Electrical Conductivity Relaxation Research Articles

Enhanced Electrocatalytic Activity of SrFe0.9Nb0.1O3-δ through In-situ Synthesis of Sr3Fe1.8Nb0.2O7-δ Coating

The influence of the heterogeneous interface is critical for the catalytic activity of the oxygen reduction reaction (ORR). This study demonstrates an enhancement of the electrocatalytic activity of the SrFe0.9Nb0.1O3-δ (SFN113) electrode through the construction of a SrFe0.9Nb0.1O3-δ-Sr3Fe1.8Nb0.2O7-δ (SFN113-SFN327) heterogeneous interface. By coating varying amounts of Sr(NO3)2 (0.1g, 0.2g and 0.3g) on SFN113 (1g), SFN113/327 composite electrodes with different amounts of triple conducting oxide SFN327 are in-situ synthesized by high temperature calcination. Electrical Conductivity Relaxation (ECR) tests show that SFN327 has superior oxygen surface exchange performance compared to SFN113, especially at lower temperatures. At 550 °C, the oxygen surface exchange parameter of SFN327 is 4.23 times higher than that of SFN113. Symmetric cell tests with SFN113/327||BaCe0.7Zr0.1Y0.1Yb0.1O3-δ (BCZYYb)||SFN113/327 configuration and single cell tests with Ni-BCZYYb||BCZYYb||SFN113/327 configuration indicate that the SFN113/327 composite electrode with a mass ratio of 1:0.2 displays the best electrocatalytic performance, achieving a power output of 502 mW cm-2 at 700 °C. The work not only in-situ synthesizes the SFN113/327 triple conducting composite electrode, but also introduces a novel method for developing proton conducting electrode materials.

Effect of hetero-valence ions on structural and electrical properties of La2Ni(Mn0.5Ti0.5)O6 ceramics

The study of powder X-ray diffraction of La2Ni(Mn0.5Ti0.5)O6 (0.5LNMT) confirms a multi-phasic composition. The monoclinic P21/n phase content dominates. Occurrence of minor rhombohedral R3‾c phase and precipitates of MnO2 and La2MnO4 were detected. The morphology was analyzed using a SEM test and ceramics showed a porous structure and variation in the grain size below 4 μm. Dielectric permittivity of marked magnitude varies from ∼30 to ∼100 000 when temperature increases. Dielectric loss coefficient frequency dependence exhibits well-defined dielectric relaxation peaks, which were found to obey the Arrhenius law with the activation energy of 0.29 eV, below the presumed phase transition. Two sets of relaxation peaks in the imaginary part of electric modulus spectra relate to relaxations of different activation energies of 0.28 eV and 0.38 eV. An optical gap magnitude of 0.8 eV was determined from the diffuse reflectance spectrum in the Vis-NIR range. It compares with the band gap estimated from the X-ray photoelectron spectroscopy test. We also compare the influence of doping ions on the crystal lattice of the surface and the bulk ceramics. Electrical conductivity relaxation processes were attributed to the electron hopping mechanism between multi-valence Mnk+ and Nin+ ions’ states, which were determined from XPS analysis. The dc resistivity shows thermally generated dependence. Activation energy Edc magnitude varies between 0.27 and 0.37 eV which indicates the occurrence of defects and structural disorder. Such disorder correlates to the variable range hopping of small polarons involved in electrical conductivity. The density of states near Fermi energy was estimated N(EF) = 2.1 × 1025 eV−1 m−3. The 0.5LNMT application prospects were discussed.

