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The depiction of nanocatalysts for water splitting, which can easily be workable in polluted water that could address the issues of freshwater and energy scarcity. The development of a stable and cost-effective catalytic system that involves alloying of precious and non-precious metals may be an efficient approach to achieve the above goal. Herein, we report a three-dimensional carbon-based tri-metallic system as a multifunctional electrocatalyst having superior catalytic activity towards water splitting and degradation of organic contaminants present in sewage. Catalytic activity towards the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is enhanced in analogous to other state-of-art catalysts. The density functional theory (DFT) strategies are applied to find the reason behind the superior activity of the designed catalyst toward wastewater electrocatalysis. Furthermore, this work provides a new approach towards the improvement of multifunctional electrocatalysts with broad potential for efficient and effective electrochemical energy storage and conversion.

We report on Ba1-xNdxFeO3-δ, a cobalt-free perovskite material, with a view to its use as a next-generation air electrode material in reversible solid oxide cells (RSOCs). BaFeO3-δ (BFO) has long been considered a potential candidate cathode material due to its high oxygen vacancy concentration and electrical conductivity; however, it is difficult to synthesize in a single phase. To overcome this problem, Nd3+ is doped into Ba-sites to reduce impurity phases and create a single perovskite phase. In-situ high temperature and room temperature X-ray diffraction analyses are carried out to investigate Nd3+-doped BFO. We find that Ba0.97Nd0.03FeO3-δ shows the highest electronic conductivity and lowest TEC value among the various doping concentrations tested, making this material most suitable for application in RSOCs. In addition, the polarization resistance of Ba0.97Nd0.03FeO3-δ has the lowest value in yttria-stabilized zirconia symmetric cells. To determine the reasons for the high catalytic activity of Ba0.97Nd0.03FeO3-δ, X-ray photoelectron spectroscopy and iodometric titration are carried out, the results demonstrate that the lower doping concentration of Nd3+ results in an advantage in terms of the number of additional oxygen vacancies created. Moreover, electrical conductivity relaxation measurements show that the Ba0.97Nd0.03FeO3-δ has a fast bulk diffusion coefficient and fast surface exchange coefficient. Hence, the solid oxide fuel cell and electrolysis mode performances when using Ba0.97Nd0.03FeO3-δ are excellent and a high power output of 1.2 W cm−2 at 800 °C can be achieved.

Here we report synthesis of undoped/doped cerium(IV) pyrophosphate compounds by a new solution phase method employing cerium(III) nitrate as metal precursor and H2O2 as oxidizing agent. The phase composition and microstructure of various samples is studied and the importance of various reactants and processing conditions in obtaining cerium(IV) pyrophosphates is analyzed. The phase development in material is studied by thermogravimetric analysis/differential thermal analysis (TGA/DTA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD), and the microstructures of powders and sintered specimen are analyzed by scanning electron microscopy (SEM) and high resolution-transmission electron microscopy (HR-TEM). XRD shows that crystalline CeP2O7 phase is obtained only when precipitation is performed at pH

A mixed-potential based sensor utilizing transition metal oxide (Ni, Co, Fe)-tin oxide nanocomposite sensing electrodes are fabricated for the first time and investigated for the gas sensing performance towards the highly toxic nitrogen dioxide. The nanocomposites are synthesized by solvo-combustion route and characterized for the physical, gas sensing and electrochemical properties in a temperature range of 600–700 ℃. The sensor equipped with Fe2O3-SnO2 (Fe:Sn = 2:1) nanocomposite sensing electrodes sintered at 1000 ℃ shows the maximum response of 60 mV towards 100 ppm NO2 with a relatively fast response and recovery dynamics at an operating temperature of 650 ℃. The sensor also shows a linear dependence of response over the logarithm of NO2 concentration with a sensitivity of ∼44 mV/decade. Additionally, the oxygen concentration dependence, cyclability and cross-sensitivity towards interfering gases are also investigated. Finally, the sensing mechanism and electrochemical activity of the sensing electrodes are studied using polarization curve measurement and electrochemical impedance spectroscopy.

The Influence of sintering temperature on the physical, electrochemical and sensing properties of α-Fe2O3-SnO2 nanocomposite sensing electrode for a mixed-potential type NOx sensor is investigated. The α-Fe2O3-SnO2 nanocomposite was synthesized by a solution combustion route and sintered at temperatures 900, 1000, 1100 and 1200 °C to form the sensing electrodes of a stabilized-zirconia based mixed-potential type NOx sensor. The influence of sintering temperatures on the physical properties was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N2 adsorption-desorption isotherm measurements. The gas sensing measurements were conducted at an operating temperature of 650 °C. A systematic increase in the response/recovery times was observed with an increase in the sintering temperature from 900 to 1200 °C. An optimum microstructure with a low surface area and large pore size leading to high electrochemical reactions at the interface and low heterogenous gas-phase decomposition of NO2 resulted in the maximum response magnitude (ΔV) and sensitivity for the electrode sintered at 1000 °C. Furthermore, the effect of sintering temperature on the electrochemical activity of the sensing electrode and its co-relation with the sensing properties was studied by dc polarization curve measurement. Moreover, the microstructure, sensing response, sensitivity, dynamics and O2 conc. dependence of the presented mixed-potential type NOx sensor is critically dependent upon the sintering temperature of the sensing electrodes.

