Optimized electrocatalytic performance of PtZn intermetallic nanoparticles for methanol oxidation by designing catalyst support and fine-tuning surface composition

Abstract

The electrode performance of fuel cells highly depends on the characteristics of catalysts and catalyst supports. In this work, small PtZn intermetallic (PtZn-i) nanoparticles (< 4 nm) with adjustable surface composition are fabricated on graphene-based nitrogen-doped porous carbon support by pyrolysis of Pt-injected ZIF-8 (ZIF-8@Pt) on electrochemically exfoliated graphene (EEG). This designed two-dimensional porous carbon is capable of providing an electron transfer network and mass transport channels for PtZn-i catalysts. Moreover, in-situ growth of PtZn-i nanoparticles embedded in the carbon wall ensures the small size and high dispersibility of the catalysts, which are beneficial for methanol oxidation on them. Besides, the surface electronic structure of PtZn-i catalysts is fine-tuned by adjusting the mole ratio of Pt to Zn. The results show that PtZn-i catalysts with slightly Zn-rich surface (Pt/Zn = 0.9) exhibit optimized electrocatalytic performance for methanol oxidation. Density functional theory calculations reveal that slightly increasing Zn atoms in the surface can enhance the adsorption of CH2OH* intermediate on PtZn-i catalysts, thereby reducing the reaction free energy of the rate-determining step of methanol oxidation reaction and promoting the electrocatalytic performance of PtZn-i catalysts. This work provides a new perspective to improve the electrocatalytic performance of intermetallic catalysts by surface modification and support design.