Elemental composition, crystallinity and electrical studies of Ni–Co phosphate-PVC composite membrane through mechanism of monovalent electrolytes

In this study, composite membranes were developed by incorporating a multimetallic nickel–cobalt phosphate into a polyvinyl chloride (PVC) polymer matrix. The membranes were fabricated using a pressure-assisted thermal casting process, and their physical and electrochemical properties were systematically investigated. X-ray diffraction analysis gave an average crystallite size of about 30 nm and a crystallinity index of 45.46%, indicating a partially crystalline structure beneficial for mechanical stability and ion transport. Fourier-transform infrared spectroscopy confirmed the presence of phosphate groups, hydroxyl and bound water, characteristic PVC backbone vibrations, and metal–oxygen bands, evidencing successful integration of Ni and Co phosphate within the polymer framework. Scanning electron microscopy revealed a homogeneous, highly porous morphology with well-dispersed fillers, providing continuous pathways for electrolyte penetration and ion migration. Electrochemical performance was evaluated by measuring membrane potential and electrical conductance in Na⁺, K⁺, and Li⁺ electrolytes. The membrane potential increased with decreasing electrolyte concentration for all salts and followed the order LiCl > NaCl > KCl, reflecting the combined effects of ion hydration and mobility. In contrast, membrane conductance decreased upon dilution and followed the order KCl > NaCl > LiCl, consistent with higher ionic mobility of K⁺ in the membrane phase. These trends confirm efficient and selective ion transport governed by the porous microstructure and the embedded Ni–Co phosphate domains. The result showed clear ion-selective responses, with membrane composition, binder ratios, and filler distribution playing essential roles in how ions are transported and how the membrane potential behaves. furthermore, this study offers valuable insights into the relationship between the membrane structure and its properties, intensifying their promising potential for use in electrochemical sensing, biomedical and ion-selective electrode applications.