Investigation Of Self-humidifying Membrane Electrode Assembly With Fe-N-S-C Catalyst For Proton Exchange Membrane Fuel Cells

Fuel cell is a kind of energy conversion device which is clean and efficient.Proton exchange membrane fuel cells?PEMFCs?have advantages such as high efficiency,low/zero emission,and fast start up,thus receiving more and more attention.Membrane electrode assembly?MEA?is the key component of a PEMFC,which is not only important for the fuel cell performance,but also significant for reducing the cost and accelerating its commercialization.The membrane and ionomer in the catalyst layer are all composed of perfluoro sulfonic acid.They need to stay hydrated to maintain high proton conductivity.In low humidity or dry conditions,the conductivity of the membrane and ionomer decreases significantly while the fuel cell performance declines consequently.To humidify the membrane,external humidification methods are normally adopted.However,external humidification methods increase the cost,weight and volume of the fuel cell system which is undesirable especially for automobile applications.Therefore,self-humidification MEAs are attractive to solve this problem.MEAs are made using Pt-C catalyst in the anode and Fe-N-S-C catalyst in the cathode.The effects of operating parameters on the fuel cell performance are investigated respectively.The results show that the optimum Fe-N-S-C loading is 2.0mg cm^-2,and the optimum ratio of ionomer and Fe-N-S-C catalyst is 3:7.Through measuring the polarization curves and electrochemical impedance at operating conditions with different relative humidity,the fuel cell shows good performance under low relative humidity.This indicates that the hydration level can be maintained at low humidity conditions.Self-humidifying MEA can be designed by adding Fe-N-S-C catalysts.Then,the dual cathode catalyst layer MEAs are made including a Pt-C catalyst layer and a Fe-N-S-C catalyst layer.The effects of the location and loading of the Fe-N-S-C catalyst layer,operating temperature and inlet gas relative humidity are evaluated.Moreover,the durability of the MEA at low humidity level is tested.The results show that the fuel cell performs better when the Fe-N-S-C catalyst layer lays between the Pt-C catalyst layer and the gas diffusion layer.The optimum Fe-N-S-C loading is 2.0 mg cm^-2,which displays excellent cell performance at 20%relative humidity and 70 ^oC.In addition,the MEA with cathode dual catalyst layer shows good durability under low humidity condition.