Iron shell formation by electrolyzing self-assembled nano-particles

Electrochemical reaction process of iron oxide reduction has been investigated for several decades, and both solid-state reaction mechanism and dissolution/re-deposition mechanism were proposed for the reduction process. The previous studies observed the reaction process from macro- and micro-scale, and how the intermediate participates in the dissolution/re-deposition route is unclear. In this study, a mixture of Fe₂O₃ nano-particles and carbon powder was electrolyzed in an alkaline solution, and the morphology of the product depended on the electrolysis temperature. The Fe₂O₃ nano-particle aggregates can be electrolyzed into micro-size hollow partciles at 60°C. To explain this phenomenon, ex-situ SEM technique combining with TEM was adopted to observe the morphology change of Fe₂O₃ particles on the surface of the glass carbon electrode at nano-scale at a series of electrode potentials. The surface of the particle was reduced to amorphous compounds firstly, and these compound was the intermediate participating in dissolution/re-deposition process to form new crystals. The solubility of these amorphous compound is relative low at 60°C, and the compouds stayed in their original position, connected and stabilized each other to form micro-size iron shell. They can dissolve into eletrolyte, migrate to somewhere, and re-deposit to construct new crystals at higher temperature. This study not only presents an innovative and efficient way to electrolyze micro-size hollow iron particles, but also provides some new discovery about Fe₂O₃ electrochemical reduction process.