Highly exfoliated Ti3C2Tx MXene nanosheets atomically doped with Cu for efficient electrochemical CO2 reduction: an experimental and theoretical study

Abstract

Ti₃C₂T_x MXene nanostructures have garnered attention for various catalytic applications due to their built-in electronic properties. Herein, we rationally design highly exfoliated two-dimensional Ti₃C₂T_x nanosheets (T_x = O, OH, and F) doped with Cu (denoted as Cu/Ti₃C₂T_x) for the electrochemical CO₂ reduction reaction (CO₂RR). The fabrication process entails the selective chemical etching of Ti₃AlC₂ followed by the delamination thereof under ultrasonic treatment and subsequent mixing with a Cu precursor to allow in situ doping. The resultant Cu/Ti₃C₂T_x are highly exfoliated nanosheets with a surface area of 46 m² g⁻¹ and are uniformly doped with Cu atoms (1.04 wt%). The CO₂RR current density of Cu/Ti₃C₂T_x (−1.08 mA cm⁻²) was 3.6 times higher than that of Ti₃C₂T_x (−0.3 mA cm⁻²) besides a lower onset reduction potential and Tafel slope, and higher stability, due to the greater surface area, electronic effect, and quicker charge transfer on Cu/Ti₃C₂T_x. The formic acid (HCOOH) faradaic efficiency on Cu/Ti₃C₂T_x (58.1%) was 3-fold higher than that on Ti₃C₂T_x (18.7%). Based on density functional theory (DFT) simulation, Cu-doping induces polarized sites with high electron density, allowing the CO₂RR path through the *HCOOH intermediate to form formic acid (HCOOH). The study presented here will open new pathways for using Ti₃C₂T_x doped with various metals for the CO₂RR.