Comprehensive understanding of charge and mass transport in BaZr0.1Ce0.7Y0.1Yb0.1O3−δ

This work reports transport properties of BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb1711), studied during oxidation/reduction and hydration/dehydration using electrical conductivity relaxation (ECR) measurements. The oxidation/reduction displayed typical monotonic conductivity relaxation behavior, attributed to the ambipolar diffusion of oxygen vacancies (Vo∙∙) and electron-holes (h∙), and oxygen surface exchange coefficient (k) were >1 order of magnitude higher than bulk diffusivities (D˜), indicating a diffusion-controlled process. Whereas, hydration/dehydration displayed a temperature-dependent gradual transition from monotonic to non-monotonic relaxation profile. At lower temperatures, transient defect concentration profile indicated that overall hydration/dehydration involved an acid-base-type reaction, comprising the diffusion of oxygen vacancy (Vo∙∙) and proton (Hi∙) couples. However, at higher temperatures and high [h∙], it involved a combination of a hydrogenation reaction (comprising component H via diffusion of h∙ and Hi∙ couple) and an oxidation reaction (involving component O via diffusion of h∙ and Vo∙∙ couple), thus giving rise to a two-fold non-monotonic relaxation profile. The k and D˜ values for oxygen vacancies (kVO∙∙; DVO∙∙) were lower than those for protons (kHi∙;DHi∙) with the respective Ea being 57.51 ± 3.14 and 60.72 ± 1.48 kJ∙mol−1 for oxygen-vacancies and 68.78 ± 12.65 and 71.05 ± 13.87 kJ∙mol−1 for protons.

Tuning the electrical conductivity and Maxwell-Wagner relaxation in BiFeO3–BaTiO3 piezoceramics

Recent research has emphasized the investigation of BiFeO3–BaTiO3 (BFO–BT) piezoelectric ceramics due to their elevated Curie temperature. Nevertheless, the substantial electrical conductivity of these ceramics poses practical challenges. This study evaluates the influence of post-annealing and manganese (Mn) doping on the conductivity, dielectric behavior, and ferroelectric properties of BFO–BT ceramics with a morphotropic phase boundary composition (x=0.33). The results demonstrate that the conductivity of the ceramics in the as-sintered state is affected by Maxwell-Wagner effects arising from variations in conductivity at grain boundaries. Annealing under specific atmospheres indicates that the electrical conductivity is of the p-type, potentially associated with Fe4+ defects. Furthermore, annealing in a carefully controlled atmosphere or the introduction of Mn doping significantly alleviate these effects, leading to an enhancement in domain switching characteristics. The insights garnered from this investigation regarding annealing and doping have the potential to advance lead-free BFO–BT piezoelectric ceramics.

Accelerating bulk proton transfer in Sr2Fe1.5Mo0.5O6-δ perovskite oxide for efficient oxygen electrode in protonic ceramic electrolysis cells

Protonic ceramic electrolysis cells (PCECs) have attracted significant attention as a promising technology for green hydrogen production and conversion. However, traditional PCECs oxygen electrodes exhibit poor electrochemical performance because of their limited hydration ability and lack of intrinsic protonic conductivity. In this study, a W-doped perovskite oxide, Sr2Fe1.5Mo0.4W0.1O6-δ (SFMW), with a strong hydration capacity and an accelerated proton mobility, was designed to serve as the oxygen electrode in PCECs. The results indicate that W doping enhances the concentration of oxygen vacancies in Sr2Fe1.5Mo0.5O6-δ (SFM) and facilitates the adsorption of H2O onto the oxygen electrode, thereby significantly accelerating proton mobility. The bulk diffusion coefficient of protons (DH) in SFMW, estimated through electrical conductivity relaxation measurement, can reach up to 2.86 × 10−5 cm∙s−1 at 750 °C, which is significantly higher than that of SFM (7.96 × 10−6 cm∙s−1). Consequently, SFMW exhibited impressive electrochemical performance, as evidenced by its lower polarization resistance (0.072 Ω⋅cm2, 700 °C in air) and higher current density (945 mA/cm2 with a voltage of 1.3 V at 650 °C) in PCECs. These results suggest that accelerating bulk proton transfer by W doping is highly feasible and holds great potential for the development of oxygen electrodes for high-activity PCECs.

