| Summary: | 2 at.% Cu + 2 at.% Ni were co-doped in ZnO nanoparticles by a simple hydrothermal method, and then the modified nanoparticles were compounded into Cu-Ni alloy coatings using an electroplating technique. The effects of the current density (15–45 mA/cm<sup>2</sup>) on the phase structure, surface morphology, thickness, microhardness, corrosion resistance, and photocatalytic properties of the coatings were investigated. The results show that the Cu-Ni-Zn<sub>0.96</sub>Ni<sub>0.02</sub>Cu<sub>0.02</sub>O nanocomposite coatings had the highest compactness and the best overall performance at a current density of 35 mA/cm<sup>2</sup>. At this point, the co-deposition rate reached its maximum, resulting in the deposition of more Zn<sub>0.96</sub>Ni<sub>0.02</sub>Cu<sub>0.02</sub>O nanoparticles in the coating. More nanoparticles were dispersed in the coating with a better particle strengthening effect, which resulted in a minimum crystallite size of 15.21 nm and a maximum microhardness of 558 HV. Moreover, the surface structure of the coatings became finer and denser. Therefore, the corrosion resistance was significantly improved with a corrosion current density of 2.21 × 10<sup>–3</sup> mA/cm<sup>2</sup>, and the charge transfer resistance was up to 20.98 kΩ·cm<sup>2</sup>. The maximum decolorization rate of the rhodamine B solution was 24.08% under ultraviolet light irradiation for 5 h. The improvement in the comprehensive performance was mainly attributed to the greater concentration of Zn<sub>0.96</sub>Ni<sub>0.02</sub>Cu<sub>0.02</sub>O nanoparticles in the coating, which played the role of the particle-reinforced phase and reduced the microstructure defects.
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