Modifying perovskite-type oxide catalyst LaNiO3 with Ce for carbon dioxide reforming of methane

Perovskite-type oxide catalysts LaNiO₃ and La_1−xCe_xNiO₃ (x ≤ 0.5) were prepared by the Pechini method and used as catalysts for carbon dioxide reforming of methane to form synthesis gas (H₂ + CO). The gaseous reactants consisted of CO₂ and CH₄ in a molar ratio of 1:1. At a GHSV of 10,000 hr⁻¹, CH₄ conversion over LaNiO₃ catalyst increased from 66% at 600 °C to 94% at 800 °C, while CO₂ conversion increased from 51% to 92%. The achieved selectivities of CO and H₂ were 33% and 57%, respectively, at 600 °C. To prevent the deposition of carbon and the sintering nickel species, some of the Ni in perovskite-type oxide catalyst was substituted by Ce. Ce provided lattice oxygen vacancies, which activated C–H bonds, and increased the selectivity of H₂ to 61% at 600 °C. XRD analysis indicates that the catalyst exhibited a typical perovskite spinel structure and formed La₂O₂CO₃ phases after CO₂ reforming. The FE-SEM results reveal carbon whisker of the LaNiO₃ catalyst and the BET analysis indicates that the specific surface area increases after the reforming reaction. The H₂-TPR results confirm that Ce metals can store and provide oxygen.     

Hydrogen production via steam reforming of methanol over Cu/(Ce,Gd)O2−x catalysts

Hydrogen production via steam reforming of methanol is carried out over Cu/(Ce,Gd)O_2−x catalysts at 210–600 °C. The CO content in reformate is about 1% at 210–270 °C, which are the typical temperature for hydrogen production via steam reforming of methanol. Largest H₂ yield and CO₂ selectivity and smallest CO content are obtained at 240 °C. The formation rate of CO increases with increasing temperature. The average formation rate of CO becomes larger than that of CO₂ at about 450 °C. The H₂ yield, the CO₂ selectivity and the CO content become constant at about 550 °C. At 240 °C, the smallest CO content is obtained with a catalyst weight of 0.5 g and a Cu content of 3 wt%. The H₂ yield, defined as H₂/(CO + CO₂) in formation rates, at 240 °C is always 3 and not affected by the variations of either the catalyst weight or the Cu content.     

Catalytic performance of Ni-Pr supported on delaminated clay in the dry reforming of methane

Mineral clay modified with Al, polyvinyl alcohol (PVA) and microwaves was used as a support to obtain a Ni-Pr catalyst. This catalytic system was evaluated in the reforming of methane with CO₂. The experiments were carried out under drastic conditions for 300 min, with a 50/50 CH₄/CO₂ mixture, total flux of 80 mL min⁻¹, without dilution gas (WHSV = 96 Lg⁻¹h⁻¹) and without previous reduction. The effect of the calcination temperature of the materials was studied at 500 °C and 800 °C as well as the effect of Pr (evaluating nominal quantities of 0, 1, 3 and 5%). The calcination temperature of the solid influenced the formation of the NiO species which had an effect on the activity and formation of coke on the material. The Pr had a promoter effect on the activity of the catalysts increasing the conversions of the CH ₄ as well as the CO₂. The formation of coke for the catalysts calcined at 500 °C presented a correlation with the praseodymium content while for those catalysts calcined at 800 °C there was no formation of coke.     

Enhancing preferential oxidation of CO in H2 on Au/α-Fe2O3 catalyst via combination with APTES/SBA-15 CO2-sorbent

Au/α-Fe₂O₃ was combined with a CO₂-sorbent (3-aminopropyltriethoxysilane (APTES) grafted on SBA-15 and hereafter denoted as APTES/SBA-15) to enhance preferential oxidation (PROX) of CO in H₂. The CO₂ molecules could be rapidly adsorbed on APTES/SBA-15 at low temperatures below 50 °C with a capacity of 0.68 mmol CO₂/g-sample, and desorbed at a temperature range of 50 °C–80 °C. Three different configurations of the Au/α-Fe₂O₃ catalyst and the CO₂-sorbent were tested in the PROX reaction, namely (i) the sorbent-free (catalyst//SBA-15//catalyst) configuration, (ii) the packed three-layer configuration (catalyst//CO₂-sorbent//catalyst), and (iii) the mechanically mixed catalyst and CO₂-sorbent configuration. Compared to configuration (i), configuration (ii) achieved an average 10% higher CO conversion at 50 °C and a GHSV of 65000 h⁻¹. However, the CO concentration could not be lowered to below 70 ppm from 2000 ppm using configuration (ii) at a GHSV of 10000 h⁻¹. Thus, a 5-layer configuration (catalyst//CO₂-sorbent//catalyst//CO₂-sorbent//catalyst) was used, and the CO concentration was lowered to ca. 25 ppm. The mechanism for enhancement of the PROX reaction by the continuous removal of CO₂ by the CO₂-sorbent is discussed and attributed to reduction of the surface carbonate on the Au/α-Fe₂O₃ catalyst formed during the PROX process.     

