Moist Hydrogen Research Articles

Electrochemical Performance of Cone-Shaped Tubular Anode Supported Solid Oxide Fuel Cells Fabricated by Low-Pressure Injection Moulding Technique

Low-pressure injection moulding (LPIM) technique was successfully developed to fabricate porous NiO-YSZ anode substrates for cone-shaped tubular anode-supported solid oxide fuel cells. A single cell, NiO-YSZ / YSZ/ LSM-YSZ was assembled and tested to demonstrate the feasibility of the technique applied. The single cell provided a maximum power density of 795 mW/cm2 at 850oC with the effective area of the cathode 1.21cm2, using moist hydrogen(75ml/min) as fuel and ambient air as oxidant. The observed open-circuit voltages (OCV) was closed to the theoretical value and the scanning electron microscope (SEM) results revealed that the microstructures of the anode substrate and the cathode layer were porous and the electrolyte film was dense.

Direct operation of cone-shaped LT-SOFCs with methane fuel for portable application

Anode-supported cone-shaped tubular solid oxide fuel cells (SOFCs) and segmented-in-series (SIS) SOFCs stack based on gadolinia-doped ceria (GDC) electrolyte film direct utilization methane as fuel are successfully developed in this study. The single cell exhibits maximum power densities of 484 mWcm −2 and 414 mWcm −2 at 600 °C by using moist hydrogen and moist methane as fuel, respectively. A durability test of the single NiO–GDC/GDC/LSCF-GDC cell is performed at a constant current density of 0.4 Acm −2 direct fueled with methane for about 140 h at 600 °C. It stabilizes with no apparent degradation during the durability test. Very little carbon is detected on the anodes, suggesting that carbon deposition is limited during cell operation. The results show that the stability and dependability of as-prepared single cell is good and it is very significant for portable application of low-temperature SOFCs (LT-SOFCs). A three-cell-stack based on the above-mentioned SOFCs is fabricated and tested by direct utilization of methane. Its typical electrochemical performance is investigated. And the stack has experienced 5 times thermal cycling test. Good thermo-mechanical properties and stability are observed and that the developed segmented-in-series LT-SOFCs stack with GDC electrolyte film is highly promising for portable application.

Fabrication and characterization of low-temperature SOFC stack based on GDC electrolyte membrane

A novel low-temperature anode-supported cone-shaped tubular solid oxide fuel cell (SOFC) and segmented-in-series (SIS) SOFC stack based on gadolinia-doped ceria (GDC) membrane which is fabricated by dip coating technique are developed in this study.The single cell, NiO–GDC/GDC (15μm)/BSCF–GDC, shows an open-circuit voltage (OCV) of 0.90V at 400°C and exhibits maximum power densities of 17, 49, 129, 268 and 429mWcm−2 at 400, 450, 500, 550 and 600°C, respectively, using moist hydrogen (50mlmin−1) as fuel and ambient air as oxidant. A two-cell-stack based on the above-mentioned cone-shaped tubular anode-supported SOFC is fabricated. And its typical operating characteristics are investigated. The results show that the two-cell-stack presents an open circuit voltage (OCV) of about 1.86V at 400°C and an output power of 0.55W (at 0.4A and 1.4V) at 550°C. This indicates that the anode-supported cone-shaped tubular SIS-SOFC stack based on GDC membrane is highly promising for low temperature SOFC of portable applications.

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

AbstractA 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 Pr2NiO4 + 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.

Fabrication and Performance of Direct Methane SOFC with a Cu-CeO<sub>2</sub>-Based Anode

Highly porous yttria stabilized zirconia (YSZ) supported dense (ZrO2)(0.89)(Sc2O3)(0.1)(CeO2)(0.01) (10ScSZ-1CeO(2)) bilayers were fabricated by removing NiO with a reduction-acid leaching method using NiO-YSZ/10ScSZ-1CeO(2) half cells that were prepared by dry-pressing. By allowing Cc and Cu nitrate solutions to infiltrate the porous YSZ matrix, single cells of Cu-CeO2-YSZ/10ScSZ-1CeO(2)/LSCF (LSCF: La0.6Sr0.4Co0.2Fe0.8O3-delta) were fabricated. The cell's structure was characterized by X-ray diffractometry (XRD) and field-emission scanning electron microscopy (FESEM). Results showed that the porous YSZ matrix of the YSZ/10ScSZ-1CeO(2) bilayers prepared by the reduction-acid leaching method was of high porosity (more than 64%) and it was highly connected, which was beneficial for the introduction of Cc and Cu nitrate by infiltration. The 10ScSZ-1CeO(2), electrolyte film with a thickness of 30 mu m was dense and pinhole-free. A single cell composed of Cu-CeO2-YSZ/10ScSZ-1CeO(2)/LSCF showed excellent generation performance with maximum power densities of 0.29 and 0.09 W.cm(-2) at 650 degrees C, as well as 0.48 and 0.21 W.cm(-2) at 700 degrees C using moist hydrogen and methane as fuel, respectively. This excellent performance is attributed to the electrolyte's small ohmic resistance, small cathode polarization resistance, and favorable anode microstructure.

