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Proton exchange membrane fuel cells with dead-ended anode simplify fuel cell system and effectively reduce its volume, weight and cost. In this study, a three-dimensional numerical model of a dead-ended anode PEMFC with single straight channel is developed. The effect of operating conditions, including operating temperature, anode inlet pressure, and cathode relative humidity on operating characteristics of dead-ended anode PEMFC was studied in detail. What's more, the purge cycle, hydrogen utilization and energy efficiency are analyzed and the reasonable purge strategy was optimized. The results indicates that the decrease of anode partial pressure caused by the accumulation of nitrogen and liquid water is the main reason for the voltage decline during dead-ended anode operation. The purge cycle is effectively prolonged by increasing anode pressure and reducing the relative humidity of cathode. The purge cycle is extended from 437s to 562.5s as the anode pressure increased from 50 kPa to 150 kPa. The purpose of optimizing the purge strategy is to fully remove the accumulated water and nitrogen, so as to prolong the purge cycle and improve hydrogen utilization and energy efficiency. From the result, the hydrogen utilization and energy efficiency of the base case are 95.77% and 40.05%. • Operating and purging characteristics of PEMFC with dead-ended anode were simulated. • Purge strategy depends on working conditions and is most affected by temperature. • Hydrogen utilization and energy efficiency were reasonably proposed. [ABSTRACT FROM AUTHOR]

Bi-directional mode switching is a crucial operation in unitized regenerative proton exchange membrane fuel cells (UR-PEMFC). Mass transfer plays a direct role in influencing the performance of both the fuel cell (FC) mode and the electrolytic cell (EC) mode, consequently impacting the round-trip efficiency (RTE). This study enhanced the three-dimensional two-phase model of UR-PEMFC by incorporating the mass transfer dynamics of the flow field. The round-trip efficiency (RTE) was systematically assessed throughout the bidirectional mode switching cycle. The results indicate that UR-PEMFC with triple-serpentine flow fields (TSF) performed well in FC mode, which was attributed to its good oxygen distribution uniformity and liquid water detachment capacity, in EC mode, its poor effective mass transfer coefficient and higher mass transfer resistance led to higher electrolytic energy consumption. However, UR-PEMFCs with TSF and parallel flow field (PFF) had better dynamic response performance during the bidirectional mode switching, and their voltage undershoot (overshoot) and response time were improved, which were attributed to uniform flow field structures. The UR-PEMFC reached optimum RTE operating at 0.1 A/cm2 in FC mode and 1.1 A/cm2 in EC mode, and the RTEs of the UR-PEMFCs with PFF and TSF were more advantageous, their highest RTEs were 36.62% and 36.30%, respectively. This study proposes two switching strategies to enhance the stability of URFC mode switching, offering a viable new approach for optimizing the flow field and improving overall performance. • A three-dimensional two-phase model of UR-PEMFC coupled with flow field is established and improved. • Mass transfer characteristics are used to analyze UR-PEMFC's steady-state performance. • Proposed switching strategies significantly enhance voltage stability during bidirectional mode transitions. • The round-trip efficiency coupled with flow field effect is evaluated during bidirectional mode switching cycle. [ABSTRACT FROM AUTHOR]

The durability and reliability of H 2 /O 2 proton exchange membrane fuel cell (PEMFC) is a key factor that prevents its wide application in the civil field. PEMFC inevitably experience different dynamic loading cycles according to different power switching requirements during practical operation. To explore the degradation behavior under different dynamic cycles, a single H 2 /O 2 PEMFC with 50 cm2 active area was operated under the circulating current density from 100 mAcm−2 to 600 mAcm−2, 100 mAcm−2 to 800 mAcm−2, and 100 mAcm−2 to 1000 mAcm−2, respectively. The change of polarization curve, performance degradation at different current density, Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) were characterized to investigate the performance degradation over dynamic current cycles. Besides, the Scanning Electron Microscopy (SEM) was used to evaluate the degradation of catalyst layer. The results indicated that the degradation rate of the fuel cell performance increased corresponding to the cycle number, at 1200 mA/cm2, it with a total performance degradation rate of 11.83% after 2000 dynamic loading cycles with the circulating current density from 100 mAcm−2 to 600 mAcm−2. The degradation of electrochemical performance such as CV and EIS was consistent with that of fuel cell performance. The degradation rate is accelerated with the increase of loading cycle number and load step amplitude. What' more, EIS provides additional sensitivity to differentiate catalyst layer degradation within PEMFC. Moreover, the degradation of the catalyst layer became much more severe under a larger load step amplitude. • Degradation behavior of H 2 /O 2 PEMFC under dynamic loading cycles was studied. • The current loading process can cause gas starvation in both anode and cathode. • Hydrogen starvation induced carbon corrosion in the anode. • Catalyst layer degradation became much more severe with a larger loading rate. [ABSTRACT FROM AUTHOR]