Gas sensing characteristics of rare-earth-based orthoferrite (GdFeO3) mesoporous nanostructures were prepared by a facile one-step hydrothermal process. The structural analyses of the obtained materials showed sphere, leaf and flower-like nanostructured architectures. Further, the chemiresistive gas-response properties of the GdFeO3 nanostructure were investigated with various combustible gases, such as nitric oxide (NO), nitrogen dioxide (NO2), carbon monoxide (CO), ammonia (NH3), hydrogen sulfide (H2S), formaldehyde (HCHO), ethanol (C2H5OH) and gasoline, at different operating temperatures. The sphere-like GdFeO3 nanostructure shows a significantly high resistance variation to NO compared with the other architectures, exhibits a high response (91%) when exposed to 100 ppm NO, and detects a level as low as 2 ppm (7%) at an optimum operating temperature of 140 °C. The GdFeO3 nanostructure shows an excellent stability and repeatability after successive repeated cycles with a fast response and recovery time when exposed to 100 ppm NO gas. The superior response and excellent selectivity of the perovskite GdFeO3 nanostructure are due to its higher catalytic activity, large surface area, oxygen deficiency, mesoporosity, and peculiar morphology. The response mechanism of NO on the GdFeO3 nanostructured surface is also discussed in detail.

In this work, polybenzimidazole based composite membranes are fabricated using polybenzimidazole, Ce0.9Gd0.1P2O7 and graphite oxide by solution casting procedure. The microstructural, mechanical and electrical properties of the phosphoric acid-doped composite membranes are characterized for fuel cell applications. Addition of graphite oxide in the composite leads to improvement in homogeneous dispersion of higher amount, 31 wt%, of Ce0.9Gd0.1P2O7. With the increasing amount of Ce0.9Gd0.1P2O7 in the composite membranes the amount of phosphoric acid loading decreases, but the proton conductivity of the composite membrane is higher than that is reported for the phosphoric acid-doped polybenzimidazole membranes. At 180 °C, a maximum conductivity of 182 mS cm−1 for polybenzimidazole/Ce0.9Gd0.1P2O7 membrane with 24 wt% Ce0.9Gd0.1P2O7 and 199 mS cm−1 for polybenzimidazole/Ce0.9Gd0.1P2O7/graphite oxide membrane with 31 wt% Ce0.9Gd0.1P2O7 is observed. The H2-Air fuel cells operating at 160 °C with ∼250 μm thick polybenzimidazole/Ce0.9Gd0.1P2O7 electrolyte shows open circuit voltage of 0.938 V and maximum power density of 255 mW cm−2 with 640 mA cm−2 current at 160 °C whereas the corresponding values with ∼200 μm thick polybenzimidazole/Ce0.9Gd0.1P2O7/graphite oxide membrane are 0.976 V and 307 mW cm−2 with 800 mA cm−2 current, respectively. However, irrespective of the increased conductivity at the higher temperatures, the maximum power density decreases with increasing temperature >160 °C.

In this work, maximum power density as the function of electrolyte thickness of a solid oxide fuel cell (SOFC) with Ce0.9Gd0.1O2-δ (GDC10) electrolyte was calculated by integrating partial conductivities of charge carriers under various DC bias conditions at a fixed oxygen chemical potential gradient at both sides of the electrolyte. Partial conductivities as a function of temperature and oxygen partial pressure (PO2) were calculated using Hebb-Wagner polarization method and spatial distribution of PO2 across the electrolyte was calculated based on Choudhury and Patterson's model [1] by considering reversible electrode conditions. At terminal voltages corresponding to SOFC and electrolysis cell operation modes, the oxygen chemical potential gradient at a electronic-stoichiometric point became maximum and minimum to compensate the contribution from electrochemical potential gradient of electron. The current-voltage characteristics in different fuel cell conditions with temperature and thickness dependence were calculated with cathodic and anodic PO2 of 0.21 and 10−22 atm, respectively. The theoretical maximum power density increased from 1.26 W·cm−2 at 500 °C to 7.39 W·cm−2 at 700 °C. Similarly, at 500 °C, power density increased two fold on reducing electrolyte thickness from 20 μm to 10 μm. The implications of these results on the development of GDC10 based SOFC systems was discussed.

We have designed the solid-state electrochemical mixed potential type NiO and yttrium-stabilized zirconia (YSZ) composite based sensing electrode for selective detection of NOx at elevated temperatures. The planner NiO-YSZ composite sensing electrode could detect NOx even at 400 °C, with acceptable response/recovery rates. The change in emf values of the sensor varied linearly with NOx concentrations on a logarithmic scale in the range of 5–100 ppm. The response characteristic of the sensor was improved by modifying the surface with different vol% of pore former. As a result, obtained porous electrodes showed better response characteristics concerning speed and response owing to higher porosity. To improve response kinetics of porous NiO-YSZ electrode, NiO nanoparticles are infiltrated into an optimized NiO-YSZ sensing electrode surface by controlled urea/cation infiltration method. The experimental results demonstrated that NiO nanoparticles infiltrated NiO-YSZ sensor electrode reveal remarkably high emf response to NOx compared that of planar electrode, suggesting that NiO nanoparticles introduction can significantly enhance catalytic activity and electrochemical performance of NiO-YSZ electrode. Finally, the porosity effect of electrode subtracts (YSZ) with NOx gases response and recovery kinetics was examined under the optimum operating temperature at 400 °C. The sensing mechanism based on the mixed potential for the surface modified NiO-YSZ composite sensing electrode was discussed based on the obtained result of sensing characterizations.

