| Proton exchange membrane fuel cell(PEMFC)is the future energy device for automobile applications.The all-embracing of PEMFC depends on its reliability and durability.Cold start-up from a very low temperature still a considerable challenge,the product water by electrochemical reaction freezes within the membrane electrode assembly(MEA)and hindered the supply of reactant to the catalyst layer(CL)which leads to start-up failure.The cold start-up failure results in an irreversible decrease in the PEMFC overall performance.A quick,stable and reliable PEMFC cold start strategy is crucial to avoid permanent degradation of the MEA.The optimum fuel cell design such as increasing water capacity,draining by purging and external heating to assist the fuel cell during cold start operation.With the flexibility and simplicity of the control,the electrical external heating based cold starter has several advantages:additional control options,uncomplicated add-on devices,and higher heating efficiency.The direct heating cathode side of the membrane electrode assemblies and bipolar plates is more effective while focusing on the inlet region,the middle region,and the outlet region,which is where most of the total current flow is generated before the peak current density is attained,which is critical for the quick successful cold start.In this research,an experimental setup with a three serpentine flow field PEMFC is designed,to achieve a successful cold start by electrical external heating using Nickel-chromium heating wire embedded on the cathode flow field flow rib to directly heat the gas diffusion layer(GDL)from five different locations on the fuel cell-active reaction areas.A D.C power supply is used to directly power the heating wires,the five heating location are considered the most crucial location during the cold start operation which includes,the inlet region,middle region,and outlet region.To obtain accurate temperature measurements,thermocouples are used to determine the real temperature distributions of the heating wire and the cathode bipolar plate.Furthermore,the voltage changes and internal ohmic resistance are analyzed during the sub-zero temperature test.This research also highlights the effect of set conditions on the design of three serpentine flow channel with counterflow arrangement during fuel cell activation,normal temperature operation and purging before cold start operation.The data indicate that better performance of a new membrane required activation at a set condition temperature of 70 ~oC,anode relative humidity of 100%,cathode relative humidity of70%,the clamping torque force of 2 Nm and purging during 30 minutes is sufficient for the design fuel cell.All independent testing is undertaken to identify and optimize the primary components design and operational set parameters for both normal temperature operation and cold start operation.It has been discovered that the most critical region during cold start set operation is the middle region which have the highest survivability rate and less heat loss according to single location external heating,followed by the inlet region due to high concentration of supply reactant,and the least is the outlet region which only serves as a passage of unused excess reactant and produced water at initial cold start operation before the membrane assembly is fully hydrated.It has also been observed that the heating of inlet and middle areas,were adequate for performing a quick cold start operation.However,the heating of all the electrochemical reaction regions yields the quickest and uniformity of reaction with possible avoidance of hot spot on the proton exchange membrane and degradation of MEA in general.The result indicates that a heating power density of 0.204 W/cm~2 is adequate to successful cold start the PEMFC at-10 ~oC.Further,it has been found that the failure of cold start can be trigger by the uneven temperature distribution inside the PEMFC membrane electrode assemble and when a reasonable portion of the electrochemical reaction area is covered with ice,especially the downstream region which affect the smooth drainage of produced water.Following an unsuccessful cold start,the PEMFC was visibly degraded.On the other hand,after a successful cold start,the degradation is relatively small.The polarization curve of the PEMFC before and after a cold start operation compared to observe the degradation of the fuel cell.The successful cold start shows a little degradation in the overall performance while the failed cold starts reach up to 18.75%of degradation in the overall performance.Finally,the research work contributes to the quick and effective cold start strategy using external electric heating wire concentrating on the most crucial regions during cold startup.This will assist in developing an optimum design and approach,which allows for further increasing the reliability and durability of the PEMFC cold start. |
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