Ali A. Ensafi, E. Heydari-Soureshjani, B. Rezaei,

Three-dimensional (3D) graphene was easily obtained by a simple hydrothermal method from two-dimensional (2D) graphene to create the interspace sites and active surface area. So, the fabrication of the 3D-graphene nanocomposite is promising for advanced energy production and storage application. The structure of the 3D-graphene nanocomposite was characterized by various techniques. Then, 3D-graphene was decorated with Pd nanoparticles. Morphological characterization shows the porous structure of 3D-Pd/rGO, so it has a high electroactive surface area. The function of the electrocatalyst toward the supercapacitor, hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) were investigated. The obtained results as a supercapacitor displayed that the supercapacitor on 3D-Pd/rGO has a high specific capacitance of 582.0 F g^–1, the high energy density of 180 (W h Kg^–1), high power density of 3750 (W Kg^–1), long potential window of 1.00 V and long life. The electrocatalyst shows the small onset potential of ‒0.08 V (vs. RHE), Tafel slope of 29 mV dec^-1 and high durability. Also, in the electroanalytical application of the nanocompound as an electrocatalyst for ORR shows an excellent onset potential of 0.90 V (vs. RHE), slow drop in the current density (34% in the presence of MeOH) and the reduction process via a four electrons pathway.