Ultrafine and Highly Dispersed PtRu Alloy on Polyacrylic Acid-Grafted Carbon Nanotube@Tin Oxide Core/Shell Composites for Direct Methanol Fuel Cells

There has been immense interest in the hierarchical design of structural composite materials as electrocatalysts with high performance for direct methanol fuel cells (DMFCs). Herein, we rationally designed and prepared a newly hierarchical quaternary nanocomposite composed of carbon nanotubes (CNTs), polyacrylic acid (PAA), SnO₂layers, and PtRu alloys. In this multiple-phase boundary nanostructure, tiny-sized PtRu alloy particles are deposited in a highly dispersed form on the robust CNT support owing to the efficient utilization of covalently grafted PAA brushes and uniformly coated SnO₂layer. The overall electrocatalytic activity of as-prepared CNT-g-PAA@SnO₂/PtRu catalysts for methanol oxidation has been thoroughly studied. Among these, the best CNT-g-PAA@SnO₂/PtRu catalyst exhibits well-balanced performance with a high mass activity (519.74 mA mg^-1of Pt), a low onset potential (0.16 V), and good I_f/I_bvalues (1.40). Furthermore, the activities of the CNT-g-PAA@SnO₂/PtRu catalysts were evaluated using the single-cell DMFC test, which reveals superior performance toward methanol oxidation as compared with the reported catalysts. The outstanding performance of the prepared CNT-g-PAA@SnO₂/PtRu catalysts is attributed to the good dispersion and small particle size of PtRu alloy nanoparticles (NPs), the high porosity, and the electrical conductivity of the CNT support and the rational synergism with the combined effect (i.e., enhancing the intrinsic activity of PtRu, promoting the formation of active OH species from water, and improving CO poisoning tolerance). This work provides some guidance for the fabrication of hierarchical composite materials for use in DMFCs.