Synthesis of hollow structured PtNi/Pt core/shell and Pt-only nanoparticles via galvanic displacement and selective etching for efficient oxygen reduction reaction

This study uses a simple galvanic displacement-acid etching method for synthesizing PtNi nanoparticles with different morphologies and surface properties. Core/shell structured Ni/PtNi nanoparticles were prepared from nickel nanoparticles subjected to a galvanic displacement reaction with Pt ions. By controlling the dealloying conditions, hollow PtNi/Pt core/shell (H-PtNi/Pt) and Pt-only (H-Pt) nanoparticles could be formed. The H-PtNi/Pt catalyst showed the highest oxygen reduction reaction (ORR) mass and specific activities (0.8 A mg⁻¹_Pt and 1520 μA cm⁻²_Pt at 0.9 V_RHE), which were 3.33- and 5.67-times higher than those of commercial Pt/C. It revealed that forming a PtNi/Pt core/shell structure with a hollow morphology plays an important role for enhancing ORR activity. The H-PtNi/Pt catalyst also showed a very low degradation in specific activity of less than 1% after extensive potential cycling (10,000 cycles) due to the stable platinum outer layer covering the hollow PtNi alloy structure.