Cathode Stoichiometry Research Articles

Multi-objective optimization of comprehensive performance enhancement for proton exchange membrane fuel cell based on machine learning

The comprehensive performance of proton exchange membrane fuel cells depends on operating conditions. This paper innovatively uses the Pearson correlation coefficient to screen the optimization objectives (uniformity index of oxygen, standard deviation of temperature, net power density), and obtains the optimal operating conditions of the proton exchange membrane fuel cell through a multi-objective optimization method. The optimized dataset comes from the simulation results of the three-dimensional numerical model, and the regression model is established through the response surface method. Moreover, the non-dominated sorting genetic algorithm-II is used for processing to obtain the Pareto front solution set, and the optimal operating conditions are obtained from it through the Technique for order preference by similarity to an ideal solution. The analysis of variance result shows that the influence of cathode operating conditions on the comprehensive performance is greater than that of anode, especially the influence of cathode stoichiometry ratio is the most significant. The optimal solution obtained 1.0981 %, 10.5845 %, and 1.0376 % enhancement compared to the optimal values in the simulation results. The differences between the three optimization objectives are only 0.8190 %, 1.0315 %, and 0.8789 % as verified by numerical simulation, thus the machine learning results are reliable and accurate.

Multi objective optimization using artificial neural network to maximize the power output of PEMFCs

ABSTRACT Designing a PEM fuel cell model is exceedingly challenging because of its multivariate in nature. Optimization is required to achieve highest operating condition. Neural Network Model is one of the possible methods to solve complex problems. The polarisation curve of a PEMFC (Proton Exchange Membrane Fuel Cell) is investigated in this paper in relation to the effects of seven parameters, including temperature, relative humidity in the cathode, relative humidity in the anode, anode stoichiometry, cathode stoichiometry, partial pressure of H2, and partial pressure of O2, using an ANN (artificial neural network) model. Where model geometric parameters i.e. Channel width, Channel depth, Channel length, Rib width, Cell width, GDL thickness, CL thickness, Membrane thickness of PEMFC was constant. Initially single Objective Function (Output Power) is predicted. The research presented here makes predictions about a PEMFC stack's electrical performance under multiple operating conditions. Mathematical model was further verified using laboratory data. Co-efficient of Determination (R2), Mean Square Error (MSE), and Mean Absolute Error (MAE) was determined using the fuel cell stack voltage model and stack power model. The model results show the possibility of using ANN in the implementation of such models to predict the PEMFC system's steady-state behaviour.

Optimization of baffle and tapering integration in the PEM fuel cell flow field employing artificial intelligence

In this study, two surrogate models are developed to investigate and enhance the performance of parallel flow field Proton Exchange Membrane Fuel Cells (PEMFCs) with two modifications. The main channels are tapered, and baffles are inserted to enhance the mass transfer. A data set is generated by the multi-phase, three-dimensional CFD model. Two different data-driven models based on Artificial Intelligence (AI) and Modified Response Surface Methodology (MRSM) provide surrogate models. Subsequently, two multi-objective optimization methods are employed to reveal the optimum case. The results show that the AI model achieves superior accuracy, whereas the MRSM model has greater simplicity. An increased number of baffles and an optimal tapering ratio contribute to higher mass flux and improved uniformity in reactant distribution. The insertion of baffles and the tapering of main channels result in a remarkable 67 % increase in output power density. Optimum tapering also reduces pressure drop, whereas baffles, while improving performance, contribute to increased pressure drop and potential PEMFC degradation. The identified optimum configuration of baffles and tapering, along with the optimum values for voltage, pressure, and anode and cathode stoichiometries, results in an impressive output power density of 0.93 W cm−2 and a parasitic power ratio of 0.17, respectively.

