Polymer Electrolyte Fuel Cell System Research Articles

Patterned hydrophobic gas diffusion layers for enhanced water management in polymer electrolyte fuel cells

Flooding of the cathode due to water accumulation is one of the biggest limiting factors in the performance of polymer electrolyte fuel cells (PEFCs). This study therefore attempts to solve this issue by fabricating gas diffusion layers (GDLs) with differently patterned hydrophobic regions. The GDLs in three different patterns (triangular, diamond, and inverted-triangular) were prepared by brushing a Polytetrafluoroethylene (PTFE) solution onto commercial carbon papers through a mask and tested in PEFCs. The patterned GDLs results in superior performance in all cases compared to a uniformly PTFE-treated GDL. Notably, the oxygen transport resistance is significantly reduced, indicating that the water accumulation in the cathode is avoided. This is attributed to the patterned hydrophobicity gradient providing distinct pathways for water and oxygen. The GDL with triangular patterning displays the highest peak power density, due to the fact that the untreated less hydrophobic region is in direct contact with the cathode outlet in this case, facilitating the removal of excess liquid water. Overall, the study confirms that the GDLs with patterned hydrophobicity could be used to enhance the performance of commercial PEFC systems by facilitating water management, potentially leading to improved efficiency and durability.

Effect of Hydrophilic and Hydrophobic Composite Microporous Layer Coated Gas Diffusion Layers on PEFC Performance

In order to widen the market application of the polymer electrolyte fuel cell (PEFC), the output power of the PEFC system must be increased. One of the barriers is the cell voltage loss under high current density conditions. This is mainly caused by the deteriorated reactant mass transport, which is blocked by the water flooding at the catalyst layer (CL), microporous layer (MPL), and gas diffusion layer (GDL). Modifying the MPL coated on the GDL is an accessible way to provide better water management for PEFCs to elongate the operating range of the cell, so a novel MPL-coated GDL should be developed to realize the goal. Previously, we evaluated double MPL-coated GDLs, which coated a thin hydrophilic layer on the hydrophobic MPL-coated GDL in the through-plane direction. The extra hydrophilic layer was influential in promoting the introduction of water into the small pores of the hydrophobic MPL, enhancing the ability to reduce flooding, and the oxygen transport resistance under high humidity conditions can be declined.The present study evaluates a novel composite MPL that the hydrophobic and hydrophilic pores are randomly allocated in the same layer. Excess water is expelled from the hydrophilic pores while maintaining gas transport by the hydrophobic pores. To determine the appropriate hydrophobic and hydrophilic compositions, we first evaluated the most commonly used hydrophobic polytetrafluoroethylene (PTFE) binder, and the contact angle of PTFE-MPL was 136°. Polyvinyl alcohol (PVA) was chosen as the hydrophilic binder, and the contact angle of PVA-MPL was 105°. The slurry containing PTFE, PVA, carbon black, and distilled water was mixed using a mixer and then spread on the carbon paper substrate by a bar coating machine. The temperature was heated at 350°C to sinter the MPL on the substrate. However, the sintering temperature of PVA should be lower than 150°C, so the PVA in the composite MPL was burned and led to a similar contact angle as the PTFE-MPL. Meanwhile, the performance enhancement could not be obtained compared with a PTFE-MPL-coated GDL. Oppositely, when decreasing the sintering temperature to 150C°, the PTFE-PVA composite MPL demonstrated strong hydrophilicity with a small contact angle value, and the performance was exacerbated than the PTFE-MPL. Therefore, to coordinate the lower sintering temperature of PVA, polyvinylidene difluoride (PVDF) was selected as the hydrophobic binder. The contact angle of PVDF-MPL was 143°. After the PVA was preserved, the unexpectedly strong hydrophilicity was exhibited in PVDF-PVA composite MPL, aggravating the liquid water accumulation in the MPL and without performance improvement. Finally, the Nafion ionomer with relatively weak hydrophobicity was used for the composite MPL. As a hydrophilicity complement, titanium dioxide (TiO2) particles were added to the slurry to control hydrophilicity. The contact angle of Nafion/TiO2-MPL was 113°. Similarly, the Nafion/TiO2-PVDF composite MPL indicated a contact angle of 114°, and the water permeability test proved that separate hydrophobic and hydrophilic pores were generated.The oxygen transport resistances were measured based on the limiting current density values of polarization curves to evaluate the ability of the MPL-coated GDL to reduce flooding under high humidity conditions. The active area of the MEA was 1.0 cm2, and the cell temperature was kept at 35°C. Pure hydrogen and diluted oxygen (2 vol% O2 and 98 vol% N2) gases were supplied at the anode and cathode, respectively, and the flow rates were set at 1000 cm3 min-1. The relative humidity of gases supplied to the anode and cathode was 200%RH, and the gas backpressure was set at zero. The oxygen transport resistance of the Nafion/TiO2-PVDF composite MPL-coated GDL was lower than that obtained with a commercial SGL-22BB GDL. Thus, an appropriate composite MPL-coated GDL effectively enhanced PEFC performance under high humidity conditions.