Improvement of hydrogen-separating performance by on-stream catalytic cracking of silane over hollow fiber MFI zeolite membrane

MFI zeolite membranes were synthesized on porous α-alumina hollow fibers by in-situ hydrothermal synthesis. The membranes were further modified for H₂ separation by on-stream catalytic cracking deposition of methyldiethoxysilane (MDES) in the zeolitic pores. The separation performance of the modified membranes was characterized by separation of H₂/CO₂ gas mixture at 500 °C. Activation of MFI zeolite membranes by air at 500 °C was found to promote catalytic cracking deposition of silane in the zeolitic pores effectively, which resulted in significant improvement of H₂-separating performance. The H₂/CO₂ separation factor of 45.6 with H₂ permeance of 1.0 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ was obtained at 500 °C for a modified hollow fiber MFI zeolite membrane. The as-made membranes showed good thermochemical stability for the separation of H₂/CO₂ gas mixture containing H₂O and H₂S, respectively.     

Preparation and characterization of Sm0.2Ce0.8O1.9/Na2CO3 nanocomposite electrolyte for low-temperature solid oxide fuel cells

Sm_0.2Ce_0.8O_1.9 (SDC)/Na₂CO₃ nanocomposite synthesized by the co-precipitation process has been investigated for the potential electrolyte application in low-temperature solid oxide fuel cells (SOFCs). The conduction mechanism of the SDC/Na₂CO₃ nanocomposite has been studied. The performance of 20 mW cm⁻² at 490 °C for fuel cell using Na₂CO₃ as electrolyte has been obtained and the proton conduction mechanism has been proposed. This communication demonstrates the feasibility of direct utilization of methanol in low-temperature SOFCs with the SDC/Na₂CO₃ nanocomposite electrolyte. A fairly high peak power density of 512 mW cm⁻² at 550 °C for fuel cell fueled by methanol has been achieved. Thermodynamical equilibrium composition for the mixture of steam/methanol has been calculated, and no presence of C is predicted over the entire temperature range. The long-term stability test of open circuit voltage (OCV) indicates the SDC/Na₂CO₃ nanocomposite electrolyte can keep stable and no visual carbon deposition has been observed over the anode surface.     

Soft-templated NiO–CeO2 mixed oxides for biogas upgrading by direct CO2 methanation

The catalytic performance in the direct CO₂ methanation of a model biogas is investigated on NiO–CeO₂ nanostructured mixed oxides synthesized by the soft-template procedure with different Ni/Ce molar ratios. The samples are thoroughly characterized by means of ICP-AES, XRD, TEM and HR-TEM, N₂ physisorption at −196 °C, and H₂-TPR. They result to be constituted of CeO₂ rounded nanocrystals and of polycrystalline needle-like NiO particles. After a H₂-treatment at 400 °C for 1 h, the surface basic properties and the metal surface area are also assessed using CO₂ adsorption microcalorimetry and H₂-pulse chemisorption measurements, respectively. At increasing Ni content the Ni⁰ surface area increases, while the opposite occurs for the number of basic sites. Using a CO₂/CH₄/H₂ feed, at 11,000 cm³ h⁻¹ g_cat⁻¹, CO₂ conversions in the 83–89 mol% range and methane selectivities >99.5 mol% are reached at 275 °C and atmospheric pressure, highlighting the very good performances of the investigated catalysts.     

