| Proton exchange membrane fuel cell（PEMFC）as an important technology that can achieve the efficient use of hydrogen,has attracted the attention of overall the world.Due to its high power density,environmental friendliness,fast response,low operating temperature,low noise,strong endurance and other outstanding advantages,the PEMFC has broad application prospects in the underwater application.In order to simplify the system and improve the utilization rate of reactants,the PEMFC applied in the underwater environment usually uses pure hydrogen and pure oxygen as reactants,and works in the dead-ended mode of both the anode and cathode.In this case,the water management inside the PEMFC becomes very complicated,and the phenomenon of hydrogen and oxygen permation across the membrane also becomes very severe.Therefore,selecting the working conditions and cell design parameters that can effectively alleviate the gas permation phenomenon and facilitate the cell performance in the dead-ended mode,and meanwhile the reasonable liquid water purging strategy in the dead-ended mode is also of great significance for maintaining the good operation of H2/O2 PEMFC.However,the revelant work still lacks in the existing literature,and the numerical work and simulation is an effective way.Therefore,this paper developes a well-established PEMFC model and carried out a series of simulation work on the above problems.The main research contents of this paper include:（1）Based on reasonable assumptions,a quasi-two-dimensional transient model of the PEMFC is developed,which considers the complex phase transition of water,gas permation across the membrane and other physical processes.The experimental data were used to conduct a comprehensive comparative verification to ensure the effectiveness of the model.（2）Under different temperature and humidity conditions,the performance and voltage losses of H2/O2 PEMFC and H2/Air PEMFC are compared,and it is found that compared with the H2/Air PEMFC,the performance of H2/O2 PEMFC under different operating conditions is generally higher,and the activation,ohmic and concentration losses are generally smaller,of which the concentration loss gap is the main factor leading to the performance gap between the two PEMFCs.（3）Under the different operating conditions and membrane parameters,the effect of hydrogen and oxygen permeation across the membrane on the working characteristics of the H2/O2 PEMFC is comprehensively studied,which confirms that the effect of gas permeation across the membrane is indeed more obvious in the smaller current density range.It is alsofound that under the conditions of the low temperature,low humidity,large inlet flow and low pressure,the larger thickness of membrane can achieve more effective mitigation of hydrogen and oxygen crossover.（4）The effects of the physical parameters of the gas diffusion layer（GDL）and operating conditions on the performance of the H2/O2 PEMFC with dead-ended anode and dead-ended cathode（DEA&DEC）and the internal liquid water transport have been investigated,and it was found that under low humidity conditions,due to the self-humidification effect,the voltage was first increased at the beginning of operation,and then gradually decreased due to the intensification of liquid water accumulation inside the cell,of which the flooding degree of cathode GDL（CGDL）was the most serious.For the cell to maintain high performance and long-term operation,the use of GDL with a larger porosity,a smaller intrinsic permeability and a larger contact angle is advantageous,of which the porosity has the greatest impact;however,increasing the relative humidity,increasing the operating temperature,reducing the the inlet pressure difference between cathode and anode,increasing the operating current density is unfavorable.（5）A voltage-based liquid water purging method has been proposed,and the effects of voltage drop rate,purge duration and cathode scavenging velocity on the purge strategy are studied;Based on this method,combined with the effects of different flow configurations and open valve operations,four purging schemes are designed and comprehensively compared and optimized.It was found that there is a peak value of cell voltage during the purging period,and the optimal purge duration is defined as the purge stops when the voltage reaches the maximum value during the purging period.The results show that the optimal purge duration decreases with the increase of cathode scavenging velocity and increases with the increase of voltage drop rate.The energy efficiency under the optimal purge duration is not necessarily the highest,but gradually approaches the highest energy efficiency with the increase of cathode scavenging velocity.Besides,compared with the counter-flow configuration,the co-flow configuration has a larger ohmic resistance,faster voltage decay rate during dead-end mode operation,and the average purge interval is shorter.Compared with the purging anode and cathode operation,the peak value of each purge cycle of the purging cathode operation decreases gradually,while the average energy efficiency is higher.The excessive accumulation of liquid water leads to a more poor uniformity of the local current density distribution（LCDD）along the channel（CH）,and the characteristics of cell temperature distribution are consistent with that of LCDD.During short-term operation,due to the highest energy efficiency of about 52.3%,the lowest fuel loss rate of 0,the second-highest output performance,the smallest ohmic impedance and the second-longest average purge interval,among the four purging schemes,the purge strategy corresponding to the scheme of purging cathode operation with counter-flow configuration is the best. |
PDF Full Text Request