Dielectric Relaxation Properties Research Articles

Starch‐based nanoparticles as a replacement for synthetic latex: A comprehensive assessment of printability and colorimetric characteristics

AbstractThe papermaking, packaging, and printing industry are actively seeking sustainable material alternatives to address growing concerns about environmental consciousness and finite resources. Synthetic latex, a frequently utilized binder in paper coating formulations, present difficulties due to their dependence on fossil fuel resources and their reduced recyclability in comparison to eco‐friendly sustainable products. In this study, synthetic latex was replaced with a starch‐based nanoparticle (starch NP) binder at a 1:1 ratio in a coating formulation. Printing trials to assess colorimetric characteristics was made using electrophotography (EP) printing, given the current upward trajectory and expansion of EP technology into the label, packaging, and folding carton sectors. The in‐depth investigations reveal that incorporating starch NP binder result in improved optical, color, and dot characteristics. Moreover, it maintains consistent and comparable coefficients of friction. Partial replacement of synthetic latex with the starch NP binder yields significant enhancements in surface roughness and text quality. Importantly, the starch NP binder not only improves the dielectric relaxation properties of the paper and enhances toner transfer but also accelerates the distribution of the electrical field compared to synthetic latex, optimizing toner transfer and thereby enhancing color gamut volume. The study demonstrates that employing the starch NP binder leads to substantial improvements in colorimetric performance without any drawbacks in EP printing, making it highly advantageous to replace 50% of the synthetic binder.

Simultaneously realizing high energy density and high efficiency in NaNbO3–BaTiO3‐based ceramic capacitors

AbstractDielectric capacitors, which can achieve tremendous power density and ultrafast charge/discharge speed, are crucial components for high power equipment. Yet, the synchronous achievement in high recoverable energy density (Wrec) and high efficiency (η) is a long‐term difficulty for dielectric ceramics. Herein, the (0.85 − x)NaNbO3–0.15BaTiO3–xBi(Mg1/3Ta2/3)O3 (NN–BT–xBMT) relaxor ferroelectric ceramics were proposed and studied. The doping of BMT was conducive to promoting the microstructure and bandgap and improving the dielectric relaxation properties of NN–BT ceramics. Finally, the sample of x = 0.10 presented a high Wrec of 5.9 J/cm3 and a high η of 90% simultaneously. In addition, the sample also exhibited superb charge/discharge performances with large power density (PD = 137 MW/cm3) and fast charge/discharge speed (t0.9 = 39 ns). The above results reveal that the NaNbO3‐based ceramics could serve as potential alternatives for advanced dielectric capacitors.

Dielectric relaxation and electrical conductivity property correlation in Gd-doped BBTO Aurivillius ceramics

Dielectric relaxation and electrical conductivity property correlation in Gd-doped BBTO Aurivillius ceramics

Understanding charge transport and dielectric relaxation properties in lead-free Cs2ZrCl6 nanoparticles.

In the exploration of perovskite materials devoid of lead and appropriate for capturing solar energy, a recent finding has surfaced concerning Cs2ZrCl6. This compound has attracted interest as a potential candidate, displaying advantageous optical and electrical features, coupled with remarkable durability under environmental stresses. This research outlines the effective production of non-toxic metal halide nanoparticles of Cs2ZrCl6 using the gradual cooling technique. Thorough examinations have been conducted to explore the structural, optical, and dielectric traits. Over the frequency range of 101-106 Hz, the dielectric constant, loss factor, electric modulus, and electrical conductivity of Cs2ZrCl6 exhibit a strong dependence on temperature. The Nyquist plot confirms the distinct contributions of grains and grain boundaries to the total impedance. In the high-frequency region, the dielectric constant tends to increase with temperature. In accordance with the modified Kohlrausch-Williams-Watts (KWW) equation, an asymmetric nature corresponding to the non-Debye type is observed in the electric modulus spectra at different temperatures. Furthermore, the imaginary part of the electric modulus spectrum shifts from the non-Debye type towards the Debye type with increasing temperature, despite not obtaining an exact Debye response. The frequency-dependent behavior of AC conductivity has been modeled using Joncher's universal law. The conduction mechanism within the Cs2ZrCl6 compound is attributed to the small polaron tunneling model (NSPT). Furthermore, Cs2ZrCl6 has the potential to function as an energy harvesting device due to its elevated dielectric constant combined with minimal dielectric loss.

