Ba0.5Sr0.5Co0.8Fe0.2O3 − δ + LaCoO3 composite cathode for Sm0.2Ce0.8O1.9-electrolyte based intermediate-temperature solid-oxide fuel cells

A novel Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ + LaCoO₃ (BSCF + LC) composite oxide was investigated for the potential application as a cathode for intermediate-temperature solid-oxide fuel cells based on a Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte. The LC oxide was added to BSCF cathode in order to improve its electrical conductivity. X-ray diffraction examination demonstrated that the solid-state reaction between LC and BSCF phases occurred at temperatures above 950 °C and formed the final product with the composition: La_0.316Ba_0.342Sr_0.342Co_0.863Fe_0.137O_3 − δ at 1100 °C. The inter-diffusion between BSCF and LC was identified by the environmental scanning electron microscopy and energy dispersive X-ray examination. The electrical conductivity of the BSCF + LC composite oxide increased with increasing calcination temperature, and reached a maximum value of ∼300 S cm⁻¹ at a calcination temperature of 1050 °C, while the electrical conductivity of the pure BSCF was only ∼40 S cm⁻¹. The improved conductivity resulted in attractive cathode performance. An area-specific resistance as low as 0.21 Ω cm² was achieved at 600 °C for the BSCF (70 vol.%) + LC (30 vol.%) composite cathode calcined at 950 °C for 5 h. Peak power densities as high as ∼700 mW cm⁻² at 650 °C and ∼525 mW cm⁻² at 600 °C were reached for the thin-film fuel cells with the optimized cathode composition and calcination temperatures.     

Structural and electrochemical studies of Ba0.6Sr0.4Co1−yTiyO3−δ as a new cathode material for IT-SOFCs

The influence of titanium doping level in Ba_0.6Sr_0.4Co_1−yTi_yO_3−δ (BSCT) oxides on their phase structure, electrical conductivity, thermal expansion coefficient (TEC), and single-cell performance with BSCT cathodes has been investigated. The incorporation of Ti can lead to the phase transition of Ba_0.6Sr_0.4CoO_3−δ from hexagonal to cubic structure. The solid solution limitation of Ti in Ba_0.6Sr_0.4Co_1−yTi_yO_3−δ is 0.15–0.3 under 1100 °C. BSCT shows a small polaron conduction behavior and the electrical conductivity increases steadily in the testing temperature range (300–900 °C), leading to a relatively high conductivity at high temperatures. The electrical conductivity decreases with increasing Ti content. The addition of Ti deteriorates the cathode performance of BSCT slightly but decreases the TEC significantly. The TEC of BSCT is about 14 × 10⁻⁶ K⁻¹, which results in a good physical compatibility of BSCT with Gd_0.2Ce_0.8O_2−δ (GDC) electrolyte. BSCT also shows excellent thermal cyclic stability of electrical conductivity and good chemical stability with GDC. These properties make BSCT a promising cathode candidate for intermediate temperature solid oxide fuel cells (IT-SOFCs).     

High lithium ionic conductivity in the garnet-type oxide Li7−X La3(Zr2−X, NbX)O12 (X = 0-2)

Lithium garnet-type oxides Li_7−XLa₃(Zr_2−X, Nb_X)O₁₂ (X = 0-2) were synthesized by a solid-state reaction, and their lithium ion conductivity was measured using an AC impedance method at temperatures ranging from 25 to 150 °C in air. The lithium ion conductivity increased with increasing Nb content, and reached a maximum of ∼0.8 mS cm⁻¹ at 25 °C. By contrast, the activation energy reached a minimum of ∼30 kJ mol⁻¹ at the same point with X = 0.25. The potential window was examined by cyclic voltammetry (CV), which showed lithium deposition and dissolution peaks around 0 V vs. Li⁺/Li, but showed no evidence of other reactions up to 9 V vs. Li⁺/Li.     