Microscale Simulation of Carbon Support Structure Degradation in Polymer Electrolyte Fuel Cell

Understanding the mechanism of Polymer electrolyte fuel cell (PEFC) degradation plays an important role in improving fuel cell performance and durability. For the PEFC system, the structure of catalyst layers (CLs) is the critical component that determines cell performance. The PEFC degradation due to the reduction of carbon on the CLs has been investigated in previous studies [1]. In our past studies, we focused on the actual heterogeneous porous structure of catalyst layer. From these results, it was found that mass transport performance of oxygen and proton in heterogeneous porous catalyst layer, which consists of carbon support, ionomer and void space, is much lower than that of theoretical prediction in homogeneous porous media [2-5]. In addition, it depends on the structure of carbon black, the coating structure of ionomer and the local distribution of these materials. Thus, it is important to understand and to predict the carbon support structure change by degradation because this structural degradation strongly affect the mass transport performance. In this work, the effect of CLs porous carbon support degradation on cell performance is investigated by microscale simulation.The CLs structures, consisting of porous carbon, ionomer, and Pt, are created by our previous study multi-block method [2,6]. In our simulation, we focus on studying the effect of CLs' beginning-of-life (BOL) and end-of-life (EOL) structure in the degradation process. The CLs creation procedure is illustrated in Fig. 1. Firstly, CLs structure are created by packing CB and covered ionomer and Pt. The amount of ionomer and Pt are assumed as constant during the degradation process. Therefore, the amount of carbon is reduced in EOL structure. In this study, various CLs structures with decreasing of carbon volume are constructed. Furthermore, the mechanical stress distribution under compression condition was simulated in each structure to understand the effect of framework of carbon on local porosity in catalyst layer. The effect of carbon corrosion in CLs is investigated by calculating the cell performance of PEFC of each CLs structure by ORR mass transport and electrochemical reaction calculation with our previous method [6].The cell performance is significantly decreased by reducing carbon. The degradation mechanism of PFEC is explained by degradation of not only effective surface area but also the porous structure change which affect oxygen diffusion performance. Moreover, compared with BOL structure the apparant thickness of covered ionomer layer is higher in EOL structures because of carbon corrosion and constancy of ionomer. Hence, the higher oxygen diffusion resistance in secondary pore and ionomer layer occur in CLs degradation structures. The effect of this dynamic structure change on cell output performance will be reported in this presentation.Acknowledgements:This research was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan, grant number P20003-20001327-0.

Synergies of fuel cell system thermal management and cryogenic hydrogen exergy utilization

Low-temperature polymer electrolyte fuel cell systems (FCSs) need to reject large amounts of low temperature heat. Often a mobile FCS’s cooling capacity limits the FCS power output. Cryogenic hydrogen is typically utilized as a direct heat sink using heat exchangers (HXs), even though HXs destroy most hydrogen exergy. This paper investigates synergies between FCS thermal management and cryogenic hydrogen exergy utilization in terms of their benchmark performance: the FCS coolant circuit supplies heat at coolant temperature level to a so named reversible cryogenic exergy utilization system (rCEUS) comprised of thermodynamically ideal heat engine processes. The rCEUS converts this heat partly to electrical energy (the value of which equals the hydrogen exergy) and rejects remaining heat to hydrogen to heat it to coolant temperature. The rCEUS output power is used to support the FCS, so the FCS rejects less heat and a significant fraction of this heat is utilized by the rCEUS. As a result, significantly less heat has to be transferred to ambient and the fuel demand decreases. In this paper, three hydrogen storage options are compared: liquid hydrogen, subcooled liquid hydrogen and cryo-compressed hydrogen. Different para- and orthohydrogen compositions are evaluated. For typical FCS operating points, rejected FCS heat to ambient is reducible by 40–67%. FCS power demand is reducible by 14–31%. FCS rejected heat to ambient reduction is 4.5–8 times larger than that of conventional HXs. Calculations are based on hydrogen’s lower heating value.

