Three-cell Stack Research Articles

Studies on anode mass composition and cathode flow field design for small-scale to large-scale direct methanol fuel cell stack systems

In this research, the performance studies of a single cell Direct Methanol Fuel Cell with three different mass compositions (20%, 40%, and 60%) of platinum at anode infused in NiTiO3/C and multiple cathode flow fields, such as serpentine, parallel, and sinuous, with 25 cm2 active area. 40% platinum mass composition has been reported with a maximum power density of 24.42 mW/cm2, which is 26.8% and 10.4% higher than the performance observed in 20% and 60% platinum mass composition, respectively, on serpentine flow field. Among the various cathode flow fields, sinuous flow field provided the maximum power density of 28.69 mW/cm2, which is 17.48% and 53.83% higher in performance than that of serpentine and parallel flow fields, respectively. The best-performing catalyst mass composition and flow field, viz., 40% mass composition and sinuous flow field are scaled up to a 100 cm2 active area, and the results showed 16% lower performance compared to a 25 cm2 active area. A three-cell stack is fabricated with the best performing combination with the 100 cm2 active area that delivered a peak power output of 5.8 W, which resulted in 19.4% lower performance than 100 cm2. The stack was tested for stability for 48 h at constant voltage mode and was found that 0.002 W deviation for the entire period.

Flooding and dehydration diagnosis in a polymer electrolyte membrane fuel cell stack using an experimental adaptive neuro-fuzzy inference system

Today the need for fault diagnosis in polymer electrolyte membrane fuel cells (PEMFCs) is felt more than ever to increase the useful life and durability of the cell. The present study proposes an indirect in-situ experimental-based algorithm for diagnosing the moisture content issues in a three-cell stack. Three adaptive neuro-fuzzy inference systems (ANFIS) approximate the system outputs (cells voltages, cathodic and anodic pressure drop) in normal conditions. The values of Pearson's correlation coefficients (0.998, 0.983, and 0.995 for outputs, respectively) show the high quality of the modeling. In unknown operating conditions, the residuals of experimental and ANFIS values are compared with obtained deviation thresholds (0.0735 V, 0.0092 bar, and 0.0047 bar for the outputs, respectively) to determine the cathode/anode flooding, membrane dehydration, or normal status. This method is helpful in commercial applications for diagnosing more than 50% of PEMFC faults because it uses accessible parameters and has low-processing demands.

Investigation of the reversible performance degradation mechanism of the PEMFC stack during long-term durability test

This paper reports on 3-cell PEMFC stack durability test of 2500 h in dynamic conditions and different recovery procedures. After electrochemical impedance spectroscopy (EIS) analysis, it was determined that the primary cause of the stack performance degradation is the oxidation of platinum (Pt), which is reversible. The air starvation operation reduced the cathode voltage to less than 0.2 V, part of PtO was reduced, and the stack performance loss was partially recovered. However, the recovery of the three cells varies due to defects in the three-cell stack and uneven gas distribution. The fast load-up operation brought the short-term severe air starvation of the three cells to a similar level, the remaining platinum oxide (PtO) was fully reduced, the stack performance improved again, and the voltage consistency of the three cells was restored significantly. With the optimization of operating parameters and combined recovery procedures, the average degradation rate of the stack voltage is 3.08 μV/h within 2500 h. The results indicated that our combined strategy is of huge importance to mitigate the reversible performance degradation and significantly extend the service life of PEMFC stack and be a very appropriate procedure used in laboratories and systems.

Distribution of relaxation times: A method for measuring air flow distribution in high-temperature proton exchange membrane fuel cell stacks

Measurement of flow distribution in the fuel cell stack is a challenging task. This study proposes a new method to measure air flow distribution in high-temperature proton exchange membrane fuel cell stacks. The characteristic frequency related to channel impedance is extracted using the distribution of relaxation times analysis. A simple correlation between the air stoichiometry and the characteristic frequency is developed. The influence of various factors on the correlation, including cell operation conditions, fluid physical properties and channel dimensions, are investigated. The experimental results show a good agreement with the correlation. Error estimation indicates that the temperature distribution of the stack, gas humidity and pressure distribution in the inlet manifold have no significant effect on the proposed method under normal conditions. The accuracy and practicability are verified using a three-cell stack with separate mass flow controller (MFC) systems. The results show less than 3.11% of relative error between the reference air stoichiometry given by the MFC and those measured from our proposed method for air stoichiometry below 3.0 at 0.1 A cm−1. The present method provides powerful support for designing high consistency stacks and the real-time monitoring cells state-of-health in stacks.

