Effect of graphene size on water evaporation rate of solar-driven steam generation

Graphene is considered a highly promising material due to its distinct properties, such as a high aspect ratio and superior mechanical, thermal, and optical characteristics. Notably, graphene and its derivatives exhibit a pronounced photothermal effect, positioning them as key materials for efficient solar energy harvesting and conversion. In this study, we evaluate the impact of the surface area of several types of commercial graphene on their water vapor generation capability. As a result, GC 750-based absorber layer shows a light absorption rate exceeding 88% across the full UV-Vis and near-infrared spectrum. This results in the highest photothermal conversion efficiency observed in the GC 750 sample, with the surface temperature of the dry film reaching 52°C under illumination. The surface area of GNPs increases from 50 to 750 m2/g, resulting in an increasing water evaporation rate from 0.717 to 0.814 kg.m-2.h-1 under 1 sun irradiation. This enhancement can also be partly attributed to the optimized structure of the GC 750-based absorb layer and the enhanced air convection properties of the material, which has a larger surface area and pore volume.