Abstract
A series of novel hierarchical nanoporous microstructures have been synthesized through one-step chemical reduction of micron size Cu2O and Co3O4 particles. By controlling the reduction time, non-porous Cu2O microcubes sequentially transform to nanoporous Cu/Cu2O/Cu dented cubic composites and hollow eightling-like Cu microparticles. The mechanism involved in the complex structural evolution is explained based on oxygen diffusion and Kirkendall effect. The nanoporous Cu/Cu2O/Cu dented cubic composites exhibit superior electrochemical performance as compared to solid Cu2O microcubes. The reduction of nonporous Co3O4 also exhibits a uniform sequential reduction process from nonporous Co3O4 to porous Co3O4/CoO composites, porous CoO, porous CoO/Co composites, and porous foam-like Co particles. Nanoscale channels originate from the particle surface and eventually develop inside the entire product, resulting in porous foam-like Co microparticles. The Kirkendall effect is believed to facilitate the formation of porous structures in both processes.
Highlights
The properties of functional materials are generally dependent on their microstructure
The formation of porous structures during the oxidation process is often explained in terms of the Kirkendall effect, which has been utilized for the formation of unique porous nanostructures[20,21,22,23]
Our work demonstrates the feasibility of fabricating porous structures via reduction process and will likely inspire interest in the preparation of practical porous materials by this facile method and further investigation of the formation mechanism
Summary
Nanoporous Microstructures via received: 23 March 2015 accepted: 05 October 2015 Published: 10 November 2015 the Kirkendall Effect in Chemical Reduction Process. By controlling the reduction time, nonporous Cu2O microcubes sequentially transform to nanoporous Cu/Cu2O/Cu dented cubic composites and hollow eightling-like Cu microparticles. Due to the complexity of the mechanism and the difficulty of controlling the compositional and structural transformations, it is unlikely that this reduction process can be extended for the synthesis of other porous structured materials. We have developed a simple solution-phase method for fabricating nanoporous Cu-based microstructures by thermal reduction of solid non-porous Cu2O microcubes. Very interesting morphologies, including nanoporous Cu/Cu2O/Cu dented cubic composites and hollow Cu with eightling (eight-fold twinning)-like structures are obtained during the reduction process. Our work demonstrates the feasibility of fabricating porous structures via reduction process and will likely inspire interest in the preparation of practical porous materials by this facile method and further investigation of the formation mechanism
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