Cathodic Zn underpotential deposition: an evitable degradation mechanism in aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are promising for large-scale energy storage, but their development is plagued by inadequate cycle life. Here, for the first time, we reveal an unusual phenomenon of cathodic underpotential deposition (UPD) of Zn, which is highly irreversible and considered the origin of the inferior cycling stability of AZIBs. Combining experimental and theoretical simulation approaches, we propose that the UPD process agrees with a two-dimensional nucleation and growth model, following a thermodynamically feasible mechanism. Furthermore, the universality of Zn UPD is identified in systems, including VO