An active bifunctional Pd-doped double perovskite air electrode for reversible protonic ceramic electrochemical cells

Reversible protonic ceramic electrochemical cells (R-PCECs) have a good application prospect as the energy conversion and storage devices. The electrode surface kinetics (i.e., oxygen reduction reaction (ORR) and water oxidation reaction (WOR)) are major technical obstacles to developing the R-PCECs. Here, we report a phase-pure Pd-doped double perovskite with a PrBa0.8Ca0.2Co1.95Pd0.05O5+δ (PBCCPd) formula. The PBCCPd air electrode displays a polarization resistance (Rp) of 0.056 Ω cm2 in the BZCYYb-based symmetrical cell at 700 °C, and also performs a peak power density (PPD) of 2.08 W cm−2 using the fuel cell mode, and a current density of -4.42 A cm−2 at 1.3 V using the electrolysis cell mode at 700 °C. Moreover, R-PCECs with PBCCPd air electrodes show excellent stability in fuel and electrolysis cells, and cycling modes with reasonable Faradaic efficiency. It is shown that Pd doping can effectively increase the oxygen vacancy, improve the oxygen surface exchange, bulk diffusion capabilities, and electrocatalytic activity and stability in the air electrode of R-RCECs, indicated by the X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectra (EIS), electrical conductivity relaxation (ECR), and distribution of relaxation time (DRT).

Cross-Validation of the Remarkably High Surface Oxygen Exchange Kinetics of PrBa0.5Sr0.5Co1.5Fe0.5O5+δ: A Combined Thin-Film Mass Relaxation and Bulk Electrical Conductivity Relaxation Study.

In this work, we measure the oxygen kinetic properties of double perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF), a material widely used as the air electrode in solid oxide electrochemical cells, by mass relaxation (MR) and electrical conductivity relaxation (ECR) experiments. MR studies are carried out using thin films deposited on a gallium phosphate piezocrystal microbalance, and ECR studies are performed using a bulk bar sample with 97% theoretical density. Measurements are performed at 600 °C over the temperature oxygen partial pressure range from 10-4 to 0.21 atm. Despite the differences in experimental formats and surface microstructural features, the ks values extracted from the two methods are found to be in good agreement with one another. The rate constant is found to increase with oxygen partial pressure with a power law dependence, rising from 1.0 × 10-6 cm/s at 3.2 × 10-4 atm to 1.2 × 10-4 cm/s at 0.24 atm, as averaged over the oxidation and reduction directions. The rates in the oxidation direction are observed to be slightly higher than those in the reduction direction for a given pair of pO2 values, suggesting that the final pO2 value controls the overall relaxation behavior. The power law exponent describing the dependence of ks on pO2 is found to be 0.74 ± 0.01. The ECR study of the bulk sample reveals that even with a diffusion length of 1.8 mm, the relaxation process is largely free of diffusion limitations, indicating that PBSCF has the high bulk transport properties required for a double-phase boundary oxidation/reduction pathway.

Modulating Lattice Oxygen Activity of Iron-Based Triple-Conducting Nanoheterostructure Air Electrode via Sc-Substitution Strategy for Protonic Ceramic Cells.

Iron-based perovskite air electrodes for protonic ceramic cells (PCCs) offer broad application prospects owing to their reasonable thermomechanical compatibility and steam tolerance. However, their insufficient electrocatalytic activity has considerably limited further development. Herein, oxygen-vacancy-rich BaFe0.6 Ce0.2 Sc0.2 O3-δ (BFCS) perovskite is rationally designed by a facile Sc-substitution strategy for BaFe0.6 Ce0.4 O3-δ (BFC) as efficient and stable air electrode for PCCs. The BFCS electrode with an optimized Fe 3d-eg orbital occupancy and more oxygen vacancies exhibits a polarization resistance of ≈ 0.175Ωcm2 at 600°C, ≈ 1/3 of the BFC electrode (≈0.64Ωcm2 ). Simultaneously, BFCS shows favorable proton uptake with a low proton defect formation enthalpy (- 81kJmol-1 ). By combining soft X-ray absorption spectroscopy and electrical conductivity relaxation studies, it is revealed that the enhancement of Fe4+ -O2- interactions in BFCS promotes the activation and mobility of lattice oxygen, triggering the activity of BFCS in both oxygen reduction and evolution reactions (ORR/OER). The single cell achieves encouraging output performance in both fuel cell (1.55 Wcm-2 ) and electrolysis cell (-2.96Acm-2 at 1.3V) modes at 700°C. These results highlight the importance of activating lattice oxygen in air electrodes of PCCs.

