Institute of Physics, Montanuniversitaet Leoben, Franz-Josef Straße 18, 8700, Leoben, Austria.
Institute for Chemistry and Technology of Materials, Graz University of Technology, Stremayrgasse 9/V, 8010, Graz, Austria.
Nat Commun. 2018 Oct 8;9(1):4145. doi: 10.1038/s41467-018-06612-4.
A fundamental understanding of ion charge storage in nanoporous electrodes is essential to improve the performance of supercapacitors or devices for capacitive desalination. Here, we employ in situ X-ray transmission measurements on activated carbon supercapacitors to study ion concentration changes during electrochemical operation. Whereas counter-ion adsorption was found to dominate at small electrolyte salt concentrations and slow cycling speed, ion replacement prevails for high molar concentrations and/or fast cycling. Chronoamperometry measurements reveal two distinct time regimes of ion concentration changes. In the first regime the supercapacitor is charged, and counter- and co-ion concentration changes align with ion replacement and partially co-ion expulsion. In the second regime, the electrode charge remains constant, but the total ion concentration increases. We conclude that the initial fast charge neutralization in nanoporous supercapacitor electrodes leads to a non-equilibrium ion configuration. The subsequent, charge-neutral equilibration slowly increases the total ion concentration towards counter-ion adsorption.
深入理解纳米多孔电极中的离子电荷存储对于提高超级电容器或电容去盐设备的性能至关重要。在这里，我们在活性炭超级电容器上进行了原位 X 射线透射测量，以研究电化学操作过程中的离子浓度变化。结果表明，在较小的电解质盐浓度和较慢的循环速度下，反离子吸附占主导地位，而在高摩尔浓度和/或快速循环时，离子取代占主导地位。计时安培测量揭示了离子浓度变化的两个截然不同的时间区间。在第一区间中，超级电容器被充电，并且反离子和共离子浓度变化与离子取代和部分共离子排斥一致。在第二区间中，电极电荷保持恒定，但总离子浓度增加。我们得出结论，纳米多孔超级电容器电极中初始的快速电荷中和导致非平衡离子构型。随后，电荷中性平衡过程缓慢增加总离子浓度，从而导致反离子吸附。
