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Schematics of water-mediated ex-solution and accordingly nano-engineered protonic ceramic fuel cell furnished with the water-mediated ex-solution on a cathode and H2 ex-solution on an anode.

Hyperstoichiometric (p-type) misfit-layered calcium cobaltites have been studied as components in various high-temperature electrochemical devices. Multiple studies have reported their applications or physical properties, but systematic studies on their defect structures and thermodynamic quantities are still insufficient. In this study, the oxygen nonstoichiometry and the electrical conductivity of Gd-Cu co-doped misfit cobalt oxide were measured as functions of temperature and oxygen partial pressure, along with thermodynamic quantities. The behavior of oxygen nonstoichiometry could not be explained by a defect structure assuming the ideal solution, as it showed a positive deviation in Raoult's law. The redesigned nonideal proposed defect structure, considering that the deviation originated from the high concentration of degenerate holes, could describe the oxygen nonstoichiometry precisely; and in this process, the values of ,

With the ever-growing demand for clean and viable energy sources, the possibility and need to use a multifunctional energy system having integrated energy storage and conversion capacity has been intensified in current times. To fulfill this requirement, a search for an active material having an efficient bifunctional capacity of both hydrogen evolution reaction (HER) and supercapacitor is an essential requirement. The metal polyphosphate with the advantage of abundance, environmental friendliness, low cost, and reliable activity make it an emerging class of novel material for the present research. Herein, for the first time, the comparison of the amorphous and crystalline form of tin polyphosphate-based electrode was assessed toward hydrogen evolution reaction and supercapacitor. Considering the synergistic influence of abundant tin polyphosphate and the three-dimension structure of nickel substrate, we unswervingly deposited well-defined hierarchical in-situ amorphous SnPxOy and ex-situ crystalline SnPxOy over Ni foam using the one-step hydrothermal route. Impressively, amorphous SnPxOy/NF electrode required less over the potential of the only 100 mV with Tafel slope of 50 mV dec−1 to attain a current density of 10 mA cm−2 in comparison to crystalline SnPxOy/NF electrode showing over the potential of the only 170 mV with Tafel slope of 80 mV dec−1 to attain the same current density in 1 M KOH. Additionally, we investigated this electrode in a supercapacitor and found that amorphous SnPxOy/NF delivers a good specific capacitance of 580 F g−1 at a current density of 1 A g−1, greater rate capability, and cyclic stability. Hopefully, this study may demonstrate a promising technique for the preparation of ample, low-cost electrodes for future applications in both HER and supercapacitors applications.

The impact of different parameters on the chemical degradation of the Nafion polymer electrolyte membrane was investigated in detail under different concentrations of Fenton solution. As a consequence of chemical degradation, the performance and durability of the perfluorosulfonic acid-based electrolyte membrane in fuel cells was studied. Quantitative estimation of fluoride emitted after chemical degradation of the electrolyte membrane is done by an ex-situ fluoride emission rate-test using a potentiometric with an ion-selective electrode. The concentration of fluoride ions is easily affected by several external factors, such as total ionic strength, pH, temperature, and stirring speed, which causes many errors while reporting the fluoride concentration. Furthermore, the micromorphology of recast Nafion membranes before and after FER rest was thoroughly examined by scanning electron microscope (SEM) and X-ray photoelectric spectroscopy. Here, we report the influence of several external parameters over total fluoride concentration during the estimation of fluoride concentration for the proper correlation of the rate of chemical degradation in polymer electrolytes. This systematic study is beneficial for removing errors while measuring fluoride concentration and removing the discrepancy present in FER results reported in the literature.

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.