High-Performance composite cathodes for solid oxide fuel cells

The composite cathodes with lanthanum-based iron and cobalt-containing perovskite La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) and Ce_0.9Gd_0.1O_1.95 (GDC) are investigated for solid oxide fuel cell (SOFC) applications at relatively low operating temperatures (700-800 °C). LSCFs with high surface areas of 55 m²g⁻¹ are synthesized via a complex method with inorganic nano dispersants. The fuel cell performances of composite cathodes on anode supported SOFCs are characterized with GDC materials of surface areas of 5 m²g⁻¹ (ULSA-GDC), 12 m²g⁻¹ (LSA-GDC), and 23 m²g⁻¹ (HAS-GDC). The maximum power density of the SOFCs increases from 0.68 Wcm⁻² to 1.2 Wcm⁻² at 780 °C and 0.8 V as the GDC surface area increases from 5 m²g⁻¹ to 23 m²g⁻¹. The area specific resistance of the porous composite cathodes with a HAS-GDC are 0.467 ohmcm² at 780 °C and 1.086 ohmcm² at 680 °C, while these values with an LSA-GDC are 0.543 ohmcm² and 0.945 ohmcm², respectively. The best compositions of the porous composite cathodes result from the morphologies of the GDC materials at each temperature due to the formation of an electron-oxygen ion-gas boundary.     

Co and Ni supported on CeO2 as selective bimetallic catalyst for dry reforming of methane

Co/CeO₂ (Co 7.5 wt.%), Ni/CeO₂ (Ni 7.5 wt.%) and Co–Ni/CeO₂ (Co 3.75 wt.%, Ni 3.75 wt.%) catalysts were prepared by surfactant assisted co-precipitation method. Samples were characterized by X-Ray diffraction, BET surface areas measurements, temperature programmed reduction and tested for the dry reforming of methane CH₄ + CO₂ → 2CO + 2H₂ in the temperature range 600–800 °C with a CH₄:CO₂:Ar 20:20:60 vol.% feed mixture and a total flow rate of 50 cm³ min⁻¹ (GHSW = 30,000 mL g⁻¹ h⁻¹). The bimetallic Co–Ni/CeO₂ catalyst showed higher CH₄ conversion in comparison with monometallic systems in the whole temperature range, being 50% at 600 °C and 97% at 800 °C. H₂/CO selectivity decreased in the following order: Co–Ni/CeO₂ > Ni/CeO₂ > Co/CeO₂. Carbon deposition on spent catalysts was analyzed by thermal analysis (TG-DTA). After 20 h under stream at 750 °C, cobalt-containing catalysts, Co/CeO₂ and Co–Ni/CeO₂, showed a stable operation in presence of a deposited amorphous carbon of 6 wt.%, whereas Ni/CeO₂ showed an 8% decrease of catalytic activity due to a massive presence of amorphous and graphitic carbon (25 wt.%).     

Biogas reforming for hydrogen production over a Ni–Co bimetallic catalyst: Effect of operating conditions

A Ni–Co bimetallic catalyst, Ni–Co/La₂O₃/Al₂O₃, was prepared by conventional incipient wetness impregnation. It shows a high level of activity and excellent stability for biogas reforming. This work examines how operating conditions, such as the reaction temperature, operating pressure, feed ratio, gas hourly space velocity (GHSV), and CO₂ excessive coefficient, affect the catalytic performances of the catalyst. The experimental biogas is simulated with CH₄ and CO₂ at a molar ratio of 1, without any dilute gas. The catalyst was also characterized by XRD, BET, TEM and TG-DSC. In a stability test of 510 h under the conditions of 800 °C, 1 atm, and a GHSV of 6000 ml g_cat⁻¹ h⁻¹, the average coking rate over the catalyst was only about 0.0374 mg g_cat⁻¹ h⁻¹. The experimental results also indicate that the dynamic equilibrium between the deposition and gasification of carbon deposited on the surface of the catalyst can be established during the reaction. The aggregation of metallic Ni/Co and the formation of filamentous carbon over the surface of the catalyst can be inhibited effectively. During the last 50 h of the 510 h stability test, the average conversion of CH₄ and CO₂, the selectivity to H₂ and CO, and ratio of H₂/CO were 95.2%, 96.7%, 95.0%, 98.3%, and 0.96, respectively.     

