Development of a novel proton conducting fuel cell based on a Ni‐YSZ support

A new proton conducting fuel cell design based on the BZCYYb electrolyte is studied in this research. In high‐performance YSZ‐based SOFCs, the Ni‐YSZ support plays a key role in providing required electrical properties and robust mechanical behavior. In this study, this well‐established Ni‐YSZ support is used to maintain the proton conducting fuel cell integrity. The cell is in a Ni‐YSZ (375 μm support)/Ni‐BZCYYb (20 μm anode functional layer)/BZCYYb (10 μm electrolyte)/LSCF‐BZCYYb (25 μm cathode) configuration. Maximum power density values of 166, 218, and 285 mW/cm² have been obtained at 600°C, 650°C, and 700°C, respectively. AC impedance spectroscopy results show values of 2.17, 1.23, and 0.76 Ω·cm² at these temperatures where the main resistance contributor above 600°C is ohmic resistance. Very fine NiO and YSZ powders were used to achieve a suitable sintering shrinkage which can enhance the electrolyte sintering. During cosintering of the support and BZCYYb electrolyte layers, the higher shrinkage of the support layer led to compressive stress in the electrolyte, thereby enhancing its densification. The promising results of the current study show that a new generation of proton conducting fuel cells based on the chemically and mechanically robust Ni‐YSZ support can be developed which can improve long‐term performance and reduce fabrication costs of proton conducting fuel cells.     

Fabrication and Characterization of Anode‐Supported Low‐Temperature SOFC Based on Gd‐Doped Ceria Electrolyte

Large‐size, 9.5 cm × 9.5 cm, Ni‐Gd_0.1Ce_0.9O_1.95 (Ni‐GDC) anode‐supported solid oxide fuel cell (SOFC) has been successfully fabricated with NiO‐GDC anode substrate prepared by tape casting method and thin‐film GDC electrolyte fabricated by screen‐printing method. Influence of the sintering shrinkage behavior of NiO‐GDC anode substrate on the densification of thin GDC electrolyte film and on the flatness of the co‐sintered electrolyte/anode bi‐layer was studied. The increase in the pore‐former content in the anode substrate improved the densification of GDC electrolyte film. Pre‐sintering temperature of the anode substrate was optimized to obtain a homogeneous electrolyte film, significantly reducing the mismatch between the electrolyte and anode substrate and improving the electrolyte quality. Dense GDC electrolyte film and flat electrolyte/anode bi‐layer can be fabricated by adding 10 wt.% of pore‐former into the composite anode and pre‐sintering it at 1,100 °C for 2 h. Composite cathode, La_0.6Sr_0.4Fe_0.8Co_0.2O₃, and GDC (LSCF‐GDC), was screen‐printed on the as‐prepared electrolyte surface and sintered to form a complete single cell. The maximum power density of the single cell reached 497 mW cm^–2 at 600 °C and 953 mW cm^–2 at 650 °C with hydrogen as fuel and air as oxidant.     

Optimization of a ScCeSZ/GDC bi-layer electrolyte fabrication process for intermediate temperature solid oxide fuel cells

Cost-effective wet ceramic coating techniques for fabricating ScCeSZ/GDC bi-layer electrolyte anode-supported button cells were investigated in this study. Aqueous ceramic slurries were prepared by ball milling and then used for Ni/ScCeSZ half cell fabrication by tape casting and spin coating. Prepared cells were tested at operating temperature between 700 and 800°C with a fuel composition of hydrogen:nitrogen 3:1 and air at the cathode. The cell with a spin coated GDC film showed the maximum power density of 1.142, 1.012, 0.813 W?cm^?2 at 800, 750, and 700°C, respectively. It was also able to produce power output around 0.7 W?cm^?2 for 500 h at 750°C, which confirms the cell operational stability. More importantly, the GDC film prepared by spin coating effectively avoided the formation of the (Zr,Ce)O₂^?based solid solution at the ceria/zirconia interface compared with the other cells with the co-casted and sintered GDC film.     

