质子交换膜燃料电池冷启动研究及策略优化现状

Strategy optimization of proton exchange membrane fuel cell cold start

质子交换膜燃料电池(proton exchange membrane fuel cell,PEMFC)汽车以其能量转换效率高、续航里程长、零排放等突出优势,在“双碳”目标的背景下引起了广泛的关注.然而,在低温环境下的冷启动问题成为限制其商业化和推广应用的一大障碍.因此,研究人员进行了大量的实验与仿真来研究燃料电池冷启动的衰减机理、水传输相变和传热机理以及启动策略优化.通过对冷启动电池的输出性能和微观结构进行测量与表征,发现由于冰的产生覆盖反应活性位点、堵塞气体通道、增大电接触阻抗导致性能下降,由于水冰相变的体积变化破坏了内部结构导致耐久性下降.通过对启动过程中水和冰的分布、传输与相变过程进行研究,发现反应产物水首先以膜态水使质子交换膜(proton exchange membrane,PEM)和催化层(catalyst layer,CL)的含水量达到饱和,接着以过冷水的形式在低温下保持液态,最后排出电池或突然结冰.通过研究冷启动的传热过程发现,电堆中间部分的电池单元和单电池的中间区域升温最快,为产热的主要区域,阴极氧还原反应(oxygen reduction reaction,ORR)产生的不可逆反应热为主要的产热来源.基于燃料电池冷启动机理,研究人员开发了多种自启动和辅助启动策略,并进行了大量的仿真和实验验证策略的优越性.本文旨在对燃料电池冷启动的研究和策略优化进行总结,并对未来的冷启动发展方向进行展望.

Under the background of“carbon peaking and carbon neutrality”goals,the proton exchange membrane fuel cell(PEMFC)vehicle attracts extensive attention due to its high energy conversion efficiency,long range and zero emission.However,the challenge of cold start in low temperature environments becomes a large obstacle to its commercialization and application.The current cold start performance of typical commercial fuel cell vehicles cannot reach the optimal target yet.Several problems such as the lack of complete mechanical systems of water transport and phase change and the absence of simulation models for on-board fuel cells at system level still exist.Thus,researchers have carried out a great number of experiments and simulations to study the mechanism of degradation,water transport,phase change and heat transfer as well as start-up strategy optimization of PEMFC cold start.By measuring the output performance,it is found that the degradation of performance is attributed to the formation of ice which covers the reaction active region,blocks the gas channel and increases the electrical contact resistance.Researchers also believe that the reduction of durability is owing to the volume change of water-ice phase change which leads to the damage of the structure by characterizing the microstructure of the fuel cell.With the help of transparent cells,neutron imaging and simulations of multiphase PEMFC models,the distribution,transport and phase change of water and ice during cold start have been studied.The results indicate that the electrochemical product water first saturates the PEM and the catalyst layer(CL)as membrane water.Then the water remains liquid in the form of supercooled water at low temperatures,and finally flows out of the cell or freezes suddenly.By studying the heat transfer process both in plane and through plane during cold start,researchers find that at central regions of the single cell and in the middle part of the stack,the temperature rises fastest.They also find that the irreversible reaction heat generated by cathodic oxygen reduction reaction(ORR)is the main source of heat generation.Based on the cold start mechanism of PEMFCs,researchers have developed various self-start and auxiliary start strategies.The start-up mode and control strategies have been optimized.The internal structure and materials of each part have been improved.And a series of auxiliary startup strategies such as gas purging,heater heating,reaction heating,gas heating as well as coolant heating have been proposed.A large number of simulations and experiments are carried out to verify the advantages of these strategies.Through these excellent cold start strategies,the commercialization and promotion process of PEMFC vehicles can be accelerated.