Understanding structure and porosity of nanodiamond-derived carbon onions

Quinone‐Decorated Onion‐Like Carbon/Carbon Fiber Hybrid Electrodes for High‐Rate Supercapacitor Applications

“…[42] However,t he loading with onions is not just filling the free interfiber space, buti s also interconnected throughl ocal sintering of the OLCs (Figure 3F), as shown in ar ecent study. [22] The partially graphitic state of OLC and CF,a nd also the OLC/CF hybrid fiber mats, is shown by the presence of characteristic Da nd Gm odes between 1200 and 1700 cm À1 ,a nd ad istinct range of overtones andc ombinational modes between 2300 and 3400cm À1 ( Figure 4A). The Gm ode between 1580 and 1600 cm À1 is af irst-order peak with E 2g symmetry and representative of sp 2 -hybridized carbon.…”

“…During this process, ND powders alone lose around 30 %o ft heir initial mass, owing to the desorptiono fo xygen-containing surfacef unctional groups and carbon etching. [22] For comparison, the mass loss of PANa lone is even more dramatic, with levels around 60 %c oming from the evolution of oxygen-,n itrogen-, and hydrogen-containing gases. [42] The hybrid systemso fP AN50, PAN250, and PAN500…”

“…[19] The excellent power-handling ability of OLC is related to the absence of intraparticle porosity and the dominance of externals urface area, giving rise to beneficially high ion mobility, [20] even at operational temperatures below 0 8C. [21] However,t he absence of internal particlep orosity [22] and the nanoscopic particle diameter of around5 -10 nm limits the total specific surfacea rea (SSA) to around2 00-600m 2 g À1 . [14,16,17] Consequently,o nly am oderate specific capacitance between 20 and 60 Fg À1 can be found in organic electrolyte, which corresponds to al ow energy density of, typically,b elow 10 Wh kg À1 .…”

“…[23] Yet, even the latter value corresponds to an energy density roughly one order of magnitude below that of lithium-ion batteries, which resultsi nv ast researche fforts being invested in exploring facile ways to enhance the energystoragec apacity of supercapacitors. [5,24] Currently,t he literatureshows two general approaches to increase the capacitance of carbon materials:1 )increasingt he operation voltage by using advanced electrolytes or 2) adding redox-active materials for so-called pseudocapacitors.I nt he case of carbons with moderate or non-optimized pore structures, there is at hird approach:3 )increasing the SSA through chemicalo rp hysicala ctivation.F or example, physical activation in air [22] or chemical activation with H 2 SO 4 /HNO 3 or KOH mixtures [25] was demonstrated to increase the surface area of OLCs to 650-820m 2 g À1 with ac apacitance of more than 120 Fg À1 in aqueous electrolytes. The finite ability of nanoporous carbons to screene lectric charges, however,p resentsa n upperc apacitance limit in this approach.…”

Highly densified carbon electrode materials towards practical supercapacitor devices

“…With a highly graphitized structure, carbon onions have high electrical conductivities and SSAs in the range of 500-600 m 2 g −1 . However, the specific gravimetric capacitance of carbon onions is relatively low, which is about 30-40 F g −1 [17][18][19][20]. The mass density of carbon onions varies in the range from 1.9 to 2.9 g cm −3 [21], depending on the graphitizing temperature.…”