Local Isomeric Polar Nanoclusters Enabled Superior Capacitive Energy Storage Under Moderate Fields in NaNbO3-Based Lead-Free Ceramics.

The high-field energy-storage performance of dielectric capacitors has been significantly improved in recent years, yet the high voltage risks of device failure and large cost of insulation technology increase the demand for high-performance dielectric capacitors at finite electric fields. Herein, a unique superparaelectric state filled with polar nanoclusters with various local symmetries for lead-free relaxor ferroelectric capacitors is subtly designed through a simple chemical modification method, successfully realizing a collaborative improvement of polarization hysteresis, maximum polarization, and polarization saturation at moderate electric fields of 20-30 kV mm-1. Therefore, a giant recoverable energy density of ≈5.0 J cm-3 and a high efficiency of ≈82.1% are simultaneously achieved at 30 kV mm-1 in (0.9-x)NaNbO3-0.1BaTiO3-xBiFeO3 lead-free ceramics, showing a breakthrough progress in moderate-field comprehensive energy-storage performances. Moreover, superior charge-discharge performances of high-power density ≈182 MW cm-3, high discharge energy density ≈4.3 J cm-3 and ultra-short discharge time <70 ns as well as excellent temperature stability demonstrate great application potentials for dielectric energy-storage capacitors in pulsed power devices. This work provides an effective and paradigmatic strategy for developing novel lead-free dielectrics with high energy-storage performance under finite electric fields.

Core-shell engineered g-C3N4@ NaNbO3for enhancing photocatalytic reduction of CO2.

Photocatalytic reduction of carbon dioxide is a technology that effectively utilizes CO2and solar energy. Sodium niobate (NaNbO3) has received much attention in the field of photocatalysis due to its excellent photocatalytic properties. However, the application of NaNbO3in the field of photocatalysis is still limited by poor reaction to visible light and easy recombination of photo-generated carriers. Heterojunction with g-C3N4to construct core-shell structure can effectively improve the above problems. Combining the two can design a core-shell composite material that is beneficial for photocatalytic reduction of CO2. Herein, we prepared a core-shell heterojunction g-C3N4/NaNbO3by uniformly impregnating urea on the surface of NaNbO3chromium nanofibers with NaNbO3nanofibers prepared by electrospinning as a catalyst carrier, and urea as a precursor of g-C3N4. The core-shell structure of g-C3N4/NaNbO3was verified by a series of characterization methods such as XPS, XRD, and TEM. It was found that under the same conditions, the methanol yield of core-shell g-C3N4/NaNbO3was 12.86µmol·g-1·h-1, which is twice that of pure NaNbO3(6.67µmol·g-1·h-1). This article highlights an impregnation method to build core-shell structures for improved photocatalytic reduction of CO2.

Construction of [NbO]6-x -xS Structure to Change Charge Density and Regulate Spontaneous Polarization to Achieve Efficient Pyro-Photo-Electric Water Splitting System of NaNbO3.

Pyroelectric materials in the field of photoelectrochemical (PEC) water splitting still face the problems of difficult low spontaneous polarization intensity and excessive carrier recombination. Based on the above problems, we altered the interaction between S-Nb-S in the [NbO]6-x -xS structure, and the constructed [NbO]6-x -xS structure achieved the regulation of charge density change and spontaneous polarization. The results show that under the stimulation of light and temperature fluctuations, the current density of the NS-4 photoanode is as high as 0.574 mA/cm2 at 1.23 VRHE , which is about 1.59 times higher than the pure NaNbO3 current density value, and the NS -4 photoanode achieves IPCE value of 16.08 %. The first-principles density-functional theory calculations (DFT) reveal the principle of the [NbO]6-x -xS structure for the suppression function of the carrier recombination and the improvement function of the pyroelectric effect. The analysis shows that the S-doping leads to the weakening of S-Nb-S interactions in the [NbO]6-x -xS structure, which improves the pyroelectric effect and suppresses the photo/pyro-generated carrier recombination, and effectively enhances the performance of the pyro-photo-electric synergistic water splitting system. This work promotes the development of pyroelectric materials in the field of photoelectrochemical water splitting.

