Polymer-/Ceramic-based Dielectric Composites for Energy Storage and Conversion

Dielectric composites boost the family of energy storage and conversion materials as they can take full advantage of both the matrix and filler.This review aims at summarizing the recent progress in developing highperformance polymer-and ceramic-based dielectric composites,and emphases are placed on capacitive energy storage and harvesting,solid-state cooling,temperature stability,electromechanical energy interconversion,and high-power applications.Emerging fabrication techniques of dielectric composites such as 3D printing,electrospinning,and cold sintering are addressed,following by highlighted challenges and future research opportunities.The advantages and limitations of the typical theoretical calculation methods,such as finite-element,phase-field model,and machine learning methods,for designing high-performance dielectric composites are discussed.This review is concluded by providing a brief perspective on the future development of composite dielectrics toward energy and electronic devices.

Correlating the electronic structure of perovskite La_(1-x)SrxCoO_(3) with activity for the oxygen evolution reaction:The critical role of Co 3d hole state

Perovskite LaCoO_(3) is being increasingly explored as an effective low-cost electrocatalyst for the oxygen evolution reaction(OER).Sr doping in LaCoO_(3)(La1-xSrxCoO_(3))has been found to substantially increase its catalytic activity.In this work,we report a detailed study on the evolution of the electronic structure of La1-xSrxCoO_(3) with 0≤x≤1 and its correlation with electrocatalytic activity for the OER.A combination of X-ray photoemission spectroscopy(XPS)and X-ray absorption spectroscopy(XAS)was used to unravel the electronic density of states(DOS)near the Fermi level(EF),which provide insights into the key electronic structure features for the enhanced OER catalytic activity.Detailed analysis on the Co L-edge XAS suggest that LaCoO_(3) has a low spin state with t_(2g)^(6) e_(g)^(0) configuration at room temperature.This implies that the high OER catalytic activity of LaCoO_(3) should not be rationalized by the occupancy of eg=1 descriptor.Substituting Sr^(2+) for La^(3+) in LaCoO_(3) induces Co4+oxidation states and effectively dopes hole states into the top of valence band.A semiconductor-to-metal transition is observed for x>0.2,due to the holeinduced electronic DOS at the EF and increased hybridization between Co 3 d and O 2 p.Such an electronic modulation enhances the surface adsorption of the*OH intermediate and reduces the energy barrier for interfacial charge transfer,thus improving the OER catalytic activity in La_(1-x)Sr_(x)CoO_(3).In addition,we found that the La_(1-x)Sr_(x)CoO_(3) surface undergoes amorphization after certain period of OER measurement,leading to a partial deactivation of the electrocatalyst.High Sr doping levels accelerated the amorphization process.

Energy band alignment at ferroelectric/electrode interface determined by photoelectron spectroscopy

The most important interface-related quantities determined by band alignment are the barrier heights for charge trans- port, given by the Fermi level position at the interface. Taking Pb（Zr, Ti）O3 （PZT） as a typical ferroelectric material and applying X-ray photoelectron spectroscopy （XPS）, we briefly review the interface formation and barrier heights at the inter- faces between PZT and electrodes made of various metals or conductive oxides. Polarization dependence of the Schottky barrier height at a ferroelectric/electrode interface is also directly observed using XPS.

The effect of temperature on ionic liquid modified Fe-N-C catalysts for alkaline oxygen reduction reaction

Modifying solid catalysts with an ionic liquid layer is an effective approach for boosting the performance of both Pt-based and non-precious metal catalysts toward the oxygen reduction reaction. While most studies operated at room temperature it remains unclear whether the IL-associated boosting effect can be maintained at elevated temperature, which is of high relevance for practical applications in low temperature fuel cells. Herein, Fe-N-C catalysts were modified by introducing small amounts of hydrophobic ionic liquid, resulting in boosted electrocatalytic activity towards the alkaline oxygen reduction reaction at room temperature. It is demonstrated that the boosting effect can be maintained and even strengthened when increasing the electrolyte temperature up to 70℃. These findings show for the first time that the incorporation of ionic liquid is a suited method to obtain advanced noble metal-free electrocatalysts that can be applied at operating temperature condition.

