Cathode Airflow Research Articles

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.

Evaluation criterion of cathode flow field in air-cooling proton exchange membrane fuel cells

In recent years, air-cooling proton exchange membrane fuel cells (PEMFCs) have become a priority choice for applications due to their lightweight and simple structure. In this work, the mechanism of cathode flow field characteristics on PEMFC performance is revealed, and the evaluation criterion of the cathode flow field is proposed. A 2 kW PEMFC stack of 100 cells is used, and the different uniformity and airflow rate of the cathode flow field are achieved by varying the position and number of cathode fans with a constant total parasitic fan power. The PEMFC power, cathode temperature distribution, and single-cell voltage consistency of different configurations are evaluated. The results show that the maximum difference in output power and maximum temperature of different PEMFC cathode flow field configurations reach 6.5% and 22.3%, respectively. Three key parameters are proposed to evaluate the PEMFC cathode flow field: total uniformity rate can evaluate the overall uniformity of the PEMFC cathode flow field, vertical uniformity rate can be used to predict and evaluate the single-cell voltage consistency of the PEMFC stack, and cathode airflow rate determines the continuous operating power of the PEMFC stack. The evaluation criterion can guide the design and optimization of air-cooling PEMFCs.

Parametric analysis of efficient desalination by coupling the fuel cell exhaust and humidification-dehumidification

Humidification-dehumidification desalination is simple and can avoid membranes. However, it has a high energy consumption especially when assigned a dedicated energy source. This research proposes to serially couple the cathode airflow of a proton exchange membrane fuel cell directly to open loop humidification-dehumidification desalination, which recycles the waste heat of the fuel cell and additionally, the water vapor generated by the electrochemical reaction. A combined experiment and simulation approach is carried out to analyze the system. Several experimental trials involving different amounts of packing materials are carried out to assess the trade-off between higher humidification efficiency and increasing resistance against airflow. Then, after model validation via the experiment, simulation studies are carried out. Results reveal that an airflow rate-specific fuel cell output power of over 40 kJ/kg is recommended to ensure the exhaust gas is over 65°C and has a relative humidity of under 20 %, which are proper conditions for humidification-dehumidification desalination. Moreover, although increasing the packing material increases the humidification efficiency, it also impacts the airflow rate and heat exchange rate, which results in a worsening desalination rate. Finally, the experiment demonstrated a maximum desalination rate of 1.13 kg/h when the seawater temperature is 35°C.

The Development of a Backup SOFC Generator at Upstart Power

Upstart Power is developing a state-of-the-art SOFC generator that provides backup power solutions for residential and industrial customers. The Upgen NXG™ fuel cell enables grid independence and pairs seamlessly with solar and/or standalone battery storage to provide extended backup power and 24/7/365 energy solutions. The system has dual fuel capability using either propane or natural gas and exports AC power via Enphase micro-inverters. Field trials are being conducted including a batch of 10 units in Puerto Rico running on propane in collaboration with Sunnova.The key technologies enabling the Upgen NXG™ system’s fast cycling and overall simplicity include:1) Integrated Hot Zone with advanced Thermal Management2) Custom dry CPOx reactor (waterless)3) Control strategy based on two thermocouple setpointsThe core of the NXG system is the Hot Zone which integrates the CPOx reactor, fuel cell stack, heat exchanger, flame sensor, spark ignitor and exhaust system. Figure 1 shows the complete subsystem layout of the NXG system, including the fuel filter, blowers, power electronics and controls. The core component of the Hot Zone is a single piece structure that comprises a thermally conductive element that conducts heat from the combustion chamber to the stack inlet. This enables both rapid start-up and enhanced performance from the stack, without the risk of cell failure due to thermal stress. Figure 2 shows a Hot Zone demonstrating 1000 rapid thermal/power cycles from operating temperature down to 200°C. The chart shows power per cycle with a heat-up time of 40 minutes. Power output was increased after 800 cycles with higher power test cycles run throughout the test.The dry CPOx reactor converts fuel gas into hydrogen and carbon monoxide for use in the fuel cell without the use of any additional water. The CPOx can operate at very low O:C ratios (< 1.2) providing stack fuel efficiencies up to 40% and is controlled by a single thermocouple in the reactor core. The other system control setpoint is the temperature in the core of the hot zone which provides a simple system control scheme with minimal yet reliable sensors.Figure 3 shows real time cycle data from the Upgen NXG™ system, with a start-up time of less than 60 minutes with 9 hours of steady state AC power exporting to the grid via Enphase micro-inverters. The cathode air flow is controlled by the thermocouple in the core of the Hot Zone (Radiated).In summary, the Upgen backup power systems outperform ICE generators and battery-only backup by providing unlimited backup solar + storage systems that are more robust, cost-effective and have lower emissions. The single wall mounted unit minimizes connections and simplifies installation over an ICE generator that typically sits on an outdoor concrete pad. With near silent operation and the absence of deadly CO emissions, the Upgen NXG™ is a safe and environmentally friendly backup power solution for residential solar and industrial customers. Figure 1