In†Situ Corrosion Fabrication of NaNbO3 /Nb3 O7 F Heterojunctions with Optimized Band Realignment for Enhanced Photocatalytic Hydrogen Evolution.

Heterostructured photocatalysis is a significant issue owing to the unique band alignment, improved spectrum absorption, and enhanced photocatalytic activity. However, the construction of uniform, controllable, and effective heterojunctions is still a huge challenge. Herein, NaNbO3 /Nb3 O7 F heterojunctions are fabricated through an in situ corrosion technique for the first time. The influence of phase transformation on the hydrogen evolution reaction (HER) activity is investigated systematically in terms of photocatalytic water splitting for H2 production. Interestingly, the band realignment and good interfacial contact endow the NaNbO3 /Nb3 O7 F heterojunctions with a high HER activity (43.3 mmol g-1 h-1 ), which is about 2.4 times that of pure Nb3 O7 F and 1.36 times that of pure NaNbO3 . The results may provide some new insights into the corrosion technique and HER activity of novel heterostructured catalysts.

Ambience-sensitive optical refraction in ferroelectric nanofilms of NaNbO3.

Optical index of refraction n is studied by spectroscopic ellipsometry in epitaxial nanofilms of NaNbO3 with thickness ∼10 nm grown on different single-crystal substrates. The index n in the transparency spectral range (n ≈ 2.1 - 2.2) exhibits a strong sensitivity to atmospheric-pressure gas ambience. The index n in air exceeds that in an oxygen ambience by δn ≈ 0.05 - 0.2. The thermo-optical behaviour n(T) indicates ferroelectric state in the nanofilms. The ambience-sensitive optical refraction is discussed in terms of fundamental connection between refraction and ferroelectric polarization in perovskites, screening of depolarizing field on surfaces of the nanofilms, and thermodynamically stable surface reconstructions of NaNbO3.

Dielectric Filler-Induced Hybrid Interphase Enabling Robust Solid-State Li Metal Batteries at High Areal Capacity.

The fillers in composite solid-state electrolyte are mainly responsible for the enhancement of the conduction of Li ions but barely regulate the formation of solid electrolyte interphase (SEI). Herein, a unique filler of dielectric NaNbO3 for the poly(vinylidene fluoride) (PVDF)-based polymer electrolyte, which is subjected to the exchange of Li+ and Na+ during cycling, is reported and the substituted Na+ is engaged in the construction of a fluorinated Li/Na hybrid SEI with high Young's modulus, facilitating the fast transport of Li+ at the interface at a high areal capacity and suppressing the Li dendrite growth. The dielectric NaNbO3 also induces the generation of high-dielectric ß phase of PVDF to promote the dissociation of Li salt. The Li/Li symmetrical cell exhibits a long-term dendrite-free cycling over 600 h at a high areal capacity of 3 mA h cm-2. The LiNi0.8Mn0.1Co0.1O2/Li solid-state cells with NaNbO3 stably cycle 2200 times at 2 C and that paired with high-loading cathode (10 mg cm-2) can stably cycle for 150 times and exhibit excellent performances at -20 °C. This work provides a novel design principle of fillers undertaking interfacial engineering in composite solid-state electrolytes for developing the safe and stable solid-state lithium metal battery.

Optimized Electrocaloric Refrigeration in Lead-Free NaNbO3-Based Ceramics via AFE ↔ FE Phase Transition Modulation.

An outstanding challenge for eco-friendly ferroelectric (FE) refrigeration is to achieve a large adiabatic temperature change within a broad temperature range originating from the electrocaloric (EC) effect, which is expected to be realized in antiferroelectric (AFE) materials owing to the large entropy change during electric field and thermally induced phase transition. In this work, a large EC response over a wide response temperature range can be achieved slightly above room temperature via designing the phase transition of NaNbO3. An irreversible to reversible AFE-FE phase transition on heating induced by the introduction of CaZrO3 into NaNbO3 plays a key role in the optimized electrocaloric refrigeration. Accordingly, accompanying the local structure transformation corresponding to the B-site ions, the transition temperature between the square polarization-electric field (P-E) hysteresis loop (the irreversible AFE-FE phase transition induced by the electric field) and the repeatable double P-E hysteresis loop (the electric field induced reversible AFE-FE phase transition) was tailored to around room temperature, in favor of extending large entropy change to the wide temperature range. This work provides an efficient approach to designing lead-free EC materials with excellent EC performance, promoting the advancement of environmentally friendly solid-state cooling technology.

