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

## TL;DR

A new eco-friendly method for making different shapes of CeO2 without using harmful chemicals is developed, which could improve its use in catalysis and energy storage.

## Contribution

The study introduces an environmentally friendly synthesis method for multi-morphology CeO2 using a solvent system and ammonium bicarbonate without surfactants.

## Key findings

- H2O in the MeOH-H2O system enhances crystallinity and promotes octahedral CeO2 formation.
- NH4HCO3 controls CeO2 size and partially replaces high-temperature calcination.
- Multiple CeO2 morphologies like plates, dendrites, and hollow structures were successfully synthesized.

## Abstract

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.