Machine learning optimization of operating parameters to achieve high power density and efficiency of polymer electrolyte membrane fuel cell

The performance of PEMFCs is significantly influenced by operating conditions, including temperature, pressure, and flow rates. To optimize the complicated nonlinearity of operational conditions such as anode pressure (AP), cathode pressure (CP), cell temperature (Temp), anode flow rate (HFL), cathode stoichiometry (CS), and current density (CD) in experiments, this study employs five machine learning (ML) regression models: Artificial Neural Network, Decision Tree, Random Forest, Gradient Boosting, and Extreme Gradient Boosting to predict key performance indicators: voltage, power density, and efficiency, thereby optimizing the fuel cell’s operational parameters. Among these, the Gradient Boosting regressor demonstrated superior performance when validated with experimental data and was subsequently employed to fine-tune the operating parameters. Leveraging the prediction model, the performance of PEMFC in terms of power density and efficiency was further assessed by varying AP, CP and CS. The optimal conditions were identified with AP, CP at 2 bar, and CS at 2.50–2.75.

Non-Invasive Measurement of Impedance Spectra Distribution in Polymer Electrolyte Fuel Cells

Localized measurement of the impedance distribution in an operating polymer electrolyte fuel cell stack is of great importance in providing information on its state of health and performance. However, the current methods’ invasiveness is a brake to a more widespread utilization. This work presents a non-invasive way to measure and interpret local impedance spectra. It is based on local AC current supply and local voltage measurements performed all around the cell via conductive pins contacting the outer surface of the flow fields. The different local spectra are measured on a single cell within a 200 cm2 six-cell stack under different operation conditions and compared to a reference case with homogeneous current density. A simple equivalent electrical circuit is used to fit the impedance spectra and to extract membrane and charge transfer resistance. The variations of these two values are analyzed at five different positions along the channel for different cathode stoichiometries and gas flow configurations.

A comprehensive investigation on performance heterogeneity of commercial-size fuel cell stacks during dynamics operation

The performance heterogeneity of commercial-size proton exchange membrane (PEM) fuel cells comprises both inter-cell consistency and intra-cell uniformity, which can lead to the generation of degrading stressors, such as harmful variations in local cell voltage and current density. However, there is a notable absence of a thorough investigation of the potential correlation between inter-cell consistency and intra-cell uniformity. To address this knowledge gap, a comprehensive experimental study was conducted via the current distribution model to assess the impact of several operating variables, including loading rate, cathode stoichiometry ratio, and cathode pressure, on the performance heterogeneity of commercial-size fuel cell stacks. The results indicate that cells situated on both end sides of the stack are more susceptible to non-equipotential phenomena owing to liquid water accumulation and the inhomogeneity of oxygen distribution, which in turn lead to the redistribution of the in-plane current as well as the deviation of the bipolar plate potential. Moreover, a significant correlation exists between inter-cell consistency and intra-cell uniformity of cells placed at both ends of the stack with a correlation coefficient > 0.85. The enhancement of fuel cell stack output performance and reduction of performance heterogeneity may be achieved by optimizing pressure and stoichiometric ratio. However, it should be noted that there exists a discrepancy in the operating conditions necessary to achieve optimal performance and minimal performance heterogeneity. Finally, the recommendations given for the implementation of cell voltage monitors (CVMs) were summarized. This study provides a comprehensive reference for analyzing complex heterogeneity issues within fuel cells, revealing significant potential in their application.

Numerical Study on the Influence of Variable Section-Enhanced Mass Transfer Flow Field Design on PEMFC Performance Based on Underrib Convection Flow

