The seawater battery (SWB) is a promising desalination technology that utilizes abundant sodium ions as an energy storage medium. Recently, the alternative desalination system, seawater battery desalination (SWBD), was developed by placing an SWB next to the desalination compartment. This SWB-D system can desalt water while charging the SWB next to it. However, only a fixed catholyte solution has been investigated, although the catholytes impact the overall SWB-D performance. Therefore, we evaluated the effect of different catholytes on the desalination performance. High-saline reverse osmosis (RO) concentrate or brackish water exhibited excellent salt removal capability (>85.3% of sodium and >76.6% of chloride ions) with relatively short operation times (36.4 h for RO concentrate and 39.5 h for brackish water) upon charging, whereas the relatively low-saline river water showed the longest operation time (81.0 h), implying that river water should be excluded as a potential catholyte. The amount of desalinated water was marginally reduced due to osmosis through the anion exchange membrane; however, the amount of treated salt was >82.9% even after the reduction in water volum e. These findings suggest that the catholyte with a resistance of >0.041 kΩ·cm can be ideal for the SWB-D.

Research on the interface between solid electrolytes and electrode materials or catholyte is important to effectively and safely use their high energy densities. However, compared to interfaces with electrode materials, the interface between solid electrolytes and liquid media lacks research. Herein, the stability of NA superionic conductor (NASICON) pellets is studied in various aqueous solutions, including deionized (DI) water and a marine environment, associated with different degradation mechanisms. A representative detrimental hydronium exchange reaction between solid electrolytes and aqueous media is suppressed with increasing concentration and ion types dissolved in the solutions. Results of density functional theory calculation and electron energy loss spectroscopy reveal the different activation energies and chemical bonding states of solid electrolytes based on the aqueous solutions’ conditions. NASICON’s ionic conductivity decreases to ∼10–6 S/cm because of severe changes in aqueous solutions with insufficient dissolved ions resulting in inferior chemical stability. Furthermore, chemical stability variations at a steady state can severely affect battery performance. Seawater batteries fabricated with NASICON in immersed DI water for 1 year exhibit a large resistance region from the first cycle; this system breaks down before 200 h, unlike a cell fabricated using NASICON immersed for 1 year in a marine environment.

Aqueous hybrid Zn2+/Na+ ion batteries (AHZSIBs) have gained considerable attention for stationary energy storage applications because of their outstanding safety, sustainability, abundance, and low raw material costs. However, the low capacity values (<100 mAh/g) of the Na+ ion deinsertion/insertion cathodes limit the overall capacity storage of AHZSIBs. Herein, we propose a novel concept to extend the charge storage performance of AHZSIBs using electrolyte with redox characteristics. The benefits of using redox aqueous electrolytes such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) and sodium ferrocyanide (Na4[Fe(CN)6]) were investigated in an AHZSB, which consists of Zn metal as an anode and sodium nickel hexacyanoferrate (Na-NiHCF) as the Na+ deinsertion/insertion cathode. The proposed AHZSB using Na4[Fe(CN)6] redox electrolyte provided a capacity (144 mAh/g) that was ~2.94 times higher than AHZSIB using a conventional Na2SO4 electrolyte (49 mAh/g). This capacity enhancement emanated from the faradaic contribution of the Fe2+(CN)64−/Fe3+(CN)63− redox pair present in the electrolyte and Fe2+/Fe3+ redox pair in the lattice of Na-NiHCF. In addition, the TEMPOL-based redox electrolyte also improved the capacity (from 49 to 120 mAh/g) through the combined faradaic contribution of the TEMPOL/TEMPOL+ redox pair dissolved in the electrolyte and the Fe2+/Fe3+ redox pair in the Na-NiHCF lattice. These results confirm the competence of the redox electrolyte in AHZSIB in enhancing the charge storage capacity. We anticipate that this proof-of-concept study will provide a new direction for developing high-capacity storage AHZSIBs. More importantly, this approach can be used in any aqueous/non-aqueous batteries.

To develop effective electrocatalytic splitting of acidic water, which is a key reaction for renewable energy conversion, the fundamental understanding of sluggish/destructive mechanism of the oxygen evolution reaction (OER) is essential. Through investigating atom/proton/electron transfers in the OER, the distinctive acid–base (AB) and direct‐coupling (DC) lattice oxygen mechanisms (LOMs) and adsorbates evolution mechanism (AEM) are elucidated, depending on the surface‐defect engineering condition. The designed catalysts are composed of a compressed metallic Ru‐core and oxidized Ru‐shell with Ni single atoms (SAs). The catalyst synthesized with hot acid treatment selectively follows AB‐LOM, exhibiting simultaneously enhanced activity and stability. It produces a current density of 10/100 mA cm−2 at a low overpotential of 184/229 mV and sustains water oxidation at a high current density of up to 20 mA cm−2 over ≈200 h in strongly acidic media.