A refractory selective solar absorber for high performance thermochemical steam reforming

The production of H-2 through steam reforming involves intensive energy consumption. Concentrated solar energy could be employed for the endothermic reaction in the steam reformer to produce H-2. However, at high operating temperatures, the solar absorber has huge radiation heat loss to the ambient as the radiation energy is proportional to the fourth power of the surface temperature. In order to avoid the large radiation heat loss and obtain higher surface temperature, here we present a 2D photonic crystal (PhC) solar selective absorber. The selective absorber is made from titanium nitride (TiN) thin film. On top of the TiN thin film, nano cavity array structure and Al2O3 coating are deposited. The absorptivity of the selective absorber is measured at room temperature and the high operating temperature performance is predicted. The fabricated selective absorber is thermal annealed at 800 degrees C for two hours and proves its thermal stability. By comparing the steam reformers with different absorbers (selective absorber and blackbody absorber), the selective absorber shows superior results including higher surface temperature, higher C3H8 conversion rate as well as higher H-2 production rate. The experimental and simulation results in this study shows that the 2D PhC solar selective absorber is a good candidate in the steam reforming application for H-2 production. (C) 2016 Elsevier Ltd. All rights reserved.