Despite the recent substantial progress in reversible protonic ceramic cells (RPCCs) it remains essential to further develop oxygen electrode materials that show superior activity and stability for oxygen reduction and evolution reactions due to the intrinsically sluggish kinetics of oxygen electrode reactions at lower temperature (

The present investigation deals with the optimization of the concentration of lattice cerium(III) and oxygen vacancy concentration, over the surface of CeO2−δ nanoparticles by varying the processing parameters. The higher value was found to be in good agreement with the smaller grain size and transformation of tetravalent lattice cerium . This transformation explains the crucial mechanism behind the excellent scavenging behavior of CeO2−δ nanoparticles, towards degradation mitigation in the polymer electrolyte membrane (PEM). The overall degradation rate was suppressed 4.2 and 2.7 times after incorporation of CeO2−δ (100 °C, 24 hours) nanoparticles annealed in the hydrogen and oxygen atmosphere, respectively. It was estimated that the intrinsic lattice strain effect on the curved surface of nanoparticles could affect their surficial reactions. The presence of a high oxygen vacancy concentration inducing higher generation has a crucial effect on the exceptional durability of the hybrid CeO2−δ integrated Nafion film.

In this work, the effect of nanocatalyst infiltration on the SOFC performance and electrode reaction characteristics was comprehensively investigated by the application of electrochemical impedance (EI) spectroscopy. The Ni-8 mol% yttria-stabilized zirconia (YSZ) anode-supported cell was fabricated using a YSZ electrolyte, and a mixed ionic electronic conductor (MIEC) La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF6428) cathode. The EI spectra were measured under various conditions (0.02 ≤ pO2,cat./atm ≤ 1; 0.2 ≤ pH2Oano./atm ≤ 0.6) in the temperature range of 600–800 °C. With the application of the equivalent circuit model (ECM) fitting using a transmission line model (TLM), the parameters (Rs,el, Rp,el, Cp,el, and QW) expressing the activation polarization of the cathode and anode were analyzed, and the chemical diffusion coefficients (), the reaction constant (k), and the effective length of the electrode reaction were calculated. A similar anode-supported cell was fabricated in which the LSCF6428 cathode was infiltrated by a monodispersed Sm0.5Sr0.5CoFe3−δ (SSC55) nanocatalyst using a sol–gel method. The cathode-infiltrated cell was measured under the same thermodynamic conditions. Each electrode was analyzed by using the TLM to evaluate the effect of the nanocatalyst on the SOFC performance and electrode reaction characteristics. With the application of nanocatalyst infiltration, the parameters (Rs,cat. and Rp,cat.) of the cathode were found to decrease by approximately one order and 40%, respectively. Similarly, Cp,cat. also fell by approximately one order of magnitude. From this investigation, it was confirmed that the diffusion of surface ions had a more significant contribution to conduction than the diffusion of bulk ions by the SSC55 nanocatalyst.

For achieving a sustainable energy future, energy consumption through renewable sources needs to be maximized and greenhouse emissions should be radically reduced. Automotive exhausts sharing the largest global NOX emissions must meet regulated standards by after-treatment systems (ATS) equipped with smart electronic feedback loops through on-board NOX monitoring. Herein, we demonstrate an efficient (Dy, W) co-doped Bi2O3-based electrochemical sensing architecture equipped with Ln2NiMnO6 double perovskite oxides (DPOs) as electrode materials for selective nitric oxides (NO) detection. The sensor configuration facilitates operation in a wide temperature range (325 °C–500 °C) with high sensitivity of 50 mV/decade, a response time below 60 sec. and detection abilities as low as 200 ppb. While investigating the impact of rare-Earth cations, a predominant Ni3+–O–Mn3+ interaction and acquisition of optimal eg 1 electron configuration of transition metal atoms in La2NiMnO6 was found responsible for improved electrocatalytic and redox chemical activity that substantiates the sensing behavior. The study carefully scrutinizes the sensing mechanism to abide by the mixed-potential model. Moreover, the durability assessed over a month of operation supported the applicability of presented sensing elements in on-board NOX monitoring systems.

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.

