Electrosorption of Ions by Mesoporous Carbon Materials

The electrical double layer (EDL) formation near a charged surface has significance in electrochemical processes, such as electrosorption of ions and energy storage in supercapacitors. Electrosorption of ions from aqueous solutions is utilized in the capacitive deionization (CDI) process for water desalination. The main objective of the present work is to study the transport of ions in mesoporous carbon materials during the CDI process and synthesize efficient carbon electrode materials for application in CDI. The electrodes used in this study are made of mesoporous carbon materials of 8-20 nm pore size, which are synthesized at Oak Ridge National Laboratory. Neutron imaging is employed to quantify ion transport in charged mesoporous carbon electrodes. Specifically, neutron imaging is used as a tool to visualize neutron-absorbing ions in carbon electrodes during the CDI process, and image analysis is used to extract the transient concentration profiles of ions. From the time-dependent concentration profiles, the effective diffusion coefficient for neutron-absorbing ions is obtained at different values of the applied potential. It was found that the effective diffusivity increased seven times from 0 to 1.2 V applied potential. Neutron imaging also reveals interesting ion-transport phenomena, which can aid in the determination of optimal conditions for the operation of the CDI process.