Metallic Mo<sub>2</sub>C Quantum Dots Confined in Functional Carbon Nanofiber Films toward Efficient Sodium Storage: Heterogeneous Interface Engineering and Charge-Storage Mechanism
Guangyuan Wang, Shichao Wang, Xuan Sun, Yang Liu, Ping Nie, Linrui Hou, Limin Chang, Changzhou Yuan
Abstract
Sodium ion capacitors (SICs) have drawn enormous interest due to their cost efficiency, superb power/energy densities, and long-span service life. Nevertheless, the imbalance of two involved electrodes in both kinetics and stability, mainly originating from battery-type anodes, restricts their practical application. Herein, we first propose a heterointerface engineering strategy to design a flexible self-supporting hybrid film anode, where metallic Mo2C quantum dots (QDs, ∼41.1 wt %) self-encapsulated in N-doped carbon nanofibers (N-CNFs) thanks to the interfacial interactions, toward advanced SICs. The synergistic effect of structural/compositional merits is highlighted with the induced interface coupling Mo–N–C toward enhanced electrochemical kinetics/stability and reinforced electrode structural integrity. The accelerating mechanism of electron migration at the heterogeneous interfaces is unveiled with density functional theory calculations. The obtained Mo2C QDs@N-CNFs film electrode is rendered with a competitive capacity of ∼160.9 mAh g–1 at 5.0 A g–1, robust pseudocapacitive contribution, and long-duration cycling stability. Besides, the Mo2C QDs@N-CNFs-based SICs exhibit exceptional electrochemical properties. More significantly, the in-depth insights into the unique Na+-(de)intercalation mechanism of Mo2C QDs@N-CNFs are rationally proposed with in situ X-ray diffraction and electrochemical techniques. This promises the enormous potential of our designed carbon-matrix-confined Mo2C QDs nanohybrid for SICs and beyond.