Preparation and characterization of Pr1−xSrxFeO3 cathode material for intermediate temperature solid oxide fuel cells

A kind of cathode material of Pr_1−xSr_x FeO₃ (x = 0–0.5) for intermediate temperature solid oxide fuel cells (IT-SOFCs) was prepared by the coprecipitation method. Crystal structure, thermal expansion, electrical conductivity and electrochemical performance of the Pr_1−xSr_xFeO₃ perovskite oxide cathodes were studied by different methods. The results revealed that Pr_l−xSr_xFeO₃ exhibited similar orthorhombic structure from x = 0.1 to 0.3 and took cubic structure when x = 0.4–0.5. The unit cell volume decreased and the thermal expansion coefficient (TEC) of the materials increased as the strontium content increased. When 0 < x ≤ 0.3, the samples exhibited good thermal expansion compatibility with YSZ electrolyte. The electrical conductivity increased with the increasing of doped strontium content. When x = 0.3–0.5, the electrical conductivities were higher than 100 S cm⁻¹. The conductivity of Pr_0.8Sr_0.2FeO₃ was 78 S cm⁻¹ at 800 °C. Compared with the La_0.8Sr_0.2MnO₃ cathode, Pr_0.8Sr_0.2FeO₃ showed higher polarization current density and lower polarization resistance (0.2038 Ω cm²). The value of I₀ for Pr_0.8Sr_0.2FeO₃ at 800 °C is 123.6 mA cm⁻². It is higher than that of La_0.8Sr_0.2MnO₃. Therefore, Pr_1−xSr_xFeO₃ can be considered as a candidate cathode material for IT-SOFCs.     

Electrochemical performance of (Ba0.5Sr0.5)0.9Sm0.1Co0.8Fe0.2O3−δ as an intermediate temperature solid oxide fuel cell cathode

This study presents the electrochemical performance of (Ba_0.5Sr_0.5)_0.9Sm_0.1Co_0.8Fe_0.2O_3−δ (BSSCF) as a cathode material for intermediate temperature solid oxide fuel cells (IT-SOFC). AC-impedance analyses were carried on an electrolyte supported BSSCF/Sm_0.2Ce_0.8O_1.9 (SDC)/Ag half-cell and a Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF)/SDC/Ag half-cell. In contrast to the BSCF cathode half-cell, the total resistance of the BSSCF cathode half-cell was lower, e.g., at 550 °C; the values for the BSSCF and BSCF were 1.54 and 2.33 Ω cm², respectively. The cell performance measurements were conducted on a Ni-SDC anode supported single cell using a SDC thin film as electrolyte, and BSSCF layer as cathode. The maximum power densities were 681 mW cm⁻² at 600 °C and 820 mW cm⁻² at 650 °C.     

La1−xSrxCoO3 (x = 0.1-0.5) as the cathode catalyst for a direct borohydride fuel cell

Direct borohydride fuel cells (DBFCs), with a series of perovskite-type oxides La_1−xSr_xCoO₃ (x = 0.1-0.5) as the cathode catalysts and a hydrogen storage alloy as the anode catalyst, are studied in this paper. The structures of the perovskite-type catalysts are mainly La_1−xSr_xCoO₃ (_x = 0.1-0.5) oxides phases. However, with the increase of strontium content, the intensities of the X-ray diffraction peaks of the impure phases La₂Sr₂O₅ and SrLaCoO₄ are gradually enhanced. Without using any precious metals or expensive ion exchange membranes, a maximum current density of 275 mA cm⁻² and a power density of 109 mW cm⁻² are obtained with the Sr content of x = 0.2 at 60 °C for this novel type of fuel cell.     

Assessment of perovskite-type La0.8Sr0.2ScxMn1−xO3-δ oxides as anodes for intermediate-temperature solid oxide fuel cells using hydrocarbon fuels

Composites formed by the infiltration of 40 wt% La_0.8Sr_0.2Sc_xMn_1−xO_3-δ (LSSM) oxides (x = 0.1, 0.2, 0.3) into 65% porous yttria-stabilized zirconia (YSZ) are investigated as anode materials for intermediate-temperature solid oxide fuel cells for hydrocarbon oxidation. The oxygen non-stoichiometry and electrical conductivity of each LSSM-YSZ composite are determined by coulometric titration. As the concentration of Sc increases, the composites show higher phase stability and the electrical conductivity of LSSM is significantly affected by the Sc doping, the non-stoichiometric oxygen content, and oxygen partial pressure (p(O₂)). To achieve better electrochemical performance, it is necessary to add ceria-supported palladium catalyst for operation with humidified CH₄. Anode polarization resistance increases with Sc doping due to a decrease in electrical conductivity. An electrolyte-supported cell with a LSSM-YSZ composite anode delivers peak power densities of 395 and 340 mW cm⁻² at 923 K in humidified (3% H₂O) H₂ and CH₄, respectively, at a flow rate of 20 mL min⁻¹.     

