Capabilities

Equipment is in place at the CFCC for fabricating complete laboratory-scale (1 to 3 cm^2) and sub-commercial scale (25 to 100 cm^2) solid oxide fuel cells that allow a wide range of material and electrochemical studies to be undertaken. High-temperature sintering ovens and processing furnaces, tape casting, screen printing and cold pressing equipment are available for fabricating SOFCs from a wide variety of state-of-the-art materials using an array of fabrication processes. Equipment of this kind has been used to good effect in fabricating fuel cells having stabilized zirconia or doped ceria electrolytes, transition metal/electrolyte cermet anodes and complex metal oxide cathodes. A class 10,000 clean room is available for pre-test assembly and post-test disassembly of SOFC components.

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The Colorado Fuel Cell Center has amassed a deep equipment base for fabrication and performance characterization of solid-oxide fuel cells and electrolyzers. Both tubular and planar architectures are actively in development. Major equipment includes five Deltek sintering furnaces rated to 1600 ºC, four Lindeburgh and Blue M furnaces rated to 1200 ºC, a programmable Carver hydraulic press, and an extrusion press. Tape casting equipment is also available in the Colorado Center for Advance Ceramics, one of the CFCC’s key partner research centers. A SonoTek ALIGN atomistic sprayer is used to carefully deposit thin electrolytes and electrode functional layers, with deposition control down to 2 mm. A demonstration of the SonoTek sprayer at the CFCC can be found here: https://www.dropbox.com/t/xIuerB1DVT9gbnJn

Cell morphology and microstructure are analyzed using extensive electron microscopy and X-ray diffraction equipment available through Mines Shared Instrumentation Facilities, another key partner to the Colorado Fuel Cell Center.

Over a dozen cell-level test stands are used to characterize electrochemical performance and durability of tubular and planar fuel cells and electrolyzers. Figure 1 presents an illustration of a planar “button” cell test stand. The cell is packaged within alumina manifolds, including metallic-mesh current collectors and contact pastes, and sealing gaskets. These assemblies are sealed using external compression hardware, and placed within test furnaces rated to 1100 ºC. Upstream mass flow controllers and humidifiers are used to synthesize a wide array of reactant streams, while product compositions are monitored using an Agilent gas chromatograph. Cell performance is regulated and monitored using Gamry electronic loads and impedance analyzers, with fundamental operation characterized through Distribution of Relaxation Times (DRT). These test stands also include high-pressure operation.

Efforts at the Colorado Fuel Cell Center regarding cell fabrication and performance characterization can be reviewed at:

J. Huang, N.P. Sullivan, A. Zakutayev, R. O’Hayre, “How reliable is distribution of relaxation times (DRT) analysis? A dual regression-classification perspective on DRT estimation, interpretation, and accuracy,” Electrochimica Acta 443 (2023) 141879, https://doi.org/10.1016/j.electacta.2023.141879.

L.Q. Le, C. Meisel, C. Herradon Hernandez, J. Huang, Y. Kim, R. O’Hayre, N.P. Sullivan, “Performance degradation in proton-conducting ceramic fuel cell and electrolyzer stacks,” Journal of Power Sources 537 (2022) 231356 DOI: 10.1016/j.powsour.2022.231356.

For further information regarding materials discovery, device fabrication and performance characterization, please contact the Director of the Colorado Fuel Cell Center.

Figure 1: Solid-oxide button-cell wiring and packaging for high-temperature electrochemical-performance characterization in either fuel-cell or electrolysis modes.

Through years of steady technological advancement, proton-conducting ceramic materials are approaching a technology readiness level that rivals more well-established oxygen-ion conductors and polymer-electrolyte membranes. Researchers at Colorado School of Mines are the nation’s leaders in developing protonic ceramics for a number of applications:

• Fuel cells for efficient electricity generation (PCFCs);
• Electrolyzers for energy storage (PCECs); and
• Membrane reactors for fuels synthesis (PCMRs).

Doped barium cerate-zirconate electrolyte materials (BaCexZr1-x-yYyO3-d) are the focus of these efforts. Devices based on these materials have demonstrated impressive performance at intermediate temperatures, often 200–300 °C below that of equivalent oxygen-ion conductors. Such lower-temperature operation can dramatically reduce device degradation rates, decrease the cost of stack and balance-of-plant materials, reduce thermal-cycling stresses and enable a wider range of integration options. Additionally, protonic-ceramics can be harnessed to generate pure hydrogen streams under electrolysis operation.

