In this paper we report an in situ template route for the synthesis of porous Ni₁₂P₅ superstructures through an improved hydrothermal synthesis strategy in the presence of a high concentration of Co²⁺ ions. The phase and morphology of the as-prepared product were characterized by means of powder X-ray diffraction (XRD), energy dispersive spectrometry (EDS), selected area electron diffraction (SAED), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Research showed that Co²⁺ ions in the system could significantly tune the shape and size of Ni₁₂P₅ and had a profound effect on the yield of Ni₁₂P₅. A possible growth mechanism was proposed based on the experimental results. Furthermore, the as-prepared porous Ni₁₂P₅ superstructures showed good adsorption capacities for Pb²⁺ and Cd²⁺ ions in water, and could strongly degrade some organic dyes such as pyronine B under irradiation of 254 nm UV light, indicating that the as-prepared product has potential applications in environmental treatments.