A facile and versatile low-cost solid-liquid interface-mediated method for the synthesis of mesoporous and amorphous NiCoBP alloys with high surface areas was developed. The precursors of Ni, Co, and P, with a controllable molar ratio, were first dissolved in ultrapure water, frozen, and treated with NaBH4 solution to form NiCoBP alloys at room temperature. Benefiting from its mesoporous and amorphous structural features, the as-prepared NiCoBP alloy exhibited high surface area and exceptional electrochemical performance for use as a cathode material in asymmetric supercapacitors, yielding specific capacitance of up to 1030.4 F g−1 at 6 A g−1 with excellent cycling stability with a retention rate of 81.9% after 2000 cycles.