In‐Plane Mo ₂ C/MoN Heterojunction Nanosheets With Interfacial Charge Redistribution for Enhanced Pseudocapacitive Energy Storage

ABSTRACT

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.