Combined pre-reformer/reformer system utilizing monolith catalysts for hydrogen production

The pre-reforming of higher hydrocarbon, propane, was performed to generate hydrogen from LPG without carbon deposition on the catalysts. A Ru/Ni/MgAl₂O₄ metallic monolith catalyst was employed to minimize the pressure drop over the catalyst bed. The propane pre-reforming reaction conditions for the complete conversion of propane with no carbon formation were identified to be the following: space velocities over 2400 h⁻¹ and temperatures between 400 and 450 °C with a H₂O/C₁ ratio of 3. The combined pre-reformer and the main reformer system with the Ru/Ni/MgAl₂O₄ metallic monolith catalyst was employed to test the conversion propane to syngas where the reaction heat was provided by catalytic combustors. Propane was converted in the pre-reformer to 52.5% H₂, 27.0% CH₄, 17.5% CO, and 3.0% CO₂ with a 331 °C inlet temperature and a 482 °C catalyst outlet temperature. The main steam reforming reactor converted the methane from the pre-reformer with a conversion of higher than 99.0% with a 366 °C inlet temperature and an 824 °C catalyst outlet temperature. With a total of 912 cc of the Ru/Ni/MgAl₂O₄ metallic monolith catalyst in the main reformer, the H₂ production from the propane reached an average of 3.25 Nm³h⁻¹ when the propane was fed at 0.4 Nm³h⁻¹.     

High temperature H2/CO2 separation using cobalt oxide silica membranes

In this work high quality cobalt oxide silica membranes were synthesized on alumina supports using a sol–gel, dip coating method. The membranes were subsequently connected into a steel module using a graphite based proprietary sealing method. The sealed membranes were tested for single gas permeance of He, H₂, N₂ and CO₂ at temperatures up to 600 °C and feed pressures up to 600 kPa. Pressure tests confirmed that the sealing system was effective as no gas leaks were observed during testing. A H₂ permeance of 1.9 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ was measured in conjunction with a H₂/CO₂ permselectivity of more than 1500, suggesting that the membranes had a very narrow pore size distribution and an average pore diameter of approximately 3 Å. The high temperature testing demonstrated that the incorporation of cobalt oxide into the silica matrix produced a structure with a higher thermal stability, able to resist thermally induced densification up to at least 600 °C. Furthermore, the membranes were tested for H₂/CO₂ binary feed mixtures between 400 and 600 °C. At these conditions, the reverse of the water gas shift reaction occurred, inadvertently generating CO and water which increased as a function of CO₂ feed concentration. The purity of H₂ in the permeate stream significantly decreased for CO₂ feed concentrations in excess of 50 vol%. However, the gas mixtures (H₂, CO₂, CO and water) had a more profound effect on the H₂ permeate flow rates which significantly decreased, almost exponentially as the CO₂ feed concentration increased.     

Hierarchical porous graphene-based carbons prepared by carbon dioxide activation and their gas adsorption properties

Hierarchical porous graphene-based carbons (HPGCs) have been prepared by a simple carbon dioxide activation of graphite oxide. The effects of activation temperature on the structural and textural properties as well as gas adsorption capacities of the resultant carbons have been investigated. The HPGCs showed hierarchically micro-meso-macroporous structures, high specific surface areas of up to 532 m² g⁻¹, and large pore volumes of up to 1.67 cm³ g⁻¹. Moreover, the HPGC materials were demonstrated to be efficient for CO₂ and H₂ adsorption. The HPGC-850, which was obtained after two hours of activation at 850 °C, exhibited the highest adsorption capacities of 7.74 wt% (1.76 mmol g⁻¹) at 273 K and 1 bar for CO₂ and of 0.75 wt% (3.76 mmol g⁻¹) at 77 K and 1 bar for H₂.     

Synthesis and properties of Sm-deficient Sm1−xBaCo2O5+δ perovskite oxides as cathode materials

Double-layered perovskite oxides of Sm_1−xBaCo₂O_5+δ (S_1−xBCO) with various A-site Sm³⁺-deficiencies (x = 0.00–0.08) were synthesized and evaluated as cathode materials of intermediate-temperature solid oxide fuel cells (IT-SOFCs). The Sm³⁺-deficiency content in S_1−xBCO was limited up to x = 0.05, and higher content x = 0.08 caused impurity phase. S_1−xBCO oxides were chemically stable with GDC electrolyte at 1050 °C and below. Introduction of Sm³⁺-deficiency caused decreased oxygen content and increased concentration of oxygen vacancy in S_1−xBCO. Electrical conductivities of S_1−xBCO decreased with increasing temperature in air, and also changed with the Sm³⁺-deficiency content. Electrochemical performance of S_1−xBCO cathodes were characterized by impedance spectra measurement based on symmetric cells. Higher Sm³⁺ deficiency content has resulted in decreased area specific resistances (ASRs) and activation energy (Ea), i.e. enhanced electrochemical reaction reactivity for the S_1−xBCO cathodes. Among the studied samples, the S_0.95BCO (x = 0.05) oxide showed the best electrochemical performance with ASR values of 0.316 Ω cm² at 600 °C, 0.137 Ω cm² at 650 °C, 0.068 Ω cm² at 700 °C and 0.038 Ω cm² at 750 °C respectively, thus it's a promising cathode material of IT-SOFCs.     

