Exploring the synergistic effect of palladium-doped molybdenum phosphate as an electrode material for high-performance asymmetric supercapacitor device

In this research, we synthesized molybdenum phosphate (MoP) and palladium-doped MoP on a porous Ni-foam substrate using a one-step hydrothermal method for supercapacitor electrodes. Various techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, and field emission scanning electron microscopy were employed to investigate the structural and morphological properties of the synthesized materials. The MoP and MoP-Pd samples exhibited hexagonal rod-like structures, which contributed to their porosity and high electrochemical activity. Electrochemical testing revealed that MoP demonstrated an areal capacitance of 3.8 F/cm² (0.60 mA/cm²). With the addition of Pd to MoP, the capacitance increased to 4.05 F/cm² (0.62 mAh/cm²) at a current density of 4 mA/cm² in a 2 M KOH electrolyte. The charge storage kinetics of both MoP and MoP-Pd indicated a dominant diffusion-controlled contribution, attributed to the Faradic redox process. The MoP-Pd electrode displayed excellent stability, retaining about 90.7% of its initial capacitance, and exhibited a coulombic efficiency of 100% over 15,000 cycles. Furthermore, we assembled an asymmetric device (ASD) using MoP-Pd as the positive electrode and activated carbon (AC) as the negative electrode. This ASD demonstrated an areal capacitance of 0.44 F/cm² (0.21 mAh/cm²), accompanied by an energy density of 0.178 mWh/cm² and a power density of 1.28 mW/cm² within a potential window of 0–1.8 V, measured at an applied current of 3 mA. These results highlight the significant supercapacitive potential of MoP, further enhanced by the addition of Pd, suggesting its promising application as an electrode material in energy storage systems.