In-Plane Mo2C/MoN Heterojunction Nanosheets With Interfacial Charge Redistribution for Enhanced Pseudocapacitive Energy Storage

Two-dimensional (2D) molybdenum carbide and nitride are promising pseudocapacitive materials, but their single-phase forms suffer from sluggish ion reaction kinetics and low active sites, leading to unsatisfactory capacitive performance. Herein, a scalable molten-salt–assisted strategy is developed to construct 2D in-plane heterostructured Mo 2 C/MoN nanosheets with tunable interfaces, which involves carbonization of bulk MoO 3 into Mo 2 C nanosheets in molten salt, followed by partial topochemical nitridation to convert Mo 2 C into MoN. Electrochemical quartz crystal microbalance and in situ Raman spectroscopy reveal that the pseudocapacitance arises primarily from reversible H + interactions with Mo–C sites in Mo 2 C, with additional contribution from Mo–N sites. Ultraviolet photoelectron spectroscopy and density functional theory calculations confirm that the interfacial electron transfer from Mo 2 C to MoN upshifts the d -band center of Mo 2 C and reduces its H + adsorption energy from −0.522 to −1.526 eV; meanwhile, electron injection into MoN weakens the Mo–N coordination and creates undercoordinated Mo sites. These two effects synergistically promote the pseudocapacitive redox activity. The optimized Mo 2 C/MoN achieves a large capacitance of 323.6 F g −1 (899.6 F cm −3 ) at 1 A g −1 , high rate capability (204.7 F g −1 at 10 A g −1 ), and 91.1% capacitance retention after 10,000 cycles in 1 M H 2 SO 4 . This paper reports a scale preparation of non-layered 2D Mo 2 C/MoN heterostructured nanosheets and demonstrates that interfacial charge redistribution boosts pseudocapacitive storage.