Enhanced breakdown strength and energy storage density of AgNbO_(3)ceramics via tape casting

Antiferroelectric materials are promising candidates for energy-storage applications due to their double hysteresis loops,which can deliver high power density.Among the antiferroelectric materials,AgNbO_(3)is proved attractive due to its environmental-friendliness and high potential for achieving excellent energy storage performance.However,the recoverable energy storage density of AgNbO_(3)ceramics is limited by their relatively low breakdown strength.Herein,the breakdown strength of the pure AgNbO_(3)ceramics prepared using the tape casting method is enhanced to 307 kV·cm^(-1),which is,to the best of our knowledge,among the highest values reported for pure AgNbO-3bulk ceramics.The high breakdown strength may be due to its dense microstructure and good crystallinity obtained by the tape casting method and the optimized sintering temperature.Owing to its enhanced breakdown strength,AgNbO_(3)ceramics show high recoverable energy storage density of 2.8 J·cm^(-3).These results have led to the development of lead-free antiferroelectric materials and devices with high energy storage density.

Local probing of the non-uniform distribution of ferrielectric and antiferroelectric phases

Piezoresponse force microscopy(PFM)is an indispensable tool in the investigation of local electromechanical responses and polarization switching.The acquired data provide spatial information on the local disparity of polarization switching and electromechanical responses,making this technique advantageous over macroscopic approaches.Despite its widespread application in ferroelectrics,it has rarely been used to investigate the ferrielectric(FiE)behaviors in antiferroelectric(AFE)materials.Herein,the PFM was utilized to study the local electromechanical behavior and distribution of FiE,and the AFE phases of PbZrO_(3)thin-film were studied,where only the FiE behavior is observable using a macroscopic approach.The FiE region resembles a ferroelectric material at low voltages but exhibits a unique on-field amplitude response at high voltages.In contrast,the AFE region only yields an observable response at high voltages.Phase-field simulations reveal the coexistence of AFE and FiE states as well as the phase-transition processes that underpin our experimental observations.Our work illustrates the usefulness of PFM as an analytical tool to characterize AFE/FiE materials and their phase-coexistence behavior,thereby providing insights to guide property modification and potential applications.

(1-x)Ba(Zr_(0.1)Ti_(0.9))O_(3)-xBa(Mg_(1/3)Ta_(2/3))O_(3)陶瓷的弛豫铁电及介电性能

采用传统固相法在1400℃在空气气氛中烧结2 h制备得到环境友好的(1-x)Ba(Zr_(1/3)Ti_(2/3))O_(3)-xBaMg_(0.1)Ta_(0.9))O_(3)(x=0,0.02,0.04,0.06,0.08)弛豫铁电陶瓷,借助SEM和XRD分别研究其表面形貌及晶体结构。同时研究BaMg_(0.1)Ta_(0.9))O_(3)对Ba(Zr_(1/3)Ti_(2/3))O_(3)陶瓷相变及介电、铁电性能的影响。结果表明:(1-x)Ba(Zr_(1/3)Ti_(2/3))O_(3)-xBa-Mg_(0.1)Ta_(0.9))O_(3)(BZT-BMT)钙钛矿单相陶瓷的平均粒径随BaMg_(0.1)Ta_(0.9))O_(3)(BMT)含量增大而减小。随着x增大,陶瓷体系出现伴有弥散相变和频率色散的弛豫铁电行为。0.98BZT-0.02BMT陶瓷具有良好的介电性能,在100 k Hz下其室温相对介电常数及介电损耗分别为6034和0.01399。随着BMT含量的增大,体系剩余极化强度及矫顽场均减小,表明室温下体系铁电相态向顺电相态的转变。

Role of matrix phase and electric field gradient in Na_(1/2)Bi_(1/2)TiO_(3)eBaTiO_(3) :ZnO composites