Effect of Flow Conditions of Anode Hydrogen on Net Water Drag Coefficient of Polymer Electrolyte Fuel Cells

The net water drag coefficient () is supposedly an essential index in water management, and must be negative for system operation for polymer electrolyte fuel cell (PEFC) systems. In this study, is carefully examined by measurement of the water content in the gases supplied to and those discharged from the cell/stack under gas supply conditions similar to those in a real PEFC system. We focus on the effect of anode hydrogen (H2) flow conditions (i.e., flow rate and relative humidity) on under a constant flow condition of cathode air. Measured characteristics of current density ()- in which the relative humidity of discharged H2 from the anode is constant at around 100%, show that is stable when exceeds a certain threshold. The value of in this stable region is particularly sensitive to changes in the stoichiometric ratio of H2. These measurements also suggest that in the stable region, almost the entire area of the membrane is fully hydrated, and the effect of back diffusion on becomes negligible. Analysis of the observed relationships between and several variables indicate that increasing the H2 circulation flow rate effectively prevents anode dry-out.

Preparation of Nanocrystalline Nb-Doped SnO2 on Mesoporous Carbon for PEFC Electrocatalysts

Pt-based catalysts on carbon support (Pt/C) is widely used as polymer electrolyte fuel cell (PEFC) electrocatalyst. However, under high potential at the cathode, Pt detachment and aggregation due to carbon corrosion can occur. Therefore, conventional Pt/C electrocatalysts have a difficulty in durability[1]. SnO2 is known to be stable at high potentials in a PEFC cathode environment. Our research group has developed an electrocatalyst that uses carbon as a support framework, with SnO2 supported on it and Pt catalyst particles on SnO2 (Pt/SnO2/Carbon), achieving high durability [2-4]. However, the electronic conductivity of tin oxide is relativity low and the ORR activity with SnO2-based support tends to be inferior to that of Pt/C, the standard catalyst.Therefore, the objective of this study is to develop an alternative electrocatalyst that exhibits high ORR activity while maintaining high durability by using mesoporous carbon (MC) with nano-sized mesopores as a support framework and reducing the amount of SnO2 used by suppressing its grain growth.Tin oxide nanoparticles were supported on mesoporous carbon (CNovel\U0001f12c, TOYO TANSO) using ethoxide reagents. Tin oxide was doped with a small amount of niobium to improve the conductivity of SnO2 [5]. Electrocatalysts were prepared by loading of Pt particles of a few nm in diameter on the prepared supports using the Pt acetylacetonate method [6].Pt loading was examined by ICP Atomic Emission Spectroscopy. The crystallite size of SnO2 and Pt, and possible alloying of Pt and Sn were checked by XRD measurements. The electrochemical surface area (ECSA) of Pt was obtained by cyclic voltammetry (CV). The oxygen reduction reaction (ORR) activity was evaluated by determining the activation-dominant current value in the rotating disk electrode (RDE) measurement. The durability of the catalysts was evaluated by applying 60,000 of potential cycles between 1.0 and 1.5 VRHE simulating the start-up and shutdown of PEFC systems. The microstructure of electrocatalysts was observed using a field emission electron scanning microscope (SU9000, Hitachi High-Tech Corporation).Figure 1 shows (a) scanning and (b) transmission electron microscope images of the electrocatalysts before Pt loading (Sn0.98Nb0.02O2/MC). It was confirmed that tin oxide was loaded within the mesopores besides the MC surface. Furthermore, as shown in the transmission image in Fig. 1(b), the particle size of SnO2 on the surface is about 10 nm, while the particle size of SnO2 within the mesopores is about 5 nm, indicating that the presence of mesopores suppresses particle growth. Latest results of electrochemical properties of Pt-based electrocatalysts using Nb-doped SnO2 and MC after Pt catalyst decoration will be reported in this presentation. References T. Takahashi, T. Ikeda, K. Murata, O. Hotaka, S. Hasegawa, Y. Tachikawa, M. Nishihara, J. Matsuda, T. Kitahara, S. M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 169, 044523 (2022).Y. Nakazato, D. Kawachino, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 165 (14), F1154 (2018).S. Matsumoto, M. Nagamine, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 165 (14), F1164 (2018).T. Yoshizumi, M. Nagamine, Z. Noda, J. Matsuda, A. Hayashi, and K. Sasaki, ECS Trans., 92 (8), 479 (2019).K. Sasaki, F. Takasaki, Z. Noda, S. Hayashi, Y. Shiratori, and K. Ito, ECS Trans., 33 (1), 473 (2010).A. Hayashi, H. Notsu, K. Kimijima, J. Miyamoto, and I. Yagi, Electrochim Acta., 53, 6117 (2008). Figure 1

A model based investigation of evaporative cooling for polymer electrolyte fuel cells – System level analysis