Temperature and frequency dependent response of electrical conduction and dielectric relaxation mechanism in CuCr2O4 tetragonally distorted spinel chromite

Herein, the polycrystalline CuCr2O4 (CCO) electro-ceramic was prepared via the sol-gel self-combustion route. The X-ray powder diffraction analysis at room temperature revealed that the CCO chromite was synthesized in a single phase tetragonally distorted normal spinel structure with I41/amd space group. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) investigated the polycrystalline nature of the compound. The microstructural analysis by field emission scanning electron microscopy (FESEM) explored the surface morphology of micron-sized grains (Gs) distinguished by well-pronounced grain boundaries (GBs) available for electrical response of the material. The color mapping images of elements by energy-dispersive X-ray spectroscopy (EDS) divulged the homogeneous distribution of elements in the compound. The surface chemistry of the compound was studied by X-ray photoelectron spectroscopy (XPS). This information helped in understanding the electronic states of the ions contributing to the electrical networks and mechanisms responsible for the charge transport within the CCO system. The dielectric relaxation and electrical transport properties were analyzed using complex impedance spectroscopy (CIS) over the experimental range of frequency and temperature from 40 Hz to 1 MHz and 243–493 K, respectively. The experimental complex impedance data were analyzed by RGQGRGBQGB equivalent circuit model which resolved the electro-active contributions of bulk and interface of the CCO spinel to its electrical dynamics. The dispersion in AC conductivity was explained by Jonscher's double power law which provided evidence of small polaron hopping (SPH) as a dominant transport mechanism governing electrical conduction in the compound. The temperature-dependent DC conductivity pattern exhibited an Arrhenius-like behavior that followed Mott and Davis's model of SPH. The analysis of complex electrical modulus M*(ω,T) professed the localized and de-localized movements of the charge carriers. The dielectric permittivity response of CCO followed Havriliak-Negami (HN) phenomenology that divulged the existence of non-Debye type dielectric relaxation processes. The interfacial polarization was observed to be accountable for the dispersion in dielectric loss spectra.

Charge transport mechanism, dielectric relaxations and relaxor ferroelectric properties of Sm2MgMnO6 double perovskite

This study investigates the charge transport mechanism, dielectric relaxation and relaxor ferroelectric properties of Sm2MgMnO6 which exhibits monoclinic crystal structure with space group P21/n. The charge carriers conduction mechanism in the temperature range 150 K–239 K and 244 K–304 K are correlated barrier hopping (CBH) and overlapping large polaron tunneling (OLPT), respectively. The maximum barrier height associated to CBH model is 0.26 meV. The dc activation energy associated to CBH and OLPT model are 0.11 eV and 0.91 eV respectively. The polaron hopping energy associated to Mott's variable range hopping model is 0.11 eV at 244 K. The value of tanδ varies from 0.004 to 3.329 in temperature range 151.07 K–306.87 K and frequency range 1 kHz–800 kHz. The temperature variation of ε′, ε″ and tanδ shows a single relaxation which follows Vogel–Fulcher (VF) law. The VF law and the shape of P–E hysteresis loop confirms the relaxor ferroelectric nature of the studied material. The saturated polarization (PMax), remnant polarization (Pr) and coercive field (Ec) depend on both the electric field (E0) and frequency (f). The loop area (A′) and dielectric breakdown field (EBD) depend on E0 as A′∝E02 and EBD∝E0, respectively. The PMax, Pr and Ec depend on f as PMax∝f−0.13, Pr∝f−0.48 and Ec∝f−0.48, respectively. The energy storage efficiency (η) varies with frequency as: η%=20.44f0.21.

Strong pyroelectric enhancement induced by the evolution of PNRs in paraelectric-phase KTN crystals

KTa1−xNbxO3 crystals exhibit excellent piezoelectric, ferroelectric, and electro-optical properties near the phase transition point, owing to the evolution of polar nanoregions (PNRs). This paper discusses the physical properties of the PNRs in three characteristic temperature ranges and analyzes the dielectric relaxation properties of the crystals. The effects of different heating rates and initial temperatures on the pyroelectric effect are discussed, and the influence of small electric fields on increasing the pyroelectric coefficient is investigated. The polarization characteristics of the crystal were obtained according to the change in the pyroelectric performance, and the influence of different conditions on the dynamic response of the PNRs was analyzed. It is proposed that the evolution of PNRs, induced by external coupling with an internal electric field, significantly affects macroscopic performance.

