Asymmetric Electrode Configuration\nfor Enhanced Membrane Capacitive Deionization

Abstract

Long-term performance of capacitive\ndeionization (CDI) and membrane-assisted capacitive deionization (MCDI)\nsingle cells equipped with the same pristine carbon xerogel (CX) electrodes\nconfigured as the anode and cathode was investigated. Unlike CDI,\nwhich was subject to performance degradation in a short period of\ntime, MCDI showed performance preservation during the 50 h of operation\ndue to its ability to mitigate charge leakage from parasitic electrochemical\nreactions that result in carbon oxidation. Differential capacitance\nmeasurements of the used CDI and MCDI electrodes revealed shifting\nof the potential of zero charge (<i>E</i>_PZC)\nof the CDI anode from −0.1 to 0.4 V but only to 0.1 V for the\nMCDI anode. CDI and MCDI cells tested with electrodes having <i>E</i>_PZCs at −0.1 and 0.5 V showed strongly\ncontrasting results depending on the anode–cathode <i>E</i>_PZC configuration. The MCDI cell configured\nwith a 0.5 V <i>E</i>_PZC cathode and −0.1\nV <i>E</i>_PZC anode displayed the best performance\nof all the tested cells, benefiting from increased counterion excess\nwithin the potential window, and the membrane was in-place to reject\nexpelled co-ions from accessing the bulk.