Thin yttria-stabilized zirconia electrolyte and transition layers fabricated by particle suspension spray

In order to develop high performance intermediate temperature (<800 °C) solid oxide fuel cells (SOFCs) with a lower fabrication cost, a pressurized spray process of ceramic suspensions has been established to prepare both dense yttria-stabilized zirconia (YSZ) electrolyte membranes and transition anode layers on NiO + YSZ anode supports. A single cell with 10 μm thick YSZ electrolyte on a porous anode support and ∼20 μm thick cathode layer showed peak power densities of only 212 mW cm⁻² at 700 °C and 407 mW cm⁻² for 800 °C. While a cell with 10 μm thick YSZ electrolyte and a transition layer on the porous anode support using a ultra-fine NiO + YSZ powder showed peak power densities of 346 and 837 mW cm⁻² at 700 and 800 °C, respectively. The dramatic improvement of cell performance was attributed to the much improved anode microstructure that was confirmed by both scanning electron microscopes (SEM) observation and impedance spectroscopy. The results have demonstrated that a pressurized spray coating is a suitable technique to fabricate high performance SOFCs and at lower cost.     

Anode-supported solid oxide fuel cell with yttria-stabilized zirconia/gadolinia-doped ceria bilalyer electrolyte prepared by wet ceramic co-sintering process

To protect the ceria electrolyte from reduction at the anode side, a thin film of yttria-stabilized zirconia (YSZ) is introduced as an electronic blocking layer to anode-supported gadolinia-doped ceria (GDC) electrolyte solid oxide fuel cells (SOFCs). Thin films of YSZ/GDC bilayer electrolyte are deposited onto anode substrates using a simple and cost-effective wet ceramic co-sintering process. A single cell, consisting of a YSZ (∼3 μm)/GDC (∼7 μm) bilayer electrolyte, a La_0.8Sr_0.2Co_0.2Fe_0.8O₃–GDC composite cathode and a Ni–YSZ cermet anode is tested in humidified hydrogen and air. The cell exhibited an open-circuit voltage (OCV) of 1.05 V at 800 °C, compared with 0.59 V for a single cell with a 10-μm GDC film but without a YSZ film. This indicates that the electronic conduction through the GDC electrolyte is successfully blocked by the deposited YSZ film. In spite of the desirable OCVs, the present YSZ/GDC bilayer electrolyte cell achieved a relatively low peak power density of 678 mW cm⁻² at 800 °C. This is attributed to severe mass transport limitations in the thick and low-porosity anode substrate at high current densities.     

Characterization of a circular 80 mm anode supported solid oxide fuel cell (AS-SOFC) with anode support produced using high-pressure injection molding (HPIM)

The current study was oriented at analyzing the performance of an anode-supported solid oxide fuel cell produced using high-pressure injection molding. The cell with a total thickness of 550 μm was produced in the Ceramic Department (CEREL) of the Institute of Power Engineering in Poland and experimentally analyzed in the Energy Department (DENERG) of Politecnico di Torino in Italy. The high-pressure injection molding technique was applied to produce a 500 μm thick anode support NiO/8YSZ 66/34 wt% with porosity of 25 vol%. The screen printing method was used to print a 3 μm thick NiO anode contact layer, 7 μm thick NiO/8YSZ 50/50 wt% anode functional layer, 4 μm thick 8YSZ dense electrolyte, 1.5 μm thick Gd_0,1Ce_0,9O₂ barrier layer and a 30 μm thick La_0,6Sr_0,4Fe_0,8Co_0,2O_3–δ cathode with porosity 25 vol%.The experimental characterization was done at two temperature levels: 750 and 800 °C under fixed anodic and cathodic flow and compositions. The preliminary studies on the application of high-pressure injection molding are discussed together with the advantages of the technology. The performance of two generations of anode-supported cells is compared with data of reference cells with supports obtained using tape casting.     