Increasing power output and isopropanol biodegradation by trickle-bed microbial fuel cells by optimizing air relative humidity and oxygen flux at cathode

The cathode air flow rate and relative humidity (RH) of a trickle-bed microbial fuel cell (TB-MFC) were optimized using the response surface methodology to obtain a high oxygen flux and a low electrical resistance at the cathode and thereby promote the oxygen reduction reaction. Under optimal air flow rate (2.20 L/min) and RH (20%) conditions, the TB-MFC system exhibited the highest oxygen flux (3.08%/cm2‧min) and the lowest resistance (5.33 Ω); its regression model had an R2 > 0.95 and the desirability coefficient was 0.78. These results demonstrate that the optimized air flow rate and RH support high oxygen flux and low resistance at the cathode. Using biochar combined with conductive carbon black (CCB) as the cathodic catalyst and optimal cathodic operating conditions, yielded a mineralization efficiency of isopropanol of 96.9% and a power density of 555 mW/m3 at an empty bed residence time and isopropanol influx concentration of 60 s and 300 ppmv, respectively. These results suggest that isopropanol can be effectively mineralized directly into CO2 and H2O by a TB-MFC, reducing the by-product accumulation, and thus increasing the power generation of the TB-MFC. Optimizing the air flow rate and RH of the biochar/CCB-based cathode in the TB-MFC increases the oxygen flux and reduces the electrical resistance of the cathode of TB-MFC, which can thus be used to treat exhaust gases that contain organics.

Impact of NaCl Spray on the Durability of PEMFC Single Cells and Stacks in Marine Environment

The present work investigates the effects of a salt spray injected into the airflow of Proton Exchange Membrane Fuel Cells (PEMFCs) at various time scales and contamination levels, with the long-term objective of identifying the appropriate protection of fuel cells for maritime applications. A dedicated experimental setup generates a sodium chloride (NaCl) mist in the cathode airflow to contaminate single cells and stacks. Constant current density tests led to lifetime shortening with partial recovery after cathode rinsing. Then, Membrane Electrode Assemblies (MEAs) post-mortem characterizations revealed that NaCl was present in the cathode gas diffusion layer, and chlorine reached the catalyst layer for high concentrations. Furthermore, chlorides enhanced current collectors and bipolar plates (BPs) degradation, as corrosion products were identified in MEAs and stack effluents. A sailboat propulsion stack operated 50 h at sea was meanwhile analyzed. As for the laboratory work, chlorine and stainless steel from BPs were found in MEAs, comforting the idea that the marine environment can damage fuel cells. Overall, this study evidences that NaCl effects on PEMFCs not only depend on the concentration but also on the MEA type, plate material, and startup/shutdown procedure.

Effects of impurities in the cathode airflow on proton exchange membrane fuel cell stacks

AbstractFuel cells for mobile applications obtain their oxygen from the ambient air in road traffic. This air has contaminations of various impurities that can have negative effects on the lifetime of fuel cell systems in vehicles. The identified most relevant contaminants are toluene, nitrogen dioxide, ammonia, and sulfur dioxide. A modified test bench enables different dosages of the above‐mentioned pollutant gas concentrations on the cathode side. We examined influences both in static cycles for quasi‐steady states and in dynamic cycles for rapid load changes to examine reversible and irreversible degradation effects. We showed that the harmful cathode gases examined could lead to a shortening of the service life of fuel cells. Whereas this is well known for higher concentrations of pollutants, this contribution provides data in the sub‐ppm range – including the effects of gas mixtures – for which literature data is still limited.Additionally, a physical fuel cell model is developed to analyze the effects of various contaminants. The overall intention is to determine acceptable contamination levels and thereby increase the lifetime of fuel cells with the help of simulations. The presented model allows for the computation of cell voltage dependent on cathode side media conditions.

