Facile one-pot transformation using structure-guided combustion waves of micro-nanostructured β-Bi ₂ O ₃ to α-Bi ₂ O ₃ @C and analysis of electrochemical capacitance

Precise phase-transformation can facilitate control of the properties of various materials, while an organic coating surrounding inorganic materials can yield useful characteristics. Herein, we demonstrate facile, selective manipulation of micro-nanostructured bismuth oxide (Bi ₂ O ₃ ) for phase transformation from microflower-like β-Bi ₂ O ₃ to micropill-like α-Bi ₂ O ₃ , with carbon-coating layer deposition, using structure-guided combustion waves (SGCWs). Microflower-like β-Bi ₂ O ₃ are synthesized as core materials and nitrocellulose is coated on their surfaces for the formation of core-shell hybrid structures of Bi ₂ O ₃ and chemical fuel. The SGCWs, which propagate along the core-material and fuel interfaces, apply high thermal energy (550–600 °C) and deposit incompletely combusted carbonaceous fuel on the microflower-like β-Bi ₂ O ₃ to enable transformation to α-phase and carbon-coating-layer synthesis. SGCW-induced improvements to the electrochemical characteristics of the developed micropill-like α-Bi ₂ O ₃ @C, compared with the microflower-like β-Bi ₂ O ₃ , are investigated. The enhanced stability from the α-phase Bi ₂ O ₃ and micropill-like structures during charge-discharge cycling improves the specific capacitance, while the carbon-coating layers facilitate increased electrical conductivity. SGCW-based methods exhibit high potential for selective phase manipulation and synthesis of carbon coatings surrounding micro-nanomaterials. They constitute a low-cost, fast, large-scale process for metal oxides, ceramics, and hybrid materials, implemented through control of the processing parameters by tuning the temperature, chemical fuel, and ambient conditions.