Photocatalysts based on strontium titanate for green hydrogen production by water splitting: study of molybdenum doping and formation of junctions p - n

Author(s)

Hígor Andrade Centurion

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT)
• Defense date: 2023-05-05

Examining board members

Renato Vitalino Gonçalves; Rose Maria Carlos; Gregorio Couto Faria; Jesum Alves Fernandes; René Alfonso Nome Silva

• Advisor: Renato Vitalino Gonçalves

Abstract

The problems associated with the use of fossil fuels, such as the emission of greenhouse gases and the depletion of natural reserves, require the development of new energy sources, especially renewable and clean. In this context, green hydrogen from the water splitting process using photocatalysts suspended in water is an important strategy to explore the use of natural light and produce a fuel with high energy density, easy to store, and free of CO2 emissions. Due to its electronic properties, SrTiO3 is a promising material to act as a photocatalyst in water splitting reactions. However, intrinsic limitations such as wide bandgap (~3.2 eV) and high rates of recombination of photogenerated charges end up limiting its photocatalytic potential. In this work, the photocatalytic activity of SrTiO3 was enhanced by using the Mo6+ ions as a dopant, as well as by using nanoparticles of NiO@Ni(OH)2 or Rh2O3/CrxO3 as cocatalysts. Pure and Mo-doped SrTiO3 were synthesized by the molten salt method and decorated with nickel nanoparticles using the sputtering technique and Rh2O3/CrxO3 nanoparticles using the impregnation method. Associated with the insertion of Mo6+ as a dopant, it was reduced the recombination of photogenerated charges and photocatalytic activity under visible irradiation, attributed to intermediate electronic levels, predicted by theoretical simulations, and confirmed by diffuse reflectance measurements in the UV-Vis region. After the deposition of NiO@Ni(OH)2 and Rh2O3/CrxO3 nanoparticles, a significant reduction in the recombination of photogenerated charges was expected, associated with the formation of p n junctions, whose band alignment simulations indicate that these cocatalysts act as hole traps, maximizing charge separation. The suppression of recombination of the photogenerated charges was confirmed by photoluminescence measurements. In its most optimized configuration, SrTiO3 doped with Mo and decorated with nickel, in the presence of water and methanol (20 vol%), presented H2 evolution rates of 20 µmol h-1 and AQY of 2,58%, being more than 30 times higher than SrTiO3 as prepared. While Mo:SrTiO3/Rh2O3/CrxO3 exhibited significant photocatalytic activity in pure water, with an H2 evolution rate of approximately 100 µmol h-1 and AQY of 5,4%. This work demonstrates that Mo-doped SrTiO3 particles have excellent potential for application as a photocatalyst in the production of H2, especially after the deposition of cocatalysts. (AU)

• FAPESP's process: 18/11059-0 - Study of electronic and structural properties of SrTiO3/Fe2TiO5, SrTiO3 BiVO4 and SrTiO3/CuWO4 junctions for the formation of tandem systems for hydrogen production from water and sunlight
• Grantee: Higor Andrade Centurion
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)