Photocatalytic production of hydrogen using TiO2 based catalysts

Abstract

Photocatalytic hydrogen production offers sustainable route to clean hydrogen production by utilizing water and sunlight. Although promising, this technology is still in its early stages, requiring advancements in materials efficiency and reactor design to achieve commercial viability. This study focused on evaluating the photocatalytic performance of TiO2 catalyst through modifications with metals such as Cu, Ni, and Cu-Ni combinations. Metal-modified TiO2 catalysts, synthesized via the incipient wetness impregnation method, were characterized to assess structural, morphological, and optical properties The results demonstrated that metal modification progressively reduced the bandgap energy of TiO2, enhancing visible light absorption and improving photocatalytic efficiency. It was also interesting to note that the bimetallic modified TiO2 resulted in lower bandgap energy compared to the monometallic modified TiO2. A further reduction in the bandgap energy was observed with increasing metal concentrations, indicating a correlation between metal loading and enhanced light absorption properties. Metal modified TiO2 catalysts exhibited improved light absorption compared to unmodified TiO2, indicating their potential for improved hydrogen production under solar irradiation. Experimental investigations conducted under varying operational conditions, including different photoreactors, sacrificial reagents, and catalyst dosage indicated active surface reactions; however, hydrogen production was not detected. This could be attributed to the recombination of photogenerated charges or hydrogen levels being below the detection limit. To further analyse hydrogen generation, an Aspen plus model incorporating Langmuir- Hinshelwood kinetics was developed to simulate and analyse photocatalytic hydrogen production. The model demonstrated good agreement with literature results and allowed investigation of process parameters that affect the hydrogen production. It was found that hydrogen production rate is significantly affected by the type and concentration of the sacrificial reagent, catalyst type, catalyst dosage and light intensity. Additionally, the study also conducted a preliminary techno-economic analysis of photocatalytic hydrogen production process using a Cu/TiO2 photocatalyst in a pilot-scale compound parabolic concentrator (CPC) reactor. The analysis revealed a specific hydrogen production cost of R872,849.00/kg, driven by the low solar-to-hydrogen (STH ) efficiency (<1%) and very limited hydrogen output. These findings emphasise the need for advanced iv materials, improved reactor designs, and larger scale systems to make this technology economically viable. Future research should focus on achieving STH efficiencies exceeding 10% and optimizing operational parameters to enhance the economic feasibility of photocatalytic hydrogen production.