The optimal design of variable section is a flow field optimization method that changes the pressure of the reacting gas in the flow channel by setting up a contraction surface in the flow channel, which is effective in improving many aspects of the proton exchange membrane fuel cell (PEMFC) performance. However, there are also problems such as uneven oxygen distribution in some of the flow channels, and the current density and net output power are not significantly improved. To find a balance among gas transfer efficiency, drainage capacity, uniformity of current density distribution, and output performance, this paper investigates the design of a variable cross-section-enhanced mass transfer flow field for PEMFC flow channel contraction by establishing a three-dimensional numerical model, starting from the sidewall width direction and the bottom height direction of the flow channel cross-section dimensions, in order to assess the effects of variable cross-section contraction at the bottom and sidewalls of the flow channel on the cell performance. The polarization curves, mass transfer capacity, current density distribution, and net output power of the variable cross-section contraction flow field are analyzed and compared with the straight flow field. On this basis, the optimum size parameters and operating parameter combinations are determined. Variable cross-sectional contraction flow field improves PEMFC output performance. The contraction of the variable cross-section contraction flow field at the sidewalls effectively improves reactive gas transfer efficiency and drainage capacity, improves current density distribution, and increases the net output power of the PEMFC. In particular, the sidewall contraction flow field has a 9.0% increase in power density, a 6.45% increase in the effective mass transfer coefficient (EMTC), a 6.52% increase in uniformity of current density distribution, and a 6.05% net power increment compared to the straight flow field, respectively. The best output performance, the highest oxygen concentration, and the lowest water concentration are achieved with a combination of parameters: number of sidewall contractions N = 6 , length L f = 6 mm , and width W f = 1.2 mm . And a wide range of air stoichiometry ratios are applied when the contraction of the variable cross-section contraction flow field is located at the sidewalls. Increasing the cathode stoichiometry ratio from 10 to 50 increased the cell power density by 25.5% and from 50 to 90 increased the cell power density by 9.5%. The simulation results can provide theoretical basis for the application of variable section flow field design for practical PEMFC.

Voltage distribution analysis and non-uniformity assessment in a 100 cm2 PEM fuel cell stack

In this study, a comprehensive set of experimental tests were carried out to investigate individual cell voltage and temperature deviation under different operating conditions in a fuel cell stack. Five key operating conditions were considered: temperature, pressure, anode and cathode relative humidity, and cathode stoichiometry. Different configurations of reactant flow within the stack were also investigated. A 100 cm2 7-cell stack was used for the experiments, and voltage and temperature measurements were taken for each individual cell. Both ANOVA and range analysis method were used to evaluate the results. The findings showed that the performance of the external cells was consistently lower than that of the central ones since its temperature, the parameter that most affected performance, was also lower due to heat losses. Additionally, voltage deviation increased with temperature deviation. The study also revealed that stack performance was improved by an increase in temperature, pressure and cathode stoichiometry, whereas the effect of anode and cathode humidity was not so significant in the studied range. Furthermore, gravity played a clear role in water management, hindering the removal of condensed water for flow configurations where reactant gases were fed from the bottom interfaces of the stack.

Numerical simulation of holomorphic microscopic metal foam as cathode flow field in proton exchange membrane fuel cells

ABSTRACT An enhanced flow field significantly improves reactant transfer and proton exchange membrane fuel cells (PEMFCs) performance. Metal foams with high porosity and electrical conductivity are promising flow field structures. This study aims to investigate the effect of metal foam porosity and pore density on PEMFC performance. A three-dimensional multi-physics PEMFC model with holomorphic microscopic metal foam (HMMF) as a cathode flow field was established using computational fluid dynamics (CFD). The HMMF with high porosity as a cathode flow field can enhance reactant transfer and accelerate the electrochemical reaction process. It is also observed that increasing the porosity of HMMF can significantly improve the peak power and current density of PEMFC. The simulation results show that the current density gains an increase of 15.3% by raising the porosity from 0.8 to 0.96. Besides, the current density increases by 4.3% when the pore density is 95 PPI compared to 21 PPI. Moreover, the effects of cathode stoichiometry ratios on oxygen molar fraction and polarization curves were studied to obtain better operating conditions for the HMMF flow field. The results indicate that increasing the cathode stoichiometry ratio can effectively enhance oxygen concentration. And the increase of the cathode stoichiometry ratio from 1.5 to 4.0 results in a 45.5% increment of current density.