Performance and stability of SOFC anode fabricated from NiO–YSZ composite particles

Ni–YSZ cermet anodes for solid oxide fuel cells (SOFCs) were fabricated at various sintering temperatures from NiO–YSZ composite particles made by spray pyrolysis (SP) technique. NiO particles covered with fine YSZ (Y₂O₃ stabilized ZrO₂) particles were used as the composite particles, and the initial ratio of Ni and YSZ was set at 75:25 (mol%). As a result, the cermet anode sintered at 1350 °C showed the morphology in which fine YSZ grains were uniformly dispersed on the surface of Ni grain network. Electrical performance such as electrochemical activity and internal resistance of a Ni–YSZ cermet anode changed with sintering temperature. The anode fabricated at 1350 °C showed the highest electrical performance. Especially, a single cell voltage with the Ni–YSZ cermet anode kept very stable for 8000 h at 1000 °C in the SOFC operation condition of H₂—3% H₂O and air. The cermet anode after a long-term test had its initial morphology. It indicates that the Ni–YSZ cermet anode fabricated from NiO–YSZ composite particles is a very promising material for its practical use as SOFCs.     

Anode-supported solid oxide fuel cell based on dense electrolyte membrane fabricated by filter-coating

A simple and cost-effective technique, filter-coating, has been developed to fabricate dense electrolyte membranes. Eight mole percent yttria-stabilized zirconia (YSZ) electrolyte membrane as thin as 7 μm was prepared by filter-coating on a porous substrate. The thickness of the YSZ film was uniform, and could be readily controlled by the concentration of the YSZ suspension and the rate of the suspension deposition. The YSZ electrolyte film was dense and was well bonded to the Ni-YSZ anode substrate. An anode-supported solid oxide fuel cell (SOFC) with a YSZ electrolyte film and a La_0.85Sr_0.15MnO₃ (LSM) + YSZ cathode was fabricated and its performance was evaluated between 700 and 850 °C with humidified hydrogen as the fuel and ambient air as the oxidant. An open circuit voltage (OCV) of 1.09 V was observed at 800 °C, which was close to the theoretical value, and the maximum power density measured was 1050 mW cm⁻². The results demonstrate that the dense YSZ film fabricated by filter-coating is suitable for application to SOFCs.     

A study of Ni + 8YSZ/8YSZ/La0.6Sr0.4CoO3−δ ITSOFC fabricated by atmospheric plasma spraying

An intermediate temperature solid oxide fuel cell (ITSOFC) based on 8YSZ electrolyte, La_0.6Sr_0.4CoO_3−δ (LSCo) cathode, and Ni − 8YSZ anode coatings were consecutively deposited onto a porous Ni-plate substrate by atmospheric plasma spraying (APS). The spray parameters including current, argon and hydrogen flow rate, and powder feed rate were investigated by an orthogonal experiment to fabricate a thin gas-tight 8YSZ electrolyte coating (80 μm). By proper selection of the spray parameters to decrease the particles velocity and temperature, the sprayed NiO + 8YSZ coating after reducing with hydrogen shows a good electrocatalytic activity for H₂ oxidation. With the same treatment, 100–170 μm dimensions LSCo particle could keep phase structure after spraying. And the deposited LSCo cathode shows a good cathode performance and chemical compatibility with 8YSZ electrolyte after operating at 800 °C for 50 h. Output power density of the sprayed cell achieved 410 mW cm⁻² at 850 °C and 260 mW cm⁻² at 800 °C. Electrochemical characterization indicated that IR drop of 8YSZ electrolyte, cathodic polarization, and the contact resistance at LSCo/8YSZ interface were the main factors restricting the cell performance. The results suggested that the use of APS cell allowed the reduction of the operating temperature of the SOFC to below 850 °C with lower production costs.     

NiO/YSZ,anode-supported,thin-electrolyte,solid oxide fuel cells fabricated by gel casting

A simple and cost-effective gel-casting technique is developed and optimized to fabricate NiO/stabilized yttria–zirconia (YSZ) anode-supported solid oxide fuel cells (SOFCs). The effect of ammonium poly-(methacrylate) (PMAA) dispersant and pH on the zeta potential of YSZ and NiO particles and the viscosity of the NiO/YSZ slurries is studied in detail. The results show that the absolute zeta potential of YSZ and NiO particles reaches a maximum value at pH value ∼10 and the viscosity of the NiO/YSZ slurry is lowest when the PMAA dispersant content is 1.5 wt.%. A gel-cast NiO/YSZ anode-supported button cell with a spin-coated, thin, YSZ electrolyte film (∼9 μm) and a La_0.72Sr_0.18MnO_3−δ (LSM)/YSZ composite cathode gives a peak power output of 1.07 and 0.65 W cm⁻² at 900 and 800 °C under humidified hydrogen and air. The effect of a graphite pore-former in the gelation and microstructure of NiO/YSZ anode substrates is investigated.     

