Fast Oxidation of Porous Cu Induced by Nano-Twinning

The fcc lattice of porous Cu prepared by dealloying Al₂Cu with HCl aqueous solution exhibits a high density of twinning defects with an average domain size of about 3 nm along the ⟨111⟩ directions. The high density of twinning was verified by X-ray diffraction and qualitatively interpreted by a structural model showing the 5% probability of twinning defect formation. Most of the twinning defects disappeared after annealing at 873 K for 24 h. Twinned Cu reveals much faster oxidation rate in comparison to that without (or with much fewer) twinning defects, as shown by X-ray diffraction and hydrogen differential scanning calorimetry. Using ab initio DFT calculations, we demonstrate that twinning defects in porous Cu are able to form nucleation centers for the growth of Cu₂O. The geometry of the V-shaped edges on the twinned {211} surfaces is favorable for formation of the basic structural elements of Cu₂O. The fast oxidation of porous Cu prepared by dealloying can thus be explained by the fast formation of the Cu₂O nucleation centers and their high density.