Multi-Morphology CeO₂ Synthesis via Synergistic Induction by Solvent and Ammonium Bicarbonate

CeO₂ is a crucial functional material in catalysis and energy applications, whose performance is highly morphology-dependent. Traditional synthesis methods often rely on organic templates or surfactants, which complicate the processes and pose environmental concerns. This study introduces an eco-friendly approach utilizing a methanol-water (MeOH-H₂O) mixed solvent system combined with NH₄HCO₃ to achieve controllable synthesis of multi-morphology CeO₂ without surfactants or templates. The effects of different solvent systems (pure H₂O, pure MeOH, and their mixtures) and NH₄HCO₃ as an inexpensive regulator on precursor phase behavior and crystallization were systematically investigated. By optimizing the Ce:N molar ratios (1:1 to 1:7) as well as reaction times (0.5 to 36 h), our findings indicate that H₂O significantly enhances crystallinity (from 40.9% to 61.4% for precursors, reaching 70.3% after calcination) and promotes octahedra formation in the MeOH-H₂O mixed system, while NH₄HCO₃ acts as a structure-directing agent to control size (e.g., ~240 nm octahedra at Ce:N = 1:1, up to 375 nm at Ce:N = 1:2) and partially substitutes for high-temperature calcination in improving crystallinity. Variety morphologies, including plates, dendrites, octahedra, and hollow structures, were successfully synthesized. This work elucidates the synergistic mechanism by which solvents and NH₄HCO₃ influence CeO₂ nucleation and growth, thereby providing an environmentally friendly synthesis route with significant potential applications in catalysis and energy storage.