Synthesis and characterization of co-doped ceria-based electrolyte material for low temperature solid oxide fuel cell

Co-doped CeO₂ (Ba_0.10Ga_0.10Ce_0.80O_3–δ) was synthesized via a cost-effective co-precipitation technique, and the electrochemical properties of the solid oxide fuel cell were studied. The microstructural and surface morphological properties were investigated by XRD and SEM, respectively. The structure of the prepared material was found to be cubic fluorite with an average crystallite size of 36?nm. The ionic conductivity of the prepared BGC (Ba_0.10Ga_0.10Ce_0.80O_3–δ) electrolyte material was measured as 0.071?S?cm^?1. The activation energy was found to be 0.46?eV using an Arrhenius plot. The maximum power density and current density achieved were 375?mW?cm^?2 and 893?mA?cm^?2, respectively, at 650?°C with hydrogen as a fuel. This study shows that the prepared co-doped electrolyte material could be used as a potential electrolyte to lower the operating temperature of solid oxide fuel cells.     

Dense 8 mol% yttria-stabilized zirconia electrolyte by DLP stereolithography

Solid Oxide Fuel Cells (SOFCs) are environmentally efficient energy conversion devices, but are partially limited by the complicated fabrication procedure. In this work, dense 8 mol% yttria-stabilized zirconia (8YSZ) ceramics were successfully realized through a DLP (digital light processing) stereolithography method and the electrolyte self-supported fuel cell was also tested at 800 °C. The sintering behavior of the as-printed planar samples were investigated and a fully dense ceramic can be achieved at 1450 °C. The total conductivity of the sintered 8YSZ can reach 2.18 × 10⁻² S cm⁻¹ at a test temperature of 800 °C, which is acceptable for practical application. For the electrolyte self-supported fuel cell test, a power density of 114.3 mW cm⁻² can be achieved when Ni-8YSZ cermet and La_0.8Sr_0.2MnO₃ (LSM) were used as anode and cathode. It was demonstrated that 3D printing is a promising processing technique to build up electrolyte self-supported SOFCs with desired structure for the future development.     

Perovskite SrFe1-xTixO3-δ (x < = 0.1) cathode for low temperature solid oxide fuel cell

Stable and compatible cathode materials are a key factor for realizing the low-temperature (LT, ≤600?°C) operation and practical implementations of solid oxide fuel cells (SOFCs). In this study, perovskite oxides SrFe_1-xTi_xO_3-δ (x?< = 0.1), with various ratios of Ti doping, are prepared by a sol-gel method for cathode material for LT-SOFCs. The structure, morphology and thermo-gravimetric characteristics of the resultant SFT powders are investigated. It is found that the Ti is successfully doped into SrFeO_3-δ to form a single phase cubic perovskite structure and crystal structure of SFT shows better stability than SrFeO_3-δ. The dc electrical conductivity and electrochemical properties of SFT are measured and analysed by four-probe and electrochemical impedance spectra (EIS) measurements, respectively. The obtained SFT exhibits a very low polarization resistance (R_p), .01 Ωcm² at 600?C. The SFT powders using as cathode in fuel cell devices, exhibit maximum power density of 551?mW?cm^?2 with open circuit voltage (OCV) of 1.15?V at 600?C. The good performance of the SFT cathode indicates a high rate of oxygen diffusion through the material at cathode. By enabling operation at low temperatures, SFT cathodes may result in a practical implementation of SOFCs.     

