Anode Outlet Research Articles

Experimental investigation on operational stability and its influencing mechanisms for PEMFC with dead-ended anode

Proton exchange membrane fuel cell (PEMFC) with dead-ended anode (DEA) suffers from nitrogen diffusion and water accumulation, leading to unstable performance. The core of this paper is to enhance the stability of DEA operation. By coupling the flow field structure with the DEA mode, the factors affecting the stability are explored, the performance degradation mechanism after DEA operation is revealed, and the purging strategy is formulated by combining the energy management with the voltage stability as a prerequisite. The experimental results show that the serpentine flow field is advantageous for maintaining the most stable DEA operation with a minimum voltage recession of 17.01 mV and a voltage undershoot of 11.63 mV. The local current density distribution exhibited a pattern of highest values at anode inlet and lowest at anode outlet, which could be improved by increasing operating pressure and reducing load current density. In this experiment, PCB was innovatively combined to investigate the degradation of each region of PEMFC after 60h of DEA operation. It is found that the most severe performance degradation occurs in anode outlet with a degradation rate exceeding 50%, while the center area has a degradation rate of no more than 20%.

Impact of fuel starvation–induced anode carbon corrosion in proton exchange membrane fuel cells on the structure of the membrane electrode assembly and exhaust gas emissions: A quantitative case study

Although the durability of proton exchange membrane fuel cells (PEMFCs) is crucial for their broad commercial applications, current durability assessments do not encompass all operational scenarios. Startup/shut-down (SUSD) are among the most significant degradation factors in the city. To bridge this gap, we examine the phenomenon of fuel starvation, which leads to the rapid and irreversible degradation of PEMFC performance, particularly during SUSD, but has not been independently examined in the context of PEMFC durability. A quantitative methodology is used to analyze anode carbon corrosion and establish correlations with critical parameters under fuel starvation conditions. In particular, we quantify carbon loss based on (i) the composition or amount of the anode outlet gas emitted under such conditions and (ii) changes in the anode thickness at three distinct locations. The corresponding carbon losses due to 10 min of fuel starvation ((i): 212.0 μg cm−2, (ii): 189.6 ± 12.9 μg cm−2) agree well with each other. The largest decrease in the anode thickness (81.3 %) is observed near the outlet. The obtained insights provide guidance for the design of high-performance PEMFCs and the development of protective measures against the detrimental effects of fuel starvation.

An experimental study on the hydrogen utilization in air-cooled proton exchange membrane fuel cell stack with a novel anode outlet design

In the realm of portable power system, air-cooled fuel cells stand out for their lightweight design and emission-free operation. Anode purging has emerged as an effective method to alleviate performance degradation in the dead-end anode stack. However, purging frequency can affect hydrogen utilization and output performance. This research aims to reduce the purging frequency and enhance hydrogen utilization of air-cooled fuel cell stacks by introducing a novel anodic outlet endplate. The novel outlet helps to remove liquid water and nitrogen from the stack, improve the output performance, and save the hydrogen usage in the air-cooled fuel cell stack. The peak power outputs of stacks equipped with the novel and conventional anodic outlets are recorded at 2313.95 W and 2213.35 W, respectively. Significantly, the novel anodic outlet configuration demonstrates a 4.54 % increase in peak power. Moreover, this configuration extends the purging interval, leading to a reduction in purging frequency. Under current load of 62 A, the novel anode outlet stack prolongs the purging interval of 134.73 s compare to its counterpart with a conventional anodic outlet than that of the conventional anode outlet. The findings presented in this study are poised to offer valuable insights into optimizing their efficiency and promoting sustainable solutions.

Stack-level analysis of the performance variation in air-cooled PEMFC with Z-type anode manifold

Air-cooled proton exchange membrane fuel cell (PEMFC) stack holds significant promise due to its potential to reduce system complexity. The anode manifold type leads to gas maldistribution in an air-cooled stack, and affects the efficiency and life span of the stack. In this study, 3D multi-physics model of stacks ranging from 10 to 40 cells are established to investigate the gas distribution characteristic of Z-type anode manifold. Considering the heat dissipation aspects only, it is advisable to keep a thin endplate while meeting the required stress tolerances. The core temperature of the stack with 20 mm endplates measures 43.8 °C, while the stack with 6 mm endplates reaches a core temperature of 45.5 °C. Under a cathode air flow velocity condition of 4 m‧s−1, the maximum net oxygen consumption reaches 1.69 mol‧s−1 in Cell-4. Furthermore, the electrochemical reaction intensity decreases sequentially from Cell-4 and Cell-5 in the middle to Cell-1 and Cell-10 in the edges of the stack. Additionally, cells near the anode inlet and outlet are prone to have the insufficient gas supply in the Z-type anode manifold stack.

