Electron paramagnetic resonance (EPR) spectroscopy is applied in situ to monitor the electrochemical capacitance of activated carbon in aqueous solutions, thereby revealing aspects of the charge storage mechanism. The EPR signal of activated carbon increases during the charging process and returns reversibly when discharged. Simulation of the spectral lineshape and its temperature dependence indicate that two kinds of spins exist: spin at defects giving rise to a narrow signal, and spins associated with surface-bound aromatic moieties causing a broad signal. A potential-dependent response of the narrow feature is seen in each of the electrolyte solutions used, while changes of the broad feature occur only at higher electrolyte concentrations. The results suggest that the observed increase of unpaired electron density on activated carbon is due to the formation of radical species due to reduction of functional groups. The potential dependence of the broad feature at higher electrolyte concentrations may be related to the further adsorption of ions into the deep porous structure of activated carbon.

中文翻译：

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原位电化学电子顺磁共振光谱作为探测双电层电容的工具†

电子顺磁共振（EPR）光谱原位应用监测活性炭在水溶液中的电化学电容，从而揭示电荷存储机制的各个方面。活性炭的EPR信号在充电过程中增加，放电时可逆地返回。光谱线形及其温度依赖性的模拟表明存在两种自旋：缺陷处的自旋产生窄信号，与表面结合的芳族部分相关的自旋引起宽信号。在所使用的每种电解质溶液中都可以看到窄特征的电势依赖性响应，而宽特征的变化仅在较高的电解质浓度下才会发生。结果表明，在活性炭上观察到的不成对电子密度的增加归因于由于官能团的减少而形成的自由基种类。在较高的电解质浓度下，宽广特征的电势依赖性可能与离子进一步吸附到活性炭的深层多孔结构中有关。