| The supercapacitor, also knowen as double-layer capacitor, is an ideal energy storage device which wouldn’t cause any environmental pollution. The supercapacitor with higher energy/power densities, excellent cycling stability, non-noisy pollution, simple structure, maintenance free et al is superior to the traditional/secondary battery. With the world energy shortage problem increasingly serious, the development of new energy storage devices such as supercapacitor has attracted more and more scientific attentions. Research shows that the most key factor influencing the electrochemical performances of the supercapacitor is the nature of electrode materials. So how to fabricate the electrode material with excellent electrochemical characteristics is one of the most significant research works.As for this problem, this paper adopts the direct template carbonization process to prepare the porous carbon materials, by changing the mass ratio between the precursor and the template, carbonization temperature, and the type of coordination compounds to acquire the control structure of carbon materials, with higher specific surface areas, large total pore volume and excellent electrochemical characteristics. The major research contents of the work are as follows:1. A series of highly nanoporous carbons have been prepared by converting benzoate-metal complexes, including zinc benzoate, magnesium benzoate and aluminium benzoate through a template carbonization process. The carbonization temperature plays a pivotal role in determining the carbon structures as well as the resultant electrochemical behaviors in supercapacitors. The carbon-Zn-900 sample derived from zinc benzoate complex has a high specific surface area (1466.4 m2 g-1), large pore volume (2.54 cm3 g-1) and hierarchical pore size distribution. It can also deliver a large specific capacitance of 314.1 F g at a current density of 0.5 A g-1, together with a large energy density of 67.2 Wh kg-1 when measured in a three-electrode system using 6 mol L-1 KOH as electrolyte. Besides, the carbon-Zn-900 sample has been tested in a two-electrode system using [EMIm]BF4/AN as electrolyte at different operation temperatures of 25/50/80℃.In addition, nitrogen-doped nanoporous carbon has been produced by the carbonization of a 5-[(4-nitrophenyl)azo]salicylate-zinc complex, which is prepared by mixing Zn2+ion and sodium 5-[(4-nitrophenyl)azo]salicylate in aqueous solution. Furthermore, zinc metal was added to the complex before carbonization to improve the electrochemical performance. It was found that the zinc metal-2:1-900 sample exhibits the best capacitive behavior. It has amorphous features and porous structure, and displays a large Brunauer, Emmett and Teller surface area of 1177.2 m2 g-1,a total pore volume of 0.89 cm3g-1, and a nitrogen content of 3.63%. Based on the three-electrode system measurement, the zinc metal-2:1-900 sample delivers a large specific capacitance of 266.2 Fg-1 at 1 Ag-1 and has good cycling stability. It also has a large energy density of 33.4 Wh kg for a power density of 0.5 Wh kg-1 when measured in a two-electrode system. More importantly, the superior electrochemical performances obtained at the operational temperatures of 25/50/80℃ in a two-electrode system can greatly increase their applications as a practical supercapacitor. The present synthesis protocol can be extended to prepare other complexes such as 5-[(4-nitrophenyl)azo]salicylate-magnesium/calcium/aluminium, which also readily yield nanoporous carbons.2. Producing nanoporous carbons that possess high porosity and superior electrochemical performance is a challenge for scientists.In this work, a simple and efficient template carbonization method, without any physical/chemical activation treatment, has been implemented to produce nanoporous carbons doped with nitrogen species. In details,4-(4-Nitrophenylazo)resorcinol serves as a carbon/nitrogen source and Mg(OH)2 as a hard template. All resultant carbon samples are amorphous, highly porous in nature and display sheet-like nanostructures. The carbon-1:3-L sample whose precursor is obtained by solution method exhibits better porosity, and larger nitrogen content, than those obtained by solid state method (the carbon-1:3-S sample). The carbon-l:3-L sample exhibits large specific surface area (SBET) of 1427.7 m2g-1,and high total pore volume (Vt) of 5.91 cm g-1, whereas those of the carbon-l:3-S sample are of 1036.6 m g-1 and 4.76 cm g-1, respectively. Notably, the present pore volumes are much higher than most of the previously reported for nanoporous carbons. As a consequence, the carbon-1:3-L sample delivers superior electrochemical behaviors, whose specific capacitance reaches up to 378.5 F g-1 when measured at 1 A g-1 in a three-electrode system, compared with that of 263.4 F g-1 of the carbon-1:3-S sample. The present Mg(OH)2-assisted template carbonization method is simple and easy to operate, indicating its potential application for producing nanoporous carbons.What’s more, A template carbonization route for producing nanoporous carbons with hierarchical porosities has been implemented by using thiocarbanilide as carbon/nitrogen precursor, and commercially available Mg(OH)2 or Ca(OH)2 powder as template. The mass ratio of thiocarbanilide and Mg(OH)2 or Ca(OH)2, as well as the carbonization temperature plays crucial roles in determining the pore structures and the resultant capacitive behaviors. It reveals that carbon-Mg sample whose template is Mg(0H)2 (with mass ratio of 1:2 at 700℃) exhibits the amorphous feature with low graphitization degree. Similar result also occurs in the case of the carbon-Ca sample. The carbon-Mg sample presents high specific surface area (1018.48 m2g-1), large pore volume (5.29 cm3g-1), while those of the carbon-Ca samples are 429.11 m2g-1 and 2.52 cm3g-1. The carbon-Mg sample delivers a high specific capacitance of 327.4 F g-1 at a current density of 1.0 A g-1, as well as a large energy density of 45.47 Wh kg-1 at a power density of 0.5 kW kg-1 in comparison with carbon-Ca sample of (260.0 F g-1) and (36.11 Wh kg-1). What’s more, the carbon-Mg sample exhibits higher capacitance retention of 95.45% after 10000 charge/discharge cycles than carbon-Ca sample of 91.62%.3. We demonstrate a multi-template carbonization approach to produce nanoporous carbon, without any complicated activation process. The mass ratio of Mg citrate, zinc Metal, and Zn(OAc)2·2H2O as well as the carbonization temperature play decisive roles in determining the carbon pore structures. The electrochemical performances were investigated in a two-electrode system, using a mixture of 1-ethyl-3-methyl imidazolium tetrafluoroborate and acetonitrile as electrolyte. More importantly, the cell configuration was measured at different operation temperatures of 25/50/80℃. The carbon-7# sample that was obtained using Mg citrate, zinc metal, and Zn(OAc)2-2H2O as starting materials (with a mass ratio between them of 1:1:1) at 800℃delivers the best electrochemical behavior mostly reflected in its large Brunauer-Emmett-Teller (BET) surface area of 1,776.3 m g-1, high pore volume of 3.82 cm3 g-1, and hierarchical pore size distribution. It can exhibit good cycling stabilities and large specific capacitances of 152.2,243.5, and 279.4 F g-1, respectively, at the operation temperatures of 25/50/80℃. The corresponding energy densities are as high as 47.5, 75.9, and 87.2 Wh kg-1, respectively, in the case of power energy of 1.5 kW kg-1. The operation temperatures of 25/50/80℃ revealed in the present work can greatly broaden the supercapacitor application of nanoporous carbons under extreme circumstances. |
PDF Full Text Request