TWO-DIMENSIONAL ELECTRODE MATERIALS WITH TUNABLE INTERLAYER SPACING AND SURFACE FUNCTIONAL GROUPS FOR EFFICIENT SODIUM-ION STORAGE AND SUPERCAPACITIVE APPLICATIONS

Abstract

Two-dimensional (2D) electrode materials with tunable interlayer spacing and controllable surface functional groups are promising candidates for sodium-ion batteries and supercapacitors, yet quantitative relationships between interlayer architecture, surface chemistry, ion diffusion kinetics, and electrochemical performance remain unclear. This study investigates three engineered platforms: Ti₃C₂Tₓ MXene with expanded interlayer spacing, molybdenum disulfide/reduced graphene oxide (MoS₂/rGO) hybrids, and nitrogen-functionalized graphene aerogels. Selective etching, hydrothermal synthesis, chemical intercalation, and surface functionalization were used to regulate interlayer spacing and functional groups. Structure and chemistry were examined by X-ray diffraction, electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, and electrochemical behavior by cyclic voltammetry, galvanostatic charge–discharge, impedance spectroscopy, and galvanostatic intermittent titration.

Interlayer spacing was varied from 0.62 to 1.28 nm in the MXene series. The optimized expanded MXene delivered 285 mAh g⁻¹ at 0.1 A g⁻¹ and retained 91.4% of its capacity after 1,500 cycles, with a capacitive contribution of 78% at 100 mV s⁻¹. The optimized MoS₂/rGO hybrid exhibited 412 F g⁻¹ at 1 A g⁻¹, and the nitrogen-functionalized graphene aerogel delivered 28.5 Wh kg⁻¹ at 850 W kg⁻¹ in a symmetric supercapacitor. Sodium-ion diffusion improved markedly with increasing interlayer spacing, accompanied by reduced charge-transfer resistance. These findings establish a structure–property–performance framework for optimizing 2D electrode architectures for sodium-ion storage and supercapacitive energy storage.