Bulk conduction and relaxation in [(ZrO2)1−x(CeO2)x]0.92(Y2O3)0.08 (0 ≤ x ≤ 1) solid solutions at intermediate temperatures

Bulk conduction and relaxation of the [(ZrO₂)_1−x(CeO₂)_x]_0.92(Y₂O₃)_0.08 (0 ≤ x ≤ 1) solid solutions were studied using impedance spectroscopy at intermediate temperatures (200-500 °C). The bulk conductivity as a function of x shows a “V-shape” variation which is a competitive effect of the defect associates and the lattice parameter. In the ZrO₂-rich region (x < 0.5) CeO₂ doping increases the concentration of defect associates which limits the mobility of the oxygen vacancies; in the CeO₂-rich region (x > 0.5) the increase of x increases the lattice parameter which enlarges the free channel for oxygen vacancy migration. Further analysis indicates the ionic radius of the tetravalent dopant determines the composition dependence of the ionic conductivity of the solid solutions. When doping YSZ with other tetravalent dopant with similar ionic radius with Zr⁴⁺, e.g., Hf⁴⁺, such “V-shape” composition dependence of the bulk conductivity cannot be observed.     

Synthesis and electrochemical performance of La0.6Ca0.4Fe1−xNixO3 (x = 0.1, 0.2, 0.3) material for solid oxide fuel cell cathode

Polycrystalline samples of La_0.6Ca_0.4Fe_1−xNi_xO₃ (x = 0.1, 0.2, 0.3) (LCFN) are prepared by liquid mix method. The structure of the polycrystalline powders is analyzed with X-ray powder diffraction data. The XRD patterns are indexed as the orthoferrite similar to that of LaFeO₃ having a single phase with orthorhombic perovskite structure (Pnma). The morphological characterization is performed by scanning electron microscopy (SEM) obtaining a mean particle size less than 300 nm.Polarization resistance is studied using two different electrolytes: Y-stabilized zirconia (YSZ) and Sm-doped ceria (SDC). Electrochemical impedance spectroscopy (EIS) measurements of LCFN/YSZ/LCFN and LCFN/SDC/LCFN test cells are carried out. These electrochemical experiments are performed at equilibrium from 850 °C to room temperature, under both zero dc current intensity and air. The best value of area specific resistance (ASR) obtained is 0.88 Ω cm², corresponding to the La_0.6Ca_0.4Fe_0.9Ni_0.1O₃ material using SDC as electrolyte. The dc four-probe measurement indicates that La_0.6Ca_0.4Fe_0.9Ni_0.1O₃ exhibits fairly high electrical conductivity, over 300 S cm⁻¹ at T > 500 °C.     

Fabrication and characterization of a co-fired La0.6Sr0.4Co0.2Fe0.8O3−δ cathode-supported Ce0.9Gd0.1O1.95 thin-film for IT-SOFCs

A dense membrane of Ce_0.9Gd_0.1O_1.95 on a porous cathode based on a mixed conducting La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ was fabricated via a slurry coating/co-firing process. With the purpose of matching of shrinkage between the support cathode and the supported membrane, nano-Ce_0.9Gd_0.1O_1.95 powder with specific surface area of 30 m² g⁻¹ was synthesized by a newly devised coprecipitation to make the low-temperature sinterable electrolyte, whereas 39 m² g⁻¹ nano-Ce_0.9Gd_0.1O_1.95 prepared from citrate method was added to the cathode to favor the shrinkage for the La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ. Bi-layers consisting of <20 μm dense ceria film on 2 mm thick porous cathode were successfully fabricated at 1200 °C. This was followed by co-firing with NiO–Ce_0.9Gd_0.1O_1.95 at 1100 °C to form a thin, porous, and well-adherent anode. The laboratory-sized cathode-supported cell was shown to operate below 600 °C, and the maximum power density obtained was 35 mW cm⁻² at 550 °C, 60 mW cm⁻² at 600 °C.     