Multi-objective optimization and evaluation of PEMFC performance based on orthogonal experiment and entropy weight method

The operating condition parameters of temperature (T), anode relative humidity (RH_a), cathode relative humidity (RH_c), anode stoichiometry ratio (St_a), and cathode stoichiometry ratio (St_c) have a coupling influence on the multiple performance objectives of current density (I), pressure drop (ΔP), temperature difference (ΔT), and non-uniformity of oxygen (N) in the actual operation process of proton exchange membrane fuel cell (PEMFC). Based on the orthogonal experiment method (OEM) and entropy weight method (EWM), a new multi-objective optimization method and mathematical expression for evaluation of a PEMFC performance were proposed to clarify the influence ability of T, RH_a, RH_c, St_a, and St_c on I, ΔP, ΔT, and N and comprehensively evaluate the performance of a PEMFC in multiple performance objectives situations. The L18(37) orthogonal array was first designed by the OEM to form eighteen groups of schemes for multi-objective optimization. By analyzing the range and variance, the significance order and optimal parameter combination were individually obtained under four performance objectives. The comprehensive performance objective of output performance (OP) was then proposed, and the EWM was used to calculate the respective weight value of four performance objectives in OP. The mathematical expression of OP was calculated as OP = 0.51 I + 0.08 ΔP + 0.19 ΔT + 0.22 N, indicating that current density was the most important parameter. Eighteen groups of schemes were scored and ranked and the OP score of Scheme 6 was the highest with a value of 0.788. Finally, the analysis of range was performed again for OP scores, and the optimal combination of T = 343.15 K, St_a = 3, St_c = 3, RH_a = 20%, and RH_c = 20% was achieved, which was better than Scheme 6. This study redresses the limitation of single-performance objective optimization and maximizes the comprehensive performance of PEMFC considering multi-objectives.

Three-Dimensional Simulation on the Effects of Different Parameters and Pt Loading on the Long-Term Performance of Proton Exchange Membrane Fuel Cells

The choice of platinum loading and the choice of the operating parameters of the cell are crucial in order to enhance a PEMFC’s endurance and, at the same time, to raise its performance. In this paper, a single-channel PEMFC counter-current model is developed to investigate the effects of a 0.3 mg/cm² Pt loading model and a 0.1 mg/cm² Pt loading model on the performance and durability of PEMFCs with different operating pressures, different cathode stoichiometry, and different channel and plate widths. It was found that increasing the PEMFC operating pressure and cathode stoichiometry would increase the cell performance and have some improvement for durability. Additionally, increasing the channel/plate width ratio would improve the cell performance while decreasing the cell durability.

Flooding Characteristics and Countermeasures in a PEM Fuel Cell System

PEM fuel cell systems in automotive application face challenging power requirements, as they must provide full load as well as part load efficiently. Especially in systems without an external humidifier, relatively low cathode stoichiometries and increased operating pressures are the key to prevent membrane dry-out by increasing the local relative humidity. During low load operation at increased temperature and pressure, low gas velocities within the flow field occur. Too low gas velocities are known to result in a transition of the two-phase flow from film flow to slug flow regime [1]. This transition within the flow field channel structure can result in a local or global blockage of the reactant paths by liquid water droplets.While the flow regime transition within simple channel geometries is well known in literature, there is a lack of experimental data for full stack situations in fuel cell systems. Some work regarding the stationary minimal flow limitation exists [2], but countermeasures enabled by dynamic operation of the whole system are seldom in focus of systematic studies. However, well guided dynamic operation enables robust low load capability. The negative impact of flooding on stack power and lifetime can be minimized and a possible dry-out can be prevented, while maintaining a relatively low required compressor energy consumption.In the work to be presented, targeted experiments conducted with an automotive fuel cell system confirm the existence of a minimum cathode gas velocity for a stable operation and its relevance in application-like operation. It is shown that during low load operation of a non-humidified system, the targets of sufficient membrane humidification and liquid water drainage are incompatible. Because of a response time of multiple seconds until flooding or dry-out occurs, an intermittent operation with periodic switching between two operating points becomes feasible. During the first phase, the membrane is humidified due to a relatively low cathode stoichiometry and an increased cathode inlet pressure. As the liquid water accumulation becomes critical, the pressure is decreased and the stoichiometry is increased for the second phase, where droplets are blown out by utilizing a high gas velocity, as shown in figure 1.The exemplary results suggest that dynamic water management analysis can widen the operating range of a fuel cell system towards lower loads due to dynamic control. It is expected that a deeper understanding of the underlying processes will allow the development of optimized control strategies in the future.[1] M. Grimm, E.J. See, S.G. Kandlikar. Modeling gas flow in PEMFC channels: Part I – Flow pattern transitions and pressure drop in a simulated ex situ channel with uniform water injection through the GDL. Int. Journal of Hydrogen Energy 37, 12489-12503 (2012).[2] D. Jenssen, O. Berger, U. Krewer. Anode flooding characteristics as design boundary for a hydrogen supply system for automotive polymer electrolyte membrane fuel cells. Journal of Power Sources 298, 249-258 (2015).Figure 1: Normalized current, high frequency resistance, cell voltages, cathode stoichiometry, cathode inlet pressure and cathode inlet velocity, measured on a system test rig during intermittent low load operation. The operating point is periodically switched between membrane humidification (green) and liquid water drainage (orange). Figure 1