Multiscale Study of PEMFC in Marine Environment: Impact of a NaCl Spray on Durability

In the wake of the growing environmental challenges, hydrogen produced from renewable energy is a good candidate as a substitute for conventional fuels. Indeed, fuel cells can produce electricity thanks to air and hydrogen, and only reject water. The use of this technology is currently emerging in various sectors, such as the maritime industry. However, sea salt aerosols, mostly composed of sodium chloride (NaCl), can damage fuel cells. So far, only a few studies have been dedicated to the impact of NaCl on Proton Exchange Membrane Fuel Cells (PEMFCs) though showing that salty air can induce a significant loss of performance without clearly identifying the underlying physicochemical mechanisms [1][2][3].Thus, the present experimental work investigates the effects of a salt spray injected into the airflow of single PEMFC cells and stacks at various time scales and contamination levels, with the final aim of identifying the appropriate PEMFC stack protection needed for maritime applications. A dedicated experimental setup generating salt spray in the cathode airflow of a single cell and 5-cells stack has been designed, realized and characterized. The NaCl concentration range used is from 10 mg/m3 to 5 g/m3, to reproduce different types of salty environments. Cells and stacks are operated in constant current density mode.The study is conducted under the conditions of accelerated stress tests. When polluted at high concentrations, single cells degradation becomes significant after only a few minutes of operation (Figure 1) and after a few hours for stacks. Even under low concentrated environments, the single cell voltage decreases faster than the baseline (ie reference voltage with pure water in air stream), leading to PEMFC lifetime shortening. It has been observed that cathode rinsing with nitrogen flow or operation under pure water results in partial cell performance recovery. Moreover, starts-up and shuts-down operated during tests can have a positive or negative influence on cell performance, depending on the break duration.Even when the tests revealed only weak decrease in power, Membrane Electrode Assemblies (MEA) and bipolar plates (BP) post-mortem characterizations highlight degradations. Scanning Electron Microscopy (SEM) studies coupled with Energy Dispersive X-ray Spectroscopy (EDS) have contributed to the identification of components in MEA and BP. As expected, chlorine reaches not only the cathode gas diffusion layer (GDL) and catalyst layer (CL) but also the anode CL by crossing the membrane [4]. According to the literature, chloride adsorption on Pt surface or Pt dissolution reduces the active area [3] whereas sodium ion contaminates the membrane [1]. Moreover, corrosion products from metallic components have been found. Corrosion marks identified as stainless steel from BP are present in the stack effluents and MEAs. As for single cell, compounds from current collectors (gold, nickel and copper) are present in the GDL and CL. In the near future, for single cell tests, non-metallic current collectors will be used in order to discriminate the effects of the direct degradation of salt spray on MEA and indirect degradation coming from corrosion products of metallic cell components.Overall, the present study reports that NaCl effects on PEMFCs not only depend on the concentration of the NaCl mist but also on the MEA type, current collectors/BP material, and startup/shutdown procedure. In the full paper and oral presentation, tests conducted with less concentrated NaCl droplets will also be presented, with the aim of determining adegradation threshold for single cells.

Dynamic performance for a kW-grade air-cooled proton exchange membrane fuel cell stack

In this study, a kW-grade air-cooled proton exchange membrane fuel cell (PEMFC) stack with a dead-end anode (DEA) operation is designed and manufactured. The gravity-assisted drainage principle is applied for the stack to design the wettability of gas diffusion layers (GDLs) and the anode channel geometry, which can help the liquid water that diffuses to the anode to drain out of the anode porous electrode and move down the anode channel outlets. As a result, the stack can stably operate in a long purge interval of 268 s and in a short purge time of 2 s. In addition, using this design, only four small-power fans are employed to pump air to the cathode to provide oxygen for the electrochemical reaction and cool the stack. With a constant load current of 30, 45, or 60 A, the stack output voltage is experimentally tested at various cathode air flow rates (CAFRs). The local temperatures (60 measurement points) inside the stack and the pressure differences across anode channels are also monitored to understand heat dissipation and the back diffusion of liquid water. In a wide range of operating conditions, the designed stack possesses superior and stable voltage output characteristics with relatively uniform temperature distributions. The measured maximum output power is 3.83 kW, and the parasitic powers of fans are only 80∼112 W.

