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 (mSiO2) 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.

中文翻译：

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亚 4 nm PtZn 金属间化合物纳米颗粒在催化电氧化反应中提高质量和比活性

原子有序的金属间化合物纳米粒子 (iNP) 凭借其卓越的电子和结构特性，在燃料电池应用中引起了极大的兴趣。然而，由于金属间相的形成通常需要高温，因此以可控方式合成小 iNP 仍然是一项艰巨的挑战。在这里，我们报告了一种在多壁碳纳米管 (MWNT) 上合成 PtZn iNPs (3.2 ± 0.4 nm) 的通用方法，通过使用牺牲介孔二氧化硅 (mSiO2) 壳的简便且无封端剂的策略。所制备的 PtZn iNPs 表现出约。与在没有 mSiO2 壳的 MWNT 上合成的较大 PtZn iNPs 相比，在酸性和碱性溶液中对甲醇氧化反应 (MOR) 的质量活性高 10 倍。密度泛函理论 (DFT) 计算预测 PtZn 系统通过 MOR 的“非 CO”途径，因为 OH* 中间体被 Zn 原子稳定，而纯 Pt 系统形成高度稳定的 COH* 和 CO* 中间体，导致催化剂失活。MOR 反向氧化峰起源的实验研究与 DFT 预测非常吻合。此外，计算表明，较小的 PtZn iNPs 上的 MOR 比较大的 iNPs 在能量上更有利，因为它们具有高密度的角位点和较低的能量通路。因此，与较大的相比，较小的 PtZn iNPs 不仅增加了 MOR 中活性位点的数量，而且还增强了活性位点的活性。