Operando X-ray radiography of liquid water distribution in 100 mm polymer electrolyte fuel cell channels

Preventing the accumulation of water in the gas diffusion layer (GDL) proves effective in enhancing the performance of polymer electrolyte fuel cells (PEFCs). To understand the water transport phenomena in GDLs and channels of PEFCs, cell hardware for operando synchrotron X-ray radiography was developed with a 100 mm channel length, facilitating the separate quantification of liquid water in the cathode and anode GDLs. The presence of liquid water in the cathode and anode GDLs was confirmed during operation with a supply of dry gas in a counter-flow configuration. Furthermore, the amount of liquid water in the cathode and anode GDLs increased toward the cathode inlet, while the amount of water in the cathode and anode channel regions increased toward each outlet. The liquid water distribution in the GDLs along the channel direction can be attributed to water transport from cathode to anode (back-diffusion), decreasing toward the anode outlet. Therefore, conducting radiography experiments aligned parallel to the GDLs and perpendicular to the channel could provide valuable insights for a more comprehensive understanding of water transport in cells.

Cathode Catalyst Layer Design in PEM Water Electrolysis toward Reduced Pt Loading and Hydrogen Crossover.

Reducing the use of platinum group metals is crucial for the large-scale deployment of proton exchange membrane (PEM) water electrolysis systems. The optimization of the cathode catalyst layer and decrease of the cathode Pt loading are usually overlooked due to the predominant focus of research on the anode. However, given the close relationship between the rate of hydrogen permeation through the membrane in an operating cell and the local hydrogen concentration near the membrane-cathode interface, the structural design of the cathode catalyst layer is considered to be of pivotal importance for reducing H2 crossover, particularly in combination with the use of thin (≲50 μm) membranes. In this study, we have conducted a detailed investigation on the cathode structural parameters, covering the Pt wt % of the Pt/C electrocatalyst, the type of carbon support (Vulcan and high surface area carbon, HSAC), and the ionomer content, with a goal to reduce Pt loading to 0.025 mgPt/cm2 while minimizing the rate of cell hydrogen crossover. We found that the electrochemical performance is mainly influenced by the changes in the interfacial contact resistance due to variations in the cathode thickness. Both the Pt wt % in Pt/C and the ionomer content showed a positive correlation with the measured H2 in O2% in the anode outlet, whereas the Pt loading exhibited an opposite trend. The rate of hydrogen crossover was analyzed in relation to the calculated local volumetric current density within the cathode catalyst layer. Based on the obtained hydrogen mass transfer coefficient, a cathode catalyst layer comprising 40 wt % Pt on HSAC support with an ionomer-to-carbon (I/C) ratio of 0.35 was found to be an optimum configuration for achieving a low Pt loading of 0.025 mgPt/cm2 and a reduced rate of hydrogen crossover.

Thermodynamic performance evaluation of a novel solar-assisted multi-generation system driven by ammonia-fueled SOFC with anode outlet gas recirculation

The cracking of ammonia to produce hydrogen and nitrogen at high temperatures, without carbon dioxide emissions, has great potential for future energy development. Hence, a novel solar-assisted multi-generation system driven by ammonia-fueled SOFC with anode outlet gas recirculation is proposed and the thermodynamic models are constructed. Under the design conditions, the exergy efficiency, and primary energy saving rate of the novel system in summer are 47.83%, and 51.36%, respectively, while in winter, they are 50.52%, and 52.01%, respectively. Meanwhile, the thermodynamic performances of the new system and two reference systems are compared, in which the reference system 1 isn't coupled with a solar collector, and SOFC adopts an anode outlet gas recirculation layout, the reference system 2 has neither coupled solar collector nor anode outlet gas recirculation arrangement for SOFC. The results demonstrate that the anode outlet gas recirculation layout and coupling solar collectors in SOFC help to reduce the fuel consumption of the system. Moreover, the subsystem's exergy flow diagrams under the design condition reveal the exergy destruction of the components. And the impacts of key factors including SOFC operating temperature, fuel utilization rate, direct normal irradiance, and hydrogen recovery factor are analyzed.

