Solvent-engineered Ni-Co selenide-Ti3C2Tx MXene heterostructures with interfacial electronic coupling for integrated water splitting and energy storage

Abstract

Developing cost-effective bifunctional materials that seamlessly integrate energy conversion and storage is critical for next-generation energy systems. Herein, we report a solvent-engineered, in situ solvothermal strategy to fabricate Ni-Co selenide-Ti 3 C 2 T x MXene (NCSM) heterostructures with tunable morphology, interfacial coupling, and pore architecture for integrated electrocatalysis and energy storage. Systematic modulation of solvent polarity (water-ethanol, ethylene glycol, and acetone) governs the nucleation kinetics and growth pathways, leading to different nanostructures and pore networks. The water-ethanol-derived composite (NCSM-WE) shows a hierarchical nanoflake network with a high surface area of 56.68 m 2 g -1 , surpassing the performance of ethylene glycol-derived nanospheres and acetone-induced nanopetals. Non-Local Density Functional Theory (NLDFT) analysis reveals solvent-dependent mesopore distribution and interconnected ion diffusion channels that facilitate electrocatalytic kinetics and capacitive charge storage. The NCSM-WE requires low overpotentials of 258 mV for the oxygen evolution and 146 mV for the hydrogen evolution reactions at 10 mA cm -2 , accompanied by small Tafel slopes (55/58 mV dec -1 ) and sustained stability over 50 h. As a battery-type supercapacitor electrode, it achieves a specific capacity of 715 C g -1 at 1 A g -1 . Moreover, a hybrid NCSM-WE//AC device delivers an energy density of 49.8 Wh kg -1 at 888 W kg -1 power density. DFT calculations on an idealized NiCo 2 Se 4 -Ti 3 C 2 (OH) heterostructure suggest favorable interfacial electronic interactions and enhanced electronic states near the Fermi level, providing mechanistic insight into the experimentally observed enhancement in catalytic and supercapacitor performance. This synergistic experimental and theoretical study provides fundamental insights for designing next-generation, high-performance multifunctional energy materials.