LEE Jordan , LI Yong, TANG Jianing ,3, CUI Xiaoli ,＊

1 Department of Materials Science, Fudan University, Shanghai 200433, P. R. China.

2 Shanghai Institute of Space Power Sources, Shanghai 200245, P. R. China.

3 Department of Advanced Materials Science and Engineering, Imperial College London, London SW72AZ, Britain.

Abstract: Since the successful synthesis of graphdiyne, graphynes have emerged as an active field in carbon materials research. Hydrogen-substituted graphyne, structurally similar to graphynes, is a kind of two-dimensional (2D) carbon-rich material composed of sp2-hybridized carbon and hydrogen from phenyl groups and sp-hybridized carbon from ethynyl linkages. The large pore size in the molecular structure of hydrogen-substituted graphyne aids the diffusion of ions and molecules. In this work, hydrogen-substituted graphyne was synthesized by a facile mechanochemical route. Calcium carbide (CaC2) was employed as the precursor of sp-hybridized carbon and 1,3,5 tribromobenzene (PhBr3) as that of sp2-hybridized carbon and hydrogen. Hydrogen-substituted graphyne was directly obtained via the cross-coupling reaction performed by ball milling under vacuum and the impurities were removed by dilute nitric acid and benzene. Mechanochemistry is a mature technology for the simple and high-yield synthesis of nanostructured materials. The composition of the as-prepared hydrogen-substituted graphyne was confirmed by Raman and 1H solid-state nuclear magnetic spectroscopies. Energydispersive X-ray (EDX) spectrum and X-ray diffraction (XRD) patterns indicated that the purity and crystallinity of the prepared samples are high, which was further confirmed by the corresponding selected area electron diffraction (SAED)patterns. Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images illustrated that samples had nanosheet structure with a layer-to-layer distance of 0.35 nm. However, owing to the lack of a substrate, the nanosheets reunite to form irregular microparticles, as shown in the scanning electron microscopy (SEM)images. Twin structure was found in the as-prepared samples, which might be relevant to the mechanochemical process.The samples were used to prepare electrodes for the photoelectrochemical and electrochemical catalytic analysis. The open circuit potential under chopped irradiation of the electrode showed that the as-prepared hydrogen-substituted graphyne was a p-type semiconductor. The band gap was calculated to be 2.30 eV by UV-Vis diffused ref l ectance (UV-Vis DRS) spectroscopy. The electrocatalytic properties of the sample were determined using a three-electrode cell in a neutral solution (Na2SO4, 0.5 mol·L−1). The onset overpotential for hydrogen evolution was −0.17 V; however, the Tafel slope was too large (1088.4 mV·dec−1), which restricted application in electrocatalytic hydrogen evolution. On the other hand, the overpotential for oxygen evolution reaction was only 0.04 V and the Tafel slope was 70.0 mV·dec−1, making applications in electrocatalytic oxygen evolution and photocatalysis possible. This strategy opens a new avenue for preparing graphyne with good electrochemical properties using readily available precursors under mild conditions.

Key Words: Hydrogen substituted graphyne; Mechanochemistry; Semiconductor; Oxygen evolution reaction

1 引言

石墨炔是继碳纳米管和石墨烯之后，又一种被誉为“超级材料”的碳材料。1968年Baughman首次从理论上预言了石墨炔结构稳定存在的可能性，其结构可视为由苯环和炔键交替连接形成的具有二维平面网络结构的全碳分子1。理论计算表明石墨炔材料存在Dirac锥结构2，具有超高载流子迁移率和量子霍尔效应，在能源环境领域拥有广阔的应用前景3,4。但是直到2010年，石墨双炔(Graphdiyne型)才第一次由李玉良院士课题组通过Glaser-Hay交叉偶联反应成功合成5，继而引发了石墨炔研究的热潮6–8。在此基础上，刘忠范/张锦、Sakamoto、Venugopal等课题组，进一步发展出了石墨炔纳米墙阵列9、纳米带10、纳米管11以及石墨炔纳米杂化物12等技术，推动了石墨炔的研究。目前，Graphdiyne型石墨双炔已在锂离子电池13、钠离子电池14、燃料电池15、超级电容器16和催化17等应用方面取得了喜人的性能。

石墨炔类材料合成的关键在于交叉偶联反应。现有的合成方法多以六炔基苯(hexaethynylbenzene)为前驱体，通过 Cu催化或高温催化的Glaser-Hay交叉偶联的方法来合成该材料5,9–15。以北京大学刘忠范、张锦课题组合成石墨炔纳米墙阵列为例9。首先利用交叉偶联反应，得到六[(3-甲基硅)乙炔基]苯{exakis[(trimethylsilyl)ethynyl]-benzene}。然后在氟化四丁铵中将其转变为六炔苯单体。最后一步以铜为催化剂，在氩气气氛下将丙酮、吡咯和六炔苯单体的混合溶液在 50 °C下避光保温 12 h，在铜板基底上获得了石墨双炔纳米墙阵列，同时验证了其优良的场发射性能。最近，该课题组把纳米墙的制备方法推广到任意形状的基体，并研究了其光电化学分解水性能18。……