Study on the electrochemical property of microporous cobalt phosphite [Co₁₁(HPO₃)₈(OH)₆]

Crystalline microporous cobalt phosphite, Co₁₁(HPO₃)₈(OH)₆, was prepared via facile hydrothermal route without the use of any templates or surfactants. The cobalt chloride hexahydrate (CoCl₂.6H₂O) and sodium hypophosphite monohydrate (NaH₂PO₂.H₂O) were employed as reactants, and sodium bicarbonate (NaHCO₃) was added to adjust the pH. The resultant Co₁₁(HPO₃)8(OH)₆ shows dumbbell-like shape with a size of several micrometers. The obtained materials were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermal gravimetric analysis (TGA), field-emission scanning electron microscopy (FE-SEM), and energy dispersive spectrometry (EDS). The Co₁₁(HPO₃)₈(OH)₆ is applied as electrochemical energy storage electrode material because of its unique microporous nature. Different aqueous electrolytes (LiOH, NaOH, and KOH) have been tested in order to study the effect of electrolyte cations on electrochemical behavior. To investigate the capacity and stability of Co₁₁ (HPO₃)₈(OH)₆ electrode, cyclic voltammetry (CV), galvanostatic charge-discharge (GC), and cycle stability were performed in aqueous electrolytes with different cations at room temperature. We found that the electrochemical behavior of these materials is strongly dependent on the species of electrolyte cations (Li⁺, Na⁺, and K⁺).