Such protonic-ceramic materials have demonstrated mixed ionic-electronic conductivity; these properties can be exploited for developing cost-effective, novel solutions and new technologies. We are currently developing fuel cell stacks based on BaCe0.2Zr0.6Y0.2O3-d (BCZY26). These protonic-ceramic fuel cells have demonstrated remarkable fuel flexibility. The effort includes a tenfold scale up in cell size, and integration into a stack package. Our three-cell stack recently achieved a power density of 180 mW cm^–2 at 0.78 V under methane fuel at 550 °C. The team is now engaged with an industrial developer to demonstrate a 0.5 kW stack based on the same technology. This effort is supported by award number DE-AR0000493. The program runs from 2015 through 2020.

We have observed more pronounced electronic conductivity under electrolysis operation. This is likely due to cerium reduction within the BCZY material under reverse bias. By reducing the cerium content to below the percolation threshold, we have confirmed great improvements in Faradaic efficiency, reaching 95% at 120 mA cm^2 and 600 °C.

We are also exploring the use of protonic ceramics for electrochemical synthesis of ammonia as a means of renewable energy storage. In this program, protonic-ceramic devices are infiltrated with ruthenium-coated calcium aluminate catalysts to convert nitrogen and water vapor into ammonia. This effort is supported by award number DE-AR0000493 and spans 2017–2020.

The market for distributed generation of electricity is vast. With over 12 million distributed-generation units and 200 GW of domestic capacity, the DG market provides a robust growth opportunity for quiet, high-efficiency fuel cells. A compact (< 25 kW), efficient, propane-powered fuel cell would provide compelling value across a number of markets spanning recreation, defense, aerospace and the developing world. The agriculture sector possesses widespread infrastructure for an ammonia-fueled protonic-ceramic fuel cell electric generator for remote power. Finally, as evidenced by FuelCell Energy’s Direct FuelCell® platform, large markets exist for MW-scale renewable or natural-gas-fueled generators. The technical goals targeted in this follow-on program mark critical milestones in development of kW- and MW-scale fuel-cell generators to fit these evolving market opportunities, while also positioning the technology as a fuel-flexible product.

Figure 1: Illustration of electrolyzer based on proton-conducting ceramic materials, with high-resolution scanning electron micrograph of electrode – electrolyte interfaces

The Colorado Fuel Cell Center utilizes a bank of three high-temperature test stands to characterize the performance and durability of fuel-cell and electrolyzer electrodes and interfaces. Shown in Figure 1, each test stand features a planar, electrolyte-supported “symmetric cell”, with identical electrodes placed on each side of a ~ 1-mm-thick electrolyte support (Figure 1a). Metallic mesh current collectors and wiring are secured to each electrode using contact pastes; metallic interconnects can also be incorporated, if desired.

The cell and current collector assembly is packaged within carefully designed alumina manifolding that maintains a constant compressive force on the assembly over thousands of hours of operation. The test coupon is placed within a quartz reactor and captured within a furnace rated to 1100 ºC. The use of a single electrode material within the symmetric cell brings simplicity to gas plumbing and performance characterization. Only a single gas composition is provided, simplifying sealing and reducing leakage concerns. Electrode performance is measured using Gamry impedance analyzer coupled to a multiplexer for simultaneous measurements across the three stands. A characteristic result for durability of an air-steam electrode is shown in Figure 1d; DC resistance is constant over this 2000-hr test, but electrode polarization resistance is found to increases as steam concentration climbs above 20% H2O in air.

The Electrode Degradation Test Bank is a useful tool for characterizing the performance of new electrode materials utilized in solid-oxide fuel cells and electrolyzers. The availability of three test stands enables long-term degradation testing while maintaining a measure of throughput for examining a wide range of materials.

For further information regarding the Electrode Degradation Test Bank, please contact the Director of the Colorado Fuel Cell Center.

Figure 1:Illustration of the Electrode Degradation Test Stand: a.) the symmetric cell with contact paste and metallic interconnect (if desired); b.) alumina packaging to form the test coupon; c.) quartz reactor within

The Colorado Fuel Cell Center has amassed a deep equipment base for fabrication and performance characterization of solid-oxide fuel cells and electrolyzers.  Both tubular and planar architectures are actively in development. Major equipment includes five Deltek sintering furnaces rated to 1600 ºC, four Lindeburgh and Blue M furnaces rated to 1200 ºC, a programmable Carver hydraulic press, and an extrusion press. Tape casting equipment is also available in the Colorado Center for Advance Ceramics, one of the CFCC’s key partner research centers. A SonoTek ALIGN atomistic sprayer is used to carefully deposit thin electrolytes and electrode functional layers, with deposition control down to 2 mm. A demonstration of the SonoTek sprayer at the CFCC can be found here:

https://www.dropbox.com/t/xIuerB1DVT9gbnJn

Cell morphology and microstructure are analyzed using extensive electron microscopy and X-ray diffraction equipment available through Mines Shared Instrumentation Facilities, another key partner to the Colorado Fuel Cell Center.

