Terpyridine-functionalized single-walled carbon nanotubes towards selectivity in the oxygen reduction reaction

Abstract

Single-walled carbon nanotubes (SWCNTs) have been widely employed as electrocatalysts due to their exceptional mechanical strength and electronic properties, despite lacking intrinsic catalytic centers. Current research efforts focus on enhancing their catalytic activity by modifying them with organometallic chelate complexes, to achieve controlled molecular-level structuring and improved performance in Proton Exchange Membrane Fuel Cells (PEMFCs). While the mechanistic understanding of their electrocatalytic behavior in relation to molecular structure remains in its early stages, it offers valuable insights for the development of efficient electrocatalysts. In this study, SWCNTs were stepwise chemically modified with terpyridine ligands both in the absence of metal and in the presence of ruthenium (Ru) in two different oxidation states. The resulting SWCNT-based nanomaterials were characterized using Raman, UV-Vis, XPS and energy-dispersive X-ray spectroscopy (EDS) coupled with transmission electron microscopy (TEM) imaging, while the degree of functionalization was assessed through thermogravimetric analysis (TGA). A comprehensive electrocatalytic investigation demonstrated how covalent modification with Ru²⁺ and Ru³⁺ terpyridine complexes influences the mechanistic pathway of the oxygen reduction reaction (ORR). This comparative analysis underscores the critical role of the first coordination sphere of precious metals in both the thermodynamics and kinetics of ORR, when anchored onto carbon nanomaterial lattices, providing valuable insights for the nanostructured design of efficient carbon-based electrocatalysts.