Controlling the Surface Reactivity of Hybrid Ti₃CNT_x MXene via In Situ Electrocatalysis

Two-dimensional (2D) carbide and nitride MXenes possess properties that are desirable for a broad range of electrocatalytic applications including hydrogen evolution reaction (HER). These properties include high surface area, hydrophilicity, heterogeneity of redox-active transition metals, and tunable surface functionalities allowing for low HER overpotentials. MXenes are prepared from their MAX precursors by etching of the Al layers, using partial etching we synthesize a hybrid Ti₃CN capable of surface modifications using in situ electrochemistry. In this presentation, we report on the cathodic etching and –O/–OH functionalization of hybrid Ti₃CN upon the application of an external potential for improved HER performance and show that the active sites for HER on this MXene catalyst are located primarily on the –O– and –OH functional groups. The overpotential for the hybrid Ti₃CN improves by 350 mV upon in-situ -O functionalization and reaches -0.46 V vs. RHE at a current density of 10 mA cm^-2. Structural and electrochemical characterization results showed that the functionalized hybrid Ti₃CNT_x MXene catalyst is structurally and electrochemically stable. Further insights into the mechanism of simultaneous in situ etching and functionalization were provided by in-situ spectroelectrochemical techniques and the results will be presented. Ultimately, these findings provide a novel path forward to controlling the surface reactivity of MXenes using in-situ functionalization and electrochemical exfoliation.