Deep‐Eutectic‐Solvent‐Assisted Synthesis of Hierarchical Carbon Electrodes Exhibiting Capacitance Retention at High Current Densities

Abstract

Nature provides a wide range of entities and/or systems with different functions that may serve as a source of bioinspiration for material chemists. Actually, materials exhibiting a 3D porous texture (combining pores at different scales, from macro-to meso-up to micropores) mimic the hierarchical structure of different systems found in living organisms (e.g., the blood circulation or the respiratory system in mammalians). Structural organization at different scales is ultimately responsible for the outstanding properties offered by hierarchical materials (not only as stationary phases in separation and catalytic processes, [1] but also as electrodes in fuel cells and capacitors)[2] because they offer not only large surface areas, but also accessibility to such a surface.A number of synthetic routes have been explored by using different carbonaceous precursors [3] and either exo or endo templates to modulate the porous texture of the resulting carbon structures.[4] Recent efforts have also been focused on the preparation of porous carbon composites containing graphitic carbon entities (e.g., carbon nanotubes [5] and nanohorns, [6] or even graphene oxide [7] ) the challenge of which is double and resides in 1) the achievement of a homogenous dispersion of these entities throughout the monolith structure and 2) the preservation of high surface areas. Baumann and co-workers have recently performed a quite extensive and stimulating work on single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) synthesized by resorcinol-formaldehyde polycondensation.[5] Particularly interesting in terms of conductivity and surface area were those composites based on DWCNTs, although the authors expressed the convenience of substituting the surfactants used for carbon-nanotube (CNT) dispersion.[5d]Ionic liquids (ILs) [8] and deep eutectic solvents (DESs, a new class of ILs obtained by complexion of quaternary ammonium salts with hydrogen-bond donors, such as acids, amines, and alcohols) [9] have lately been the solvent of choice in a number of chemical processes because of special features: for example, they are nonreactive with water, nonvolatile, and biodegradable as well as excellent solvents for a wide variety of solutes, such as different substrates, enzymes, and even microorganisms of catalytic and biocatalytic interest.[10] Of particular interest for the purpose of this work are those processes for which the capability both as solvents for CNT dispersion [11] and structure-directing agents in the synthesis of different materials [12] was demonstrated. Actually, ILs and DESs have been used as solvents for preparation of CNT-based carbon composites [13] and even as carbonaceous precursors of both nontextured and textured carbons. [14] In particular, we have recently described the preparation of DESs based on mixtures of resorcinol and choline chloride, the rupture of which (via resorcinol polycondensation and subsequent segregation of choline chloride) resulted in the formation of bimodal porous ca...

Nitrogen- and phosphorus-co-doped carbons with tunable enhanced surface areas promoted by the doping additives

“…IL based syntheses of carbon materials have been established in manifold ways in recent years of research. [1][2][3][4][5][6][7][21][22][23][39][40][41][42][43][44][45][46][47][48] Especially liquid salts with dicyanamide anions are a powerful precursor for N-doped carbons, [1][2][3][4][5][6][7] and for advanced co-doping with S. 27 Herein we present a modified IL route using phosphonium additives, paving the way towards P-and N-co-doped carbonsa class of materials only rarely reported in the literature so far. 36 BMP-dca with 40 mol% of tetrabutyl-phosphonium-bromide (TBuPBr) as a phosphorus source was therefore carbonised at 1000 1C in a constant flow of inert gas (see ESI † for details).…”

Progress in Bionanocomposite and Bioinspired Foams

“…[ 28 ] In this case, electrodes can be either bare carbon or carbon-carbon nanotube nanocomposite foams, the preparation of which with a hierarchical structure (such as those found in Nature) is not based on ice segregation but on the segregation (in a spinodal decomposition-like process) of a certain compound that, besides the carbonaceous precursor, forms a deep eutectic solvent (DES). [ 29 ] It is worth noting that the recovering of one of DES counterparts (and its reutilization in subsequent synthetic reactions) confers an interesting ''green'' character to this sort of synthetic processes. [ 30 ] …”

Carbon aerogel evolution: Allotrope, graphene-inspired, and 3D-printed aerogels

“…Gutiérrez et al 47 achieved enhanced performance in CNT-based aerogels by adapting the organic sol-gel method to deep eutectic solvents (DESs) that readily disperse CNTs. Gutiérrez et al report that DESs catalyze the polycondensation of furfuryl alcohol to form a bicontinuous porous architecture consisting of colloidal particles.…”

“…Thus by using the RF sol-gel method to form sp 2 carbon junctions between CNTs, CNT aerogels that simultaneously exhibited good electrical conductivity and mechanical robustness were realized. 42,47,48 Recently, De Marco et al 49 demonstrated another route to synthesis of CNT aerogels with covalent carbon bonds starting from SWCNT anions in N,N-dimethylacetimide (DMAc). A major advantage of working with SWCNT anions in DMAc is that one can start with a true solution of individualized CNTs at high concentrations without damaging the CNTs with sonication or oxidation.…”