Insight into the Effect of Glycerol on Dielectric Relaxation and Transport Properties of Potassium-Ion-Conducting Solid Biopolymer Electrolytes for Application in Solid-State Electrochemical Double-Layer Capacitor.

The increased interest in the transition from liquid to solid polymer electrolytes (SPEs) has driven enormous research in the area polymer electrolyte technology. Solid biopolymer electrolytes (SBEs) are a special class of SPEs that are obtained from natural polymers. Recently, SBEs have been generating much attention because they are simple, inexpensive, and environmentally friendly. In this work, SBEs based on glycerol-plasticized methylcellulose/pectin/potassium phosphate (MC/PC/K3PO4) are investigated for their potential application in an electrochemical double-layer capacitor (EDLC). The structural, electrical, thermal, dielectric, and energy moduli of the SBEs were analyzed via X-ray diffractometry (XRD), Fourier transforms infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS), transference number measurement (TNM), and linear sweep voltammetry (LSV). The plasticizing effect of glycerol in the MC/PC/K3PO4/glycerol system was confirmed by the change in the intensity of the samples' FTIR absorption bands. The broadening of the XRD peaks demonstrates that the amorphous component of SBEs increases with increasing glycerol concentration, while EIS plots demonstrate an increase in ionic conductivity with increasing plasticizer content owing to the formation of charge-transfer complexes and the expansion of amorphous domains in polymer electrolytes (PEs). The sample containing 50% glycerol has a maximal ionic conductivity of about 7.5 × 10-4 scm-1, a broad potential window of 3.99 V, and a cation transference number of 0.959 at room temperature. Using the cyclic voltammetry (CV) test, the EDLC constructed from the sample with the highest conductivity revealed a capacitive characteristic. At 5 mVs-1, a leaf-shaped profile with a specific capacitance of 57.14 Fg-1 was measured based on the CV data.

Impedance spectroscopy and DFT/TD-DFT studies of diyttrium trioxide for optoelectronic fields

Yttrium (III) oxide or so-called diyttrium trioxide (Y 2 O 3 ) is an excellent candidate ceramic material for optoelectronic applications. Structural, electrical conductivity, and dielectric relaxation properties of bulk yttrium (III) oxide are studied. X-ray diffraction (XRD) results indicate that the yttrium (III) oxide compound has a crystalline cubic phase. FTIR technique is used to ascertain the chemical structure of the yttrium (III) oxide compound. Impedance spectroscopy was used to analyze frequency-dependent electrical properties as a function of temperature in the range of 303–423 K and frequency range 0.1 Hz–2 MHz. Impedance spectroscopy parameters such as dielectric constant, dielectric loss, loss factor, electric modulus, and complex impedance of the yttrium (III) oxide compound have been studied. The Nyquist plot describes the complex impedance of the yttrium (III) oxide for different temperatures. The universal Jonscher’s power law was used for the analysis of the complex electrical conductivity of the yttrium (III) oxide compound. It is found that the real ( σ ′ ) and imaginary ( σ ˊ ˊ ) parts of the complex conductivity increase with increasing frequency. The exponent frequency (s) equals unity which confirms that the predominant conduction mechanism is a nearly constant loss (NCL) mechanism. DFT/TD-DFT studies using B3LYP/LanL2DZ level of theory were used to provide comparable theoretical data and electronic energy gap of HOMO→LUMO. Spatial plot of HOMO and LUMO of yttrium (III) oxide with their energy gap.

