Rational Confinement of NiMo6 Polyoxometalates in a Single-Walled Carbon Nanotube: A High-Filling-Ratio Strategy for Enhanced Electrochemical Activity.

This study successfully developed an efficient one-dimensional confinement strategy to encapsulate polyoxometalate NiMo6 clusters densely and uniformly within the cavities of a single-walled carbon nanotube (SWCNT), constructing a unique core-shell NiMo6@SWCNT composite electrocatalyst. Comprehensive characterization including high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and ultraviolet-visible absorption spectroscopy (UV-Vis) systematically confirmed the uniform dispersion and structural integrity of NiMo6 within the SWCNT channels. Key evidence encompasses: (1) EDS elemental mapping revealing high co-localization of Ni/Mo signals inside the lumens; (2) transmission electron microscopy (TEM) images confirming the effectiveness of the filling process. The composite achieved an exceptionally low overpotential of 308 mV to drive a current density of 10 mA cm-2 (significantly outperforming pure NiMo6 at 365 mV and pristine SWCNT at 519 mV), exhibited a remarkably low Tafel slope of 96.64 mV dec-1, possessed a high electrochemical active surface area (10.75 mF cm-2), and very low charge transfer resistance. Critically, it showed negligible current density decay during prolonged chronoamperometric operation over 35,000 s (>9.7 h). This work not only validates the confined encapsulation as a viable strategy for fabricating highly active polyoxometalate/carbon composites, but also elucidates that the performance enhancement stems from a "triple synergy": the intrinsic catalytic activity of NiMo6, the highly conductive/mass-transport network provided by SWCNT, and the synergistic effects arising from the confined interface-namely stress regulation and electronic coupling. This insight provides a novel perspective for designing high-performance non-precious metal electrocatalysts.