Engineered nanocomposites through embedding of smaller “organic inorganic” nanoparticles in thermoplastic Poly(2-Vinylpyridine) polymer matrix

Polymer nanocomposites (PNCs) are significant for modern and future applications owing to their multifunctionality promoted by morphology and tailored interfaces between the constituents. However, ‘forward’ engineered polymer (host) composites with smaller size nanoparticles (guest) providing desired properties remains challenging as they depend upon nanoparticles aggregation, size, shape, and loading (volume or weight) fraction. This study strategically designs and develops PNCs comprising thermoplastic poly (2-vinylpyridine) (P2VP) polymer matrix impregnated with spherical polyhedral oligomeric silsesquioxane (N-POSS) nanoparticles (diameter ∼2–5 nm) and anisotropic planar nitrogenated graphene nanoribbons (GNR, strip width ∼5–10 nm) commensurate with polymer chain radius of gyration, Rg, (or segment length ∼1.5 nm) and comparable energy scales of electrostatic interaction and attractive hydrogen bonding. We investigated static and dynamic structure and thermophysical properties to correlate with interfacial regions and the results are compared with larger graphene oxide (GO, lateral dimension ∼100–200 nm) nanosheets and silica (SiO2, ∼25–50 nm) particles. While electron microscopy revealed nanoparticle distribution, the lattice bonding, conjugation length, and mechanical properties are determined from micro-Raman spectroscopy and atomic force microscopy, respectively. The differential scanning calorimetry provided a measure of glass transition temperature, Tg, with positive shift of ∼10–18 °C with nanoparticles loading indicating strength of structural relaxation/chain rigidity behavior and thermogravimetric analysis displayed increased thermal stability and conductivity (decreased interfacial resistance). We also measured temperature dependent dc electrical conductivity and dielectric relaxation spectroscopy gaining insights into percolation and dynamic interfacial layer. This study signified understanding of interactions and interfacial regions, key element to demystify the microscopic structure-property relationships.

Electromagnetic and microwave absorption properties of flexible fabric coatings containing Ag decorated spherical graphene powders with FSS incorporation

Flexible textile microwave absorbing materials own the advantages of flexibility, foldability and cuttability, have become a research hotspot in electromagnetic stealth technology. In this study, a microwave absorbing coating was prepared on a fabric substrate using Ag decorated spherical graphene (SG) as the absorbent. XRD results demonstrated the metallic Ag ion was successfully reduced. TEM photographs showed the silver nanoparticles were stuck to the spherical graphene. The complex permittivity was enhanced after compositing with Ag particles. Along with the increase of silver content from 0 to 20 wt%, the complex permittivity rises from 3.29–0.42j to 6.93–2.22j owing to its higher electric conductivity and stronger relaxation effect. Meanwhile, the flexible coating containing Ag decorated spherical graphene (Ag@SG) also exhibited better microwave absorption performance. The minimum reflection loss (RLmin) for the coating with a thickness of 3.0 mm was −15 dB. And the effectively absorbing broadband (EAB) is located at 9.08–11.52 GHz. In addition, the microwave absorbing performance was greatly enhanced after being combined with periodic frequency selective surface (FSS). The EAB was obtained over the entire X-band frequency range, and the RLmin value achieved −41.72 dB at 10.25 GHz. What's more, the coating owned an EAB in a wide range incident angle of 60°–90°. This work was help to developing high performance flexible fabric coating containing Ag decorated spherical graphene with FSS incorporation.

