In-Plane Heterostructured MoN/MoC Nanosheets with Enhanced Interfacial Charge Transfer for Superior Pseudocapacitive Storage

2D transition metal carbide/nitride heterostructures are emerging pseudocapacitive materials for supercapacitors (SCs); however, the lack of efficient synthesis methods and an in-depth understanding of the pseudocapacitive storage mechanism of these potentially important materials impede their applications in SCs. Herein, 2D MoN/MoC nanosheets with a precisely regulated interface are prepared controllably by a scalable salt-assisted method with bulk MoS 2 as the precursor. In operando infrared spectroscopy and electrochemical quartz crystal microbalance results reveal that the pseudocapacitance of the MoN/MoC nanosheets originates from the reversible reaction between Mo–N sites and H + in the acidic electrolyte. Density-functional theory calculations and X-ray photoelectron spectroscopy disclose that the MoC/MoN heterointerface induces the internal electric field from the accumulated negative charges at the Mo–N sites by electron donation from MoC, leading to enhanced H + adsorption at the Mo–N sites and superior pseudocapacitive storage. The heterostructured MoN/MoC nanosheets show a large volumetric capacity of 1045.3 F cm −3 at 1 A cm −3 , high-rate capability of 702.8 F cm −3 at 10 A cm −3 , and superior cyclability with capacity retention of 98% after 10,000 cycles, which outperform reported Mo-based carbides and nitrides. The results provide new insights into the development of high-performance 2D heterostructured materials for superior pseudocapacitive storage.