Structure-reactivity relationships of Ni-NiO core-shell co-catalysts on Ta₂O₅ for solar hydrogen production

Ni-NiO core-shell co-catalyst structures on Ta₂O₅ have been investigated for solar H₂ production. Core-shell co-catalysts with different morphologies resulted in large changes in photocatalytic activity. Increased H₂ production was found to be related to an increase in the thickness of NiO shell due to suppression of the back reaction. Atomic level transmission electron microscopy showed that the core-shell co-catalyst structures deactivated primarily due to a loss of metallic Ni from the core structure. During deactivation, the catalyst transformed either to structures consisting of NiO nanoblocks or hollow NiO shells. The phase transformations occurring during deactivation were associated with Ni diffusion processes that are driven by light illumination.