Targeting the shortcomings of low round-trip efficiency (RTE) in unitized regeneration proton exchange membrane fuel cell (UR-PEMFC), a model incorporated combined cooling, heating, and power (CCHP) technology for UR-PEMFC was proposed, which integrated a three-dimensional two-phase flow field model with a zero-dimensional system model. Additionally, a multi-criterion evaluation system was introduced for the URFC-CCHP system, which encompasses three decision-making methods. To illustrate the applicability of the model, the assessments of four typical flow field configurations were utilized as case studies and presented their rankings. The results reveal that, compared to a system focused on electrical power output, the system exhibited a remarkable enhancement in RTE, increasing from 35.96 % to 76.67 %. Notably, during the cold season, the RTE surpassed that of the warm season by 8.74 %–10.62 %. Operating under a cyclic condition of fast charging and slow discharging proved to be conducive to maintaining the optimal RTE of the system. Furthermore, the computational outcomes of the three decision-making methods in the multi-criterion evaluation system exhibited consistency, unanimously identifying the optimal flow field as the three-serpentine flow field, while designating the single-serpentine flow field as the least favorable. It aims to present a novel technology for enhancing the RTE of UR-PEMFC. • The CCHP technology was introduced to enhance the overall efficiency of UR-PEMFC. • The RTE of the system increased from 35.96 % to 76.67 % compared to a system focused on electrical power output. • The URFC-CCHP's nine performance metrics were derived by coupling a 3-D model with a 0-D model. • A multi-criteria evaluation system with three methods was introduced for the URFC-CCHP system. • Four typical Flow field configurations are assessed by the evaluation system as a case study. [ABSTRACT FROM AUTHOR]

The operating parameters of proton exchange membrane fuel cell (PEMFC) are critical to its performance and working life. This study presents a data-driven modeling approach combining a surrogate model with the particle swarm optimization algorithm to optimize operating parameters for PEMFC and obtain the maximum power density. The results show that the operating parameters significantly influence power density under high current densities, with inlet temperature having the most significant effect. Lower inlet temperature, relative humidity in the cathode and anode, along with higher operating pressure yield improved output performance. The Genetic Algorithm-Backpropagation Neural Network based surrogate model exhibits excellent predictive performance with correlation coefficients of 0.99896 and 0.99815 for the training and test sets, respectively. Optimized conditions achieve a 3.3% increase in power density compared to initial settings, with only a 0.15% error in simulation calculations. This data-driven approach provides valuable insights for maximizing PEMFC efficiency and performance. • An approach combining surrogate model with PSO algorithm to predict PEMFC performance is proposed. • The GA-BP-based surrogate model exhibits excellent predictive performance. • Maximum power density and corresponding operating parameters are achieved. [ABSTRACT FROM AUTHOR]

• The three-dimensional two-phase model for UR-PEMFC is established. • The accuracy of the model is validated through performance experiments. • The water–gas transport behavior of PEM-URFC during mode-switching is investigated. • Quantitative analysis of the FC mode startup dynamic response is conducted. • An optimized purging strategy benefiting FC startup and energy usage is proposed. The water–gas transport behavior of unitized regenerative proton exchange membrane fuel cell (UR-PEMFC) plays a key role in the rapid and stable mode-switching requirement. In this work, a UR-PEMFC is assembled and experimentally evaluated for its two modes performance. An experimentally validated three-dimensional two-phase model for UR-PEMFC is established, which considers transformed boundary conditions and multiphysics field governing equations, to investigate the water–gas two-phase transport behavior during mode-switching. The purge time, purge gas relative humidity (RH), and startup current density are used to quantify the dynamic response characteristics of the FC mode startup. The result shows that, compared with 0 % RH gas, after the 30 s purging, the average dissolved water content of catalyst-coated membrane (CCM) at 50 % RH and 100 % RH increased by 263.8 % and 365.9 %, respectively. Water saturation in the oxygen catalytic layer decreased by 4.14 % and 5.12 %, respectively. The FC startup exhibited the best response characteristics when purged for 28 s at 100 % RH and started with 0.1 A/cm2, the minimum voltage undershoot is 16 mV and the startup time is 37.8 s. Compared to the 0.2 A/cm2 and 0.3 A/cm2 startup, voltage undershoot decreased by 68.38 % and 134.9 %, and the startup time decreased by 8.21 % and 9.62 %, respectively. Moreover, with the purge gas RH between 52 % and 83 %, and the purge time between 16 s and 20 s, it is conducive to rapid and stable mode switching and efficient energy utilization. [ABSTRACT FROM AUTHOR]

