Oxyhydroxide Nanosheets with Highly Efficient Electron-Hole Pair Separation for Hydrogen Evolution

The facile electron-hole pair recombination in earth-abundant transition-metal oxides is a major limitation for the development of highly efficient hydrogen evolution photocatalysts. In this work, the thickness of a layered -CoOOH semiconductor that contains metal/hydroxy groups was reduced to obtain an atomically thin, two-dimensional nanostructure. Analysis by ultrafast transient absorption spectroscopy revealed that electron-hole recombination is almost suppressed in the as-prepared 1.3nm thick -CoOOH nanosheet, which leads to prominent electron-hole separation efficiencies of 60-90% upon irradiation at 350-450nm, which are ten times higher than those of the bulk counterpart. X-ray absorption spectroscopy and first-principles calculations demonstrate that [HO-CoO6-x] species on the nanosheet surface promote H+ adsorption and H-2 desorption. An aqueous suspension of the -CoOOH nanosheets exhibited a high hydrogen production rate of 160molg(-1)h(-1) even when the system was operated for hundreds of hours.