Effects of Ga-doping on the electrochemical properties of PtNi octahedral catalysts for oxygen reduction reaction in PEM fuel cells

Abstract

Here, we report a gallium (Ga) metal doped on the surface of PtNi octahedral nanoparticles on the carbon support (Ga-PtNi/C) for oxygen reduction reaction (ORR) in PEM fuel cells. As- prepared Ga-PtNi/C catalyst had $1.24 A/mg_{pt}$ in mass activity, which represents a 19-fold and 2.7-fold increase compared with commercial $Pt/C (0.066 A/mg_{pt})$ and undoped PtNi/C catalysts $(0.464 A/mg_{pt})$, respectively. The Ga-PtNi/C catalyst not only showed remarkable enhancement in an initial ORR performance, but also exhibited a great stability with high Ni atoms content up to 40 atomic % in its nanoparticles. It maintained the initial octahedral shape even after 30,000 cycles, while the PtNi/C catalyst lost its initial octahedral shape, and the Ni atoms of the PtNi/C catalyst could be very easily dissolved in electrolyte only after 4,000 cycles. Only a small amount of Ga on the surface of PtNi octahedral catalysts contributed significantly to not only enhance ORR activity, but also hinder Ni atoms dissolution from PtNi nanoparticles. The addition of Ga modified the electronic structure of PtNi octahedral nanoparticles that enable the enhancement of the initial electrocatalytic activity and cycling stability as well. Furthermore, we fabricated a membrane electrode assembly (MEA) to demonstrate the possibility of using Ga-PtNi/C catalyst in practical applications. It showed higher polarization curves than that of commercial Pt/C, and Pt loading in cathode was only $0.15 mg_{pt}/cm^2$ in cathode. This result demonstrates that Ga-PtNi/C catalyst could be utilized as a catalyst in a real-life application.