▎ 摘　　要

In the field of energy storage by high-rate supercapacitors, there has been an upper limit for the total interfacial capacitance of carbon-based materials. This upper limit originates from both quantum and electric double-layer capacitances. Surpassing this limit has been the focus of intense research in this field. Here, we precisely investigate the effect of chemical functional groups and physical confinement on the electrochemical performance of graphene nanoribbons. We present the results of a quasi-one-dimensional single-layer graphene nanoribbon (120 nm in width and similar to 100 mu m in length) microelectrode fabricated by mechanical exfoliation of graphite, followed by electron beam lithography process and oxygen plasma etching treatment. We directly measure the interfacial capacitance as a function of frequency at different potentials in an aqueous electrolyte using a three-electrode electrochemical system. Electrochemical impedance spectroscopy and cyclic voltammetry tests show an average capacitance of 75 mu F cm(-1) at 100 kHz to 1.16 mF cm(-2) at 1 Hz and 0.35 +/- 0.04 mF cm(-2), respectively, well above the upper capacitance limit of carbon-based electrodes. First principle density functional calculations and cyclic voltammetry (at varies scan rates) illustrate that presence of oxygen functional groups passivating the nanoribbon edges and lateral structural confinement, as well as occurrence of pseudocapacitive reactions, lead to such very large capacitances at low and high frequencies. Our results suggest a new and closer sight on nanoribbons as a potent candidate for energy storage devices and provide a fundamental platform for studying the effect of lateral structural confinements accompanied by the presence of various functional groups on the electrochemical performance of single/few-layer carbon-based materials.