Visualization study of improving anode water management by variable pressure hydrogen supply in proton exchange membrane fuel cell

To alleviate the prolonged closure of anodic outlet, which causes water to gradually accumulate in the porous layers that hinder hydrogen transfer in dead-ended anode mode. This study proposes an anode variable-pressure hydrogen supply strategy. The hydrogen supply pressure is suddenly reduced for a period before triggering purging, creating a pressure difference between the membrane assembly electrode and flow channels to induce water discharging into the flow channels, then directly purging out of the cell. Optical visualization is utilized to observe and analyze the effect of this strategy on water distribution and quantified through voltage, power, purging pressure change, and water coverage rate. Experiments indicate that the sudden pressure change in the variable pressure hydrogen supply mode effectively promotes water discharge from the porous layers, provides higher water coverage within the entire flow field, and promotes the fusion of neighboring droplets to form larger ones for better water management. Compared to normal mode, the proposed strategy achieves 3.4% performance improvement at 0.32A/cm2. Furthermore, a higher abrupt pressure difference favors porous layers drainage, but the optimal low-pressure duration requires a trade-off between drainage facilitating hydrogen transport and recovery of the membrane water content.

Effect of Asymmetrically Reinforced Membrane on Anion Exchange Membrane Fuel Cell

Anion Exchange Membrane Fuel Cells (AEMFCs) is promising for the generation of electric power from hydrogen, with the expected possible replacement of precious metal catalysts by Earth abundant ones.[1-2] Beyond the independent properties of core materials (AEM, anode and cathode catalysts), the water management during operation is key to achieving high power density, but also high longevity. Thin AEMs are critical to achieve high AEMFC power performance, as the back-diffusion of water from anode to cathode critically helps to mitigate anode flooding. [3] Due to the high swelling of hydrated AEMs, good mechanical durability of thin AEMs however typically requires the introduction of a reinforcement, often a porous polytetrafluoroethylene (PTFE) membrane filled with the anion exchange ionomer.Here, we investigated the structure of different commercial AEMs and their behavior in operating AEMFC. We identified that the position of the reinforced layer (PTFE or other) strongly differs from one type of AEM to another. In the case of strongly asymmetric through-plane position of the PTFE layer (Fig. 1a), the positioning of the PTFE reinforcement close to anode or to cathode has a significant impact on initial power performance (Fig. 1b). A better performance and improved stability was observed with the PTFE layer close to the anode, suggesting that the asymmetric structure can improve the water management in such configuration. The presentation will discuss the results obtained on different commercial AEMs, and whether the asymmetric structure of AEM can be combined with PTFE hydrophobized anodes for even improved performance. The effect of the reinforcement position on the water management was also studied operando by two techniques. With high energy X-ray diffraction technique on an AEMFC under current load, the water distribution profile across the MEA thickness could be obtained from phase deconvolution analysis. With the use of relative humidity sensors at the outlet of anode and cathode of a regular AEMFC setup, [4] the water balance at a given current load could be established and compared for the two different positionings of reinforced AEM.The results shed light on the importance of identifying the position of PTFE reinforcement in commercial or in-house AEM for AEMFC application, with potential implications also for AEM electrolyzers or water-CO2 co-electrolyzers.

Analysis of the performances of a solid oxide fuel cell fed by biogas in different plant configurations: An integrated experimental and simulative approach

Solid Oxide Fuel Cells (SOFC) are efficient, modular and fuel-flexible high temperature electrochemical devices. SOFC systems can be coupled to biogas from anaerobic digestion plants to obtain efficient and decentralized CHP systems, maximizing the valorization of biogas in virtuous waste-to-energy schemes. The main challenges for biogas-SOFC plants are related to performance stability and degradation at process level. In this work the performance and stability of an electrolyte supported SOFC single cell (100 cm2) fed with biogas mixtures derived from different integrated biogas-SOFC CHP plant configurations (hot/cold recirculation; UFf 65–85% - obtained from previous simulation work) has been analyzed with an integrated experimental and simulative approach. To support the experimental results, a chemical equilibrium model of the gas conversion processes coupled with the electrochemical conversion route is developed in MATLAB in order to simulate the gas composition at the anode outlet, which is compared and validated with experimental data obtained by Gas Chromatography (GC). Results show that suitable and stable cell performances are obtained while feeding the SOFC samples by biogas (720–800 mV; 0.16–0.2 W/cm2 at 0.25 A/cm2) where the main performance losses are related to steam content - as well as other gas species, deriving from the pre-processing of the biogas. The gas composition and UFf simulation results show good correspondence with the GC data (error range <5% for the matrix gases and <10% for water) highlighting that the SOFC processes under clean biogas can be successfully represented - to a certain extent - by a chemical equilibrium model.

