Development of thermally stable carbon nanotube tapes by incorporating FeCl3

•Combination of electrical conductivity and thermal stability by two-step process.•Formation of FeCl2(H2O)4 species by introducing an aggressive oxidation process.•Preferential oxidation of FeCl2(H2O)4 suppresses CNT oxidative degradation. An effective process for incorporating FeCl3 into carbon nanotube (CNT) tapes is reported that harnesses high electrical conductivity and thermal stability. By actively introducing a controlled oxidation process, the intermediate iron species FeCl2(H2O)4, responsible for providing the high-temperature tolerance to CNT tapes, was successfully stabilized to increase the oxidative decomposition of CNTs by 75 °C, as compared with their unmodified counterparts. Thermal and structural characterizations revealed that the transformed FeCl2(H2O)4 was located inside the CNTs. This result expands the application of CNT tapes, as good lightweight and flexible conductors, for high-temperature industrial applications.