Study On Water/Gas Distribution During Load Variation And Carbon Corrosion In A PEM Fuel Cell

Proton exchange membrane fuel cell(PEMFC),as a highly efficient energy conversion device,can be used as a substitute for traditional vehicle power due to the advantage of zero emission.In the practical application of PEMFCs,water-gas management has been concerned by researchers.And the PEMFC needs a good dynamic response for complicated vehicle operational mode.Firstly,the thesis analyzed the effect of flow channel structure on the water/gas distribution in the cathode.The results showed that,oxygen distribution in the cathode was more uniform with the increasing of the width of outlet converging channel.The zone with highest water concentration was gradually moving towards the outlet of the fuel cell,which was beneficial to the water management of the cathode.The gas velocity was lower with the increasing of the width in the inlet distributing channel,and the poor uniformity of pressure drops in the channel also leaded to the non-uniformity of oxygen distribution in the flow field.Moreover,it was helpful to improve the oxygen concentration under the ridge and increase the uniformity of the oxygen distribution by using the oblique inlet distributing channel and the proper channel design.Secondly,time evolutions were studied under different load variations.The results showed that,the concentration of the reactant was increasing with the increasing of the operation pressure in PEMFC,which could reduce the voltage undershoot rate under load variation.The concentration of water in the anode decreased with the increasing of the hydrogen stoichiometry at 50% relative humidity(RH),resulting in the dehydration of membrane and the tiny decrease of the voltage in a short time.However,there was slight variation in the stable and transient performance by increasing the stoichiometry of the cathode gas.Whereas,increasing the loading amplitude and decreasing the loading time has a notable great effect on the PEMFC performance.Oxygen concentration was the main affecting factor on the performance.It had less effect on the performance and hydrogen starvation did not occur when the hydrogen supply was not timely.Contrarily,the oxygen concentration dropped to zero under the rib when air was not supplied in time.The oxygen consumed more and faster at higher current density,and the concentration in the cathode could also drop to zero,resulting in the oxygen starvation.Finally,the carbon corrosion rate was deduced theoretically according to the reaction dynamic mechanism of carbon and water.The carbon corrosion rate was a function of the Gibbs free energy,humidity,operation pressure,temperature and current density.The increase in the operation temperature,current density and relative humidity would promote the carbon corrosion,while it could mitigate the carbon corrosion rate by the increase of operation pressure.