Supercapacitors (SCs) as a kind of novel energy storage devices have emerged to meet the urgent requirement of environmentally friendly clean energy storage equipment. However, unsatisfactory energy density and low operating voltage tremendously restrict their practical application. Herein, petal-like lamellar NiMn-layered double hydroxide (NiMn–LDH) was successfully fabricated through a simple Ni(NO₃)₂ etching method with Mn MOF-74 as a sacrificial template. This NiMn–LDH 3/NF electrode exhibited an improved specific capacitance of 1410.2 F g⁻¹ at a current density of 1 A g⁻¹ (Mn MOF-74/NF: 172.2) owing to its high redox activity, compositional flexibility and intercalating capability. Importantly, NiMn–LDH was further optimized via a facile hydroperoxide treatment to harvest NiMn–LDH (O–LDH) with abundant oxygen vacancies, exhibiting remarkable improvement in specific capacitance (990%) compared to original MOF-74 before modification. The preparation of O–LDH enriches the electrode material engineering strategy and achieves improved electrochemical performance for application in new-generation SCs.