Experimental Demonstration of the Electric Efficiency with BZYb based Protonic Ceramic Fuel Cell

Protonic Ceramic Fuel Cell (PCFC) is expected to be the next-generation fuel cell for its higher energy conversion efficiency and lower operation temperature. BaZrO3 based oxide are potential materials as PCFC electrolyte because they have a high chemical stability under CO2 condition and high proton conductivity. We have developed PCFC using BaZr0.8Yb0.2Ox (BZYb) as the electrolyte and performed max power density 0.49 W cm–2 at 873 K. For practical use of PCFC, it is needed to conduct the higher electric efficiency and to improve the durability. Especially, improving the electric efficiency of PCFC might be difficult due to the internal current leakage by the hole creation.In this work, we have evaluated the electric efficiency using a Φ60mm anode supported PCFC (active electrode area: Φ45mm, 15.9 cm2). Thin and dense BZYb electrolyte is supported on porous Ni-BZYb cermet anode and La0.6Sr0.4CoOx cathode. The effect of fuel utilization on PCFC cell was examined and the electric efficiency of PCFC was calculated as follows:η = V / (-ΔH / nF) × Ufwhere the n and F are the mole number and the Faraday constant, respectively. ΔH is the standard combustion enthalpy of hydrogen or methane. The value of -ΔH / nF is 1.24 V or 1.04 V in the case of hydrogen supply or methane supply respectively. V is the cell voltage and Uf is the fuel utilization.Φ60mm anode supported PCFC was fabricated by tape-casting process used for the industrial production of ceramic electronic devices. NiO-BZYb anode slurry and BZYb electrolyte slurry were prepared by mixing the powder, binder, solvents and plasticizer. And then, these slurries were tape-casted respectively. The anode green sheets and the electrolyte green sheets were stacked and pressed. The anode electrolyte half-cell was obtained by firing this laminate at 1673–1773 K for 2 h. La0.6Sr0.4CoO3-δ (LSC) paste was applied to the surface of the half-cell by screen–printing, and then, fired at 1223 K for 2 h to form a cathode.The electrochemical performance of the Φ60mm anode supported PCFC was investigated at 873 K under the conditions of a humid fuel gas (i.e., 3% H2O, 48.5% N2 and 48.5% H2) and a humid air (i.e. 3% H2O and 97% air). Fuel flow rate were determined by the operational current and the fuel utilization (Uf), and air flow rate were constant at 264 cc min–1, which the air utilization (Uair) was 30% at the current of 0.3 A cm–2.Figure 1 shows the comparison of the current-voltage (I-V) and current-power (I-P) characteristics of Φ60mm and Φ20mm BZYb cell. Fuel flow rate was 100 cc min–1 at this experiment. The same electrochemical performance was observed, and the maximum power reached 7 W at 12.9 A in the case of the Φ60mm cell.Figure 2 shows the cell performance of 0.3 A cm–2 current density under the various Uf condition. The theoretical voltage line was also drawn in the figure, which was calculated by Nernst equation used the PH2 in the anode outlet gas, PO2 and PH2O in the cathode outlet gas. Cell voltage followed the same path as the theoretical voltage in the low Uf condition (Uf≦70%). On the other hand, the gap between the cell voltage and theoretical one was larger in the higher Uf condition (Uf≧80%). Anode gas diffusion overvoltage might be increased by PH2 decreasing in anode gas or the imbalanced gas flow due to decreasing the anode gas flow rate. We demonstrated that BZYb based PCFC could be operated at high Uf condition (i.e., Uf=90%) and the maximum electric efficiency was 55% (DC). This presentation is partially based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

Thermodynamics assessment and dynamic simulation of a low-carbon syngas-fueled SOFC system using a green hydrogen blend

