An OH-slow-release strategy was established to controllably tune the (α- and β-) phase of nickel cobalt binary hydroxide in the presence of ammonium chloride. Ammonium chloride is added to the ionic solution to regulate the pH of the solution and slow down the release of OH, effectively regulating the phase, nanostructure, interlayer spacing, surface area, thickness, and the performance of binary Ni–Co hydroxide. The ion-slow-release mechanism is conducive to the formation of α-phase with larger interlayer spacing and thinner flakes rather than β-phase. Attributed to the enlarged interlayer spacing, thinner nanosheets, and more exposed active sites, the resultant α-phase hydroxides (NCNS-5.2), displayed much lower over potential of 285 mV with respect to the dense-stacked β-phase hydroxides (362 mV) for OER at 10 mA/cm. It also exhibited high specific capacitance of 1474.2 F/g, when tested at 0.5 A/g within a voltage range of 0–0.45 V vs. Hg/HgO. This composite was also stable for water oxidation reaction and supercapacitor. The proof-of-concept of using controlled-release agent may provide suggestive insights for the material innovation and a variety of applications.