Multiscale Study of PEMFC in Marine Environment: Impact of a NaCl Spray on Durability

The present work investigates the effects of a salt spray injected into the airflow of Proton Exchange Membrane Fuel Cells (PEMFCs) at various time scales and contamination levels, with the final aim of identifying the appropriate protection for maritime applications. A dedicated experimental setup generates a sodium chloride (NaCl) mist in the cathode airflow to contaminate single cells and stacks. Constant current density tests led to lifetime shortening with partial recovery after cathode rinsing. Then, Membrane Electrode Assemblies (MEAs) post-mortem characterizations revealed that NaCl was present in the cathode gas diffusion layer, and chlorine reached the catalyst layer for high concentrations. Furthermore, chlorides enhanced current collectors and bipolar plates degradation as corrosion products were identified in MEAs and stack effluents. Overall, this study reports that NaCl effects on PEMFCs not only depend on the concentration but also on the MEA type, plate material, and startup/shutdown procedure.

Rapid load transition for integrated solid oxide fuel cell – Gas turbine (SOFC-GT) energy systems: A demonstration of the potential for grid response

Rapid load transition is an essential requirement for integrated energy systems to maintain grid resilience as more renewable resources are added to the grid. Integrated solid oxide fuel cell – gas turbine (SOFC-GT) systems can provide high efficiency and low carbon emissions over a broad range of turndown. These hybrids also have the potential to enable rapid grid response. The challenge has been to demonstrate effective control strategies to manage load transitions. In the present study, a load transition of ∼50% was achieved in 10 s using a novel but simple strategy. Power demand on the SOFC and the GT were ramped down concurrently. During this transition, the SOFC anode fuel was manipulated to maintain SOFC fuel utilization while the cathode inlet air flow and temperature were also manipulated to thermally protect the SOFC. This study was conducted using the Hybrid Performance (Hyper) facility at the National Energy Technology Laboratory (NETL) in a co-simulation environment with the Idaho National Laboratory (INL)’s grid-simulation. The load ramping strategy was tested using a hardware-based cyber-physical simulation methodology. The results demonstrate a high-fidelity representation of SOFC-GT hybrid dynamics and validation of the control strategy. Thermal and electrochemical transients indicated that the SOFC was well protected during rapid load turndown without violating operability constraints. This demonstration revealed the non-linear nature of tightly coupled SOFC-GT system components, especially the non-linear response of SOFC cathode air flow and inlet temperature controls. These results highlight the needs and challenges in developing adaptive automatic controls for autonomous rapid load transitions. This work demonstrates that SOFC-GT hybrids are a viable option to provide the fast-ramping characteristics essential to accommodate high levels of variable renewable power while maintaining grid resilience, reliability, and environmental performance. The results also demonstrate the utility of co-simulation in advancing the tightly-coupled integrated energy systems needed to meet goals for zero-carbon power generation.

Experimental study on temperature and performance of an open-cathode PEMFC stack under thermal radiation environment

The open-cathode proton exchange membrane fuel cell stack is an air-cooled stack, and has the characteristics of small footprint and high power density because of its unique configuration, combining oxidizer and coolant via axial fan. Depending on the demands of the application, proton exchange membrane fuel cells inevitably operate in harsh environments, such as high pressure, low or high temperature, etc. In this study, the performance of a 10-cell open-cathode PEMFC stack under thermal radiation was evaluated. The variations in cathode air temperature and relative humidity, stack temperature, output power and single-cell voltage under three different radiant heat fluxes were obtained by changing the load current and cathode air flow rate. The experimental results show that, even if the thermal radiation is beneficial to improve the stack temperature, the stack performance is not improved in all tested cases. Conversely, the degradation of stack power and failure of the stack continuous operation can be observed, especially for higher radiant heat flux, higher load current and lower air velocity. For the highest radiant heat flux in current study, the temperature of the first single cell closest to the radiant heat source exceeds the maximum allowable operating temperature of 65 °C due to the insufficient capacity of air cooling and the heating effect of radiant heat source. The significant drop in the first single-cell voltage results in the rapid degradation of the overall performance of the stack, and finally the stack fails to run continuously.

