(625h) Optimizing the Properties of Ti2n Mxene through Decoupling Surface and Bulk Structure and Phenomena

The continued rise in global energy consumption, along with the associated environmental hazards, pose a significant risk to our society’s infrastructure unless the main source is changed. Electrocatalysis involving hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), and oxygen reduction reaction (ORR), provide a pathway for energy storage and conversion due to their enhanced environmental friendliness and efficient energy input compared to their thermocatalytic counterparts. Currently, the state-of-the-art electrocatalysts suffer from scarcity and high cost. MXenes, a novel family of two-dimensional (2D) transition metal carbide and nitride materials, show potential as cost-efficient and highly abundant electrocatalysts with limited knowledge on their electrocatalytic mechanisms. This is especially true when considering the often-overlooked nitride family of MXenes. Herein, we investigate the electrocatalytic performance of a Ti₂N nitride MXene under different electrolytic environment. The effect of surface phenomena is investigated through manipulation of the surface passivation layer, as evidenced by Raman and Fourier-transform infrared (FTIR) spectroscopies, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Successful decoupling of the bulk and surface phenomena is achieved through Raman laser power attenuation. Under acidic medium, the surface reactivity towards HER is poor but the bulk reactivity for NRR is favored, making it an optimal NRR catalyst. Under alkaline medium, the surface reactivity of the pristine Ti₂N MXene for ORR is high, but also leads to surface passivation and thus hinders the long-term electrocatalytic activity. Overall, these results provide fundamental insights into future optimization strategies of the Ti₂N nitride MXene, along with other electrocatalysts, towards electrocatalytic applications.