# Assessing the Efficacy of Seawater Batteries Using NASICON Solid Electrolyte
## 4 Discussion
### Testing the Performance of Seawater Batteries Containing the NASICON Membrane  
At the beginning of our battery testing experiments containing the NASICON selective membrane, we conducted membrane stability tests (degradation) in seawater at different pH levels (5.1, 6.8 and 8.5) for 90 days. The NASICON membrane degradation over time was achieved with an excess of 6% with the best ionic conductivity (NAS 6-1200) through an immersion test in a concentration solution \(\sim\)25 g NaCl L\({}^{-1}\). Each membrane was submerged in 70 mL of NaCl solution and put in bottles with the lid to prevent it from penetrating the air. In addition to measuring the pH and ionic conductivity of the solution, X-ray diffraction (XRD) measurements were also made to see if changes in the chemical composition of the membrane take place over time. A Rigaku MiniFlex 600 X-Ray (Tokyo, Japonica) speaker was employed for performing XRD measurements, which utilized a CuK-a X-ray source with a wavelength of 1.541838\({}^{\circ}\). A monochromator was used to scan from 10\({}^{\circ}\) to 60\({}^{\circ}\) at high resolution, with a step scan of 0.01\({}^{\circ}\) and a scan speed of 1.0\({}^{\circ}\) min\({}^{-1}\), with a goal to reduce noise levels. Thus, XRD measurements were made on NASICON membranes immersed in NaCl solution of different pH levels: 5.1, 6.8 and 8.5, after 60 and 90 days. XRD spectra (Figure 11) were obtained through long scans and with the addition of a monochromator to suppress noise levels. The NASICON samples were converted into suspension using ethanol to allow deposition by evaporation and sedimentation. The spectra were smoothed and corrected according to the baseline. It was observed that there were no differences between the samples in terms of spectra--the apparent differences in intensity between the profiles being the result of scaling. It was found that the stability of the NASICONmembrane is determined according to the pH of the NaCl solution and the sinking time. Thus, after 90 days, NaCl solutions had pH values of 7.65, 7.81 and 7.85, while the ion conductivity of the three solutions had values of 6.0 mS cm\({}^{-1}\), 6.13 mS cm\({}^{-1}\), respectively 6.35 mS cm\({}^{-1}\)[33]. The NASICON ceramic membranes with the highest conductivity were chosen for the battery's fabrication. The high conductivity membrane we chose had excess sodium that was sintered at 1200 \({}^{\circ}\)C (6.19 \(\times\) 10\({}^{-4}\) S cm\({}^{-1}\)). The electrochemical cell with a capacity of 2.0 L was tested for reproducibility using a Pt/C catalyst with a concentration of platinum of 0.00033 g at different currents (0.05 and 0.1 mA). The loading/unloading tests were carried out with seawater with a concentration of \(\sim\)25 g NaCl L\({}^{-1}\) and CO\({}_{2}\) flowing at a speed of 0.5 L min \({}^{-1}\). The duration of a cycle was 2 h.  
Chemical reactions [34; 35] are used to describe the mechanism of CO\({}_{2}\) dissolution (Equations (11) and (12)). \[CO_{2}\ +H_{2}O\leftrightarrow H_{2}CO_{3} \tag{11}\]  
\[H_{2}CO_{3}\ \leftrightarrow\ HCO_{3}^{-}+H^{+} \tag{12}\]  
Both the anodic oxidation reaction (Equation (13)) and the cathodic hydrogen release reaction (Equation (14)) of metallic sodium are electrochemical reactions (Equation (15)). \[\text{Anode}:\ 2 Na\to 2 Na^{+}+2e^{-} \tag{13}\]  
\[\text{Cathode}:\ 2H^{+}+2e^{-}\to H_{2} \tag{14}\]  
\[\text{Net reaction}:\ 2 Na^{+}+2H^{+}\to 2 Na^{+}+H_{2} \tag{15}\]  
Figures 12-15 show the charge/discharge curves for potential, power, energy, and capacity, which have currents of 50 and 100 \(\mu\)A.