Green hydrogen is currently eye-catching in terms of its production, storage and delivery to facilitate energy transition. In the present research, it is tried to demonstrate the capability of green hydrogen in blending with syngas (produced by biomass gasification) to feed an SOFC system in order to supply electrical power and heating for an existing educational building. Dynamic simulation has been performed in TRNSYS Software to calculate the hydrogen production annually at different scenarios. Effects of hydrogen concentration in the fuel mixture on the performance of the proposed CHP system are assessed. Results indicated that utilizing a reasonable roof area can offer approximately 10,000 kg H2 and 70,000 kg H2 per year in cases of grid-zero connected and grid 85% connected, respectively. It is revealed that increasing the hydrogen share in fuel mixture from 5% to 30% increases noticeably the hydrogen gas percentage at the SOFC anode inlet and outlet while it has a reverse effect on the H2O amount. In addition, the studied increment in hydrogen share could increase 18% of the net output power from the system. Finally, related to the CO2 emission from the system, it is found that 58% reduction could be achieved by increasing the hydrogen share in the fuel blended.

Thermodynamic and economic performance study of SOFC combined cycle system using biomass and LNG coupled with CO2 recovery

The search for more efficient, energy-saving and cleaner methods of energy utilization is a current research focus. In this study, a novel solid oxide fuel cell (SOFC) combined cycle system fueled by biomass syngas and natural gas is studied, with carbon capture by using liquefied natural gas (LNG) cold energy. In the proposed system, the exhaust from the cathode and anode outlets of SOFC is split to do work instead of the traditional approach of exhaust mixing, thus achieving CO2 capture using LNG cold energy more efficiently. The system is simulated by Aspen Plus software with embedded Fortran. The energy analysis and exergy analysis of the system are performed. The results indicate that under design conditions, the thermal efficiency, electrical efficiency and exergy efficiency of the system are 60.28 %, 66.20 % and 55.59 %, respectively. The amount of carbon capture purity and the mass flow rate of liquid CO2 are 99.35 % and 54.50 kg/h. The largest exergy loss occurs in heat exchangers, which accounts for 35.63 %. In addition, sensitivity analysis of the system is performed and the variation law of thermodynamic and economic performance with parameters is obtained based on the simulation results. This study not only provides a theoretical basis for subsequent research on the way to improve the efficiency of SOFC combined cycle system, but also provides new ideas for the efficient utilization of biomass combined with natural gas.

Photometric Method to Determine Membrane Degradation in Polymer Electrolyte Fuel Cells

A new method for measuring membrane degradation in polymer electrolyte fuel cells (PEFCs) is proposed. The method is based on the detection of fluoride ions in effluent water from the cathode- and anode outlet of the PEFC using photometry (PM). The fluoride emission rate (FER) is an indicator of the membrane’s state of health (SoH) and can be used to measure the chemical membrane degradation. Commercial catalyst-coated membranes (CCMs) have been tested at 80 °C and 90 °C at 30% relative humidity (RH) to investigate the reliability of the developed method for fuel cell effluent samples. To verify the measurement, a mean-difference plot was created by measuring the same data with a fluorine selective electrode. The average difference was at ±0.13 nmol h−1 cm−2, which indicates good agreement between the two methods. These new findings imply that PM is a promising method for quick and simple assessment of membrane degradation in PEM technology.

Numerical analysis on the effects of manifold design on flow uniformity in a large proton exchange membrane fuel cell stack

The size and configuration of manifold can affect the flow characteristics and uniformity in proton exchange membrane fuel cell (PEMFC) stack; then its efficiency and service life. Based on the simulation results of a single fuel cell considering electrochemical reaction, a stack model with 300 porous media is established to numerically investigate the performances of a large commercial PEMFC stack. The effects of manifold width and configuration type on the pressure drop and species concentration are studied by computational fluid dynamics (CFD). The results show that the uniformity for most cases of U-type configuration is better than those of Z-type configuration. For U-type configuration, a very good uniformity can be obtained by selecting anode inlet manifold width of 20 mm and anode outlet manifold in range from 25 to 30 mm; the uniformity is bad for all cathode inlet manifold width, relatively better uniformity can be achieved by adjusting cathode outlet manifold width. For Z-type configuration, bad uniformity is found for cathode inlet and outlet manifold with all width; a relatively good uniformity can be obtained with suitable anode manifold width of 35 mm. The research can provide some references to improve gas distribution uniformity in large PEMFC stacks.

