Synthesis of anisotropic β-Ni(OH)2 platelets and global kinetics of their thermal decomposition into nanostructured NiO

Abstract

Nickel-based materials are widely used in energy storage technologies, where their electrochemical performance is closely related to their microstructural characteristics. Morphology and microstructure can also influence solid-state thermal transformations and, consequently, their thermokinetic behavior. Therefore, understanding these effects is important for controlling the thermal conversion of Ni(OH)2 to NiO with defined structural characteristics.In this work, β-Ni(OH)2 with an anisotropic platelet-like microstructure was synthesized to investigate the kinetics of its thermal decomposition into nanostructured NiO. The material was obtained by alkaline precipitation, exploiting the heat released during NaOH dissolution. X-ray diffraction revealed pronounced crystallite-size anisotropy, while electron microscopy showed nanoscale platelets. The thermal behavior was subsequently studied by differential scanning calorimetry under multiple non-isothermal programs, which revealed a single apparent endothermic event associated with NiO formation and H2O release.The thermokinetic behavior was investigated using the Friedman isoconversional method, the Kissinger method, and combined kinetic analysis applying truncated Šestak-Berggren and interface-controlled contraction (R+) models. The results showed a nearly constant activation energy across the entire conversion range, supporting a single-step, rate-limiting process. The observed kinetic behavior was consistent with the anisotropic morphology and microstructure of the precursor. Microstructural and electron microscopy evidence supported a deceleration mechanism consistent with interface-controlled contraction in the platelet system and the formation of nanostructured NiO. The process was characterized by E = 136.5 kJ mol−1, ln(A/^s-1) = 25.6, and an R+ kinetic model (n = 0.74 and μ = 1.78). The resulting kinetic parameters allowed accurate reconstruction of the experimental curves and reliable prediction of thermal behavior under conditions outside the experimental range.