Interfacial oxygen bridges engineering between NbO and graphene towards advanced sodium ion capacitors.

NbO has become a focus of research for its suitability as an anode material in sodium ion capacitors (SICs), due to its open ionic channels. The integration of NbO with reduced graphene oxide (rGO) is known to boost its electrical conductivity. However, the sluggish interfacial charge transfer kinetics and interface collapse of NbO/rGO pose challenges to its rate capability and durability. In this study, oxygen bridges (C-O-Nb bonds) are deliberately incorporated to study how their densities affect the electrochemical characteristics of NbO/rGO. Initially, HO is applied as the functional additive to realize in-situ grafting of oxygen functional groups on graphene oxide (GO), which is referred as GO-H. And GO-H matrix serves as a space confiner to transform the crystallization of NbO from larger microflower structures to smaller nanocrystals. The resulting NbO/rGO with high oxygen bridges (named as NbO/rGO-H) exhibits a substantial proportion of C-O-Nb bonds (47 %), which enhances the charge transfer from rGO to NbO, along with the stabilization of the interface. This leads to the high specific capacity (301.7 mAh g at 0.05 A g), commendable rate capability (98.0 mAh g at 10 A g), and exceptional durability (91.1 % mAh g capacity retention after 2000 cycles). Moreover, a SIC device fabricated with NbO/rGO-H and active carbon (AC) demonstrates an impressive energy density of 149.6 W h kg (at 200 W kg). This investigation underscores the pivotal role of interfacial oxygen bridges in optimizing the charge transfer dynamics and stability of nanoscale energy storage materials.