2. Select foamed iron with a three-dimensional porous structure as the substrate and iron source, and construct in-situ "leaf-shaped" columnar arrays (Fe3O4) rich in defects intertwined with each other through high-temperature oxidation and partial reduction.
2, select the foam iron with three-dimensional porous structure as the base and iron source, through high temperature oxidation and partial reduction in place to build a rich defect interleaving "leaf-shaped" column array (Fe3O4).