Self-supported electrodes comprising carbon fiber paper (CP) integrated with bifunctional nickel phosphide (Ni-P) electrocatalysts are fabricated by electrodeposition of Ni on functionalized CP, followed by a convenient one-step phosphorization treatment in phosphorus vapor at 500 degrees C. The as-fabricated CP@Ni-P electrode exhibits excellent electrocatalytic performance toward hydrogen evolution in both acidic and alkaline solutions, with only small overpotentials of 162 and 250 mV, respectively, attaining a cathodic current density of 100 mA cm(-2). Furthermore, the CP@Ni-P electrode also exhibits superior catalytic performance toward oxygen evolution reaction (OER). An exceptionally high OER current of 50.4 mA cm(-2) is achieved at an overpotential of 0.3 V in 1.0 M KOH. The electrode can sustain 10 mA cm(-2) for 180 h with only negligible degradation, showing outstanding durability. Detailed microstructural and compositional studies reveal that upon OER in alkaline solution the surface Ni-P is transformed to NiO covered with a thin Ni(OH)(x) layer, forming a Ni-P/NiO/Ni(OH)(x) heterojunction, which presumably enhances the electrocatalytic performance for OER. Given the well-defi ned bifunctionality, a full alkaline electrolyzer is constructed using two identical CP@Ni-P electrodes as cathode and anode, respectively, which can realize overall water splitting with effi ciency as high as 91.0% at 10 mA cm(-2) for 100 h.