Excellent Energy-Storage Performance of (0.85 - x)NaNbO3-xNaSbO3-0.15(Na0.5La0.5)TiO3 Antiferroelectric Ceramics through B-Site Sb5+ Driven Phase Transition.

NaNbO3-based relaxor antiferroelectric (AFE) ceramics are receiving more and more attention for high power pulse applications. A commonly used design strategy is to add complex perovskites with lower tolerance factors. Herein, a new lead-free AFE system of (0.85 - x)NaNbO3-xNaSbO3-0.15(Na0.5La0.5)TiO3 was specially designed considering the substitution of Sb5+ for Nb5+ reduces the polarizability of B-site ions but increases the tolerance factor. The formation of nanodomains with stable AFE orthorhombic R phase symmetry contributes to a slim and double-like polarization-field hysteresis loop, while the increased resistivity and activation energy as a result of sintering aids lead to an enhanced breakdown strength. Therefore, an excellent energy density Wrec ≈ 6.05 J/cm3, a high energy efficiency η ≈ 80.5%, and good charge-discharge performances (power density PD ≈ 155 MW/cm3 and discharging rate t0.9 ≈ 44.6 ns) were achieved in MnO2-doped x = 0.03 ceramics. The experimental results demonstrate that the B-site Sb5+ driven orthorhombic P-R phase transition and increased local structure disorder should provide a new strategy to design high-performance NaNbO3-based relaxor AFE capacitors.

Interface-Mediated Mechanoluminescence Enhancement from Heterojunction Phosphors: Experiment and Theory.

Mechanoluminescence (ML) phosphors have made significant progress in various fields, such as artificial intelligence, the Internet of Things, and biotechnology. However, enhancing their weak ML intensity still remains a challenge. Here, we report a new series of Na1-xMgxNbO3:Pr3+ (x = 0.00, 0.10, 0.20, 0.40, 0.60, 0.80, and 1.00 mol %) heterojunction systems, which exhibit significant ML enhancement as compared with either the Pr3+-doped NaNbO3 or MgNbO3, and the physical mechanisms behind the ML enhancement have been explored comprehensively from both the experiment and theory points of view. Experimental tests, including thermoluminescence and positron annihilation lifetime measurements, combined with first-principles calculations, consistently indicate that the ML enhancement observed in these newly reported systems is due to the formation of heterojunctions, which plays a crucial role in modulating the defect configuration of the phosphors and facilitating efficient charge transfer. By controlling the Na/Mg ratio in conjunction with Pr3+ doping, continuous changes in the band offset and the concentrations of certain types of traps in the forbidden gap are achieved, leading to the optimum conditions in the 8/2 ratio samples. These findings demonstrate a novel type of ML phosphor and provide a theoretical basis for the design of high-performance ML phosphor.

High Piezoelectricity in Eco-Friendly NaNbO3-Based Ferroelectric Relaxor Ceramics via Phase and Domain Engineering.

To meet the requirements of environmental friendliness, high-performance lead-free piezoelectric materials have become important materials for next-generation electronic devices. Here, lead-free and potassium-free NaNbO3 (NN)-based ceramics with high piezoelectric (d33 = 361 ± 10 pC/N) and dielectric (εr = 4500) properties were obtained by tolerant preparation techniques. The excellent piezoelectric and dielectric properties can be attributed to the relaxor morphotropic phase boundaries (R-MPB) and coexisting domain regions, which are beneficial in lowering the free energy and greatly improving the dielectric response and domain switching capability. Furthermore, the d33 of NaNbO3-10Ba(Ti0.7Sn0.3)O3-1.5NaSbO3 (NN-10BTS-1.5NS) ceramics can be maintained at 350 pC/N over the range of 25-80 °C with a change rate of less than 10%, exhibiting excellent temperature stability. Based on a series of in situ characterizations, the variations of the phase and domain structures of NN-based relaxor piezoelectric ceramics with temperature are clearly demonstrated. This work not only proposes new materials for sensors and actuators but also provides an excellent strategy for designing high-performance piezoelectric ceramics through phase and domain engineering.