In the present work, we report a method of fabrication of dense 10 mol% Mg 2+ -doped cerium pyrophosphate-phosphate (Ce 0.9 Mg 0.1 P 2 O 7 -P m O n ; CMP-P) composites by microwave heat-treatment of the preformed Ce 0.9 Mg 0.1 P 2 O 7 substrates in the presence of phosphoric acid. The composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The microwave heating at 375 °C for 5 min resulted in the formation of dense CMP-P composites which retained most of the pyrophosphate phase. The electrical conductivity was extracted from the EIS data and for the CMP-P composite prepared by H 3 PO 4 loading for 10 h and microwave heat-treatment for 5 min it was found to be >10 −2 S m −1 in 100–250 °C range with a maximum of 0.062 S cm −1 at 190 °C, which was significant for its application as electrolyte in intermediate temperature fuel cells.

The sluggish kinetics of oxygen electrode reactions represent one of the most significant barriers to realizing effective reversible protonic ceramic cells (RPCCs) at intermediate temperatures. Maximization of oxygen ion and proton conduction characteristics through hydration of electron-conducting solid oxides is a key technology that can solve this issue. We report on the exceptional performance at the oxygen electrode in RPCCs achieved using a highly defective material with excessive oxygen nonstoichiometry, Nd1.5Ba1.5CoFeMnO9−δ (NBCFM). Use of this material enables a superior reaction rate and conductivity during oxygen electrode reactions, maximizing the concentration of protons (with a high degree of hydration) as a guest ion as well as intrinsic oxygen vacancies. The peak power densities of this NBCFM cell are quite high, and a 1.4 V electrolyzing potential is achieved by NBCFM at −2.34 A‧cm−2 at 600 °C. Furthermore, these NBCFM cells are stable under prolonged (960 h) continuous operation at 600 °C.

Fully stabilized zirconia containing 8 mol% of yttria was synthesized by solid state reaction method and deposited as a thick film by plasma spray coating. The crystal structure and phases developed were characterized by X-ray diffraction (XRD). The surface structure, surface morphology and microstructure developed were studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The actual doping content was measured by electron probe micro-analyzer ( EPMA ). The plasma sprayed YSZ was characterized for its electrolytic properties by ac and dc conductivity measurements. The maximum conductivity for plasma sprayed YSZ was found to be −1.62 Scm −1 , which was lesser than the conductivity of standard 8YSZ of −1.03 Scm −1 at pO 2 =0.21 atm. However; conductivity trends in the arrhenius plot was observed to be similar for entire YSZ's, suggesting that the conductivity mechanism is same and dominated by oxygen ion conductivity independent of oxygen partial pressure. These promising electrolytic properties of thermal sprayed YSZ suggest that the thermal spray coating method may lead to be used as a potential method for the fabrication of NOx sensor.

Here we present a report on synthesis and characterization of tetravalent metal pyrophosphate (TMP) and alkali carbonate (A2CO3; A = Li and/or Na) composites. The TMP-carbonate composites are prepared by mixing indium-doped tin pyrophosphate or yttrium-doped zirconium pyrophosphate with Li2CO3 or an eutectic mixture of Li2CO3-Na2CO3 in different wt.% ratios. The phase composition, microstructure and electrical conductivity of the sintered specimen are analyzed. In addition, the effect of different TMP and A2CO3 phases is investigated. A maximum ionic conductivity of 5.5 × 10−2 S cm−1 at 630 °C is observed in this study with a Sn0.9In0.1P2O7-Li2CO3 composite. Based on the literature data, TMP-carbonate composites can be considered to be primarily a proton and oxygen-ion co-ionic conductor and, therefore, have strong potential as electrolytes in fuel cells in 500–700 °C range.

A Pd-YSZ cermet membrane that performs coupled operations of hydrogen separation from a mixed-gas stream and simultaneous hydrogen production by non-galvanic water-splitting, and have high sulfur tolerance is fabricated. It is proved that in H 2 S containing atmosphere the Pd-YSZ membrane has self-repairing capability, originating mainly from the conversion of Pd 4 S back to metallic Pd and SO 2 by ambipolar-diffused oxygen obtained from water-splitting. The performance of membrane was analyzed at different temperatures in high H 2 S containing (0–4000 ppm H 2 S) mixed gas feed during the operation as a hydrogen separation membrane as well as during the coupled operation of hydrogen separation and hydrogen production. At 900 °C with the feed-stream having ≥2000 ppm H 2 S, the hydrogen flux was severely affected due to the formation of some liquid phase of Pd 4 S, resulting in the segregation of hydrogen permeating Pd-phase at the membrane surface. But at 800 °C, though the membrane was affected by the Pd 4 S formation in high H 2 S environment (up to 1200 ppm H 2 S), its self-repairing capability and additional hydrogen production by water-splitting is capable of maintaining the hydrogen flux around ~1.24 cm 3 (STP)/min.cm 2 , a value expected by the same membrane while performing only the hydrogen separation function in H 2 S-free environment.

Co-ionic (H + /O 2− ) electrolytes are fabricated by compositing both proton conductor (BaZr 0.85 Y 0.15 O 3-δ , BZY) and oxygen-ion conductor (Nd 0.1 Ce 0.9 O 2−δ , NDC) for intermediate temperature-solid oxide fuel cells (IT-SOFCs). This hybrid electrolyte decreases the electronic loss of NDC under reducing atmospheres and improves the poor sinterability of BZY. The electronic conduction caused by the NDC reduction is effectively blocked by the BZY in the composite electrolyte, thus offering both advantages of BZY with its high OCV and more rigid electro-chemo-mechanical property. In addition, the composite BZY-NDC electrolyte also exhibits great chemical stability against exposure to steam and CO 2 . Furthermore, the compositing of BZY and NDC improves the proton conductivity of the electrolytes, and the conductivity of composite electrolyte is higher than that of single BZY at temperatures >600 °C.

