## 1 Introduction  
Capacitive deionization (CDI) is considered as a promising desalination technology because of its environmental benign and energy-efficient characteristics. In a typical CDI system, while the feed water passes through the porous carbon electrodes, ions in the feed water are captured on the electrodes when a potential is applied between the electrodes shown in Figure 1. The water desalination process of CDI is based on the principle of the electrical double layer capacitor (EDLC), and ions in feed water are removed by the electrical adsorption onto the surface of the electrodes [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11].  
The conventional CDI system consists of a pair of porous carbon electrodes and open-meshed spacers for a flowing influent, and the desalination process in the CDI system is an interfacial process between the electrolyte and the electrode surfaces. Thus, the characteristics of a porous carbon electrode such as the surface area, pore size, electrical conductivity, chemical stability, and wettability are the major parameters to determine the desalination performance of the CDI system [5, 6, 12, 13, 14, 15]. To develop a CDI electrode with high performance, a porous carbon electrode should have a large specific surface area, optimal pore size distribution, high electrical conductivity, and good wettability to the electrolyte. Various carbon materials with different surface areas and pore size distributions have been investigated, and among them, activated carbons are one of the most suitable materials for CDI electrodes because of their large surface area and economic merits. However, CDI electrodes based on activated carbon materials exhibit a hydrophobic behavior, disturbing the accessibility of ions to the pore structure. Accordingly, various surface modifications of the activated carbon electrodes have been reported to overcome this limitation by treating with acidic and alkaline solutions, attaching functional groups, and coating the organic or inorganic materials [16; 17; 18].  
Layered double hydroxides (LDHs), known as anion exchangeable clays containing transition metal hydroxides, are a lamellar type of compound built by two-dimensional positive charged layers. The typical LDH structure is expressed with the chemical formula [M\({}^{\text{H}}\)1-xM\({}^{\text{H}}\)1-x (OH)2]x+(A\({}^{\text{n}-}\))x/m yH2O, where M\({}^{\text{H}}\) and M\({}^{\text{H}}\) represent the divalent and trivalent metal cations, and A\({}^{\text{n}-}\) means the interlayer anion [19; 20; 21]. LDH materials have many potential applications including adsorbents, catalysts, anticorrosive, metal oxide precursors, and supercapacitors in aqueous solutions not only because of their anion exchange capacity and high stability but also because of their exceptional hydrophilicity [22; 23]. Recently, using the LDH precursor, various substrates were successfully coated with a well-oriented porous LDH structure, attributing to the enhanced durability as well as their wettability. [24; 25].  
Hence, the purpose of this paper is to improve the wettability of the porous carbon electrodes through LDH coating and to enhance the desalination performance. The LDH crystals on the surface of the activated carbon were aligned vertically using an in-situ growth method under a hydrothermal condition. The characteristics of the LDH coated activated carbon electrode were then analyzed with the scanning electron microscopy (SEM), the cyclic voltammetry, and the contact angle measurements. Furthermore, ion adsorption/desorption tests were conducted to evaluate the desalination performance.