Investigation On Non-precious Metal Catalysts Based Membrane Electrolyte Assemblys For Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells（PEMFCs）which can directly convert chemical energy of hydrogen into electrical energy has attracted great attentions due to its high efficiency and zero emission.Nowadays,the performance of the PEMFC depends on the platinum group metal catalysts to catalyze the sluggish oxygen reduction reaction（ORR）in the cathode.However,the expensive cost of platinum hinders the commercial application of the PEMFC.Thus,developing the membrane electrolyte assembly（MEA）based on non-precious metal catalysts（NPMCs）instead of commercial Pt/C catalysts is of great significance.In this work,a home-made Fe-N-C catalyst was incorporated into the MEA with an initial peak power density of 1.0 W cm^-2 after optimization.A quantitative investigation on the properties including activities,electric resistance and oxygen transport resistance of the MEA with a catalyst loading gradient has been carried out by electrochemical measurements.The results show that the ORR activities and catalyst layer proton conduction resistance increase linearly with the catalyst loading increasing.However,the oxygen transport resistance first gets down and then rises up with the catalyst loading increasing.Further physical characterization implies that the small active surface area and the poor pore size distribution result in high oxygen local transport resistance.Meanwhile,the MEA suffered a rapid performance loss of 52%after a20-h degradation test.The experiment results and theoretical calculation reveal that the leaching of Fe ions in the active sites is the main cause of the activity loss.The proton exchange membrane and the ionomer in the catalyst layer are further contaminated by the leaching Fe ions,which results in an enlarged performance loss.At last,a dry out experiment carried out in this work indicate that the possible water flooding had little effect on degradation.Overall,the above study findings are of great significance for the development and application for the NPMCs based MEA.