Synthesis and conductivity measurement of carbon spheres by catalytic CVD using non-magnetic metal complexes

► Non-magnetic metal complexes of La, Nb, and Ti as catalyst. ► Catalytic chemical vapor deposition (CCVD). ► Micrometer-sized carbon spheres (CSs). ► CSs with good electrical and thermal conductivity comparable to commercial Vulcan XC72. Carbon spheres (CSs) have been an important subject of research in recent years. Catalytic chemical vapor deposition (CCVD) was carried out in this work to synthesize solid-core CSs at mild temperatures from 720 to 810 °C. Non-magnetic metal complexes of La, Nb, and Ti, dispersed on porous kaolin support, were tried out as catalyst. X-ray diffraction patterns revealed the graphitic structures of CSs. TEM analysis showed no encapsulated transition-metal nanoparticles inside the CSs. It was found by Raman spectra that the La catalyst resulted in CSs with higher graphitization. To examine the potential applications of CSs to the fields such as catalysis, electrochemistry, and electronic device, values of the thermal and electrical conductivity of the prepared CSs using different catalysts were measured and found to be comparable to those of the commercial carbon black.