Phase Selective Synthesis of Cubic WN and Hexagonal WC Carbide via Solid-phase Reaction Pathways Controlling for Electrochemical Applications

Abstract

Organic-inorganic hybrid materials (OIHM) by high-temperature carbonization for synthesizing TMCs is advantageous due to its safety, uniform carbonization, and controllable composition. In this study, WO3 and C2H4N4 were used as precursors, mixed by mechanical grinding, and carbonized in Ar atmosphere to synthesize tungsten carbide. The effects of the amount of C2H4N4 added, carbonization temperature, and carbonization time on the synthesized products were explored. The synthesis of WN and WC/C, as well as composite phases of WC&W2C&WC1-x, WC&W2C, and WC&WC1-x, was achieved. Lithium-ion storage mechanisms and electrochemical performance of WN and WC/C as anodes for Lithium-ion capacitors (LICs) were investigated systematically. Compared to WN, WC/C exhibited superior rate performance, pseudocapacitive contribution, and DLi+, but lower specific capacity at various current densities. Ex-situ XRD analysis revealed that WN stores energy through transformation reactions in addition to some WN that doesn't undergo phase transformation during electrochemical reactions. In contrast, WC/C doesn't undergo phase transformation during the reaction. WN//AC and WC/C//AC devices achieved energy density of 83.25 Wh kg-1 and 44.25 Wh kg-1 at 195 W kg-1, respectively, and 32.24 Wh kg-1 and 13.26 Wh kg-1 at 9.36 kW kg-1. This investigation reveals the significant promise of tungsten carbide and tungsten nitride in LICs.