Nitrogen-doped carbon quantum dots decorated on platinum catalysts for improved oxygen reduction reaction

Nitrogen-doped carbon quantum dots (N-CQDs) decorated on platinum (Pt) nanoparticles (Pt@N-CQDs) were synthesized for use as catalysts in the oxygen reduction reaction (ORR). Pt@N-CQDs were prepared by hydrothermal and reduction methods, and an optimum concentration of N-CQDs was demonstrated. The weight percentage of CQDs to Pt was tested at 10, 20, and 30 wt% to optimize the ORR performance. In particular, Pt@20N-CQDs with 20 wt% N-CQDs exhibit superior electrochemical performance, such as onset potential (E_onset) of ~0.925 V, half-wave potential (E_1/2) of ~0.834 V, and limited-current density of −3.83 mA cm⁻² at 0.5 V. In the durability test for ORR catalytic activity, Pt@20N-CQDs showed low potential degradation and superior long-term stability of 20 mV (90.6%) at E_1/2 after 5000 cycles in 0.1 M KOH electrolyte. These performance improvements are owing to improved electrical properties by N doping in the CQDs and the increased number of active sites with oxygen-containing functional groups.