Molten salt synthesis of cobalt-based electrodes: investigating the effect of the salt on phase, morphology, and electrochemical properties

Molten salt synthesis (MSS) represents an emerging green and environmentally friendly approach for engineering the structural and phase characteristics of multifunctional materials. In this study, we report the rapid synthesis of cobalt (Co)-based electrodes through MSS under 15 min with high yield. Our findings reveal that the selection of salt precursor significantly influences the crystal phase and morphology of the Co-based electrodes as well as the electrochemical properties. Hydroxide-based salts yielded layered Na_xCoO₂ with a thin hexagonal morphology, while nitrate-based salts resulted in spinel phase Co₃O₄ with octahedral structures. Our proposed mechanism highlights the critical role of ionic bonding in these phenomena. The electrochemical evaluation demonstrates that the layered Na_xCoO₂ electrodes exhibit a specific capacitance of 59 F g⁻¹ (47.2 C g⁻¹) at 1 A g⁻¹ and excellent long-term capacity retention. On the other hand, spinel Co₃O₄ electrodes, when employed as oxygen evolution reaction (OER) catalysts, exhibit an overpotential of 341 mV to drive a current density of 10 mA cm⁻², which is comparable to Co₃O₄ prepared using other methods that required a significant amount of synthesis time.