We report solutions (durable material and degradation prevention method) to minimize the performance degradation of cell components occurring in the solid oxide fuel cell (SOFC) operation. Reliability testing is carried out with the Ni Nd0.1Ce0.9O2-δ (NDC) anode-supported intermediate temperature-SOFCs. For the cathode materials, single perovskite structured Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) and double perovskite structured NdBa0.5Sr0.5Co1.5Fe0.5O5+δ (NBSCF) are prepared and evaluated under harsh SOFC operating conditions. The double perovskite NBSCF cathode shows excellent stability in harsh SOFC environments of high humidity and low flow rate of air. Furthermore, we propose the concurrent fuel and air starvation mode, in which the cell potential is temporarily reduced due to the formation of both fuel-starvation (in the anode) and air-depletion (in the cathode) concurrently under a constant load. This is carried out in order to minimize the performance decay of the stable NBSCF-cell through the periodic and extra reduction of a H 2 O (and a O 2 ) in the anode. The operating-induced degradation of SOFCs, which are ordinarily assumed to be unrecoverable, can be completely circumvented by the proposed periodical operation logic to prevent performance degradation (concurrent fuel-starvation and air-depletion mode).

The exhaust monitoring for in-situ quantification of gas pollutants has always been a challenge due to the harsh thermo-chemical environments, for which the solid-electrolyte based gas sensors appear as a realistic solution. In this work, an ultrahigh-sensitive mixed-potential ammonia sensor was developed using a new dual-functional NiWO4 electrocatalyst, synthesized through a low-temperature molten-salt synthesis route. The electrode morphology and diffusion lengths were tuned for optimum performance. The sensor operated at 550 ℃ displayed response of −100 mV to 80 ppm NH3, with response/recovery times of 28/68 s and a record-high sensitivity of 90 mV/decade. Besides, it displayed excellent selectivity and trace-level NH3 detection ability upto 400 ppb. While examining the sensing mechanism, the sensor exhibited an NH3 concentration-dependent transformation of rate-determining kinetics from charge-transfer limited Butler-Volmer type to diffusional mass-transport limited reaction kinetics. Moreover, the remarkable long-term stability with negligible response degradation (

Urea infiltration is the most extensively and ubiquitous method for depositing the multi-cation oxide catalyst layer on the electrode backbone in the SOFC area. The stoichiometry and composition are the two vital parameters for deposited multi-cation oxide nanocatalyst layer on which the catalytic activity and selectivity depend. However, the understanding behind the mechanism of multi-cation oxide nanocatalyst by urea infiltration is still missing, which restricts the reproducibility of this infiltration approach. The infiltration technique of Sm0.5Sr0.5CoO3-δ (SSC) nanoparticle by urea method is highly irreproducible due to the intermediate phase’s formation. This may result from the varying cation stoichiometry being formed along with the final product, and it is assumed to arise mainly due to the difference in precipitation tendency of cations present in the urea precursor solution. We investigate the influence of variation in the urea concentration effect on the stoichiometry of SSC nanoparticles. The difference in several parameters, such as electronegativity, ionic potential, cationic charge, and hydroxylation tendency, brings a competitive reaction within the three cations inside the urea infiltrated precursor solution. Thus, a different instrumental analysis was used to interpret the internal composition and heterostructure of the SSC nanoparticles. By applying, transmission electron microscopy with X-ray powder diffraction, the crystal structure of synthesized SSC nanoparticle was confirmed with the appropriate stoichiometry, and a comprehensive understanding of the mechanism was done for further improving the present urea syntheses protocol with proper reproducibility.

Because of a high global energy demand and challenging sustainability requirements, hydrogen has been promoted as a clean and green energy carrier allowing the potential replacement of nonrenewable fossil fuels. Hydrogen is a renewable energy carrier that does not contribute to CO2 emissions, and it holds the highest gravimetric energy density. It can be produced by the electrochemical splitting of water into hydrogen and oxygen molecules. Herein, we investigate the bifunctional activity of bimetallic oxide, sulfide, and selenide nanostructures in water electrolysis. Spinel-type, phase-pure NiCo2O4, NiCo2S4, and NiCo2Se4 with comparable morphological properties were synthesized by a hydrothermal method. The electrocatalytic characterization of NiCo2Se4 was found to demonstrate higher oxygen and hydrogen evolution reaction activities (245 mV and 122 mV @ 10 mA cm−2, respectively) compared to those of NiCo2O4 and NiCo2S4. Furthermore, a lab-scale water-splitting system was fabricated to examine the bifunctional properties of bimetallic nanostructures. A NiCo2Se4-based water-splitting system was found to require a cell voltage of 1.58 V, which is lower than that required by NiCo2S4 (1.64 V)- and NiCo2O4 (1.75 V)-based systems. In summary, this study explores bimetallic NiCo2Se4 as an efficient electroactive material that can be employed in various electrochemical energy systems.

AlN ceramics have been prepared with CeO 2 as a sintering aid at a sintering temperature of 1900 °C. The effect of CeO 2 contents on the microstructure, density, thermal conductivity and hardness was investigated. Addition of CeO 2 exerted a significant effect on the densification of AlN ceramics and hence on the microstructure. Thermal conductivity of AlN ceramics increased with CeO 2 content and was greater than that of Y 2 O 3 -doped AlN ceramics at a similar sintering temperature. The resulting AlN ceramics with 1.50 wt% of CeO 2 had the highest relative density of 99.94%, thermal conductivity of 156 W m −1 K −1 and hardness of 72.46 kg/mm 2 .