Study on the effect of purging time on the performance of PEMFC with dead-ended anode under gravity

In the working process of proton exchange membrane fuel cell (PEMFC) with dead-ended anode (DEA), the accumulation of water and nitrogen in the anode flow channel will cause its transient working performance to degrade. Generally, the transient working performance is recovered by periodically opening the anode outlet for gas purging. However, the purging time under gravity will change the distribution state of water and gas in the anode flow channel, thus seriously affecting the working performance of PEMFC with DEA. In this paper, the influence mechanism of purging time on the performance of PEMFC with DEA under gravity is investigated by theoretical analysis and experimental method. The results show that if the purging time under gravity is shorter, the faster the transient working performance of PEMFC with DEA decreases in the next working cycle, and the area with high current density distribution is always close to the gas inlet of the flow channel, as well as the area with low current density distribution is always close to the gas outlet of the flow channel. Moreover, the effect of different purging times on the local current density distribution will lasts for a long time, and also have significant effects on the accumulation and distribution status of water at the anode side under gravity. The results can provide an important guidance for optimizing the purging strategy of PEMFC with DEA.

Oxygen and Carbon Dioxide Separation at Cathodes of Anion Exchange Membrane Cells

From the development of anion exchange membrane fuel cells it is known that airborne CO2 is easily absorbed in this type of membranes and has a detrimental effect on the conductivity of the membrane1. It was also found, however, that at sufficiently high current densities carbonate and hydrogen carbonate ions are flushed out of the membrane and ion conduction occurs predominantly via hydroxyl ions1. This behavior led to the idea of using AEM based cells for gas separation for two different type of applications. So, during the first waves of COVID-19 medical oxygen became a scarce resource. Local production of oxygen by separation from air is an interesting approach to overcome this issue. This should be feasible using an anion exchange membrane cell with an air side oxygen reduction electrode and an oxygen evolution electrode. The hope is that in combination of these two reactions the required cell voltage can be kept much below typical water electrolysis voltages so that operation with simple PV cells or modules is possible. At the same time the question is if current densities can be achieved at which the OH- transport and thus the anodic release of O2 dominates, as an enrichment of CO2 must be avoided for this application. On the opposite there are worries about the effect of increasing CO2 concentration in occupied confined rooms like vehicles. Here a device that removes CO2 from air without consuming much oxygen is desirable. The removal of CO2 from the air supply to AEM fuel cells by an additional cell placed upstream of the cathode inlet and downstream of the anode outlet was demonstrated by Matz at al.2. As for CO2 separation only, no hydrogen is available for the anode reaction here again the operation against an oxygen evolution electrode is required, optimized, however, towards the CO2 transport minimizing O2 transport.In this study for one type of AEM membrane and ionomer, namely Fumapem FAA3 and Fumion (both Fumatech BWT, Germany) the effect of different cathode electrodes and electrode materials as well as the effect of operation conditions towards the selectivity of oxygen or CO2 transport were investigated. For that purpose, test set-ups were used were the cathode side was supplied with synthetic air, compressed air or synthetic air with added CO2 and the anode side with an inert gas N2 or helium. Nass spectrometry and dedicated CO2 concentration sensors were used to determine the anodic release of O2 and CO2 as well as the reduction of O2 and CO2 concentrations on the cathode side.First measurements of the oxygen transfer using a cell with a silver cathode (Oxag, Gaskatel, Germany) and a nickel foam anode (Gaskatel, Germany) it was found that the oxygen transfer had a promising faradaic efficiency exceeding 80% (cf. Fig. 1). The cell voltage of 1.5 V at 90 mA cm-2 was however still too high for the application. Replacing the Oxag silver electrode by an industrial ORR electrode for alkaline cells did not yield an improvement (cf. fig 2). Increasing humidification to 100 % r.H. improved the current density (cf. Fig 3). Using high humidification conditions, the CO2 effect was studied by switching from synthetic air to pressured air and back and 160 mA cm-2. A rapid increase of the anodic CO2 concentration to values exceeding 2000 ppm was observed (cf. Fig. 4). Comparing CO2 transfer for cells with Oxag cathode and the commercial ORR cathode again showed that the latter would not improve the situation. It proves however, that the CO2 transfer rate can be influenced by the cathode catalyst. Regarding the CO2 separation test with synthetic air with added 3.85 Vol% of CO2 as cathode feed have shown that under such conditions, mainly CO2 is transported (cf. Fig. 5). In total it will be shown that CO2 separation with state-of-the-art materials is already possible. The use of O2 separation regarding onside production of medical O2 today fails due to still too high CO2 selectivity. The fact that CO2 selectivity seems to be dependent on the cathode catalyst may allow further optimization also valuable for AEMFC fuel cell developments.Acknowledgment: The work received financial support in parts from the Fraunhofer-Gesellschaft by the Demo-medVer project part project e3C-O2 as part of the Fraunhofer cs. Corona program. M. Inaba, Y. Matsui, M. Saito, A. Tasaka, K. Fukuta, S. Watanabe and H. Yanagi, Electrochemistry, 79, 322–325 (2011). 2. S. Matz, B. Setzler, C. M. Weiss, L. Shi, S. Gottesfeld and Y. Yan, Meet. Abstr., MA2020-02(34), 2227 (2020). Figure 1