Multi-perspective analysis of CO poisoning in high-temperature proton exchange membrane fuel cell stack via numerical investigation

To comprehensively understand the CO poisoning effect on high-temperature PEMFC stack (HT-PEMFCs), a 3-D numerical HT-PEMFCs model is developed. The crucial anodic kinetic parameters are obtained from experimental data to improve the accuracy of the model. Then, multi-perspective analysis is conducted on different HT-PEMFC stacks with 1, 3, and 5 cells working at 160 °C with 3 mol% CO in H2. Besides, parametric simulations are conducted on the three-cell stack. It is found that the CO and H2 coverage varies between cells in the stack due to the temperature distribution difference, and the stack with more cells as well as the middle-cell of multi-cell stack have better performance, higher H2 coverage, lower CO coverage due to higher internal temperature. However, too high local temperature not only reduce the CO coverage but reduce the H2 coverage and increase the anode overpotential. The resistance to CO poisoning can be improved by increasing operating temperature, but when CO2 and water vapor are introduced into the anode, the H2 coverage decreases and the CO coverage increases due to the decrease of H2 concentration. The study clearly demonstrated that high performance and high CO resistance can be achieved by carefully regulating the operating conditions.

Scale up of Proton-Conducting Ceramics into Multi-Cell Stacks

Proton-conducting ceramics are emerging as an enabling material for efficient electricity generation, energy storage, and fuels synthesis. While recent advancements at the lab-scale are highly encouraging, there are few reports of scaling cell size beyond the button cell, and no demonstrations of multi-cell stacks. Through support from the U.S. Department of Energy, researchers at the Colorado School of Mines are scaling up protonic-ceramic devices from the button-cell level into small, multi-cell stacks as illustrated in the figure. Both fuel-cell and electrolyzer stacks are in development. The order-of-magnitude increases in the physical size of the delicate membrane-electrode assembly (MEA) bring concerns regarding mechanical strength and robustness. The compatibility of protonic-ceramic materials with stack-packaging materials – metallic interconnects, current collectors, glass-ceramic sealants, and gaskets – has witnessed limited study. In this presentation, we describe selection and tuning of materials, fabrication procedures, and operating conditions to achieve reasonable performance and low degradation in protonic-ceramic fuel cells (PCFCs) stacks.We find highest stack electrochemical performance and durability when utilizing electrolytes based on BaCe0.4Zr0.4Y0.1Yb0.1O3-d (BCZYYb). The anode support is a nickel-electrolyte composite, while the cathode is BaCe0.4Fe0.4Zr0.1Y0.1O3-d (BCFZY). The planar MEAs reach 5 cm2 in active area. The circular stack design enables a measure of flexibility in MEA physical size and shape, and provides balance in stress distribution from thermal- and chemical-expansion. The MEAs are packaged within ferritic-steel interconnects and macor frames to form multi-cell stacks. Our three-cell stack demonstrates encouraging performance, reaching 0.69 and 0.47 W cm-2 under H2 and CH4 fuels, respectively, at 600 ºC. A cathode-electrolyte interlayer of 10%-gadolinium-doped ceria proves critical in achieving stack degradation as low as 1.5% kh-1. Figure 1

Proton-conducting ceramic fuel cells: Scale up and stack integration

We present our efforts to scale up proton-conducting ceramic fuel cells (PCFCs) from the button-cell level into small, multi-cell stacks. While recent advancements with lab-scale PCFCs are encouraging, there are few reports of scaling PCFC technology to the stack level. The compatibility of protonic-ceramic materials with stack-packaging materials - metallic interconnects, current collectors, glass-ceramic sealants, gaskets - has not been demonstrated. Here we show that through tuning of materials, fabrication procedures, and operating conditions, protonic-ceramic fuel cell stacks can achieve reasonable performance and low degradation.The MEA is based around barium cerate-zirconate perovskites. Better long-term stack durability is found with BaCe0.4Zr0.4Y0.1Yb0.1O3−δ (BCZYYb) electrolyte. The anode support is a nickel-electrolyte composite, while the cathode is BaCo0.4Fe0.4Zr0.1Y0.1O3−δ (BCFZY). Planar MEAs reach 5 cm2 in active area, and are packaged within ferritic-steel interconnects and macor frames to form multi-cell stacks. Our three-cell stack demonstrates encouraging performance, reaching 0.69 and 0.47 W cm−2 under H2 and CH4 fuels, respectively, at 600 ∘C. A gadolinium-doped ceria cathode-electrolyte interlayer reduces degradation rates to 1.5% kh−1 at 0.1 A cm−2 and 3.3% kh−1 at 0.4 A cm−2 at 550 ∘C. No chromium transport is observed. Degradation mechanisms and the role of the GDC interlayer are postulated.

