A high-performance Gd0.8Sr0.2CoO3–Ce0.9Gd0.1O1.95 composite cathode for intermediate temperature solid oxide fuel cell

Powders of Gd_0.8Sr_0.2CoO₃ (GSC) were prepared by a glycine–nitrate process. Symmetrical cathodes of GSC–50Ce_0.9Gd_0.1O_1.95 (GDC) (50:50 by volume) powders were deposited on GDC electrolyte pellets, and the electrochemical properties of the interfaces between the porous cathode and the electrolyte were investigated at intermediate temperature (500–750 °C) using electrochemical impedance spectroscopy. The addition of 50 vol.% GDC to GSC resulted in an additional factor ≈3 decrease in the area-specific resistance (ASR). The ASR values for the GSC–50GDC cathodes were as low as 0.064 Ω cm² at 700 °C and 0.16 Ω cm² at 600 °C, respectively. The maximum power density of a cell using the GSC–50GDC cathode was 356 mW cm⁻² at 700 °C.     

Layered perovskite PrBa0.5Sr0.5Co2O5+δ as high performance cathode for solid oxide fuel cells using oxide proton-conducting electrolyte

The layered perovskite PrBa_0.5Sr_0.5Co₂O_5+δ (PBSC) was investigated as a cathode material for a solid oxide fuel cell using an oxide proton conductor based on BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY). The sintering conditions for the PBSC-BZCY composite cathode were optimized, resulting in the lowest area-specific resistance and apparent activation energy obtained with the cathode sintered at 1200 °C for 2 h. The maximum power densities of the PBSC-BZCY/BZCY/NiO-BZCY cell were 0.179, 0.274, 0.395, and 0.522 W cm⁻² at 550, 600, 650, and 700 °C, respectively with a 15 μm thick electrolyte. A relatively low cell interfacial polarization resistance of 0.132 Ω cm² at 700 °C indicated that the PBSC-BZCY could be a good cathode candidate for intermediate temperature SOFCs with BZCY electrolyte.     

Behavior of 3 mol% yttria-stabilized tetragonal zirconia polycrystal film prepared by slurry spin coating

A dense and uniform 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3YSZ) electrolyte film of 6 μm in thickness was fabricated by slurry spin coating on a porous NiO/3YSZ anode substrate. Composite cathodes of La_0.7Sr_0.3MnO₃ impregnated with Sm_0.2Ce_0.8O_1.9 were fabricated on the 3YSZ films. A single cell produced in this way was tested at 700, 750 and 800 °C with hydrogen as fuel and stationary air as oxidant. Test results revealed an open-circuit voltage of 1.04 V at 800 °C, and maximum power density of 551, 895 and 1143 mW cm⁻² at 700, 750 and 800 °C, respectively. Impedance spectra results demonstrated that the cell performance was determined by the polarization resistance of the cathode.     

Infiltrated multiscale porous cathode for proton-conducting solid oxide fuel cells

A Sm_0.5Sr_0.5CoO_3−δ (SSC)-BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY) composite cathode with multiscale porous structure was successfully fabricated through infiltration for proton-conducting solid oxide fuel cells (SOFCs). The multiscale porous SSC catalyst was coated on the BZCY cathode backbones. Single cells with such composite cathode demonstrated peak power densities of 0.289, 0.383, and 0.491 W cm⁻² at 600, 650, 700 °C, respectively. Cell polarization resistances were found to be as low as 0.388, 0.162, and 0.064 Ω cm² at 600, 650 and 700 °C, respectively. Compared with the infiltrated multiscale porous cathode, cells with screen-printed SSC-BZCY composite cathode showed much higher polarization resistance of 0.912 Ω cm² at 600 °C. This work has demonstrated a promising approach in fabricating high performance proton-conducting SOFCs.     