Dielectric constant, dielectric loss, conductivity, capacitance and model analysis of electronic electroactive polymers

In this study, the dielectric constant, dielectric loss, conductivity and capacitance of the electronic electroactive polymer (EEAP) were systematically tested experimentally, and the effects of different frequencies, effective voltages, electrode types, and specimen thicknesses on the dielectric relaxation properties of polymers were analyzed, and finally the Debye, Cole-Cole and Havriliak-Negami functions were used to model the dielectric constants. The experimental results show that the dielectric constant of the polymer depends strongly on the frequency, especially in the low frequency stage from 10−1 to 100 Hz. The effect of different effective voltages on the dielectric properties is basically identical, and the accuracy of the test can be improved at this AC voltage avoiding the effect of electrostatic stress. At the same effective voltage and thickness, the polymer with G-C electrodes shows the best electrical parameters, the composite electrode form of G-C electrodes contributes to the conductive properties of the polymer and can be applied to the later design of actuators. Compared with the Debye model, the errors of the experimental and calculated values of the Cole-Cole and Havriliak-Negami models are smaller, 1.1102 and 0.7130, respectively. The dielectric behavior of EEAPs differs from that of epoxy materials, probably due to the influence of electric dipole moments, bound charges, and dipole effects. The paper has some reference value for further revealing the dielectric properties and relaxation time distribution of the polymer, and provides guidance for the later application of EEAP materials in flexible robots.

Dielectric relaxation studies of poly(ethylene oxide) with the addition of salt or nanofiller

AbstractPoly(ethylene oxide) (PEO)–lithium perchlorate (LiClO4) serves as the classical model of polymer–salt systems with good polymer–salt molecular interaction at low salt concentration, whereas titanium dioxide (TiO2) without any surface treatment when added to PEO serves as a classical model of polymer–filler systems with weak polymer–filler molecular interaction. The correlation of molecular interactions of polymer–salt or polymer–filler with thermal properties of the systems, which govern the formation of morphologies of the systems, was attempted in a previous study. Hence, this work focuses on the correlation of morphologies and dielectric relaxation properties of PEO with the addition of LiClO4 or TiO2 investigated using polarized optical microscopy and electrochemical impedance spectroscopy over the frequency range from 50 Hz to 1 MHz at 25 °C. The effects of the addition of LiClO4 or TiO2 on the dynamics and relaxations of the polymer chain of PEO are discussed empirically following the fluctuation–dissipation effects from the common electrochemical terms and equivalent circuit model. The PEO–LiClO4 system seems to be one of the promising polymer electrolytes for application in lithium rechargeable batteries where the charged entities may arise from the interaction of salt with the ether oxygen of PEO in the amorphous region. Meanwhile, the PEO–TiO2 system may be analogous to a polar polymer with longitudinal dipoles along the PEO backbone, ethylene oxide monomers (from PEO) of which may represent the molecular dipole or charged entity. The findings show that the transport of charged entities in the PEO systems after the addition of LiClO4 or TiO2 is dominated by short‐range motion at room temperature. © 2022 Society of Industrial Chemistry.

High piezoelectric, dielectric relaxation and semiconductor properties in a one-dimensional organic–inorganic hybrid complex: [2-methyl-1,5-pentanediamine][BiCl5

Molecular-based multifunctional material [2-methyl-1,5-pentanediamine][BiCl5] has interesting properties, such as phase transition, piezoelectric, second harmonic generation, dielectric relaxation, semiconductor and so on.

Influence of incorporation of Fe2O3 content on the structural and the dielectric relaxation properties of lithium boro-vanadate oxide glass: toward ideal cathode glasses

Influence of incorporation of Fe2O3 content on the structural and the dielectric relaxation properties of lithium boro-vanadate oxide glass: toward ideal cathode glasses

Temperature Dependent Dielectric Relaxation Studies of 2-Nitrotoluene-DMSO mixture using Time Domain Relectometry from 10MHz to 50GHz

The dielectric relaxation properties of 2-Nitrotoluene (2-NT) with DMSO for 11 different concentrations has been studied in the frequency range from 10 MHz to 50 GHz using time domain reflectometry (TDR) method. In this frequency range Dielectric relaxation spectra of 2-NT-DMSO mixtures shows Debye type behavior. The temperature dependent static dielectric constant and relaxation time have been determined from 20oC to 5oC. Effective Kirkwood correlation factor is calculated to determine the effect of strong directional forces such as microwaves on heterogeneous molecules under different temperatures. The excess permittivity and excess inverse excess relaxation time is found to be negative for 2-NT-DMSO system with weak molecular interactions. The activation enthalpy have been calculated to find the energy required to rotate the molecules

Stronger B-site ionic disorder boosting enhanced dielectric energy-storage performance in BNT-based relaxor ferroelectric ceramics