Performance of cone-shaped tubular anode-supported segmented-in-series solid oxide fuel cell stack fabricated by dip coating technique

A simple and feasible technique is developed successfully to fabricate the cone-shaped tubular segmented-in-series solid oxide fuel cell (SOFC) stack. The cone-shaped tubular anode substrates and yttria-stabilized zirconia (YSZ) electrolyte films are fabricated by dip coating technique. After sintering at 1400 °C for 4 h, a dense and crack-free YSZ film with a thickness of about 35.9 μm is successfully obtained. The single cell, NiO–YSZ/YSZ/LSM–YSZ, provides a maximum power density of 1.08 and 1.35 W cm−2 at 800 and 850 °C, respectively, using moist hydrogen (75 ml/min) as fuel and ambient air as oxidant. A two-cell-stack based on the above-mentioned cone-shaped tubular anode-supported SOFC was assembled and tested. The maximum total power at 800 °C was about 3.7 W.

A novel design and performance of cone-shaped tubular anode-supported segmented-in-series solid oxide fuel cell stack

Abstract A novel design of cone-shaped tubular segmented-in-series solid oxide fuel cell (SOFC) stack is presented in this paper. The cone-shaped tubular anode substrates are fabricated by slip casting technique and the yttria-stabilized zirconia (YSZ) electrolyte films are deposited onto the anode tubes by dip coating method. After sintering at 1400 °C for 4 h, a dense and crack-free YSZ film with a thickness of about 7 μm is successfully obtained. The single cell, NiO–YSZ/YSZ (7 μm)/LSM–YSZ, provides a maximum power density of 1.78 W cm −2 at 800 °C, using moist hydrogen (75 ml min −1 ) as fuel and ambient air as oxidant. A two-cell-stack based on the above-mentioned cone-shaped tubular anode-supported SOFC is fabricated. Its typical operating characteristics are investigated, particularly with respect to the thermal cycling test. The results show that the two-cell-stack has good thermo-mechanical properties and that the developed segmented-in-series SOFC stack is highly promising for portable applications.

Fabrication and Performance of Cone‐Shaped Segmented‐In‐Series Solid Oxide Fuel Cells

A new design of segmented‐in‐series solid oxide fuel cells (SOFCs) is presented in this paper. The small cone‐shaped anode tubes were fabricated by slip casting and the yttria‐stabilized zirconia (YSZ) electrolyte membranes were deposited onto the anode tubes by dip coating. After sintering at 1400°C for 4 h, a dense and crack‐free YSZ membrane with a thickness of 20 μm was successfully obtained. The single cell, using moist hydrogen as a fuel and ambient air as an oxidant, provides maximum power densities of 1.15, 0.8, 0.47, 0.26, 0.14, and 0.07 W/cm2 at 850°C, 800°C, 750°C, 700°C, 650°C, and 600°C, respectively.

Enhancement of Solid Oxide Fuel Cell Performance by La0.6Sr0.4Co0.2Fe0.8O3 − δ Double-Layer Cathode

cells with either a single-layer or a double-layer cathode were fabricated and tested. The single-layer LSCF cathode was made by stencil printing, while the double-layer cathode was prepared by depositing a thin porous layer on the SDC electrolyte using electrostatic spray deposition (ESD) before stencil printing. The cells were tested with moist hydrogen as fuel and air as oxidant. The maximum power density increased from at and at when the ESD-LSCF layer was introduced. The interfacial area specific resistances (ASRs) of electrodes for both cells were also measured under open-circuit condition. In comparison to that in the single-layer cathode cell, the electrode ASRs were reduced to half with the addition of the ESD-LSCF cathode layer.