Internal shorting and fuel loss of a low temperature solid oxide fuel cell with SDC electrolyte

A solid oxide fuel cell with Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte of 10 μm in thickness and Ni–SDC anode of 15 μm in thickness on a 0.8 mm thick Ni–YSZ cermet substrate was fabricated by tape casting, screen printing and co-firing. A composite cathode, 75 wt.% Sm_0.5Sr_0.5CoO₃ (SSCo) + 25 wt.% SDC, approximately 50 μm in thickness, was printed on the co-fired half-cell, and sintered at 950 °C. The cell showed a high electrochemical performance at temperatures ranging from 500 to 650 °C. Peak power density of 545 mW cm⁻² at 600 °C was obtained. However, the cell exhibited severe internal shorting due to the mixed conductivity of the SDC electrolyte. Both the amount of water collected from the anode outlet and the open circuit voltage (OCV) indicated that the internal shorting current could reach 0.85 A cm⁻² or more at 600 °C. Zr content inclusions were found at the surface and in the cross-section of the SDC electrolyte, which could be one of the reasons for reduced OCV and oxygen ionic conductivity. Fuel loss due to internal shorting of the thin SDC electrolyte cell becomes a significant concern when it is used in applications requiring high fuel utilization and electrical efficiency.     

Fabrication and performance of gadolinia-doped ceria-based intermediate-temperature solid oxide fuel cells

Anode-supported solid oxide fuel cells (SOFC) based on gadolinia-doped ceria (GDC) are developed in this study. A carbonate co-precipitation method is used to synthesize the nano-sized GDC powders. A dense GDC electrolyte thin film supported by a Ni–GDC porous anode is fabricated by dry-pressing and spin-coating processes, respectively. In comparison with dry pressing, it is easy to prepare a thinner electrolyte film by the novel spin-coating method. Cell performance is examined using humidified (3% H₂O) hydrogen as fuel and air as oxidant in the temperature range of 500–700 °C. Cell performance is strongly dependent on the electrolyte thickness. With a porous Ni–GDC anode, a dense 19-μm GDC electrolyte film and a porous La_0.6Sr_0.4Co_0.2Fe_0.8O₃–GDC cathode, the cell exhibits maximum power densities of 130, 253, 386 and 492 mW cm⁻² at 500, 550, 600 and 650 °C, respectively. It is also found that at the low operating temperature about 500 °C, the cell resistance is significantly dominated by the electrode polarization resistance.     

Performance of La0.75Sr0.25Cr0.5Mn0.5O3−δ perovskite-structure anode material at lanthanum gallate electrolyte for IT-SOFC running on ethanol fuel

Perovskite-structure La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCM) powders were prepared using a simple combustion process. Thermal analysis was carried out on the perovskite precursor to investigate the oxide-phase formation. The structural phase of the powders was determined by X-ray diffraction. These results showed that the decomposition of the precursors occurs in a two-step reaction and temperatures higher than 1100 °C are required for these decomposition reactions. For the electrochemical characterization, LSCM anode materials and (Pr_0.7Ca_0.3)_0.9MnO₃ (PCM) cathode materials were screen-printed on two sides of dense La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ (LSGM) electrolyte layers prepared by tape casting with a thickness of about 600 μm, respectively. The morphology of the screen-printed La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ perovskite thick films (65 μm) was investigated by field emission scanning electron microscope and showed a porous microstructure. In addition, fuel cell tests were carried out using humidified hydrogen or ethanol stream as fuel and oxygen as oxidant. The performance of the conventional electrolyte-supported cell LSCM/LSGM/PCM while operating on humidified hydrogen was modest with a maximum power density of 165, 99 and 62 mW cm⁻² at 850, 800 and 750 °C, respectively, the corresponding values for the cell while operating on ethanol stream was 160, 101 and 58 mW cm⁻², respectively. Cell stability tests indicate no significant degradation in performance has been observed after 60 h of cell testing when LSCM anode was exposed to ethanol steam at 750 °C, suggesting that carbon deposition was limited during cell operation.     