Na_(1/2)Bi_(1/2)TiO_(3)-based materials exhibit potential for applications in high-power ultrasonics.The com-posites of Na_(1/2)Bi_(1/2) TiO_(3)-yBaTiO_(3)(NBTyBT;y denotes mole%)with ZnO inclusions were demonstrated to stabilize a ferroelectric equilibrium that led to enhanced thermal depolarization temperature(T_(d))and increased mechanical quality factor(Q_(m)).This work addresses the influence of the matrix NBTyBT phase by investigating two limiting choices based on symmetry(tetragonal/rhombohedral)and polar(relaxor/ferroelectric)nature.While the composites constituting the tetragonal NBT9BT(non-ergodic relaxor at room temperature)matrix phase exhibit improved T d,the critical temperatures in the composites with rhombohedral NBT3BT(displaying spontaneous ferroelectric order at room temperature)exhibit only marginal changes.Further,NBT3BT composites feature a 45%increase in Q m,while the corresponding increase is roughly three-fold for the NBT9BT composites.A 3-D Finite Element Method is used to simulate the electric field gradient at the matrix/inclusion interface,with the effective field distribution estimated to be higher than the applied field for highly conducting ZnO inclusions.The electrical properties indicate that,while the deviatoric stress at the matrix/inclusion interface stabilizes the ferroelectric equilibrium for the relaxor matrix phase,the stresses disrupt the long-range order for the ferroelectric matrix phase.These results establish the volume-limit of the second phase to stabilize a ferroelectric equilibrium,in addition to substantiating the role of residual stress evidenced by changes in the polar nature.Finally,a comparison of the composites with different NBTyBT phases is presented,with NBT6BT:ZnO composites demonstrating an optimal increase in both T_(d) and Q_(m).

Relation between half-cell and fuel cell activity and stability of FeNC catalysts for the oxygen reduction reaction

FeNC catalysts are promising substitutes of platinum-type catalysts for the oxygen reduction reaction(ORR).While previous research disclosed that high pyrolysis temperatures are required to achieve good stability,it was identified that a trade-off needs to be made regarding the active site density.The central question is,if a good stability can also be reached at milder pyrolysis conditions but longer duration retaining more active sites,while enabling the defect-rich carbon to heal during a long residence time?To address this,a variation of pyrolysis temperatures and durations is used in FeNC fabrication.Carbon morphology and iron species are characterized by Raman spectroscopy and Mössbauer spectroscopy,respectively.Fuel cell(FC)activity and stability data are acquired.The results are compared to ORR activity and selectivity data from rotating ring disc electrode experiments and resulting durability in accelerated stress tests mimicking the load cycle and start-up and shut-down cycle conditions.It is discussed how pyrolysis temperature and duration affect FC activity and stability.But,more important,the results connect the pyrolysis conditions to the required accelerated stress test protocol combination to enable a prediction of the catalyst stability in fuel cells.

Inductive effect of Ti-doping in Fe_(2)O_(3)enhances the photoelectrochemical water oxidation

Hematite(α-Fe_(2)O_(3))is an ideal oxide semiconductor candidate for photoelectrochemical(PEC)water splitting.Doping of Fe_(2)O_(3)is known to benefit the PEC water oxidation efficiency,but despite extensive research efforts,the underlying mechanism still remains elusive.In this work,we report a comprehensive study on the relationship between the electronic structure,interfacial reaction kinetics and PEC activity of Ti-doped Fe_(2)O_(3)photoanodes.The results show that the interfacial charge transfer efficiency at the Fe_(2)O_(3)/electrolyte interface is the main factor in the significant increase of the PEC activity of doped Fe_(2)O_(3).Electrochemical impedance spectroscopy reveals that the interfacial charge transfer efficiency is determined by energy overlap between the water oxidation potential and energy distribution of an intermediate surface state that has been identified as Fe^(IV)=O groups on Fe_(2)O_(3)surface generated during PEC process.Interestingly,the potential energy distribution of this intermediate surface state can be modulated by Ti doping,and a shift towards a more positive potential of the intermediate surface state increases the overlap with the water oxidation potential and thus enhances the kinetics of charge transfer for PEC water splitting.The origin of such potential energy modulation is traced to the inductive effect from Ti-doping on the Fe^(3+)/Fe^(4+)redox transition and the Fe-O bond covalency.Our results provide new insight into the mechanism for the doping effect on the PEC water splitting,introducing new strategies to optimize the PEC activity by tuning the redox properties of active metal oxides.