Fabrication and Performance of Solid Oxide Fuel Cells with La0.2Sr0.7TiO3–δ as Anode Support and La2NiO4+δ as Cathode

A novel fabrication process for solid oxide fuel cells (SOFCs) with La_0.2Sr_0.7TiO_3–δ (LST_A–) as anode support and La₂NiO_4+δ (LNO) as cathode material, which avoids complicated impregnation process, is designed and investigated. The LST_A– anode‐supported half cells are reduced at 1,200 °C in hydrogen atmosphere. Subsequently, the LNO cathode is sintered on the YSZ electrolyte at 1,200 °C in nitrogen atmosphere and then annealed in situ at 850 °C in air. The results of XRD analysis and electrical conductivity measurement indicate that the structure and electrochemical characteristics of LNO appear similar before and after the sintering processes of the cathode. By using La_0.6Sr_0.4CoO_3–δ (LSC) as current collector, the cell with LNO cathode sintered in nitrogen atmosphere exhibits the power density at 0.7 V of 235 mW cm⁻² at 800 °C. The ohmic resistance (R_S) and polarization resistance (R_P) are 0.373 and 0.452 Ω cm², respectively. Compared to that of the cell with the LNO cathode sintered in air, the sintering processes of the cell with the LNO cathode sintered in nitrogen atmosphere can result in better electrochemical performance of the cell mainly due to the decrease in R_S. The microstructures of the cells reveal a good adhesion between each layer.     

Intermediate Temperature Anode‐Supported Fuel Cell Based on BaCe0.9Y0.1O3 Electrolyte with Novel Pr2NiO4 Cathode

A proton conducting ceramic fuel cell (PCFC) operating at intermediate temperature has been developed that incorporates electrolyte and electrode materials prepared by flash combustion (yttrium‐doped barium cerate) and auto‐ignition (praseodymium nickelate) methods. The fuel cell components were assembled using an anode‐support approach, with the anode and proton ceramic layers prepared by co‐pressing and co‐firing, and subsequent deposition of the cathode by screen‐printing onto the proton ceramic surface. When the fuel cell was fed with moist hydrogen and air, a high Open Circuit Voltage (OCV > 1.1 V) was observed at T > 550 °C, which was stable for 300 h (end of test), indicating excellent gas‐tightness of the proton ceramic layer. The power density of the fuel cell increased with temperature of operation, providing more than 130 mW cm^–2 at 650 °C. Symmetric cells incorporating Ni‐BCY10 cermet and BCY10 electrolyte on the one hand, and Pr₂NiO_{4 + δ} and BCY10 electrolyte on the other hand, were also characterised and area specific resistances of 0.06 Ω cm² for the anode material and 1–2 Ω cm² for the cathode material were obtained at 600 °C.     

Improved electrochemical performance of Bi doped La0.8Sr0.2FeO3-δ nanofiber cathode for IT-SOFCs via electrospinning

In this study, perovskite La_0.8-xBi_xSr_0.2FeO_3-δ (LBSF, x = 0.0–0.5) nanofibers with great crystallinity were prepared by electrospinning method and used as cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). The symmetric cells of nanofiber-based LBSF electrode on Sm_0.2Ce_0.8O_1.9 (SDC) electrolyte show excellent electrochemical performance. The La_0.4Bi_0.4Sr_0.2FeO_3-δ (LBSF4) cathode has the best performance with a polarization resistance (R_P) of 0.126 Ω cm² at 650 °C. The anode-supported single cell with LBSF4 as the cathode film and Ni-SDC as the anode has a maximum power density of 448 mW cm^-2 at 650 °C using wet H₂ as the fuel. In addition, the LBSF4 cathode with fibrous structure exhibits outstanding electrochemical behavior. The catalytic activity of the cathode was improved due to the incorporation of the Bi element, indicating that LBSF4 is promising as a cathode material in the field of IT-SOFCs.     

