质子交换膜燃料电池(PEMFCs)将化学燃料转化为电能,具有能量转换效率高、清洁、零排放等特点,被认为是未来重要的能源利用装置.与阳极发生的氢氧化反应相比,阴极发生的氧还原反应(ORR)是动力学缓慢的过程,严重阻碍了燃料电池的广泛应用,因此迫切需要开发高活性的电催化剂来降低其电化学过电位,提高反应动力学.铂基纳米晶是氧还原反应有效的电催化剂,但存在成本高、储量少且耐用性差等问题.将铂(Pt)与过渡金属(Fe,Co,Ni等)合金化可以提升催化活性,且最外层有序的Pt原子层可以有效地避免过渡金属的腐蚀溶解,同时,利用金(Au)与Pt基合金形成核壳结构可以有效地降低催化剂成本,同时增强稳定性.然而,在以Au作为核时,很难通过退火处理获得富含Pt层的核壳催化剂.本文利用钛(Ti)原子与Au原子合金化后的协同作用,成功地制备了核壳AuTi@PtNi氧还原催化剂.由于Ti与Au的强相互作用,使得该催化剂即使经高温退火处理,依旧可以使Au保持在内部,同时可以获得富Pt壳层.利用配备有电子能量损失谱的透射电子显微镜及X射线电子能谱对催化剂进行表征,结果表明,Ti的引入可大大提升催化剂的热稳定性.由于具有核壳结构及富Pt的PtNi壳层,退火后的AuTi@PtNi-400催化剂在0.9 V(RHE)时的质量比活性(5.26 A mgPt-1)和面积比活性(2.72 mA cm-2)分别是商业化Pt/C催化剂的19.26倍和9.84倍.另外,AuTi@PtNi-400催化剂在20000圈循环测试后质量活性衰减不到10％,稳定性好于商业化Pt/C催化剂和未经过退火的AuTi@PtNi催化剂.进一步对AuTi@PtNi-400进行电催化测试,结果表明,在功率密度达到0.61 W cm-2的同时可产生1.31 A cm-2的电流密度,该结果优于商业化Pt(1.05A cm-2和0.34 W cm-2)以及Ti-Au@PtNi/C(1.25 A cm-2和0.62 W cm-2),峰值功率密度高达0.80 W cm-2,这表明所制备的Ti-Au@PtNi/C-400催化剂不仅在三电极体系中具有较好的性能,在电堆测试中也展现出高性能,可以较大地满足和促进燃料电池的发展和应用.综上所述,对于燃料电池阴极催化剂,可结合形貌工程及协调作用,制备出低成本高性能的ORR催化剂,为燃料电池的进一步应用提供新思路.
A novel core-shell nanostructure of Ti-Au nanocrystal with PtNi alloy skin:Enhancing the durability for oxygen reduction reaction
The sluggish oxygen reduction reaction(ORR)at the cathode largely hinders the practical applica-tion of the proton-exchange membrane fuel cells(PEMFCs).Pt-based nanocrystals are the most effective electrocatalysts for the oxygen reduction reaction,however,suffer high cost,scarcity and unsatisfied durability.Herein,we report a new category of annealed multimetallic core-shell cata-lyst of gold core doped with titanium and platinum-nickel(PtNi)shell with Pt-rich surface as a highly active and robust electrocatalyst for ORR.The introduction of titanium can effectively stabi-lize the gold core,avoiding the outward migration of Au atoms and ensuring the exposure of Pt-Ni active sites.The experimental findings revealed that the annealed Ti-Au@PtNi NPs catalyst provides 19.26 and 9.84 times higher mass and specific activities than commercial Pt/C catalysts for the oxygen reduction reaction.Moreover,durability tests of annealed Ti-Au@PtNi NPs show no notice-able activity loss even after 20000 potential cycles between 0.6 and 1.0 V vs.RHE,demonstrating a promising catalyst for the oxygen reduction reaction.
万方数据
维普
