| Utilizing sustainable biomass for the energy applications has received much attention because of the scarcity of fossil energy. Due to biomass is an environmentally friendly, renewable and low-cost resource, the use of biomass or biomass wastes as precursors for the preparation of porous carbons for energy storage and conversion has received extensive attention.Researchers recently found the nitrogen-rich carbons(NCs) have superior performance than those of primary carbons in various energy applications, including supercapacitors, lithium ion batteries and oxygen reduction reaction(ORR). The critical factor for the improvement of the performance of biomass-based NCs is to prepare carbons with high surface areas, appropriate pore structure and high nitrogen content. However, the use of traditional activation regents(KOH/Na OH) may result in more or less severe disadvantages, such as the low nitrogen content, the strong corrosion of the instrument and equipment and high cost, which will hamper their practical use widely.It is known to be an urgent challenge to derive carbons with high nitrogen content, high specific surface areas and high specific capacity abd rate performance for supercapacitors from a facile, green and low cost route, which uses sustainable biomass/biomass wastes as carbon precursors. After analysis on the factors for the relevance between the structures and properties of carbon materials, in this thesis, a series of NCs were prepared by a facile method using biomass/biomass wastes as carbon resources, to improve the performance of carbon-based materials for supercapacitors. The main contents are as follows:(1) A novel approach to synthesize hierarchical porous nitrogen-rich carbons(HPNCs) via one-step fabrication process using calcium chloride(Ca Cl2) as the catalyst, sugar cane bagasse as the carbon source and urea as the nitrogen source is developed. The obtained HPNCs could be effectively tailored by adjusting the carbonization temperature, the ratio of sugar cane bagasse, urea, and Ca Cl2. For the typical sample(S122), obtained from pyrolysis of the mixture of sugar cane bagasse, urea, and Ca Cl2 in a mass ratio of 1:2:2 at 800 oC for 2 h under N2 atmosphere, shows a high specific capacitance(with 323 F g-1 at the discharge/charge current densities of 1 A g-1), excellent rate capability(with 213 F g-1 at the discharge/charge current densities of 30 A g-1), and outstanding cycle performance(a negligible capacitance loss after 10000 cycles at 5 A g-1).(2) One-step calcium chloride(Ca Cl2) activation sugar cane bagasse with thiourea, for the preparation of porous N,S-codoped carbons(PNSCs) is realized. The structure features and N and S contents of the PNSCs were seriously affected by the carbonization temperature. For the typical sample(NS122-800), obtained from pyrolysis of the mixture of sugar cane bagasse, thiourea, and Ca Cl2 in a mass ratio of 1:2:2 at 800 oC for 2 h under N2 atmosphere, shows a medium specific capacitance(with 189 F g-1 at the discharge/charge current densities of 1 A g-1), excellent rate capability(with 139 F g-1 at the discharge/charge current densities of 30 A g-1).(3) A series of activated porous nitrogen-rich carbons were also fabricated by one-step calcium chloride(Ca Cl2) activation method when lacebark pine, wood chips, and wheat straw were respectively used different carbon precursors. For the typical sample(S-122), obtained from pyrolysis of the mixture of lacebark pine, urea, and Ca Cl2 in a mass ratio of 1:2:2 at 800 oC for 2 h under N2 atmosphere, shows a high nitrogen contents(8.90%), medium-range specific surface areas(815.49 m2 g-1) and total pore volume(0.65 cm3 g-1).(4) The carbon materials(S122-1:1), obtained from further chemical activation of the S122 using KOH activation agents(S122:KOH with the mass ratio of 1:1), increases the specific surface areas and reduces the nitrogen content obviously. The S122-1:1 displays an outstanding specific capacitance(as high as 295 F g-1 at a current density of 1 A g-1), and excellent rate capability(with 230 F g-1 at the discharge/charge current densities of 100 A g-1). |
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