Evaporative cooling is a promising concept to reduce the fuel cell system volume and mass significantly. This paper investigates the interactions between the fuel cell stack and the balance of plant in an evaporatively cooled polymer electrolyte fuel cell system (PEFCS). For this, a zero-dimensional PEFCS model, comprising the fuel cell stack, air compressor, charge air cooler, humidifier, hydrogen recirculation blower, condensing radiator and water separator has been developed and analyzed. Two evaporative cooling system architectures are compared to conventional, liquid cooling. Optimal operating conditions are determined by a numerical optimization of the net system power output. Main results show that evaporative cooling works on the system level over a wide range of operating conditions. The optimum system power and highest efficiencies are achieved at high temperatures (80–90 °C), low pressure (125–150 kPa) and a corresponding cathode stoichiometry between 1.5 and 3, allowing for a closed water loop at the same time. The air compressor shows an increased power demand, compared to conventional cooling and the exhaust gas condenser is identified as the one critical component for evaporative cooling. Its performance is key to an efficient operation and closed water loop at all ambient conditions.

Integration of air-cooled multi-stack polymer electrolyte fuel cell systems into renewable microgrids

Currently, there is a growing interest in increasing the power range of air-cooled fuel cells (ACFCs), as they are cheaper, easier to use and maintain than water-cooled fuel cells (WCFCs). However, air-cooled stacks are only available up to medium power (<10 kW). Therefore, a good solution may be the development of ACFCs consisting of several stacks until the required power output is reached. This is the concept of air-cooled multi-stack fuel cell (AC-MSFC). The objective of this work is to develop a turnkey solution for the integration of AC-MSFCs in renewable microgrids, specifically those with high-voltage DC (HVDC) bus. This is challenging because the AC-MSFCs must operate in the microgrid as a single ACFC with adjustable power, depending on the number of stacks in operation. To achieve this, the necessary power converter (ACFCs operate at low voltages, so high conversion rates are required) and control loops must be developed. Unlike most designs in the literature, the proposed solution is compact, forming a system (AC-MSFCS) with a single input (hydrogen) and a single output (high voltage regulated power or voltage) that can be easily integrated into any microgrid and easily scalable depending on the power required. The developed AC-MSFCS integrates stacks, balance of plant, data acquisition and instrumentation, power converters and local controllers. In addition, a virtual instrument (VI) has been developed which, connected to the energy management system (EMS) of the microgrid, allows monitoring of the entire AC-MSFCS (operating temperature, purging, cell voltage monitoring for degradation evaluation, stacks operating point control and alarm and event management), as well as serving as a user interface. This allows the EMS to know the degradation of each stack and to carry out energy distribution strategies or specific maintenance actions, which improves efficiency, lifespan and, of course, saves costs. The experimental results have been excellent in terms of the correct operation of the developed AC-MSFCS. Likewise, the accumulated degradation of the stacks was quantified, showing cells with a degradation of >80%. The excellent electrical and thermal performance of the developed power converter was also validated, which allowed the correct and efficient supply of regulated power (average efficiency above 90%) to the HVDC bus, according to the power setpoint defined by the EMS of the microgrid.

Operando Spectroscopic Study of the Dynamics of Ru Catalyst during Preferential Oxidation of CO and the Prevention of Ammonia Poisoning by Pt.

Hydrogen is a promising clean energy source. In domestic polymer electrolyte fuel cell systems, hydrogen is produced by reforming of natural gas; however, the reformate contains carbon monoxide (CO) as a major impurity. This CO is removed from the reformate by a combination of the water–gas shift reaction and preferential oxidation of CO (PROX). Currently, Ru-based catalysts are the most common type of PROX catalyst; however, their durability against ammonia (NH3) as an impurity produced in situ from trace amounts of nitrogen also contained in the reformate is an important issue. Previously, we found that addition of Pt to an Ru catalyst inhibited deactivation by NH3. Here, we conducted operando XAFS and FT-IR spectroscopic analyses with simultaneous gas analysis to investigate the cause of the deactivation of an Ru-based PROX catalyst (Ru/α-Al2O3) by NH3 and the mechanism of suppression of the deactivation by adding Pt (Pt/Ru/α-Al2O3). We found that nitric oxide (NO) produced by oxidation of NH3 induces oxidation of the Ru nanoparticle surface, which deactivates the catalyst via a three-step process: First, NO directly adsorbs on Ru0 to form NO-Ruδ+, which then induces the formation of O-Run+ by oxidation of the surrounding Ru0. Then, O-Rum+ is formed by oxidation of Ru0 starting from the O-Run+ nuclei and spreading across the surface of the nanoparticle. Pt inhibits this process by alloying with Ru and inducing the decomposition of adsorbed NO, which keeps the Ru in a metallic state.

