Enhanced Oxygen Reduction Reaction Activity on the Melamine-Modified Pt-High-Entropy Alloy Single-Crystal Lattice Stacking Surface

We investigated the enhancement behaviors of oxygen reduction reaction (ORR) properties for Pt/Cr–Mn–Fe–Co–Ni (Cantor alloy)/Pt(111) and (110) lattice stacking surfaces in 0.1 M HClO4 by varying melamine concentrations from 0.01 to 10 μM using a rotating disk electrode method. The ORR activity and structural stability of the Pt surfaces are surely correlated with the melamine concentration. The initial specific activity of Pt/Cantor alloy/Pt(111) depended on the added melamine concentration; activity enhancement factors vs the activity estimated without melamine addition increased with melamine concentration up to 0.1 μM and then decreased. In contrast, the activity of the Pt/Cantor alloy/Pt(110) decreased monotonically with increasing melamine concentration. These results suggested that melamine molecules tended to adsorb on the (110) surface sites of Pt and then on the (111) terrace sites with an increasing melamine concentration. Furthermore, the addition of 0.1 μM melamine effectively suppressed the structural degradation of both Pt/Cantor alloy/Pt(111) and (110) surfaces induced by the potential cycle loadings of 0.6–1.0 V vs the reversible hydrogen electrode. This study clearly demonstrates that optimizing the melamine surface coverage of Pt- or Pt-based alloy surfaces is crucial for enhancing the ORR properties (activity and durability), thereby improving the polymer electrolyte membrane fuel cell performance.