MOF-derived spinel NiMn₂O₄/CoMn₂O₄ heterojunction and its application in a high-performance photocatalyst and supercapacitor

Metal oxide heterojunctions have attracted considerable attention in photocatalyst and supercapacitor applications. In this study, NiMn2O4/CoMn2O4 (NMO/CMO) heterojunctions were synthesized using ternary metal-organic frameworks (MOFs) as precursors. After calcination at 500 °C, the as-prepared NMO/CMO composite maintains the porous sheet-like morphology of the ternary MOF, exhibiting a highly porous structure. The heterostructured NMO/CMO composite demonstrates enhanced photocatalytic performance compared with pure NMO and CMO. This enhancement may be attributed to the well-aligned energy levels at the NMO/CMO interface, which effectively reduces charge recombination and facilitates the efficient transport of photogenerated carriers. In addition, the NMO/CMO heterojunction exhibits enhanced supercapacitor performance owing to the increased number of active redox sites and reduced charge transfer resistance. When tested at 3 A/g, the NMO/CMO composite displays a higher capacitance (756.4 F/g) than pure NMO (579.6 F/g) and CMO (519.6 F/g) and remarkable rate capability, maintaining a capacitance of 639 F/g even at 10 A/g. Notably, asymmetric supercapacitors fabricated using NMO/CMO and activated carbon can achieve an energy density of 32.18 W h/kg at 750 W/kg and superior cycling life, retaining 92.1% of its initial capacitance after 3000 cycles.