Basal Plane Functionalization-Driven Catalytic Enhancement in Pristine and Metal-Incorporated MNenes for Hydrogen Evolution Reaction

Abstract

Two-dimensional (2D) MXenes have emerged as promising electrocatalysts for the hydrogen evolution reaction (HER) due to their tunable surface chemistry and high electrical conductivity, but a systematic study of the effect of metal incorporation on their HER activity is lacking. Existing metal-incorporated MXene studies focus on noble metals rather than their less expensive and abundant counterparts. Here, we systematically investigate the electrocatalytic HER activity of pristine Ti3CNTxcarbonitride, Ti4N3Tx, and Ti2NTxnitride MXenes (MNenes) and their metal-incorporated (Ni, Co, Fe) counterparts in alkaline environments. The pristine MNenes initially exhibited high overpotentials and sluggish kinetics. However, prolonged electrolysis resulted in significant HER activity enhancement, reducing overpotentials and improving reaction kinetics. A mechanistic investigation suggests that alkaline electrolysis likely induces the formation of −OH groups, creating more active sites. The transition metal incorporation improved HER performance, especially for MNenes, with the lowest overpotentials observed for Fe-incorporated Ti4N3Txand Ti2NTx, reaching 340 and 315 mV at 10 mA cm–2, respectively. However, its effect was minimal for Ti3CNTxafter extended electrolysis, where the pristine material showed comparable performance. Tafel slope analysis suggests a Volmer–Heyrovsky mechanism with the Volmer step as the rate-determining step for all catalysts. Overall, these findings demonstrate the use of metal-incorporated MNenes as effective electrocatalysts in alkaline HER.