木质素制备燃料电池阴极电催化炭材料研究(Ⅲ)——改性酶解木质素炭的微观结构演变

doi:10.3969/j.issn.0253-2417.2021.06.003

摘要/Abstract

摘要：

为了研究木质素基炭微观结构演变规律，以阔叶材酶解木质素及其尿素改性和三聚氰胺改性木质素为原料，在300~900 ℃之间炭化制备木质素基炭。采用X射线衍射、氮气吸附/脱附等温线、电阻率测试和扫描电镜分析了木质素基炭的微观结构、导电性和孔隙结构，全面分析了改性处理对木质素基炭的微观结构和孔隙结构演变过程的影响。研究结果表明：不管木质素是否改性，当炭化温度从600 ℃升高到700 ℃时，木质素基炭的导电性急剧提高，并从绝缘体转变为半导体，木质素基炭的类石墨微晶结构快速发展。然而，尿素和三聚氰胺改性导致类石墨微晶中碳网平面层间距的缩小，且氮含量越高的三聚氰胺改性变化更加明显；同时可以明显提高炭化温度低于700 ℃时炭化得到的木质素基炭的导电性，并降低炭化温度高于700 ℃时炭化得到的炭的导电性。非常突出的是，尿素和三聚氰胺改性显著阻碍了木质素基炭孔隙结构的发展，甚至完全抑制了微孔的形成。在700 ℃下制得的未改性、尿素改性和三聚氰胺改性木质素基炭的比表面积分别为524、102和69 m²/g。

关键词: 木质素, 炭材料, 电催化, 尿素, 三聚氰胺, 微观结构

Abstract:

Three series of lignin-based chars were prepared from three raw materials, hardwood enzymatic hydrolysis lignin and their urea-modified and melamine-modified counterparts, through carbonization in the temperature range of 300-900 ℃ in order to elucidate the microstructure evolution of lignin chars. X-ray diffraction, nitrogen adsorption, electric resistivity analysis and scanning electron microscope were employed to characterize the graphite-like microcrystallite structure, electric conductivity and pore structure of their lignin-based chars. The results consistently showed that when the carbonization temperature was increased from 600 ℃ to 700 ℃, the electronic resistivity of the chars was sharply promoted leading to the rapid transition of lignin-based chars from an insulator to a semiconductor, and the development of the graphite-like microcrystallite component in the chars was remarkably enhanced, whether lignin as raw materials was modified by nitrogen-containing substances or not. However, urea or melamine modification lead to a reduction of interlayer spacing in the graphite-like microcrystallites, with a more reduction for melamine modification of more nitrogen content. Moreover, urea or melamine modification could obviously promote the electron conductivity of the chars prepared below 700 ℃ but lessen a little for the char prepared above 700 ℃. Outstandingly, urea and melamine modification remarkably suppressed the development of pore structure of lignin-based chars, especially totally the formation of microporosity. Specifically, the surface area of the chars prepared from the unmodified lignin, urea-modified one and melamine-modified one have a big difference with the value of 524, 102 and 69 m²/g, respectively.

Key words: lignin, carbon materials, electrocatalysis, urea, melamine, microstructure

中图分类号:

TQ35

左宋林, 金凯楠, 桂有才, 申保收, 王珊珊, 杨梦梅. 木质素制备燃料电池阴极电催化炭材料研究(Ⅲ)——改性酶解木质素炭的微观结构演变[J]. 林产化学与工业, 2021, 41(6): 19-26.

Songlin ZUO, Kainan JIN, Youcai GUI, Baoshou SHEN, Shanshan WANG, Mengmei YANG. Studies on Lignin-based Carbon Materials as Electrocatalysts of Fuel Cells Cathode Ⅲ: Microstructure Evolution of Lignin Derived Chars[J]. Chemistry and Industry of Forest Products, 2021, 41(6): 19-26.

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样品 sample	电阻率/(mΩ·cm^-1) resistivity	样品 sample	电阻率/(mΩ·cm^-1) resistivity	样品 sample	电阻率/(mΩ·cm^-1) resistivity
L-300		L-U-300		L-M-300
L-400		L-U-400		L-M-400
L-500		L-U-500		L-M-500	5550
L-600	52200	L-U-600	5090	L-M-600	353
L-700	11.990	L-U-700	12.540	L-M-700	52.800
L-800	0.814	L-U-800	1.061	L-M-800	3.410
L-900	0.315	L-U-900	0.380	L-M-900	0.558

样品sample	S_BET/(m²·g^-1)	V_tot/(cm³·g^-1)	V_mic/(cm³·g^-1)	V_mes/(cm³·g^-1)
L-300	61	0.039	0.005	0.034
L-400	34	0.046	0.003	0.043
L-500	383	0.277	0.208	0.069
L-600	457	0.238	0.186	0.052
L-700	524	0.287	0.214	0.073
L-800	416	0.254	0.192	0.062
L-900	316	0.250	0.175	0.075
L-U-300	140	0.139	0.012	0.127
L-U-400	43	0.055	0.002	0.053
L-U-500	66	0.067	0.002	0.065
L-U-600	33	0.055	0.007	0.048
L-U-700	102	0.125	0.036	0.089
L-U-800	50	0.069	0.007	0.062
L-U-900	88	0.105	0.007	0.098
L-M-300	64	0.087	0.001	0.086
L-M-400	77	0.069	0.007	0.062
L-M-500	69	0.064	0.008	0.056
L-M-600	33	0.034	0.002	0.032
L-M-700	69	0.053	0.008	0.045
L-M-800	49	0.065	0.005	0.060
L-M-900	57	0.067	0.002	0.065

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