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Graphene 2018：垂直石墨烯网络的合成与应用

平松峰男

石墨烯（单层和多层）是一种二维材料，面内和面外方向具有较大的各向异性。碳纳米墙（CNW）是具有开放边界的几层石墨烯，垂直站立在基板上。这些片材形成了迷宫状墙壁结构的自支撑网络。CNW 和类似的石墨烯结构可以通过几种等离子体增强化学气相沉积 (PECVD) 技术合成。CNW 有时用金属纳米粒子和生物分子装饰。具有大表面积的 CNW 结构适合电化学和生物传感应用的平台。CNW薄膜可用作电化学传感器、电容器、染料敏化太阳能电池、聚合物电解质燃料电池（PEFC）和植入式葡萄糖燃料电池（GFC）的电极。在这些当中，燃料电池中的 CNW 电极应使用 Pt 等催化纳米颗粒进行装饰。从实践的角度来看，控制 CNW 结构（包括相邻纳米墙之间的间距和结晶度）非常重要。此外，应建立催化金属纳米颗粒的形成方法。它是使用 CH4 /H2 /Ar 混合物使用 PECVD 进行 CNW 生长，重点是 CNW 的结构控制。据报道，离子轰击和催化金属对垂直纳米石墨烯成核的影响，实现了相邻壁之间间隙的主动控制。此外，通过氯铂酸还原或超临界流体金属有机化学沉积，在 CNW 表面装饰 Pt 纳米粒子。

The Last Decade attested an enormous breakthrough in the research of graphene. Graphene an allotrope of carbon in the shape of two-dimentional (2D) SP2- hybridized crystalline sheet has a special mixture of outstanding properties such as excellent mechanical strength and elasticity, extreme carrier mobility, excessive service mobility, supreme electrical and thermal conductivity, and excessive optical transmission. These properties, together with its quite massive surface area, without problems modifiable surfaces, and tunable structure by means of incorporating foreign atoms, make graphene versatile in diverse application areas ranging from electronic devices, sensors, catalysis, to power harvesting and storage. In particular, along with the growing necessities of flexible, safe, and portable devices, utilization of graphene and graphene‐based composite electrodes has led to prominent growth in creating new electrochemical energy storage and conversion systems, such as supercapacitors, batteries, and fuel cells.

The structural design of an electrode is one of the most essential factors affecting its reaction kinetics, the capability of mass transportation with electrolyte, and subsequently the performance of an electrochemical power storage or conversion system. A profitable approach that has been widely established is to assemble a 3D nanoscale‐structured electrode, which enables more suitable ion and electron transport, increased active material loading, and improved mechanical stability. Based on its outstanding properties, graphene has shown first-rate promises as a constructing cloth for the development of new electrodes in electrochemical systems. Moreover, a 3D graphene‐based porous framework should be employed concurrently as the structural spine and cutting-edge collector in a free‐standing and binder‐free electrode, which benefits the fabrication of lightweight and bendy devices. In line with this strategy, more than a few 3D graphene structures have been synthesized and utilized for energy storage and conversion, which can be genuinely categorized to graphene foams (GFs) and vertically aligned graphene nanosheet arrays (VAGNAs).

 

Recently, another kind of 3D graphene, i.e., Vertically Aligned Graphene Nanosheet Arrays (VAGNAs), has attracted increasing Interest for its application as electrochemical electrodes due to its optimum reaction kinetics and mass transportation capability to that of GFs. With a thickness of a number of to tens of graphite carbon layers, Vertically Aligned Graphene Nanosheet Arrays are also named as carbon nanoflake arrays or carbon nano wall arrays elsewhere. Vertically Aligned Graphene Nanosheet Arrays are normally synthesized via PECVD with gaseous carbon sources, in which 2D graphene nanosheets are grown perpendicularly to the substrates to construct a 3D ordered and interconnected array shape with enriched edges of graphene sheets exposed. The Synthesis is processed at relatively low temperatures ranging from 300 to 800 °C, which approves more choice of substrates for the development of Vertically Aligned Graphene Nanosheet Arrays. VAGNAs can be easily and uniformly embellished with other energetic materials, which further leads to a exceptional variety for their application.

基于这些固有的优势，垂直排列石墨烯纳米片阵列已被应用于独特的领域，如气体传感器、生物传感器、电催化剂、场电子发射、表面增强拉曼光谱（SERS）、EDLC、法拉第赝电容器、LIB和燃料电池，如 中所总结的。最近，在电化学能量存储和转换中高效集成电极应用的垂直排列石墨烯纳米片阵列及其复合材料的开发方面取得了一些必要的进展。相信重新审视最近对这组纳米材料的研究是非常及时和必要的，特别是随着新兴的柔性和可穿戴设备对电力存储元件的需求不断增加。与该领域之前的批评相比，当前的工作更多地强调了 VAGNA 和相关复合材料在电化学电极功能方面的成功，这些成功源于其结构和性能的出色优点。形貌和石墨化程度对 VAGNA 电极的性能也有重要影响。事实证明，与低温（约750℃）制备的垂直排列石墨烯纳米片相比，在高温（约850℃）下生长的垂直排列石墨烯纳米片具有额外的弯曲表面。因此，在高温下生长的 VAGNA 具有较大的可接触表面位置和更大的缺陷密度，这反过来又导致了更高的电容 目前的工作更多地强调 VAGNA 和相关复合材料在电化学电极功能方面的成功源于其结构和性能的出色优点。形貌和石墨化程度对 VAGNA 电极的性能也有重要影响。事实证明，与低温（约750℃）制备的垂直排列石墨烯纳米片相比，在高温（约850℃）下生长的垂直排列的石墨烯纳米片具有额外的弯曲表面。因此，在高温下生长的 VAGNA 具有较大的可接触表面位置和更大的缺陷密度，这反过来又导致了更高的电容 目前的工作更多地强调 VAGNA 和相关复合材料在电化学电极功能方面的成功源于其结构和性能的出色优点。形貌和石墨化程度对 VAGNA 电极的性能也有重要影响。事实证明，与低温（约750℃）制备的垂直排列石墨烯纳米片相比，在高温（约850℃）下生长的垂直排列的石墨烯纳米片具有额外的弯曲表面。因此，在高温下生长的 VAGNA 具有较大的可接触表面位置和更大的缺陷密度，这反过来又导致了更高的电容 事实证明，与低温（约750℃）制备的垂直排列石墨烯纳米片相比，在高温（约850℃）下生长的垂直排列石墨烯纳米片具有额外的弯曲表面。因此，在高温下生长的 VAGNA 具有较大的可接触表面位置和更大的缺陷密度，这反过来又导致了更高的电容 事实证明，与低温（约750℃）制备的垂直排列石墨烯纳米片相比，在高温（约850℃）下生长的垂直排列石墨烯纳米片具有额外的弯曲表面。因此，在高温下生长的 VAGNA 具有较大的可接触表面位置和更大的缺陷密度，这反过来又导致了更高的电容

文章首先简要介绍了垂直排列石墨烯纳米片阵列的合成方法和生长机理，并总结了垂直排列石墨烯纳米片阵列的物理和化学性质。然后，我们重点介绍了新型垂直对齐石墨烯纳米片阵列电极的最新发展状况，以及与其他 3D 石墨烯基电极相比的优缺点，并阐述了它们的整体性能。最后谈谈VAGNA对于新型电化学能源同样发展的任务和机遇