Abstract
Carbon‐based black materials exhibit strong solar absorptance (αsolar >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 (αsolar ≈ 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.
Highlights
The effective utilization of solar radiation has greatly boosted the burgeoning research fields including solar thermal,[1] photovoltaic,[2] thermophotovoltaic,[3] thermoelectric,[4] and many other systems.[5]conversion efficiency tremendously
The surface color of reduced graphene oxide (rGO)-Spectrally selective absorbers (SSAs) changes from almost transparent to black (Figure 1e and Figure S3, Supporting Information), which could be resulted from strong absorption enhancement for π-band transition in graphene lattice in the reduction process.[20]
For rGO-SSAλcut-fixed, growing speed of balanced temperature becomes slower than rGOSSAλcut-optimized when Copt > 10. Both of rGO-SSAλcut-optimized and rGO-SSAλcut-fixed approach ≈800 °C under much lower Copt than BB absorber (×75, ×18, and ×10 for BB, rGO-SSA1, and rGOSSA2, respectively). These analyses indicate selecting λcut(Copt, Tw) of rGO-SSA according to optical concentration and working temperature will approach the best performance in solar energy harvesting systems
Summary
The effective utilization of solar radiation has greatly boosted the burgeoning research fields including solar thermal,[1] photovoltaic,[2] thermophotovoltaic,[3] thermoelectric,[4] and many other systems.[5]. Huge thermal radiation to environment of conventional solar absorbers always thermal emittance of this rGO-SSA is largely reduced by ≈95.8% and the causes tremendous heat losses, restricting cutoff wavelength of rGO-SSA is broadband-tunable that can range from 1.1 to 3.2 μm. Comparing to conventional carbonbased black assemblies, thermal emittance of rGO film based spectrally selective absorber (rGO-SSA: ε100 ≈ 0.04) is largely reduced by ≈95.8% while solar absorptance remains at a high level (αsolar ≈ 0.92). The efficient utilization of solar radiation of rGO-SSA allows high surface temperature and fast surface solar steam escape speed (0.94 mg cm−2 s−1) when directly exposed to 6 sun radiation for superheated droplet boiling This discovery will promote the development of convenient and high-performance carbon-based intrinsic SSAs, opening their creative applications in various solar thermal conversion areas
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