Abstract
Owing to their unique nanosize effect and surface effect, pseudocapacitive quantum dots (QDs) hold considerable potential for high‐efficiency supercapacitors (SCs). However, their pseudocapacitive behavior is exploited in aqueous electrolytes with narrow potential windows, thereby leading to a low energy density of the SCs. Here, a film electrode based on dual‐confined FeOOH QDs (FQDs) with superior pseudocapacitive behavior in a high‐voltage ionic liquid (IL) electrolyte is put forward. In such a film electrode, FQDs are steadily dual‐confined in a 2D heterogeneous nanospace supported by graphite carbon nitride (g‐C3N4) and Ti‐MXene (Ti3C2). Probing of potential‐driven ion accumulation elucidates that strong adsorption occurs between the IL cation and the electrode surface with abundant active sites, providing sufficient redox reaction of FQDs in the film electrode. Furthermore, porous g‐C3N4 and conductive Ti3C2 act as ion‐accessible channels and charge‐transfer pathways, respectively, endowing the FQDs‐based film electrode with favorable electrochemical kinetics in the IL electrolyte. A high‐voltage flexible SC (FSC) based on an ionogel electrolyte is fabricated, exhibiting a high energy density (77.12 mWh cm−3), a high power density, a remarkable rate capability, and long‐term durability. Such an FSC can also be charged by harvesting sustainable energy and can effectively power various wearable and portable electronics.
Highlights
Many elucidates that strong adsorption occurs between the ionic liquid (IL) cation and the efforts have been dedicated to achieving electrode surface with abundant active sites, providing sufficient redox pseudocapacitive quantum dots (QDs) by reducing the reaction of FeOOH QDs (FQDs) in the film electrode
We report a film electrode based on dual-confined FeOOH QDs with superior pseudocapacitive behavior in the 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) IL electrolyte, where pseudocapacitive FQDs (≈5 nm) are steadily dual confined in a 2D heterogeneous nanospace supported by graphite carbon nitride (g-C3N4) and Ti-MXene (Ti3C2)
We have successfully developed a new strategy to obtain a unique FQDs/CNTC film electrode, which was realized by the dual confinement of pseudocapacitive FQDs in porous g-C3N4 and conductive Ti3C2 nanosheets
Summary
High-conductivity Ti3C2 nanosheets were successfully prepared by etching the Al layers in Ti3AlC2 using a mixture of LiF and HCl, followed by liquid sonication exfoliation (Figure S1, Supporting Information). The Cd–E curve of the FQDs/ CNTC electrode is nearly asymmetric, in which the differential capacitance is significantly increased when the electrode is negatively charged, indicating a high-accumulated EMIM+ ion density in the stern layer This phenomenon is mainly due to the abundant active sites consisting of numerous lone pair electrons, such as N defects of g-C3N4 and surface functionality of Ti2C3 in the FQDs/CNTC electrode, which overlap with the electron cloud of the positively charged imidazole ring. The rich porous structure of g-C3N4 provides accessible channels for IL ions (blue arrows) Both these factors ensure that IL ions are involved in the sufficient redox reaction with FQDs, leading to the FQDs/CNTC film electrode exhibiting a high specific capacitance. This study introduces a new avenue for flexible energy-storage devices, which is of great significance for the development of sustainable wearable and portable electronics
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