Flow channel optimization is an important method to improve the water-gas transport capacity and enhance the performance of proton exchange membrane fuel cells. In this study, the size ratio of the opposite sinusoidal wave flow channel (OSWFC) is optimized, and three-dimensional numerical models are developed to evaluate the comprehensive performance. The results show that OSWFCs obtain performance enhancement compared to the parallel flow channel. 1:1 wave channel has a maximum improvement of 19.53% in mass transfer capacity by the most frequent flow disturbance, while 1:3 has a maximum increasement of 37.5% in water removal performance by the virtue of gentle wave structure. Large pressure loss decreases the mass transfer efficiency, although it with the maximum mass transfer capacity, the mass transfer evaluation criterion of 1:1 wave channel is less than that of 1:3. Moreover, a significant correlation between water-gas transport capacity and electrochemical performance is demonstrated by Pearson correlation coefficient. [Display omitted] • The OSWFC has a significant performance enhancement at high current densities. • The wave flow channel with ratio of 1:1 has the best mass transfer capacity. • The wave flow channel with ratio of 1:3 has the best water removal performance. • MTEC is proposed to evaluate the mass transfer efficiency. • PCC is proposed to evaluate the comprehensive performance of PEMFC. [ABSTRACT FROM AUTHOR]

The performance improvement and mitigate degradation of hydrogen-oxygen proton exchange membrane fuel cells (PEMFCs) are of great significance for accelerating the practical application of clean energy and alleviating the energy crisis. In this work, a PEMFC with an active area of 25 cm2 was designed based on multilayer printed circuit board technology for high-resolution current density mapping. The characteristics of uneven distribution of local current density under dynamic loading and its influence on performance degradation are further analyzed. The results show that the uneven density distribution at low current density is caused by membrane dehydration and gas starvation, while at high current density, it is caused by the combined effect of gas starvation, and the uneven current density distribution is even worse at high current density. In addition, oxygen starvation causes more worse uneven density distribution than that of hydrogen starvation, and the lowest current density is concentrated near the cathode outlet. What's more, the uneven distribution of local current density led to serious performance degradation, the performance degradation reached 40.03%, the electrochemical active surface area decreased by 31.87% and charge transfer resistance increased by 22.08%. The scanning electron microscope and energy dispersive X-ray spectrometry show that performance degradation is due to the loss of catalysts, especially near the cathode outlet. [ABSTRACT FROM AUTHOR]

The instantaneous voltage overshoot caused by current loading is one of the important factors for the performance degradation of hydrogen-oxygen proton exchange membrane fuel cells (PEMFCs). In this study, the dynamic response characteristic parameters, including first-stage delay (FTD), second-stage delay (STD), and voltage undershoot (VU), were studied quantitatively to analyze the voltage changes during current loading. The effects of loading range and operating parameters including temperature, stoichiometric ratio, and relative humidity on dynamic response characteristics were experimentally analyzed. The results show that the FTD and the STD were shortened by a smaller loading amplitude. The FTD under the loading range of 200 mA/cm2-600 mA/cm2 was 0.5 s shorter than that under 200 mA/cm2-1000 mA/cm2, and the STD was shortened by 7.5 s. The STD was reduced by 30.9% with the operating temperature increased from 55 °C to 75 °C. What's more, the FTD and VU reached minimum values with the relative humidity of the anode and cathode controlled at 50% and 70%, respectively. In addition, it was found that after the current loading experiment, the performance decreased by 2.5%, the charge transduction resistance increased by 8.94%, and the electrochemical active surface area decreased by 11.68%. The findings reported are expected to provide guidance for optimizing the working conditions of hydrogen-oxygen PEMFC, to reduce the performance degradation caused by current loading and thus improve its working life. • Dynamic response characteristic parameters during loading were studied quantitatively. • Gas transportation characteristics during loading was analyzed combining with real-time ohmic resistance variation. • Guidance of optimizing the working conditions for reducing the performance degradation was proposed [ABSTRACT FROM AUTHOR]