Preparation of NaNbO3 microcube with abundant oxygen vacancies and its high photocatalytic N2 fixation activity in the help of Pt nanoparticles.

In this study, the photocatalytic N2 immobilization performance of NaNbO3 is enhanced via oxygen vacancy introduction and Pt loading. The designed Pt-loaded NaNbO3 with rich oxygen defects (Pt/O-NaNbO3) is synthesized by combining ion-exchange and photodeposition methods. Characterization result indicates that the O-NaNbO3 has hollow microcube morphology and higher surface area than NaNbO3. The introduced oxygen defects greatly affect the energy band structure. The band gap is slightly narrowed and the conduction band is raised, allowing O-NaNbO3 to generate electrons with strong reducibility. Moreover, the oxygen defects reduced the work function of NaNbO3, leading to increased charge separation in the bulk phase. The loaded Pt nanoparticles can further increase the surface charge separation via the formed Schottky barriers between Pt and O-NaNbO3, which was thought to be the primary cause of the increased photocatalytic activity. Additionally, the oxygen vacancies and metal Pt also contribute to the adsorption and activation of N2. Under the combined effect of the above changes, Pt/O-NaNbO3 presents much higher photoactivity than NaNbO3. The optimized NH3 production rate reaches 293.3 µmol/L g-1h-1 under simulated solar light, which is approximately 2.2 and 20.2 times higher than that of O-NaNbO3 and NaNbO3, respectively. This research offers a successful illustration of how to improve photocatalytic N2 fixation and may shed some light on how to design and construct efficient photocatalysts by combining several techniques.

Ultrahigh Energy Storage Density and High Efficiency in Lead-Free (Bi0.9Na0.1)(Fe0.8Ti0.2)O3-Modified NaNbO3 Ceramics via Stabilizing the Antiferroelectric Phase and Enhancing Relaxor Behavior.

Dielectric capacitors have attracted growing attention because of their important applications in advanced high power and/or pulsed power electronic devices. Nevertheless, the synergistic enhancement of recoverable energy storage density (Wrec > 10 J/cm3) and efficiency (η > 80%) is still a great challenge for lead-free dielectric bulk ceramics. Herein, by introducing complex perovskite compound (Bi0.9Na0.1)(Fe0.8Ti0.2)O3 with a smaller tolerance factor into an NaNbO3 matrix (NN-BNFT), we have achieved and explored stable relaxor antiferroelectric ceramics with enhanced relaxor behavior. Of particular importance is the composition of 0.88NN-0.12BNFT, which exhibits a large electric breakdown strength Eb of 87.3 kV/mm, an ultrahigh Wrec of 12.7 J/cm3, and a high efficiency η of 82.5%, as well as excellent thermal reliability and an ultrafast discharge speed, resulting from the dense microstructure, the moderate dielectric constant, the reduced grain size, the dielectric loss, and the sample thickness. The outstanding energy storage properties of NN-BNFT display great promise in advanced dielectric capacitors for energy storage applications.

Robust route to H2O2 and H2 via intermediate water splitting enabled by capitalizing on minimum vanadium-doped piezocatalysts.

