Manipulating the interaction of Pt NPs with N-hollow carbon spheres by F-doping for boosting oxygen reduction/methanol oxidation reactions

Abstract

Highly dispersed Pt NPs anchored in hierarchically N,F co-doped hollow carbon spheres (Pt@N,F-HCS) were synthesized through a template-assisted strategy followed by fluorination and wet chemical reduction. Due to the introduction of F heteroatoms into the carbon skeleton, the degree of d–π electron conjugation between Pt NPs and N,F-HCS can be enhanced. This will lead to higher Pt^x+ content in Pt species, which is beneficial for the effective adsorption of *OOH intermediates and is conducive to O–O bond breaking and triggers the direct 4-electron transfer mechanism for the ORR. In particular, the onset potential and half-wave potential values for the ORR are more positive than Pt@N-HCS without F doping, even outperforming 20%Pt/C. Besides, the Pt@N,F-HCS catalyst also possesses the smallest onset potential and largest methanol oxidation current for the MOR. In alkaline media, abundant OH⁻ will be adsorbed around the Pt^x+ sites due to its higher positive valence, and the reaction intermediate CO_ads generated in Pt^x+ sites will be further oxidized to the final product, CO₂, thus improving the MOR activity and CO tolerance capacity. This heteroatom-doping strategy is favorable for enhancing the interaction between Pt NPs and the carbon-based support, and also provides insight to promote the activity and selectivity for direct methanol fuel cells.