Performance analysis and optimization of a novel vehicular power system based on HT-PEMFC integrated methanol steam reforming and ORC

In this paper, a novel vehicular high temperature proton exchange membrane fuel cell (HT-PEMFC) power system integrated with methanol steam reforming (MSR) and Organic Rankine Cycle (ORC) is proposed. The system uses waste heat from the HT-PEMFC to provide the MSR subsystem for hydrogen production, and the ORC subsystem recovers the remaining heat to generate electrical power. The thermodynamic model of the system and multi-criteria evaluation are established. Numerical results show that increasing the current density and decreasing the cathode pressure and stoichiometry is favorable for improving the net output power of the system, but also increasing the levelized cost of energy and carbon mass specific emission of the system. Higher operating temperatures and anode pressures are beneficial to overall performance. Moreover, the system is optimized using the NSGA-II algorithm to obtain the three-dimensional (3D) Pareto solution and the optimal set of operating parameters. The optimized system net output power, levelized cost of energy and carbon mass specific emission at the Final Optimal Point are 36.98 kW, 0.2138 $/kWh and 0.5583 kg/kWh, respectively. Compared to the un-optimized system, the system working at optimal parameters has better thermodynamic, economic and environmental performance.

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.

Cathode side transport phenomena investigation and Multi-Objective optimization of a tapered parallel flow field PEMFC

A Proton Exchange Membrane Fuel Cell (PEMFC) provides stable, emission-free, high-efficiency power. Water management and durability of PEMFCs are directly affected by transport phenomena at the cathode side. In the present study, transport phenomena are investigated and optimized in a tapered parallel flow field. Main channels in the flow field are tapered, which increases limiting current density by 41%. Two objectives, i.e. water saturation and transport resistance, are considered metrics for transport phenomena in a tapered parallel flow field PEMFC. Operating pressure, temperature, stoichiometries at both sides, and the porosity of gas diffusion layers are selected as parameters to be optimized. Two functions are generated for objectives by integrating 3D multiphase-flow computational fluid dynamics and Response Surface Methodology. Multi-Objective Optimization (MOO) is carried out with two different methods. Multi-Objective Particle Swarm Optimization (MOPSO) and Non-dominated Sorting Genetic Algorithm II (NSGA-II) are employed to produce two challenging Pareto fronts. The results demonstrate that MOPSO performs better than NSGA-II. MOPSO recognized quite the same Pareto front with lower runtime. In the last step, the Technique of Order Preference Similarity to the Ideal Solution (TOPSIS) is used to select an optimum point from the Pareto front. The results are compared against experimental data, and good correspondence is observed. The optimum features are temperature 323, pressure 1 atm, anode stoichiometry 3, cathode stoichiometry 2.62, and porosity 0.68. The porosity and pressure played the most significant roles in determining water saturation and resistance.

