Synthesis of core-shell MoC@C(Nx) nanoparticles by DC arc plasma as highly efficient and durable oxygen reduction reaction catalyst for zinc-air battery

Zinc-air batteries (ZABs) have received much attention, but their commercial applications are limited by the sluggish kinetics of the oxygen reduction reaction (ORR) on the cathode. The key is to design non-precious metal ORR catalysts with low-cost and high-efficiency. Herein, nitrogen-doped carbon-coated molybdenum carbide nanoparticles (MoC@C(Nx) NPs) were prepared by DC arc plasma method and subsequent heat treatment. The energy state of the working arc plasma during the synthesis of MoC@C NPs precursor was diagnosed by real-time optical emission spectroscopy (OES). And the electron temperature (Te) in the local equilibrium plasma was 14,464.3 K. The obtained MoC@C(N1.09) NPs catalysts exhibited superior ORR catalytic activity with an onset potential (Eonset) of 0.88 V and a half-wave potential (E1/2) of 0.78 V, which are comparable to that of commercial Pt/C. Moreover, the stability and methanol resistance of MoC@C(N1.09) NPs catalysts are significantly better than those of Pt/C. The liquid ZABs assembled with MoC@C(N1.09) NPs presented a high open circuit voltage of 1.43 V, an excellent peak power density of 132.27 mW center dot cm(-2), a long discharge time of 95 h with a satisfactory specific capacity of 796.12 mAh center dot g(-1) and energy density of 969.28 Wh center dot kg(-1), which are superior to those of Pt/C-based ZAB. It is believed that the use of DC arc plasma as a powerful thermal source provides a convenient and efficient way to develop low-cost and high-efficiency non-precious-metal-based catalysts for ZABs.