Phase Transformations of Cobalt Oxides in Co_xO_y-ZnO Multipod Nanostructures via Combustion from Thermopower Waves

Abstract

The study of combustion at the interfaces of materials and chemical fuels has led to developments in diverse fields such as materials chemistry and energy conversion. Recently, it has been suggested that thermopower waves can utilize chemical-thermal-electrical-energy conversion in hybrid structures comprising nanomaterials and combustible fuels to produce enhanced combustion waves with concomitant voltage generation. In this study, this is the first time that the direct phase transformation of Co-doped ZnO via instant combustion waves and its applications to thermopower waves is presented. It is demonstrated that the chemical combustion waves at the surfaces of Co3O4-ZnO multipod nanostructures (deep brown in color) enable direct phase transformations to newly formed CoO-ZnO(1-x) nanoparticles (olive green in color). The oxygen molecules are released from Co3O4-ZnO to CoO-ZnO(1-x) under high-temperature conditions in the reaction front regime in combustion, whereas the CoO-ZnO multipod nanoparticles do not undergo any transformations and thus do not experience any color change. This oxygen-release mechanism is applicable to thermopower waves, enhances the self-propagating combustion velocity, and forms lattice defects that interrupt the charge-carrier movements inside the nanostructures. The chemical transformation and corresponding energy transport observed in this study can contribute to diverse potential applications, including direct-combustion synthesis and energy conversion.

Scalable Synthesis of Triple‐Core–Shell Nanostructures of TiO2@MnO2@C for High Performance Supercapacitors Using Structure‐Guided Combustion Waves

“…The overall trend was similar to that of the 1st SGCW, owing to the fuel (NC) and structural conditions of the hybrid composites being identical. Furthermore, the instant high thermal energy, produced by the SGCW, leads to a sudden increase and decrease in the temperature, thus inducing the incomplete combustion of the carbonaceous fuel, due to the short duration of the combustion and the oxygen deficiency in the NPs . Those specific conditions resulted in the formation of a thin carbon shell surrounding the NPs, which did not affect either the morphology or dimensions of the NPs (Figure d).…”

Facile One-pot Transformation of Iron Oxides from Fe2O3 Nanoparticles to Nanostructured Fe3O4@C Core-Shell Composites via Combustion Waves

“…The reaction velocity in the hybrid composite is somewhat faster than that in the nitrocellulose-only layer. The direct supply of oxygen from the metal oxides enhances the velocity of the combustion wave, which consumes the surrounding oxygen38. This implies that the Fe 2 O 3 nanoparticles in this hybrid composite film might lose oxygen from the inner structures to the chemical reaction in the combustion wave.…”

“…In the first experiment, high-temperature annealing at 740 °C, approximately the average surface temperature in the combustion wave, was performed for 3 h on the thin reddish-brown film of Fe 2 O 3 nanoparticles. This provided high-temperature conditions with a sufficient supply of thermal energy3851 without creating the chemical environment produced by combustion waves inside the thin film. Interestingly, no color change was observed after annealing, and no phase transformation occurred.…”

Direct Electricity Generation Mediated by Molecular Interactions with Low Dimensional Carbon Materials—A Mechanistic Perspective

“…7e). [95] Systematic efforts in optimizing reactant compositions [189][190][191][192][193][194] and nano-structured conduit types [188,[195][196][197][198][199][200][201][202][203][204][205][206] have proven to be indispensable in TPW output enhancements (Fig. 7e).…”