摘要
燃料电池作为一种清洁、高效的能量转换装置,其大规模应用受到阴极氧还原反应(ORR)动力学缓慢以及铂资源稀缺和价格高昂等的极大制约.尽管研究人员在过去几十年中付出了巨大努力,但研制高效、耐用的低Pt合金催化剂仍亟待突破.近年的研究表明,Pt的一些高指数晶面能够表现出比Pt(111)晶面更高的ORR活性,尤其是Pt(332),Pt(331)和Pt(554)等.同时,合金化能够通过电子与几何效应减弱含氧物种在Pt表面的吸附能,提升Pt合金催化剂的ORR活性.因此,高指数晶面和合金化的结合将是设计开发高性能电催化剂的有效手段.本文提出一种气氛调控的液相合成方法,通过在油胺中加热还原Pt化合物和Cu化合物,不添加其它保护剂,仅通过反应气氛的调控,成功制备了不同形貌的Pt-Cu合金纳米结构(纳米多脚、纳米凹立方体、纳米枝晶).通过反应前期引入氧化性气氛随后切换为惰性气氛的调控策略,合成具有高指数晶面的具有纳米枝晶结构的PtCu3合金;进一步对其进行电化学去合金化形成富Pt壳层,既保持其纳米枝晶形貌和高指数晶面,又形成具有梯度组成的PtCu_(3)@Pt_(3)Cu@Pt纳米枝晶.相比而言,全程惰性气氛下生长得到纳米多脚结构,全程氧化性气氛下生长则得到纳米凹立方体.电化学测试结果表明,在0.1 M HClO4电解液中,PtCu_(3)@Pt_(3)Cu@Pt纳米枝晶展现出较高的ORR活性,在0.9 V(vs.RHE)处的Pt质量活性和面积活性高达1.55 A mgPt^(-1)和2.4 mA cmPt^(-2),分别为商业Pt/C催化剂的14倍和24倍;此外,PtCu_(3)@Pt_(3)Cu@Pt纳米枝晶具有良好的电化学稳定性能,经0.7~1.1 V(vs.RHE)电势范围内循环5000圈,其催化活性保持稳定.DFT计算表明,Cu合金效应和高指数晶面结构共同增强了Pt的ORR活性,其中PtCu_(3)@Pt_(3)Cu@Pt纳米枝晶高指数晶面台阶位点的氧结合能接近最优值,从而表现出火山顶点附近的ORR活性.
Alloying and nanostructuring are two strategies used to facilitate the efficient electrocatalysis of the oxygen reduction reaction(ORR)by Pt,where the high index surfaces(HISs)of Pt exhibit superior activity for ORR.Here,we report the fabrication of PtCu3 nanodendrites possessing rich spiny branches exposing n(111)×(110)HISs.The dendrites were formed through an etching‐modulated seeding and growing strategy.Specifically,an oxidative atmosphere was initially applied to form the concaved nanocubes of the Pt‐Cu seeds,which was then switched to an inert atmosphere to promote an explosive growth of dendrites.Separately,the oxidative or inert atmosphere failed to produce this hyperbranched structure.Electrochemical dealloying of the PtCu3 nanodendrites produced Pt3Cu shells with Pt‐rich surfaces where HIS‐exposed dendrite structures were maintained.The resulting PtCu_(3)@Pt_(3)Cu@Pt nanodendrites in 0.1 M HClO4 exhibited excellent mass and area specific activities for ORR,which were 14 and 24 times higher than that of commercial Pt/C,respectively.DFT calculations revealed that Cu alloying and HISs both contributed to the significantly enhanced activity of Pt,and that the oxygen binding energy on the step sites of HISs on the PtCu_(3)@Pt_(3)Cu@Pt nanodendrites approached the optimal value to achieve a near peak‐top ORR activity.
作者
廖宇翔
李俊
张世明
陈胜利
Yuxiang Liao;Jun Li;Shiming Zhang;Shengli Chen(College of Chemistry and Molecular Sciences,Wuhan University,Hubei Key Laboratory of Electrochemical Power Sources,Wuhan 430072,Hubei,China;Institute for Sustainable Energy,College of Sciences,Shanghai University,Shanghai 200444,China)
基金
国家自然科学基金(21832004,21633008)
上海市青年科技启明星计划(18QB1404400).
