自支撑过渡金属碳化物纤维薄膜电极的构建以及在柔性储能器件领域的应用研究

Flexible and thin all-solid-state supercapacitors hold great promise as one of the most efficient energy storage devices. The key challenge is to realize flexible electrode materials and construct integrated electrode with designed configurations. Transition metal carbides have been found outstanding properties, such as high hardness, high stability, high melting point, as well as excellent electrical conductivity, which exhibits the most advantages over metal oxides when applying in supercapacitors. However, the synthesis method of nanostructing metal carbides is very much limited at current stage. New strategy to synthesis carbides with small particle size and high surface area are highly demanded. . In this project, we propose a facile strategy to prepare self-standing film of transition metal carbides nanofiber. Polymer and various transition metal salt will be well mixed and applied as carbon and metal precursors, respectively. With a facile electrospinning technique, the precursor nanofiber with large surface area will be obtained. Following a subsequent heat treatment, the polymer is transformed into pyrolysis carbon, which (1) acts as the carbon source; (2) prohibits the grain agglomoration and growth further to large carbide particles. The unique 1D nanoarchitectur enables the hybrid fibers highly flexible, large specific surface area to quickly absorb a large amount of solution and provide fast ion/elctron transport paths. The porous and flexible nature buffers the volume change of nanocrystalline carbides during charge/discharge and therefore maintains the stability of the material configuration. Thus this novel self-standing hybrid film will be directly applied as electrode of supercapacitors without adopting additional binder, conductive agent and current collector benefiting from metallic property of metal carbides. To the best of our knowledge, this is the first work to synthesis of flexible self-standing film of transition metal carbide nanofiber. The mechanisms of the formation of metal carbides, the flexibility and the energy storage capability will be thorough studied and discussed. Applications on flexible and all solid state supercapacitors of obtained Molybdenum (tungsten) carbide materials will be processed. Relationships of material properties to device performance will be investigated and high performance devices will be persued.

过渡金属碳化物具备与金属媲美的导电性能，其自支撑性电极材料在柔性储能领域表现出优异的性能和极大的应用潜力。但由于受到制备方法的制约，自支撑过渡金属碳化物报道的种类很少，缺乏系统化与规律化的研究，不同电极材料的储能性能和储能机制仍不明确，严重制约了过渡金属碳化物电极材料的应用发展。本项目拟采用静电纺丝法，开发种类丰富的自支撑性的一维过渡金属碳化物纤维薄膜电极材料。通过其材料特性及其作为柔性电极材料的化学性能综合研究，明晰过渡金属碳化物纤维在充放电过程中发生的化学反应、相变以及结构变化机理，厘清其独特的微米/纳米多级孔结构以及高导电性对电子/离子传输路径、储能比容量、和循环稳定性的影响情况，阐明其高效储能的机理。为推进过渡金属碳化物材料在柔性储能领域的广泛应用，提供实验数据和理论指导。

高导电聚合物对碳纳米管的均匀改性包覆，极大程度的保留碳纳米管优异的机械柔韧性以及表面结构的完整性，电子传输性能优良，对后续储能材料的生长及形貌有很大的影响，相对于没有包覆的碳纳米管复合材料，其储能容量、功率密度以及循环稳定性都有很大的提高。自支撑碳化钼纤维电极储能容量、倍率性能和循环稳定性的提升，实施两个研究策略：1）碳化钼纳米纤维与高储能密度的赝电容活性材料复合，其中硫化镍/碳复合材料在高达300A/g的大电流密度下有良好的倍率性能，具有充放电10万次以上的优异的循环稳定性能；MoS2@C/CNTs同轴纳米结构复合物被用作超级电容器负极材料时，嵌入MoS2片层间的无定型碳提供了电子传输的快速通道，包覆在表面的无定型碳薄层则可以有效防止电化学中MoS2体积变化，从而提高稳定性。该电极展现出优秀的比电容与循环稳定性，在1A/g电流密度下比电容可以达到335F/g，经过40000次循环后比电容维持为初始比电容的127%。2）氮掺杂碳化钼N-Mo2C的电化学储能比容量性能，N-Mo2C比容量是纯相Mo2C电极的两倍。氮掺杂在碳化钼晶格中产生了更多的载流子，N-Mo2C比电容增强，电导率明显提高，具有出色的倍率能力。离子液体作为电解质组装柔性储能器件，克服水系电解质溶液工作电压较窄的局限性，有效提高了储能器件的工作电压窗口和能量密度。工作电压可以高达3.5V，具有良好的柔韧性和工作稳定性。.Mo2C的费米能级与铂类似，是优异的HER铂替代电催化剂。首次将自支撑Mo2C/C纳米纤维膜应用于电催化水分解催化电极，在20mA cm-2的电流密度下稳定工作340h无明显衰减。经过Ni掺杂改性的Mo2C（Ni-Mo2C/C）的自支撑柔性纤维膜，则实现了同时具有析氢（HER）和析氧（OER）双功能催化性能。在碱性环境中，具有1000次循环的良好稳定性，与商用Pt/C、RuO2电极性能相当。目前自支撑的过渡金属碳化物催化水分解的报道还很少，我们这项工作为探索高效稳定的低成本双功能水分解催化剂柔性电极提供一条重要思路。