V–VO2 core–shell structure for potential thermal switching

Abstract

Since the cold start of the internal combustion engine is not fuel efficient for vehicles, a warm start is desired. In this work, we propose to use thermal switching materials to warm-up the engine quickly at the cold start. We found that the V–VO₂ core–shell structure can be a thermal switching material, which yields a higher electrical conductivity due to the electron transfer from V to VO₂ above the insulator to metal transition temperature. The surface of V particles was converted into VO₂ by controlled annealing in air, resulting in a V–VO₂ core–shell structure. With such a V–VO₂ core–shell structure, electrical conductivity increased from 2.1 × 10⁵ to 5.1 × 10⁵ S m⁻¹ through the insulator-to-metal transition, resulting in an electronic thermal conductivity increase from 1.51 to 4.87 W m⁻¹ K⁻¹.