Upgrading the performance of La2Mo2O9-based solid oxide fuel cell under single chamber conditions

Various anode-supported solid oxide fuel cells (SOFC), based on 10 mol% Dy-doped La₂Mo₂O₉ (LDM) electrolyte, are prepared analytically and operated under single chamber conditions to explore the connections between electrode and power performance. The cathode of tested SOFCs is compositionally graded with three composites of samarium strontium cobaltite and Gd-doped ceria (GDC) to relax the thermal stress, because of sizable thermal expansion differences above 400 °C. We focus the research attention on varying the anode pore structure and composition to promote the power performance in methane/air mixture at 700 °C. For the one-layer support of GDC+NiO+LDM anode, addition of 10 wt% graphite minimizes its mass transport resistance through creating 8–5 μm long and ∼1 μm wide slit-shaped pores. The graphite pore former raises the peak power value by 80 mW cm⁻². Adopting a more porous and active outer layer, the double-layer support further enhances the cell power. The peak power was first raised by 48 mW cm⁻², using an outer layer that was prepared with 63 wt% NiO. Dosing 3% Pd on this outer layer uplifts another 59 mW cm⁻². In this study, with an improved anode, the peak power value reaches 437 mW cm⁻².     

Fabrication and characterization of planar-type SOFC unit cells using the tape-casting/lamination/co-firing method

In this study, solid oxide fuel cells (SOFCs) consisting of a NiO-YSZ anode, a NiO/YSZ-YSZ functional layer, YSZ electrolyte and a (La_0.8Sr_0.2)MnO₃ + yttria-stabilized zirconia (LSM-YSZ) cathode were fabricated by tape-casting, lamination, and a co-firing process. NiO/YSZ-YSZ nano-composite powder was synthesized for the anode functional layer via the Pechini process in order to improve cell performance. After optimization of the slurries for the anode functional anode, electrolyte and cathode, all components were casted so as to fabricate the monolithic laminate. The co-firing temperature was optimized to minimize second phase formation between the (La_0.8Sr_0.2)MnO₃ (LSM) and yttria-stabilized zirconia (YSZ) and to increase the sinterability of the YSZ electrolyte. The YSZ electrolyte was fully sintered with the addition of 0.5 wt% CuO, and the second phases of La₂Zr₂O₇ and SrZrO₃ did not form at 1350 °C. Ni-YSZ anode-supported unit cells were fabricated by co-firing at 1250-1400 °C. The unit cells co-fired at 1250 °C, 1300 °C, 1325 °C, 1350 °C and 1400 °C had maximum power densities of 0.18, 0.18, 0.30, 0.46 and 0.036 W/cm², respectively, in humidified hydrogen (∼3% H₂O) and air at 800 °C.     

High-performance NdSrCo2O5+δ–Ce0.8Gd0.2O2-δ composite cathodes for electrolyte-supported microtubular solid oxide fuel cells

NdSrCo₂O_5+δ (NSCO) is a perovskite with an electrical conductivity of 1551.3 S cm⁻¹ at 500 °C and 921.7 S cm⁻¹ at 800 °C and has a metal-like temperature dependence. This perovskite is used as the cathode material for Ce_0.8Gd_0.2O_2-δ (GDC)-supported microtubular solid oxide fuel cells (MT-SOFCs). The MT-SOFCs fabricated in this study consist of a bilayer anode, comprising a NiO–GDC composite layer and a NiO layer, and a NSCO–GDC composite cathode. Three cell designs with different outer tube diameters, GDC thicknesses, and NSCO/GDC ratios are designed. The MT-SOFC with an outer tube diameter of 1.86 mm, an electrolyte thickness of 180 μm, and a 5NSCO–5GDC composite cathode presents the best performance. The flexural strength of the aforementioned cell is 177 MPa, which is sufficient to confer mechanical integrity to the cell. Moreover, the ohmic and polarization resistance values of the cell are 0.22 and 0.09 Ω cm² at 700 °C, respectively, and 0.15 and 0.03 Ω cm² at 800 °C, respectively. These results indicate that the NSCO-GDC composite exhibits high electrochemical activity. The maximum power densities of the cell at 700 and 800 °C are 0.46 and 0.67 W cm⁻², respectively, exceeding those of existing electrolyte-supported MT-SOFCs with similar electrolyte thicknesses.     

