A ternary deep-eutectic solvent (DES) system was constructed using glycerol, urea, and cobalt chloride. And a three-dimensional nanoflower-like nickel foam-supported CoCO₃-NiOOH catalyst (CoCO₃-NiOOH/NF(D) was fabricated through one-step deep-eutectic solvothermal method. The results show that the foam nickel support in situ reacts with the ternary DES under solvothermal conditions, resulting in a composite of CoCO₃ and NiOOH enriched with oxygen vacancy defects. The three-dimensional conductive network effectively promotes interfacial electron transfer and the exposure of active sites. The prepared CoCO₃-NiOOH/NF(D) catalyst exhibits excellent electrocatalytic oxygen evolution (OER) performance. The overpotential is only 295 mV at a current density of 20 mA/cm² and the Tafel slope is 78.1 mV/dec. The performance is much better than the CoCO₃-NiOOH/NF(W) catalyst synthesized by the traditional hydrothermal method ( 407 mV, 112.8 mV/dec). Additionally, the CoCO₃-NiOOH/NF(D) catalyst also demonstrates excellent cycling stability, maintaining a current density retention rate of 92% after a long-term stability test of 60 h.