H2O2 is an environmentally friendly chemical for a wide range of water treatments. The industrial production of H2O2 is an anthraquinone oxidation process, which, however, consumes extensive energy and produces pollution. Here we report a green and sustainable piezocatalytic intermediate water splitting process to simultaneously obtain H2O2 and H2 using single crystal vanadium (V)-doped NaNbO3 (V-NaNbO3) nanocubes as catalysts. The introduction of V improves the specific surface area and active sites of NaNbO3. Notably, V-NaNbO3 piezocatalysts of 10 mg exhibit 3.1-fold higher piezocatalytic efficiency than the same catalysts of 50 mg, as more piezocatalysts lead to higher probability of aggregation. The aggregation causes reducing active sites and decreased built-in electric field due to the neutralization between different nano-catalysts. Remarkably, piezocatalytic H2O2 and H2 production rates of V-NaNbO3 (10 mol%) nanocubes (102.6 and 346.2 µmol·g-1·h-1, respectively) are increased by 2.2 and 4.6 times compared to the as-prepared pristine NaNbO3 counterparts, respectively. This improved catalytic efficiency is attributed to the promoted piezo-response and more active sites of NaNbO3 catalysts after V doping, as uncovered by piezo-response force microscopy (PFM) and density functional theory (DFT) simulation. More importantly, our DFT results illustrate that inducing V could reduce the dynamic barrier of water dissociation over NaNbO3, thus enhancing the yield of H2O2 and H2. This facile yet robust piezocatalytic route using minimal amounts of catalysts to obtain H2O2 and H2 may stand out as a promising candidate for environmental applications and water splitting. Electronic Supplementary Material: Supplementary material (typical Raman spectra of NaNbO3 and V-NaNbO3 with various doping concentrations (Fig. S1). XPS spectra of Na 1s (Fig. S2). PL spectra of solution obtained from the piezocatalytic system using NaNbO3 and V-NaNbO3 (10 mol%) as the catalysts after 1 h (Fig. S3). The length of NaNbO3 and V-NaNbO3 nanocubes calculated from XRD data of their (101) planes (Table S1)) is available in the online version of this article at 10.1007/s12274-022-4506-0.

A Combined Optimization Strategy for Improvement of Comprehensive Energy Storage Performance in Sodium Niobate-Based Antiferroelectric Ceramics.

Sodium niobate (NaNbO3, NN)-based lead-free antiferroelectric (AFE) ceramics are currently the focus of most attention on account of their outstanding energy storage density. Nevertheless, the high loss energy density (Wloss) by unique field-induced AFE-ferroelectric (FE) phase transition in pure NN ceramic and low breakdown electric field (Eb) largely restrict their practical application. Here, a combined optimization strategy was aimed at ameliorating energy storage characteristics of NN-based ceramics. First, the introduction of BiFeO3-SrTiO3 binary solid solution in pure NN ceramics destroys the long-range polar ordering and reduce the tolerance factor (t), thus reducing the polarization hysteresis, stabilizing the AFE phase and enhancing the energy storage efficiency. Then, the two-step sintering method was used to improve the compactness of ceramics and reduce the grain size. Finally, the VPP method was used to reduce the porosity, and thin the ceramic disk to a thickness of ∼100 µm. The high compactness and small thickness could effectively enhance the maximum breakdown electric field of ceramics. Ultimately, the optimum energy storage characteristics were obtained by the improvement of a combined optimization strategy, namely, an exceptional recoverable energy storage density (Wrec = 5.29 J/cm3) and efficiency (η = 82.1%) at a very high breakdown electric field (Eb = 380 kV/cm). This combined optimization strategy establishes a universal approach to ameliorate the energy storage characteristics of NN-based AFE ceramics for energy storage.

Synergistic Piezo-Photocatalysis of BiOCl/NaNbO3 Heterojunction Piezoelectric Composite for High-Efficient Organic Pollutant Degradation.