Silver infiltrated La0.6Sr0.4Co0.2Fe0.8O3 cathodes for intermediate temperature solid oxide fuel cells

Porous La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) electrodes on anode support cells were infiltrated with AgNO₃ solutions in citric acid and ethylene glycol. Two types of solid oxide fuel cells with the LSCF–Ag cathode, Ni–YSZ/YSZ/LSCF–Ag and Ni–Ce_0.9Gd_0.1O_1.95(GDC)/GDC/LSCF–Ag, were examined in a temperature range 530–730 °C under air oxidant and moist hydrogen fuel. The infiltration of about 18 wt.% Ag fine particles into LSCF resulted in the enhancement of the power density of about 50%. The maximum power density of Ni–YSZ/YSZ/LSCF was enhanced from 0.16 W cm⁻² to 0.25 W cm⁻² at 630 °C by infiltration of AgNO₃. No significant degradation of out-put power was observed for 150 h at 0.7 V and 700 °C. The Ni–GDC/GDC/LSCF–Ag cell showed the maximum power density of 0.415 W cm⁻² at 530 °C.     

Influence of water vapor on long-term performance and accelerated degradation of solid oxide fuel cell cathodes

The influence of water vapor in the air on the performance and durability of solid oxide fuel cell (SOFC) has been investigated for the-state-of-the-art cathodes, (La_0.8Sr_0.2)_0.98MnO₃ (LSM) and La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF). Durability experiments were carried out at 800 °C up to 1000 h with various water vapor containing-air fed to the cathode side. Both types of cathode materials were basically stable under typical water vapor concentrations in the ambient air. Degradations could be accelerated at much higher water vapor concentrations, which could be associated with the decomposition of the cathode materials. Temperature dependence of this degradation was analyzed between 700 °C and 900 °C under 10 vol% water vapor concentration, which showed that the effect of water vapor depends strongly on the temperature and led to a severe degradation at 700 °C within a short time period for both cathode materials.     

Development of LSCF–GDC composite cathodes for low-temperature solid oxide fuel cells with thin film GDC electrolyte

La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) powder was prepared by glycine–nitrate combustion method. The electrochemical properties of porous LSCF cathodes and LSCF–Gd_0.1Ce_0.9O_1.95 (GDC) composite cathodes were evaluated at intermediate/low temperatures of 500–700 °C. The polarization resistance of pure LSCF cathode sintered at 975 °C for 2 h was 1.20 Ω cm² at 600 °C. The good performance of pure LSCF cathode is attributed to its unique microstructure—small grain size, high porosity and large surface area. The addition of GDC to LSCF cathode further reduced the polarization resistance. The lowest polarization resistance of 0.17 Ω cm² was achieved at 600 °C for LSCF–GDC (40:60 wt%) composite cathode. An anode-supported solid oxide fuel cell (SOFC) was prepared using LSCF–GDC (40:60 wt%) composite as cathode, GDC film (49-μm-thick) as electrolyte, and Ni–GDC (65:35 wt%) as anode. The total electrode polarization resistance was 0.27 Ω cm² at 600 °C, which implies that LSCF–GDC (40:60 wt%) composite cathode used in the anode-supported SOFC had a polarization resistance lower than 0.27 Ω cm² at 600 °C. The cell generated good performance with the maximum power density of 562, 422, 257 and 139 mW/cm² at 650, 600, 550 and 500 °C, respectively.     

Performance of metal-supported SOFCs with infiltrated electrodes

Metal-supported solid oxide fuel cells (SOFCs) with thin YSZ electrolyte films and infiltrated Ni and LSM catalysts are operated in the temperature range 650–750 °C. A five-layer structure consisting of porous metal-support/porous YSZ interlayer/dense YSZ electrolyte film/porous YSZ interlayer/porous metal current collector is prepared at 1300 °C in reducing atmosphere. This cell structure is then sealed and joined to a cell housing/gas manifold using a commercially available braze. Finally, the porous YSZ interlayers are infiltrated with Ni and LSM catalyst precursor solutions at low temperature prior to cell testing. Infiltrating the catalysts after the high temperature sintering and brazing steps avoids undesirable decomposition of LSM, Ni coarsening, and interdiffusion between Ni catalyst and FeCr in the support. Maximum power densities of 233 and 332 mW cm⁻² were achieved at 650 and 700 °C, respectively, with air as oxidant. With pure oxygen as oxidant, power densities of 726, 993, and >1300 mW cm⁻² were achieved at 0.7 V at 650, 700, and 750 °C, respectively.     