Contribution of numerical modelling to design oxygen electrode for micro-solid oxide cells: A case study of high-performance nano-columnar La2NiO4 thin films

This article presents a numerical study that aims to guide the development of nano-columnar La2NiO4 thin films as high performing oxygen electrodes for micro-Solid Oxide Cell (μSOC). La2NiO4 thin films were deposited by Pulsed Injection Metal Organic Chemical Vapor Deposition (PI-MOCVD) and their performance is characterized by Electrochemical Impedance Spectroscopy (EIS) and Electrical Conductivity Relaxation (ECR). Excellent performance is obtained for 1 μm thick film with an Area Specific Resistance (ASR) of 0.12 Ω cm2 at 600 °C, making them suitable for low-temperature μSOCs. A Finite Element Method (FEM) model has been implemented and used to predict the ASR and impedance spectra in order to guide further optimization of the film thickness and morphology. After experimental validation of the model using various electrode thicknesses, the optimal value is estimated to be between 3 and 4 μm for the temperature range of 450–650 °C. For each temperature and thickness, the model can clearly predict whether the electrode is limited by the surface exchange reactions or the bulk diffusion. The simulations revealed that the gas diffusion process is not rate-limiting when the electrode thickness is below 5 μm and the temperature is below 650 °C. Furthermore, a geometrical parameters analysis study allowed to determine the ideal nano-columnar morphology for this promising electrode composition.

(Invited) Proton Surface Exchange Kinetics and Stability of Thin-Film Triple Conducting Oxides for Protonic Ceramic Electrolysis Cells

Protonic ceramic electrolysis cells (PCECs) have been attracting attention due to their ability to operate in the intermediate temperature (300 - 500 ˚C) sweet-spot. These temperatures enable fast kinetics, inexpensive materials (no precious metals; stainless interconnects), and lower operating voltage for producing green hydrogen, without the accelerated degradation that may be observed at higher temperatures. The steam electrodes often support triple conduction and thereby host the proton exchange / oxygen evolution process at the surface, where steam is split. Steam electrode materials development is at a relatively early stage, with open questions around the relationships among bulk composition, evolving surface chemistry, kinetic quantities, and degradation mechanisms. We are investigating the proton exchange surface coefficient (k) and its evolution over time on model thin film electrodes in order to ultimately develop highly active and long-term stable steam electrodes for PCECs.ABO3 perovskites with Ba on the A-site and nominally multivalent ions on the B-site are candidates for steam electrodes given the varied compositions in this class that can transport oxide ions, protons, and electronic species, and the lowering of hydration enthalpies by the basicity introduced by Ba. However, very few measurements of k exist for these materials, and the evolution of surface chemistry and thus k is poorly understood.In this work, we fabricated and compared two perovskite triple conducting oxides by growing geometrically well-defined films of Ba(Pr,Y)O3-x (BPY) and Ba(Co,Fe,Zr,Y)O3-x (BCFZY) with pulsed laser deposition. We examined the proton surface exchange coefficients (k-values) using simultaneous in-situ optical transmission relaxation and electrical conductivity relaxation measurements upon switching pH2O at a temperature of 400 ˚C, and continued these switches as a function of time to assess stability. To our knowledge, this is the first use of an optical transmission method to probe elevated temperature steam splitting kinetics, and we interpret the optical (and electrical) changes as indicative of redox during the hydrogenation process. The k-values of BPY thin films were approximately ten times higher than those of the BCFZY thin films, and BPY also retained higher k-values over time. The bulk and surface chemical compositions of BPY and BCFZY thin films before and after relaxation measurements were compared using Rutherford backscattering spectrometry, angle-resolved X-ray photoelectron spectroscopy, and scanning transmission electron microscopy with spectroscopy. Pronounced Ba enrichment and Si contamination (from the quartz tube) were evident at the surface of BPY by both S/TEM-EDS and XPS, whereas for BCFZY these surface chemical features were only detectable by XPS and absent in S/TEM-EDS. Implications for materials design of steam electrodes will be discussed, considering efficiency and lifetime.

