Heteroatom Polymer-Derived 3D High-Surface-Area and Mesoporous Graphene Sheet-Like Carbon for Supercapacitors

Abstract

Current supercapacitors suffer from low energy density mainly due to the high degree of microporosity and insufficient hydrophilicity of their carbon electrodes. Development of a supercapacitor capable of simultaneously storing as much energy as a battery, along with providing sufficient power and long cycle stability would be valued for energy storage applications and innovations. Differing from commonly studied reduced graphene oxides, in this work we identified an inexpensive heteroatom polymer (polyaniline-PANI) as a carbon/nitrogen precursor, and applied a controlled thermal treatment at elevated temperature to convert PANI into 3D high-surface-area graphene-sheet-like carbon materials. During the carbonization process, various transition metals including Fe, Co, and Ni were added, which play critical roles in both catalyzing the graphitization and serving as pore forming agents. Factors including post-treatments, heating temperatures, and types of metal were found crucial for achieving enhanced capacitance performance on resulting carbon materials. Using FeCl as precursor along with optimal heating temperature 1000 °C and mixed acid treatment (HCl+HNO), the highest Brunauer-Emmett-Teller (BET) surface area of 1645 mg was achieved on the mesopore dominant graphene-sheet-like carbon materials. The unique morphologies featured with high-surface areas, dominant mesopores, proper nitrogen doping, and 3D graphene-like structures correspond to remarkably enhanced electrochemical specific capacitance up to 478 Fg in 1.0 M KOH at a scan rate of 5 mV s. Furthermore, in a real two-electrode system of a symmetric supercapacitor, a specific capacitance of 235 Fg using Nafion binder is obtained under a current density of 1 Ag by galvanostatic charge-discharge tests in 6.0 M KOH. Long-term cycle stability up to 5000 cycles by using PVDF binder in electrode was systematically evaluated as a function of types of metals and current densities.

Engineering nanostructures of PGM-free oxygen-reduction catalysts using metal-organic frameworks

“…In parallel to the development of low-platinum group-metal (PGM) catalyst with continuously increased activity and durability [6][7][8][9][10][11], significant effort has been on PGM-free ORR electrocatalysis in the past decade, which has results in great progress [12][13][14][15][16][17]. Compared to other studied oxides, sulfides, and carbides [18][19][20][21][22][23][24], carbon-based catalysts have many obvious advantages including low cost, high electrical conductivity, high surface areas, easy functionalities and processibility [25,26]. Therefore, carefully engineering nanostructure, morphology, and doping of carbon materials would yield high performance PGM-free ORR catalysts with significantly increased density of active sites and strengthened bonding structures.…”

Engineering Favorable Morphology and Structure of Fe‐N‐C Oxygen‐Reduction Catalysts through Tuning of Nitrogen/Carbon Precursors

“…In this work, for the first time, we employed different nitrogen/carbon precursors to prepare various Fe‐N‐C catalysts with an aim to tuning catalyst morphology and structure, which will further link with catalyst activity and stability. Among available precursors, three often studied, that is, polyaniline (PANI), dicyandiamide (DCDA), melamine (MLMN), were identified to be effective to yield sufficient ORR catalytic activity. Although these precursors have been investigated individually, a comparative study of catalyst morphology and performance from various binary combinations under similar reaction conditions has not been done yet.…”

“…furtherl ink with catalyst activity and stability.A mong available precursors, three often studied, that is, polyaniline (PANI), [8,[26][27][28][29][30][31][32] dicyandiamide (DCDA), [33,34] melamine (MLMN), [35] were identified to be effective to yield sufficient ORR catalytic activity.A lthought hese precursors have been investigated individually, ac omparatives tudy of catalyst morphology andp erformance from variousb inary combinations under similarr eaction conditions has not been done yet. Moreover,g iven the identical nature of active sites, our hypothesis is that catalystp erformance governed by morphologya nd structures (e.g.,n itrogen doping, porosity,s urface areas, graphitization degree, and nanostructure) could be optimized through possible synergistic effects by using multiple nitrogen/carbon precursors.…”

3D direct writing fabrication of electrodes for electrochemical storage devices

“…The electrolyte plays the role of a medium for ion transfer between two electrodes [9]. Table 1 shows that supercapacitors have several advantages, such as long cycle life (>10k cycles), rapid charging-discharging rate at relative high power density (10k W kg -1 ) and operate in a safe manner [10][11][12]. However, current supercapacitors suffer from a wellknown disadvantage of poor energy density which is generally around 5-10 Wh kg -1 [13].…”