电解池电化学反应过程的运动衬度X射线成像

Move contrast X-ray imaging of electrochemical reaction process in electrolytic cell

电化学反应过程中离子迁移、氧化还原反应的原位动态观测对研究电解池和电池充放电性能、离子迁移特性、缺陷产生和预防等具有重要意义.采用电解池模型研究电化学反应过程以方便实验参数调控,基于运动衬度X射线成像实验研究了其离子迁移和氧化还原反应过程.结果表明,同等条件下运动衬度X射线成像比传统的时间减影成像的衬噪比高一个量级以上.基于运动衬度X射线成像成功观测到起始阶段电化学反应特性,发现电化学反应在电解池内所有位置同时发生,而不是通常理解的电场力作用下离子迁移到阴极、得到电子被还原.电极投影位置运动衬度信号强于电解液其他位置,说明电极位置氧化还原反应更密集.在通电电压低到一个临界值、传统时间减影成像很难观测到离子迁移或原子团聚的时候,运动衬度成像仍可明确揭示离子迁移(原子团簇运动)轨迹.因此,运动衬度X射线成像可大幅提升电解质中离子(原子)迁移的观测灵敏度,在电池、电解池电化学反应特性的原位动态研究中具有重要应用前景.

The in-situ dynamic observation of ion migration and redox reactions during electrochemical reactions is critical for the understanding of the charging and discharging performance, ion migration characteristics, causes and preventives of defects in cells and electrolytic cells. For the convenience of parameter tuning, an electrolytic cell is adopted to investigate the electrochemical reaction. The processes of ion migration and redox reaction are investigated based on move contrast X-ray imaging. The experimental results demonstrate that the contrast-to-noise ratio of move contrast X-ray imaging is one order higher than that of the conventional temporal subtraction imaging. The initial status of the electrochemical reaction is successfully revealed by move contrast X-ray imaging. The images show that at the very beginning of the reaction, the signals of move contrast distribute almost evenly in the electrolytic cell, which implicates that the ion migration is initiated as soon as the cell is switched on and redox reaction occurs simultaneously all over the cell, other than the fact that ions are driven by electric field, approach to the cathode and then are reduced through electron gain. The signals of move contrast imaging are obviously stronger at positions inside the shadow of the electrodes than elsewhere.This means that the redox processes react densely at the electrodes. When the electrical voltage is adjusted to a critical value and the conventional methods are hard to observe ion migration or atom accumulation, the move contrast X-ray imaging can still disclose evidently the trace of ion migration or movement of atom clusters.Therefore, the move contrast X-ray imaging can improve significantly the sensitivity of observation to the trace of ions or atoms in the electrolyte and has great potentials in in-situ investigating the characteristics of electrochemical reactions.