• Voltage response of hydrogen and oxygen starvation is fitted by polynomials. • The PEMFC is poorer tolerant to hydrogen starvation than to oxygen starvation. • Properly raising temperature effectively alleviate the damage by gas starvation. Hydrogen and oxygen starvation during operation have an irreversible impact on performance of proton exchange membrane fuel cell (PEMFC), which seriously restricts its working life. In this study, the voltage response characteristics of hydrogen–oxygen PEMFC under different degrees of hydrogen and oxygen starvation were experimentally studied, and the gas starvation tolerance was further analyzed through polynomial fitting. The results show that the response of voltage changes from stable to gradual decay with time under a certain degree of gas starvation. In the case of hydrogen starvation, the response voltage decreases in a parabolic trend, which indicates that PEMFC have poor tolerance to hydrogen starvation. While the response voltage basically shows a linear downward trend in oxygen starvation condition, and it lags behind the change of oxygen concentration. In addition, compared with oxygen starvation, hydrogen starvation causes more serious damage. It was found that after hydrogen starvation experiment, the performance was deceased by 39.36%, the electrochemical active surface area decreased by 18.37%, and the charge transduction resistance increased by 47.24%. It is also found that increasing the working temperature effectively alleviate this degradation phenomenon, which is expected to be an effective mitigation strategy for the damage by gas starvation. [ABSTRACT FROM AUTHOR]

Hydrogen-oxygen proton exchange membrane fuel cell with good application prospect in the special occasions of space exploration and underwater navigation, its durability is still a key problem to be solved. In this research, current cyclic loading durability experiment of a hydrogen-oxygen proton exchange membrane fuel cell with an active area of 50 cm2 was carried out. The performance degradation was characterized by polarization curves, Cyclic Voltammetry and Electrochemical Impedance Spectroscopy. Finally, the decay of catalyst and membrane was evaluated by Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy and Transmission Electron Microscope. After 2500 loading cycles, it with a total performance degradation of 31.05% at 1200 mA cm−2. The electrochemical active surface Area decreased by 61.6% and electrochemical Impedance increased by 33.04%. What' more, the catalyst layer in outlet area had been partially damaged, and its Pt particles have agglomerated and grown. More seriously, Pt particles had migrated and lost. The decay phenomenon was also found in the proton exchange membrane, in which element F, S and C were partially lost, especially element F. The findings reported here are expected to provide more insights into the effect of current loading on the decay of membrane electrode assembly. ∙ Gas starvation accompanied by cyclic loading leaded to MEA damage. ∙ Pt particles at PEMFC outlet have obviously agglomerated, grown and lost. ∙ PEM structure is damaged and elements F, C, S were lost seriously. [ABSTRACT FROM AUTHOR]

• Cathode flow fields of PEMFCs with great water–gas transfer capacity are optimized. • PEMFC obtains 9.30% performance enhancement with the optimal cathode flow field. • Visualization experiment verify water removal advantage and performance benefits. • PCC is firstly proposed to evaluate the correlation of PEMFC performance indexes. Flow field design plays a key role in enhancing the performance of proton exchange membrane fuel cell (PEMFC). In this work, the cathode flow field is optimized to enhance the performance of PEMFC by improving the capacity of mass transfer and water removal, and a three-dimensional, two-phase, isothermal numerical model is established to evaluate its performance. Additionally, visualization experiment is carried out to verify the simulation results. It shows that the opposite sinusoidal wave flow fields (OSWFFs) with single-inlet, dual-inlet and the block provide 6.86%, 1.26%, and 2.31% performance enhancement, respectively, compared with the parallel flow fields (PFFs), which positively affects the mass transfer capacity and water removal performance. Among them, the dual-inlet OSWFF with block is the most helpful for performance enhancement, with an enhancement of 9.30% at 2.2 A cm−2 compared to the PFF. Moreover, Pearson correlation coefficient (PCC) is proposed for the first time to evaluate the correlation between each index and PEMFC performance. The comparison of stoichiometric ratios shows that the more significantly correlated indexes contribute to the dual-inlet OSWFF outperforming the single-inlet OSWFF at high inlet velocities, verifying the applicability of PCC in PEMFC. [ABSTRACT FROM AUTHOR]