In this work, a novel CoP/NiCoP heterostructure with hollow nanoflower morphology is designed and constructed. Benefiting from the hollow nanoflower morphology and tuned electronic structure, the heterostructured CoP/NiCoP hollow nanoflowers are demonstrated as both high-performance supercapacitor electrode materials and superior bifunctional electrocatalysts in overall water splitting. The CoP/NiCoP delivers a high capacitance of 1476.6 F g⁻¹ at 1.0 A g⁻¹ and shows enhanced rate capability. The constructed asymmetric supercapacitor achieves a high energy density of 32.4 Wh kg⁻¹ at 800.5 W kg⁻¹ and high power density of 16.5 kW kg⁻¹ at 20.0 Wh kg⁻¹. The CoP/NiCoP hollow nanoflowers are also proven to be remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalyst which achieves the current density of 10.0 mA cm⁻² under an overpotential of 110.4 mV for HER and 310.7 mV for OER with superior stability in alkaline solution. In addition, the constructed CoP/NiCoP||CoP/NiCoP cell with CoP/NiCoP as both cathode material and anode material only requires 1.63 V @ 10.0 mA cm⁻² for overall water splitting. This study sheds lights on the rational design and construction of bimetallic phosphides for both supercapacitor and overall water splitting.