Intercalation‐Induced Reversible Electrochromic Behavior of Two‐Dimensional Ti₃C₂T_<i>x</i> MXene in Organic Electrolytes

Abstract MXenes, a large family of two‐dimensional materials, have attracted tremendous attention due to their unique physical and chemical properties. Reversible ion intercalation between MXene layers allows modification of the optical, thermal, magnetic, and chemical properties. The electrochemical charge/discharge of MXenes in aqueous electrolytes was reported to lead to reversible electrochromic behavior. In this work, the electrochromic effect of semitransparent Ti 3 C 2 T x MXene film was probed by electrochemical intercalation of Li ions. Correspondingly, a peak shift of 100 nm was observed in the UV‐vis spectrum. By combining in‐situ Raman spectroscopy, in‐situ X‐ray diffraction, and density functional theory calculations, we show that the electrochromic shift is primarily due to the formation of robust O−Li bonds and the emerging bands induced changes of inter‐band excitations. Understanding the mechanism of electrochromic behavior in Ti 3 C 2 T x lays the foundations of designating 2D materials with durable, controllable, and efficient intercalation‐induced electrochromic behaviors.