Characterizing Stack Degradation in Proton-Conducting Ceramic Fuel Cells and Electrolyzers

We present our efforts to scale-up proton-conducting ceramic fuel cells (PCFC) for integration into small multi-cell stacks. Proton-conducting ceramics are an exciting new class of materials that are now emerging from research laboratories to address societal challenges in electricity generation, energy storage, and fuels synthesis. While there are many technologies under investigation, intermediate temperature proton-conducting fuel cells (PCFC) have been drawing attention due to their high performance at low temperatures in fuel cell mode (up to ~2 Wcm2 at 600 ºC) and their high efficiency (90 – 98 % Faradic efficiency) when operated in electrolysis mode. However despite the impressive achievements at lab-scale PCFC technology limited investments have been made on the scaling up process due to the challenges that the PCFC fabrication procedure represents. In fact, there are no stack demonstrations reported to date in the archival literature. In this presentation we will review our efforts at Colorado School of Mines to increase the size of PCFCs beyond the button-cell level, and to integrate these cells into multi-cell stack assemblies. The stability of our PCFC stack reached the degradation rates of 3.5% and 2.1% per 1000 hours, respectively, under fuel cell and electrolysis modes.An illustration of our stack design is shown in Figure 1, and includes a photograph of a fully assembled three-cell stack after performance testing. The design is centered on three repeating components: the protonic-ceramic electrolysis cells, the composite-ceramic frames in which the cells are bonded, and the thin metallic interconnect / bipolar plates that conduct electricity between adjacent cells. The cells feature a dense, 20 μm-thick BaCe0.4Zr0.4Y0.1Yb0.1O3- d (BCZYYb4411) electrolyte on a porous Ni-BCZYYb4411 anode fabricated through reactive-sintering methods. The cathode is a novel BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) atop of the BCZYYb4411 electrolyte with the maximum active area of ~ 7cm2 per single unit cell. Reactive gases are fed through fuel and oxidizer ports machined into the frame. The metallic interconnect is a ferritic steel developed for intermediate-temperature solid-oxide fuel cells and electrolyzers, and is compression sealed to the frame. Metallic meshes (not shown) electrically connect the electrodes to the interconnects.High protonic-ceramic cell performance operating at 550 0C has been previously demonstrated at Colorado School of Mines. While the lower operating temperature should present benefits for the long-term stability of the stack it also brings questions regarding the behavior of stack materials such as the interconnects which represent a source of degradation in performance depending on the composition of the scale that is grown on them. In an effort to better understand the root causes behind performance degradation processes in our protonic-ceramic stacks, we have integrated numerous voltage-taps throughout the stack shown in Figure 1. In this presentation, we will review our results for long-term protonic-ceramic stack operation under both fuel cell and electrolysis mode, discuss after-test interconnects analysis showing high-iron-content scale and present strategies for reducing degradation rates and extending stack life. Figure 1

Berlin green-based battery deionization-highly selective potassium recovery in seawater

As the global demand for potassium continues to increase, the potassium in natural resources is gradually insufficient. The potassium resources in the ocean are extremely rich. In this paper, a new battery deionization method (BDI) was developed to selectively recover potassium from seawater using a Fe[Fe(CN)6] (BG) battery electrode. The BG-based electrode exhibited totally different insertion behavior to the most abundant cations in seawater, with the capacity order of K+>Na+>Li+>Ca2+>Mg2+. Using the battery cell assembled with BG and activated carbon electrode, the recovery capacity of K+ arrived at 177 μmoL/g under the discharge stage of battery from 0.8 to 0 V, and no significant variation was found even in the presence of 37 times higher concentration of Na+ than that of K+. In synthetic seawater, the BG battery electrode still kept the recovery of 69.6% for K+ with the separation factor α(K+/Na+) of 141.7. Moreover, energy consumption is calculated to be 15.4 kJ/mol, 10 times lower than that of the capacitive deionization method. Meanwhile, the BG battery electrode is very stable with the adsorption amount retaining 86% over 150 cycles. The three-cell stack test in synthetic seawater proves that the current BDI device is easy to be amplified for recovering potassium from seawater.

