Polyallylamine-directed green synthesis of platinum nanocubes. Shape and electronic effect codependent enhanced electrocatalytic activity

Abstract

The synthesis of Pt nanocrystals with controlled size and morphology has drawn enormous interest due to their particular catalytic activity. We present a facile and green hydrothermal method for synthesizing monodisperse Pt nanocubes (Pt-NCs) with polyallylamine hydrochloride (PAH) as a complex-forming agent, capping agent and facet-selective agent, and formaldehyde as a reductant. The formation mechanism, particle size and surface composition of the Pt-NCs were investigated by Ultraviolet and visible spectroscopy (UV-vis), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), etc. In the proposed PAH–K₂PtCl₄–HCHO synthesis system, the raw material could be reutilized to re-synthesize the Pt-NCs, and the particle size of the Pt-NCs could be readily controlled by the reduction rate of the Pt^II species in the Pt^II–PAH complex. After UV/Ozone and electrochemical cleaning, the residual PAH on the Pt-NC surfaces still strongly influenced the d-band centre of Pt due to the strong N–Pt interaction. The as-prepared 6 nm Pt-NCs showed superior electrocatalytic activity (mass activity and specific activity) and stability towards the oxygen reduction reaction (ORR) in both H₂SO₄ and HClO₄ electrolytes compared to the commercial E-TEK Pt black, owing to the combination of the facets effect and electronic effect.