Characterizing SOFC Stack Electrochemical Performance at Elevated Pressure

In this report, we present our work to characterize the electrochemical performance of solid-oxide fuel cell stacks under elevated-pressure operation. The effort is part of a five-year U.S. DoE ARPA-E INTEGRATE program to combine the high efficiency of solid-oxide fuel cells with the low-cost of reciprocating engines to demonstrate an 70%-efficient hybrid electric generator. Within this hybrid system, solid-oxide fuel cells (SOFCs) convert natural gas into electricity. Unconverted fuel leaving the SOFC stacks feeds a downstream reciprocating engine that drives an electric generator. In this architecture, the stacks are hydraulically placed upstream of the engine, necessitating stack operation at elevated pressures of 2-5 barg. SOFC stack performance at elevated pressure has witnessed limited study. The team at the Colorado School of Mines is characterizing SOFC stack performance at elevated pressure through design and commissioning of the pressurized stack electrochemical test stand shown in the figure. The facility is used to explore the performance of 5-kW SOFC stack test modules (Ceres Power, Ltd., Horsham, UK) at the unusual operating conditions presented by the hybrid system, including pressurized operation at high anode tail-gas recycle.A simulant of steam-reformed natural gas with anode tail-gas recycle is synthesized using mass flow controllers. A fuel processor will be incorporated into the stand at a later stage of the research program. Reactants flow through a preheat furnace and into a pressure vessel to reach the insulated solid-oxide fuel cell stack test module. The pressure within this vessel is matched to the operating pressure of the SOFC stack, minimizing pressure differentials between the internal flow channels of the stack and the surrounding environment. Following electrochemical conversion, exhaust gases exit the stack and the pressure vessel, and are cooled through a series of heat exchangers. Back-pressure regulators near the end of the flow stream regulate stack and vessel operating pressure.The stand has been used to explore the impacts of elevated pressure operation on the electrochemical performance of Ceres SteelCell stacks. Additional parameters being explored include fuel composition, anode recycle, and internal fuel reforming. In this talk, we will present our findings on the effects of these variables on stack performance, and their impact in achieving the aggressive performance targets of the SOFC-engine hybrid electric generator.A principal concern during performance testing at elevated pressures is minimizing pressure differentials across the anode and cathode gas-flow streams. Such differentials can bring substantial mechanical stress to the metal-supported membrane-electrode assemblies. Pressure differentials in this work are below +/- 25 mbar at 5 barg operating pressure, well below manufacturer’s specifications. The stacks show steady, stable performance over all conditions tested.In addition to exploring the electrochemical-performance impacts brought by pressurization and anode recycle, experiments explore the roles of methane internal reforming and cathode air flow on stack cooling. The endothermicity of methane steam reforming can bring meaningful reductions in cooling-air flow rate, raising system efficiency. The results of these studies and the trajectory of the research will be presented. Figure 1

Improvements of Micro-CHP SOFC System Operation by Efficient Dynamic Simulation Methods