A way to limit the long-term degradation of solid oxide fuel cell cathode by decorating the surface with K2NiF4-Structure Pr4Ni3O10+δ phase

Prolonged annealing of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) at 700 °C for 1000 h resulted in phase segregation on the surface in the form of submicron-sized SrO on the grains and micron-sized CoFe2O4 particles near the grain boundaries during electrical conductivity relaxation (ECR) measurements. The presence of segregated particles results in a substantial decrease in the surface exchange coefficient, kchem. To mitigate this issue, the LSCF electrodes underwent a systematic coating process with the K2NiF4-structure Pr4Ni3O10+δ (PNO), while varying the loading content, thickness, and porosity. This is achieved by adjusting the gap between the nozzle exit and LSCF surface, ranging from 2 cm to 9 cm, coupled with the application of ultrasonic vibration of the nozzle chamber operating between 40 kHz and 180 kHz. Optimal surface coverage with a loading content of 0.28 mg cm−2 referred to as PNO5 results in a significant increase in kchem by up to one and a half order of magnitude compared to bare LSCF. The PNO coating effectively suppresses phase segregation during prolonged exposure, resulting in a substantial decrease in degradation. The improved performance is attributed to the optimal surface coverage of coated particulates, which enhances the active sites for oxygen reduction reaction (ORR) and the triple phase boundary (TPB) area. These exceptional characteristics position PNO coated LSCF as a highly promising cathode option for low temperature solid oxide fuel cells (SOFCs).

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.

Label-free multimodal electro-thermo-mechanical (ETM) phenotyping as a novel biomarker to differentiate between normal, benign, and cancerous breast biopsy tissues.

Technologies for quick and label-free diagnosis of malignancies from breast tissues have the potential to be a significant adjunct to routine diagnostics. The biophysical phenotypes of breast tissues, such as its electrical, thermal, and mechanical properties (ETM), have the potential to serve as novel markers to differentiate between normal, benign, and malignant tissue. We report a system-of-biochips (SoB) integrated into a semi-automated mechatronic system that can characterize breast biopsy tissues using electro-thermo-mechanical sensing. The SoB, fabricated on silicon using microfabrication techniques, can measure the electrical impedance (Z), thermal conductivity (K), mechanical stiffness (k), and viscoelastic stress relaxation (%R) of the samples. The key sensing elements of the biochips include interdigitated electrodes, resistance temperature detectors, microheaters, and a micromachined diaphragm with piezoresistive bridges. Multi-modal ETM measurements performed on formalin-fixed tumour and adjacent normal breast biopsy samples from N = 14 subjects were able to differentiate between invasive ductal carcinoma (malignant), fibroadenoma (benign), and adjacent normal (healthy) tissues with a root mean square error of 0.2419 using a Gaussian process classifier. Carcinoma tissues were observed to have the highest mean impedance (110018.8 ± 20293.8 Ω) and stiffness (0.076 ± 0.009 kNm-1) and the lowest thermal conductivity (0.189 ± 0.019 Wm-1K-1) amongst the three groups, while the fibroadenoma samples had the highest percentage relaxation in normalized load (47.8 ± 5.12%). The work presents a novel strategy to characterize the multi-modal biophysical phenotype of breast biopsy tissues to aid in cancer diagnosis from small-sized tumour samples. The methodology envisions to supplement the existing technology gap in the analysis of breast tissue samples in the pathology laboratories to aid the diagnostic workflow.

