N,P-Doped Carbon-Based Freestanding Electrodes Enabled by Cellulose Nanofibers for Superior Asymmetric Supercapacitors

Abstract

The preparation of freestanding electrodes with excellent conductivity and mechanical strength plays a vital role in simplifying the electrode fabrication process and reducing the electrode cost. Herein, a N,P-doped self-supporting carbon electrode is synthesized via a combined templating/activating coassisted carbonization procedure and vacuum filtration process. The glucose precursor was first transformed into N,P-doped carbon nanosheets (NPCNs) with a large specific surface area (2073 m 2 g −1 ) and rich heteroatom-doping (phosphorus: 2.1 atom %; nitrogen: 4.1 atom %) with the assistance of P 2 O 5 and dicyandiamide, and then the compact freestanding electrode (NPCN-f) with outstanding mechanical strength was constructed via vacuum filtration using a mixture of NPCN and conductive cellulose nanofibers. The resultant freestanding electrode exhibits a high capacitance of 318 F g −1 at 1 A g −1 and retains 188 F g −1 at 100 A g −1 in an alkaline electrolyte. Furthermore, excellent electrochemical performances are also exhibited in the asymmetric supercapacitor assembled using NPCN-f as the negative electrode and NPCN/MnO 2 -f synthesized by a self-controlled redox process as the positive electrode. The asymmetric device can deliver a high energy density of 41.5 Wh kg −1 at a power density of 182.0 W kg −1 and excellent cyclability with 93% capacitance retention after 10 000 cycles in a neutral electrolyte. This work sheds light on the design of self-supporting electrodes for advanced energy storage devices.

Oxygen Engineering Enables N-Doped Porous Carbon Nanofibers as Oxygen Reduction/Evolution Reaction Electrocatalysts for Flexible Zinc–Air Batteries

“…Furthermore, the electrical conductivity of NPCNF-O and NCNF was measured using the four-probe technique. As-designed NPCNF-O shows the high electrical conductivity of 117 S m −1 , which is comparable or superior to that of NCNF (98 S m −1 ) and previously reported carbonbased materials (such as NPCN -f (113 S m −1 ), 81 SGN-900 (152.9 S m −1 ), 82 CNS-800 (226 S m −1 ), 83 and activated carbon (33 S m −1 )). 83 This implies that good conductivity, developed porous structure, and large specific surface area can significantly promote charge and mass transfer during the electrode reaction.…”

Highly Porous Activated N-Doped Carbon as an Ideal Electrode Material for Capacitive Energy Storage and Physisorption of H2, CO2, and CH4

“…The pyrrolic and pyridinic N generally follow the redox process in alkaline electrolyte. 14 It was observed that the CV curves of NPC-X (X = 1, 2, 3, and 4) show a rectangular shape and the area under the CV curves is maximum for NPC-2. As the KOH/C ratio increased from 1 to 2, the area under the CV curve increased to maximum and then decreased a little for NPC-3 and NPC-4.…”

“…A slight hump near −0.6 V can be attributed to the redox behavior of material arising from the presence of N atoms in the carbon structure. The pyrrolic and pyridinic N generally follow the redox process in alkaline electrolyte …”

“…Also, to access the internal pores present in the carbon material, heteroatom doping has been a feasible method, and as a result, the heteroatoms present in the material improve the wettability of the material and provide pseudocapacitance to the carbon material. Moreover, the presence of heteroatoms such as S, O, and N can provide hierarchical structure which facilitates rapid ion transport. − Overall, it is necessary to design better functionalized carbon based electrode materials with high specific capacitance and SSA values which can meet the emerging demand for fast charge storage devices.…”

Cellulose-Derived Nanostructures as Sustainable Biomass for Supercapacitors: A Review

“…This free-standing electrode showed a high capacitance (318 F/g at 1.0 A/g) and maintained 188 F/g at 100 A/g in an alkaline electrolyte. Furthermore, an asymmetric supercapacitor composed of NPCN-f (as the negative electrode) and NPCN/MnO2-f syntheiszed by a self-regulated redox method as the positive electrode exhibited a high energy density (41.5 Wh/kg at 182.0 W/kg power density) and remarkable capacitance retention of 93% after 10,000 cycles in a neutral electrolyte [ 131 ]. Surface area plays an important role in developing conductive CNFs, and with the application of doping materials, their conductivity could be remarkable improved.…”