Hard and tough novel high-pressure γ-Si_(3)N_(4)/Hf_(3)N_(4) ceramic nanocomposites

Cubic silicon nitride(-Si_(3)N_(4))is superhard and one of the hardest materials after diamond and cubic boron nitride(cBN),but has higher thermal stability in an oxidizing environment than diamond,making it a competitive candidate for technological applications in harsh conditions(e.g.,drill head and abrasives).Here,we report the high-pressure synthesis and characterization of the structural and mechanical properties of a γ-Si_(3)N_(4)/Hf_(3)N_(4) ceramic nanocomposite derived from single-phase amorphous silicon(Si)-hafnium(Hf)-nitrogen(N)precursor.The synthesis of the-Si_(3)N_(4)/Hf_(3)N_(4) nanocomposite is performed at~20 GPa and ca.1500 ℃ in a large volume multi anvil press.The structural evolution of the amorphous precursor and its crystallization to-Si_(3)N_(4)/Hf_(3)N_(4) nanocomposites under high pressures is assessed by the in situ synchrotron energy-dispersive X-ray diffraction(ED-XRD)measurements at~19.5 GPa in the temperature range of ca.1000-1900℃.The fracture toughness(K_(IC))of the two-phase nanocomposite amounts~6/6.9 MPa·m^(1/2) and is about 2 times that of single-phaseγ-Si_(3)N_(4),while its hardness of ca.30 GPa remains high.This work provides a reliable and feasible route for the synthesis of advanced hard and tough-Si_(3)N_(4)-based nanocomposites with excellent thermal stabililty.

Unravelling the protracted U-Pb zircon geochronological record of high to ultrahigh temperature metamorphic rocks:Implications for provenance investigations

The assessment of detrital zircon age records is a key method in basin analysis,but it is prone to several biases that may compromise accurate sedimentary provenance investigations.High to ultrahigh temperature(HT-UHT)metamorphism(especially if T>850℃)is herein presented as a natural cause of bias in provenance studies based on U-Pb detrital zircon ages,since zircon from rocks submitted to these extreme and often prolonged conditions frequently yield protracted,apparently concordant,geochronological records.Such age spreading can result from disturbance of the primary U-Pb zircon system,likewise from(re)crystallization processes during multiple and/or prolonged metamorphic events.In this contribution,available geochronological data on Archean,Neoproterozoic and Palaeozoic HT-UHT metamorphic rocks,acquired by different techniques(SIMS and LA-ICP-MS)and showing distinct compositions,are reassessed to demonstrate HT-UHT metamorphism may result in modes and age distributions of unclear geological meaning.As a consequence,it may induce misinterpretations on UPb detrital zircon provenance analyses,particularly in sedimentary rocks metamorphosed under such extreme temperature conditions.To evaluate the presence of HT-UHT metamorphism-related bias in the detrital zircon record,we suggest a workflow for data acquisition and interpretation,combining a multi-proxy approach with:(i)in situ U-Pb dating coupled with Hf analyses to retrieve the isotopic composition of the sources,and(ii)the integration of a petrochronological investigation to typify fingerprints of the HT-UHT metamorphic event.The proposed workflow is validated in the investigation of one theoretical and one natural example allowing a better characterization of the sedimentary sources,maximum depositional ages,and the tectonic setting of the basin.Our workflow allows to the appraisal of biases imposed by HT-UHT metamorphism and resulting disturbances in the U-Pb detrital zircon record,particularly for sedimentary rocks that underwent HT-UHT metamorphism and,finally,suggests ways to overcome these issues.

Enhanced electromagnetic wave absorption via optical fiber-like PMMA@Ti_(3)C_(2)T_(x)@SiO_(2) composites with improved impedance matching

Ti_(3)C_(2)T_(x) nanosheets have attracted significant attention for their potential in electromagnetic wave absorption(EWA).However,their inherent self-stacking and exorbitant electrical conductivity inevitably lead to serious impedance mismatch,restricting their EWA application.Therefore,the optimization of impedance matching becomes crucial.In this work,we developed polymethyl methacrylate(PMMA)@Ti_(3)C_(2)T_(x)@SiO_(2) composites with a sandwich-like core–shell structure by coating SiO_(2) on PMMA@Ti_(3)C_(2)T_(x).The results demonstrate that the superiority of the SiO_(2) layer in combination with PMMA@Ti_(3)C_(2)T_(x),outperforming other relative graded distribution structures and meeting the requirements of EWA equipment.The resulting PMMA@Ti_(3)C_(2)T_(x)@SiO_(2) composites achieved a minimum reflection loss of-58.08 dB with a thickness of 1.9 mm,and an effective absorption bandwidth of 2.88 GHz.Mechanism analysis revealed that the structural design of SiO_(2) layer not only optimized impedance matching,but also synergistically enhanced multiple loss mechanisms such as interfacial polarization and dipolar polarization.Therefore,this work provides valuable insights for the future preparation of high-performance electromagnetic wave absorbing Ti_(3)C_(2)T_(x)-based composites.