Direct hybridization of PEMFC and supercapacitors: Effect of excess hydrogen on a single cell fuel cell durability and its feasibility on fuel cell stack

The present paper focuses on the effect of reduced hydrogen stoichiometry on the dynamic behavior of a PEMFC directly hybridized with SC or non-hybridized, using the European standard cycling protocol (FC-DLC) for transport applications. Two gas stoichiometry factors have been considered, at 1.2 and 1.1. Whereas direct hybridization of a single cell enables to reduce the hydrogen overconsumption from 28% to 20% at hydrogen stoichiometry of 1.2, the overconsumption was further reduced to 10% by reducing the stoichiometry to 1.1.The durability of a single fuel cell has been investigated by comparing the long-term cycling operation depending on the hydrogen stoichiometric conditions, for both hybridized and non-hybridized fuel cell. The non-hybridized fuel cell, at hydrogen stoichiometry of 1.2, was operated for 687 h (end of life), whereas the non-hybridized fuel cell at 1.1, could not be operated due to the sudden, excessive voltage drop in the high current density period of the cycle. On the contrary, the hybridized fuel cell was successfully submitted to cycling for more than 1000 h at both conditions of hydrogen stoichiometry. The GDL appears to be responsible for the failure of non-hybridized fuel cell performance, whereas no particular degradation was evidenced with hybridized configurations. Finally, the technique has been successfully applied to a three-cell stack, with very comparable voltage profiles of the individual cells over the cycling protocol.

Fabrication and Performance Investigation of Three-Cell SOFC Stack Based on Anode-Supported Cells With Magnetron Sputtered Electrolyte

A planar solid oxide fuel cell (SOFC) was fabricated using a commercial Ni/yttria-stabilized zirconia (YSZ) anode support, an YSZ/gadolinium-doped ceria (GDC) thin-film electrolyte, and a composite cathode of La0.6Sr0.4Co0.2Fe0.8O3/Gd0.1Ce0.9O1.95 (LSCF/GDC). A small, three-cell, SOFC stack is assembled using 10 cm × 10 cm single cells, metallic interconnects, and glass-based sealing. The stack performance was examined at various fuel flow rates of H2 + N2 and air at a fixed temperature of 750 °C. The three-cell stack with a crossflow design produced peak power density of 0.216 W/cm2 or about 39 W total power at 750 °C.

Simultaneous removal of fluoride and arsenic from groundwater by electrocoagulation using a filter-press flow reactor with a three-cell stack

Abstract An electrocoagulation (EC) process to remove fluoride and arsenic from groundwater (fluoride 5.5 mg L−1, arsenic 50.4 µg L−1, hydrated silica 132 mg L−1, sulfate 40 mg L−1, nitrate 6.7 mg L−1, phosphate 0.55 mg L−1, hardness 23 mg L−1, alkalinity 59.0 mg L−1, pH 8.5 and conductivity 824.5 µS cm−1) was investigated. The EC was carried out in a filter-press flow reactor, containing a three-cell stack equipped with aluminum electrodes. The influence of current density (j), mean linear flow rate in the EC reactor (ur) and the co-existing ions on the fluoride and arsenic removal efficiencies was analyzed. All EC tests, performed at 0.23 ≤ ur ≤ 0.93 cm s−1 and 5 ≤ j ≤ 7 mA cm−2, satisfied the World Health Organization (WHO) standard for fluoride (CF- ≤ 1.5 mg L−1). The EC tests that satisfied the WHO standard for arsenic (CAs ≤ 10 µg L−1) were at 0.23 cm s−1 and 6 ≤ j ≤ 7 mA cm−2. Spectroscopic analyses on aluminum flocs showed that these are mainly composed of aluminum silicates. Fluoride replaces a hydroxyl group from aluminum flocs and arsenates adsorb on aluminum aggregates. The best EC test in terms of energy consumption (6.7 kWh m−3) was obtained at 0.23 cm s−1 and 6 mA cm−2.

