Phase-selective synthesis of cubic WN and hexagonal WC carbide via solid–phase reaction pathways controlling for electrochemical applications

Abstract

Transition-metal nitrides and carbides hold significant promise in electrocatalysis and energy storage owing to their metallic-like electronic structures. Nevertheless, their synthesis is encumbered by demanding conditions, intricate thermodynamic-kinetic processes, and challenges in structural regulation. Achieving controlled synthesis in high-temperature environments presents a notable challenge. Herein, utilizing WO₃ as a precursor and C₂H₄N₄ as a reductant alongside carbon and nitrogen sources, we realized the phase-selective synthesis of cubic WN and hexagonal WC by synergistically adjusting the C₂H₄N₄ content, reaction temperature, and reaction time. Detailed investigation of the W-based oxide evolution under various reaction conditions revealed that temperature is the decisive parameter for phase separation between WN and WC, whereas the amount of C₂H₄N₄ governs the selective formation of different tungsten-carbide polymorphs. Furthermore, the lithium storage properties of WN and WC were investigated. As the anode, WC/C exhibits markedly superior kinetics. Ex situ XRD and in situ XRD analysis revealed that WN stores energy through transformation reactions in addition to some WN not undergoing phase transformation during electrochemical reactions. In contrast, WC/C does not undergo phase transformation during the reaction. The results of this study provide an experimental basis for the controllable synthesis of transition-metal nitrides and carbides and their application in energy-storage devices.