NiO–YSZ cermets supported low temperature solid oxide fuel cells

Solid oxide fuel cells with thin electrolyte of two types, Sm_0.2Ce_0.8O_1.9 (SDC) (15 μm) single-layer and 8 mol% Yttria stabilized zirconia (YSZ) (5 μm) + SDC (15 μm) bi-layer on NiO–YSZ cermet substrates were fabricated by screen printing and co-firing. A Sm_0.5Sr_0.5CoO₃ cathode was printed, and in situ sintered during a cell performance test. The SDC single-layer electrolyte cell showed high electrochemical performance at low temperature, with a 1180 mW cm⁻² peak power density at 650 °C. The YSZ + SDC bi-layer electrolyte cell generated 340 mW cm⁻² peak power density at 650 °C, and showed good performance at 700–800 °C, with an open circuit voltage close to theoretical value. Many high Zr-content micro-islands were found on the SDC electrolyte surface prior to the cathode preparation. The influence of co-firing temperature and thin film preparation methods on the Zr-islands’ appearance was investigated.     

Anode performance control of micro-tubular SOFC via wet coating method

A cathode-supported micro SOFC was prepared via co-sintering technique of a scandia-stabilized zirconia (ScSZ) electrolyte layer and a micro-tubular (La,Sr)_xMnO_3−δ (LSM) support, and subsequent deposition of various anode layers by dip-coating method. The micro-tubular SOFCs were electrochemically evaluated in a humidified H₂ (3% H₂O) atmosphere. An LSM-Ce_0.9Gd_0.1O_1.95 activation layer was also introduced between the cathode tube and the electrolyte layer in order to improve the catalytic activation at the cathode side. The micro SOFCs exhibited a stable open circuit voltage above 1.05 V at 650 °C, and the cells with the anode film thicknesses of 8, 30 and 50 μm generated a maximum power density of 36, 49 and 126 mW/cm², respectively. And, the cell with 50 μm thick anode layer showed about 10 times higher exchange current density than the others, which indicates that the anode performance on the cathode-supported micro SOFC was greatly affected by the thickness of the anode coating layer.     

Combined Cu‐CeO2 /YSZ and Ni/YSZ dual layer anode structures for direct methane solid oxide fuel cells

In this study, a conventional Ni/yttria‐stabilized zirconia (YSZ) anode and a new Cu‐CeO₂‐YSZ anode structure were assembled in an attempt to combine the advantages of both structures for use in direct methane solid oxide fuel cells. For this purpose, only a limited region (≤20 μm) of NiO/YSZ was deposited at the boundary of the electrolyte to benefit from the superior catalytic activity of Ni in the cells, while the rest of the cell benefited from the Cu‐CeO₂‐YSZ anode structure, which does not cause cracking reactions. First, the effects of different pore formers on the anode skeleton, as well as the interactions of the Ni‐Cu species in the anode skeleton, are discussed. Then, the NiO/YSZ‐interlayer‐containing button cells with different thicknesses (≤20) and different ratios of NiO (40 wt%, 50 wt%, and 60 wt%) were studied. After the examination of the cells, 2 model cells with outstanding performance and 2 additional internal reference cells, conventional Ni/YSZ and Cu‐CeO₂‐YSZ, were scaled up, and performance analysis and long‐term stability studies were carried out. As a result, for solid oxide fuel cells with increased carbonization resistance (around 6% performance loss due to carbonization after 100‐hour stability testing) and 86.1% of the initial performance of the conventional Ni/YSZ anode structure, a 15‐μm‐thick 40 wt% NiO/60 wt% YSZ interlayer with a dual layer anode structure is proposed.     