Numerical and experimental assessment of a novel SOFC-based system for micro-power generation

In this work, a novel micro-scale system based on solid oxide fuel cells (SOFCs) is studied for operation at low temperature, assessing the expected performance numerically and the actual cell operation experimentally. The potential application is powering gas-connected but off-electric-grid remote electronic devices with nominal capacity of tens of watts, such as those necessary to monitor and operate the gas grid, using methane as feed. Since water is generally not available in such distributed uses, feed pre-treating is critical and poses technical challenges for the high and stable performance of the SOFC. Several promising design configurations for the system are defined. The use of commercial YSZ-based SOFCs is envisioned, and recirculation is needed to avoid carbon deposition, which is predicted by the calculation of carbon activity and confirmed by the experimental observations. A higher anodic recirculation is required at low (≤50%) fuel utilization in order to decrease the estimated carbon activity, due to a lower content of oxygen atoms in the anode outlet stream. The anode inlet composition was numerically estimated assuming a fuel utilization factor of 70% with 60% anodic recirculation, then was experimentally tested, achieving a stable power generation without carbon deposition.

Experimental study on the dynamic performance of an air-cooled proton exchange membrane fuel cell stack with ultra-thin metal bipolar plate

In this paper, a compact 3 kW air-cooled fuel cell stack consists of 95 single cells with metallic bipolar plate is designed. Compared with graphite bipolar plates, metal stamping bipolar plates are lighter in weight, smaller in size and faster in heat conduction, therefore the transient behaviors of the voltage and temperature of each cell are analyzed. The results show that the heat distribution of the air-cooled fuel cell is very uniform, and the temperature difference between the inlet and outlet of cathode air of the fuel cell is lower than 15 °C. The individual cell voltage uniformity percentage variation value reaches 7% when the drop in the loading current is over 25 A. Moreover, the voltage uniformity variation value is higher than 4% when the loading current output exceeds 35A. Thus, a large drop in loading and a high loading current easily increase the voltage uniformity variation value. Long-term continuous operation has a negative influence on the performance of the stack, especially the last fuel cell near the anode outlet. Anode purging can effectively alleviate the uniformity percentage variation in the voltages. The designed air-cooled fuel cell exhibits good performance and strong environmental adaptability.

Modeling and analysis of water vapor dynamics in high-temperature proton exchange membrane fuel cell coupling gas-crossover phenomena

A 3-D numerical model coupling gas-crossover phenomena for high-temperature proton exchange membrane fuel cell (HT-PEMFC) is developed to investigate the water vapor behavior. After model validation, sensitivity analysis of the water vapor diffusion coefficient is carried out, which does not further affect the water vapor behavior, when the order of magnitude of diffusion coefficient is higher than 10−5m2/s. It is also found that the water vapor transport flux decreases with increasing membrane thickness. However, the flux increases slightly with increasing the catalyst layer. In addition, Increasing the pressure and humidity on the anode side will cause water vapor to diffuse from the anode to the cathode, while increasing the current density or the pressure of cathode, the rate of water vapor transport from the cathode to the anode is enhanced. In the dead-end mode, the accumulation of water vapor at the anode outlet is the main cause for the reversible performance decline, which can be restored through reasonable purge strategies. This work contributes to improve the water management strategy of HT-PEMFC operating in dead-end mode.