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Pt Immobilization within a Tailored Porous-Organic Polymer–Graphene Composite: Opportunities in the Hydrogen Evolving Reaction

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journal contribution
posted on 2017-10-24, 15:07 authored by Ahmed B. Soliman, Mohamed H. Hassan, Tran Ngoc Huan, Arwa A. Abugable, Worood A. Elmehalmey, Stavros G. Karakalos, Manuel Tsotsalas, Marita Heinle, Mady Elbahri, Marc Fontecave, Mohamed H. Alkordi
A facile, postsynthetic treatment of a designed composite of pyrimidine-based porous-organic polymer and graphene (PyPOP@G) with ionic Pt, and the subsequent uniform electrodeposition of Pt metallic within the pores, led to the formation of a composite material (PyPOP-Pt@G). The pyrimidine porous-organic polymer (PyPOP) was selected because of the abundant Lewis-base binding sites within its backbone, to be combined with graphene to produce the PyPOP@G composite that was shown to uptake Pt ions simply upon brief incubation in H2PtCl6 solution in acetonitrile. The XPS analysis of PyPOP@G sample impregnated with Pt ions confirmed the presence of Pt­(II/IV) species and did not show any signs of metallic nanoparticles, as further confirmed by transmission electron microscopy. Immediately upon electrochemical reduction of the Pt­(II/IV), metallic Pt (most likely atomistic Pt) was observed. This approach stands out, as compared to Pt monolayer deposition techniques atop metal foams, or a recently reported atomic layer deposition (ALD), as a way of depositing submonolayer coverage of precious catalysts within the 1–10 nm pores found in microporous solids. The prepared catalyst platform demonstrated large current density (100 mA/cm2) at 122 mV applied overpotential for the hydrogen evolution reaction (HER), with measured Faradaic efficiency of 97(±1)%. Its mass activity (1.13 A/mgPt) surpasses that of commercial Pt/C (∼0.38 A/mgPt) at the overpotential of 100 mV. High durability has been assessed by cyclic and linear sweep voltammetry, as well as controlled potential electrolysis techniques. The Tafel plot for the catalyst demonstrated a slope of ∼37 mV/decade, indicating a Heyrovsky-type rate-limiting step in the observed HER.

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