Structural and transport properties of LixNi1−y−zCoyMnzO2 cathode materials

In this work structural and transport properties of layered LiNi_1−y−zCo_yMn_zO₂ (y = 0.25, 0.35, 0.5 and z = 0.1) cathode materials are presented. In the considered group of oxides, LiNi_1−y−zCo_yMn_zO₂, there is no clear correlation between electrical conductivity and the a parameter (M-M distance in the octahedra layers). A non-monotonic modification of electrical properties of Li_xNi_0.65Co_0.25Mn_0.1O₂ cathode materials is observed upon lithium deintercalation.     

Synthesis and electrochemical properties of Li1−xFe0.8Ni0.2O2–LixMnO2 (Mn/(Fe + Ni + Mn) = 0.8) material

A new type of Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ (Mn/(Fe + Ni + Mn) = 0.8) material was synthesized at 350 °C in air atmosphere using a solid-state reaction. The material had an XRD pattern that closely resembled that of the original Li_1−xFeO₂–Li_xMnO₂ (Mn/(Fe + Mn) = 0.8) with much reduced impurity peaks. The Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell showed a high initial discharge capacity above 192 mAh g⁻¹, which was higher than that of the parent Li/Li_1−xFeO₂–Li_xMnO₂ (186 mAh g⁻¹). We expected that the increase of initial discharge capacity and the change of shape of discharge curve for the Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell is the result from the redox reaction from Ni²⁺ to Ni³⁺ during charge/discharge process. This cell exhibited not only a typical voltage plateau in the 2.8 V region, but also an excellent cycle retention rate (96%) up to 45 cycles.     

Electrical conduction behavior of La,Co co-doped SrTiO3 perovskite as anode material for solid oxide fuel cells

The effects of La- and Co-doping into SrTiO₃ perovskite oxides on their phase structure, electrical conductivity, ionic conductivity and oxygen vacancy concentration have been investigated. The solid solution limits of La in La_xSr_1 − xTiO_3 − δ and Co in La_0.3Sr_0.7Co_yTi_1 − yO_3 − δ are about 40 mol% and 7 mol%, respectively, at 1500 °C. The incorporation of La decreases the band gap and thus increases the electrical conductivity of SrTiO₃ remarkably. La_0.3Sr_0.7TiO_3 − δ shows an electrical conductivity of 247 S/cm at 700 °C. Co-doping into La_0.3Sr_0.7TiO_3 − δ increases the oxygen vacancy concentration and decreases the migration energy for oxygen ions, leading to a significant increase in ionic conductivity but at the expense of some electrical conductivity. The electrical and ionic conductivities of La_0.3Sr_0.7Co_0.07Ti_0.93O_3 − δ are 63 S/cm and 6 × 10⁻³ S/cm, respectively, at 700 °C. Both La_0.3Sr_0.7TiO_3 − δ and La_0.3Sr_0.7Co_0.07Ti_0.93O_3 − δ show relatively stable electrical conductivities under oxygen partial pressure of 10⁻¹⁴–10⁻¹⁹ atm at 800 °C. These properties make La_0.3Sr_0.7Co_0.07Ti_0.93O_3 − δ a promising anode candidate for solid oxide fuel cells.     

Synthesis of nano-crystalline (Ba0.5Sr0.5)Co0.8Fe0.2O3−δ cathode material by a novel sol–gel thermolysis process for IT-SOFCs

Nano-crystalline (Ba_0.5Sr_0.5)Co_0.8Fe_0.2O_3−δ powder has been successfully synthesized by a novel sol–gel thermolysis method using a unique combination of PVA and urea. The decomposition and crystallization behaviour of the gel precursor was studied by TG/DTA analysis. The gel precursor was calcined at different temperatures and the phase evoluation was studied by X-ray diffraction (XRD) analysis. From the result of X-ray diffraction patterns, it is found that a cubic perovskite (Ba_0.5Sr_0.5)Co_0.8Fe_0.2O_3−δ was formed by calcining the precursor at 450 °C for 5 h, but the well-crystalline cubic perovskite (Ba_0.5Sr_0.5)Co_0.8Fe_0.2O_3−δ was obtained by calcining the precursor at 650 °C for 5 h. Morphological analysis of the powder calcined at various temperatures was done by scanning electron microscope (SEM). Thermogravimetric (TG) results showed the lattice oxygen loss of the product was about ∼2% in its original weight in the temperature range 40–900 °C. Finally, thermal expansion and electrical conductivity of the synthesized material were measured by dilatometer and four-probe dc method, respectively.     

