In the contemporary literature, diminished salt removal in a CDI device is primarily due to carbon oxidation at the anode in aqueous solutions. Therefore, an anion exchange polymer is used to prepare a composite carbon as a CDI anode. Results from repetitive CDI testing shows that more efficient and consistent long-term salt removal is achieved when a flow-through CDI stack is configured with composite anodes compared to polymer-free anodes. Analysis of the effluent pH and steady-state current indicates that this performance improvement may be due to the minimization of parasitic reactions by shielding of the carbon electrodes with the selective polymer layer coated at the anode.

Alternating polarization (AP) at ±1.2/0 V is performed on a capacitive deionization stack assembled with carbon xerogel (CX) electrodes. Long-term testing shows enhanced cycling stability without the formation of inversion peaks. AP also leads to an arch-shaped plot of salt adsorption capacity (SAC) versus cycling time, with the highest SAC of approximately 3 mg (NaCl) g-1 (CX) during this long-term test. Characterization of both the freshly prepared and cycled electrodes depict that AP results in surface charge of all the electrodes being modified from positive to negative character. By leveraging balances of electronic, surface, and ionic charges in carbon micropores, it is found that a portion of the electronic charge contributes to the ionic charge for salt adsorption, and another portion is parasitically consumed to balance the surface charge during the charge reconciliation process. When the consumption of electronic charge for charge reconciliation becomes minimal, both the positive and negative surface charges are nearly equivalent on the CX electrode. Under such a condition, the highest SAC values can be achieved for AP testing.

Résumé -Effet des cendres sur l'activité des porteurs d'oxygène dans la combustion du charbon en boucle chimique -L'application de la combustion en boucle chimique (CLC) aux combustibles solides est actuellement étudiée à l'Université du Kentucky, au Centre de Recherche de l'Energie Appliquée (CAER) dans le but de développer un procédé de gazéification/combustion en boucle chimique pressurisé (PCLC/G) afin de générer de l'électricité à partir de charbon. Un des principaux aspects de la combustion en boucle chimique de combustibles solides est la compréhension de l'effet des cendres sur la réactivité des porteurs d'oxygène (OCs). L'effet des cendres sur la capacité de transfert

Inverted capacitive deionization (i-CDI) is examined using microporous Spectracarb carbon electrodes in 10 mmol L–1 NaCl solution without deaeration. i-CDI testing shows that using conventional operational methods, i.e., V ch = 0.8 V and V dis = 0 V (0.8/0 V), cannot stabilize salt separation after approximately 409 h with an averaged salt adsorption capacity (SAC) of 6.0 ± 0.8 mg g–1. The cycled anode possesses a collapsed cyclic voltammogram due to an increase in the sheet resistance by the formation of a surface oxide layer. This layer eventually suppresses electronic charge utilization in the i-CDI cell causing degraded salt separation. By analysis of potential distributions incorporated with the modified Donnan model, an improved i-CDI operational method is proposed by reducing V ch to 0.4 V and V dis to −0.4 V (0.4/–0.4 V) while maintaining a voltage window (V ch–V dis) of 0.8 V. The improved i-CDI testing demonstrates that not only is the separation process stabilized up to approximately 420 h but the SAC also increases to 7.2 ± 0.3 mg g–1. Additionally, operation at 0.4/–0.4 V possesses more stable pH and dissolved oxygen (DO) responses than that at 0.8/0 V. We believe that such improved performance stems from a reduced V ch mitigating carbon oxidation at the anode and DO reduction at the cathode while the reduced V dis compensates for salt removal capacity.

Scenarios (a)–(c) are created to study the effect of the chemical surface charge of carbon electrodes on capacitive deionization using symmetric carbon electrode pairs.