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质子交换膜燃料电池(PEMFC)因能量转化率高、电流密度大、对负荷响应快及环境友好等优点而应用前景广阔.然而,Pt基催化剂的大量使用使得PEMFC成本居高不下,阻碍了其商业化进程.金属Ir具有良好的稳定性和相比Pt较低的成本,可替代金属Pt催化燃料电池阳极氢氧化反应.但是,Ir基催化剂的催化活性比Pt低,难以满足商业化要求.通过合金调控Ir纳米晶的电子结构和几何结构是降低Ir用量、提高Ir催化剂氢氧化活性的有效方法.本文研究了Ir基合金纳米晶中合金元素(Fe,Ni,Co)所产生的合金效应在酸碱性介质中对催化氢氧化的影响.采用溶剂蒸发-氢气还原法合成了具有相近合金度且平均粒径小于5 nm的Ir Fe,Ir Ni和Ir Co纳米合金催化剂.电化学测试表明,Ir Ni合金催化剂具有最高的催化氢氧化活性.在酸性介质中,Ir Ni合金催化剂的质量比活性达到152 A/gIr(@0.1 V vsRHE),高于Ir Fe(146 A/gIr)和Ir Co(133 A/gIr)合金催化剂以及商业化Pt/C催化剂(116 A/gPt).而在碱性介质中,Ir基合金催化剂活性较酸性介质中低,各合金催化剂优劣次序与酸性介质中一致.结构分析表明,合金化致使Ir晶格收缩,收缩程度以Ir Fe,Ir Ni和IrCo的顺序依次降低.Ir Ni合金催化剂中Ni合金元素诱导Ir发生晶格收缩适中,使催化剂与中间物种(H_(ad),OH_(ad))的相互作用适度,从而获得最优的催化性质.另外,合金效应在不同pH介质中影响不一:在酸性介质中,由合金元素(Fe,Ni,Co)导致的Ir–H_(ad)相互作用弱化是提高氢氧化活性的主要原因;在碱性介质中,催化剂表面的亲氧效应决定了电极表面的OH_(ad)吸/脱附性质和H_(ad)表面覆盖度,从而影响催化氢氧化活性.
Due to the advantages of high energy conversion rate, high current density, fast response to load and environmental friendliness, proton exchange membrane fuel cells (PEMFCs) have a wide application prospect.However, the large use of Pt-based catalysts makes PEMFCs cost prohibitive Commercialization.Metal Ir has good stability and low cost compared with Pt, which can replace the anode hydrogenation reaction of Pt catalytic fuel cell.However, the catalytic activity of Ir-based catalyst is lower than that of Pt, which is difficult to meet the commercial requirements. The electronic structure and geometrical structure of Ir nanocrystals are controlled by the alloy, which is an effective way to reduce the amount of Ir and improve the activity of Ir catalysts. In this paper, the effect of alloying elements (Fe, Ni, Co) The effect of hydrogenation on the catalytic hydrogenation in acidic medium was studied.The Ir Fe, Ir Ni and Ir Co nano-alloy catalysts with similar alloy degree and average particle diameter less than 5 nm were synthesized by solvent evaporation-hydrogen reduction method.The results of electrochemical tests , Ir Ni alloy catalyst has the highest catalytic hydrogenation activity.In the acidic medium, the Ir Ni alloy catalyst has a specific activity of 152 A / gIr (@ 0.1 V vsRHE), higher than that of Ir Fe (146 A / g-Ir) and Ir-Co (133 A / g-Ir) alloy catalysts and commercial Pt / C catalysts (116 A / g Pt) .In alkaline medium, the activity of Ir-based alloys was lower than that in acidic medium. The order is the same as that in acidic medium.The structural analysis shows that the alloying causes the Ir lattice to shrink and the degree of shrinkage decreases in order of Ir Fe, Ir Ni and IrCo.The Ni alloy elements in the Ni-Ni alloy catalyst induce moderate lattice shrinkage, (H_ (ad), OH_ (ad)) moderately to obtain the best catalytic properties.In addition, the effect of the alloy in different pH media have different effects: in acidic medium, the alloying elements The weakening of the Ir-H_ (ad) interaction caused by Fe, Ni, Co is the main reason to increase the hydrogenation activity. In alkaline medium, the oxygen affinity of the catalyst surface determines the OH_ (ad) Desorption properties and H_ (ad) surface coverage, thus affecting the catalytic hydrogenation activity.