| Proton exchange membrane fuel cell(PEMFC)is a clean and efficient new energy representative.It is considered to be the most promising source of automobile power supply.Oxygen reduction reaction(ORR)plays a key role in PEMFC.It is worth noting that the ORR speed in the cathode is several orders of magnitude slower than hydrogen oxidation reaction(HOR)in the anode,in PEMFC.Because of the slow reaction speed of ORR,a large number of noble metal platinum(Pt)is needed by the catalytic process of ORR.Excessive dependence on platinum is the main bottleneck of fuel cell application.The high cost of manufacturing greatly hinders the commercial application.Therefore,the research and development of non-platinun ORR catalytic materials with high activity and low cost is of great significance to promote the application of PEMFCIn this paper,the synthesis and modification of melamine resin,the preparation of non-platinum metal ORR catalytic materials and the performance test of fuel cell were optimized.The purpose is to improve the catalytic activity and stability of melamine composite resin based fiiel cell non noble metal catalytic material.The main contents of this paper are as follows(1)The mixing method of melamine formaldehyde resin and carbon black was improved.The soluble trimethylokmelanmne resin formed by melamine and formaldehyde was used before curing.It was fully mixed with carbon black after surface modification,and melamine formaldehyde resin composite was prepared as catalyst precursor.Next,we prepared the catalyst by one-step pyrolysis.The effects of the dispersion of several precursors,iron content,carbon content,pyrolysis temperature and time on the oxygen reduction performance of the catalyst were studied by comparison.In the synthesis process of MF resin supported by porous carbon black,we creatively used surfactant(Tween 80),which improved the ORR activity of the catalyst.The results show that the catalyst has remarkable ORR activity in both acid and alkaline electrolyte.The initial potential of oxygen reduction was 0.86 V(RHE)and half wave potential was 0.77 V(RHE)at 0.1M HC104 and 900 rpm at 25?.It is a promising ORR catalytic material for fuel cells.(2)The Schiff base polymer was synthesized by using melamine and terephthalaldehyde.We use the previous MF resin based non noble metal catalyst preparation process for reference.Fe/N-C non noble metal oxygen reduction catalyst was prepared by two-step pyrolysis.Compared with the catalyst based on MF resin,the redox activity of RDE is much higher than that of the catalyst based on MF resin.The initial reduction potential of 0.1 M HC104 at 25? and 900 rpm was 1.02 V(RHE)and half wave potential was 0.83 V(RHE).This is one of the most active non noble metal catalyst materials reported in the literature.In addition,the main raw materials of precursors,melamine and p-benzaldehyde,were also discussed.Their influences on the ORR activity were discussed in the aspects of the mixing way in the early stage of high temperature polymerization and the heat treatment temperature.Based on the Fe/N-C catalyst,the cathode of hydrogen fuel cell was prepared.The highest power density of single cell is 790 mW/cm2.(3)The influence of the ink formulation of the catalyst on the performance of Fe/N-C non-precious metal oxygen reduction catalyst for the preparation of oxygen reduction electrode was investigated.A set of L9(34)orthogonal experiments were designed to study the synergistic effect of Nafion content,catalyst loading,water content and vitamin E content on the catalytic performance and stability of catalyst for oxygen reduction.And try to find out the best combination level of these four factors.It is inferred that the formulation of catalyst slurry with 20 wt%Nafion,1.14 mg/cm2 catalyst,30 wt%water and 5 w%vitamin E has both ORR catalytic activity and electrochemical stability.(4)The catalyst layer was prepared by Fe/N-C non-noble metal catalyst,and the appropriate amouunt of vitamin E was added,and the performance of fuel cell was verified.Vitamin E remains in the catalyst and Nafion resin porous catalytic layer.Even if there is phase separation between vitamin E and Nafion resin,it will not cause any problems of membrane mechanical stability and local hydrogen permeation.It can also quickly capture superoxide radicals and hydrogen peroxide near the three-phase interface,and then protect the catalyst and proton exchange membrane to the greatest extent.The results show that vitamin E additive reduced the maximum power density of MEA,but it also significantly improved the stability of this kind of Fe/N-C catalyst fuel cell. |
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