Comparative Study Of Various Flow Modes In A Proton Exchange Membrane Fuel Cell

Proton exchange membrane fuel cell(PEMFC)has attracted wide attention on the field of transportation due to its high efficiency,zero pollution,room-temperature operation and fast response.However,there are still some technical obstacles to be solved in the process of large-scale commercialization,such as further reducing costs,improving stability and increasing durability.As an important operating condition of fuel cell,the flow mode is closely related to the transport of reactant gases,the flow of water,the diffusion of heat and other factors,which directly affects the performance and internal distribution characteristics of the cell,and then affects the stability and durability.In this paper,based on an improved in-situ measurement method of temperature and humidity in a PEM fuel cell,co-flow and counter-flow were compared from three aspects: output performance,temperature and humidity distribution characteristics and dynamic response.And the optimal flow mode was proposed to different operating conditions.This will be helpful to improve the performance,stability and lifetime of PEMFC and promote the commercialization.In this paper,an improved in-situ measuring method of temperature and humidity in PEMFC has been developed.Compared with the existing methods at home and abroad,it was simple to operate and low in cost.It can also realize the insitu measurement of temperature and humidity in the cell without damaging the structure of the cell.The feasibility of the method was evaluated by the polarization curve,and the results showed that the insertion of the sensor would lead to a slight degradation of the cell performance,but that would not affect the subsequent study.An internal temperature and humidity in-situ measurement system of PEMFC has been designed and built to study the influence of different flow modes on the steady-state performance of a single cell.The results showed that increasing the inlet humidity could improve the output voltage of the cell,regardless of the flow mode.Under the same inlet humidity condition,when the cell worked at low(0.3 A cm-2)or medium(0.9 A cm-2)current density,the selection of counter-flow would make the cell get higher output voltage and more uniform temperature and humidity distributions.However,when the current density was high(1.2 A cm-2),especially when the inlet humidity was also high,the choice of co-flow could enable the cell to maintain high performance,smaller temperature difference and avoid the phenomenon of water flooding.The influence of flow modes on the dynamic response characteristics of temperature and humidity in a PEMFC during the step change of current density was also studied.The results showed that,when the inlet relative humidity was anode 50% and cathode 0%,the fluctuation of temperature and humidity was small and the humidity response was quick when the flow mode was counter-flow,so counter-flow was a better choice.When the inlet relative humidity exceeded 50%,the temperature responses of co-flow and counter-flow were similar,but the change of humidity was more than 10% when the flow mode was counter-flow,which was not conducive to the stability and durability of the cell,so co-flow was a better choice.