Over a dozen cell-level test stands are used to characterize electrochemical performance and durability of tubular and planar fuel cells and electrolyzers. Figure 1 presents an illustration of a planar “button” cell test stand.  The cell is packaged within alumina manifolds, including metallic-mesh current collectors and contact pastes, and sealing gaskets.  These assemblies are sealed using external compression hardware, and placed within test furnaces rated to 1100 ºC. Upstream mass flow controllers and humidifiers are used to synthesize a wide array of reactant streams, while product compositions are monitored using an Agilent gas chromatograph.  Cell performance is regulated and monitored using Gamry electronic loads and impedance analyzers, with fundamental operation characterized through Distribution of Relaxation Times (DRT). These test stands also include high-pressure operation [insert hyperlink to new Capabilities sub-page: 1-kW High-Pressure Test stand].

Efforts at the Colorado Fuel Cell Center regarding cell fabrication and performance characterization can be reviewed at:

10. Huang, N.P. Sullivan, A. Zakutayev, R. O’Hayre, “How reliable is distribution of relaxation times (DRT) analysis? A dual regression-classification perspective on DRT estimation, interpretation, and accuracy,” Electrochimica Acta 443 (2023) 141879, https://doi.org/10.1016/j.electacta.2023.141879.

L.Q. Le, C. Meisel, C. Herradon Hernandez, J. Huang, Y. Kim, R. O’Hayre, N.P. Sullivan, “Performance degradation in proton-conducting ceramic fuel cell and electrolyzer stacks,” Journal of Power Sources 537 (2022) 231356 DOI: 10.1016/j.powsour.2022.231356.

For further information regarding materials discovery, device fabrication and performance characterization, please contact the Director of the Colorado Fuel Cell Center.

Figure 1: Solid-oxide button-cell wiring and packaging for high-temperature electrochemical-performance characterization in either fuel-cell or electrolysis modes.

The Colorado Fuel Cell Center completed commissioning of the 36-kW_e solid-oxide fuel cell and electrolyzer test bed shown in Figure 1 in mid-2023. The grid-connected facility features a 1.2-m (4-ft) diameter pressure vessel rated to 10 bar_g. Plumbing, power, and diagnostics are routed into the vessel through 18 feedthroughs, and include:

• Cabling for fuel-cell / electrolyzer power and voltage wiring;
• Plumbing for reactant, product, and vessel-sweep gas streams;
• 72 thermocouples;
• 16 pressure taps;
• Power to 36-kW_e and 18-kW_e inline heaters.

The test bed includes an upstream natural-gas fuel processor, a boiler for steam supply, and numerous mass flow controllers for synthesis of a wide array of fuel compositions. Three downstream back-pressure regulators with independent electronic controllers modulate pressure of the fuel, air / steam, and vessel-sweep gas streams. Pressure differentials between these three gas streams can be kept below 50 mbar, minimizing mechanical stress on the delicate membrane electrode assemblies within the solid-oxide stacks. Inconel heat exchangers regulate exhaust-gas temperatures, while condensers knock out water prior to ventilation of exhaust gases. Data acquisition and component control are achieved with National Instruments cRIO hardware and LabView software.

Stack power and voltage are controlled and monitored with three (3) 6-kW_e Chroma load banks and one (1) 18-kW_e, grid-connected, Chroma regenerative load. The test bed can produce up to 36 kW_e of fuel-cell output power, or can drive up to 18 kW_e of electrolyzer power.  Higher power levels can be achieved through linking of additional load banks.

The pressurized solid-oxide fuel cell and electrolyzer stack test bed can be used to characterize performance of multi-stack modules that often form the building block of MW-scale commercial systems.  Stack operation under pressure can simulate conditions found in Unmanned Underwater Vehicle (UUV) or Unmanned Aerial Vehicle (UAV) applications. Test bed design, construction, and commissioning was funded through the generous support of the U.S. Department of Energy Advanced Research Projects Agency – Energy (DoE – ARPA-E).

Test-bed operation can be reviewed at:

10. Cadigan, C. Chmura, G. Floerchinger, P. Frankl, S. Hunt, S. Jensen, C. Boushehri, T.L. Vincent, R. Braun, N.P. Sullivan, “Performance characterization of metal-supported solid-oxide fuel cell stacks at elevated pressure,” Journal of Power Sources 573 (2023) 233083, https://doi.org/10.1016/j.jpowsour.2023.233083.