Ni-SDC cermet anode fabricated from NiO–SDC composite powder for intermediate temperature SOFC

We report a cost-effective processing method for fabricating intermediate temperature solid oxide fuel cells (SOFCs) with Ni-samaria doped ceria (SDC) anode. First, SDC and NiO powders were mechanically treated to make their composite powder. Then, the composite powder was applied into a ceramic tape casting method to form a thick layer for the anode supporting. Finally, an anode supported single cell with a configuration of Ni-SDC/SDC/La_0.6Sr_0.4Co_0.2Fe_0.8O_3 − δ (LSCF) was prepared. Because of the usage of the composite powder, homogenous distribution and connection of each Ni and SDC were achieved. Peak power densities of 460, 750 and 910 mW cm⁻² were obtained on the single cell at 550, 600 and 650 °C, respectively.     

Effect of magnetron sputtered anode functional layer on the anode-supported solid oxide fuel cell performance

Nickel oxide-yttria stabilized zirconia (NiO-YSZ) thin films were reactively sputter-deposited by pulsed direct current magnetron sputtering from the Ni and ZrY targets onto heated commercial NiO-YSZ substrates. The microstructure and composition of the deposited films were investigated with regard to application as thin anode functional layers (AFLs) for solid oxide fuel cells (SOFCs). The pore size, microstructure and phase composition of both as-deposited and annealed at 1200 °C for 2 h AFLs were studied by scanning electron microscopy and X-ray diffractometry and controlled by changing the deposition process parameters. The results show that annealing in air at 1200 °C is required to improve structural homogeneity of the films. NiO-YSZ films have pores and grains of several hundred nanometers in size after reduction in hydrogen. Adhesion of deposited films was evaluated by scratch test. Anode-supported solid oxide fuel cells with the magnetron sputtered anode functional layer, YSZ electrolyte and La_0.6Sr_0.4Co_0.2Fe_0.8O₃/Ce_0.9Gd_0.1O₂ (LSCF/CGO) cathode were fabricated and tested. Influence of thin anode functional layer on performance of anode-supported SOFCs was studied. It was shown that electrochemical properties of the single fuel cells depend on the NiO volume content in the NiO-YSZ anode functional layer. Microstructural changes of NiO-YSZ layers after nickel reduction-oxidation (redox) cycling were studied. After nine redox cycles at 750 °C in partial oxidation conditions, the cell with the anode NiO-YSZ layer showed stable open circuit voltage values with the power density decrease by 11% only.     

Behavior of lanthanum-doped ceria and Sr-, Mg-doped LaGaO3 electrolytes in an anode-supported solid oxide fuel cell with a La0.6Sr0.4CoO3 cathode

Anode-supported solid oxide fuel cells (SOFCs) with lanthanum-doped ceria (LDC)/Sr-, Mg-doped LaGaO₃ (LSGM) bilayered or LDC/LSGM/LDC trilayered electrolyte films were fabricated with a pure La_0.6Sr_0.4CoO₃ (LSC) cathode. The behaviors of the two electrolytes in cells were investigated by using scanning electron microscopy, impedance spectroscopy and cell performance measurements. The reactions between LSGM and anode material can be suppressed by applying a ca. 15 μm LDC film. Due to the Co diffusion from the LSC cathode to the LSGM electrolyte during high temperature sintering, the electronic conductivity of the LDC electrolyte cannot be completely blocked with an LSGM layer below 50 μm, which leads to open-circuit potentials of these cells of ca. 0.988 V at 800 °C. The electrical conductivities of LDC and LSGM electrolytes in the cells under operation conditions are obtained from the dependence of the cell ohmic resistance on the electrolyte thickness. The electrical conductivity of LDC electrolyte is ca. 0.117 S cm⁻¹ at 800 °C on the bilayered electrolyte cells with a 50 μm LSGM layer. The bilayer electrolyte cells with a 25 μm LDC layer at 800 °C, had a cell ohmic resistance two-stage linear dependence on the LSGM layer thickness, which showed the electrical conductivity of ca. 1.9 S cm⁻¹ for the LSGM layer below 50 μm and 0.22 S cm⁻¹ for the LSGM layer above 100 μm. With a LDC/LSGM/LDC trilayered electrolyte film for the anode-supported cell, an open-circuit potential of 1.043 V was achieved.     

