A mild temperature sequential reduction method in aqueous medium is reported for the synthesis of Au@Ni nanoparticles with a core–shell morphology. The nickel shell thickness with a gold core in the nanostructure can be tuned from 2 nm up to about 10 nm. Near ambient pressure XPS (NAPXPS) studies under oxygen atmosphere show that Au₈₀@Ni₂₀ with an extremely thin nickel shell (∼2 nm) follows a distinctly different decomposition pathway of metastable Ni(OOH) species compared to those with larger shell thickness which behave more like individual nickel surfaces. Thus, Ni(OOH) on Au₈₀@Ni₂₀ decomposes to metallic Ni at 100 °C and is found to resist oxidation at 0.1 mbar oxygen at this temperature. Those with a larger nickel shell thickness behave more like monometallic Ni in terms of their decomposition and oxidation properties. The Au@Ni system with an ultra thin metallic nickel overlayer (2 nm) shows high catalytic activity and selectivity for phenylacetylene hydrogenation under mild conditions which outweighs their monometallic counterparts and those with higher nickel shell thickness.

中文翻译：

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近环境压力（NAP）XPS探测Au @ Ni核壳纳米粒子中Ni表面的多样反应趋势

据报道，在水介质中采用温和的温度顺序还原法可合成具有核-壳形貌的Au @ Ni纳米粒子。纳米结构中具有金核的镍壳厚度可以从2 nm调整到大约10 nm。氧气气氛下的近环境压力XPS（NAPXPS）研究表明，与壳厚度较大的亚稳态Ni（OOH）物种相比，具有极其薄的镍壳（〜2 nm）的Au ₈₀ @Ni ₂₀遵循截然不同的分解途径。表现得更像单个镍表面。因此，Au ₈₀ @Ni ₂₀上的Ni（OOH）在100°C时分解为金属Ni，并且在此温度下可抵抗0.1 mbar的氧气氧化。那些具有较大镍壳厚度的金属在分解和氧化性能方面表现得更像单金属镍。具有超薄金属镍覆盖层（2 nm）的Au @ Ni系统在温和的条件下显示出较高的催化活性和对苯乙炔加氢的选择性，这超过了它们的单金属对应物和镍壳厚度较高的对应物。