High proton conductivity and chemical stability of electrolyte materials are the bottleneck challenges to be overcome for the practical feasibility of protonic ceramic fuel cells (PCFCs). Therefore, the fundamental electrochemical properties of electrolyte materials under cell operating conditions are critical. In this study, the partial conductivities, mobilities, and equilibrium constants of the electrolyte BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb1711) are determined by a DC four-probe conductivity measurement in the temperature range of 600–750 °C. The electrolyte acts as a proton conductor due to the dominant proton regime with a conductivity of 1.3 × 10−2 S cm−1 under an air atmosphere (3% H2O) at 600 °C, whereas mixed-ion conduction appears from 750 °C. The theoretical power densities were calculated from both oxygen ion and proton chemical potential gradient profiles based on the partial conductivities of the mobile charge carriers in the electrolyte. The results show a theoretical peak performance of around 5.28 W cm−2 for a 10 μm thick electrolyte at 600 °C without considering any electrode polarization. Most importantly, at this temperature, the peak performance of the BZCYYb1711 electrolyte is remarkable, about two times higher than that of conventional oxygen ion conductors, yttrium doped zirconia (YSZ) and gadolinium doped ceria (GDC), as an electrolyte for SOFCs. This indicates that the perovskite proton conductor BZCYYb1711 is an excellent candidate for a protonic fuel cell operated at intermediate temperatures (≤600 °C). Consequently, our work provides performance limits based on the transport properties of the electrolyte as a guideline for the further development of suitable electrode materials for PCFCs.

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.

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 NiWO

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.

The thermodynamic activity of Li2O in Li0.23La0.61TiO3 (LLT) was measured by an electrochemical galvanic cell using YSZ as the reference electrode to determine the phase boundary of reaction of dif...

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.

ZrP2O7-CeP2O7 solid solutions, Zr1-xCexP2O7; x = 0–0.2 and (Zr0.92Y0.08)1-yCeyP2O7; y = 0–0.1, were prepared by partially replacing Zr4+ with Ce4+ and its effect on the phase composition, sintering behavior, microstructure, and ionic conductivity is analyzed. Ce4+-doped specimens showed improved sintering behavior due to the partial reduction of Ce4+ to Ce3+, as confirmed by X-ray photoelectron spectroscopy (XPS). In unhumidified atmosphere, the electrical conductivity of Zr1-xCexP2O7 increased with increasing cerium content, which can be attributed to the increase in densification and formation of oxygen vacancies due to the partial reduction of Ce4+ to Ce3+. For (Zr0.92Y0.08)1-yCeyP2O7; y = 0–0.1 specimens, the electrical conductivity increased ≥ 4 orders of magnitude during humidification in air (pH2O = 0.12 atm). At 80 °C, specimen (Zr0.92Y0.08)0.9Ce0.1P2O7 (ZYCP10) showed a maximum of 1.72 × 10−2 S cm−1 which decreased sharply at 100 °C. Furthermore, Zr0.92Y0.08P2O7 (ZYP), (Zr0.92Y0.08)0.95Ce0.05P2O7 (ZYCP5), and ZYCP10 specimens humidified at 160 °C showed the maximum conductivity of 1.04 × 10−3, 1.32 × 10−3, and 8.09 × 10−3 S cm−1, respectively, at 190 °C.

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.

This paper reports a systematic investigation of the radical scavenging behaviour of ceria with different morphological shapes inside Nafion membrane. All the ceria nanostructure is synthesized using a template-free hydrothermal route. Distinct crystal planes of CeO2 have different numbers of broken bonds and reaction sites having different surface energies. So, the preparation of CeO2 with various uncovered planes may enhance its scavenging activity. The crystal structure, morphology, and lattice structure are investigated using transmission electron microscopy (TEM), and x-ray diffraction (XRD). The results show that the radical scavenging efficiency of ceria strongly depends on the active surface plane, and decreases in the following order: nanorods > nanocube > nanosphere. Furthermore, the concentrations of surface oxygen vacancies and lattice cerium (III) are correlated with the morphology of the nanoparticles. This relationship clarifies the vital scavenging mechanism of CeO2 that mitigates degradation inside the polymer electrolyte membrane. This is because the inherent lattice strain on the active planes of nanosized ceria with different shapes affects their surficial reactions. The existence of prominent concentration of oxygen vacancy in the nanometric dimension of ceria leading to greater Ce3+ generation by exposed active phase CeO2 nanoparticles is key to achieve a durable hybrid Nafion membrane.

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.