More Ca²⁺, Less Na⁺: Increase the Desalination Capacity and Performance Stability of Na_xCa_yCoO₂

Abstract

Faradaic deionization (FDI) provides an effective solution to respond to the global water crisis. However, the ions intercalation/ deintercalation process with multiple redox reactions leads to structural collapse and unstable cyclability. Here, we develop an asymmetrical FDI device assembled by Ca 2+ -decorated Na x CoO 2 (x ≤ 0.71, y ≤ 0.05) as the Faradaic negative electrode and activated carbon as the positive electrode. Na 0.27 Ca 0.03 CoO 2 •0.6H 2 O was synthesized via a facile sol−gel and chemical oxidation method, which delivered a desalination capacity of 83.5 ± 2.4 mg g −1 and a charge efficiency close to 1, and an inappreciable capacity fading was observed after 50 cycles. It is found that the presence of Ca 2+ residing in the face-sharing sites helps to maintain the layered structure and promotes efficient deintercalation of Na + by anchoring the CoO 2 slabs, which results in its unexpected desalination capacity and good cyclability. Moreover, electrochemical quartz-crystal microbalance (EQCM) was successfully used to reveal Faradaic intercalation mechanism.

A Review of Battery Materials as CDI Electrodes for Desalination

“…To stabilize the structure of NCO is the key point to get a good desalination performance. Zhou et al (2019) [90] synthesized the Na 0.27 Ca 0.03 CoO 2 •0.6H 2 O from Co(NO 3 ) 2 , Ca(NO 3 ) 2 , NaNO 3 and citric acid. Compared to the undoped NCO, the new material got almost the same pair of oxidation/reduction peaks but a higher capacitance of 292 F•g −1 .…”

Enhanced Desalination Capacity and Stability of Alkylamine-Modified Na0.71CoO2 for Capacitive Deionization

“…For example, doped Zn 2+ ions can improve the electron conductivity, and doped Ca 2+ ions can enhance the capacity. 36,37 However, simultaneously boosting the ion and electron transfer remains a major challenge. In order to enhance the specific capacity and improve the cycling stability of Na x MO 2 , preintercalation of the electrode has been adopted as an effective method to improve the electrochemical performance by introducing the guest species including inorganic ion or organic molecules into the host interlayer.…”

“…Previous works have demonstrated that desalination capacity can be enhanced by controlling the sodium content through chemical and electrochemical preactivation. , Our team has proved that a doped heteroatom strategy between the interlayer and slab is an effective way to improve the electrochemical characteristics for CDI application. For example, doped Zn 2+ ions can improve the electron conductivity, and doped Ca 2+ ions can enhance the capacity. , However, simultaneously boosting the ion and electron transfer remains a major challenge. In order to enhance the specific capacity and improve the cycling stability of Na x MO 2 , preintercalation of the electrode has been adopted as an effective method to improve the electrochemical performance by introducing the guest species including inorganic ion or organic molecules into the host interlayer .…”

Self-Regenerating Hybrid Anion Exchange Process for Removing Radium, Barium, and Strontium from Marcellus-Produced Wastewater Using Only Acid Mine Drainage

“…Because chloride is the only predominant anion present in the produced water, regulated cations, namely, barium and radium, are soluble and highly mobile. Consequently, they pose long-term health and environmental hazards …”

“…Consequently, they pose long-term health and environmental hazards. 46 The same Marcellus geographic region in the northeastern United States also has long been confronted with severe acid mine drainage (AMD) problems. AMD is a natural biogeochemically formed water stream primarily from tens of abandoned mines that are acidic and contain significant amounts of sulfate resulting from biological oxidation of sulfide ores.…”