## 3 Results and Discussion
### Effect of Electrode Configuration  
To study the key factors for Cl\({}^{-}\) complete desorption more intensively, electrodesorption experiments were explored by varying the electrode configuration. The operation was carried out by assembling the electrodes in five configurations, as shown in Table 1, where two were symmetric and three were asymmetric. The cathode potential was measured by adjusting the cell voltage and controlling the anode potential to +1.2 V, which is the electrochemical stability window of water [46]. In addition, Cl\({}^{-}\) oxidation may occur in the presence of the NaCl electrolyte [47; 48; 49] when the anode potential is higher than +1.2 V. However, when the anode potential was +1.2 V for Group 2, the cell voltage reached +15 V. To take into consideration the energy consumption, the measurement experiment of Group 2 was performed at the same cell voltage as that for Group 5. Figure 3a and Table 1 show the experimental data measured in the three-electrode system. Clearly, the cathode potential of Group 5 (\(-\)1.08 V) is higher than that of the other groups, which was determined under  
Figure 2: Electrosorption and desorption cycles. (**a**) Comparison of Cl\({}^{-}\) adsorption capacity at OCP and 1.2 V. (**b**) The concentration of Cl\({}^{-}\) with and without cathodic polarization (**c**) cycles for adsorption and electrosorption. (**d**) The curve of anode potential changed with cell voltage in the electrosoption process. the same anode potential (+1.2 V), especially for the titanium anode-titanium cathode combination. However, the cathode potential of Group 5 is much less than that of Group 2 (\(-\)1.7 V) when determined at the same cell voltage. These results indicate that the cathode potential is dependent on the electrode configuration, which decreased in the order of Group 2 > Group 5 > Group 3 > Group 4 > Group 1. Five sets of desorption experiments were performed under the acquired cathode potential. After 5 h, the desorption experiments were nearly complete, and the results are shown in Figure 3b. The desorption efficiency increased as the desorption time increased from 0 to 300 min for all groups. However, after 5 h, Group 2, Group 5, and Group 3 exhibited higher desorption efficiencies of 100%, 95%, and 68%, respectively, compared with Group 4 and Group 1, with values of 52% and less than 30%, respectively. The results indicate that different electrode combinations greatly influence the desorption efficiency because the cathode potential depends on the electrode combinations. Furthermore, an asymmetric electrode structure (G-Ti, G-Pb, and G-Cu) is more propitious to the electrodesorption of Cl\({}^{-}\) than a symmetrical structure (Ti-Ti and G-G). In comparison to the previous reports, the desorption efficiency was higher in our work (Table 2). However, further optimization of the operating conditions will be needed for decreasing the desorption time. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Group** & **Anode** & **Cathode** & **Sign** & **Cathode Potential/V** \\ \hline
1 & Titanium (Ti) & Titanium (Ti) & Ti-Ti & \(-\)0.22 \\
2 & Graphite (G) & Titanium (Ti) & G-Ti & \(-\)1.70 \\
3 & Graphite (G) & Lead (Pb) & G-Pb & \(-\)0.88 \\
4 & Graphite (G) & Graphite (G) & G-G & \(-\)0.71 \\
5 & Graphite (G) & Copper (Cu) & G-Cu & \(-\)1.08 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The different electrode configurations within the CDI devices for the experiments. Figure 3: Effect of electrode configuration. **(a)** The cathode potential development of different electrode types. **(b)** The desorption efficiency of Cl\({}^{-}\) using different electrode types. **(c)** The corresponding cathode potential (pink streak). It is worth noting that the broadest cathode potentials measured in Group 2 and Group 5 were \(-\)1.7 V and \(-\)1.08 V, respectively, at a cell voltage of +5.0 V (Figure 3a).