Influence of particle morphology on solar thermal conversion performance and sensible heat storage capacity: A case study of TiO2@Go binary nanofluid.

Abstract

Photothermal catalytic hydrogen production driven by the full spectrum of outdoor solar radiation, represents a highly promising and efficient approach for hydrogen generation. This method is widely anticipated by researchers due to its potential to enhance photon utilization efficiency at the reaction source. However, limited attention has been devoted to the variations in photothermal conversion performance of particle reaction suspensions caused by objective fluctuations of solar irradiation, especially when the morphology of the nanostructure changes, which is a crucial factor for practical applications in hydrogen production. Based on this bottleneck, we prepared the typical photo-responsive TiO₂@Go composite with varied dimensions (i.e., nanosphere TiO₂@Go, nanorod TiO₂@Go, nanosheet TiO₂@Go) as research models, and systematically investigated their thermal conversion and sensible heat conversion performance under different working conditions. The results showed that at low nanofluid concentration, nanosphere TiO₂@Go and nanosheet TiO₂@Go exhibit better sensible heat conversion. As the particle concentration increases, the sensible heat conversion efficiency of all nanofluids decreases. It can also be found that the latent heat conversion efficiency tends to increase with the increase of concentration, but the nanorod TiO₂@Go show the opposite, which should be closely related to the uniformity of the particle size in different directions. In addition, for the sensible heat storage properties of nanofluids, smaller particle size and abundant porosity due to particles aggregation were found to be more beneficial for varied shapes. The underlying functional mechanisms were elucidated associated with the analysis of particle structures, interfacial properties, and optical characteristics. We contend that our research could provide valuable insights for the large-scale implementation of solar photothermal hydrogen production and a reasonable selection of photothermal material morphology for outdoor working conditions.