Phosphorus, nitrogen and oxygen co-doped polymer-based core-shell carbon sphere for high-performance hybrid supercapacitors

Co-doping heteroatoms of the carbon lattice has been proven as an efficient strategy that can improve the capacitive performance, due to the synergetic effect of several dopants. Herein, a series of phosphorus, nitrogen and oxygen, co-doped polymer-based carbon spheres were prepared by the suspension polymerization method and chemical activation with phosphoric acid at different temperatures. The presence of heteroatoms was confirmed by X-ray photoelectron spectroscopy and elemental analysis. The structure of the carbons was characterized by scanning electron microscopy, Raman spectroscopy and nitrogen adsorption. Carbon obtained at 800 degrees C with a P, N and O doping level of 11.17 at%, 2.79 at% and 11.77 at% respectively, shows a capacitance of 157 F g(-1) at the current density of 0.05 A g(-1). Moreover, the electrode can survive at a wide potential window of 1.5 V with only 15% decrease in capacity after 10000 cycles at a current density of 5 A g(-1), providing a high energy density of 10 Wh kg(-1) and a high power density of 750 W kg(-1). For the outstanding features, it is expected that the phosphorus, nitrogen and oxygen co-doped carbons will be a very suitable material not only for supercapacitors, but also for lithium batteries and oxygen reduction reaction. In addition, the co-doping method described here might be extended to the preparation of other kinds of porous carbon materials. (c) 2018 Elsevier Ltd. All rights reserved

Ethyl -butyl ether synthesis using carbon catalysts from lignocellulose

Porous structure, surface chemistry and catalytic properties of carbon catalysts with various acid groups in ethyl tert -butyl ether synthesis were studied. Carbon catalysts were obtained by phosphoric acid activation followed by sulphonation of lignocellulosic feedstocks of different origin. Porous structure of carbon catalysts was characterized by nitrogen adsorption. Surface chemistry was investigated by potentiometric titration. Carbon catalysts obtained from lignosulphonate and sucrose showed the highest catalytic activity in ethyl tert-butyl ether synthesis (reaction rate at 120℃ is 4.3–5.2 × 10 −6  mol·g −1 ·s −1 ), is comparable to activity of Amberlyst-15 (5.0 ×10 −6  mol·g −1 ·s −1 ). Calculated turnover frequency (TOF) of sulphonic groups (pK a  = −2.5) equals 0.00116 s −1 , polyphosphate groups (pK a  = 1.9) 0.01019 s −1 , strong carboxylic (pK a  = 3.6) 0.00202 s −1 and 0 s −1 for weak carboxylic (pK a  = 6) groups. The activity of acid groups with pK a lower than 3.6 is higher than the activity of sulphonic groups of Amberlyst-15 (TOF 0.00115 s −1 )

Structural Evolution of Polyimide-Derived Carbon during Phosphoric Acid Activation

Carbon adsorbents were obtained by carbonization of polyimide polymer with and without the presence of phosphoric acid at temperatures in the range of 400–1000 °C. Carbons produced in the presence of phosphoric acid have been demonstrated to contain up to 13.2% phosphorus. The structure of phosphorus-containing compounds was investigated by XPS and 31P MAS NMR methods. Deconvolution of the P 2p peak with variable binding energy showed the presence of only phosphates/polyphosphates. However, a low value of the O/P ratio is an indirect indication of the possible presence of phosphonates. A 31P MAS NMR study revealed the existence of several kinds of phosphates as well as a minor quantity (1–9%) of phosphonates. All discovered phosphorus-containing compounds are acidic and therefore give carbon the ability to absorb metal cations. The study of copper ion adsorption demonstrated that phosphorus-containing carbon shows a significant adsorption capability even in extremely acidic conditions. At pH 3–6, phosphorus-containing carbon may completely remove copper from the aqueous solution. Phosphorus-containing carbon has a higher adsorption capacity for copper ions than ion exchange resins with carboxyl or sulfo groups

Assessment of the structural evolution of polyimide-derived carbons obtained by phosphoric acid activation using Fourier transform infrared and Raman spectroscopy

Two series of carbons obtained by carbonization of porous copolymer of 4,4′-bis(maleimidodiphenyl) methane (50 mol%) and divinylbenzene (50 mol%) with and without phosphoric acid (impregnation ratio 1.1) at temperatures 400–1000℃. The carbons were characterized using elemental analysis, nitrogen adsorption, potentiometric titration, Fourier transform infrared and Raman spectroscopy. It has been shown that phosphoric acid causes structural and chemical changes in polyimide copolymer as compared to thermally treated carbons. Structural changes: phosphoric acid promotes transformation of polyimide copolymer to carbon structure at lower temperatures as compared to thermally treated carbons. Phosphoric acid is responsible for formation of highly developed micro/mesoporous structure that is different from that of thermally treated carbons. Chemical changes: phosphoric acid causes elimination of hydrogen and nitrogen, introduction of phosphorus and oxygen as phosphate-like structure. Significant amount of phosphorus imparts acid properties to carbon

Oxygen and phosphorus enriched carbons from lignocellulosic material

10 pages, 10 figures, 3 tables.-- Printed version published Sep 2007.Activated carbons were prepared by phosphoric acid activation of fruit stones in air at temperatures 400–1000°C. The surface chemistry was investigated by elemental analysis, cation exchange capacity, infrared spectroscopy and potentiometric titration. The porous structure was analyzed from adsorption isotherms (N2 at 77 K and CO2 at 273 K). It was demonstrated that all carbons show considerable cation exchange capacity, the maximum (2.2 mmol g−1) being attained at 700°C, which coincides with the maximum contents of phosphorus and oxygen. The use of air instead of argon during thermal treatment increased the amount of cation exchangeable surface groups for carbons obtained at 400–700°C. Proton affinity distributions of all carbons show the presence of three types of surface groups with pK 1.8–3.1 (carboxylic and polyphosphates), 4.8–6.3 (second dissociation of carboxylic, weak acid in polyphosphates and enol structures) and 8.1–9.7 (phenols and enol structures). Carbons obtained in air at 400–600°C show enhanced copper adsorption from 0.001 mol L−1 Cu(NO3)2 in acidic solutions as compared to carbons obtained in argon. Carbons obtained in air show well-developed porous structure that is equivalent or higher as compared with carbons obtained in argon; the difference being progressively increased with increasing treatment temperature.This research was made possible in part by the NATO Collaborative Linkage Grant EST.CLG.979588.Peer reviewe