Triazine compounds for the high enhancement of the ORR activity and durability of Pt/C

The effects of triazines on the oxygen reduction reaction activity and durability of Pt/C were examined. Pt/C treated with triazines besides melamine exhibited lower ORR activity than that treated with melamine. Triazines, with the exception of melamine, were not strongly adsorbed on the Pt surface, and the weak interaction with Pt/C resulted in a low enhancement effect. In contrast, when triazines were dissolved in an electrolyte solution, a strong enhancement effect (> 4-fold at an optimized concentration) was observed because they were supplied from the solution. The dependence of activity on the concentration of triazine in the solution was also examined. The concentration at which maximum activity is observed varied based on the triazine used, reflecting the strength of the interaction between triazines and Pt. Furthermore, triazines with amino group(s) considerably enhanced the durability of Pt/C, whereas cyanuric acid without an amino group did not suppress degradation. While the surface area of Pt decreased by 63 % after a degradation test (0.6 V(3 s)–1.0 V(3 s), 10,000 cycles, at 80 °C) in the absence of triazines, it only decreased by less than 20 % in the presence of aminotrizines. Transmission electron microscopy observations clearly show that aminotriazines significantly attenuated the increase in the Pt nanoparticle size after the degradation test. Cyclic voltammograms of Pt/C in the presence of aminotriazines suggested that the suppression of degradation may be due to the suppression of the Pt surface oxidation and the protection of vulnerable sites on Pt nanoparticles.