# Assessing the Efficacy of Seawater Batteries Using NASICON Solid Electrolyte
## 4 Discussion
### The NASICON Principles Used in seawater Electrolytic Processes
During 1440 h of submersion in seawater, both the blank sample and the sample submerged in it did not exhibit significant changes in the phase structure of XRD peaks, as noted [3; 17]. NASICON proved its chemical compatibility with seawater during extensive testing, demonstrating electrochemical stability for more than a year [13]. Redox reactions are initiated by Na\({}^{+}\) (Equation (3)) at the negative electrode and seawater at the positive electrode during SWB's operations. The positive electrode releases electrical energy through the use of ambient oxygen gases, which results in a reduction reaction called the oxygen reduction reaction (ORR) (Equation (4)). Chlorine evolution is outnumbered by the thermodynamically favored oxygen evolution reaction (OER) (Equation (5)), or the charging cycle could result in the formation of chlorine oxyacids (Equations (6)-(8)). Overall reactions are expressed as (Equation (9)) [20]:  
\[Na^{+}+e^{-}\ \to Na\ E_{0}\ =-2.71\ \mathrm{V}\ vs.\ SHE \tag{3}\]  
\[2H_{2}\ O+2e^{-}\ \to\ 2 OH^{-}+H_{2}\ E_{0}=-0.49\ \mathrm{V}\ (\mathrm{at}\ \mathrm{pH}=8.3) \tag{4}\]  
\[4 OH^{-}\to 2H_{2}O+O_{2}+4e^{-}\ E_{0}=0.73\ \mathrm{V}\ vs.\ SHE\ (\mathrm{at}\ \mathrm{pH}=8.3) \tag{5}\]  
\[Cl^{-}+H_{2}O\to ClO^{-}+2H^{+}+2e^{-}\ E_{0}=1.15\ \mathrm{V}\ vs.\ SHE\ (\mathrm{at}\ \mathrm{pH}=8.3) \tag{6}\]  
\[Cl^{-}+H_{2}O\to HOCl+H^{+}+2e^{-}\ E_{0}=1.20\ \mathrm{V}\ vs.\ SHE\ (\mathrm{at}\ \mathrm{pH}=7.3) \tag{7}\]  
\[2 Cl^{-}\ \to\ Cl_{2}+2e^{-}\ E_{0}=1.35\ \mathrm{V}\ vs.\ SHE\ (\mathrm{at}\ \mathrm{pH}=2.12) \tag{8}\]  
\[4 Na+O_{2}\ +H_{2}\ O\ \to 4\ Na^{+}+OH^{-}\ E^{0}cell=3.48\ \mathrm{V} \tag{9}\]  
The negative electrode is essential in the capacity of a SWB. Na metallic is the most promising material because it can provide high specific capacity (1.166 mAh g\({}^{-1}\)) and enable the construction of anode SWBs that can utilize more efficient seawater as an active component [20]. Reversibility of deposition/stripping and safety of cell operation is hindered by the higher restriceness of Na compared to Li metal. To address these worries, it is necessary to implement an effective strategy that involves forming a stable passivation layer (SEI) on the surface and engineering the anodic components to ensure reversible behavior. The use of Na metal presents challenges, leading to the investigation of various alternatives for negative electrodes. NASICON's ability to effectively block electron transfer between the negative electrode and seawater prevents short circuits while incorporating analyte into SWB, even with the electronic conductivity of the anolyte. Anolytes, such as sodium biphenyl (Na-BP in DEGDME), are represented by sodium biphenyl. Na-BP is proven to effectively prevent problems like gas evolution, sodium dendrite growth, and dead capacitance formation, which are common concerns with conventional electrodes and liquid electrolytes,according to research. The specific capacity of 17 mAh g\({}^{-1}\) at 0.25 mA cm\({}^{-2}\) was demonstrated, which provides a significant advantage by complementing the current electrode capacity [20; 31; 32]. Alkaline metals such as Na are capable of effectively storing hydrogen under normal temperature and pressure conditions, as they generate hydrogen gas when interacting with water. Without any interference from water splitting, NASICON can harvest Na metals from seawater. An electrochemical bridge is made between seawater (source Na\({}^{+}\)) and the electrode (Na metal) to achieve this, which gives Na\({}^{+}\) a pathway and prevents water from passing through the electrode. Using a SWB platform, it is possible to create a hydrogen storage system based on NASICON. Na metal is formed during the charging process (Equation (10)) as Na\({}^{+}\) moves from seawater to the negative electrode. During the charging process, electrodeposition occurs on the current collector at the negative electrode during the selective extraction of Na metal from seawater, as previously confirmed by previous research.