We report the synthesis of new carbon nanomaterial-based metal chelates that enable the effective electronic coupling to electrocatalytic transition metals. In particular, multi-walled carbon nanotubes (MWCNTs) and few layered graphene (FLGs) were covalently functionalized by the microwave-assisted cycloaddition with nitrile oxides to form metal-binding isoxazoline functional groups with high densities. The covalent attachment was evidenced by Raman Spectroscopy and the chemical identity of the surface functional groups were confirmed by XPS and ToF-SIMS. The functional carbon nanomaterials effectively chelate precious metals Ir(III), Pt(II) and Ru(III), as well as earth-abundant metals such as Ni(II), to afford materials with metal contents as high as 3.0 at%. The molecularly dispersed nature of the catalysts is confirmed by STEM-EDS elemental mapping. The interplay between the chelate structure on graphene surface and its metal binding ability has also been investigated by a combination of experimental and computational studies. The defined ligands on the graphene surfaces enable the formation of structurally precise heterogeneous molecular catalysts. The direct attachment of the isoxazoline functional on the graphene surfaces provides strong electronic coupling between the chelated metal species and the conductive carbon nanomaterial support. We demonstrate that the metal-chelated carbon nanomaterials are effective heterogeneous catalysts in the oxygen evolution reaction with low overpotentials and tunable catalytic activity.

Electrocatalytic isoxazoline-nanocarbon metal complexes

ACS Fall 2021

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