To improve TiO2 for H2 generation, one strategy for the separation of photogenerated charges is the formation of heterostructures with other materials. In particular, NiO is a photocatalyst known for its good stability and low cost. However, no studies at pilot scale using solar energy have been described. Consequently, an evaluation of a physical NiO:TiO2 mixture at pilot scale (25 L) with natural irradiation (2.10 m2 of sun-exposed surface) and with simultaneous glycerol photoreforming was explored. NiO:TiO2 50 mg·L−1 resulted in the highest hydrogen production, showing an STH = 1.44%, considering only the UV fraction of the solar irradiation. H2 and CO2 production were analysed by on-line GC; Glycerol, dissolved organic carbon, carboxylic acids and nickel leaching were also evaluated. The NiO:TiO2 mixtures rendered a systematically lower H2 production in natural water than in high-purity water. The increase of ionic strength increased the mean size of particle clusters, promoting rapid sedimentation. All this indicates the importance of testing under real field conditions for attaining reliable solar to hydrogen (STH) efficiency.

The authors wish to thank the Ministerio de Ciencia, Innovación y Universidades (MCIU), under the SolarChem 5.0 Project (TED2021–130173B-C43/ AEI/10.13039/501100011033/ Unión Europea NextGenerationEU/PRTR). J. Sowik acknowledges funding from the Polish National Agency for Academic Exchange (NAWA PRELUDIUM BIS No. PPN/STA/2021/1/00005/U/00001).

Peer reviewed