Formation of nickel nanoparticles in nickel – ceramic anodes during operation of solid-oxide fuel cells

Abstract The microstructure of solid-oxide fuel cell anodes, consisting of nickel particles embedded in either doped zirconia or ceria, was characterized in three different stages: (i) as sintered, (ii) after reduction, and (iii) after fuel cell operation for 500 h in an atmosphere of moist hydrogen. After 500 h of operation, we found that both types of anodes, those based on zirconia and those based on ceria, contained nanoparticles of elemental nickel. We propose that these nanoparticles form from nickel hydroxide, synthesized during fuel cell operation and precipitating elemental nickel where the partial pressure of water is low at the periphery of triple-phase boundaries or on cooling down from the operating temperature to room temperature.

Silver infiltrated La 0.6Sr 0.4Co 0.2Fe 0.8O 3 cathodes for intermediate temperature solid oxide fuel cells

Porous La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF) electrodes on anode support cells were infiltrated with AgNO 3 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 AgNO 3. 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.

Nickel-cermet anode for fuel cells with the LSGM electrolyte

The effect of some technological parameters (firing temperature, thickness of an interphase layer made of solid electrolyte Ce0.82Gd0.18O1.91 (GDC), the GDC electrolyte amount in nickel-cermet) on the electrochemical and electric properties of a nickel-cermet (Ni-GDC) anode intended for fuel cells with the La0.88Sr0.12Ga0.82Mg0.18O2.85 (LSGM) electrolyte is studied. The polarization resistance of such an electrode is shown to hardly depend on the thickness of the interphase layer (4.5–23.5 μm) and the GDC electrolyte amount in nickel-cermet and to increase with the anode firing temperature. It is established that the contact resistance is concentrated in cells with the developed nickel-cermet electrode at the GDC/LSGM interface. At a temperature of 700°C the developed anodes may ensure a current density of 1 A cm−2 at an overvoltage of less than 100 mV when using both moist hydrogen and a methane-oxygen mixture as the fuel.

Thermodynamic Properties of Hydrogen-Water Vapor and Air-Water Vapor Mixtures in Fuel Cells

This paper provides calculated values of specific enthalpy, specific entropy and specific Gibbs energy associated with moist hydrogen and air. They cover the range of interest in humidity control and measurement methods for fuel cell applications from water vapor content of dew-point temperatures 60 {degree sign}C to 200 {degree sign}C with absolute pressures of 0.1 MPa, 0.5 MPa, 1 MPa and 2 MPa. Molar enthalpy, molar entropy and molar Gibbs free energy of moist hydrogen and air are expressed explicitly in terms of the associated water vapor density. The values of the molar quantities are the sum of three parts due to: 1. The mole fraction of water vapor in a gas mixture; 2. The mole fraction of dry hydrogen or dry air in a gas mixture ; and 3. The effects of interaction between water molecules and hydrogen as well as air molecules.

Effect of Nickel Oxide/Yttria-Stabilized Zirconia Anode Precursor Sintering Temperature on the Properties of Solid Oxide Fuel Cells

An NiO/yttria-stabilized zirconia (YSZ) layer sintered at temperatures between 1100° and 1500°C onto dense YSZ electrolyte foils forms the precursor structure for a porous Ni/YSZ cermet anode for solid oxide fuel cells. Conflicting requirements for the electrochemical performance and mechanical strength of such cells are investigated. A minimum polarization resistance of 0.09 Ω.cm2at 1000°C in moist hydrogen is obtained for sintering temperatures of 1300°–1400°C. The mechanical strength of the cells decreases with increased sintering temperature because of the formation of channel cracks in the electrode layers, originating in a thermal expansion coefficient mismatch between the layers.

Oxidation Behavior of Ferritic Stainless Steels under SOFC Interconnect Exposure Conditions

The oxidation of ferritic stainless steels has been studied under solid oxide fuel cell (SOFC) interconnect “dual” exposure conditions, i.e., simultaneous exposure to air on one side of the sample, and moist hydrogen as the fuel on the other side. The scales grown on the air side under these dual exposure SOFC conditions can be significantly different from scales grown on samples exposed to air on both sides. In contrast, no substantial difference was observed between scales grown on the fuel side of the dual atmosphere samples and scales grown on samples exposed to moist hydrogen on both sides. The anomalous oxidation of stainless steels at the air side depends on both alloy composition and thermal history. AISI430, with 17% Cr, suffered localized attack via formation of hematite-rich nodules on the air side of dual exposure samples, while the spinel top layer of the air side scale of Crofer22 APU (23% Cr) was enriched in iron. For E-brite, with the highest Cr content (27%), no unusual phases were found in the scale on the air side, but the air side scale was less dense and appeared to be more prone to defects than the scale grown in air only. Increasing temperature and thermal cycling both accelerated the anomalous oxidation, which appeared to be related to the transport of hydrogen through the steel and its subsequent presence in the air side scale. © 2004 The Electrochemical Society. All rights reserved.

