier and the depolarization field, leading to the evolution of the system from a single domain of downward polarization to polydomain states. Accompanied by such modulation on self-polarization, we further tailor the symmetry of the resistive switching behaviors and achieve a colossal on/off ratio of ∼1.1 × 106 in the corresponding SrRuO3/BiFeO3/Pt ferroelectric diodes (FDs). In addition, the present FD also exhibits a fast operation speed of ∼30 ns with a potential for sub-nanosecond and an ultralow writing current density of ∼132 A/cm2. Our studies provide a way for engineering self-polarization and reveal its strong link to the device performance, facilitating FDs as a competitive memristor candidate used for neuromorphic computing.

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Energy conversion and storage devices are highly desirable for the sustainable development of human society. Hybrid organic–inorganic perovskites have shown great potential in energy conversion devices including solar cells and photodetectors. However, its potential in energy storage has seldom been explored. Here the crystal structure and electrical properties of the 2D hybrid perovskite (benzylammonium)2PbBr4 (PVK‐Br) are investigated, and the consecutive ferroelectric‐I (FE1) to ferroelectric‐II (FE2) then to antiferroelectric (AFE) transitions that are driven by the orderly alignment of benzylamine and the distortion of [PbBr6] octahedra are found. Furthermore, accompanied by field‐induced AFE to FE transition near room temperature, a large energy storage density of ≈1.7 J cm−3 and a wide working temperature span of ≈70 K are obtained; both of which are among the best in hybrid AFEs. This good energy storage performance is attributed to the large polarization of ≈7.6 µC cm−2 and the high maximum electric field of over 1000 kV cm−1, which, as revealed by theoretical calculations, originate from the cooperative coupling between the [PbBr6] octahedral framework and the benzylamine molecules. The research clarifies the discrepancy in the phase transition character of PVK‐Br and shed light on developing high‐performance energy storage devices based on 2D hybrid perovskite.

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