For further information regarding the 36-kWe pressurized test bed, please contact the Director of the Colorado Fuel Cell Center.

Figure 1: Photograph of 36-kW_e pressurized solid-oxide fuel-cell and electrolyzer test bed

The Colorado Fuel Cell Center recently commissioned the high-pressure fuel-cell and electrolyzer test stand shown in Figure 1. Individual cells or multi-cell stacks can be packaged within the high-pressure vessel rated to 150 barg and 600 ºC. Four internal cartridge heaters are used to achieve a high cell-operating temperature, while a zirconia thermal shield and an external cooling jacket maintain a cool vessel-wall temperature. Reactant, product, and vessel-sweep gases are routed to and from the cells through the vessel head, as is wiring for cell power and voltage. Upstream mass flow controllers and humidifiers are used to create a wide array of fuel and oxidizer streams. Downstream back-pressure regulators with independent electronic control maintain target operating pressures. Fuel cell and electrolyzer power and voltage are monitored and controlled through Gamry and Chroma electronic loads and impedance spectrometers. Data acquisition and component control are achieved with National Instruments cRIO hardware and LabView software. An Agilent gas chromatograph monitors reactant, product and vessel-sweep gas compositions.

The illustration shown in Figure 1 presents a cross section of a 10-cell tubular electrolyzer bundle for hydrogen production. Individual cells and planar architectures can also be accommodated.

This high-pressure, high-temperature electrochemistry can bring many benefits, including:

· Production of pressurized hydrogen through water electrolysis, reducing the need, complexity, and associated cost of downstream hydrogen compression for storage;

· Compatibility with chemical-synthesis chemistries, where high pressures and high temperatures are desirable, such as ammonia synthesis;

· Heightened efficiency in both fuel-cell and electrolysis modes through a reduction in cell-level activation and concentration polarizations.

Pressure vessel operation can be further reviewed at:

C. Herradon, L. Le, C. Meisel, J. Huang, C. Chmura, Y.D. Kim, C. Cadigan, R. O’Hayre, N.P. Sullivan, “Proton-conducting ceramics for water electrolysis and hydrogen production at elevated pressure,” Frontiers in Energy Research, 10 (2022) 1020960 https://doi.org/10.3389/fenrg.2022.1020960.

For additional information regarding the 1-kWe-scale high-pressure test stand, please contact the Director of the Colorado Fuel Cell Center.

Figure 1: Illustration of 1-kWe high-pressure solid-oxide fuel-cell and electrolyzer test vessel. The illustration depicts a tubular electrolyzer bundle; individual cells and planar architectures can also be accommodated.

The Colorado Center for Advanced Ceramics houses a variety of ceramics processing instrumentation available to the CFCC. This includes numerous controlled atmosphere and air sintering furnaces, a Thermal Technologies vacuum hot press (2000ËšC 25 tons, capability to run in Ar or N2), a cold isostatic press, uniaxial presses, ball mills and powder preparation facilities and a plasma etcher.

The Electron Microscopy Laboratory is equipped with three scanning electron microscopes (Quanta 600 with heating stage to 1500°C and an in-situ Ernest-Fullam tensile stage; JEOL FEG SEM with EBSP and photolithography capabilities installed 3/2006; JEOL JXA-840 SEM with EDS;) and two transmission electron microscopes (Philips CM200 STEM with EDS and heating stage to 1500°C; Philips EM400 TEM). The laboratory is fully equipped with TEM sample preparation facilities including dimplers, ion beam thinners, and vacuum coaters.

Thermal analysis equipment available at the Colorado Center for Advanced Ceramics includes a Netzsch simultaneous thermal analyzer, a Netzsch high temperature dilatometer, a Netzsch differential scanning calorimeter, a Netzsch thermal conductivity tester, a Seiko TG/D and Cahn TGA both interfaces to a Fisons mass spectrometer, a Fourier transform infrared spectrometer and a controlled atmosphere microbalance.

The Metallurgical and Materials Engineering Department houses numerous mechanical testing facilities, including 4 MTS computer-controlled, servo-hydraulic uniaxial testing units, 2 MTS screw-driven uniaxial testing units, fracture toughness fixtures, impact testers, fatigue testing for bending and torsion, hot and cold rolling mills, numerous hardness testers, a MTS XP Nanoindenter.

In addition to the Electron Microscopy Lab, we have capabilities in AFM. Extensive use is made of X-ray diffraction and small angle x-ray scattering. Extensive use is made of the Mines NMR facility which has three spectrometers from 200 to 400 MHz. A thermo-nicolet IR spectrometer equipped with ATR and a heatable variable atmosphere cell is avaialvle to the CFCC personnel and several Raman spectrometers.