Hierarchically ordered mesoporous carbons and silver nanoparticles as asymmetric electrodes for highly efficient capacitive deionization

•The HOMC and Ag nanoparticles as asymmetric electrodes have been developed for CDI.•The asymmetric CDI increase 63.3% of electrosorption efficiency compared to symmetric electrode.•The specific electrosorption capacity of Ag-HOMC electrodes for Na+ removal is 356.3 μmol g− 1 at 1.2 V.•The high efficiency of asymmetric CDI is attributed to the water chemistry of Ag+ and Cl− ions.

In this study, a novel capacitive deionization (CDI) technology by using silver nanoparticles and hierarchically ordered mesoporous carbons (HOMCs) as the anode and cathode electrodes, respectively, was developed to enhance the desalination efficiency of sodium ions. The TEM images show that HOMCs are 2-D hexagonal mesostructures with highly ordered 1-D strip-like channels and Ag is spherical with mean diameter of 30 nm. The electrochemical performance of HOMCs and activated carbons (ACs) show rectangular voltammograms at 5–100 mV s− 1, while two peaks with Faradic reaction occur for Ag electrode. The specific capacitance of HOMC electrode is 104.2 F g− 1 at 5 mV s− 1, which is 2.84 times higher than that of ACs. In addition, the asymmetric Ag ||HOMC electrodes show excellent electrosorption capacity and high stability toward sodium ion removal and the specific electrosorption capacity (SEC) is 356.3 and 251.6 μmol g− 1 at 1.2 V in batch and continuous flowing solutions, respectively, which is 1.4–2.7 and 2.2–2.7 times higher than those of symmetric carbon-based electrodes. Results obtained in this study clearly indicate that the asymmetric Ag ||HOMC electrode is a promising alternative nanomaterial which can open an innovative CDI technology to treat grey and brown waters that need high desalination efficiency.

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