Real-time diagnostic synthesis of nitrogen-doped carbon-coated VC@C(Nx) core-shell nanoparticles by DC arc plasma as efficient ORR electrocatalysts

Abstract

The high complexity and cost of synthesis methods, along with the instability of catalytic activity, pose significant challenges in the search for viable non-precious metal alternatives to commercial Pt/C catalysts for oxygen reduction reaction (ORR). In this study, we employed a highly efficient and cost-effective method, namely, DC arc plasma, to synthesize carbon-coated vanadium carbide (VC@C) core-shell nanoparticles in a one-step process. The synthesized VC@C material was subsequently nitrogen-doped using urea as a nitrogen (N) source in a tube furnace, resulting in the formation of N-doped carbon-coated VC [VC@C(Nx)] catalysts for ORR electrocatalysis in alkaline media. Real-time optical emission spectroscopy (OES) analysis offers an in-depth comprehension of the energy states involved in the synthesis process of VC@C nanocrystalline powders. Highlighting the plasma states at various stages throughout the synthesis, provides a solid basis for dissecting the formation of VC@C nanoparticles and elucidating the intricate nature of their core-shell structures. Compared to the VC@C catalyst, the VC@C(N10) catalyst exhibited a significant improvement in both half-wave and onset potential, approaching the performance levels comparable to Pt/C catalysts. Moreover, VC@C(N10) demonstrated superior ORR kinetics, stability, and methanol tolerance. The exceptional performance of VC@C(N10) could be primarily attributed to the introduction of nitrogen doping, which generated more active sites and enhanced the synergistic cooperation between the VC core and the nitrogen-doped carbon shell. Additionally, the protective effect from the carbon shell prevented corrosion and oxidation of the VC core. This study represents a new exploration in the quest for the development of stable and efficient non-precious metal catalysts for ORR applications.