In this work, Sr2 + and Y3 + co-doped BaCeO3-based perovskite Ba0.9Sr0.1Ce0.85Y0.15O3 − δ (BSCY) was synthesized by solid-state reaction method, and its mass transport behavior was studied using electrical conductivity relaxation (ECR) measurements in 600–800 °C range with respect to variations in oxygen partial pressure (pO2) and water vapor pressure (pH2O). During oxidation/reduction process, the electrical conductivity showed a monotonic relaxation behavior and in − 2.65 ≤ log(pO2/atm) ≤ − 0.67 range the values of oxygen chemical diffusivity ( D ˜ vO ) and surface exchange coefficient (κvO) varied in 10− 6–10− 4 cm2 ⋅ s− 1 and 10− 4–10− 2 cm ⋅ s− 1 range, respectively. However, during hydration/dehydration process, the electrical conductivity showed a non-monotonic twofold relaxation behavior, and hydrogen, and oxygen chemical diffusivities ( D ˜ iH ) and ( D ˜ vH ) values were in 10− 5–10− 3 and 10− 6–10− 4 cm2 ⋅ s− 1 range, respectively, whereas hydrogen and oxygen surface exchange coefficient (κiH) and (κvH) values were in 10− 3–10− 2 and ~ 10− 4–10− 2 cm ⋅ s− 1 range, respectively. The comparison of H and O diffusivities of BSCY with BaCe0.85Y0.15O3 − δ (BCY) showed that during hydration/dehydration the diffusivities of BSCY were lower than that of BCY. The long-term electrical conductivity measurement for ~ 800 h in humidified conditions showed a gradual decrease, which might be due to the gradual appearance of rhombohedral phase in otherwise orthorhombic BSCY, as confirmed by the X-ray diffraction (XRD) measurements.

In the present research, Proton conducting Ceramic electrolyte Fuel Cell (PCFC) has been fabricated with BaZr 0.4 Ce 0.45 Y 0.15 O 3− δ electrolyte, NiO–BaZr 0.4 Ce 0.45 Y 0.15 O 3 − δ as anode and Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3 − δ as a cathode material. The effects of anodic and cathodic gas flow rates and partial pressures on PCFC performance are studied by varying the gas flow rates between 50 and 200 sccm while partial pressures between 0.25 and 1 atm at one electrode by keeping constant gas flow rate and partial pressure at another electrode. The different electrode processes occurring at the electrodes and electrode/electrolyte interfaces are analyzed by electrochemical impedance spectroscopy. It is observed that gas flow rate doesn’t affect more on the fuel cell performance while increase in gas partial pressure changes the performance of PCFC. The variation in cathodic p O 2 shows that the oxygen dissociation and charge transfer at cathode electrode are the major contributors toward overall electrode polarization resistance. A peak power density of ~0.80 W/cm −2 is achieved at 700 °C with 200 sccm of wet H 2 and air. The stability of the PCFC is also studied under CO 2 condition and it has shown stable performance without any degradation.

The poor sintering-ability of tetravalent metal pyrophosphates MP2O7 (M=Sn, Zr, Ce) has restricted their application as electrolyte in proton-conducting ceramic-electrolyte fuel cells (PCFCs). In this work, the effect of doping of MnO on the sinterability and ionic conductivity of MP2O7 is analyzed. MnO-doped MP2O7 is synthesized via a solid state reaction method. The phase composition and microstructure of MnO-doped MP2O7 are studied with X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the ionic conductivity of the sintered sample is measured by electrochemical impedance spectroscopy (EIS). It is observed that, compared to the undoped sintered samples, the porosity of the MnO-doped sintered samples is greatly decreased and the ionic conductivity is significantly improved.

Decreasing the operating temperature leads to an issue of high polarization that results in slow electrode kinetics. Infiltration of multi-cation oxide nanoparticle catalyst layer over the cathode backbone can provide low activation energy in catalyzing several electrochemical processes. The adoption of cetrimonium bromide(CTAB)-amino acid (glycine) route can become an efficient route to infiltrate particle with proper stoichiometry due to three-dimensional network forming nature owing to the zwitterionic form of the amino acid. Herein, we report a novel route for the development of discrete Sm0.5Sr0.5CoO3-δ(SSC) nanoparticles on the cathode backbone. In particular, the full cell shows enhancement in electrochemical property with a power density of 1.57 W cm−2 at 700 °C and 100 h durability test under 1 A cm−2. These observations indicate that the selection of the CTAB-amino acid route for the infiltration process of SSC nanoparticle on the surface La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF6428) backbone is a significant step towards electrochemically viable SOFC performance improvement.

A mixed-potential type NH3 sensor equipped with CuFe2O4 and SnO2@CuFe2O4 sensing electrode is presented. The CuFe2O4 spinel-oxide and SnO2@CuFe2O4 composites were synthesized by a modified-Pechini route. The electrode materials were characterized for the physical properties by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) and Energy dispersive spectroscopy (EDS) analysis. It was found that the sensing characteristics were critically dependent on the extent of Triple-phase boundary (TPB) lengths and operating conditions of the sensor. Furthermore, the sensing performance of CuFe2O4 spinel-oxide was enhanced by compositing with SnO2 nanocrystals resulting in a synergistically enhanced response (ΔV) of −40 mV towards 80 ppm NH3, almost double and quadruple of the response of bare CuFe2O4 and SnO2 electrodes at 650 ℃, respectively. The sensor also displayed excellent stability towards oxygen and humidity variations, along with low cross-sensitivities towards interfering gases; e.g. NO, CO, CH4, and NO2. The complex impedance spectra (EIS) and dc polarization (I–V) measurements were performed for an insightful analysis of the sensing mechanism conforming to the mixed-potential model.

