Reduced Graphene Oxide-Based Spectrally Selective Absorber with an Extremely Low Thermal Emittance and High Solar...

Carbon-based black materials exhibit strong solar absorptance (α_solar >0.90), which play key roles in transforming solar energy into available power for solar-thermal, thermophotovoltaic, thermoelectric, and many other systems. However, because of high thermal emittance (>95%), these carbon-based materials always cause huge energy loss that hinders the solar-thermal conversion efficiency tremendously. In this study, a reduced graphene oxide-based spectrally selective absorber (rGO-SSA) is demonstrated, which possesses a recorded low thermal emittance (≈4%) and high solar absorptance (α_solar ≈ 0.92) by easily regulating the reduction level of inner 2D graphene sheets. Compared to conventional carbon-based black materials, thermal emittance of this rGO-SSA is largely reduced by ≈95.8% and the cutoff wavelength of rGO-SSA is broadband-tunable that can range from 1.1 to 3.2 µm. More importantly, this simply sol-gel coated rGO-SSA has high temperature tolerance at 800 °C for 96 h that is hardly achieved by other cermet-based or photonic-based SSAs. Based on this rGO-SSA, ultrafast solar steam escape (0.94 mg cm^-2 s^-1) under concentrated solar irradiance is achieved directly. The insight from this study will provide a new strategy for constructing thermally stable carbon-based SSAs and greatly facilitate the solar-thermal practical significance.