Methane-Fueled Proton-Conducting Ceramic Fuel Cell Stacks

We present our recent work on scale-up and stack development of fuel cells based on proton-conducting ceramic materials. Through steady improvement in materials and fabrication methods, protonic ceramics are emerging from the laboratory as potential solutions in electricity generation, energy storage, and chemical synthesis. “Button-scale” protonic ceramic fuel cells (PCFCs) based on barium zirconates have demonstrated high power density at low operating temperatures, reaching 450 mW / cm2 at 500 ºC under hydrogen fuel, and 300 mW / cm2 at 550 ºC under direct methane-steam fuel. While these materials show great promise, scale up of protonic-ceramic fuel cells beyond the “button-cell” level remains limited. In this presentation, we review our progress in extending previous button-cell experiments to small fuel-cell stacks. First, fabrication procedures have been developed to increase PCFC active area by a factor of 10. These planar, circular membrane electrode assemblies (MEAs) are packaged within the stack architecture shown in the figure. MEAs are bonded within a ceramic frame, and the frame is packaged within ferritic-steel interconnects. Numerous multi-cell stack prototypes have been demonstrated. A three-cell stack based on BaCe0.2Zr0.6Y0.2O3-d (BCZY26) electrolyte shows near-theoretical open-circuit voltage and promising power density under methane fuel (183 mW / cm2 at 500 ºC). In this presentation, we will review our continuing efforts to improve the performance and durability of protonic-ceramic fuel cell stacks. Figure 1

(Invited) Proton-Conducting Ceramics for Fuels Synthesis

This presentation is centered on an exciting new class of proton-conducting ceramic materials that are emerging from the laboratory to play important roles in the commercial sector. While proton-conducting ceramics have been studied since the early 1980s, the unique properties of these materials are only now being harnessed to address societal challenges. Faculty and staff at the Colorado School of Mines (CSM) are actively developing protonic ceramics for use as fuel cells for efficient electricity generation (PCFCs), electrolyzers for energy storage (PCECs), and membrane reactors for fuels upgrading (PCMRs). Doped barium cerate-zirconate materials (BaCexZr1-x-yYyO3-d) are the focus of these efforts at CSM. The mixed ionic-electronic conductivity of these protonic ceramics can be exploited for developing cost-effective, novel solutions and new products. Many previous approaches used to advance solid-oxide fuel cells are equally relevant for tuning the properties of protonic ceramics to meet the diverse needs of these different applications. In this talk, we will present several such efforts now underway at CSM. As part of an ARPA-E-funded program, our team recently demonstrated a fuel-cell stack based on BaCe0.2Zr0.6Y0.2O3-d (BCZY26) protonic-ceramic materials. To the authors’ knowledge, this is the first reported result of a PCFC stack. The effort included a ten-fold scale up in cell size, and integration of these cells into a stack package. A three-cell stack achieved a power density of 180 mW cm-2 at 0.78 V under methane fuel at 550 ºC. While this PCFC performance is encouraging, we found that similar protonic-ceramic materials demonstrated inefficient operation in electrolysis mode. Heightened electronic conductivity was observed under reverse bias, likely due to cerium reduction. By reducing the cerium content to below the percolation threshold, greatly improved Faradaic efficiency was confirmed. The team is now developing PCEC stacks using BaCe0.1Zr0.8Y0.1O3-d (BCZY18) electrolytes; 95% Faradaic efficiency was observed at 120 mA cm-2 and 600 ºC. Electronic conduction is undesirable in fuel cells and electrolyzers; however, it may prove advantageous for hydrogen-separation membranes and membrane reactors. In an effort to increase flux through “passive” hydrogen-separation membranes, CSM is developing protonic-ceramic composites to increase membrane electronic conductivity. By mixing the BCZY material with an electronic conductor, a two-phase membrane with more balance between protonic and electronic conduction can be realized. Both ceramic (Ce0.8Y0.2O2-d) and metallic (Cu) electronic conductors are being explored as the second phase. While at an early stage of development, these two-phase hydrogen-separation membranes have demonstrated some of the highest thickness-normalized hydrogen fluxes ever observed through ceramic materials. In this presentation, these efforts will be reviewed, with latest results presented.