Performance Investigation of Proton‐Exchange Membrane Fuel Cell with Dean Flow Channels

Herein, a novel fuel cell flow field with 3π/2 radian Dean flow channels and its impact on the performance of proton exchange membrane fuel cells are presented. With a multidisciplinary numerical model, flow characteristics, concentration distribution, and current density contour in the fuel cell are compared between straight and Dean flow channel cases. The unstable vortices formed in the Dean flow channels are shown to enhance mass transfer of both reactants and water. As a result, although the voltage under low current density is slightly lower than that of fuel cells with straight channels, the output performance under high current density is observably improved. It is also found that the enhancement of oxygen transport with the Dean channel is more significant at relatively small cathode stoichiometry. In addition, by reducing the gas diffusion layer porosity, the membrane is kept at high humidity, yielding an improvement in power output and stability of the fuel cell at low cathode inlet pressure operation.

(Invited) Electrochemical Separation of Carbon Dioxide Using Anion Exchange Membranes

Anion exchange membranes provide a useful platform for electrochemical separation of carbon dioxide from dilute gas streams. Electrochemically-driven acid gas separations require a cathode reaction that generates hydroxide and an anode reaction that consumes hydroxide. Hydroxide generated at the cathode reacts with CO2 to make carbonate, which is transported across the membrane to the anode. The reverse process at the anode drives release of CO2. The reactions must be compatible with the gas mixtures present and must function over a pH range of about 7-12 for anode and 12-14 for cathode. These requirements allow flexibility for a range of electrode reactions. Four cells can be made from the reactions of hydrogen, oxygen, and water: the fuel cell1, electrolyzer, hydrogen pump, and oxygen pump2. Additionally, certain battery electrodes, such as nickel hydroxide / oxyhydroxide can be used to eliminate the gaseous reactants or byproducts.We will present experimental and model results for electrochemical separators using various electrode reactions. Applications include direct air capture of CO2 and scrubbing of air to >99% CO2 removal for use in hydroxide exchange membrane fuel cells. To date, the best studied system is the separator using fuel cell chemistry in a scrubbing application. Recent progress is shown in Figure 1. In the past three years, an order of magnitude improvement in air scrubbing capacity has been achieved through careful optimization of mass transport.Electrochemical separation of CO2 is well described by standard electrochemical models and much insight can be gained into the methods to improve performance. The role of membrane resistance provides a clear example. A pH gradient must be maintained between anode and cathode, both to create the thermodynamic driving force to transport CO2 from low partial pressure to high and to increase the kinetics of CO2 capture by providing excess hydroxide at cathode. Anion diffusion tends to reduce this pH gradient, while migration strengthens the gradient. As a result, the CO2 capture rate at constant current density tends to increase with increasing membrane resistance1, and the best fuel cell membranes have too high of conductivity to make optimized electrochemical separators. Figure 2 shows an experimental validation of the effect of membrane resistance. CO2 separation is greatly improved as membrane resistance increases, both in the case of intentionally degraded membranes and fresh membranes of reduced conductivity. The performance difference is greatest at the lowest current density, where the potential gradient across the membrane is smallest. References Matz, S. et al. Demonstration of Electrochemically-Driven CO 2 Separation Using Hydroxide Exchange Membranes . J. Electrochem. Soc. 168, 014501 (2021).Rigdon, W. A. et al. Carbonate Dynamics and Opportunities With Low Temperature, Anion Exchange Membrane-Based Electrochemical Carbon Dioxide Separators. J. Electrochem. Energy Convers. Storage 14, 020701 (2017). Figure 1: Progression of electrochemical carbon dioxide separation performance from 2018-2020 using 25 cm2 single cells with fuel cell chemistry. Air with 400 ppm CO2 was fed to the cathode. Cell temperature & relative humidity: 70 °C, 80% (2018-1, 2018-2) or 60 °C, 70% (2019-1, 2019-2, 2020); current density: 20 mA/cm2 (2018-1, 2018-2, 2019-1, 2019-2) or 35 mA/cm2 (2020); outlet pressure: 100 kPaa (2018-1, 2018-2, 2019-1), 175 kPaa (2019-2), or 250 kPaa (2020). Anode hydrogen flow rate was 50 sccm (2018-1, 2018-2), 7 sccm (2019-1, 2019-2), or 12 sccm (2020). EDCS:FC ratio is the active area of electrochemical separator divided by the active area of the fuel cell that it could supply based on the air flow rate, assuming 1.5 A/cm2 fuel cell current density and 1.5x cathode stoichiometry. Figure 2: Effect of membrane area-specific resistance on CO2 separation performance. Conditions: 60 °C cell temperature, 90% relative humidity, 20 sccm H2 flow at anode, 1000 sccm air (w/ 400 ppm CO2) at cathode, atmospheric pressure. Membrane details: A) PAP-TP-85 membrane B) Same as A, but slightly degraded to increase resistance (140 h dry exposure in 80 °C oven). C) Same as A, but moderately degraded to increase resistance (96 h dry exposure in 97 °C oven). D) Fumasep FAA-HM membrane from FuMA-Tech Gmbh. Figure 1

