Multimodal Computational Insights Into Hydrogen Evolution Reaction Mitigation in Zn Electrolytes: The Role of Anion‐Surface Coupling

Aqueous zinc‐based batteries are desirable options for large‐scale energy storage due to their excellent safety, affordability, and environmental friendliness. However, their electrochemical performance is often hampered by unwanted side reactions such as the hydrogen evolution reaction (HER), which are closely linked to the solvation structure of Zn 2+ ions. Molecular dynamics simulations were used in this study to explain how anion chemistry controls the Zn 2+ solvation environment and how that affects interfacial HER activity. Five electrolytes, ZnCl 2 , Zn(ClO 4 ) 2 , ZnSO 4 , Zn(OTF) 2 , and Zn(TFSI) 2 , were systematically examined. Zn 2+ maintains a water‐rich first solvation shell in systems with small, strongly hydrated anions (Cl − , ClO 4 −, SO 4 2‐ ), according to radial distribution function and coordination analyses. However, in electrolytes with bulky, weakly coordinating anions (OTF ‐ and TFSI ‐ ), partial substitution of water molecules takes place due to their delocalized charge and fluorinated structures. Higher free‐water content electrolytes naturally show a stronger tendency toward HER because free water molecules are more easily reduced than bound water. To investigate interfacial effects, the representative solvation structures were further examined on Cu, Sn, and Zn surfaces, revealing that Sn effectively mitigate HER. These results offer atomistic insights into the interaction of surface reactivity, solvation structure, and anion identity, guiding the rational development of stable and effective aqueous Zn‐based energy storage devices.