Synthesis And Electrocatalytic Performance For Oxygen Reduction Of Iron-nitrogen-carbon Film Electrocatalysts

Fuel cell is a kind of ideal energy technology, which has many advantages suchas high energy conversion efficiency, low environmental impact and fast response, etc.The oxygen reduction reaction (ORR) at the cathode in fuel cell plays an importantrole in determining the performance of the energy conversion devices. Traditionally,Pt-based materials have often been used as catalysts for ORR due to their highcatalytic activity, but high cost, limited supply of Pt become major barriers for thewidespread commercialization of fuel cell. Among various non-noble metal catalysts,Fe-N-C catalysts have been considered as promising alternative electrocatalysts forORR due to their high electrocatalytic activity, stability and methanol tolerance.In this work, Fe-N-C film catalysts for ORR can be obtained by using twomethods (sputtering-annealing and sputtering-impregnation-annealing), and the effectof Fe content and annealing temperature on the struction, morphology and catalyticactivity is studied. The structure for the Fe-N-C film catalysts is characterized byX-ray diffraction (XRD). The morphology for the Fe-N-C film catalysts ischaracterized by scanning electron microscope (SEM). The composition and chemicalbonding state of the Fe-N-C film catalysts are characterized by X-ray photoelectronspectroscopy (XPS). The electrocatalytic activity, stability and methanol tolerance ofthe Fe-N-C film catalysts for ORR are characterized by electrochemical workstation.The Fe-N-C film catalysts can be obtained by sputtering-annealing method. Withthe increase of the Fe content, the catalytic activity of the Fe-N-C film catalystsdescreases. By adjusting the annealing temperature (600-900°C), the chemicalbonding states of N can be tuned, the catalytic activity of the Fe-N-C film catalysts is optimized, and we find that the pyridinic N plays a key role in ORR. The Fe-N-C filmcatalyst with an Fe content of1.4at.%annealed at700°C shows the highest catalyticactivity, for which the onset potential is0.04V, the limiting current density is4.12mA cm2, the kinetic current density is15.56mA cm2and the electron transfernumber is3.42.The Fe-N-C film catalysts with trace Fe are prepared bysputtering-impregnation-annealing. Via adjusting the Fe content and annealingtemperature, the catalytic activity of the Fe-N-C film catalysts is optimized and thecatalytic active site is studied. We find that the Fe-N-C film catalyst with an Fecontent of0.3at.%annealed at800°C shows the highest catalytic activity, in whichFe atoms favorably form high active FeN4sites with pyridinic N. For the optimizedFe-N-C film catalyst, the onset potential is0.07V, the limiting current density is4.51mA cm2, the kinetic current density is18.56mA cm2and the electron transfernumber is3.86.Moreover, the stability and methanol tolerant for the Fe-N-C film catalystssynthesized by the two methods (sputtering-annealing andsputtering-impregnation-annealing) are much better than commercial Pt/C catalyst inan alkaline environment. Therefore, the Fe-N-C film catalyst is a cost-effectivenon-noble metal catalyst.