Current density and temperature distribution measurement and homogeneity analysis for a large-area proton exchange membrane fuel cell

Homogeneous distribution of electro-chemical reaction rates among the activation surface is critical for improving the performance and durability of automotive proton exchange membrane fuel cells (PEMFCs). Segmented measurement technology is commonly used to characterize the local physical-parameter distribution in the PEMFC. In this study, the local current density (LCD) and temperature distributions of a PEMFC with the activation area of 108 cm2 and various cathode flow fields are experimentally investigated. A homogeneity parameter is introduced to evaluate the homogeneity of LCD distribution. The results show that the performance and LCD distribution uniformity of the cell with dot-parallel flow field are much better than that with parallel and parallel-serpentine flow fields. The temperature distribution is generally positively correlated with LCD distribution. For the LCD distribution, the high LCD region firstly appears in the cathode downstream region, and gradually transfers upstream with increasing the current load. With the increase of inlet humidity, the LCD near the cathode inlet is improved due to the improvement of membrane hydration. Increasing the cathode stoichiometry can effectively improve the uniformity of LCD distribution, and mitigate the local oxygen starvation, especially at high loads.

Effective and practical parameters of electrochemical Li-ion battery models for degradation diagnosis

The pseudo-2-dimensional (P2D) model parameters of Li-ion batteries are important indicators of their properties, characteristics, and conditions. For safe operation, it is essential to discover the effective P2D model parameters closely related to the degradation state of the battery. This paper proposes a practical method for identifying and selecting effective P2D model parameters that significantly change with battery aging. As per the proposed procedure, the aging parameters distinctly correlated with the battery degradation states are selected, and effectively and reliably identified through experiments with multiple profiles, such as constant current–constant voltage (CCCV) chirp sequences, hybrid pulse power characterization (HPPC) cycles, and driving cycles. To identify the optimal parameters, the obtained experimental data are fitted to the P2D model using the genetic algorithm. The mean error between the experimental data and the output voltages of the P2D model with the identified parameters is 18.79 mV, showing high accuracy. Certain parameters that converge to distinctly different values at the beginning-of-life (BOL) and end-of-life (EOL) of a battery are selected as the aging parameters. Consequently, the cathode particle surface area, stoichiometry limits, and porosities were selected as aging parameters, and it is demonstrated that those parameters shift with aging.

Study on the performance and characteristics of fuel cell coupling cathode channel with cooling channel

Water flooding in the cathode channel of the proton exchange membrane fuel cell (PEMFC), which reduce the current density output and affect fuel cell lifetime. Hence, to suppress water flooding, a novel channel is proposed in this study, that is to perforate hole between the cooling channel and cathode channel. A 3D numerical model is used to investigate the influence of the parameters including the hole's dimension, position, numbers, the operation conditions of the PEMFC and the slope angle (θ) of the incline cooling channel. The numerical results indicate that the optimal single hole parameters are 0.4 mm long, 0.5 mm wide and 20 mm position, which can maximum the current density output of the PEMFC. Increasing the hole numbers for novel channels can improve water removal. In addition, in comparison with the conventional channel with θ = 0.20° at 1.8 cathode stoichiometry, the H5 (novel channel with five holes) with θ = 0.20° decreases by 43.10% in the maximum water saturation of cathode channel, while increases by 12.54% in current density output. What's more, all the novel channel structure research hardly raises the pressure drop of channels.