Suppressing water reactivity and manipulating zinc ion deposition by a composite polyacrylamide / graphitic carbon nitride hydrogel electrolyte for durable aqueous zinc metal batteries

The HER side reaction and uncontrollable dendrite problem severely impede the practical use of aqueous zinc ion batteries (ZIBs). In this work, we find that a 2D graphitic carbon nitride (g-C₃N₄) additive can act as effective Zn²⁺ flux regulator and achieve smooth zinc plating/stripping. As verified by experimental investigations and theoretical calculations, the porous 2D g-C₃N₄ additives can not only homogenize the zinc ions flux but also effectively promote the dehydration kinetics of zinc ions. Meanwhile, the C₃N₄ nanosheets can reduce the activity of free water molecules through interacting with H₂O molecular by hydrogen bonding, thereby inhibiting the hydrogen evolution side reaction. Based on the polyacrylamide-C₃N₄ composite hydrogel electrolyte, Zn||Zn symmetric cells can operate over 500 hours at an ampere density of 5 mA cm⁻², while Cu||Zn asymmetric cells exhibit a remarkable cycling stability of one thousand cycles with coulombic efficiency near 99 %. Our findings will enlighten practical electrolyte design strategies for reliable quasi-solid-state rechargeable zinc metal batteries in the future.