Transient Behavior of Ni@NiO(x) Functionalized SrTiO(3) in Overall Water Splitting

[Image: see text] Transients in the composition of Ni@NiO(x) core–shell co-catalysts deposited on SrTiO(3) are discussed on the basis of state-of-the-art continuous analysis of photocatalytic water splitting, and post-XPS and TEM analyses. The formation of excessive hydrogen (H(2):O(2) ≫ 2) in the initial stages of illumination demonstrates oxidation of Ni(OH)(2) to NiOOH (nickel oxyhydroxide), with the latter catalyzing water oxidation. A disproportionation reaction of Ni and NiOOH, yielding Ni(OH)(2) with residual embedded Ni, occurs when illumination is discontinued, which explains repetitive transients in (excess) hydrogen and oxygen formation when illumination is reinitiated.