Enhanced sintering behavior of LSGM electrolyte and its performance for solid oxide fuel cells deposited by vacuum cold spray

How to obtain dense La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ (LSGM) electrolyte at low sintering temperature (<1300 °C) is a challenge to improve solid oxide fuel cell (SOFC) performance at intermediate operation temperature. In this study, a double-layer design method for vacuum cold spray (VCS) prepared-LSGM electrolyte assisted with two-step sintering at a low temperature was proposed. The sintering behavior of VCS deposited LSGM layers at 1200 °C was investigated. The LSGM layers became denser in most regions except the appearance of some cracks. Subsequently, the effect of a second LSGM layer on the sintered top layer was studied to block cracks. Results showed that the co-sintered layer with a thickness of approximately 5 μm presented a maximum open circuit voltage of ∼0.956 V at 650 °C and a maximum power density of 592 mW/cm² at 750 °C. Result indicates that the sintering assisted VCS is a promising method to prepare the LSGM electrolyte applied in intermediate temperature SOFCs.     

Preparation of Pt-Pd catalysts for direct formic acid fuel cell and their characteristics

Pt-Pd catalysts were prepared by using the spontaneous deposition method and their characteristics were analyzed in a direct formic acid fuel cell (DFAFC). Effects of calcination temperature and atmosphere on the cell performance were investigated. The calcination temperatures were 300, 400 and 500 °C and the calcination atmospheres were air and nitrogen. The fuel cell with the catalyst calcined at 400 °C showed the best cell performance of 58.8 mW/cm². The effect of calcination atmosphere on the overall performance of fuel cell was negligible. The fuel cell with catalyst calcined at air atmosphere showed high open circuit potential (OCP) of 0.812 V. Also the effects of anode and cathode catalyst loadings on the DFAFC performance using Pt-Pd (1: 1) catalyst were investigated to optimize the catalyst loading. The catalyst loading had a significant effect on the fuel cell performance. Especially, the fuel cell with anode catalyst loading of 4 mg/cm² and cathode catalyst loading of 5 mg/cm² showed the best power density of 64.7 mW/cm² at current density of 200 mA/cm². This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Investigation of LSM-8YSZ cathode within an all ceramic SOFC. Part I: Chemical interactions

This work focuses on a novel, co-sintered, all-ceramic solid oxide fuel cell (SOFC) concept. The objective is the understanding of interaction and degradation mechanisms of the cathode and current collector layers within the design during co-sintering. Half cells consisting of silicate mechanical support, lanthanum strontium manganite (LSM) current collector, LSM mixed with 8 mol% yttria-stabilized zirconia (8YSZ) composite cathode and 8YSZ electrolyte were co-sintered at 1150 °C < T < 1250 °C. Crystallographically stable LSM compositions within the design were identified. However, the cathode and silicate/electrolyte interacted by interdiffusion of Zn (gas diffusion) and Mn (solid diffusion), and by the formation of several reaction phases (between silicate and cathode only). Introducing silicate poisoning decreased the electrochemical performance of the cell by around 40%. This is likely due to the formation of the Zn- and Mn-rich phase in the cathode, but may also be caused by a higher ohmic resistance of the current collector.     

Fabrication of Solid Oxide Fuel Cells with a Thin (La0.9Sr0.1)0.98(Ga0.8Mg0.2)O3–δ Electrolyte on a Sr0.8La0.2TiO3 Support

This paper describes Sr_0.8La_0.2TiO₃ (SLT)‐supported solid oxide fuel cells with a thin (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3–δ (LSGM) electrolyte and porous LSGM anode functional layer (AFL). Optimized processing for the SLT support bisque firing, LSGM electrolyte layer co‐firing, and LSGM AFL colloidal composition is presented. Cells without a functional layer yielded a power density of 228 mW cm^–2 at 650 °C, while cells with a porous LSGM functional layer yielded a power density of 434 mW cm^–2 at 650 °C. Cells with an AFL yielded a higher open circuit voltage, possibly due to reduced Ti diffusion into the electrolyte. Infiltration produced Ni nanoparticles within the support and AFL, which proved crucial for the electrochemical activity of the anode. Power densities increased with increasing Ni loadings, reaching 514 mW cm^–2 at 650 °C for 5.1 vol.% Ni loading. Electrochemical impedance spectroscopy analysis indicated that the cell resistance was dominated by the cathode and electrolyte resistance with the anode resistance being relatively small.     

