Recent Progress in Ruthenium Oxide‐Based Composites for Supercapacitor Applications

Abstract

Electrochemical energy storage has emerged as one of the principal topics of present‐day research to deal with the high energy demands of modern society. Accordingly, besides fuel cells and battery technologies, interesting and challenging results have been observed in the recent past, during the materialization of “supercapacitors” or “ultracapacitors”, which have provoked a sharp increase in research inclination to revisit this aspect of renewable and sustainable energy storage. Supercapacitor performances are largely dependent on electrode materials, the nature of the electrolyte used, and the range of voltage windows employed. Carbon‐based electrode materials have tunable properties such as electrical conductivity, extensive surface area, and faster electron transfer kinetics with low fabrication costs. But their specific capacitances are found to be too low for commercialization. Ruthenium dioxide (RuO2), owing to its high theoretical specific capacitance value (1400–2000 F g−1), has been extensively recognized as a favorable material for supercapacitor devices, but high production cost and agglomeration effects stand as high barriers preventing marketable usage. Consequently, RuO2‐based nanocomposites have been widely studied to optimize the material cost, with simultaneous improvement in the electrochemical performances. This Review describes comprehensively the recent progress in terms of the fabrication and design, electrochemical performance, and achievements of RuO2 and its nanocomposites as electrode materials for supercapacitors, which will be beneficial for further research designing high‐performance supercapacitor devices.

Carbon nano-fiber forest foundation for ruthenium oxide pseudo-electrochemical capacitors

“…This performance is significantly higher than just that of CNF electrodes, and the ability to deliver higher specific power at higher specific energy is enhanced when compared to many carbon and metal oxide based electrodes. [77][78][79] The present specific energy results are comparable to other high specific capacitance yielding electrodes, such as RuO 2 -CNT/CNF-based electrodes, 50,63,64,72 RuO 2 -graphene oxide-based electrodes 54,73 and other RuO 2composite based electrodes. 49,74…”

Heteroatom‐Doped and Oxygen‐Functionalized Nanocarbons for High‐Performance Supercapacitors

“…Comparison of the gravimetric capacitance of supercapacitor electrode materials. The data for gravimetric capacitance of supercapacitor materials with some selected nanostructures are taken from the corresponding articles: pristine carbon, [13] MnO 2 -based materials, [22] Fe-based materials, [18,23] RuO 2 -based structure, [15] VN structure, [24] 2D materials, [16,21] and conducting polymers. [13] Specific capacitance of doped nanocarbon is taken from the references cited in this article and also presented are the electrode performances in details in Table 1 (AC: activated carbon; MWCNT: multiwalled carbon nanotube; CDC: carbide derived carbons; rGO: reduced graphene oxide; HPC: hierarchical porous carbon; BP: black phosphorene; RP: red phosphorene; PANI: polyaniline; PPy: polypyrrole; PTh: polythiophene; PMT: poly(3-methylthiophene); PEDOT: poly(3,4-ethylenedioxythiophene); PEPT: poly(4-flourophenyl-3-thiophene)), VN: vanadium nitride.…”

“…[234] The underlying observation is that unstable carboxyl groups are neutralized and reduced during charge-discharge while the electrodes are subjected to KOH medium. [227] It has also been reported that the acidic sites (carboxyl, phenol) on nanocarbon surface play a dominant role and react with OH − ions in alkaline medium (Equations (15) and (16)) while the basic sites are unfavorable for the redox reactions [49,227] On the other hand, O-functionalized nanocarbons show better supercapacitive performance in H 2 SO 4 medium due to the higher ionic mobility and better accessibility of the surface by smaller ions. [216] Meanwhile, the basic functional groups (carbonyl and quinone) present on the nanocarbons react with protons contributing pseudocapacitance in acidic aqueous electrolyte.…”

“…hydroxides, nitrides, and sulfides. [12][13][14][15][16][17][18][19][20][21][22][23][24] From morphological perspective, vertically oriented nanostructures with multiple large surfaces support efficient ion transport, enable gainful use of the entire (active) surface thus leading to much improved charge accumulation, storage, and release. [25][26][27][28][29][30] These materials are classified based on the way they store electric charge, following either the electrostatic double-layer (EDL) capacitance or the pseudocapacitance mechanisms.…”

Oxygen Vacancy‐Engineered Ti−Mo−Ni Ternary Oxide Nanotubes as Binder‐Free Supercapacitor Electrodes with Exceptional Potential Window

“…Ruthenium oxide showed the best performance among all tested TMOs so far due to its highly reversible redox reactions, good thermal stability, wide potential window, metallic-type conductivity, and long cycle life. [16] However, the practical use of RuO 2 -based electrodes is limited by the high cost and low abundance. Therefore, many studies were directed to explore low-cost alternatives to RuO 2 such as Ni 2 O 3 , NiO, V 2 O 5 , Fe 3 O 4 , MnO 2 , MnO, MoO 3 , black TiO 2 , and their composites.…”