Durability and characterization studies of chromium carbide coated aluminum fuel cell stack

Corrosion and interfacial contact resistance measurements were performed on chromium carbide coated aluminum 6061 and as-received aluminum 6061 samples. The coating was thermally sprayed onto the aluminum sample using the High Velocity Oxygen Fuel (HVOF) thermal spray technique. The chromium carbide coating consists of Cr3C2 top layer and CrCNi intermediate layer. The coating thickness was approximately 150 μm. A three-cell stack with chromium carbide coated aluminum bipolar plates was also fabricated for the durability and characterization studies. The coating thicknesses on the lands of the ribs and the walls of the valleys were approximately 300 μm and 150 μm, respectively. The stack was operated at the temperatures of 37 °C for 250 h and 80 °C for additional 500 h. The scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) analysis shows that the thickness, chemistry, and surface morphology of the coating material remained consistent after 750 h of operation. The inductively coupled plasma – optical emission spectroscopy (ICP-OES) analysis was performed on the samples of membrane electrode assembly (MEA) and byproduct water that was produced during the fuel cell electrochemical reaction.

Protonic Ceramic Fuel Cell Stacks

In this report, we present our work on development of fuel cell stacks based on proton-conducting ceramic materials. Such protonic-ceramics have demonstrated great promise for addressing the technological challenges now facing the solid-oxide fuel cell community. Protonic ceramic fuel cells (PCFCs) based on BaCe0.7Zr0.1Y0.1Yb0.1O3-δ have demonstrated high power density at low operating temperatures, achieving 450 mW / cm2 at 500 ºC under hydrogen fuel [1, 2]. PCFCs may also be more amenable to internal reforming of hydrocarbon fuels (CH4 + H2O => 3 H2 + CO). Proton conduction removes H2from the anode stream, thereby shifting the internal-reforming equilibrium chemistry towards the products, promoting higher methane conversion. While these materials show great promise, no multi-cell PCFC stacks have been fabricated to date. In this presentation, we review our progress in extending previous single “button-cell” experiments to small fuel-cell stacks. The stack design is shown in Figure 1; PCFC membrane-electrode assemblies (MEAs) are bonded within a ceramic frame, and the frame is packaged within ferritic-steel interconnects. Fabrication of MEAs involves solid-state reactive sintering (SSRS), where the protonic-ceramic fuel cell material is formed from simple parent oxides during co-sintering of the anode-electrolyte assembly. This single-step fabrication greatly reduces MEA-manufacturing costs and improves yields. Multi-cell stack prototypes have been demonstrated. A three-cell stack based on BaCe0.2Zr0.6Y0.2O3-δ electrolyte shows open-circuit voltage that approaches the theoretical Nernst potential (Figure 1), and demonstrates excellent stability over 500 hours of continuous operation. The stack also yields reasonable power density, reaching 250 mW/cm2at 650 ºC. Moving forward, higher performance is expected as we improve fabrication and packaging methods. Citations: [1] C. Duan, J. Tong, M. Shang, S. Nikodemski, M. Sanders, S. Ricote, A. Almansoori, R.P, O’Hayre, “Readily processed protonic ceramic fuel cells with high performance at low temperatures,” Science 349: 6254 (2015) 1321-1326. [2] J. Kim, S. Sengodan, G. Kwon, D. Ding, J. Shin, M. Liu, G. Kim, “Triple-conducting layered perovskites as cathode materials for proton-conducting solid oxide fuel cells,” ChemSusChem 7(2014) 2811–2815. Figure 1

Hydrogen Production with a Simple and Scalable Membraneless Electrolyzer

Ion-conducting membranes are essential components in many electrochemical devices, but they often add substantial cost, limit performance, and are susceptible to degradation. This work investigates membraneless electrochemical flow cells for hydrogen production from water electrolysis that are based on angled mesh flow-through electrodes. These devices can be fabricated with as few as three parts (anode, cathode, and cell body), reflecting their simplicity and potential for low-cost manufacture. 3D printing was used to fabricate prototype electrolyzers that were demonstrated to be electrolyte agnostic, modular, and capable of operating with minimal product crossover. Prototype electrolyzers operating in acidic and alkaline solutions achieved electrolysis efficiencies of 61.9% and 72.5%, respectively, (based on the higher heating value of H2) when operated at 100 mA cm−2. Product crossover was investigated using in situ electrochemical sensors, in situ imaging, and by gas chromatography (GC). GC analysis found that 2.8% of the H2 crossed over from the cathode to the anode stream under electrolysis at 100 mA cm−2 and fluid velocity of 26.5 cm s−1. Additionally, modularity was demonstrated with a three-cell stack, and high-speed video measurements tracking bubble evolution from electrode surfaces provide valuable insight for the further optimization of electrolyzer design and performance.