Ternary layered boride MoAlB:A novel thermo-regulation microwave absorbing ceramic material

In the context of the fifth-generation(5G)smart era,the demand for electromagnetic wave(EMW)-absorbing materials has become increasingly prominent,so it is necessary to explore promising candidate materials.This work focuses on the exploration of the material absorbing properties of a MoAlB MAB(MAB represents a promising group of alternatives,where M stands for a transition metal,A typically denotes Al,and B is boron)phase system.First,the first-principles calculations were performed to reveal the unique crystal and layered structure of the MoAlB ceramics and to predict their potential for use as an EMW absorption material.Subsequently,a series of MoAlB ceramics were synthesized at temperatures ranging from 800 to 1300℃,and the influence of temperature on the phase compositions and microstructures of the obtained MoAlB ceramics was characterized and analyzed.Finally,the practical EMW absorption performance of the prepared MoAlB ceramics was evaluated via a combination of experiments and radar cross-sectional calculations.The MoAlB sample synthesized at 900℃ exhibits superior EMW absorption performance,achieving an impressive minimum reflection loss(RL)of−50.33 dB.The unique layered structure and good electrical conductivity of the MoAlB samples are the main reasons for their enhanced wave absorption performance,which provides interfacial polarization and multiple dielectric loss mechanisms.Therefore,this study not only contributes to the understanding of the preparation of MoAlB materials but also provides potential guidance for their utilization in the realm of electromagnetic wave absorption.

Boron-modified perhydropolysilazane towards facile synthesis of amorphous SiBN ceramic with excellent thermal stability

SiBN ceramics are widely considered to be the most promising material for microwavetransparent applications in harsh environments owing to its excellent thermal stability and low dielectric constant.This work focuses on the synthesis and ceramization of single-source precursors for the preparation of SiBN ceramics as well as the investigation of the corresponding microstructural evolution at high temperatures including molecular dynamic simulations.Carbon-and chlorine-free perhydropolysilazanes were reacted with borane dimethyl sulfide complex at different molar ratios to synthesize single-source precursors,which were subsequently pyrolyzed and annealed under N2 atmosphere(without ammonolysis)to prepare SiBN ceramics at 1100,1200,and 1300℃with high ceramic yield in contrast to previously widely-used ammonolysis synthesis process.The obtained amorphous SiBN ceramics were shown to have remarkably improved thermal stability and oxidation resistance compared to amorphous silicon nitride.Particularly,the experimental results have been combined with molecular dynamics simulation to further study the amorphous structure of SiBN and the atomic-scale diffusion behavior of Si,B,and N at 1300℃.Incorporation of boron into the Si–N network is found to suppress the crystallization of the formed amorphous silicon nitride and hence improves its thermal stability in N2 atmosphere.

Advancing oxygen separation:insights from experimental and computational analysis of La_(0.7)Ca_(0.3)Co_(0.3)Fe_(0.6)M_(0.1)O_(3-δ)(M=Cu,Zn)oxygen transport membranes

In this study,perovskite-type La_(0.7)Ca_(0.3)Co_(0.3)Fe_(0.6)M_(0.1)O_(3-δ)(M=Cu,Zn)powders were synthesized using a scalable reverse co-precipitation method,presenting them as novel materials for oxygen transport membranes.The comprehensive study covered various aspects including oxygen permeability,crystal structure,conductivity,morphology,CO_(2) tolerance,and long-term regenerative durability with a focus on phase structure and composition.The membrane La_(0.7)Ca_(0.3)Co_(0.3)Fe_(0.6)M_(0.1)O_(3-δ)exhibited high oxygen permeation fluxes,reaching up to 0.88 and 0.64 mL·min^(−1)·cm^(−2) under air/He and air/CO_(2) gradients at 1173 K,respectively.After 1600 h of CO_(2) exposure,the perovskite structure remained intact,showcasing superior CO_(2) resistance.A combination of first principles simulations and experimental measurements was employed to deepen the understanding of Cu/Zn substitution effects on the structure,oxygen vacancy formation,and transport behavior of the membranes.These findings underscore the potential of this highly CO_(2)-tolerant membrane for applications in high-temperature oxygen separation.The enhanced insights into the oxygen transport mechanism contribute to the advancement of next-generation membrane materials.

