Precise diameter control derived intermetallic PtNiCo nanowires: a simple two-step synthesis and operando XAS insight

Abstract

Developing efficient and high-performance catalysts is imperative for the commercial deployment of proton exchange membrane fuel cells (PEMFCs). Ordered intermetallic Pt-based nanowires emerge as a promising candidate, offering a powerful combination of remarkable catalytic activity due to their well-defined atomic arrangements, which modulate the d-band center of Pt and enhance oxygen reduction reaction (ORR) kinetics. However, synthesizing ordered nanowire structures with superior ORR activity remains a formidable challenge as the high-temperature treatment required to induce atomic ordering often leads to the collapse or fragmentation of ultrathin wires, while thicker nanowires, though structurally intact, frequently exhibit suboptimal catalytic activity due to limited surface reactivity and mass transport constraints. Herein, for the first time, we report a facile hydrothermal synthesis followed by direct annealing to produce structurally robust, ordered PtNiCo intermetallic nanowires (I-PtNiCo-NW/C) with precisely controlled diameters, eliminating the need for protective coatings or harsh post-treatment to preserve nanowire morphology. By systematically tuning the nanowire diameters (<5 nm, ∼15 nm, and ∼30 nm), we demonstrate that intermediate-diameter ordered nanowires (∼15 nm) strike an optimal balance between structural integrity and catalytic performance, and display superior ORR performance after the ordering procedure, with a specific activity of 3594 µA cm⁻², which is 2.5-fold higher than that of their disordered counterpart, and a mass activity of 1431 A g_Pt⁻¹ at 0.9 V vs. RHE. Notably, besides activity, the catalyst maintains exceptional durability, showing only a 5 mV loss in half-wave potential after 10 000 cycles. Operando X-ray absorption spectroscopy (XAS) revealed that enhanced local structure ordering and shorter Pt–Pt bond distances effectively suppress Pt–O formation during the ORR, increasing the activity and stability of the ordered phase. Hence, this study demonstrates a simple and scalable strategy for fabricating robust intermetallic nanowire catalysts with controlled diameters and provides operando evidence linking structural ordering with high ORR activity and durability, offering key design principles for future PEMFC catalyst development.