Electrochemical performance and long-term durability of a 200 W-class solid oxide regenerative fuel cell stack

The electrochemical performance and durability of a 200 W-class solid oxide regenerative fuel cell (SORFC) stack are investigated for cyclic mode-changing and long-term operation. Three unit cells (10 cm × 10 cm), each based on a Ni – yttria-stabilized zirconia (YSZ) fuel electrode, a scandia-stabilized zirconia (ScSZ) electrolyte and a Sr-doped LaCoO3 (LSC) – gadolinia-doped ceria (GDC) air electrode, are used for the stack development. Delamination of the air electrode is suppressed by using a mixed ionic- and electronic-conducting air electrode with no oxygen excess non-stoichiometry, and gas leakage is minimized by using novel glass-ceramic composite sealants. Excellent electrochemical performance is achieved in a single cell level by minimizing the ohmic and electrode polarizations, and the three-cell stack is successfully configured without major performance loss associated with electrical contacts, gas supply or sealing. Stable operation is confirmed at a thermal neutral voltage for 1000 h in the solid oxide electrolysis cell (SOEC) mode, and the periodic change of the operation mode between the solid oxide fuel cell (SOFC) and SOEC is found to accelerate the performance degradation. The effect of cyclic mode-changing on the stability of the SORFC stacks is discussed in detail based on the observations from the post-mortem microstructural analysis.

Study of a Single‐Chamber Solid Oxide Fuel Cell Microstack with V‐Shaped Congener‐Electrode‐Facing Configuration

AbstractSingle‐chamber solid oxide fuel cell (SC‐SOFC) microstacks with V‐Shaped congener‐electrode‐facing configuration were fabricated and operated successfully in a box‐like stainless steel chamber. Two gas channels with small gas inlets were used to transport the fuel and oxygen to the anodes and cathodes, respectively. The temperature of an anode‐facing‐anode two‐cell stack was higher than that of a cathode‐facing‐cathode two‐cell stack during the test procedure. For a three‐cell stack, the cell in the middle region presented the highest power output. The open circuit voltage (OCV) and maximum power output of the three‐cell stack in a gas mixture of 100 sccm N2, 120 sccm CH4, and 80 sccm O2 were 3.0 V and 413 mW, respectively.

Design and Experimental Characterization of a High-Temperature Proton Exchange Membrane Fuel Cell Stack

Proton exchange membrane (PEM) fuel cells based on polybenzimidazole (PBI) polymers and phosphoric acid can be operated at temperature between 120 °C and 180 °C. Reactant humidification is not required and CO content up to 1% in the fuel can be tolerated, only marginally affecting performance. This is what makes high-temperature PEM (HTPEM) fuel cells very attractive, as low quality reformed hydrogen can be used and water management problems are avoided. From an experimental point of view, the major research effort up to now was dedicated to the development and study of high-temperature membranes, especially to development of acid-doped PBI type membranes. Some studies were dedicated to the experimental analysis of single cells and only very few to the development and characterization of high-temperature stacks. This work aims to provide more experimental data regarding high-temperature fuel cell stacks, operated with hydrogen but also with different types of reformates. The main design features and the performance curves obtained with a three-cell air-cooled stack are presented. The stack was tested on a broad temperature range, between 120 and 180 °C, with pure hydrogen and gas mixtures containing up to 2% of CO, simulating the output of a typical methanol reformer. With pure hydrogen, at 180 °C, the considered stack is able to deliver electrical power of 31 W at 1.8 V. With a mixture containing 2% of carbon monoxide, in the same conditions, the performance drops to 24 W. The tests demonstrated that the performance loss caused by operation with reformates, can be partially compensated by a higher stack temperature.