In situ high temperature neutron powder diffraction study of La2Ni0.6Cu0.4O4+δ in air: Correlation with the electrical behaviour

The knowledge of the thermal evolution of the crystal structure of a cathode material across the usual working conditions in solid oxide fuel cells is essential to understand not only its transport properties but also its chemical and mechanical stability in the working environment. In this regard, high-resolution neutron powder diffraction (NPD) measurements have been performed in air from 25 to 900 °C on O₂-treated (350 °C/200 bar) La₂Ni_0.6Cu_0.4O_4+δ. The crystal structure was Rietveld-refined in the tetragonal F4/mmm space group along all the temperature range. The structural data have been correlated with the transport properties of this layered perovskite. The electrical conductivity of O₂-treated La₂Ni_0.6Cu_0.4O_4+δ exhibits a metal (high T)-to-semiconductor (low T) transition as a function of temperature, displaying a maximum value of 110 S cm⁻¹ at around 450 °C. The largest conductivity corresponds, microscopically, to the shortest axial Ni–O2 distance (2.29(1) Å), revealing a major anisotropic component for the electronic transport. We have also performed a durability test at 750 °C for 560 h obtaining a very stable value for the electrical conductivity of 87 S cm⁻¹. The thermal expansion coefficient was 12.8 × 10⁻⁶ K⁻¹ very close to that of the usual SOFC electrolytes. These results exhibit La₂Ni_0.6Cu_0.4O_4+δ as a possible alternative cathode for IT-SOFC.     

The influence of compositional change of 0.3Li2MnO3·0.7LiMn1−xNiyCo0.1O2 (0.2 ≤ x ≤ 0.5, y = x − 0.1) cathode materials prepared by co-precipitation

Cathode materials prepared by a co-precipitation are 0.3Li₂MnO₃·0.7LiMn_1−xNi_yCo_0.1O₂ (0.2 ≤ x ≤ 0.4) cathode materials with a layered-spinel structure. In the voltage range of 2.0-4.6 V, the cathodes show more than one redox reaction peak during its cyclic voltammogram. The Li/0.3Li₂MnO₃·0.7LiMn_1−xNi_yCo_0.1O₂ (x = 0.3, y = 0.2) cell shows the initial discharge capacity of about 200 mAh g⁻¹. However, when x = 0.2 and y = 0.1, the cell exhibits a rapid decrease in discharge capacity and poor cycle life.     

New Nb-doped SrCo1−xNbxO3−δ perovskites performing as cathodes in solid-oxide fuel cells

The high-temperature cubic phase of SrCoO_3−δ is a promising cathode material for solid oxide fuel cells (SOFC) due to its high electrical conductivity and oxygen permeation flux. However, this phase is not stable below 900 °C where a 3C-cubic to 2H-hexagonal phase transition takes place when the sample is slowly cooled down. In this work we have stabilized a 3C-tetragonal P4/mmm structure for SrCo_1−xNb_xO_3−δ with x = 0.05. We have followed the strategy consisting of introducing a highly-charged cation at the Co sublattice, in order to avoid the stabilization of the unwanted 2H structure containing face-sharing octahedra. The characterization of this oxide included X-ray (XRD) and neutron powder diffraction (NPD) experiments. SrCo_0.95Nb_0.05O_3−δ adopts a tetragonal superstructure of perovskite with a = a₀, c = 2a₀ (a₀ ≈ 3.9 Å) defined in the P4/mmm space group containing two inequivalent Co positions. Flattened and elongated (Co,Nb)O₆ octahedra alternate along the c axis sharing corners in a three-dimensional array (3C-like structure). In the test cell, the electrodes were supported on a 300-μm-thick pellet of the electrolyte La_0.8Sr_0.2Ga_0.83Mg_0.17O_3−δ (LSGM). The test cells gave a maximum power density of 0.4 and 0.6 W/cm² for temperatures of 800 and 850 °C, respectively, with pure H₂ as fuel and air as oxidant. The good performance of this material as a cathode is related to its mixed electronic-ionic conduction (MIEC) properties, which can be correlated to the investigated structural features: the Co³⁺/Co⁴⁺ redox energy at the top of the O-2p bands accounts for the excellent electronic conductivity, which is favored by the corner-linked perovskite network. The considerable number of oxygen vacancies, with the oxygen atoms showing high displacement factors suggests a significant ionic mobility.     

