Rapid microwave-assisted hydrothermal synthesis of morphology-tuned MnO2 nanocrystals and their electrocatalytic activities for oxygen reduction

• Four types of MnO2 structures were synthesized by a microwave-assisted route.
• The γ-MnO2 nanosheets and β-MnO2 octahedrons were prepared for the first time.
• The growth time does not exceed 10 min in any type of the synthesis.
• The electrocatalytic activities of the synthesized MnO2 for ORR have been studied.
• The α-MnO2 nanorods possessed a higher electrocatalytic activity than that of others.

A rapid and facile microwave-assisted hydrothermal route has been developed to synthesize MnO2 nanocrystals with exquisitely tuned structures/morphologies by reducing potassium permanganate in the presence of hydrochloric acid. δ-MnO2 microspheres, α-MnO2 nanorods, γ-MnO2 nanosheets and β-MnO2 octahedrons have been obtained with 0.05, 0.10, 0.25 and 0.75 mL HCl (37 wt%), respectively. More importantly, γ-MnO2 nanosheets and β-MnO2 octahedrons were prepared for the first time by a one-step microwave-assisted method. The electrocatalytic activities of the synthesized MnO2 in KOH solution have been determined by cyclic voltammetry and the results show that all manganese dioxides can catalyze the oxygen reduction reaction (ORR) in alkaline medium with different catalytic activities. α-MnO2 nanorods appear to hold the highest catalytic activity due to their crystal phase/morphology with appropriate oxygen adsorption mode.

δ-MnO2 microspheres, α-MnO2 nanorods, γ-MnO2 nanosheets, β-MnO2 octahedrons and hollow prismatic microrods have been obtained by a one-pot microwave-assisted hydrothermal route.Figure optionsDownload as PowerPoint slide