Synthesis and electrochemical properties of (Pr–Nd)1−ySryMnO3−δ and (Pr1−xNdx)0.7Sr0.3MnO3−δ as cathode materials for IT-SOFC

(Pr–Nd)_1−ySr_yMnO_3−δ (P-NSM, y = 0.2, 0.25, 0.3, 0.35) powders made from commercial Pr–Nd mixed oxide, as well as (Pr_1−xNd_x)_0.7Sr_0.3MnO_3−δ (PN3SM, x = 0, 0.5, 0.7, 1) were synthesized by a glycine-nitrate process and characterized as cathode materials for intermediate temperature solid oxide fuel cell (IT-SOFC). XRD patterns showed the powders had formed pure perovskite phase after being calcined at 800 °C for 2 h. (Pr–Nd)_0.7Sr_0.3MnO_3−δ (P-N3SM) achieved a high conductivity of 194 S cm⁻¹ at 500 °C and showed a good chemical stability against YSZ at 1150 °C. And the thermal expansion coefficient of P-N3SM/YSZ cathode was 11.1 × 10⁻⁶ K⁻¹, which well matched YSZ electrolyte film. The tubular SOFC with P-N3SM/YSZ cathode exhibited the maximum power densities of 415, 367, 327 and 282 mW cm⁻² at 850, 800, 750 and 700 °C, respectively, which indicated P-N3SM was potentially applied in SOFC for low cost.     

Characteristics and performance of lanthanum gallate electrolyte-supported SOFC under ethanol steam and hydrogen

This study is focused on the electrochemical performance of perovskite-type materials based on doped LaGaO₃. La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ (LSGM) and La_0.8Sr_0.2Ga_0.8Mg_0.115Co_0.085O_3−δ (LSGMC) were used as electrolytes and (Pr_0.7Ca_0.3)_0.9MnO₃ (PCM) and La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCM) as cathode and anode material, respectively. LSGM and LSGMC electrolytes were prepared by tape casting with a thickness of about 600 μm. The performance of LSCM/LSGMC/PCM was slightly superior to that obtained on LSCM/LSGM/PCM at different temperatures in both humidified hydrogen and ethanol steam atmospheres, good values of power output in LSCM/LSGMC/PCM were 182 and 169 mW cm⁻² using humidified hydrogen and ethanol steam as fuel, respectively, and oxygen as oxidant at 850 °C. Cell stability tests indicate no significant degradation in performance after 60 h of cell testing when LSCM anode was exposed to ethanol steam at 750 °C. Almost no carbon deposits were detected after testing in ethanol steam at 750 °C for >60 h on the LSCM anodes, suggesting that carbon deposition was limited during cell operation.     

Sulfuric acid decomposition on Pt/SiC-coated-alumina catalysts for SI cycle hydrogen production

Sulfuric acid decomposition was conducted at atmospheric pressure and a GHSV of 72,000 mL/g_cat h in the temperature ranges from 650 to 850 °C. The Pt–Al (1wt% Pt/Al₂O₃) and and Pt–SiC–Al (1wt% Pt/SiC-coated-Al₂O₃) catalysts were prepared by an impregnation method. The Pt–Al catalyst rapidly deactivated at 650 and 700 °C, but was stable at 750 and 850 °C. The aluminum sulfate was observed on the spent Pt–Al catalyst by an FT-IR, an X-ray spectroscopy and a TGA/DSC analyzer, which was suggested to be a cause of the deactivation at lower reaction temperature. The alumina support was coated with SiC by a CVD method with methyltrichlorosilane (MTS) to get a non-corrosive support (SiC–Al) with high surface areas. The thermal analysis of the spent Pt–SiC–Al showed that the aluminum sulfate formation was suppressed during the sulfuric acid decomposition. The Pt–SiC–Al catalyst was not only active higher than the Pt–Al catalyst, but was also stable at all the tested reaction temperature.     

