Lu Yu-Xuan, Tsai Ming-Hsiu, Lin Cheng-Yu, Woon Wei-Yen, Lin Chih-Ting
Graduate Institute of Electronics Engineering, National Taiwan University, Taipei 10617, Taiwan.
Department of Physics, National Central University, Jungli 32054, Taiwan.
ACS Appl Mater Interfaces. 2025 Jan 22;17(3):5419-5429. doi: 10.1021/acsami.4c16362. Epub 2025 Jan 13.
Graphene-based supercapacitors have gained significant attention due to their exceptional energy storage capabilities. Despite numerous research efforts trying to improve the performance, the challenge of experimentally elucidating the nanoscale-interface molecular characteristics still needs to be tackled for device optimizations in commercial applications. To address this, we have conducted a series of experiments using substrate-free graphene field-effect transistors (SF-GFETs) and oxide-supported graphene field-effect transistors (OS-GFETs) to elucidate the graphene-electrolyte interfacial arrangement and corresponding capacitance under different surface potential states and ionic concentration environments. For SF-GFET, we observed that the hysteresis of the Dirac point changes from 0.32 to -0.06 V as the ionic concentration increases. Moreover, it results in the interfacial capacitance changing from 4 to 2 F/g. For OS-GFET, the hysteresis of the Dirac point remains negative (-0.15 to -0.07 V). Furthermore, the corresponding capacitance of OS-GFET decreases (53-16 F/g) as the ionic concentration increases. These suggest that the orderly oriented water structure at the graphene-water interface is gradually replaced by ionic hydration clusters and results in the difference of capacitance. The relationship between Dirac-point hysteresis value and ionic concentration can be modeled by using the first-order Hill equation to obtain the half occupation value ( = 1.0131 × 10 for KCl solution and = 6.6237 × 10 for MgCl solution). This also agrees with the variances of two minerals in ion hydration within the inner water layer at the interface. This work illustrates the influence of interfacial nanoscale arrangement on interface capacitance formation and layout implications for the development of supercapacitors.
基于石墨烯的超级电容器因其卓越的能量存储能力而备受关注。尽管众多研究致力于提高其性能，但在商业应用中，为实现器件优化，仍需应对通过实验阐明纳米级界面分子特性这一挑战。为解决此问题，我们进行了一系列实验，使用无基底石墨烯场效应晶体管（SF-GFET）和氧化物支撑的石墨烯场效应晶体管（OS-GFET），以阐明在不同表面电势状态和离子浓度环境下石墨烯-电解质界面排列及相应电容。对于SF-GFET，我们观察到随着离子浓度增加，狄拉克点的滞后现象从0.32 V变为-0.06 V。此外，这导致界面电容从4 F/g变为2 F/g。对于OS-GFET，狄拉克点的滞后现象保持为负（-0.15 V至-0.07 V）。此外，随着离子浓度增加，OS-GFET的相应电容降低（从53 F/g降至16 F/g）。这些表明，石墨烯-水界面处有序排列的水结构逐渐被离子水合簇取代，从而导致电容差异。狄拉克点滞后值与离子浓度之间的关系可以用一阶希尔方程建模，以获得半占据值（对于KCl溶液， = 1.0131 × 10 ；对于MgCl溶液， = 6.6237 × 10 ）。这也与界面内水层中两种矿物质在离子水合方面的差异相符。这项工作阐明了界面纳米级排列对界面电容形成的影响以及对超级电容器发展的布局意义。
