Aqueous iodine based electrochemical energy storage is considered a potential candidate to improve sustainability and performance of current battery and supercapacitor technology. It harnesses the redox activity of iodide, iodine, and polyiodide species in the confined geometry of nanoporous carbon electrodes. However, current descriptions of the electrochemical reaction mechanism to interconvert these species are elusive. Here we show that electrochemical oxidation of iodide in nanoporous carbons forms persistent solid iodine deposits. Confinement slows down dissolution into triiodide and pentaiodide, responsible for otherwise significant self-discharge via shuttling. The main tools for these insights are in situ Raman spectroscopy and in situ small and wide-angle X-ray scattering (in situ SAXS/WAXS). In situ Raman confirms the reversible formation of triiodide and pentaiodide. In situ SAXS/WAXS indicates remarkable amounts of solid iodine deposited in the carbon nanopores. Combined with stochastic modeling, in situ SAXS allows quantifying the solid iodine volume fraction and visualizing the iodine structure on 3D lattice models at the sub-nanometer scale. Based on the derived mechanism, we demonstrate strategies for improved iodine pore filling capacity and prevention of self-discharge, applicable to hybrid supercapacitors and batteries.

碘基电化学储能被认为是提高当前电池和超级电容器技术的可持续性和性能的潜在候选者。它在纳米多孔碳电极的受限几何结构中利用碘化物、碘化物和聚碘化物的氧化还原活性。然而，目前对这些物种相互转化的电化学反应机制的描述是难以捉摸的。在这里，我们展示了纳米多孔碳中碘化物的电化学氧化形成持久的固体碘沉积物。限制会减缓溶解成三碘化物和五碘化物，否则会导致通过穿梭产生的显着自放电。这些见解的主要工具是原位拉曼光谱和原位小广角 X 射线散射（原位 SAXS/WAXS）。原位拉曼确认三碘化物和五碘化物的可逆形成。原位 SAXS/WAXS 表明大量固体碘沉积在碳纳米孔中。结合随机建模，原位 SAXS 允许量化固体碘的体积分数，并在亚纳米尺度的 3D 晶格模型上可视化碘结构。基于推导出的机制，我们展示了提高碘孔填充能力和防止自放电的策略，适用于混合超级电容器和电池。原位 SAXS 允许量化固体碘的体积分数，并在亚纳米尺度的 3D 晶格模型上可视化碘结构。基于推导出的机制，我们展示了提高碘孔填充能力和防止自放电的策略，适用于混合超级电容器和电池。原位 SAXS 允许量化固体碘的体积分数，并在亚纳米尺度的 3D 晶格模型上可视化碘结构。基于推导出的机制，我们展示了提高碘孔填充能力和防止自放电的策略，适用于混合超级电容器和电池。