Lee et al./ACS Catalysis
These scanning electron microscopy images show the copper catalyst structure at different stages. (a) The catalyst prior to running any reactions. The cube structures on the surface are a result of the oxide. (b) What the catalyst looks like after running the CO reduction chemistry; all the oxygen is gone. (c) The catalyst after intentionally adding oxygen back to the metal as a way of recovering the performance of the catalyst. Copper oxide has formed in small nanoparticles on top of the smooth copper metal surface.