Piezo-photocatalytic technique is a new-emerging strategy to alleviate photoinduced charge recombination and thus enhance catalytic performance. The heterojunction construction engineering is a powerful approach to improve photocatalytic performance. Herein, the BiOCl/NaNbO3 with different molar ratios piezoelectric composites were successfully synthesized by hydrothermal methods. The piezo/photodegradation rate (k value) of Rhodamine B (RhB) for BiOCl/NaNbO3 (BN-3, 0.0192 min-1) is 2.2 and 5.2 times higher than that of BiOCl (0.0089 min-1) and NaNbO3 (0.0037 min-1), respectively. The enhanced performance of BN-3 composite can be attributed to the heterojunction construction between BiOCl and NaNbO3. In addition, the piezo/photodecomposition ratio of RhB for BN-3 (87.4%) is 8.8 and 2.2 times higher than that of piezocatalysis (9.9%) and photocatalysis (40.4%), respectively. We further investigated the mechanism of piezocatalysis, photocatalysis, and their synergy effect of BN-3 composite. This study favors an in-depth understanding of piezo-photocatalysis, providing a new strategy to improve the environmental pollutant remediation efficiency of piezoelectric composites.

Two-in-one: Portable piezoelectric and plasmonic exciton effect-based co-enhanced photoelectrochemical biosensor for point-of-care testing of low-abundance cancer markers.

In-depth exploration of the local surface plasmon resonance and piezoelectric effects associated with metal can help develop efficient biosensors. Here, we presented for the first time the localized surface plasmon resonance (LSPR) and piezoelectric effects co-enhance the construction of an efficient intra-body phase electric field for the construction of efficient photoelectrochemical (PEC) biosensors. Briefly, the LSPR enhancement and piezoelectric enhancement effects between Ag nanoparticles and the piezoelectric material NaNbO3 were investigated in a PEC biosensor system under the excitation of portable UV light. Notably, the simplified treatment of the basic building blocks of the PEC sensor, including a handheld UV flashlight instead of a physical excitation light source and a digital multimeter instead of an electrochemical workstation. The capture and immunoincubation process of target PSA occurs on separated microtiter plates and hydrogen peroxide, generated by enzyme-linked immunization, induces the directional separation of electrons and holes in the composite heterogeneous material under the excitation of light. The coupling with a digital multimeter allows for real-time monitoring of photocurrents. Further, the effect of Ag deposition on piezoelectric perovskite NaNbO3 was obtained by density functional theory (DFT) calculations. Impressively, under optimized conditions, the system exhibits an ultra-wide linear range and ultra-low detection limits for the target PSA. The system is also comparable to commercially available ELISA kits at the 95% confidence level. This work provides a novel idea of enhanced PEC biosensor for rapid and accurate detection of cancer-related proteins.

Synergy of a Stabilized Antiferroelectric Phase and Domain Engineering Boosting the Energy Storage Performance of NaNbO3-Based Relaxor Antiferroelectric Ceramics.

Relaxor antiferroelectric (AFE) ceramic capacitors have drawn growing attention in future advanced pulsed power devices for their superior energy storage performance. However, state of the art dielectric materials are restricted by desirable comprehensive energy-storage features, which have become a longstanding hurdle for actual capacitor applications. Here, we report that a large energy density Wrec of 5.52 J/cm3, high efficiency η of 83.3% at 560 kV/cm, high power density PD of 114.8 MW/cm3, ultrafast discharge rate t0.9 of 45 ns, and remarkable stability against temperature (30-140 °C)/frequency (5-200 Hz)/cycles (1-105) are simultaneously achieved in 0.7 NaNbO3-0.3 CaTiO3 relaxor AFE ceramics via the synergy of stabilized AFE R phase and domain engineering in combination with breakdown strength enhancement. The structural origin for these achievements is disclosed by probing the in situ microstructure evolution by means of the first-order reversal curve method, piezoelectric force microscopy, and Raman spectroscopy. The highly dynamic polar nanoregions and stabilized AFE R phase synergistically generate a linear-like and highly stable polarization field response over a wide temperature and field scope with concurrently improved energy density and efficiency. This work offers a new solution for designing high-performance next-generation pulsed power capacitors.

Realizing Stable Relaxor Antiferroelectric and Superior Energy Storage Properties in (Na1-x/2Lax/2)(Nb1-xTix)O3 Lead-Free Ceramics through A/B-Site Complex Substitution.

