Na2Zn0.5Co0.5P2O7 Diphosphate: Sol-gel synthesis, physico-chemical studies, and prospects as a novel supercapacitor electrode material

Abstract

For the first time, a mixed-metal diphosphate Na2Zn0.5Co0.5P2O7 has been successfully synthesized via the sol-gel method. The sample was characterized by means of XRD, DTA/TGA, SEM/EDX, UV–vis, Raman, IR and color measurements (CIE-L*a*b*). Its structure was determined through X-ray powder diffraction, in tetragonal system, with space group P42/mnm. The 3D structure of the material consists of infinite chains formed by [Zn/CoO4] tetrahedra and [P2O7] diphosphate units sharing corners. Sodium cations occupy two types of interstitial positions between the infinite chains [Zn/CoP2O7]2-. Raman and Infrared spectra of the studied phosphate have been investigated. A factor group analysis leads to determination of internal modes of the P2O74− anion. Tetrahedral environment of Co2+ ions was confirmed by mean of optical analysis, in which numerous bands in the region 475-675 nm, assigned to the forbidden and allowed d–d transitions of Co2+ are detected and the gap energy is extracted from Tauc and Kubelka-Munk plots. The prepared Na2Zn0.5Co0.5P2O7 diphosphate was extensively investigated for its potential use as an electrode material for supercapacitors. The electrode was prepared by depositing the active material on a conductive substrate (nickel foam) and demonstrated significant electrochemical performance with a specific capacitance of 277 F.g-1 at a scan rate of 5 mV.s-1. This outstanding performance underlines its relevance for supercapacitor applications.