Hierarchical manganese-iron-layered double hydroxide nanosheets for asymmetric supercapacitors

This work presents a synthesis of hierarchical manganese-iron-layered double hydroxide (MnFe-LDH) nanostructured electrodes using the hydrothermal synthesis route by varying the reaction time for electrochemical energy storage applications. The electrochemical behavior of the MnFe-LDH electrodes synthesized at different reaction times was analyzed in a three-electrode cell configuration using 2 M KOH electrolyte. The uniform and well-organized MnFe-LDH nanosheet electrode (MnFe-12h) showed the maximum areal capacitance of 2013 mFcm⁻² at a 5 mVs⁻¹ scan rate, and 1886 mFcm⁻² at a 25 mA applied current. Furthermore, the electrochemical behavior of MnFe-12h was examined by assembling an asymmetric cell device using activated carbon (AC) as a negative electrode and MnFe-12h as a positive electrode and it was tested in a wide voltage window range of 0.0 to 1.6 V. This asymmetric cell device achieved an appropriate energy density of 44.9 µW h cm⁻² (55.01 W h kg⁻¹), with a power density of 16 mW cm⁻² (5000 W kg⁻¹) at an applied current of 10 mA, and had a long-term cycling stability (93% capacitance retention after 5000 cycles) within the 1.6 V operating voltage window.