Engineering of 3D NaxCoO2 nanostructures for enhanced capacitive deionization: performance and mechanism

Abstract

Layered Na_xCoO₂ (NCO) has been demonstrated as a promising candidate for highly efficient capacitive deionization (CDI). To further improve the desalination performance of NCO, we have developed a facile method to prepare polygon-like 3D NaCoO₂ and Na_0.6CoO₂ nanostructures employing ZIF-67 as a template for enhanced CDI. On the basis of electrochemical measurements, the 3D Na_0.6CoO₂ electrode shows a higher specific capacitance and conductivity than 3D NaCoO₂, implying better CDI performance. As a result, the salt removal capacity of 3D Na_0.6CoO₂ is 64.48 mg g⁻¹ in NaCl solution with an initial conductivity of 2000 μS cm⁻¹ and cell voltage of 1.2 V. Moreover, the desalination mechanism of 3D Na_0.6CoO₂ electrode is proposed by taking cyclic voltammetry measurements and ex situ X-ray diffraction into account, realizing the transformation from Na-rich to Na-lean during the desalination. Besides, benefiting from the novel 3D architecture, the long cyclic desalination performance of 3D Na_0.6CoO₂ electrode is much superior to that of 2D NCO. Thus, this work highlights the significance of the 3D spatial structure on the CDI performance enabled by sodium layered oxides.