Chloride Ions: Essential Agents for Achieving Spontaneous Delamination of MXene

Despite significant advancements in MXene synthesis, the etching and delamination processes remained largely empirical, with limited understanding of their underlying mechanisms. Here, we uncover the pivotal role of chloride ions (Cl^-) in enabling spontaneous delamination by facilitating Li⁺ ion intercalation through interlayer expansion and surface termination during the etching. In all cases, delamination is not observed where Cl^- was absent in the etchant, and spontaneous delamination occurs only in samples where chlorine terminations are formed during the etching. Our findings are utilized to develop a one-step, maximized spontaneous MXene synthesis method with high delamination efficiency, yielding an 83.6% production rate and an enhanced electrical conductivity of ∼15 000 S/cm. It shows superior performance in transparent conductive films and Joule heating devices, showcasing their potential for next-generation electronic and energy systems. This delamination mechanism and synthesis approach are not limited to Ti₃AlC₂ MAX but can be extended to other MAX phases, highlighting their broad applicability. Observations made in this effort should serve as the foundation for designing new synthesis routes for diverse MAX phases and advancing MXene-based applications.