Solid Oxide Fuel Cell (SOFC) technology is of high interest for stationary decentralized generation of electricity and heat in combined heat and power systems (CHP) for the residential sector. Application scenarios for SOFC systems in an electricity-regulated mode play an important role, especially in places where an electrical grid connection is not available or rather unstable. The advantages of SOFC systems are the high fuel flexibility and the high efficiencies also under partial load operation compared to other decentralized power generation technologies. Due to the long, energy-consuming system heat-up and the limited partial load capability, SOFC systems do not reach the performance of conventional power generation technologies. Furthermore, stack thermal cycling is associated with power degradation and should be minimized. In this paper, the improvement of these drawbacks are investigated for hotbox-based SOFC systems in the 1 kWel-class for residential applications. Since experimental investigations of the high-temperature systems are limited, modeling tools are established, enabling the visualization of internal system characteristics and providing the opportunity to simulate system operation in critical regions. To achieve this, a methodology for dynamic SOFC system modeling in a process engineering manner is developed based on the modeling language Modelica. A suitable approach is particularly important for modeling and simulation of the strong thermal interaction between the hot system components within the hotbox. The parametrized and validated models are used for the investigation of different dynamic effects, such as the system heat-up and the operation in low partial load points. A second reduced thermal system model aims for annual simulations of the SOFC system together with a battery to investigate the number of thermal cycles and the advantage of a hot standby operation. As a result, it is found that an adequate control of the power input at the start-up device and the cathode air flow has a high improvement potential to increase the stack heating rate and accelerate the heat-up in an energy-saving way. The hotbox-internal thermal management is identified as a crucial issue to reach low partial load points. To avoid the risk of stack cooling, lower heat losses and/or additional heat sources are of importance. Furthermore, the robustness of the tail gas oxidizer is found to be crucial for a higher load flexibility during partial load and the end of life stack operation. The annual simulation results indicate that operating the battery hybrid system with a hot standby mode requires much lower battery capacity for a high grid independence and a complete avoidance of system shutdown and associated power degradation.

Thermodynamic analysis of an improved integrated biomass gasifier solid oxide fuel cell micro combined heat and power system

Limited overall efficiency and excessive complexity can hinder the competitiveness of biomass gasifier solid oxide fuel cell micro combined heat and power systems. To overcome these problems, hydrocarbons direct internal reforming is analysed as a strategy to increase efficiency and reduce system complexity. To the same end, two biosyngas heating-up strategies are compared: catalytic partial oxidation and afterburner off gases utilization. A comprehensive approach combining thermodynamic equilibrium calculations, experimental measurements, and system modelling was used. The gas cleaning unit should operate at 400 °C to decrease H2S and HCl below 1 ppmv. A tar amount of 120–130 g Nm−3 dry biosyngas for woodchips and 190 g Nm−3 for straw pellets was measured and 2-methoxyphenol, hydroxyacetic acid and hydroxyacetone were selected as representative compounds. With direct internal reforming the cathode air flow rate decreases from approximately 90 kg h−1 to 60 kg h−1. This leads to an increase of around 1% point in electrical efficiency and of even 5–6% points in thermal efficiency. Direct internal tar reforming seems therefore an advantageous strategy. The catalytic partial oxidation unit increases the system overall efficiency but reduces the electric efficiency from roughly 38%–30% and is therefore not advised.

Nonlinear multivariable control of an integrated PEM fuel cell system with a DC-DC boost converter

The proton exchange membrane (PEM) fuel cell faces problem when there is an abrupt load demand that is common in transport/vehicle application. This is because of the slow response of underlying electrochemical and thermodynamic processes, abrupt voltage drop proportional to the increased power demand, control system failure, among others. To overcome this shortcoming and to ensure the uninterrupted power delivery, a DC-DC boost converter is coupled with the PEM fuel cell integrated system that additionally includes a few auxiliary subsystems along with a fuel recirculation and a heat exchange unit. For the controlled operation of the entire integrated complex system, a nonlinear observer-based sliding mode controller (SMC) is synthesized. To address a couple of major concerns involved in fuel cell operation, the control objectives are selected at stabilizing the fuel cell power, cathode air flow from the compressor and stack operating temperature. To have the knowledge of unmeasured state information, two nonlinear observers namely, extended Kalman filter (EKF) and sliding mode observer (SMO) are constructed using a low-order process model. The observer-based controller is simulated in MATLAB/SIMULINK environment for their comparative performance. Overall, the closed-loop response of the proposed SMO-SMC and EKF-SMC are found superior to a traditional PI controller.