Perspective on antiferroelectrics for energy storage and conversion applications

As a close relative of ferroelectricity,antiferroelectricity has received a recent resurgence of interest driven by technological aspirations in energy-efficient applications,such as energy storage capacitors,solid-state cooling devices,explosive energy conversion,and displacement transducers.Though prolonged efforts in this area have led to certain progress and the discovery of more than 100 antiferroelectric materials over the last 70 years,some scientific and technological issues remain unresolved.Herein,we provide perspectives on the development of antiferroelectrics for energy storage and conversion applications,as well as a comprehensive understanding of the structural origin of antiferroelectricity and field-induced phase transitions,followed by design strategies for new lead-free antiferroelectrics.We also envision unprecedented challenges in the development of promising antiferroelectric materials that bridge materials design and real applications.Future research in these directions will open up new possibilities in resolving the mystery of antiferroelectricity,provide opportunities for comprehending structure-property correlation and developing antiferroelectric/ferroelectric theories,and suggest an approach to the manipulation of phase transitions for real-world applications.

Modulus spectroscopy for the detection of parallel electric responses in electroceramics

Impedance spectroscopy has become one of the most versatile and essential investigation methods concerning electrical properties of materials for electronic and energy applications.Deriving knowledge about physical mechanisms,however,often demands excellent expertise in evaluating the spectra.Investigating different representations of the same data set can help elucidate the underlying physics,but this is rarely applied.In this work,the importance of using the modulus representation to identify parallel electric responses is rationalized.Those responses result from parallel conducting pathways,e.g.,at grain boundaries,or from regions with differing permittivity,e.g.,in composites.Qualitative and quantitative data can be obtained,as it is illustrated based on experimental data from electroceramics and respective physical simulation results using the finite element method.The findings should help to study intricate electric responses of materials with chemical or structural heterogeneity.

Review on field-induced phase transitions in lead-free NaNbO_(3)-based antiferroelectric perovskite oxides for energy storage

Emerging new applications of antiferroelectric perovskite oxides based on their fascinating phase transformation between polar and nonpolar states have provided considerable attention to this class of materials even decades after the discovery of antiferroelectricity.After presenting the challenge of formulating a precise definition of antiferroelectric materials,we briefly summarize proposed applications.In the following,we focus on the crystallographic structures of the antiferroelectric and ferroelectric phases of NaNbO_(3),which is emerging as a promising alternative to PbZrO_(3)-based systems.The field-induced phase transition behavior of NaNbO_(3)-based AFE materials in the form of single crystals,bulk ceramics,and multilayer ceramic capacitors is reviewed.Recent advances in a group of materials exhibiting high energy storage performance and relaxor-like behavior are also covered.The influence of electrode geometry on phase transition behavior and thus on the energy storage property is briefly addressed.The review concludes with an overview of the remaining challenges related to the fundamental understanding of the scientific richness of AFE materials in terms of structure,microstructure,defect transport under high fields,and phase transition dynamics required for their future development and applications.

CuSbS_(2)薄膜光阴极的电子结构及其在光电催化分解水制氢的应用

硫化锑铜(CuSbS_(2))是一种p型半导体,带隙为1.5 eV,同时拥有较大的光吸收系数(>105cm-1),因此在光电催化领域拥有广阔的应用前景.但是目前国内外的研究还缺乏对CuSbS_(2)电子结构以及其如何影响PEC性能的深入理解.为了进一步改善CuSbS_(2)的PEC性能,对其电子结构进行一系列表征分析是非常重要的.本文中,我们利用同步辐射技术揭示了CuSbS_(2)的电子结构.结果表明,CuSbS_(2)的价带(VB)由S 3p和Cu 3d的强杂交态组成,同时Sb 5p/5s也有部分影响.基于以上理论指导,我们设计了一种高质量Cu Sb S_(2)薄膜的制备技术,并使用FTO/CuSbS_(2)/CdS/Pt光电阴极在0.0 V下实现了CuSbS_(2)基材料的高光电流密度(6.3 mA cm^(-2)).