Owing to its high thermal and electrical conductivities, its ductility and its overall non-toxicity1-3, copper is widely used in daily applications and in industry, particularly in anti-oxidation technologies. However, many widespread anti-oxidation techniques, such as alloying and electroplating1,2, often degrade some physical properties (for example, thermal and electrical conductivities and colour) and introduce harmful elements such as chromium and nickel. Although efforts have been made to develop surface passivation technologies using organic molecules, inorganic materials or carbon-based materials as oxidation inhibitors4-12, their large-scale application has had limited success. We have previously reported the solvothermal synthesis of highly air-stable copper nanosheets using formate as a reducing agent13. Here we report that a solvothermal treatment of copper in the presence of sodium formate leads to crystallographic reconstruction of the copper surface and formation of an ultrathin surface coordination layer. We reveal that the surface modification does not affect the electrical or thermal conductivities of the bulk copper, but introduces high oxidation resistance in air, salt spray and alkaline conditions. We also develop a rapid room-temperature electrochemical synthesis protocol, with the resulting materials demonstrating similarly strong passivation performance. We further improve the oxidation resistance of the copper surfaces by introducing alkanethiol ligands to coordinate with steps or defect sites that are not protected by the passivation layer. We demonstrate that the mild treatment conditions make this technology applicable to the preparation of air-stable copper materials in different forms, including foils, nanowires, nanoparticles and bulk pastes. We expect that the technology developed in this work will help to expand the industrial applications of copper.

中文翻译：

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表面配位层钝化铜的氧化

由于其高导热性和导电性、延展性和整体无毒性1-3，铜被广泛用于日常应用和工业中，特别是在抗氧化技术中。然而，许多广泛使用的抗氧化技术，例如合金化和电镀1、2，通常会降低某些物理性能（例如，导热性和导电性以及颜色）并引入有害元素，例如铬和镍。尽管已经努力开发使用有机分子、无机材料或碳基材料作为氧化抑制剂的表面钝化技术4-12，但它们的大规模应用取得了有限的成功。我们之前报道了使用甲酸盐作为还原剂的高空气稳定性铜纳米片的溶剂热合成。在这里，我们报告了在甲酸钠存在下对铜进行溶剂热处理导致铜表面的晶体学重建和超薄表面配位层的形成。我们发现表面改性不会影响体铜的导电性或导热性，但会在空气、盐雾和碱性条件下引入高抗氧化性。我们还开发了一种快速室温电化学合成方案，所得材料表现出同样强的钝化性能。我们通过引入链烷硫醇配体与未被钝化层保护的台阶或缺陷位点进行配位，进一步提高了铜表面的抗氧化性。我们证明了温和的处理条件使该技术适用于制备不同形式的空气稳定铜材料，包括箔、纳米线、纳米颗粒和块状糊剂。我们预计这项工作中开发的技术将有助于扩大铜的工业应用。