Optimization of Interfacial Interaction and Defect Structure of Holey Metal Nitride Matrices to Boost Supercapacitor Electrode Activity of Metal–Organic Frameworks

Metal-organic frameworks (MOFs) have received significant interest because of their promising applications of MOFs for gas separation/storage and energy production/storage. However, the low electrical conductivities and limited electrochemical activities of MOFs hinder their application as electrodes. In this study, a defect-assisted hybridization strategy is developed to improve the electrode performances of MOFs, wherein conductive holey metal nitride (TiN, MoN, and NbN) nanosheets are employed as hybridization matrices. The presence of coordinatively unsaturated defect sites in the holey metal nitride nanosheets led to a significant enhancement of the supercapacitor electrode functionality of the hybridized MOFs. Among the nanohybrids, the MoN-MOF delivered the optimal electrode functionality with a large specific capacitance of ≈3021 F g^-1 at 10 mV s^-1, representing one of the most outstanding performances reported for MOF-based electrode materials. The benefit of hybridization with holey metal nitride nanosheets is ascribable to the defect-assisted electronic coupling between the hybridized species, resulting in the improvement of the redox activity and the charge/mass transport capabilities. The superior efficacy of hybridization with holey MoN nanosheets over those with holey NbN and TiN nanosheets originates from the higher electronegativity and larger number of unpaired 4d electrons in the Mo³⁺ ions, leading to optimized interfacial interactions.