Inert substrate-supported microtubular solid oxide fuel cells based on highly porous ceramic by low-temperature co-sintering

Inert substrate-supported microtubular solid oxide fuel cells (MT-SOFCs) are attractive due to their advantages, including high reduction–oxidation (redox) cycling stability and thermal cycling tolerance. A method involving sequential dip-coating, leaching, and co-sintering was developed and applied to fabricate inert substrate-supported MT-SOFCs through acid leaching nickel from the conventional Ni–yttria-stabilized zirconia (YSZ) anode. A thin current collector was deposited onto the support surface to minimize the current collection losses by collecting current from the entire surface area of the anode. A dense electrolyte could be obtained at a co-sintering temperature of 1250?°C. The produced MT-SOFC with the configuration of porous zirconia support/Ni–Scandia-stabilized zirconia (SSZ) anode current collector/Ni-SSZ anode/SSZ electrolyte/strontium-doped lanthanum manganite (LSM)-SSZ cathode/LSM cathode current collector was evaluated by electrochemical characterization tests. The inert substrate-supported MT-SOFC exhibited the maximum power densities of 616, 542, 440, and 300?mW?cm^?2 at 800, 750, 700, and 650?°C, respectively using dry hydrogen and air. In addition, the thermal cycling stability of the MT-SOFC was evaluated. The cell survived from thermal cycling tests and came out intact after 50 thermal cycles between 700?°C and 400?°C during an operation time of 50?h.     

A parametric study of a platinum ruthenium anode in a direct borohydride fuel cell

Data on the performance of a direct borohydride fuel cell (DBFC) equipped with an anion exchange membrane, a Pt–Ru/C anode and a Pt/C cathode are reported. The effect of oxidant (air or oxygen), borohydride and electrolyte concentrations, temperature and anode solution flow rate is described. The DBFC gives power densities of 200 and 145 mW cm⁻² using ambient oxygen and air cathodes respectively at medium temperatures (60 °C). The performance of the DBFC is very good at low temperatures (ca. 30 °C) using modest catalyst loadings of 1 mg cm⁻² for anode and cathode. Preliminary data indicate that the cell will be stable over significant operating times.     

Synthesis and applications of composite cathode based on Sm0.5Sr0.5Co3−δ for solid oxide fuel cell

Cobaltite based perovskites, such as Sm_0.5Sr_0.5Co_3?δ (SSC), are attractive solid oxide fuel cell (SOFC) cathodes due to their high electrochemical activity and electrical conductivity. To obtain higher fuel cell performance with smaller particles, nano-sized SSC powders were synthesized by a complex method with/without carbon black, HB170. However, during synthesis, carbon black reacted with Sr, and unfortunately formed SrCO₃. To obtain pure perovskite SSC, a calcination temperature of 900 °C is needed. At 680 °C, an SOFC with SSC (calcined at 700 °C and synthesized without HB170) exhibited a higher fuel cell performance, of 0.68W·cm^?2, than that with SSCHB (calcined at 900 °C and synthesized with HB170), of 0.58W·cm^?2. Adding GDC for composite cathode is more effective in SSCHB porous cathodes than in SSC porous cathodes. At 680 °C, the composite cathode of SSCHB6-GDC4 exhibited the highest maximum power density of 0.72W·cm^?2 which results from the combined effects of lowered charge transfer polarization and mass transfer polarization. To obtain higher fuel cell performance, optimum composition and processes are necessary.     