Syngas production at intermediate temperature through H2O and CO2 electrolysis with a Cu-based solid oxide electrolyzer cell

Solid Oxide Electrolyzer Cells (SOECs) are promising energy devices for the production of syngas (H₂/CO) by H₂O and/or CO₂ electrolysis. Here we developed a Cu–Ce_0.9Gd_0.1O_2−δ/Ce_0.8Gd_0.2O_2−δ/Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ-Ce_0.8Gd_0.2O_2−δ cell and performed H₂O and CO₂ electrolysis experiments in the intermediate temperature range (600°C–700 °C). As a baseline, the cell was first tested in fuel cell operation mode; the sample shows a maximum power density peak of 104 mW cm⁻² at 700 °C under pure hydrogen and air. H₂O electrolysis testing revealed a steady production of hydrogen with a Faraday's efficiency of 32% at 700 °C at an imposed current density of −78 mA cm⁻². CO production was observed during CO₂ electrolysis but higher cell voltages were required. A lower efficiency of about 4% was obtained at 700 °C at an imposed current density of −660 mA cm⁻². These results confirm that syngas production is feasible by water and carbon dioxide electrolysis but further improvements from both the manufacturing and the electrocatalytic aspects are needed to reach higher yields and efficiencies.     

Hydrogen production from carbon dioxide reforming of methane over highly active and stable MgO promoted Co–Ni/γ-Al2O3 catalyst

CoNi/Al₂O₃ and MgCoNi/Al₂O₃ catalysts are investigated for hydrogen production from CO₂ reforming of CH₄ reaction at the gas hourly space velocity of 40,000 mL g⁻¹ h⁻¹. The MgO promoted CoNi/Al₂O₃ catalyst shows much higher conversions (97% for CO₂ and 95% for CH₄ at 850 °C) than the CoNi/Al₂O₃ catalyst. In addition, the stability is maintained for 200 h in CO₂ reforming of CH₄. The outstanding catalytic activity and stability of the MgO promoted CoNi/Al₂O₃ catalyst is mainly due to the basic nature of MgO, an intimate interaction between Ni and the support, and rapid decomposition/dissociation of CH₄ and CO₂, resulting in preventing coke formation in CO₂ reforming of CH₄.     

High pressure palladium membrane reactor for the high temperature water-gas shift reaction

The water-gas shift (WGS) catalytic membrane reactor (CMR) incorporating a composite Pd-membrane and operating at elevated temperatures and pressures can greatly contribute to the efficiency enhancement of several methods of H₂ production and green power generation. To this end, mixed gas permeation experiments and WGS CMR experiments have been conducted with a porous Inconel supported, electroless plated Pd-membrane to better understand the functioning and capabilities of those processes. Binary mixtures of H₂/He, H₂/CO₂, and a ternary mixture of H₂, CO₂ and CO were separated by the composite membrane at 350, 400, and 450 °C, 14.4 bar (P_tube = 1 bar), and space velocities up to 45,000 h⁻¹. H₂ permeation inhibition caused by reversible surface binding was observed due to the presence of both CO and CO₂ in the mixtures and membrane inhibition coefficients were estimated. Furthermore, WGS CMR experiments were conducted with a CO and steam feed at 14.4 bar (P_tube = 1 bar), H₂O/CO ratios of 1.1-2.6, and GHSVs of up to 2900 h⁻¹, considering the effect of the H₂O/CO ratio as well as temperature on the reactor performance. Experiments were also conducted with a simulated syngas feed at 14.0 bar (P_tube  = 1 bar), and 400-450 °C, assessing the effect of the space velocity on the reactor performance. A maximum CO conversion of 98.2% was achieved with a H₂ recovery of 81.2% at 450 °C. An optimal operating temperature for high CO conversion was identified at approximately 450 °C, and high CO conversion and H₂ recovery were achieved at 450 °C with high throughput, made possible by the 14.4 bar reaction pressure.     

