Insights into oxygen reduction reaction on pristine carbon nanoparticles synthesized by the plasma-in-liquid process

Abstract

Carbon-based materials have been widely studied as promising energy conversion materials that can replace noble metal catalysts. In addition, the plasma-in-liquid process has recently been used to synthesize heteroatom-doped carbon materials for oxygen reduction reactions, such as nitrogen-, boron-, and halogen-doped carbon. However, there has been a lack of insight into pristine carbon, which is the base material for such reactions. In this study, pristine carbon materials (Cx-P) were synthesized using a plasma-in-liquid process, and the material properties and oxygen reduction reaction (ORR) performance were analyzed with respect to heat treatment. Cx-P was successfully synthesized as a carbon nanoparticle and redesigned as partially crystallized carbon with various pore-size distributions using heat treatment. The 2-electron-transfer ORR pathway was identified as the intrinsic reduction route. On the other hand, the electrochemical activity increased with heat treatment, showing an unexpectedly superior kinetic current density of ~18.30 mA cm−2 (at 0.5 V vs. RHE). Our results are expected to provide an important reference to the ORR performance of the relevant carbon materials, including insights into the basic material properties of partially crystallized porous carbon synthesized using the plasma-in-liquid process.