Despite several disadvantages with the electronic conduction of ceria, researchers report the high performance of ceria-based solid oxide fuel cells (SOFCs) at intermediate temperatures with advanced cathode materials. However, it appears the long-term stability of ceria-based SOFCs in the anode-supported cell configuration have still not been proved experimentally at practical operating conditions. In particular, the chemical expansion of ceria electrolytes can cause potentially irreversible failure of SOFCs under large P O 2 gradients. Hence, we investigate the degradation behavior of NiO-Nd0.1Ce0.9O2-δ anode-supported cells with Nd0.1Ce0.9O2-δ electrolyte in dynamic electrical modes, load trip (0.7–0 A cm−2), load cycle (0.2–0.12 A cm−2), and constant load operation (0.2 A cm−2), at 650 °C. We identify the specific degradation phenomenon of ceria-based cells by analyzing the electrochemical characteristics in post-mortem investigations after durability testing under various electrical load conditions. Additionally, we suggest a possible operation strategy to mitigate the performance degradation of cells under various electrical stresses through understanding of the main degradation mechanism.

In order to comprehend the enhancement mechanism of oxygen permeability by surface coating in the zirconia-based dual-phase membrane, it is necessary to comprehend surface exchange reactions in coated-membrane. Surface exchange reactions significantly contribute to oxygen permeability in a thin membrane with a thickness lower than characteristic thickness; thus, it is extremely important to define the correlation of surface exchange kinetics between the membrane and coating material. The permeation fluxes of zirconia-rich composite membrane [70 vol% Zr0.79Sc0.2Ce0.01O2-δ (ScSZ): 30 vol% La0.7Sr0.3MnO3±δ (LSM), LSM30] in the thickness range of 40–340 μm have been investigated as a function of oxygen partial pressure on the feed and permeate sides to elucidate the enhancement in the permeation flux by a Nd2NiO4+δ (NNO)-coating layer. The oxygen permeation resistances were estimated from oxygen fluxes as a function of P O 2 through the oxygen permeation model. The surface exchange ( k ' and k ' ' ) and diffusion ( D ) coefficients are obtained from the resistances. The diffusion coefficient of the coated membrane is similar to that of ScSZ, which corresponds to the main element of the membrane as the ionic conductor. Additionally, the surface exchange coefficient of the coated membrane is similar to that of NNO as the coating material. The surface exchange reaction on the feed side is faster than that on the permeate side under the operating condition. In order to ensure a more detailed elucidation, the k values obtained from the permeation model are compared with those obtained from the electrical conductivity relaxation method and characteristic length (LC). Despite differences in the experimental conditions such as morphologies, the surface exchange coefficients exhibited similar values and trend in the temperature range of 750–900 °C, irrespective of the experimental method.

We studied the energetically-favorable distribution of oxygen vacancies and metal atoms in perovskite BaCexZr1−xY0.15O2.925 solid solution structures using a genetic algorithm and lattice statics. The solid solution structures were made by mixing Ce, Zr, and Y at site B and removing O at site O in ABO3. Because of the huge number of configurational solid solution structures in the 3 × 3 × 3 ABO3 supercell, we employed a genetic algorithm and lattice statics to help identify energetically-favorable solid solution structures. Oxygen vacancies in the solid solution structures preferred Zr when the Ce composition was small, and the preference changed to Y with an increase in the Ce composition.

In this study, we report the effects of various ceramic processing methods with different sintering aids on the relative density, crystallinity, microstructure, and electrical conductivity of proton conducting BaZr0.85Y0.15O3−δ (BZY) pellets in details. First, the BZY ceramic pellets are fabricated by the solid-state reactive sintering by adding diverse sintering aids including CuO, NiO, ZnO, SnO, MgO, and Al2O3. Among these, CuO is found to be the most effective sintering aid in terms of the sintering temperature and total conductivity. However, transition metals as sintering aids have detrimental effects on the electrical conductivity of the BZY electrolytes. Second, the BZY electrolytes have been synthesized by four different methods: the solid-state, combustion, hydrothermal, and polymer gelation methods. The BZY pellets synthesized by the polymer gelation method exhibit dense microstructure with a high relative density of 95.3%. Moreover, the electrical conductivity of the BZY pellets synthesized by the polymer gelation method is higher than those prepared by the solid-state methods under the same test conditions: 1.28 × 10−2 S cm−1 (by the polymer gelation method) vs. 0.53 × 10−2 S cm−1 by the solid-state method at 600 °C in wet 5% H2 in Ar.

The oxygen permeation performance of a number of La 0.1 Sr 0.9 Co 0.8 Fe 0.2 O 3− δ (LSCF1982)-based membranes, consisting of dense LSCF1982 layer with/without porous LSCF1982 layer, was analyzed on the basis of the thickness of the dense layer and catalytic effect of the porous layer. A 0.27 mm thick dense membrane gives oxygen permeation flux ( J O 2 ) of 2.33 sccm min −1 cm −2 at 900 °C, which is increased to 3.55 sccm min −1 cm −2 on applying a porous layer of LSCF1982 onto the dense membrane. The membrane gives a stable flux for 300 h. The flux was further improved by reducing the thickness of the dense LSCF1982 layer and at 950 °C a flux of 4.47 sccm min −1 cm −2 is obtained with 0.012 mm thick membrane.