Achieving Fast Oxygen Reduction on Oxide Electrodes by Creating 3D Multiscale Micro-Nano Structures for Low-Temperature Solid Oxide Fuel Cells.

Fast oxygen reduction reaction (ORR) at the cathode is a key requirement for the realization of low-temperature solid oxide fuel cells (SOFCs). While the design of three-dimensional (3D) structures has emerged as a new and promising approach to improving the electrochemical performance of SOFC cathodes, achieving versatile structures and structural stability is still challenging. In this study, we demonstrate a novel architectural design for a superior cathode with fast ORR activity. By employing a completely new fabrication process comprising a 3D printing technique and pulsed laser deposition (PLD), we design 3D La0.8Sr0.2CoO3-δ (LSC) micro-nano structures with the desired shape. 3D-printed yttria-stabilized ZrO2 (YSZ) microstructures significantly increase the ratio of surface area to volume while maintaining suitable ionic conductivity comparable to that of single-crystalline YSZ substrates. Scanning electron microscopy and energy dispersive X-ray microanalysis reveal the formation of crack- or void-free YSZ microstructures and the uniform deposition of LSC films by PLD on the YSZ microstructures. The 3D LSC micro-nano structures show significantly enhanced oxygen surface exchange coefficients (kchem) extracted from electrical conductivity relaxation (ECR) measurements by up to 3 orders of magnitude relative to the bulk LSC. Furthermore, electrochemical impedance spectroscopy measurements verify the kchem values from ECR and no directional difference in the measured ORR activity depending on the shape of 3D microstructures. The dramatic enhancement of the ORR activity of LSC is attributed to the increased film surface areas resulting from the 3D YSZ microstructures.

Effective dielectric attenuation for excellent microwave absorption with broadband response of carbon hollow microspheres derived from resin

Carbon hollow microspheres as microwave absorption materials (MAMs) are of great significance in the research focuses owing to their lightweight, good impedance matching, and modifiable dielectric properties. However, it is still a huge challenge to distinguish the contribution of dielectric attenuation between carbon intrinsic feature and hollow structure due to the lack of appropriate model materials. Then, the inadequate analysis of effective dielectric attenuation resulted in the construction of carbon hollow microspheres semiempirical and often lacked precise modification of microstructure. Herein, a series of carbon hollow microspheres with controllable graphitization and thickness of shell derived from phenolic resin coated on polystyrene microspheres that fully decomposed were synthesized, which is free of the impact of template residue. The carbon fragments ground from hollow microspheres exhibit the same broadband response as hollow microspheres, with effective bandwidth (RL ≤ –10 dB) of 7.6 GHz, while their electromagnetic wave loss mechanisms are distinct. The high dielectric loss of carbon fragments with the same intrinsic characteristics as carbon hollow microspheres is mainly caused by dipole polarization relaxation and enhancement of electrical conductivity ascribed to overlapping between carbon sheets. For the hollow structure, in addition to dipole polarization relaxation attributed to carbon intrinsic feature, the effective dielectric loss is also comprised of the interfacial polarization in advantage due to the effective heterogeneous interface between air and carbon shell. This work provides a simplified model to clarify the effect of carbon intrinsic feature and microstructure on the dielectric loss of carbon hollow microspheres.

Enhancing oxygen exchange kinetics of solid oxide fuel cell cathode: Unleashing the potential of higher order Ruddlesden-Popper phase surface modification

