Giant Room-Temperature Electrocaloric Effect of Polymer-Ceramic Composites with Orientated BaSrTiO3 Nanofibers.

Cooling based on the electrocaloric effect (ECE) is a promising solution to environmental and energy efficiency problems of vapor-compression refrigeration. Ferroelectric polymer-ceramics nanocomposites, integrating high electric breakdown of organic ferroelectrics and large EC strength of ceramics, are attractive EC materials. Here, we tuned the orientation of Ba0.67Sr0.33TiO3 nanofibers (BST nfs) in the P(VDF-TrFE-CFE) polymer. When the nfs were aligned parallel to the field, a ΔT of 11.3 K with an EC strength of 0.16 K·m/MV was achieved in the blends. The EC strength not only surpasses advanced nanocomposites but also is comparable to ferroelectric ceramics. The simulation indicates that a significantly higher electric field is concentrated in polymer regions around the ends of the orientated nfs, contributing to easier flipping of polymer chains for large ECE. This work provides a new method to obtain large ECE in composites for next-generation refrigeration.

A gold electrode modified with a gold-graphene oxide nanocomposite for non-enzymatic sensing of glucose at near-neutral pH values.

A nanocomposite was prepared from gold and graphene oxide via one-step electrodeposition and used to modify the surface of a gold electrode (Au-Gr/GE) that was then applied to non-enzymatic determination of glucose. The effects of deposition time and supporting substrate on the morphology, structure, and electrochemical properties of the nanocomposite were optimized. The morphologies and crystal structures were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results indicate that gold nanoparticles grew on the surface of two-dimensional graphene oxide. The electrocatalytic activity of the modified electrode towards glucose oxidation was evaluated by cyclic voltammetry and amperometric methods at pH 7.4. The Au-Gr/GE, typically operated at a potential of 0.00 V (vs. Ag/AgCl), has a linear response in the 0.05-14 mM and 14-42 mM glucose concentration range, high sensitivity (604 and 267 µA cm-2 mM-1) and a low detection limit (12 µM). The modified GE was applied to quantify glucose in sweat where it exhibited excellent sensitivity and accuracy. Graphical abstract The gold electrode modified with a gold-graphene (Au-Gr/GE) is prepared via a direct electrodeposition. The Au-Gr/GE is used for glucose detection in the neutral solution and it can achieve the effect of non-intrusive detection.

Enhanced Energy Storage Performance by A-B Site Ambipolar Co-Doping in Antiferroelectrics.

Antiferroelectric materials are promising to be used for power capacitive devices. To improve the energy storage performance, solid-solution and defect engineering are widely used to suppress the long-range order by introducing local heterogeneities. However, both methods generally deteriorate either the maximum polarization or breakdown electric field due to damaged intrinsic polarization or increased leakage. Here, we show that forming defect-dipole clusters by A-B site acceptor-donor co-doping in antiferroelectrics can comprehensively enhance the energy storage performance. We took the La-Mn co-doped (Pb0.9Ba0.04La0.04)(Zr0.65Sn0.3Ti0.05)O3 (PBLZST) as an example. For co-doping with unequal amounts, high dielectric loss, impurity phase, and decreased polarization were observed. By contrast, La and Mn in an equal amount of co-doping can significantly improve the overall energy storage performance. An over 48% increasement in both the maximum polarization (62.7 µC/cm2) and breakdown electric field (242.6 kV/cm) was obtained in 1 mol % La and 1 mol % Mn equally co-doped PBLZST, followed by a nearly two-time enhancement in Wrec (6.52 J/cm3) compared with that of the pure matrix. Moreover, a high energy storage efficiency of 86.3% with an enhanced temperature stability over a wide temperature range can be achieved. The defect-dipole clusters associated with charge-compensated co-doping are suggested to contribute to an enhanced dielectric permittivity, linear polarization behavior, and maximum polarization strength compared with that of the unequal co-doping cases. The defect-dipole clusters are suggested to couple with the host, leading to a high energy storage performance. The proposed strategy is believed to be applicable to modify the energy storage behavior of antiferroelectrics.

Ultrahigh Energy Efficiency and Large Discharge Energy Density in Flexible Dielectric Nanocomposites with Pb0.97La0.02(Zr0.5SnxTi0.5-x)O3 Antiferroelectric Nanofillers.

Flexible dielectric capacitors have been widely studied recently on account of their fast charge-discharge speed, high power density, and superior wearable characteristics. Inorganic ferroelectric fillers/polymer matrix composites combining large maximum electric displacement (Dmax) of ferroelectric materials with good flexibility and high electric breakdown strength (Eb) of the polymer are regarded as the most promising materials for preparing flexible dielectric capacitors with superior energy storage properties. However, simultaneously achieving large discharge energy density (Wd) and high energy efficiency (η) in these composites remains challenging on account of a large remnant electric displacement (Dr) and low Dmax - Dr values of ferroelectric fillers. In contrast, antiferroelectrics (AFEs) exhibit near zero Dr and larger Dmax - Dr values and are thus attractive composite fillers to simultaneously achieve large Wd and high η. On the basis of these factors, in this report, we design and prepare Pb0.97La0.02(Zr0.5SnxTi0.5-x)O3 (PLZST) AFE nanoparticles (NPs)/poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) nanocomposites and investigate the effects of the Sn and AFE NPs contents on the energy storage capacity of the nanocomposites. Through reasonable adjustment of the Sn content and the PLZST AFE fillers content, because of the large Dmax - Dr value of 7.75 µC/cm2 and small Dr value of 0.26 µC/cm2 at the Eb as high as 3162 kV/cm, the Pb0.97La0.02(Zr0.5Sn0.38Ti0.12)O3 AFE NPs/P(VDF-HFP) polymer nanocomposite with 7 wt % fillers exhibits the most superior energy storage properties with an ultrahigh η of 93.4% and a large Wd of 12.5 J/cm3. These values are superior to those of the recently reported dielectric nanocomposites with a single-layer structure containing ferroelectric nanowires, nanofibers, nanobelts, nanotubes, and nanosheets or core-shell structure fillers, which are prepared via a very complicated method. This work not only shows that, in principle, the polarization characteristics of the composites depend mainly on those of the inorganic fillers but also demonstrates a convenient, effective, and scalable way to fabricate dielectric capacitors with superior flexibility and energy storage capacities.