Non-equilibrium surface reconstruction of MXene via nitridation modification for pseudocapacitance-dominated sodium storage

• Millisecond urea-assisted Joule heating replaces –F/–OH with Ti–N termination. • • RJH preserves the 2D lamellar framework that furnace annealing collapses. • • R-MXene-700 sustains 5000 sodium-storage cycles with only 0.0087% decay per cycle. Two-dimensional MXenes are promising sodium-ion battery anodes, but their inert −F/–OH surface terminations impede Na + transport, and the thermal treatments used to remove them inevitably collapse the lamellar framework. Here we demonstrate a millisecond non-equilibrium surface reconstruction of MXenes via a urea-assisted Rapid Joule Heating (RJH) technique that resolves this trade-off. The transient thermal shock substantially removes the −F/–OH terminations and incorporates a low level of nitrogen at the surface termination sites while preserving the 2D lamellar structure that is destroyed by furnace annealing at the same temperature. The reconstructed surface sustains fast, surface-dominated sodium storage — a pseudocapacitive contribution of 82% at 1.0 mV s −1 that rises to 88% at 2.0 mV s −1 — while delivering a substantially higher specific capacity than the furnace-annealed control at every current density, together with ultra-long cycling stability (5000 cycles with only 0.0087% capacity decay per cycle). Density functional theory calculations attribute the enhanced kinetics to reduced Na⁺ migration barriers upon nitrogen doping. This non-equilibrium strategy offers a general route to tune MXene surface chemistry while preserving structural integrity, with broad implications for high-rate sodium storage. Urea-assisted rapid Joule heating (RJH) reconstructs the MXene surface within 60 s, removing the inert –F/–OH terminations and grafting nitrogen at the surface termination sites while preserving the two-dimensional lamellar framework that furnace annealing collapses. A urea-free control confirms that the nitrogen termination, rather than the thermal shock itself, governs the sodium-storage kinetics. The optimized R-MXene-700 electrode delivers 193 mAh g −1 at 0.5 A g −1 and 173.4 mAh g −1 in the second cycle at 5 A g −1 , with only 0.0087% capacity decay per cycle over 5000 cycles. Download: Download high-res image (98KB) Download: Download full-size image