*2.1. Materials*

The slurry of activated carbon was made by mixing commercial activated carbon power (YP-50F, Kuraray Chemical Company, Tokyo, Japan) with a polyvinylidene fluoride binder (Kynar HSV 900 PVDF, Arkema, France) at a ratio of 90:10 wt%. The mixture was dispersed in N-methylpyrrolidone (NMP, 99%, Sigma Aldrich, Milwaukee WI, USA) and was stirred for 12 h to form a homogeneous slurry. It was then cast on a titanium plate and dried in an oven at 80 ◦C for 2 h to form the carbon sheet electrode. Each electrode had a size of 30 mm × 60 mm and a total weight of about 0.08 g.

The structure of raw activated carbon and the fabricated electrode was both determined by the nitrogen adsorption/desorption isotherm (Micromeritics ASAP 2000) that was based on the Brunauer–Emmett–Teller (BET) method. The average pore diameter and pore volume were estimated by the Barrett–Joyner–Halenda (BJH) method and t-plot method, respectively. The experimental results are listed in Table 1; note that the pore thickness (*Hp*) is defined as the ratio of the micropores' volume (*Vmicro*) to the microporous area (*Smicro*) [28]. As seen in Table 1, there are reductions in some structural parameters of the fabricated electrode (including the specific surface area, micropore surface area, total volume and micropore volume) compared to the same parameters of raw activated

carbon. The reason for this may be attributed to the PVDF binder in the fabricated electrode. Nevertheless, there is not much difference in the average pore diameter between activated carbon and fabricated electrode.

**Figure 1.** (**a**) Photograph of the CDLE cell, from left to right: acrylic plate, titanium current collector with electrode, silica gel tablet, titanium current collector with electrode, acrylic plate. (**b**) Schematic of the CDLE experiment setup.

**Table 1.** The specific surface area (*SBET*), microporous surface area measurement (*Smicro*), total volume of pores (*Vtot*), volume of micropores (*Vmicro*), characteristic pore thickness (*Hp*) and average pore diameter (*DBJH*) results of activated carbon and electrode.


With the fabricated electrodes, the CDLE cell was also self-made. As illustrated in Figure 1 for the structure and component, it was composed of two rectangular acrylic plates, one pair of activated carbon electrodes, one pair of titanium current collectors and a hollow silica gel tablet with a thickness of 0.5 mm that form a flow channel between two electrodes.
