Charge Transfer Salt and Graphene Heterostructure-Based Micro-Supercapacitors with Alternating Current Line-Filtering Performance.

The rapid development of lightweight and wearable devices requires electronic circuits possessing compact, high-efficiency, and long lifetime in very limited space. Alternating current (AC) line filters are usually tools for manipulating the surplus AC ripples for the operation of most common electronic devices. So far, only aluminum electrolytic capacitors (AECs) can be utilized for this target. However, the bulky volume in the electronic circuits and limited capacitances have long hindered the development of miniaturized and flexible electronics. In this work, a facile laser-assisted fabrication approach toward an in-plane micro-supercapacitor for AC line filtering based on graphene and conventional charge transfer salt heterostructure is reported. Specifically, the devices reach a phase angle of 73.2° at 120 Hz, a specific capacitance of 151 µF cm-2 , and relaxation time constant of 0.32 ms at the characteristic frequency of 3056 Hz. Furthermore, the scan rate can reach up to 1000 V s-1 . Moreover, the flexibility and stability of the micro-supercapacitors are tested in gel electrolyte H2 SO4 /PVA, and the capacitance of micro-supercapacitors retain a stability over 98% after 10 000 cycles. Thus, such micro-supercapacitors with excellent electrochemical performance can be almost compared with the AECs and will be the next-generation capacitors for AC line filters.

C-I...NC halogen bonding in two polymorphs of the mixed-valence 2:1 charge-transfer salt (EDT-TTF-I2)2(TCNQF4), with segregated versus alternated stacks.

Oxidation of diiodoethylenedithiotetrathiafulvalene (EDT-TTF-I2), C8H4I2S6, with the strong oxidizer tetrafluorotetracyanoquinodimethane (TCNQF4), C12F4N4, affords, depending on the crystallization solvent, two polymorphs of the 2:1 charge-transfer salt (EDT-TTF-I2)2(TCNQF4), represented as D2A. In both salts, the TCNQF4 is reduced to the radical anion state, and is associated through short C-I...NC halogen bonds to two EDT-TTF-I2 molecules. The two polymorphs differ in the solid-state association of these trimeric D-A-D motifs. In polymorph (I) the trimeric motif is located on an inversion centre, and hence both EDT-TTF-I2 molecules have +0.5 charge. Together with segregation of the TTF and TCNQ derivatives into stacks, this leads to a charge-transfer salt with high conductivity. In polymorph (II) two crystallographically independent EDT-TTF-I2 molecules bear different charges, close to 0 and +1, as deduced from an established correlation between intramolecular bond lengths and charge. Overlap interactions between the halogen-bonded D(0)-A-∙D+∙ motifs give rise, in a perpendicular direction, to diamagnetic A2(2-) and D(0)-D2(2+)-D(0) entities, where the radical species are paired into the bonding combination of respectively the acceptor LUMOs and donor HOMOs. The strikingly different solid-state organization of the halogen-bonded D-A-D motifs provides an illustrative example of two modes of face-to-face interaction between π-type radicals, into either delocalized, uniform chains with partial charge transfer and conducting behaviour, or localized association of radicals into face-to-face A2(2-) and D2(2+) dyads.