Electrochemical Double‐Layer Capacitor Energized by Adding an Ambipolar Organic Redox Radical into the Electrolyte

Abstract

Carbon-based electrochemical double-layer capacitors (EDLCs) generally exhibit high power and long life, but low energy density/capacitance. Pore/morphology optimization and pseudo-capacitive materials modification of carbon materials have been used to improve electrode capacitance, but leading to the consumption of tap density, conductivity and stability. Introducing soluble redox mediators into electrolyte is a promising alternative to improve the capacitance of electrode. However, it is difficult to find one redox mediator that can provide additional capacitance for both positive and negative electrodes simultaneously. Here, an ambipolar organic radical, 2, 2, 6, 6-tetramethylpiperidinyloxyl (TEMPO) is first introduced to the electrolyte, which can substantially contribute additional pseudo-capacitance by oxidation at the positive electrode and reduction at the negative electrode simultaneously. The EDLC with TEMPO mediator delivers an energy density as high as 51 Wh kg , 2.4 times of the capacitor without TEMPO, and a long cycle stability over 4000 cycles. The achieved results potentially point a new way to improve the energy density of EDLCs.

Redox‐Mediator‐Enhanced Electrochemical Capacitors: Recent Advances and Future Perspectives

“…Many efforts have been devoted to the redox‐mediator‐enhanced supercapacitors. As a result, a variety of redox mediators and electrolyte systems have been developed …”

“…Therefore, the CV curve of the positive electrode now shows a pair of redox peaks and the negative one a rectangular shape (Figure g) and the GCD curve of the positive electrode exhibits the sloping potential plateaus whereas the potential of the negative electrode varies linearly with time (Figure h). After the first successful attempt of enhancing the capacitance by introducing Ag + as mediator, a large number of redox mediators were developed for supercapacitors . Based on the used redox mediators, the single‐redox‐mediator‐enhanced supercapacitors can be divided into three categories: metal‐mediator‐based supercapacitors, inorganic‐mediator‐based supercapacitors, and organic‐mediator‐based supercapacitors.…”

“…A solution would be the development of ambipolar redox mediators that can contribute pseudocapacitance for the positive and negative electrodes at the same time. Recently, our group reported an ambipolar‐redox‐mediator‐enhanced EDLC using TEMPO as redox mediator . TEMPO, a stable radical, can be oxidized and reduced reactions by losing/obtaining one electron resulting in additional pseudocapacitance at the positive and negative electrodes simultaneously (Figure a).…”

“…Recently,o ur group reported an ambipolar-redox-mediator-enhanced EDLC using TEMPO as redox mediator. [79] TEMPO, as table radical, can be oxidized and reduced reactions by losing/obtaining one electron resulting in additional pseudocapacitance at the positive and negative electrodes simultaneously (Figure9a). The capacitors consisted of activated carbon as the electrode materials, aqueous solution containingT EMPO as the active electrolyte, and an ion-exchange membrane as the separator ( Figure 9b).…”

Engineering Ultrathin MoS2 Nanosheets Anchored on N‐Doped Carbon Microspheres with Pseudocapacitive Properties for High‐Performance Lithium‐Ion Capacitors

“…Lithium‐ion capacitors (LICs) as a hybrid system, combining faradaic feature and capacitance behavior, is regarded as one of the most promising EES at present . Concretely, LICs generally consist of the battery‐type anode and capacitor‐type cathode by means of organic lithium salt electrolyte.…”