Heteroatom (N, Co) Doped MXene with Tunable Doping for Enhanced Hydrogen Evolution Reaction and Energy Storage

Abstract

Ti₃C₂Tₓ MXene exhibits strong potential for energy storage and electrocatalysis, but its performance is constrained by limited active sites and moderate catalytic activity. In this study, the influence of nitrogen (N) and cobalt (Co) co-doping on the electrochemical performance of MXene is systematically examined by introducing a total dopant content of 5 wt.% and 10 wt.% (N + Co), prepared separately. Increasing the total dopant concentration to 10 wt.% results in slightly reduced performance, indicating limited benefit from higher loading, likely due to excess defects, disrupted ion transport, and partial blockage of active sites. These observations highlight the importance of optimizing the dual-doping level, with intermediate co-doping (5 wt.%) providing the most effective balance between structural modification and electrochemical functionality. The N and Co co-doped Ti₃C₂Tₓ MXene electrode with 5 wt.% doping exhibits the highest specific capacitance (~112 F g-1) compared to 10 wt.% (107 F g-1) and pristine (~88 F g-1) counterparts in KOH electrolyte. In HER measurements, the 5 wt.% N and Co co-doped electrode delivers a Tafel slope of ~93 mV dec⁻¹ and an overpotential of 245 mV (at 10 mA cm⁻²). Increasing the doping level to 10 wt.% results in a slightly higher Tafel slope of 99 mV dec⁻¹ and an overpotential of 252 mV. In comparison, the pristine MXene shows activity, with a Tafel slope of 115 mV dec⁻¹ and an overpotential of 298 mV at 10 mA cm⁻². The study shows that controlled co-doping is critical for optimizing MXene catalytic and capacitive performance.