Operation of solid oxide fuel cells at reduced temperatures

The fuel cell arrangement La 0.6Sr 0.4Co 0.2Fe 0.8O 3 / Ce 0.9Gd 0.1O 1.95 / Ni-YSZ, incorporating a dense film (5–10 μm) of the Ce 0.9Gd 0.1O 1.95 electrolyte tape cast onto the supporting anode, was investigated for intermediate temperature operation (550–650°C). Open circuit voltages of 0.75–0.8 V were obtained at 550–650°C using moist hydrogen as the fuel. These open circuit voltages were consistent with theoretical predictions taking into account the electronic/ionic leakage of the electrolyte film. Power outputs in excess of 125 mW/cm 2 were obtained at 650°C (in excess of 30 mW/cm 2 at 550°C) and the cell resistance was approximately 1 Ω.cm 2 (4 Ω.cm 2 at 550°C). Most of the cell resistance was derived from the cathode according to A.C. impedance measurements and a great deal of effort was spent in testing a double layer cathode structure and a Pd promoted cathode. Hence power outputs in excess of 150 mW/cm 2 were obtained at 650°C (in excess of 50 mW/cm 2 at 550°C), although greater improvements were anticipated. Experiments were also carried out at 600°C using direct methanol fuels at the anode, and the maximum power output was approximately half of that obtained with hydrogen.

Development of solid oxide fuel cells based on a Ce(Gd)O 2−x electrolyte film for intermediate temperature operation

Initial tests have been carried out with the fuel cell arrangement La 0.6Sr 0.4Co 0.2Fe 0.8O 3∥Ce 0.9Gd 0.1O 1.95∥Ni/YSZ, incorporating dense film (5–10 μm) Ce 0.9Gd 0.1O 1.95 electrolyte tape cast onto the supporting anode, to investigate the feasibility of intermediate temperature operation (500–700°C). A good open circuit voltage of approx. 0.8 V was obtained at 550°C using moist hydrogen as the fuel. Slightly lower open circuit voltages were found at higher temperatures, which may have been caused by minor gas leakage and the electronic conductivity of the electrolyte. Power outputs in excess of 100 mW/cm 2 were obtained at 650°C, and the cell resistance was 0.8Ω cm 2 at this temperature. This resistance, and the greater resistance at lower temperature, was predominantly due to the cathode according to AC impedance measurements. Experiments were also carried out at 600°C using direct methanol fuels at the anode; the maximum power output was approximately half of that obtained with hydrogen.

Effects of water vapor on hydrogen induced slow crack growth in stainless steels

Three types of stainless steel—austenitic, ferritic, duplex—were subjected to sustained load crack propagation tests in moist hydrogen gas. Three-stage crack velocity vs stress intensity behavior was observed for the unstable austenite alloy just as for pure hydrogen gas tests. Moisture essentially eliminated this behavior for the ferritic and duplex alloys. The fractographic features of all specimens failed in moist hydrogen are very similar to those for pure hydrogen. There is a continuous transition from brittle to ductile fracture appearance in the range from 25 °C to 100 °C. These results are rationalized on the basis of an inhibition of hydrogen entry into the metal due to H2O.

Sintering cermets based on molybdenum, nickel, and alumina in atmospheres of dry and moist hydrogen

We studied the sintering of cermets based on molybdenum, nickel, and aluminum oxide in an atmosphere of dry and moist hydrogen. It was established that the presence of water vapors facilitates a reduction in the sintering temperature of molybdenum-containing cermets, and yields dense nickel-containing ones. In the concluding stages of sintering the density of the cermets can be adequately high, which apparently is due to the reduction in the rate of growth of the corundum crystals.

Optimum Conditions for Baking of Indium

Calculations of partial pressure over an indium melt with dissolved silicon in a moist hydrogen atmosphere are reported. The results are given as a function of temperature, water vapor pressure, and concentration of silicon in the melt, both with and without present. The influence of the total pressure in the baking system is considered, and the calculations indicate that by using a pressure lower than atmospheric, the efficiency of the baking should be significantly increased. The time constant of the baking process is, furthermore, shown to be critically dependent on water vapor partial pressure. These results should be valuable when one wants to find the optimum baking procedure to remove residual silicon from indium.