Synthesis And Performance Of Fe-based Oxygen Electrode Catalysts

At present,the development of efficient and low-cost catalysts for oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?has become the key to the commercialization of the renewable energy devices,such as fuel cells and metal-air batteries.In particular,the in-depth understanding of the three-phase?gas-liquid-solid?interface and related kinetics in the ORR/OER reaction for the catalysts is not comprehensive enough,which further increases the difficulty of rational design of high efficient ORR/OER catalysts,so it is necessary to carry out relevant research in these aspects.In this paper,we devoted to the studies of Fe-based oxygen electrode catalysts by combining modern spectroscopic microscopy and electrochemical methods.These studies were derived from the design of the catalysts and their ORR/OER performance in different electrolyte.The specific work is as follows:?1?The FeNi@NCNT catalyst was prepared via a facile one-pot pyrolysis method using ammonium ferric citrate,nickel?II?chloride hexahydrate and dicyandiamide as precursors.Physical characterizations results revealed that the FeNi@NCNT showed a bamboo-like carbon nanotubes structure?CNT?,the FeNi nanoparticles and Fe3O4 were coated with carbon layer and located in or at the top of the N-doped CNT,which was helpful to promote the catalysts ORR and OER performance.The electrochemical results indicated that the obtained FeNi@NCNT catalyst showed a good ORR and OER activity??E=0.85 V?.Moreover,its ORR and OER curves were almost no change after 8000 and 2000 continuous cycles scanning tests,respectively,indicating that the super ORR and OER stability for FeNi@NCNT catalyst.Such excellent ORR and OER activity mainly results from the formation of FeNi nanoparticles,and the superior stability can be attributed to N-doped graphitic carbon layers.?2?The model FePc/CNT catalyst was prepared by a simple ball-milling method,and then systematically studied its ORR performance in 0.1 M KOH+c EDTA?2Na?c=0⁰.20M?.Physical characterizations revealed that the exist of FePc on CNT.The morphology,lattice and N 1s peak of FePc/CNT were not changed after measured in 0.1 M KOH+0.05 M EDTA?2Na electrolyte,while the Fe 2p peak was affected by the use of Nafion?including F?during the preparation of the working electrode.Electrochemistry measurements demonstrated that the ORR onset potential?Eo?of FePc/CNT was decreased linearly with the increasing concentration of EDTA?2Na?c=0⁰.20 M?in 0.1 M KOH,while its super durability and methanol tolerance were not affected by EDTA?2Na.Through comparing the ORR performance of FePc/CNT catalyst in Britton-Robinson buffer solution which had the similar pH values with 0.1 M KOH+c EDTA?2Na?c=0⁰.20 M?,we could speculate that the different ORR activity of FePc/CNT in 0.1 M KOH+c EDTA?2Na?c=0⁰.20 M?was mainly caused by the change of the electrolyte's pH value and the complexation between EDTA?2Na and Fe-N_x could be neglected.?3?A series of non-noble metal M-N_x/C materials?FePc/KB,CoPc/KB,Fe-N/C and Co-N/C?were prepared by non-pyrolysis and pyrolysis of metal phthalocyanine?MPc,M=Fe,Co?and Ketjenblack?KB?.Then we devoted to investigated the ORR performance of these catalysts in 0.1 M KOH with the addition of KCl,KBr and KSCN by the electrochemical tests.The electrochemical results showed that the ORR activity of these catalysts were increased due to the binding ability of K⁺to H₂O.However,the ORR activity of these catalysts will no longer increase when the concentration of K⁺incredsed to 0.4 M.The decrease of these catalysts'ORR activity were due to the poisoning effect of anions?Cl^-,Br^-,SCN^-?and the poisoning effect of Cl^-and Br^-to Fe-and Co-based non-noble metal oxygen reduction catalysts were less than that of SCN^-.