Sub-4 nm PtZn Intermetallic Nanoparticles for Enhanced Mass and Specific Activities in Catalytic Electrooxidation Reaction
Sub-4 nm PtZn Intermetallic Nanoparticles for Enhanced Mass and Specific Activities in Catalytic Electrooxidation Reaction
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DOI：
10.1021/jacs.6b12780
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发表时间：
2017-04-05
影响因子：
15
通讯作者：
Huang, Wenyu
中科院分区：
文献类型：
--
作者：
Qi, Zhiyuan;Xiao, Chaoxian;Huang, Wenyu
原子有序金属间化合物纳米颗粒(INPS)以其独特的电子和结构特性在燃料电池领域引起了人们的极大兴趣。然而，由于形成金属间化合物相通常需要较高的温度，以可控的方式合成小的INP仍然是一个巨大的挑战。在这里，我们报道了一种合成PtZn的一般方法。利用牺牲的介孔二氧化硅(mSiO(2))壳，通过一种简单且无封顶剂的策略，在多壁碳纳米管(MWNT)上制备了INPS(3.2+/-0.4 nm)。在酸性和碱性溶液中，制备的PtZn INPS对甲醇氧化反应(MOR)的质量活性是在无mSiO_2壳层的MWNT上合成的较大PtZn INPS的10倍左右。密度泛函理论(DFT)计算表明，由于锌原子对OH~*中间体的稳定作用，PtZn体系在MOR反应中会经历“非CO”途径，而纯铂体系会生成高度稳定的COH~*和CO~*中间体，从而导致催化剂失活。对MOR反向氧化峰来源的实验研究与密度泛函理论预测吻合较好。此外，计算还表明，在较小的PtZn INPS上的MOR比较大的INPS在能量上更有利，这是因为它们具有较高的角位密度和较低的能量路径。因此，与较大的PtZn INPS相比，较小的PtZn INPS不仅增加了MOR中活性中心的数量，而且增强了活性中心的活性。这项工作为合成具有更多不协调和增强的活性中心的小型INPS开辟了一条新的途径，用于燃料电池应用。
Atomically ordered intermetallic nanoparticles (iNPs) have sparked considerable interest in fuel cell applications by virtue of their exceptional electronic and structural properties. However, the synthesis of small iNPs in a controllable manner remains a formidable challenge because of the high temperature generally required in the formation of intermetallic phases. Here we report a general method for the synthesis of PtZn. iNPs (3.2 +/- 0.4 nm) on multiwalled carbon nanotubes (MWNT) via a facile and capping agent free strategy using a sacrificial mesoporous silica (mSiO(2)) shell. The as-prepared PtZn iNPs exhibited ca. 10 times higher mass activity in both acidic and basic solution toward the methanol oxidation reaction (MOR) compared to larger PtZn iNPs synthesized on MWNT without the mSiO2 shell. Density functional theory (DFT) calculations predict that PtZn systems go through a "non-CO" pathway for MOR because of the stabilization of the OH* intermediate by Zn atoms, while a pure Pt system forms highly stable COH* and CO* intermediates, leading to catalyst deactivation. Experimental studies on the origin of the backward oxidation peak of MOR coincide well with DFT predictions. Moreover, the calculations demonstrate that MOR on smaller PtZn iNPs is energetically more favorable than larger iNPs, due to their high density of corner sites and lower-lying energetic pathway. Therefore, smaller PtZn iNPs not only increase the number but also enhance the activity of the active sites in MOR compared with larger ones. This work opens a new avenue for the synthesis of small iNPs with more undercoordinated and enhanced active sites for fuel cell applications.