The delamination of oxygen electrode during the electrolysis mode operation, which is mainly attributed to interfacial stress arising from the inability of oxygen electrode to accommodate oxygen species transported by oxide ion conducting electrolyte at the three phase boundary (TPB), has been major concern in the development of reversible solid oxide cell (RSOC) systems. The use of lanthanum nickelate, La2NiO4+δ (LNO) as a RSOC oxygen electrode, because of its ability to accommodate excess oxygen species in interstitial positions, can be helpful in reliving such interfacial stresses and thus mitigating the problem of delamination. In this work, the possibility of using LNO as an oxygen electrode in RSOCs is examined. The button cells with 10% gadolinium doped ceria (GDC10) electrolyte, Ni-GDC10 fuel electrode and LNO oxygen electrode are fabricated and their current–voltage–power (I–V–P) performance is analyzed in different gas conditions while operating in fuel cell mode in 500–650 °C range. The button cell shows a maximum power density of ~0.19 W cm−2 at a current density of ~0.5 A cm−2 at 650 °C. Electrochemical impedance spectroscopy was performed in open circuit voltage (OCV) condition to analyze the various factors affecting the fuel cell performance. The long term operation of the fuel cell at a fixed input current of 0.1 A cm−2 for 100 h at 600 °C indicates that the fuel cell is capable of stable performance. The microstructural analysis of the fuel cell after the long term operations indicates no structural degradation.

Dense Gd3+-doped cerium pyrophosphate–phosphate (CGP–P) composites are prepared by infiltrating H3PO4 into partially sintered CGP substrates and then heat-treating at 375–400 °C. The phase composition and microstructure of CGP–P composites are studied by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM), which shows that the H3PO4 reacts with CGP to form phosphate phases in the pores and results in a dense CGP–P composite. The ionic conductivity of CGP–P composite is studied by electrochemical impedance spectroscopy (EIS) in dry and humid atmosphere in 90–230 °C range for its application as electrolyte in proton-conducting ceramic-electrolyte fuel cells (PCFCs). It is observed that the ionic conductivity of the composite GCP–P-1h/375, formed by 1 h acid-treatment followed by heat-treatment at 375 °C, is 2.73×10−6 S cm−1 at 230 °C in unhumidified air but in humidified air (water vapor pressure, pH2O=0.12 atm) it shows a maximum of 0.051 S cm−1 at 170 °C, which is significant for its application as electrolyte in PCFCs.

Unlike other tetravalent metal pyrophosphates, cerium pyrophosphates have shown significant sinterability even at temperatures 1 order of magnitude higher conductivity than that of SnP2O7. The present method of improving the sinterability and ionic conductivity of metal pyrophosphate by partial replacement of tetravalent metal ion by Ce4+ions has potential to be extended to other metal pyrophosphates such as ZrP2O7 and TiP2O7.

This study focuses on mechanisms and symptoms of several simulated failure modes, which may have significant influences on the long-term durability and operational stability of intermediate temperature-solid oxide fuel cells (IT-SOFCs), including fuel/oxidation starvation by breakdown of fuel/air supply components and wet and dry cycling atmospheres. Anode-supported IT-SOFCs consisting of a Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF)-Nd 0.1 Ce 0.9 O 2-δ (NDC) composite cathode with an NDC electrolyte on a Ni-NDC anode substrate are fabricated via dry-pressings followed by the co-firing method. Comprehensive and systematic research based on the failure mode and effect analysis (FMEA) of anode-supported IT-SOFCs is conducted using various electrochemical and physiochemical analysis techniques to extend our understanding of the major mechanisms of performance deterioration under SOFC operating conditions. The fuel-starvation condition in the fuel-pump failure mode causes irreversible mechanical degradation of the electrolyte and cathode interface by the dimensional expansion of the anode support due to the oxidation of Ni metal to NiO. In contrast, the BSCF cathode shows poor stability under wet and dry cycling modes of cathode air due to the strong electroactivity of SrO with H 2 O. On the other hand, the air-depletion phenomena under air-pump failure mode results in the recovery of cell performance during the long-term operation without the visible microstructural transformation through the reduction of anode overvoltage.

The ionic charge of transport ( α i ⁎ ) and partial electronic conductivity under an ion-blocking condition ( σ ′ e ), and chemical diffusivity of oxygen ( D ˜ ) of La 2 NiO 4+ δ (LNO) is measured as a function of oxygen partial pressure ( p O 2 ) at 1000 °C. The defect diffusivity of interstitial oxygen ( D i ) and oxygen self-diffusivity ( D O ) are calculated from the data of D ˜ . The values of Onsager transport coefficients are extracted from the blocking cell data by constructing an Onsager matrix. Various results are compared with the data in literature, which show close agreement.

Perovskite-type oxide BaCe0.65Zr0.2Y0.15O3−δ (BCZY2015) was synthesized by a solid state reaction method. BCZY2015 samples were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The time dependent variation in electrical conductivity of BCZY2015 was monitored during the oxidation/reduction in oxygen partial pressure (pO2) range of −2.28 ⩽ log (pO2/atm) ⩽ −0.68 at a fixed water vapor pressure (pH2O), and during the hydration/dehydration in −3.15 ⩽ log (pH2O/atm) ⩽ −2.35 range in air. The electrical conductivity showed a monotonic relaxation behavior by the ambipolar diffusion of V o and OH o during the oxidation/reduction and the relaxation process was governed by the diffusivity of oxygen ( D vO ). On the other hand, during the hydration/dehydration process, a non-monotonic twofold relaxation behavior was observed due to the decoupled diffusion of H and O components with the mediation of holes, and the conductivity relaxation process was governed by the diffusivities of both H ( D iH ) and O ( D vH ). The values of surface exchange coefficients and diffusivities of oxygen and hydrogen were calculated from Fick’s second law by the nonlinear least squares fitting of the conductivity data, as proposed by Yoo et al. (2008).