Because of their possible applications in dielectric energy-storage capacitor devices, (Bi0.5Na0.5)TiO3-based (BNT) relaxor ferroelectric (RFE) ceramics are feasible alternatives to lead-containing electroceramics. Good energy-storage performance (ESP), including high recoverable energy density (Wrec) and good energy discharge efficiency (η), is required to achieve device miniaturization and long device lifetimes. An advanced method was used to overcome the challenges of A-site ionic disordered RFE in achieving high inducible polarization and low hysteresis, with the former dictating a large Wrec and the latter dictating a high η. In this study, an ABO3 perovskite-structured complex end-member Bi(Mg2/3Nb1/3)O3 (BMN) was added to a 0.7Bi0.5Na0.4K0.1TiO3–0.3Ba0.5Sr0.5TiO3 (0.7BNKT–0.3BST) matrix. The differences in the valence states and ionic radii of Mg2+, Ti4+, and Nb5+ increased the local electric field fluctuation, which contributed to the expanded dielectric relaxation properties. The combined substantial prevention of hysteresis and remanent polarization suggests high potential applicability for ESP. Finally, an enhancement in Wrec to 4.98 J/cm3 was achieved in 0.595BNKT–0.255BST–0.15BMN with an ultrahigh η of 97.3% in a medium-strength electric field of 300 kV/cm. The ESP also demonstrated good thermostability between 30 and 120 °C. Furthermore, the strategy used in this study to generate RFEs can serve as a guide for future research.

Dielectric relaxation properties, and AC conductivity of Erbium(III)-Tris(8-hydroxyquinolinato) nanostructured films

Thin films of Erbium (III)-Tris (8-hydroxyquinolinato (ErQ3) were accomplished by thermal evaporating procedure. The thermal stability of ErQ3 powder was studied by the differential scanning calorimeter (DSC). The SEM image of ErQ3 thin film revealed that the surface morphology of ErQ3 is composed from several of islands structure, meanwhile each island look like algae-shape. The variation of the dielectric real and imaginary parameters versus temperature and frequency were discussed. The real dielectric constant and dielectric loss show a remarkable dependence on the frequency and temperature. The activation energy of the relaxation process (ΔE) was found to be 0.428 eV. In addition, the density of localized states at Fermi levels N(Ef) was estimated to be 1.33×1018eV−1cm−3. AC conductivity at various frequencies and temperatures was investigated. At high frequency regime, the AC conductivity behavior was explained by Jonscher formalism. The charge transport mechanism was found to be controlled by the barrier hopping model (CBH). The decrease of the potential barrier height (Wm) as temperature increases unveils the growing of diffusion charges as the temperature increases. The decrease of the activation energy of the AC conductivity (ΔEAc) as the frequency increases confirms the effect of the applied frequency in the enhancement of the eletrons hopping between the two nieghoburing sites. Overall, the relatively small value of the potential barrier height (Wm) and the extensive localized electronic states encourages the utilizing of ErQ3 in designing the solar cell units.

Dielectric Relaxation and Ferroelectric Properties of PNN–PZT Ceramics with Different Ni/Nb Ratios

0.35Pb(NixNb1−x)O3–0.65Pb(Zr0.39Ti0.61)O3 (x = 1/4,1/3,1/2 and 2/3) ceramics are prepared by the conventional solid reaction method and their structure, dielectric, and ferroelectric properties are studied. All compositions show tetragonal perovskite structure and Ni2+ segregated at grain boundaries in ceramics with high Ni/Nb (x = 1/2,2/3). Oxygen vacancies exist in nonstoichiometric ceramics and increase with the increase in Ni/Nb. Due to the pinning effect of defects, the P–E loops become unsaturated, accompanied by a softening–hardening transition. Dielectric relaxation is detected in both PNN–PZT(x = 1/2) and PNN–PZT(x = 2/3), and the activation energies of relaxation and conduction are calculated by Arrhenius law. The results show that both grain and grain boundary contribute to dielectric relaxation which can be explained on the basis of equivalent circuit containing two parallel RC elements connected in series. The relaxation at low frequency is induced by dipoles concentrating on the grain boundary while the relaxation at high frequency is attributed to the first ionization of oxygen vacancies in the grain.