Accumulation of Inert Impurities in a Polymer Electrolyte Fuel Cell System with Anode Recirculation and Periodic Purge: A Simple Analytical Model

Anode recirculation with periodic purge is commonly used in polymer electrolyte fuel cell systems to control the accumulation of nitrogen, water, and other impurities that are present in the fuel or diffuse through the membrane from the cathode compartment. In this work, we develop a simple, generalized analytical model that simulates the time dependence of the accumulation of inert impurities in the anode compartment of such a system. It is shown that, when there is transport out of the anode chamber, the inert species is expected to accumulate exponentially until equilibrium is reached when the rate of inert entering the anode in the fuel supply and/or via crossover from the cathode is balanced by the rate of leakage and/or crossover to the cathode. The model is validated using recently published experimental data for the accumulation of N2, CH4, and CO2 in a recirculated system. The results show that nitrogen accumulation needs to be taken into account to properly adjust system parameters such as purge rate, purge volume, and recirculation rate. The use of this generalized analytical model is intended to aid the selection of these system parameters to optimize performance in the presence of inerts.

PEFC System Reactant Gas Supply Management and Anode Purging Strategy: An Experimental Approach

In this report, a 5 kW PEFC system running on dry hydrogen with an appropriately sized Balance of Plant (BoP) was used to conduct experimental studies and analyses of gas supply subsystems. The improper rating and use of BoP components has been found to increase parasitic loads, which consequently has a direct effect on the polymer electrolyte fuel cell (PEFC) system efficiency. Therefore, the minimisation of parasitic loads while maintaining desired performance is crucial. Nevertheless, little has been found in the literature regarding experimental work on large stacks and BoP, with the majority of papers concentrating on modelling. A particular interest of our study was the anode side of the fuel cell. Additionally the rationale behind the use of hydrogen anode recirculation was scrutinised, and a novel anode purging strategy was developed and implemented. Through experimental modelling, the use of cathode air blower was minimised since it was found to be the biggest contributor to the parasitic loads.

Carbon Corrosion in Polymer Electrolyte Fuel Cells: A Complex Interplay between Morphological Changes and Electrochemical Performance

Due to the high gravimetric energy density of hydrogen, the focus of implementation of polymer electrolyte fuel cells (PEFCs) has shifted from light duty passenger vehicles to heavy duty vehicles such as buses, trucks, locomotives and marine vessels1. A mechanistic understanding of degradation is therefore necessary to improve durability and efficiency. During start-up and shut-down (SUSD) of PEFC systems, the catalyst (Pt nanoparticles embedded on carbon support) undergoes local potentials ∼ 1 - 1.5 V caused by a combination of fuel (H2) starvation, mixed fuel region and cell reversal2. This leads to a series of degradation phenomenon including reduction in cathode catalyst layer (cCL) thickness and porosity, loss in electrochemical surface area (ECSA), ionomer degradation and loss in electrical contact, therefore resulting in severe performance loss2. The convoluted relationship between these individual degradation mechanisms, their chronology and their effects on electrochemical performance are yet unresolved.In this study, the complex interplay between morphological changes due to carbon corrosion and its effects on the electrochemical performance were analyzed using a combination of detailed electrochemical characterization, spectroscopy, and electron microscopy techniques. Commercially available catalyst coated membranes were subjected to the Department of Energy carbon corrosion accelerated stress test (AST) protocol. It was found that carbon corrosion in PEFCs can be divided into two phases. In the first phase (∼500 cycles), disordered domains of the carbon containing Pt nanoparticles oxidized faster with a severe loss of cCL thickness. Pt nanoparticles detached from the support and became electrically isolated and hence electrochemically inactive. Electrochemical surface area decreased rapidly in this phase with little change in the cCL pore structure. Both kinetic and mass transport overpotentials (due to decrease in roughness factor) increased. In the second phase (remaining 1500 cycles), a severe pore structure collapse was observed (see Figure 1). Porosity, mean pore size, and the pore connectivity decreased considerably. Pressure independent oxygen mass transport resistance showed anomalous increase. The oxygen-reduction reaction kinetics were impeded, reflected by an increase in the Tafel slope. This was caused due to severe mass transport limitation, even at low current densities of 0.1 A.cm-2 in oxygen environment owing to pore structure collapse. In addition, the AST did not change the concentration of oxides on carbon, however, the overall water management in the cCL deteriorated as the pores lost percolation. Ionomer degradation was observed in the second phase. Sheet capacitance and sheet resistance also decreased with carbon corrosion. Figure 1. a) 3D reconstructions of the cCL using FIB-SEM micrographs, b) porosity as a function of thickness. Scale bar is 1 µm.

