High-Coordination and Nb-Bridging of Bimetallic Amorphous P6-Nb-W-P5 Clusters in Carbon Nanospheres for High-Performance Sodium-Ion Hybrid Capacitors

Abstract

Amorphous clusters are gaining prominence as prospective hosts for sodium-ion hybrid capacitors (SIHCs), but their efficacy is still affected by atomic coordination. Optimization of ion storage and charge transport can be achieved through high coordination and bimetallic configurations. Herein, high-coordination amorphous P₆-Nb-W-P₅ (Nb/W-P) clusters are skillfully tailored by bridging Nb into the second shell of W in the W-P₅ configuration, nested in situ in conductive and stable N, P co-doped carbon nanospheres (Nb/W-P@NPC). Such clusters with high atom utilization can offer profuse Na⁺ storage sites due to their high coordination. As an electron donor, Nb-bridging can subtly modify the electronic structure of clusters, and broaden the hybridization of d-p orbitals, thus improving charge transfer efficiency and fostering diversified active sites. Compared with the low-coordinated W-P_L@NPC and the high-coordinated W-P@NPC, the reversible capacity of Nb/W-P@NPC upgrades to 556.3 mAh g⁻¹ at 0.1 A g⁻¹, alongside exceptional cycling stability at high rates. When integrated into SIHCs, the high energy density and high-power output (223.6 and 9800 W kg⁻¹) are achieved. By systematically exploring the effect of high coordination and bimetallic design on the storage efficacies of amorphous clusters, this study has greatly advanced the development of SIHC technologies.