Härtel Andreas, Janssen Mathijs, Samin Sela, van Roij René
Institute for Theoretical Physics, Center for Extreme Matter and Emergent Phenomena, Utrecht University, Leuvenlaan 4, 3584 CE Utrecht, The Netherlands.
J Phys Condens Matter. 2015 May 20;27(19):194129. doi: 10.1088/0953-8984/27/19/194129. Epub 2015 Apr 29.
Capacitive mixing (CAPMIX) and capacitive deionization (CDI) are promising candidates for harvesting clean, renewable energy and for the energy efficient production of potable water, respectively. Both CAPMIX and CDI involve water-immersed porous carbon (supercapacitors) electrodes at voltages of the order of hundreds of millivolts, such that counter-ionic packing is important for the electric double layer (EDL) which forms near the surfaces of these porous materials. Thus, we propose a density functional theory (DFT) to model the EDL, where the White-Bear mark II fundamental measure theory functional is combined with a mean-field Coulombic and a mean spherical approximation-type correction to describe the interplay between dense packing and electrostatics, in good agreement with molecular dynamics simulations. We discuss the concentration-dependent potential rise due to changes in the chemical potential in capacitors in the context of an over-ideal theoretical description and its impact on energy harvesting and water desalination. Compared to less elaborate mean-field models our DFT calculations reveal a higher work output for blue-energy cycles and a higher energy demand for desalination cycles.
电容混合（CAPMIX）和电容去离子（CDI）分别是获取清洁可再生能源以及实现饮用水高效节能生产的有潜力的方法。CAPMIX和CDI都涉及在数百毫伏量级的电压下浸入水中的多孔碳（超级电容器）电极，因此反离子堆积对于在这些多孔材料表面附近形成的双电层（EDL）很重要。因此，我们提出一种密度泛函理论（DFT）来对双电层进行建模，其中将White-Bear II基本度量理论泛函与平均场库仑和平均球近似类型的校正相结合，以描述密集堆积与静电之间的相互作用，这与分子动力学模拟结果吻合良好。我们在过度理想的理论描述背景下讨论了由于电容器中化学势变化而导致的浓度依赖性电势升高及其对能量收集和海水淡化的影响。与不太精细的平均场模型相比，我们的DFT计算表明蓝色能源循环的功输出更高，而海水淡化循环的能量需求更高。