Thermal management of open-cathode proton exchange membrane fuel cell stack with thin vapor chambers

Proton exchange membrane fuel cell (PEMFC) is one of the most promising electricity-generating devices with zero pollution. However, a large amount of waste heat will be generated during the operation. The waste heat must be dissipated in time to prevent performance deterioration and irreversible damage. In this paper, a novel cooling strategy is proposed and implemented. Five thin vapor chambers (VCs) are integrated into a 10-cell open-cathode PEMFC stack to enhance its heat dissipation effect. PEMFC stack with VCs has been successfully fabricated and tested experimentally. Results show that VCs can effectively reduce the operating temperature of PEMFC and the minimum in-plane temperature difference can be reduced to 0.5 °C, which provides a reliable and stable thermal environment for safe operation. The effects of VCs on the through-plane and in-plane temperature distribution is studied and analyzed in detail. In addition, when the cathode air flow is small, the thermal management of the stack is significantly affected by the inclination angle. This study has fully demonstrated the feasibility of integrating VCs in PEMFC stack to improve thermal management, and provides guidance for designing and developing a better cooling system of PEMFC stack.

Integrated Cathode Air Flow Management for Fuel Cell Electric Vehicles

Highly efficient cathode air filters are required to enable the required fuel cell system´s lifetime, especially under severe operating conditions. In addition, components like water separators, compressors, air ducts, coolers, humidifiers, sensors etc. are essential to supply cathode air at the right cleanliness, pressure, and temperature. The paper focuses on cathode air flow management on the stack inlet and outlet side. The approach to system design is holistic, meaning that not individual components are optimized independently, but on system level. Special emphasis is given to transferring state-of-the-art technology and products from internal combustion engine vehicle´s air intake systems to the cathode air path. Adaption of these components to the operating conditions of fuel cells and combining them with fuel cell-specific components yield intake and outlet systems with cost-, energy- and acoustically optimized functionality.

Investigation of current density spatial distribution in PEM fuel cells using a comprehensively validated multi-phase non-isothermal model

In this study, a three-dimensional (3D) multi-phase non-isothermal model of proton exchange membrane (PEM) fuel cell is present to investigate the current density spatial distributions under different output voltages, temperatures, current densities and relative humidities (RH). Two sets of experimental data are selected for validation, including those from the Los Alamos National Laboratory in the United States and the University of Waterloo in Canada. Reasonable agreements are achieved between the model prediction and experimental measurements, indicative of the validity of this 3D model. In addition, it is found that under a higher RH of 50%, most electric current is produced near the cathode inlet, which is primarily due to the local availability of abundant oxygen and hence small transport polarization. Low current occurs near the outlet of the cathode air flow, as a result of oxygen consumption by the oxygen reduction reaction (ORR). Under a lower RH of 25%, the high current density region shifts to the middle of the fuel cell, which is primarily attributed to hydration of the dry membrane by water production. In our case study, the operating temperature has little impact on the current density distribution.

Heat and mass transfer in PEM-based electrolytic air dehumidification element with an optimized anode-side electrochemical model

Electrolytic dehumidification based on a polymer electrolyte membrane (PEM) is promising due to the fast humidity control, safe operation and ultra-compactness. However, predictions with existing methods deviated widely, mainly due to the inaccurate calculations of the anode-side over-potential and heat/mass transfer. In this paper, an improved theoretical model was developed, by optimizing the anode-side prediction using newly developed equations for the exchange current density and heat/mass transfer coefficient. The equations were derived by the multi-parameter fitting, with a database obtained by making the simulation results as close as possible to the experimental data under various operating conditions. Compared to the results of previous models, the developed model showed a data trend that was much closer to the experimental data. The overall errors for the moisture removal rate and operating current under most conditions were less than 15% with acceptable average errors of 10.4% and 7.1%, respectively. Particularly, this model showed much higher accuracy at higher air flow rates or larger electrical fields, especially for the current prediction. When the air Reynolds number was above 2 or the applied voltage was above 3 V, the deviation of the prediction could reduce by more than 50% with the new model. And the common problem of overestimation for current prediction (up to 4–5 times) in existing models could be solved. In addition, the parameter analysis of the optimal exchange current density and heat/mass transfer coefficient was conducted. It could be found that the applied voltage during dehumidification had the largest influence. The influences of the anode air inlet temperature, flow rates and inlet relative humidity were also significant. But the effects of cathode air temperature and flow rates were slight. This research significantly improves the prediction accuracy and provides a good guidance for the performance optimization of electrolytic dehumidification systems.