Development and testing of anode-supported solid oxide fuel cells with slurry-coated electrolyte and cathode

A laboratory setup was designed and put into operation for the development of solid oxide fuel cells (SOFCs). The whole project consisted of the preparation of the component materials: anode, cathode and electrolyte, and the buildup of a hydrogen leaking-free sample chamber with platinum leads and current collectors for measuring the electrochemical properties of single SOFCs. Several anode-supported single SOFCs of the type (ZrO₂:Y₂O₃ + NiO) thick anode/(ZrO₂:Y₂O₃) thin electrolyte/(La_0.65Sr_0.35MnO₃ + ZrO₂:Y₂O₃) thin cathode have been prepared and tested at 700 and 800 °C after in situ H₂ anode reduction. The main results show that the slurry-coating method resulted in single-cells with good reproducibility and reasonable performance, suggesting that this method can be considered for fabrication of SOFCs.     

Achieving high mechanical-strength CH4-based SOFCs by low-temperature sintering (1100 °C)

Despite much progress achieved in the past decades in the process of advancing the low-temperature sintering technologies for Solid oxide fuel cells (SOFCs), such as via the structure design of the electrode materials, the practical application of low-temperature sintered SOFCs (with disqualified mechanical strength) remains challenging. In this work, first, we demonstrate that the appropriate amount of CuO as sintering aids can successfully reduce the co-firing temperature of conventional micron size NiO-YSZ (yttrium-stabilized zirconia (Y₂O₃)_0.08–(ZrO₂)_0.92) anode from about 1400 °C to only 1100 °C. Second, the quantitative structure-activity relationship among the mechanical strength (low-temperature sintering ability) of anode cermets with the inclusion of CuO contents and the densification of YSZ electrolyte was synthetically evaluated, and the optimal Cu–NiO-YSZ anode composition demonstrates almost the equal mechanical strength when compared with the traditional NiO-YSZ anode (sintering at 1400 °C). At last, by comprehensive assessment, 8%Cu–52NiO-40YSZ (8%CuO–NiO-YSZ) shows excellent low-temperature sintering ability, high mechanical strength, optimal power output, and anti-carbon deposition when using as hydrocarbon-based anode for SOFCs.     

In situ screen-printed BaZr0.1Ce0.7Y0.2O3−δ electrolyte-based protonic ceramic membrane fuel cells with layered SmBaCo2O5+x cathode

In order to develop a simple and cost-effective route to fabricate protonic ceramic membrane fuel cells (PCMFCs) with layered SmBaCo₂O_5+x (SBCO) cathode, a dense BaZr_0.1Ce_0.7Y_0.2O_3?δ (BZCY) electrolyte was fabricated on a porous anode by in situ screen printing. The porous NiO–BaZr_0.1Ce_0.7Y_0.2O_3?δ (NiO–BZCY) anode was directly prepared from metal oxide (NiO, BaCO₃, ZrO₂, CeO₂ and Y₂O₃) by a simple gel-casting process. An ink of metal oxide (BaCO₃, ZrO₂, CeO₂ and Y₂O₃) powders was then employed to deposit BaZr_0.1Ce_0.7Y_0.2O_3?δ (BZCY) thin layer by an in situ reaction-sintering screen printing process on NiO–BZCY anode. The bi-layer with 25 μm dense BZCY electrolyte was obtained by co-sintering at 1400 °C for 5 h. With layered SBCO cathode synthesized by gel-casting on the bi-layer, single cells were assembled and tested with H₂ as fuel and the static air as oxidant. A high open-circuit potential of 1.01 V, a maximum power density of 382 mW cm^?2, and a low polarization resistance of the electrodes of 0.15 Ω cm² was achieved at 700 °C.     

Metal-supported solid oxide fuel cells with in-situ sintered (Bi2O3)0.7(Er2O3)0.3–Ag composite cathode

Metal-supported solid oxide fuel cells (SOFCs) containing porous 430L stainless steel support, Ni-YSZ anode and YSZ electrolyte were fabricated by tape casting, laminating and co-firing in a reduced atmosphere. (Bi₂O₃)_0.7(Er₂O₃)_0.3–Ag composite cathode was applied by screen printing and in-situ sintering. The polarization resistances of the composite cathode were 1.18, 0.48, 0.18, 0.09 Ω cm² at 600, 650, 700 and 750 °C, respectively. A promissing maximum power density of 568 mW cm⁻² at 750 °C was obtained of the single cell. Short-term stability was measured as well.