ZnO nanoparticles doped with chromium (Cr) were synthesized through a simple sol gel route. The successful Cr doping into the ZnO lattice has been evidenced via several characterisation techniques i.e., XRD and XPS. A high oxygen vacancies (OV) density has been located through Photoluminescence (PL) and EPR studies for the Cr doped ZnO (1 %) (ZnCr1) sample. The high density of OV defects induced from Cr doping in ZnO lattice was considered at the origin of the improved electrochemical performances by promoting efficient electron transfer ability with intercalation process of the electrolyte's ions during charge-discharge mechanism. The ZnOCr1 electrode displays an important capacitance value (367 F.g−1), ultrahigh capacitance retention (86 %) while changing the current from 1 to 20 A·g−1, and marvellous stability of 84 % during 4000 cycles. An asymmetric supercapacitor based ZnOCr1 electrode achieves significant potential window up to 1.6 V with encouraging specific energy density. The device showcases a satisfactory specific energy of 27.1 Wh·Kg−1 at specific power of 480 W·Kg−1 and a great retention of 17 % decay after 4000 cycles at current density of 10 A g−1. This opens door to the developed ZnO-Cr1 material for its application in future supercapacitor devices.