Study of the impact of etching mixtures on the surface chemistry and electrocatalytic activity of multilayer Ti3C2Tx MXenes

Ti₃C₂Tₓ MXenes are commonly obtained through the chemical etching of the Ti₃AlC₂ MAX phase; however, the influence of the composition of the etching medium on their physicochemical properties and electrocatalytic performance requires further detailed understanding. This study comparatively evaluates the effect of three fluorine-based etching systems (HF, HF–LiCl, and HF–HCl) on the structure, surface chemistry, and electrocatalytic activity of multilayered MXenes. The main contribution of this study is establishing a relationship between the etching medium composition, the structural and surface modifications of Ti₃C₂Tₓ, and its response applied to the hydrogen evolution reaction (HER). The results showed that incorporating LiCl and HCl into the HF medium significantly modifies the Al removal process and the final characteristics of the MXene. In particular, the HF–LiCl and HF–HCl systems facilitate more efficient Al removal and produce more homogeneous morphologies than concentrated HF. Furthermore, the HF–HCl system yields greater interlayer spacing and a higher presence of Ti–O and Ti–OH functional groups, thereby enhancing active site accessibility and charge transfer. These modifications impacted directly the electrochemical performance since the MXene obtained using HF–HCl exhibits the highest HER activity, associated with a larger electrochemically active surface area and lower charge-transfer resistance. Overall, the results demonstrated that the chemistry of the etching medium is a decisive parameter for simultaneously controlling the structure, surface chemistry, and electrocatalytic behavior of Ti₃C₂Tₓ. These findings highlight the importance of optimizing synthesis conditions as a materials engineering strategy to obtain MXenes with tailored properties for energy conversion and electrocatalysis applications.