In-situ Simultaneous ESR and Conductivity Measurements for Polyaniline

本论文工作通过设计新型的电解池 ,首次实现了导电聚合物的电化学现场ESR_电导同步测量 .从获得的聚苯胺ESR信号及膜电阻随电极电势变化的精细图象看出 ,极化子晶格的形成与消亡决定了聚苯胺的导电行为 .从不同电势下聚苯胺的ESR饱和行为也得到Curie自旋与Pauli自旋相互转化的新证据 .With a new cell design, simultaneous electrochemical ESR and conductance measurements were realized for the first time. The in_situ cell consisted of a dual working electrode, a counter electrode and a reference electrode accommodated in a capillary of 1mm diameter. The dual working electrode was composed of two closely spaced Pt electrodes: a Pt disk electrode(0.5 mm diameter)sealed in a thin glass tube and a Pt layer deposited on the outside wall of the glass tube.The two working electrodes were separated by the glass gap about 20 μm thick. Two potentiostats were used to control electrode potential and maintain 10 mV potential difference between the two working electrodes. The conductivity of the polyaniline was deduced from the current passing through the polymer across the glass gap. With the new technique, an unprecedented detailed picture was obtained revealing the potential dependences of conductivity and ESR behaviors, including ESR intensity, lineshape, and saturation. Experimental results showed that the conduction mechanism could be well interpreted within the framework of the polaron lattice model. The ESR saturation data also provided a new experimental evidence for the transformation between Curie spins and Pauli spins.作者联系地址：武汉大学!化学与环境科学学院!湖北武汉430072,武汉大学!化学与环境科学学院!湖北武汉430072,武汉大学!化学与环境科学学院!湖北武汉430072Author's Address: College of Chemistry and Environmental Science,Wuhan University, Wuhan 430072, Chin

Magnetic Resonance Studies on Lithium Intercalation into Carbons

　本文综述了十数年来电子自旋共振(ESR)和7Li核磁共振(7Li-NMR)技术用于锂嵌碳研究的进展.ESR研究发现锂嵌碳材料中存在两种电子自旋.一种来自碳材料中的载流子电子,称为Pauli自旋.从Pauli自旋的ESR强度可推算给定锂嵌碳样品的电子态密度曲线,并进而计算能带模型机理对该样品嵌锂容量的贡献.另一种来自局域化自旋,即Curie自旋,其与嵌锂位置的关系尚不清楚.7Li-NMR测试已发现几个不同的谱峰,其峰位和强度随碳样品性质和嵌锂深度而异.一般认为,45±5×10-6(即ppm,下同)处的NMR谱线源于深度嵌锂(在LixC6中x=0.5～1)石墨化结构中的Li+,属于Knight位移;而明显小于45×10-6的谱峰则可能是来自碳材料中石墨化微结构中低浓度Li+的Knight位移,也可能是于无序微结构中共价结合的Li的化学位移.ESR与7Li-NMR在研究锂嵌碳方面有很强的互补性,联合应用此两技术可望对深入认识锂嵌碳材料的构效关系作出新贡献.The electron spin resonance(ESR) and 7Li_NMR magnetic resonance (7Li_NMR) studies on lithium intercalation into carbons were reviewed based on recently published papers, including those by the authors of this review. Two kinds of electronic spins were found in ESR studies. One corresponds to the charge carrier electrons and is called the Pauli spin. From the ESR intensity of Pauli spins, the curve of the density of electronic states can be deduced for the carbon material studied and, in turn, the contribution of the band model mechanism to the lithium intercalation can be calculated for the given carbon sample. The other is the Curie spin associated with localized spins but its relations with intercalation siteds are not clear at present. 7Li_NMR measurements revealed a number of different signals, their position and intensity depenging on the nature of carbon and the degree of intercalation. It is generally accepted that the NMR peak at 45±5×10-6 corresponds to the Li+ of LixC6(x=0.5～1) in the graphitised structure and this peak shift is the Knight Shift. The NMR peaks with a shift below 45 ×10-6 may correspond to the low concentration Li+ in the graphitised microstructures or the covalently bonded lithium in the disordered microstructures.It is pointed out that ESR and 7Li_NMR are well complementary to one another in the study of lithium intercalation into carbons and combined use of these two techniques will hopefully contribute much to the understanding of the structure_property relationship of lithiated carbons.作者联系地址：武汉大学化学与分子科学学院,武汉大学化学与分子科学学院,武汉大学化学与分子科学学院,武汉大学化学与分子科学学院 湖北武汉430072 ,湖北武汉430072 ,湖北武汉430072 ,湖北武汉430072Author's Address: Colllege of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, Chin