Micelle-templated synthesis of Pt hollow nanospheres for catalytic hydrogen evolution

Abstract

As an alternative to galvanic replacement reactions and hard-template strategies, we report an efficient, mild and simple synthesis strategy for fabrication of colloidal platinum (Pt) hollow nanospheres. An aqueous asymmetric triblock copolymer poly(styrene-b-vinyl-2-pyridine-b-ethylene oxide) [PS(20.1k)–PVP(14.2k)–PEO(26.0)] micelle with core–shell–corona architecture has been found to be an efficient soft scaffold for the synthesis of Pt hollow nanospheres using K₂PtCl₆ as a metal precursor and NaBH₄ as a reducing agent. In the core–shell–corona type micelles, the core serves as a template for void volume creation, the shell domain acts reaction site for inorganic precursors, and the corona stabilizes the composite particles. The polymer/Pt composite particles were solvent-extracted by refluxing with dimethyl formamide (DMF) at 160 °C to remove polymeric materials and obtain hollow particles. Investigation of precursor concentrations suggested that the wall-structures become irregular and uneven as the molar ratio of PVP/Pt(IV) increases from 1 : 12 to 1 : 25, whereas the use of polymers with large PS block length [PS(45k)–PVP(16k)–PEO(8.5)] results in the formation of spherical particles with slightly increased hollow void-space diameters. The polymeric micelles and Pt hollow nanospheres were thoroughly characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), infra-red (FT IR), thermal (TG/DTA) and nitrogen sorption analyses. The catalytic activity of the Pt hollow nanospheres was investigated for hydrogen liberation from ammonia–borane (AB) by hydrolysis reaction at room temperature. The catalytic activity of the Pt hollow nanospheres reveals that they can serve as a promising heterogeneous catalyst towards hydrogen generation system using AB as solid hydrogen storage materials.