Quaternary transition metal molybdate (Mn _0.25Ni_0.25Co_0.25Fe_0.25MoO₄) design to improve the kinetics of the redox reaction in supercapacitors

In this work, we report on a new Mn_0.25Ni_0.25Co_0.25Fe_0.25MoO₄ (denoted as MNCFMo) material synthesized by a one-step hydrothermal method and studied the electrochemical performance of this quaternary molybdate as a pseudocapacitive material. The exact formation of the structure was confirmed with the aid of X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) which reveal a pure crystal structure and nanorods-like morphology with the expected elemental composition. At current density of 2 A/g, MNCFMo exhibited promising electrochemical performance with calculated specific capacitance up to 1097 F/g compared to 897 F/g for Mn_0.33Ni_0.33Co_0.33MoO₄ (denoted as MNCMo) and could maintain a high capacitance of 413.6 F/g even at 40 A/g signifying an excellent rate material, which are ascribed to the additional fast reversible reaction offered by iron (Fe) insertion. Remarkably, the energy density could reach up to 38.1 Wh/kg at power density of 322.8 W/kg. Moreover, this material delivers a superior cycling stability with approximately 20% capacity loss after 5000 cycles at 10 A/g. Electrochemical impedance spectroscopy results reveal low solution resistance (R_s) of 0.307 Ω and charge transfer resistance (R_ct) of 12.40 Ω respectively. These profound outputs are attributed to the cumulative redox effects from Mn, Ni, Co and Fe implying a high consideration for MNCFMo as an electrode in advanced supercapacitor application.