System behavior prediction by artificial neural network algorithm of a methanol steam reformer for polymer electrolyte fuel cell stack use

AbstractIn this paper, a novel membrane reactor (MR) for methanol steam reforming is modeled to produce fuel cell grade hydrogen, which can be used as the inlet fuel for a later developed 500‐W horizon polymer electrolyte fuel cell (PEFC) stack. The backpropagation (BP) neural network algorithm is employed to develop the mapping relation model between the MR's prime operational parameters and fuel cell output performance for future integration system design and control application. Simulation results showed that the MR model performs well for hydrogen production and the developed PEFC system presents good agreement with experimental results. Finally, the BP method captures an accurate mapping relation model between the MR inputs and PEFC output, for example, predicts the system's behavior well.

A multi‐input and single‐output voltage control for a polymer electrolyte fuel cell system using model predictive control method

Efficient and robust control strategies can greatly contribute to the reliability of fuel cell systems, and a stable output voltage is a key criterion for evaluating a fuel cell system's reliability as a power source. In this study, a polymer electrolyte fuel cell (PEFC) system model is developed, and its performances under different operating conditions are studied. Then two different novel controllers—a proportional integral derivative (PID) controller and a model predictive control (MPC) controller—are proposed and applied in the PEFC system to control its output voltage at a desired value by regulating the hydrogen and air flow rates at the same time, which features a multi-input and single-output control problem. Simulation results demonstrate that the developed PEFC system model is qualified to capture the system's behavior. And both the developed PID and MPC controllers are effective at controlling the PEFC system's output voltage. While the MPC controller presents superior performance with faster response and smaller overshoot. The proposed MPC controller can be easily employed in various control applications for fuel cell systems.

An online adaptive model for the nonlinear dynamics of fuel cell voltage

Polymer electrolyte fuel cells have been widely used in automotive applications, in which fast-response and highly accurate fuel cell systems are required to achieve good performance. To fulfill this requirement, an adaptive fuel cell model is developed herein for a polymer electrolyte fuel cell system. The model is established on the basis of a least squares support vector machine. A genetic algorithm is employed to set the initial values of the internal parameters of the model by incorporating existing data from previous experiments. Then, an adaptive process is further conducted to provide an online update of the model’s internal parameters. The genetic algorithm can effectively avoid the initial parameters by falling to a local minimum. Moreover, the online updating of the parameters makes the model more adaptive to load changes in the real-time application of the fuel cell system. The proposed model is experimentally-tested on a fuel cell test rig. The results indicate that the proposed model can accurately and effectively predict fuel cell voltage. In addition, two reference models are employed to compare with the online adaptive model, by which the advantages of the genetic algorithm and parameter updating are verified. The model accuracy is improved significantly with the genetic algorithm, indicating the importance of initial parameters setting. The gradient method also benefits the model’s accuracy in online modeling and predicting, but its efficiency still depends on the initial parameters. This online adaptive model can easily address frequent load change and the long term operation of fuel cells.

Voltage Control for a Polymer Electrolyte Fuel Cell System By Model Predictive Control Controller

Due to its high power density, fast start up ability, low operating temperature, noiseless and environmental friendliness, polymer electrolyte fuel cells (PEFCs) have been regarded as the most promising alternative power sources for a variety of applications, such as transportation system, domestic system, stationary system and so on. Stable and effective control strategy is essential for the efficient and safe operation of PEFC systems. Voltage control is always a research hotspot in PEFCs’ control study. When using a PEFC system to supply power in a real application, it is of great significance to maintain a stable output voltage to avoid an adverse voltage drop under sudden load change, which can reduce the maintenance costs of the PEFC generation system. The output voltage of the PEFC system can be easily affected by the inlet flow rate of the reactant gas, i.e., the reactions inside the fuel cell system will be more sufficient with higher input flow rate of the reactant gas to produce higher electrical voltage, otherwise, less electrical voltage is generated. Therefore, the focus of this study is to control the output voltage of a PEFC system by regulating its hydrogen and air flow rates, which stands for a multi input and single output control problem.Model predictive control (MPC) is an advanced method of process control with stronger robustness and faster response compared with conventional controllers. Its main advantage is that it allows the current timeslot to be optimized while keeping future timeslots in account. Moreover, the MPC is rather suitable for solving systems with constraints, which makes a good choice for the voltage control of the PEFC system since the fuel cell system is a complicated nonlinear and strongly coupled system, with many constraints that need to be considered to ensure the coordination and balance between every subsystem.The first part of this study is to develop a PEFC system dynamic model, which is based on the NedStack PS6 of 6kW rated power. Its polarization behavior based on different reactant flowrates are evaluated. Then based on the developed model, a novel MPC controller is designed to control the PEFC system’s output voltage at 48V, assuming that the PEFC system can be an alternative power source for an electric bicycle with 48 V by regulating the input hydrogen and air flow rates. The following figure gives an overview of the voltage control of the PEFC system. It can be seen the input of the MPC controller contains the reference stack voltage, the state vector, the actual stack voltage and the current. It should be noted that the current is the our test signal. Figure 1

