Pd-Doped RuO<sub>2</sub>: A Promising Electrode Material\nwith Battery–Supercapacitor Hybrid Characteristics

Supercapacitors\nhave emerged as promising energy storage devices\ndue to their high power density, rapid charging/discharging rates,\nand long cycle life. Ruthenium dioxide (RuO<sub>2</sub>) is a promising\nmaterial for supercapacitor electrodes due to its excellent electrical\nconductivity and pseudocapacitive behavior. Here, we synthesize Ru<sub>1–<i>x</i></sub>Pd<sub><i>x</i></sub>O<sub>2</sub> (<i>x</i> = 0, 0.05, 0.10, and 0.17) by a solid-state\nroute, expecting to alter the electronic structure and specific capacitance\nwith Pd doping. The X-ray diffraction (XRD) analysis suggests that\nall prepared samples are formed in the desired composition, showing\nthat the crystallite size increases successively with increasing Pd\nconcentration. Cyclic voltammetry (CV) measurements demonstrate that\nthe systematic substitution of 17% Pd in RuO<sub>2</sub> contributes\nto enhancing specific capacitance by ∼15 times (∼1163\nF/g) in comparison to parent RuO<sub>2</sub> (∼79 F/g), indicating\nits superior charge storage ability. Further, the decay in specific\ncapacitance with increasing scan rate is only 5% (<i>x</i> = 0.17) in comparison to undoped RuO<sub>2</sub>, indicating the\nhigher stability of the electrode. The CV of Ru<sub>1–<i>x</i></sub>Pd<sub><i>x</i></sub>O<sub>2</sub> (<i>x</i> = 0.17) exhibits both Faradaic and capacitive electrochemical\nprocesses at the electrode/electrolyte interface, suggesting hybrid\nbattery–supercapacitor characteristics. Ru<sub>1–<i>x</i></sub>Pd<sub><i>x</i></sub>O<sub>2</sub> (<i>x</i> = 0.17) represents a promising electrode material for\nhybrid battery–supercapacitors, offering synergistic enhancements\nin specific capacitance and stability.