Multi-field tuning of dielectric relaxation in epitaxial multiferroic hexaferrite thin film around room temperature: Property and mechanisms

Understanding the dielectric relaxation properties of multiferroic hexaferrite thin films is crucial for device applications. This work investigates the dielectric relaxation characteristics (DRC) of multiferroic hexaferrite BaFe10.2Sc1.8O19 (BFSO) thin film under multi-fields. The alternative driving voltage and biasing voltage Vb were found to have significant effects on the DRC of BFSO/electrode interface dipoles, but negligible effects on the intrinsic dipoles in BFSO film. The DRC mechanism of a BFSO film capacitor under a magnetic field is opposite to that of Vb; is dominated by intrinsic dipoles in BFSO, and is thermally activated. The temperature-dependent magnetodielectric spectra confirm that multiferroic dipoles in BFSO significantly impact the DRC of the capacitor, which is different from the DRC of nonmagnetic ceramic capacitors. The above findings can clarify the DRC mechanisms and integration of multiferroic hexaferrite thin films in magnetoelectric devices.

Study of ionic conduction, dielectric relaxation, optical and electrochemical properties of AgPO3/graphene glasses for magnesium battery applications

Developing suitable cathode material for alkali ion batteries is the most significant challenge facing commercialization. The effect of graphene nanoplatelets (GNP) on the physical and optical properties of AgPO3 glass is demonstrated. For the first time, AgPO3/Graphene glasses have been synthesized by melt-quenching method to assess the physical and the electrochemical performance as a cathode for a Magnesium ion battery. The complex impedance method determines bulk conductivity; the bulk conductivity increases with increasing temperature and graphene content. AgPO3_2 wt%GNP (sample 2) shows the optimum stoichiometric ratio with linear conductivity-temperature growth up to fast-ionic conductivity ∼ 1.79×10−2 (ohm. cm)−1 at 150 °C. The study of frequency dependence of both dielectric constant and dielectric loss have been explained based on ion hopping beside the ionic polarization mechanism. Optical properties such as the refractive index, optical energy gap, molar refractivity, molecular polarizability, dispersion, and oscillator energy of AgPO3 glass with different graphene nanoplatelets are investigated. The data reveal the lowest energy gap for the glass sample (AgPO3/2 wt%GNP). On the contrary, the values of refractive index, dispersion energy, molar refractivity and molecular polarizability are the highest for (AgPO3_2%wt%GNP) sample. The coin cell has been fabricated with the cell configuration Mg//electrolyte//AgPO3 and Mg//electrolyte//AgPO3_2 w%GNP. The cell with AgPO3_2 wt% GNP electrode has a high initial discharge capacity of ∼187 mAh/g compared with AgPO3 electrodes of ∼100 mAh/g.

Assessment of proton conductivity, dielectric relaxation and other physicochemical properties of LTA zeolite blended chitosan composites for membrane applications

Novel chitosan biopolymer based solid electrolyte system consisting of surfactant-modified zeolite A are fabricated via simple solvent-casting technique to yield thin film proton exchange membrane. The zeolite LTA (Linde type-A) is synthesized and then it is impregnated with a surfactant, sodium dodecyl sulfate. The interfacial compatibility as well as the strong interaction in the polymer-filler system, modification of zeolite-A as well as its elemental composition is confirmed using FTIR, XRD and SEM-EDAX analysis. The physicochemical characteristics of the prepared membranes such as water uptake, IEC, hydration number and dimensional stability found to increase with increasing concentrations of the doped zeolitic filler. The appreciable mechanical as well as oxidative stability displayed by the membranes is due to the strong H-bond interaction between the polymer and modified zeolite. Overall, CSA-1.0 composite membrane showed the highest proton conductivity of 4.45 mS cm−1 at 80 °C, good thermal stability with Tmax = 217 °C and lesser gas permeability around 5 barrer. By determining the bound water content of the membranes using TGA analysis, the self-humidification characteristics were investigated. Good compatibility and interfacial interaction in the composite membranes has resulted in the creation of non-tortuous pathways for efficient proton transfer predominantly through Grotthus type mechanism. The relevant mechanism for the proton transfer along the membranes is evaluated in terms of complex impedance analysis, dielectric permittivity and electric modulus spectra. On the whole, the results obtained from various analysis suggests that the fabricated composite membranes are good alternatives as proton exchange membranes for fuel cell applications.