Exceptional Capacitance Enhancement of a Non‐Conducting COF through Potential‐Driven Chemical Modulation by Redox Electrolyte

Abstract

Capacitors are the most practical high‐storage and rapid charge‐release devices. The number of ions stored per unit area and their interaction strength with the electrode dictates capacitor‐performance. Microporous materials provide a high storage surface and optimal interactions. Adsorbing electron‐rich and easily polarizable molecules into microporous electrodes is expected to boost Faradaic pseudo‐activity. If such electrode–electrolyte interactions can be made as a potential‐driven reversible process, the resulting capacitors would be adaptable and device‐friendly. A composite covalent organic framework (COF)‐carbon electrode with redox‐active KI is combined in an H2SO4 electrolyte for the first time. This composite electrode benefits from the redox‐functionality of COF and electronic conductivity of carbon, leading to superior capacitative activity. Operando spectro‐electrochemical measurements reveal the existence of multiple polyiodide species, although the I3− is the predominantly electroactive species adsorbing on the microporous triazine‐phenol COF electrode. A systematic fabrication of the flexible solid‐state devices using the COF‐redox‐electrolyte reveals a high areal capacitance of 270 ± 11 mF cm−2 and gravimetric capacitance of 57 ± 8 F g−1. The inclusion of KI in H2SO4 (electrolyte) yields an approximately eight‐fold enhancement in solid‐state gravimetric specific capacitance. The imine‐COF retains 89% of its capacity even after 10 000 cycles.

2D Covalent‐Organic Framework Electrodes for Supercapacitors and Rechargeable Metal‐Ion Batteries

“…Doping 2D-COFs by external chemical agent can also be pursued as an effective future strategy in order to improve the conductivity of 2D-COFs for the electrochemical applications. [156] d) Micropore structure of graphene and graphene@COF. e) Micropore structure of graphene@COF before and after CO 2 adsorption.…”

“…Doping 2D‐COFs by external chemical agent can also be pursued as an effective future strategy in order to improve the conductivity of 2D‐COFs for the electrochemical applications. [ 156 ]…”

The Increasing Number of Electron Reservoirs in Nonporous, High‐Conducting Coordination Polymers CuxBHT (x = 3, 4, and 5, BHT = Benzenehexathiol) for Improved Faradaic Capacitance

“…[11] The apparently separated oxidation/reduction peaks is the characteristic of the Faradaic battery-type behavior, implying the capacitive contribution of Cu 3 BHT is dominated by the fast, non-diffusion limited redox reactions. [18] It can be known from the structural analysis of the Cu 3 BHT that the structures consisted of planar tetracoordinated Cu atoms and benzene rings can be regarded as the copper bisdithiolene coordination units [Cu(SS) 2 ] 0 (SS = dithiolene). According to our previous study on the intrinsic characteristic of Cu 3 BHT, [13] we infer that there might be two free radicals in the structure (see Figure S8, Supporting Information).…”

“…So, in Cu 5.5 BHT, there is only one copper atom from every 11 copper atoms forming planar four-coordination CuS 4 subunit. Here, it is noteworthy that the structure composed Small 2022,18, 2203702…”

Incorporating Conducting Polypyrrole into a Polyimide COF for Carbon‐Free Ultra‐High Energy Supercapacitor

“…Recently, we used redox modulator in the electrolyte to gain a drastic enhancement of the pseudocapacitive behavior, but in some cases, it leads to poor cycling stability. [32][33][34][35] The heteroatoms containing redox active functional groups (pyridine, imide, and carbonyls) in the polyimide linked COF become active sites for storing H + ions in an acidic electrolyte and this storage is mainly confined to a positive potential window (with respect to Ag/AgCl reference electrode) typically between 0 and 1 V. [23] Expanding the window to higher potential stores more H + ions, but this challenges the COF stability, especially for the widely-studied and easily accessed imine-based COFs. On a positive note, the large micro-mesopores of COFs allow the diffusion and storage of larger counter anions along with the cations.…”