Numerical Simulation of Cerium Ion Migration and Distribution in a Polymer Electrolyte Membrane

Ionomer membrane degradation in polymer electrolyte fuel cell (PEFC) becomes one of the most urgent and critical problems that decrease the longevity of a PEFC, thereby limiting its development with good efficiency and affordability 1. Adding ceria into the PEFC system has proven to be a promising and sustainable way to mitigate this chemical membrane degradation, as the cerium ions can quench the radicals before they attack the ionomer membrane 2. Understanding the distribution and movement of cerium ions within a fuel cell membrane is essential for improving the design of a PEFC system, in terms of its operating environment, material properties, boundary conditions, etc., whereas this has rarely been studied. Due to the experimental limitations of measuring cerium ions transport in an operating fuel cell, numerical simulation becomes a practical approach to quantitatively analyse cerium ions migration under certain conditions.In this study, we aim to provide: (1) a reliable and practical simulation approach to investigate 2D distribution of the cerium ions under specific conditions; and (2) a flexible strategy to analyse the migration of cerium ions attributed to a variety of factors. These techniques would support future research into the development of a promising fuel cell not only with longevity but also at a sustainable cost.From the simulation, we quantified many factors that have impacts on the migration of cerium ions. The diffusion coefficient of cerium ion with respect to the local water content, as well as how the ions are drugged by the local water diffusion, was obtained at first by performing molecular dynamics simulations. Then, by combining these results into a computational fluid dynamics simulation using finite volume method, transport of the cerium ions under certain conditions was resolved (see Figure 1).Along the direction of the path from anode to cathode side, the ion transport in the membrane is affected more substantially by the electric field rather than the water convection and its self-diffusion. Meanwhile in the membrane cross-section plane, it is mainly affected by the water diffusion and its self-diffusion. As the primary finding, the electric field has the greatest influence on the transport of cerium ions, while local distribution of the water content plays an important role when the electric potential difference is small. Credibility of these preliminary simulation results was confirmed by comparing against experimental observations at the similar fuel cell operating environments.Detailed settings of the material properties and results on the reactions of cerium ions to various fuel cell environments will be discussed in the presentation. Acknowledgement This study is support by New Energy and Industrial Technology Development Organisation (NEDO) and the integrated supercomputer system at Institute Fluid Science, Tohoku University. Reference [1] Wang, Y.; Chen, K. S.; Mishler, J.; Cho, S. C.; Adroher, X. C. A Review of Polymer Electrolyte Membrane Fuel Cells: Technology, Applications, and Needs on Fundamental Research. Appl. Energy 2011, 88 (4), 981–1007.[2] Wong, K. H.; Kjeang, E. In-Situ Modeling of Chemical Membrane Degradation and Mitigation in Ceria-Supported Fuel Cells. J. Electrochem. Soc. 2017, 164 (12), F1179–F1186. Figure 1

High Efficiency Operation Conditions in Polymer Electrolyte Fuel Cell System with Hydrogen Circulation