An evaluation of hydrogen production from the perspective of using blast furnace gas and coke oven gas as feedstocks

Blast furnace (BF) is a large-scale reactor for producing hot metal where coke and coal are consumed as reducing agent and fuel, respectively. As a result, a large amount of CO₂ is liberated into the atmosphere. The blast furnace gas (BFG) and coke oven gas (COG) from the ironmaking process can be used for H₂ production in association with carbon capture and storage (CCS), thereby reducing CO₂ emissions. In this study thermodynamic analyses are performed to evaluate the feasibility of H₂ production from BFG and COG. Through the water gas shift reaction (WGSR) of BFG, almost all CO contained in BFG can be converted for H₂ production if the steam/CO (S/C) ratio is no less than unity and the temperature is at 200 °C, regardless of whether CO₂ is captured or not. The maximum H₂ production from WGSR is around 0.21 Nm³ (Nm³ BFG)⁻¹. Regarding H₂ production from COG, a two-stage reaction of partial oxidation (POX) followed by WGSR is carried out. It is found the proper conditions for syngas formation from the POX of COG is at the oxygen/fuel (O/F) ratio of 0.5 and the temperature range of 1000-1750 °C where the maximum syngas yield is 2.83 mol (mol hydrocarbons)⁻¹. When WGSR is subsequently applied, the maximum H₂ production from the two-stage reaction can reach 0.83 Nm³ (Nm³ COG)⁻¹.     

Thermal stability study of La0.9Sr0.1Ga0.8Mg0.2O2.85–(Li/Na)2CO3 composite electrolytes for low-temperature solid oxide fuel cells

Novel composite materials based on La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM) and a binary eutectic carbonates (52 mol% Li₂CO₃:48 mol% Na₂CO₃) are potential electrolytes for low-temperature solid oxide fuel cells (LTSOFCs) operating at 400–600 °C. However, thermal stability of the LSGM–(Li/Na)₂CO₃ composites remains in doubt due to the molten state of the carbonates at elevated temperature. In this paper, XRD, SEM, TGA and EIS were employed for thermal ageing and cycling studies of the LSGM–(Li/Na)₂CO₃ composites. XRD and SEM results showed that ageing induced a slight effect on the structure and morphology of the composites. TGA and EIS results indicated that the composites had a good stability during cycling. The LSGM–20 wt% (Li/Na)₂CO₃ sample showed a relatively stable conductivity (7–9 × 10⁻² S cm⁻¹) during a 650 h measurement under air at 600 °C. Single cell based on the composite electrolytes was reported for the first time, a maximum power density of 617 W cm⁻² and the open circuit voltage (OCV) of 1.01 V were achieved at 600 °C for the composite containing 20 wt% carbonates. The notable thermal stability together with fairly high performance emphasize the promise of LSGM–(Li/Na)₂CO₃ composite electrolytes for long-term LTSOFCs.     

Impedance spectroscopy studies of Gd-CeO2-(LiNa)CO3 nano composite electrolytes for low temperature SOFC applications

Electrical properties of 20 mol % Gd doped CeO₂ with varying amounts of (LiNa)CO₃ have been investigated by employing AC-impedance spectroscopic technique. The impedance spectra show a high frequency depressed arc, represents the bulk composite and low frequency incomplete semicircle representing electrode contribution. The bulk resistance of the composites decreases with increasing carbonate content up to 30 wt% (LiNa)CO_3, thereafter the resistance increases, whereas all the compositions show a decrease in resistance with increasing temperature. The typical nature of the impedance spectra of the composite shows the possibility of coexistence of multi ionic transport or existence of space charge effect at the interface of Gd-CeO₂ and carbonate phase. The composite containing 25 wt% (LiNa)CO₃ shows the highest ionic conductivity of 0.1757 S cm⁻¹ at 550 °C and lowest activation energy of 0.127 eV in the temperature range 550-800 °C. A symmetric cell is fabricated with GDC-25 wt% (LiNa)CO₃ electrolyte, NiO-GDC(LiNa)CO₃ anode and lithiated NiO-GDC(LiNa)CO₃ cathode. Pure H₂ and air are used as fuel and oxidant. The cell delivers a maximum power density of 45 mW/cm², 58 mW/cm² and 92 mW/cm² at 450, 500 and 550 °C, respectively.