Tailoring the electrode surface represents a promising strategy to enhance electrochemical performance while preserving base material integrity. Achieving appropriate surface coverage with catalytic active oxide material is critical for efficient oxygen transport at the triple phase boundary (TPB). To further explore this approach, the perovskite structure La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) is decorated with a higher order Ruddlesden-Popper phase Pr4Ni3O10+δ (PNO). This combination is being investigated using electrical conductivity relaxation (ECR) technique to study the oxygen exchange kinetics. Samples with varying surface coverage of PNO are examined in a temperature range of 650 °C–850 °C, with a step change in pO2 between 0.1 atm and 0.21 atm. The chemical diffusion coefficient, Dchem, remains invariant across all the samples, however, the surface exchange coefficient, kchem, varies with the surface coverage of PNO. Notably, the coated sample with a PNO loading content of 0.28 mg cm−2, referred to as PNO5, demonstrates a significant enhancement of nearly two orders of magnitude in kchem compared to bare LSCF at 650 °C. This substantial improvement is ascribed to the increased active sites of ORR within the TPB region and the facilitated electron access through tunneling from LSCF to the coated phase. Pulse isotopic exchange (PIE) measurements on the fractionated powders confirm the fast surface exchange kinetics of PNO. Such remarkable oxygen exchange characteristics encourage the use of PNO, along with LSCF, as potential candidates for SOFC cathodes.

Delving into the properties of nanostructured Mg ferrite and PEG composites: A comparative study on structure, electrical conductivity, and dielectric relaxation

Magnesium ferrite (MgFe2O4) and polyethylene glycol (PEG) are materials known for their versatility in various applications. This study presents a comprehensive comparative analysis of the electrical conductivity and dielectric relaxation of nanostructured MgFe2O4 and its composites with PEG. Through experimentation, it was observed that incorporating PEG into MgFe2O4 did not lead to a high relative observed decrease or increase in electrical conductivity at room temperature. The study revealed that the composites maintained stable electrical behavior at room temperature, with a dielectric constant value of around 9 and a loss tangent value of around 0.1 at high frequency (around 7 MHz). The electron-hole hopping mechanism was identified as the underlying cause for the strong dielectric dispersion with frequency. The low dielectric loss and conductivity of the MgFe2O4 and PEG/ferrite composites make them promising candidates for high-frequency switching applications and microelectronic devices, particularly in scenarios where negligible eddy currents are essential. Additionally, complex impedance data analysis demonstrated that the capacitive and resistive properties of the composites are primarily attributed to grain boundary processes. This study provides a comprehensive analysis of the electrical and dielectric properties of MgFe2O4 and PEG composites and highlights their potential for many applications in materials science, particularly in electrical and electronic devices.

BaCo0.4Fe0.4Zr0.1Y0.1O3-Σ Cathode Performance for Proton Conducting Solid Oxide Fuel Cells with BaZr0.8-XCexY0.1Yb0.1O3-Δ Electrolytes

BaCo0.4Fe0.4Zr0.1Y0.1O3-σ (BCFZY) is a proton, oxygen-ion, and electron-hole triple conducting cathode material for solid oxide fuel cells. Its electrode reaction mechanism including the rate-limiting step in air with moisture are not well understood. Therefore, we fabricated three types of symmetric cells with the same BCFZY cathode over three related proton conducting electrolytes: BaZr0.8-xCexY0.1Yb0.1O3-δ (x = 0.1, 0.4, and 0.7; Fig.1 are SEM images showing the surface of three different electrolytes). The cathode shows different electrochemical behaviors for the three electrochemical cells including the response to the introduction of moisture. The differences are hypothesized to relate to mutual diffusion at the cathode/electrolyte interface, which are tested by various techniques such as XRD Rietveld refinement of BCFZY cathode in mixtures with different electrolytes after firing, thermogravimetric analysis (TGA) for oxygen vacancy concentration and hydration behavior, electrical conductivity relaxation (ECR) for conductivity changes between dry and moist atmosphere, and energy-dispersive X-ray spectroscopy (EDS) line scanning for element concentration distribution at the cathode/electrolyte interface.Fig1. SEM images of electrolytes (a) BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (Ce-rich), (b) BaZr0.4Ce0.4Y0.1Yb0.1O3-δ (ZrCe-bal) and (c) BaZr0.7Ce0.1Y0.1Yb0.1O3-δ (Zr-rich) Figure 1