The development of environmentally friendly energy storage dielectrics with high energy storage density has attracted increasing attention in power electronics. The combination of antiferroelectric ceramics with relaxor characteristics proves to be an efficient way to greatly improve energy storage properties. In this work, a novel (Na1-x/2Lax/2)(Nb1-xTix)O3 lead-free bulk ceramic exhibits excellent energy storage properties of a giant recoverable energy storage density Wrec ≈ 6.5 J/cm3, a relatively high efficiency η ≈ 66%, and an ultrafast discharge speed t0.9 ≈ 50 ns at x = 0.18, showing outstanding potential for pulsed power capacitors. The Rietveld structural refinement and Raman spectra suggest a relaxor antiferroelectric orthorhombic R phase at room temperature as x > 0.16. Obviously enhanced breakdown strength can be ascribed to ultrafine grains of ∼0.21 µm and largely improved resistivity after BaCu(B2O5) doping. The detailed analysis of high-resolution transmission electron microscopy and in situ field Raman spectra clearly discloses the existence and rapid response feature of antipolar nanoregions and the resulting high driving field (∼30 kV/mm) for the antiferroelectric-to-ferroelectric phase transition, laying a solid foundation for the achievement of desirable energy storage characteristics. These results would provide a reliable strategy and a good understanding for designing new energy storage capacitor dielectrics.

Achieving Remarkable Amplification of Energy-Storage Density in Two-Step Sintered NaNbO3-SrTiO3 Antiferroelectric Capacitors through Dual Adjustment of Local Heterogeneity and Grain Scale.

Antiferroelectric (AFE) materials exhibit outstanding advantages against linear or ferroelectric (FE) dielectrics in high-performance energy-storage capacitors. However, their energy-storage performances are usually restricted by both extremely large hysteresis and insufficiently high driving field of the AFE-FE phase transition, which has been a longstanding issue to be overcome in the community. In this work, we report a two-step sintered 0.83NaNbO3-0.17SrTiO3 (NN-ST) lead-free relaxor AFE R-phase ceramic with high relative density of ≥95% and large spans of average grain sizes from 1.2 to 8.2 µm, strikingly achieving a giant amplification of recoverable energy-storage density (Wrec) by 176%. Analyses of permittivity-temperature curves, Raman spectrum and microstructure demonstrate that remarkably enhanced Wrec values should be ascribed to the dual adjustment of local heterogeneity (nanoscale) and grain scale (microscale), resulting in the enhanced threshold field strength for dielectric breakdown and the increased critical electric fields for the AFE-FE phase transition. A high Wrec ≈ 1.60 J/cm3, a fast discharging rate t0.9 ≈ 520 ns, large current density ∼788 A/cm2, and large power density ∼55 MW/cm3 are achieved at room temperature in the NN-ST ceramic sample with an average grain size of ∼1.2 µm. These results suggest that the multiscale structure regulation should be an efficient way for achieving enhanced energy-storage properties in NN-ST relaxor AFE ceramics through a two-step sintering technique.

Efficient and Stable Photocatalytic Hydrogen Evolution Activity of Multi-Heterojunction Composite Photocatalysts: CdS and NiS2 Co-modified NaNbO3 Nanocubes.

In this study, a NaNbO3/CdS/NiS2 ternary composite photocatalyst containing no precious metals was successfully prepared by a simple hydrothermal method. The prepared ternary photocatalyst has a significant improvement in photocatalytic performance of hydrogen production from water splitting under visible light irradiation. The best sample NCN40% hydrogen production rate is 4.698 mmol g-1 h-1, which is about 24.7 times that of pure CdS sample. In addition, the stability of the composite catalyst in the long-term photocatalytic hydrogen production cycle is also improved. The reason for the enhanced hydrogen production performance may be the optimization of the microstructure of the catalyst and the reduction of photogenerated electron-hole recombination. The construction of multi-heterojunctions (NaNbO3-CdS, CdS-NiS2, and NaNbO3-NiS2) helps to reduce the recombination of carriers. Furthermore, the in-situ-formed NiS2 nanoparticles can serve as active sites for hydrogen evolution. All of these factors induced the improved photocatalytic activity of the as-prepared ternary photocatalyst.