Pt-loaded nitrogen/sulfur co-doped graphene aerogel microspheres prepared by airflow-assisted electrostatic spraying for methanol electrooxidation

Abstract

The Pt-loaded nitrogen and sulfur co-doped graphene composite aerogel microspheres (Pt/NS-GAMs) are created through air-assisted electrostatic spraying of an aqueous dispersion of graphene oxide and l-cysteine, followed by freezing, freeze-drying, high-temperature carbonization, doping, and platinum (Pt) loading through a solvothermal reduction reaction. The Pt/NS-GAMs have an average microsphere size of 59.24 μm and a specific surface area of 331.36 m² g⁻¹. The formation of the hierarchical and interconnected pores in the small aerogel microspheres facilitates the Pt loading and dispersion. The N/S co-doping enhances the interaction between Pt and graphene, suppresses the agglomeration of Pt, promotes their uniform distribution and the formation of smaller size Pt nanoparticles (Pt NPs), and also improves the electrode's charge transfer capability. Furthermore, the N/S co-doping can increase the proportion of highly active Pt(111) crystal planes and modulate the Pt electronic structure. Consequently, the Pt/NS-GAMs electrode exhibits excellent electrocatalytic methanol oxidation performance with a mass activity of up to 1459.74 mA·mg⁻¹_Pt, which is 4.35 times higher than that of commercial Pt/C electrodes. The Pt/NS-GAMs electrode also demonstrates long-term electrocatalytic stability. The role of the formed pyrrolic-N and thiophenic-S by N/S-doping in tuning the Pt's electronic structure and its subsequent impact on the electrocatalytic reaction (MOR) on the Pt surface is disclosed by DFT theoretical calculations. The N and S co-doped structure lowers the energy of the Pt d-band centre, and weakens the adsorption strength of CO on the Pt active site by sacrificing partial electron transfer.