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Three-dimensional (3D) nickel phosphide/reduced graphene oxide (rGO)/nickel oxide composite on nickel foam (Ni2P/rGO/NiO/NF) is fabricated as a supercapacitor (SC) electrode material via the two-step electrochemical deposition of graphene oxide (GO) and nickel phosphide on the nickel foam. Typically, rGO/NiO/NF is fabricated at first by the electrochemical treatment of nickel foam at 10 V in 0.1 M sulfuric acid with GO for 10 min. The result reveals that NiO nanosheets are vertically grown on the surface of nickel foam and rGO is deposited on the surface of NiO/NF, leading to the enhancement of capacity. Secondly, nickel phosphide is electrochemically deposited on the surface of rGO/NiO/NF in the sodium hypophosphite-based aqueous solution at 10 mA cm−2 to yield the Ni2P/rGO/NiO/NF. The deposition of Ni2P leads to a much higher capacity. The optimal areal and mass specific capacities are obtained as 3.59 C cm−2 and 742 C g−1 at the electrochemical deposition time of 30 and 10 min, respectively. The high capacity reveals that the proposed two-step electrochemical fabrication process is facile and effective. In addition, the Ni2P/rGO/NiO/NF electrode-based all-solid-state asymmetric SC was fabricated and could successfully turn on a light-emitting diode light. This revealed its feasibility in practical application and confirmed that the resulting 3D Ni2P/rGO/NiO/NF has a great potential as the SC electrode material. [ABSTRACT FROM AUTHOR]