Fabrication and performance of a proton-conducting solid oxide fuel cell based on a thin BaZr0.8Y0.2O3−δ electrolyte membrane

A dense BaZr_0.8Y_0.2O_3−δ (BZY) proton-conducting electrolyte membrane is successfully fabricated on a NiO-BaZr_0.1Ce_0.7Y_0.2O_3−δ (NiO-BZCY) anode substrate by a co-pressing process after co-firing at 1400 °C. BZY powders are synthesized via a citric acid-nitrate gel combustion process after calcination at 1100 °C. The SEM results reveal that the BZY membrane is crack-free, very dense, and 20 μm thick. A single cell with Sm_0.5Sr_0.5CoO_3−δ-Ce_0.8Sm_0.2O_2−δ (SSC-SDC) as the cathode is assembled and tested with wet hydrogen (2% H₂O) as the fuel and static air as the oxidant. The open circuit voltages (OCVs) are 0.953, 0.987, 1.014, and 1.039 V at 700, 650, 600, and 550 °C, respectively. A maximum power density of 170 mW cm⁻² is obtained at 700 °C. Resistances of the testing cell are investigated under open circuit conditions at different operating temperatures by impedance spectroscopy.     

Performance and durability of nanostructured (La0.85Sr0.15)0.98MnO3/yttria-stabilized zirconia cathodes for intermediate-temperature solid oxide fuel cells

In this communication we report the fabrication of nanostructured (La_0.85Sr_0.15)_0.98MnO₃ (LSM)/yttria-stabilized zirconia (YSZ) composite cathodes consisting of homogeneously distributed and connected LSM and YSZ grains approximately 100 nm large. We also investigate for the first time the role of the cathode nanostructure on the performance and the durability of intermediate-temperature solid oxide fuel cells. The cathodes were fabricated using homogenous LSM/YSZ nanocomposite particles synthesized by co-precipitation, using YSZ nanoparticles of 3 nm as seed crystals. Detailed microstructural characterization by transmission electron microscopy with energy-dispersive X-ray spectroscopy revealed that many of the LSM/YSZ junctions in the cathode faced the homogeneously connected pore channels, indicating the formation of a considerable number of triple phase boundaries. The nanostructure served to reduce cathodic polarization. As a result, these anode-supported solid oxide fuel cells showed high power densities of 0.18, 0.40, 0.70 and 0.86 W cm⁻² at 650, 700, 750 and 800 °C, respectively, under the cell voltage of 0.7 V. Furthermore, no significant performance degradation of the cathode was observed during operation at 700 °C for 1000 h under a constant current density of 0.2 A cm⁻².     

High performance metal-supported intermediate temperature solid oxide fuel cells fabricated by atmospheric plasma spraying

The LSGM(La_0.8Sr_0.2Ga_0.8Mg_0.2O₃) electrolyte based intermediate temperature solid oxide fuel cells (ITSOFCs) supported by porous nickel substrates with different permeabilities are prepared by plasma spray technology for performance studies. The cell having a porous nickel substrate with a permeability of 3.4 Darcy, an LSCM(La_0.75Sr_0.25Cr_0.5Mn_0.5O₃) interlayer on the nickel substrate, a nano-structured LDC(Ce_0.55La_0.45O₂)/Ni anode functional layer, an LDC interlayer, an LSGM/LSCF(La_0.58Sr_0.4Co_0.2Fe_0.8O₃) cathode interlayer and an LSCF cathode current collector layer shows remarkable electric output power densities such as 1270 mW cm⁻² (800 °C), 978 mW cm⁻² (750 °C) and 702 mW cm⁻² (700 °C) at 0.6 V cell voltage under 335 ml min⁻¹ H₂ and 670 ml min⁻¹ air flow rates. SEM, TEM, EDX, AC impedance, voltage and power data with related analyses are presented here to support this high performance. The durability test of the cell with the best power performance shows a degradation rate of about 3% kh⁻¹ at the test conditions of 400 mA cm⁻² constant current density and 700 °C. Results demonstrate the success of APS technology for fabricating high performance metal-supported and LSGM based ITSOFCs.     

