Piezoelectric effect, commonly known as a change in electric polarization in piezoelectric/ferroelectric materials under mechanical stress, is extensively employed as a driving force for the catalytic degradation of organic pollutants. However, the relationship between electric polarization and piezocatalytic activity is still unclear. In this work, we investigated the role of ferroelectric polarization in the piezocatalytic activity of BaTiO nanoparticles through annealing BaTiO at different temperatures or poling BaTiO at different electric fields. The BaTiO nanoparticles annealed at 800 °C exhibit effectively enhanced piezocatalytic activity compared with those annealed at other temperatures. The polycrystalline particles annealed at higher temperatures exhibit a greatly reduced catalytic activity. After poling, the piezocatalytic activity of the polycrystalline BaTiO particles was obviously improved. In addition, we identified the free radical species and the intermediate products of the catalytic reaction. We also well-explained the dependence of electric polarization in the BaTiO piezocatalyst on annealing temperature and ultrasonic vibration theoretically. Our study indicates that increasing ferroelectric polarization (but not crystallite size) can effectively enhance the piezocatalytic activity. We believe that the present work provides a clear understanding of the role of ferroelectric polarization in piezocatalysis.

Hard carbon materials derived from biomass sources, such as sucrose, glucose, cotton, holly leaf, and eggshell membrane, have been intensively investigated as anodes for SIBs because of their high capacity. [4] However, these materials usually exhibit a very low initial coulombic efficiency (ICE), which hampers their practical application. [4a,d,e] For example, Pan and co-workers fabricated hard carbon microspheres using sucrose as a precursor, and their ICE was 40%. [4a] Palacín and co-workers prepared a hard carbon material using sugar as a precursor, and its ICE was ≈62%. [5] Li et al. used carbonized eggshell membrane as an anode for sodium storage, but its ICE was 45%. [4e] Zhang and co-workers prepared a hard carbon sheet-like structure using cherry petals as the raw material and achieved ICE of 67.3%. [6] Hu and co-workers prepared a carbonized leaf membrane from natural leaf as a binder-free anode for SIBs, and this anode exhibited ICE of 74.8%. [4d] Many previous studies attribute the low ICE of hard carbon materials to their large specific surface area, which may result in side reactions with the electrolyte, and these side reactions can be reduced by surface modification, such as coating the surface with soft carbon. [7] However, some experiments have demonstrated that a low specific surface area does not necessarily result in an enhancement of the ICE. [8] For instance, Billaud and co-workers fabricated pitch-based carbon fibers with specific areas as low as 1.2 and 1 m 2 g −1 , but their ICE values were only ≈33% and 15%, respectively. [9] Cao et al. synthesized hard carbon nanoparticles and hollow carbon nanowires by pyrolysis of a polyaniline precursor at the same temperature. [10b] The surface area of the hard carbon nanoparticles (23.5 m 2 g −1 ) was 30% smaller than that of the hollow carbon nanowires (31.4 m 2 g −1 ), but the ICE of the hard carbon nanoparticles (51.6%) was only 1.2% higher than that of the hollow carbon nanowires (50.5%). Mitlin and co-workers found that although the progressively decreasing surface area (from 55 to 21 m 2 g −1 ) plays a role in the increasing ICE (from 43.9% to 60.1%) as the carbonization temperature of carbonized peat moss increases (from 600 to 1400 °C), the ICE of the optimized materials was larger than that reported for high-performance carbonaceous materials (51.6%) with lower surface areas (31.4 m 2 g −1 ). [10b,11] These results suggested that other factors are responsible for the low ICE. Hard carbon Practical application of hard carbon materials in sodium-ion batteries (SIBs) is largely limited by their low initial coulombic efficiency (ICE), which may be improved by increasing the graphitization degree. However, biomassderived hard carbon is usually nongraphitizable and extremely difficult to graphitize by direct heating even at 3000 °C. Herein, a general strategy is reported for fabricating hard carbon materials with graphite crystals at 1300 °C promoted by external graphite that serves as a crystal template for the growth of graphite cry...

No abstract

Ferroelectricity and X‐ray detection property have been recently implemented for the first time in hybrid bromide double perovskites. It sheds a light on achieving photosensitive and ferroelectric multifunctional materials based on 2D lead‐free hybrid halide double perovskites. However, the low Tc, small Ps, and relatively low X‐ray sensitivity in the reported bromide double perovskites hinder practical applications. Herein, the authors demonstrate a novel 2D lead‐free iodide double perovskite (4,4‐difluoropiperidinium)4AgBiI8 (1) for high‐performance X‐ray sensitive ferroelectric devices. Centimeter‐sized single crystal of 1 is obtained and exhibits an excellent ferroelectricity including a high Tc up to 422 K and a large Ps of 10.5 μC cm−2. Moreover, due to a large X‐ray attenuation and efficient charge carrier mobility (μ)–charge carrier lifetime (τ) product, the crystal 1 also exhibits promising X‐ray response with a high sensitivity up to 188 μC·Gyair−1 cm−2 and a detection limit below 3.13 μGyair·s−1. Therefore, this finding is a step further toward practical applications of lead‐free halide perovskite in high‐performance photoelectronic devices. It will afford a promising platform for exploring novel photosensitive ferroelectric multifunctional materials based on lead‐free double perovskites.

Piezoelectric materials are technologically important, and the most used are perovskite ferroelectrics. In recent years, more and more emerging areas have put forward new requirements for piezoelectric materials, such as light weight, low acoustic impedance, good flexibility, and biocompatibility. In this context, hybrid organic–inorganic perovskite ferroelectrics have emerged as promising supplements, because they combine attractive features of inorganic and organic materials. Among them, hybrid double-metal perovskites have recently been found to exhibit excellent ferroelectricity. However, their potential as piezoelectric materials has not been exploited. Here, we describe large piezoelectric response in hybrid rare-earth double perovskite relaxor ferroelectrics (RM3HQ)2­RbLa­(NO3)6 and (RM3HQ)2­NH4La­(NO3)6 (RM3HQ = R-N-methyl-3-hydroxyl­quinuclidinium). They are simultaneously ferroelectric and ferroelastic crystals, with the R3 ferroelectric phase and P213 paraelectric phase. We found that ferroelectric polar microdomains and paraelectric nonpolar regions coexist in a wide temperature range through variable-temperature piezoresponse force microscopy images. The two-phase coexistence reveals low energy barriers of transitions between the two phases and between the polar microdomains with different polarization directions. These lead to the easy polarization rotation of the polar microdomains upon applying a stress and, accordingly, the large piezoelectric response up to 106 pC N–1 for (RM3HQ)2­RbLa­(NO3)6. This finding represents a significant step toward novel applications of piezoelectric materials based on lead-free hybrid perovskites.