Insight into Zn2+ Storage in Ti3C2T x MXene within the Underpotential Deposition Region

Abstract The search for alternatives to Li-ion batteries is accelerating the development of aqueous Zn-based electrochemical energy-storage systems such as Zn-ion batteries and Zn-ion hybrid supercapacitors. Despite the increasing use of Ti3C2Tx MXene as an interfacial material for Zn electrochemistry, the mechanisms governing Zn2+ behavior in the underpotential deposition (UPD) regime remain poorly understood. Here, we present a comprehensive multitechnique investigation of Zn2+ storage on inkjet-printed Ti3C2Tx MXene thin films. Electrochemical analyses combined with low-scan-rate kinetic studies, in situ Raman spectroscopy, SEM, XRD, and XPS reveal the emergence of a surface-confined process between –0.8 and –1.0 V vs Ag/AgCl that precedes bulk Zn deposition. The collected evidence indicates Zn2+ adsorption coupled with partial charge transfer and the formation of a quasi-two-dimensional Zn adlayer or nanocluster phase stabilized by Ti=O surface terminations. These findings shed light on the complexity of Zn2+ storage on Ti3C2Tx MXene and provide a coherent mechanistic framework describing the transition from capacitive charge storage to zinc metal nucleation. Understanding and controlling this UPD-like regime offers opportunities for engineering MXene interfaces toward highly reversible Zn plating and advanced aqueous Zn-based energy-storage devices.