Metallic nanoparticles loaded Al–SrTiO3 supported with RhCr2O3 and CoOOH cocatalysts for overall water splitting

Abstract

Developing new renewable, carbon-neutral fuels to diminish the amount of released CO2 in the atmosphere and to solve global challenges such as global warming and climate change is significant. Among them, hydrogen (H2) is attracting much attention due to its high energy density, ease of transportation, and multiple means of production. To meet the global demand of H2, photocatalytic water splitting is one of the most promising methods for large scale production. Herein, Al-doped SrTiO3 photocatalyst (Al–SrTiO3) was prepared by a molten flux method. Then, plasmonic metal nanoparticles (Au, Cu, Pt), and cocatalysts Rh/Cr2O3 and CoOOH were selectively deposited onto the reductive and oxidative active sites of Al–SrTiO3 using multi-step photodeposition-impregnation methods for water splitting and H2 production under UV-rays, UV–Vis. Light, and visible light (λ ≥ 400 nm). Our results showed that, compared with Pt and Cu loaded Al–SrTiO3 photocatalyst supported with Rh/Cr2O3 and CoOOH cocatalysts, Au-loaded samples showed the highest H2 production efficiency under both UV (920 μmol/h - EQE = 41% at 365 nm) and UV–Vis (100.5 μmol/h) rays. In addition, the amount of evolved H2 decreased by increasing the weight ratio of Au nanoparticles (NPs) due to the overlap between Au NPs and Rh/Cr2O3 cocatalyst. Although Au 0.3 wt%-loaded sample showed high activity under both UV and UV–Vis. Rays, it exhibited almost no efficiency under visible light because of the large bandgap of Al–SrTiO3 (3.1 eV) and the poor absorption in the visible region. Visible light absorption was then enhanced by increasing the loaded amount of Au NPs and by separating Au NPs and Rh/Cr2O3 cocatalyst responsible for H2 evolution by combining both photodeposition and impregnation methods. Under visible light, Rh/Cr2O3-loaded Al–SrTiO3 with 4 wt % Au NPs showed the highest H2 evolution efficiency (41 μmol/3 h). This was attributed to the efficient hot electron transfer from Au NPs to Al–SrTiO3 then to RhCr2O3, resulting in charge separation needed for efficient H2 generation.