Crystallinity control of NiMn-LDH via potentiostatic oxidation for enhanced charge storage capacity

Amorphous electrode materials offer distinct advantages for supercapacitor applications, yet the influence of crystallinity on their electrochemical performance remains underexplored. Here, we introduce a simple potentiostatic oxidation approach ‌to fine-tune the ‌crystallinity of NiMn layered double hydroxide (LDH) ‌and systematically assess its charge-storage behavior under identical conditions. The NiMn-LDH grown on carbon cloth was subjected to potentiostatic oxidation via a standard three-electrode assembly bathed in 2 M KOH solution. The potentiostatic oxidation increased the Mn 4+ content, ‌which‌ altered the crystal structure of NiMn-LDH and reduced its crystallinity. With oxidation times from 0 to 1200 s, crystallinity decreased steadily, reaching an optimal state at 900 s (denoted O-900s). The O-900s electrode provides a notable specific capacity of 206.3 mAh   g −1 at 1   A   g −1 and retains 79.9% of that value after 4000 cycles. Additionally, the assembled asymmetric supercapacitor device exhibits an energy density of 30.1 Wh   kg −1 at a power density of 775 W   kg −1 . Our work delivers a robust framework for tuning crystallinity to optimize NiMn-LDH electrodes and advance high-performance supercapacitor design.