Synthesis of nitrogen doped hierarchically porous carbon nanosheets for supercapacitor by mixed salt template

doi:10.11949/0438-1157.20201320

Abstract

Abstract:

Hierarchically porous carbons have shown great potential in the fields of electrochemical energy storage. The template strategy coupled with activation technique is considered as one of the most effective ways to produce hierarchically porous carbon. However, this method uses strong acids and strong bases, causing pollution to the environment. Therefore, it is urgent to develop an acid-free and base-free technique to prepare hierarchically porous carbons. Herein, nitrogen doped hierarchically porous carbon nanosheets (NHCNs) are synthesized from cal tar pitch by using the mixture salt of NaCl and Na₂CO₃ as template coupled with K₂CO₃ activation. The templates and activators can be removed by water washing without the use of strong acids and bases, and this work provides an acid-free and base-free technique for synthesizing hierarchically porous carbon nanosheets. The as-made NHCNs possess high specific surface area (1597 m²·g^-1), abundant micro-/mesopores together with a moderate content of O, N heteroatom. These unique structures give NHCNs electrodes excellent supercapacitor performance. In the KOH electrolyte, NHCNs electrodes show high specific capacitance and good cycle stability.

Key words: supercapacitor, acid-free and base-free technique, activated carbon, activation, electrochemistry

摘要：

分级多孔碳在电化学储能方面展现了巨大的潜力。模板与活化法相耦合是制备分级多孔碳最有效的方法之一。然而，该方法使用强酸和强碱，对环境造成污染。因此，开发一种无酸无碱制备分级多孔碳的方法迫在眉睫。以氯化钠和碳酸钠混合盐为模板，煤沥青为碳前体，碳酸钾为活化剂，合成了氮掺杂分级多孔碳纳米片（NHCNs）。模板与活化剂可以通过水洗除去，无需使用强酸和强碱，该工作为合成分级多孔碳纳米片提供了一种无酸无碱的技术。合成的NHCNs具有大的比表面积（1597 m²·g^-1）、丰富的微/中孔、适量的氧和氮杂原子。这些独特结构赋予NHCNs电极优异的超级电容性能。在KOH电解液中，NHCNs电极显示了高的比电容和好的循环稳定性。

关键词: 超级电容器, 无酸无碱的技术, 活性炭, 活化, 电化学

CLC Number:

O 646

JIAO Shuai, YANG Lei, WU Tingting, LI Hongqiang, LYU Huihong, HE Xiaojun. Synthesis of nitrogen doped hierarchically porous carbon nanosheets for supercapacitor by mixed salt template[J]. CIESC Journal, 2021, 72(5): 2869-2877.

焦帅, 杨磊, 武婷婷, 李宏强, 吕辉鸿, 何孝军. 混合盐模板法制备超级电容器用氮掺杂分级多孔碳纳米片[J]. 化工学报, 2021, 72(5): 2869-2877.

Figures/Tables 9

Fig.1 The schematic for the preparation of NHCNs

Fig.2 FESEM images of NHCN3 (a), NHCN4 (b), NHCN5 (c); TEM image of NHCN4 (d); High resolution TEM image of NHCN4 (e)

Fig.3 Nitrogen adsorption-desorption isotherms (a); Pore size distribution (b); XRD pattern (c); Raman spectra of NHCNs (d)

Table 1 The pore structure parameters of NHCNs

Samples

D_ap/

S_BET/

(m²·g^-1)

S_mic/

(m²·g^-1)

V_t/

(cm³·g^-1)

V_mic/

(cm³·g^-1)

NHCN₃

NHCN₄

NHCN₅

Fig.4 Full XPS spectra of NHCNs (a); N 1s spectrum of NHCN4 (b)

Table 2 Contents of carbon, oxygen and nitrogen elements in NHCNs

Samples	Element content/%(atom)			N 1s content/%(atom)
Samples	C 1s	O 1s	N 1s	N-5	N-6	N-Q
NHCN₃	86.76	9.61	3.63	1.11	1.35	1.17
NHCN₄	89.46	6.82	3.72	1.46	0.86	1.40
NHCN₅	93.04	4.94	2.03	0.59	0.75	0.69

Fig.5 CV curves of NHCN electrodes at the scan rate of 2 mV·s-1(a); CV curves of NHCN4 electrode at different scan rates (b); GCD curves of NHCN electrodes at 0.05 A·g-1 (c); Specific capacitance of NHCN electrodes at various current densities (d)

Table 3 The specific capacitance of different carbon electrode materials

Samples	Specific capacitance/(F·g^-1)	Ref.
NHCN₄	239 (0.05 A·g^-1)	this work
PB-15	199 (0.5 A·g^-1)	[31]
ET-rGO	124 (0.1 A·g^-1)	[32]
HPC/500/1/6∶1	143 (0.625 A·g^-1)	[33]
P-C-600	168 (1 A·g^-1)	[34]
N-HPC-900	128.5 (0.2 A·g^-1)	[35]

Fig.6 Ragone plots of NHCN capacitors(a); Nyquist plots of NHCN electrodes (b); Bode plots of NHCN electrodes (c); Capacitance retention of NHCN4 electrode at 5 A·g-1 after 10000 cycles (d)

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