Suppressing H₂ evolution by using a hydrogel for reversible Na storage in Na₃V₂(PO₄)₃

Aqueous electrolytes are widely used in energy storage due to their low cost and safety. However, their electrochemical stability window is limited, often restricted by hydrogen evolution. Researchers have explored various strategies to expand this window. Some studies have focused on modifying electrolyte composition. Others have examined the role of polymer additives. Despite these efforts, hydrogen evolution remains a challenge in aqueous systems. This gap motivated the search for new materials that can suppress hydrogen evolution. No prior work had resolved the issue of hydrogen evolution in sodium-ion aqueous electrolytes. This study addresses that limitation by introducing a hydrogel-based approach.

This study aimed to develop a low-cost hydrogel electrolyte to suppress hydrogen evolution in aqueous sodium-ion systems. The researchers focused on sodium vanadium phosphate as a potential anode material. They wanted to determine if a polymer additive could improve the electrochemical stability window. The motivation was to enable reversible sodium-ion intercalation in aqueous electrolytes. Previous studies had not demonstrated this in such systems. The team hypothesized that the polymer network could interact with water molecules. They proposed that this interaction might limit hydrogen evolution. The study tested this hypothesis using a specific polymer and electrolyte combination.

The researchers prepared a hydrogel by adding 3 wt% poly(acrylate sodium) to a 1 M sodium sulfate aqueous solution. They evaluated the electrochemical stability window using stainless steel and titanium current collectors. The hydrogen evolution potential was measured against a silver/silver chloride reference electrode. The team used cyclic voltammetry to assess the electrochemical behavior. They tested the sodium-ion intercalation in Na3V2(PO4)3 as an anode material. The polymer’s interaction with water molecules was analyzed through structural characterization. The hydrogel’s effect on hydrogen evolution was compared to the base electrolyte. The study focused on the first demonstration of reversible sodium-ion storage in this system.

The hydrogel electrolyte achieved an electrochemical stability window of 2.45 V on stainless steel. This is an improvement over the 2.12 V observed in the base sodium sulfate electrolyte. The hydrogen evolution potential was measured at -1.75 V vs. Ag/AgCl on titanium. This result suggests the polymer network effectively limits hydrogen evolution. The polymer interacts with water molecules, reducing their availability for hydrogen production. The sodium vanadium phosphate anode demonstrated reversible sodium-ion intercalation. This is the first time such behavior has been reported in an aqueous system. The results support the hypothesis that the hydrogel suppresses hydrogen evolution.

The study demonstrates that a hydrogel electrolyte can suppress hydrogen evolution in aqueous sodium-ion systems. The polymer network interacts with water molecules, limiting hydrogen production. This interaction broadens the electrochemical stability window of the electrolyte. The sodium vanadium phosphate anode shows reversible sodium-ion intercalation. This is a first-time observation in an aqueous electrolyte. The hydrogel approach is low-cost and scalable for practical applications. The findings suggest this method could improve the performance of aqueous sodium-ion batteries. The results support further investigation into polymer-based electrolyte modifications.