ZIF-8 is proposed as a model to elucidate the effect of the crystal orientation of surface coatings on Zn foils on electrochemical performance. The preferential orientation of ZIF-8(200) reduces the hydrogen evolution reaction (HER) reactivity, blocks the deleterious species, and improves the interface stability, promoting the electrochemical performance of Zn foils.

Abstract

Zinc metal, as the mainstream anode material of aqueous batteries, faces severe side reactions and notorious dendrite growth. Surface passivation of Zn anodes with a protective layer is one of the effective strategies to address these issues. The previous reports have focused on applying different components as surface layers while neglecting the impact of their crystallographic orientation on electrochemical performance. Here, a ZIF-8 layer is prepared as a model to elucidate this effect on the Zn anode. DFT calculations indicate that ZIF-8(200), compared to ZIF-8(110) and ZIF-8(211), exhibits a lower d-band center, a smaller difference in d-p band centers, and a weaker H₂O adsorption, thereby inhibiting hydrogen evolution as confirmed by experimental results. Meanwhile, ZIF-8(200) also increases the interfacial interaction between ZIF-8 and Zn, enhances the mechanical properties, and suppresses the dendrite growth. The small pores of ZIF-8 restrict the migration of SO₄ ²ˉ, I₃ˉ, and VO₂ ⁺, thus enabling the selective transport of Zn²⁺. Thus, the preferential orientation of ZIF-8(200) significantly improves the electrochemical performance of the Zn anodes. These results demonstrate a new way to improve the electrochemical performance of Zn anodes through crystal engineering of surface layers.