分级多孔“核-笼-笼”结构Co3O4/石墨烯纳米筛用于高负载量超级电容器

Graphene, owing to its desirable conductivity, has been proven to be effective to improve the cyclic ability and conductivity of the supercapacitor electrodes of metallic compounds (MXn) by the coverage of graphene onto MXn nanoparticles. Yet, the MXn/graphene composites are still encountering the challenges of poor rate capability and low mass loading of electrode materials. Building expedite transportation routes of ions and electrons in the electrodes is crucial for breaking through the challenges. In this project, cuboidal Co3O4 nanoparticles are to be used as the representative research object of MXn. Graphene nanomesh (GNM) with uniform and controllable pores along with the Co3O4 are developed to build up a three-dimensional “core-cage-cage” structure, which can provide the effective electrical conductivity and ion diffusion for the supercapacitor electrodes. The Co3O4@GNM, the GNM covered on the Co3O4 nanoparticle, is synthesized by a hot compression technique. The coverage of Co3O4 with the GNM can notably enhance the electrical conductivity, rate capability, and cyclic ability of Co3O4, thanks to the formation of ion transportation channels on the GNM “cage”. Subsequently, hierarchically porous GNM network is synthesized by building up the covalent bonds among GNM flakes around the Co3O4@GNM nanoparticles, building up a “core-cage-cage” structure. This structure is able to achieve the high electrode mass loading due to the construction of highly efficient ion diffusion and electron transportation networks. In this sense, this research will provide theoretical and experimental experiences for improving the mass loading and rate capability of MXn-based supercapacitor electrodes. Therefore, it has great potential and significance for the research of MXn-based supercapacitors.

研究报道已发现利用石墨烯包覆金属化合物（MXn）能够解决基于MXn的超级电容器电极循环寿命短、导电性差的问题，但MXn/石墨烯电极尚面临倍率性能差和电极负载量低的挑战。构筑具有畅通的离子传输和电子传导的电极结构为解决此挑战的关键。本项目拟以Co3O4为代表性研究对象，利用均匀可控造孔的石墨烯纳米筛（GNM）构筑具有高效电子传导和离子传输的“核-笼-笼”结构。通过气相热压法制备“核-笼”结构的Co3O4@GNM，在GNM“笼”上创建电解液离子传输通道，增强Co3O4的导电性、倍率性能及循环寿命；构筑分级多孔GNM网络结构，在Co3O4@GNM外围通过化学交联构筑GNM网络骨架，形成“核-笼-笼”结构的高效电子传导与离子传输网络，实现电极材料的高质量负载。本研究工作可为提升基于MXn的电极材料的负载量及倍率性能提供理论依据和实验基础，对基于MXn的超级电容器研究具有重要意义。

金属化合物具有极高的理论电容量，但因导电性不佳影响其实际应用效果。通过与石墨烯等高导电碳基材料复合可提高导电性和机械性能进而实现储能性质的提升。构筑通畅的离子通道和便于电子传导的三维电极结构可实现高的电容量、能量密度、优异的倍率性能等电化学特性。本项目利用石墨烯材料构筑多孔导电网络，开展了电极结构设计、电极制备、性质分析及构效关系研究。本课题首先利用水热法合成了石墨烯纳米筛（GNM）和不同粒径的Co3O4立方纳米颗粒，研究发现百纳米Co3O4立方最适合用作超级电容器电极材料。通过调节其和GNM的不同比例，实现了Co3O4/GNM复合材料2538F/g的超高质量比容、165Wh/kg的能量密度和优良的倍率性能（78%电容保持率）；通过将GNM插入MXene片层间，解决了MXene作为超级电容器电极材料时自堆积严重的问题，获得了优异的倍率性能（电容保持率77.5%）和循环稳定性（一万次循环后96%电容量保持率）。另外，课题组还构建了多孔、森林形、墙形三种形貌的三维竖直石墨烯电极网络，对比发现多孔竖直石墨烯具有14.03F/cm3的最高体积比电容。此外我们还突破了三维竖直石墨烯电极生长过程中的高度饱和现象，生长出超高三维竖直石墨烯。其作为超级电容器电极取得了260mF/cm2的超高面积比电容。进一步通过电路设计将其应用于小型风力发电模型系统中，展示出了此电容器良好的应用效果。另外，为了实现电极材料形貌的有效控制，项目组对PECVD系统进行了改造，实现了长达40cm的超长生长区域。选择其中三种代表性的竖直石墨烯形貌，研究了形貌与性质之间的关系并应用于光催化、应变传感器、超吸光领域中。综合上述研究成果，本研究为基于金属化合物的超级电容器电极电容量、电子传导和离子传输效率的提升提供了有效的理论和实验依据，对三维石墨烯网络的构建提供了重要的技术指导作用。