Mn2+-doped Sn1−xMnxP2O7 (x = 0–0.2) are synthesized by a new co-precipitation method using tin(II)oxalate as tin(IV) precursor, which gives pure tin pyrophosphate at 300 °C, as all the reaction by-products are vaporizable at 10−3 S cm−1 in 100–200 °C range. The maximum conductivity is shown by Sn0.88Mn0.12P2O7 with 9.79 × 10−6 S cm−1 at 550 °C in ambient air and 2.29 × 10−3 S cm−1 at 190 °C in humidified air. It is observed that the humidification of Sn1−xMnxP2O7 samples is a slow process and its rate increases at higher temperature. The stability of Sn1−xMnxP2O7 samples is analyzed.

In this work, mass and charge transport properties of acceptor doped lanthanum nickelate, La2Ni0.95Al0.05O4.025+δ (LNAO), were analyzed. The thermal expansion, electrical conductivity and thermoelectric power of LNAO were measured as a function of temperature in 25–1000 °C range and oxygen partial pressure (pO2) in −14 ⩽ log (pO2/atm) ⩽ −1 range. The average thermal expansion coefficient was 13.77 × 10−6 K−1. The electrical conductivity was analyzed in relation to the thermoelectric power to elucidate the positive deviation of the activity coefficient of hole on the basis of the delocalized electron model. The thermoelectric power measurement shows a p-type to n-type transition. The chemical diffusion coefficient ( D chem ) and surface exchange coefficient (ksurf.) were calculated by 4-probe DC conductivity measurement and ksurf. was slightly higher than ( D chem ). The best-estimated hole-mobility values showed very weak temperature dependence. The results were compared with the literature results on La2NiO4+δ.

This paper explores the potential to design a “superprotonic conductor” for operation in the intermediate temperature (IT) range through a doping approach with a conventional proton conductor. This approach is validated scientifically, based on the enhanced macroscopic transport properties of the oxide ion conductor. This system consists of a BaZr0.8Y0.2O3−δ (BZY) proton conductor and a small amount of palladium oxide (PdO). The influence of the PdO on the sinter activity of the highly refractory BZY material is not significant, with low rates of grain growth under typical sintering conditions, even though the addition of some PdO favors the grain growth of BZY materials to some extent. The conductivity of PdO-modified BZY (BZPY) is higher than that of BZY in the IT range, in all atmospheres and at all temperatures. The conductivity of 3 mol.% PdO-modified BZPY was 8.60 × 10−3 S cm−1 at 600 °C in wet 5% H2. The electrical conductivity of BZPY increases systematically with increasing PdO content (0.5–3 mol.%) in all atmospheres investigated.

The high catalytic properties of LSCF1982 arise from its defect structure. In this work, the oxygen nonstoichiometry (δ) of LSCF1982 was analyzed as a function of oxygen partial pressure ( P O 2 ) and temperature for the - 6 ⩽ log ( P O 2 / atm ) ⩽ 0 and 800 ⩽ T/°C ⩽ 1000 ranges. A defect structure model for LSCF1982 was presented, which fitted well with the experimental data for δ. The equilibrium constants of appropriate defect reactions were determined. Analysis of the defect structure of LSCF1982 suggested that the conduction mechanism of LSCF1982 is governed by hopping conduction and band conduction of p-type carriers, which was determined by the analysis of thermoelectric power. The characteristic membrane thickness (Lc), indicating the transition from predominantly bulk-diffusion controlled reaction to surface-exchange controlled reaction, had a value of 3.5 ± 0.9 × 10−2 cm. The oxygen vacancy diffusivity was calculated from the relationship between oxygen flux and oxygen chemical potential gradient. The chemical expansion was measured as a function of P O 2 and temperature in the 10 - 3 ⩽ P O 2 / atm ⩽ 0.21 and 800 ⩽ T/°C ⩽ 1000 ranges. The chemical expansion model based on the relative change in mean ionic radius was employed to compute the chemical expansion vs. δ, which indicated that the spin states of B-site transition metal ions are a mixture of high-spin and low-spin states, and made the transition from the low-spin to the high-spin state with an increase in δ and temperature.

Two-phase composite materials consisting of a BZY matrix phase and a binary eutectic carbonate (Li–0.5Na) 2 CO 3 phase are designed in order to promote the densification and ionic conductivity of BaZr 0.85 Y 0.15 O 3 − δ (BZY) proton conductors at intermediate temperature. In the presence of carbonate phase, a considerable change in microstructure for the densification of BZY electrolytes sintered at 670 °C for 4 h is clearly visible in SEM analysis. This sintering effect is due to the formation of molten phase associated with carbonates at low temperature (495 °C) by TG–DTA analysis. The conductivity of composite electrolytes is significantly higher than that of BZY over the entire temperature and atmosphere range studied by AC impedance and DC four-probe methods. In addition, the change of the carbonate content in the composite electrolyte presents a great influence on the conductivity. The composite containing 25 wt.% (Li–0.5Na) 2 CO 3 shows the highest ionic conductivity of 0.176 S cm −1 at 550 °C and lowest activation energy of 0.127 eV in the temperature range of 500–650 °C.