A Jointly Triggered H₂ Evolution Model Modulated Polyanionic Hydrogel Electrolyte for Reversible Zn Chemistry

Abstract Hydrogen evolution reaction (HER) significantly deteriorates the stability of electrolytes and Zn anodes, yet the dominant factor of different H 2 evolution stages is still unclear, especially in hydrogel electrolytes. Herein, a Zn 2+ ‐solvated water deprotonation and free water ionization jointly triggered HER model is revealed by an anionic group gradient regulating strategy in a polyanionic hydrogel electrolyte system (PAHE). Combining experimental characterizations and theoretical calculations, this confirms that solvated water and free water are the key variables dominating the onset potential and intensity of HER, respectively. An in‐depth understanding of the HER process realizes better HER inhibition through synchronously weakening onset potential and HER activity. Additionally, fixed multi‐polyanions and salt anions endow PAHE with high cation transfer efficiency and accelerated desolvation kinetics by forming cooperative ion pairs. Consequently, structurally and electrochemically stable PAHE optimizes the Zn‐electrolyte interface, markedly enhancing Zn chemistry reversibility. As a proof‐of‐concept, Zn/PAHE/LFP batteries yield superior capacity retention (>99.88% pre‐cycle), rate capability (up to 25 C), cycling durability (over 10000 cycles), and wide‐temperature adaptability.