Topotactic Thermal Decomposition of α ‐Co(OH) ₂ Nanorods to Morphology‐Preserved Co ₃ O ₄ Supercapacitors

This study investigates the topotactic conversion of cobalt hydroxide (CHY) to cobalt oxide (COX) and its influence on electrochemical performance. CHY was synthesized by a simple precipitation method and thermally decomposed in a muffle furnace at 300°C for 2 h to obtain Co ₃ O ₄ . The CHY and COX were thoroughly characterized by thermogravimetric analysis (TGA), X‐ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. Field emission scanning electron microscopy (FESEM) images revealed that the nanorod morphology of the hydroxide was retained after calcination. Characterizations confirmed successful topotactic transformation of α ‐Co(OH) ₂ to Co ₃ O ₄ without any secondary phase. Electrochemical measurements demonstrated a significant difference in charge‐storage behavior: CHY exhibited a specific capacitance of 570 F g ⁻¹ at 1 A g ⁻¹ , while COX showed 188 F g ⁻¹ under identical conditions. Cyclic voltammetry performed at scan rates from 2.5 to 100 mV s ⁻¹ and galvanostatic charge–discharge (GCD) at 0.5–8 A g ⁻¹ further supported the enhanced pseudocapacitive behavior of CHY. Electrochemical impedance spectroscopy (EIS) revealed a much lower charge‐transfer resistance for CHY compared to COX, indicating faster electron transport. The results confirm that the topotactic transformation preserves morphology and improves structural stability, although it reduces ion diffusion and available active surface area, resulting in lower capacitance in the oxide phase.