IntroductionWater management is an essential problem to achieve PEFC’s maximum performance. Hydrogen circulation is one of methods to humidify the cell with water produced in oxygen reduction reaction (ORR), while the overall hydrogen utilization can be 100 %. Additionally, by controlling the operation conditions such as gas flow direction, one-pass conversion and humidifying temperature, the cell performance can be improved. The purpose of this study is to investigate the effects of these parameters, and to optimize the cell performance. Water transport in the PEFC system is analyzed in the through-plane direction at steady state, when the dry hydrogen and humidified air are supplied to an 80 oC isothermal system, and the molar flowrate ratio of hydrogen to oxygen at cell inlet is 2.Numerical SimulationGas channels were regarded as straight lines and the gas flow inside was plug flow. The water permeation flux through PEM, which is determined by electroosmosis and back diffusion, was calculated by Eq. (1) [1]. The properties of PEM were assumed as constants, and the equilibrium moisture content λ was assumed and calculated by Springer’s equation [1].Local current density i was calculated by Eq. (2) [2], where k vcm represents 1st-order cathode reaction rate constant per layer volume, which is the function of IR-corrected cell voltage E cm expressed by Eq. (3), p Oc represents partial pressure of oxygen at cathode catalyst layer (CCL) - gas diffusion layer (GDL) boundary and F e is effectiveness factor of CCL, represents the ratio of observed rate to intrinsic rate. According to our previous work, F eis only determined by 4 dimensionless moduli M Om , M pm , P Om and y Oc [2]. M Om represents the ratio of oxygen diffusion resistance to ORR resistance (Thiele modulus). M pm represents the ratio of proton transport resistance to ORR resistance (our modulus). P Om represents the ratio of convection to oxygen diffusion (Péclet mumber).Results and DiscussionFig. 1 shows the distribution of relative humidity (RH) along gas channels, and water permeation flux through PEM in cases of co-current and countercurrent at the fixed one-pass conversion and current density. The total water permeation rate is 0 since the make-up H2 supplied into the system is dry and no water leaves the cell at steady state. The RH in cathode gas channel increases monotonically in case of countercurrent; the RH has a maximum value in case of co-current, since the water permeation flux varies in a greater region than co-current.The effect of one-pass conversion on performance is the competition of mass transport and reaction. As shown in Figs. 2 and 3, when the one-pass conversion increases at the fixed cell voltage, the average RH in gas channels increase, due to the decrease in gas flowrate in the gas channels. However, the inflection points in Fig. 2 exist around x H = 0.3, which indicates when the one-pass conversion is lower than 0.3, the gas flowrate is too high for water produced in ORR to humidify anode gas sufficiently. As the RH increasing, the average proton conductivity of PEM increases and average oxygen partial pressure in cathode gas channel decreases, as shown in Figs. 4 and 5, which indicates the proton transport is enhanced due to the humidification by water produced in ORR, and the reaction rate is reduced since the concentration of reactant decreases. As the result, by increasing the one-pass conversion, the current density firstly increases and then decreases, as shown in Fig. 6.In addition, when the one-pass conversion is high enough, the RH in gas channel will reach 1, and flooding will happen more likely inside the cell than at the exit in case of countercurrent, since RH has a maximum value in gas channel. To prevent flooding, the maximum operation conversion should be lower than the value calculated by Eq. (4), according to the material balance, where the RH2 [C] represents the cathode outlet RH, which is 1 for co-current and lower than 1 for countercurrent.ConclusionsThe optimized one-pass conversion is determined by the competition of mass transfer and reaction. As the one-pass conversion increases, the proton transfer resistance decreases due to the humidification by water produced in ORR, and reaction rate decreases due to the consumption of oxygen. The optimized one-pass conversion should be higher than 0.3 to ensure the sufficient humidification, and lower than the value calculated from Eq. (4) to prevent flooding.

PEMFC Transient Response Characteristics Analysis in Case of Temperature Sensor Failure

In this study, transient responses of a polymer electrolyte fuel cell system were performed to understand the effect of sensor fault signal on the temperature sensor of the stack and the coolant inlet. We designed a system-level fuel cell model including a thermal management system, and a controller to analyze the dynamic behavior of fuel cell system applied with variable sensor fault scenarios such as stuck, offset, and scaling. Under drastic load variations, transient behavior is affected by fault signals of the sensor. Especially, the net power of the faulty system is 45.9 kW. On the other hand, the net power of the fault free system is 46.1 kW. Therefore, the net power of a faulty system is about 0.2 kW lower than that of a fault-free system. This analysis can help in understanding the transient behavior of fuel cell systems at the system level under fault situations and provide a proper failure avoidance control strategy for the fuel cell system.

High Efficiency Operation Conditions in Polymer Electrolyte Fuel Cell System with Hydrogen Circulation

Water management is an essential problem to achieve PEFC’s maximum performance. Hydrogen circulation is one of the methods to humidify the cell with water produced in oxygen reduction reaction (ORR), while the overall hydrogen utilization can be 100%. Additionally, by controlling the operating conditions, such as gas flow direction, one-pass conversion, and humidifying temperature, the cell performance can be improved. Water transport distribution along the gas channel was analyzed by numerical simulation, and the competition of the proton transfer resistance, the oxygen transfer resistance, and the reaction resistance were discussed quantitatively. The results indicate that the countercurrent mode attains better performance due to higher moisture content at high humidification conditions, and the co-current mode can be chosen at low humidification condition. The one-pass conversion higher than 0.30 is required to humidify the cell sufficiently.