Interface Density Engineering on Heterogeneous Molybdenum Dichalcogenides Enabling Highly Efficient Hydrogen Evolution Catalysis and Sodium Ion Storage.

Constructing active heterointerfaces is powerful to enhance the electrochemical performances of transition metal dichalcogenides, but the interface density regulation remains a huge challenge. Herein, MoO 2 /MoS 2 heterogeneous nanorods are encapsulated in nitrogen and sulfur co-doped carbon matrix (MoO 2 /MoS 2 @NSC) by controllable sulfidation. MoO 2 and MoS 2 are coupled intimately at atomic level, forming the MoO 2 /MoS 2 heterointerfaces with different distribution density. Strong electronic interactions are triggered at these MoO 2 /MoS 2 heterointerfaces for enhancing electron transfer. In alkaline media, the optimal material exhibits outstanding hydrogen evolution reaction (HER) performances that significantly surpass carbon-covered MoS 2 nanorods counterpart (η 10 : 156 mV vs 232 mV) and most of the MoS 2 -based heterostructures reported recently. First-principles calculation deciphers that MoO 2 /MoS 2 heterointerfaces greatly promote water dissociation and hydrogen atom adsorption via the O-Mo-S electronic bridges during HER process. Moreover, benefited from the high pseudocapacitance contribution, abundant "ion reservoir"-like channels, and low Na + diffusion barrier appended by high-density MoO 2 /MoS 2 heterointerfaces, the material delivers high specific capacity of 888 mAh g -1 , remarkable rate capability and cycling stability of 390 cycles at 0.1 A g -1 as the anode of sodium ion battery. This work will undoubtedly light the way of interface density engineering for high-performance electrochemical energy conversion and storage systems.