YSZ films fabricated by a spin smoothing technique and its application in solid oxide fuel cell

A dense single-layer YSZ film has been successfully fabricated by a spin smoothing method. Followed by a simplified slurry coating, an additional spin smoothing process was conducted to obtain a thinner and smoother film. By employment of high-viscosity slurry including high YSZ content, the film has a suitable thickness by a single coating cycle. With Sm_0.2Ce_0.8O_1.9 (SDC)-impregnated La_0.7Sr_0.3MnO₃ (LSM) cathode and porous NiO–YSZ anode, single solid oxide fuel cell (SOFC) based on an 8-μm-thick YSZ film was obtained. Open-circuit voltage (OCV) of the cell was 1.04 V at 800 °C, and maximum power densities were 676, 965 and 1420 mW cm⁻² at 700, 750 and 800 °C, respectively, using H₂ at a flow rate of 40 mL min⁻¹ as fuel and ambient air as oxidant. The power density could be increased to 1648 mW cm⁻² at 800 °C when the flow rate of H₂ was enhanced to 200 mL min⁻¹.     

High-performance cathode-supported SOFCs prepared by a single-step co-firing process

Cathode-supported solid oxide fuel cells (SOFCs), comprising porous Pr_0.35Nd_0.35Sr_0.3MnO_3−δ (PNSM)/Sm_0.2Ce_0.8O_1.95 (SDC) cathode supports, SDC function layers, YSZ electrolyte membranes and NiO/SDC anode layers, were successfully fabricated via suspensions coating and single-step co-firing process. The microstructures of electrolyte membranes were observed with scanning electron microscope (SEM). The assembled single cell was electrochemically characterized with humidified hydrogen as fuel and ambient air as oxidant. The open circuit voltage (OCV) of the cell was 1.036 V at 650 °C, and the peak power densities were 657, 472, 290 and 166 mW cm⁻² at 800, 750, 700 and 650 °C, respectively. Impedance analysis indicated that the performance of cathode-supported cell was determined essentially by electrode polarization resistance, which suggested that optimizing electrodes was especially important for improving the cell performance.     

A high performance BaZr0.1Ce0.7Y0.2O3-δ-based solid oxide fuel cell with a cobalt-free Ba0.5Sr0.5FeO3-δ–Ce0.8Sm0.2O2-δ composite cathode

A cobalt-free Ba_0.5Sr_0.5FeO_3-δ–Ce_0.8Sm_0.2O_2-δ (BSF–SDC) composite is employed as a cathode for an anode-supported proton-conducting solid oxide fuel cells (H-SOFCs) using BaZr_0.1Ce_0.7Y_0.2O_3-δ (BZCY) as the electrolyte. The chemical compatibility between BSF and SDC is evaluated. The XRD results show that BSF is chemically compatible with SDC after co-fired at 1000 °C for 6 h. A single cell with a 20-μm-thick BZCY electrolyte membrane exhibits excellent power densities as high as 792 and 696 mW cm⁻² at 750 and 700 °C, respectively. To the best of our knowledge, this is the highest performance reported in literature up to now for BZCY-based single cells with cobalt-free cathode materials. Extremely low polarization resistances of 0.030 and 0.044 Ωcm² are achieved at 750 and 700 °C respectively. The excellent performance implies that the cobalt-free BSF–SDC composite is a promising alternative cathode for H-SOFCs. Resistances of the tested cell are investigated under open circuit conditions at different operating temperatures by impedance spectroscopy.