Electrochemical performance of La2Cu1−xCoxO4 cathode materials for intermediate-temperature SOFCs

K₂NiF₄-type structure oxides La₂Cu_1−xCo_xO₄ (x = 0.1, 0.2, 0.3) are synthesized and evaluated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). The materials are characterized by XRD, SEM and electrochemical impedance spectrum (EIS), respectively. The results show that no reaction occurs between La₂Cu_1−xCo_xO₄ electrode and Ce_0.9Gd_0.1O_1.95 (CGO) electrolyte at 1000 °C. The electrode forms good contact with the electrolyte after sintering at 800 °C for 4 h in air. The electrode properties of La₂Cu_1−xCo_xO₄ are studied under various temperatures and oxygen partial pressures. The optimum composition of La₂Cu_0.8Co_0.2O₄ results in 0.51 Ω cm² polarization resistance (R_p) at 700 °C in air. The rate limiting step for oxygen reduction reaction (ORR) is the charge transfer process. La₂Cu_0.8Co_0.2O₄ cathode exhibits the lowest overpotential of about 50 mV at a current density of 48 mA cm⁻² at 700 °C in air.     

On Ba0.5Sr0.5Co1−yFeyO3−δ (y = 0.1–0.9) oxides as cathode materials for La0.9Sr0.1Ga0.8Mg0.2O2.85 based IT-SOFCs

Ba_0.5Sr_0.5Co_1−yFe_yO_3−δ (y = 0.1–0.9) (BSCF) oxides have been evaluated as cathode materials for intermediate solid oxide fuel cells with La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM) as electrolyte. The increase of iron content in BSCF materials results in an increase of the area-specific resistance (ASR), e.g. 0.04, 0.08 and 0.13 Ω cm² for compositions with y = 0.2, 0.4 and 0.6 respectively at 1073 K. The influence of iron content in BSCF oxides on the unit cell volume via high temperature X-ray diffraction, the overall electrical conductivity and the thermal expansion coefficient (TEC) has also been investigated. The lattice cell parameters for the BSCF series increase as a function of the temperature and exhibit a non-linear behaviour, with a sudden increase at around 673 K due to the loss of lattice oxygen, which in turn is caused by the reduction of Co⁴⁺ and Fe⁴⁺ to lower oxidation states. This was determined by O₂ temperature-programmed desorption and thermogravimetric analysis. Such oxygen non-stoichiometry results in a significant thermal expansion and conductivity change for all compositions at the same temperature.     

Investigation of cobalt-free perovskite Ba0.95La0.05FeO3−δ as a cathode for proton-conducting solid oxide fuel cells

Cobalt-free perovskite Ba_0.95La_0.05FeO_3−δ (BLF) was synthesized. The conductivity of BLF was measured with a DC four-point technique. The thermal expansion coefficient of the BLF was measured using a dilatometer. The BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7) electrolyte based proton conducting solid oxide fuel cells (SOFCs) were fabricated. A composite cathode with BLF + BZCY7 was used to mitigate the thermal expansion mismatch with the BZCY7 electrolyte. The polarization processes of the button cell NiO-BZCY7/BZCY7/BLF + BZCY7 were characterized using the complicated electrochemical impedance spectroscopy technique. The open circuit voltage of 0.982 V, 1.004 V, and 1.027 V was obtained at 700 °C, 650 °C, and 600 °C, respectively, while the peak power density of 325 mW cm⁻², 240 mW cm⁻², and 152 mW cm⁻², was achieved accordingly.