Fabrication and performance of PEN SOFCs with proton-conducting electrolyte

A positive-electrolyte-negative (PEN) assembly solid oxide fuel cell (SOFC) with a thin electrolyte film for intermediate temperature operation was fabricated. Instead of the traditional screen-printing method, both anode and cathode catalysts were pressed simultaneously and formed with the fabrication of nano-composite electrolyte by press method. This design offered some advantageous configurations that diminished ohmic resistance between electrolyte and electrodes. It also increased the proton-conducting rate and improved the performance of SOFCs due to the reduction of membrane thickness and good contact between electrolyte and electrodes. The fabricated PEN cell generated electricity between 600°C and 680°C using H₂S as fuel feed and air as oxidant. Maximum power densities 40 mW·cm⁻² and 130 mW·cm⁻² for the PEN configuration with a Mo-Ni-S-based composite anode, nano-composite electrolyte (Li₂SO₄+Al₂O₃) film and a NiO-based composite cathode were achieved at 600°C and 680°C, respectively.     

Electrochemical properties related to the thickness control of the solid oxide fuel cell component layer using decalcomania paper

We fabricated anode-supported solid oxide fuel cells using decalcomania paper. To investigate the changes in thickness of the component layer and electrical properties in a unit cell, the number of layers of cathodes and the electrolyte decalcomania paper is changed. As a result, the thickness of the electrolyte and cathode layer regularly increases with an increase in the number of decalcomania papers attached. In addition, when only one electrolyte decalcomania paper is attached to an anode support, a tight and dense 8 μm electrolyte layer is obtained. A unit cell with a cathode thickness of 120 μm to which decalcomania paper is attached nine times is shown to have an open circuit voltage (OCV) of 1.08 V and a maximum power density (MPD) of 902 mW cm^?2 at 800 °C.     

Pr Doped Barium Cerate as the Cathode Material for Proton‐Conducting SOFCs

BaCe_0.8Pr_0.2O₃ (BCP20) and BaCe_0.6Pr_0.4O₃ (BCP40) powders are successfully synthesized through the Pechini method and used as the cathode materials for proton‐conducting solid state oxide fuel cells (SOFCs). The prepared cells consisting of the structure of a BaZr_0.1Ce_0.7Y_0.2O_3–δ (BZCY7)‐NiO anode substrate, a BZCY7 anode functional layer, a BZCY7 electrolyte membrane, and a cathode layer, are measured from 600 to 700 °C with humidified hydrogen (∼3% H₂O) as the fuel and static air as the oxidant. The electricity results show that the cell with BCP40 cathode has a higher power density, which could obtain an open‐circuit potential of 0.99 V and a maximum power density of 378 mW cm^–2 at 700 °C. The polarization resistance measured at the open‐circuit condition of BCP40 is only 0.16 Ω cm² at 700 °C, which was less than BCP20.     

Fabrication of BaZr0.1Ce0.7Y0.2O3 – δ ‐Based Proton‐Conducting Solid Oxide Fuel Cells Co‐Fired at 1,150 °C

Dense proton‐conducting BaZr_0.1Ce_0.7Y_0.2O_{3 – δ} (BZCY) electrolyte membranes were successfully fabricated on NiO–BZCY anode substrates at a low temperature of 1,150 °C via a combined co‐press and co‐firing process. To fabricate full cells, the LaSr₃Co_1.5Fe_1.5O_{10 – δ}–BZCY composite cathode layer was fixed to the electrolyte membrane by two means of one‐step co‐firing and two‐step co‐firing, respectively. The SEM results revealed that the cathode layer bonded more closely to the electrolyte membrane via the one‐step co‐firing process. Correspondingly, determined from the electrochemical impedance spectroscopy measured under open current conditions, the electrode polarisation and Ohmic resistances of the one‐step co‐fired cell were dramatically lower than the other one for its excellent interface adhesion. With humidified hydrogen (2% H₂O) as the fuel and static air as the oxidant, the maximum power density of the one‐step co‐fired single cell achieved 328 mW cm^–2 at 700 °C, showing a much better performance than that of the two‐step co‐fired single cell, which was 264 mW cm^–2 at 700 °C.