Electrophoretically deposited carbon nanotube spectrally selective solar absorbers

Abstract

Three types of carbon nanotubes (CNT) have been investigated regarding their suitability as spectrally selective solar thermal absorbers. The CNT coatings were electrophoretically deposited on aluminum substrates using kinetically stable CNT aqueous suspensions, of which two CNT aqueous suspensions (N-CNT and P-CNT suspensions) were prepared as part of this study and the third one (T-CNT suspension) was purchased. The CNT suspension systems are simple and consist of only CNTs, DI water and a cathodic surfactant. Heat treated CNT coatings are visibly uniform. The CNT coating thickness, surface morphology and reflectance of CNT absorbers were characterized by White Light Interferometry, Scanning Electron Microscopy and Spectrophotometry, respectively. T-CNT absorber achieved a solar absorptance α of 0.79 and a thermal emittance ε of 0.14. N-and P-CNT absorbers achieved better spectral selectivity, with α=0.90 and ε=0.14 for N-CNT absorber, α=0.90 and ε=0.13 for P-CNT absorber. The effect of CNT coating thickness, deposition parameters and peak heat treatment temperature on the spectral selectivity were studied. For these CNT suspension systems, the thickness and the heat treatment peak temperature are the key factors to achieving a good spectral selectivity.

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

“…As shown in Figure a, λ cut of rGO‐SSAs(Al|rGO|ARC) ranging from 1.3 to 3.2 µm are fabricated with the thickness of rGO films changed from ≈50 to ≈150 nm (Figure 1c, Figures S1b and S8, Supporting Information). For λ cut varying from 1 to 3 µm, all rGO‐SSAs(Al|rGO|ARC) sustain the lowest thermal emittance (ε 100 < 0.05), and still approach the highest solar absorptance (α solar ≈ 0.92) (Figure 4b and Figure S9, Supporting Information), which is outstanding to the performances of reported carbon‐containing SSAs17a,b,27 as far as we know, and is comparable to the best achieved of other SSAs by sol‐gel method (Table S1, Supporting Information) . To strengthen the high‐temperature stability of rGO‐SSA, we have used tungsten to replace Al as IR reflector (Figure 4c).…”

Anti-reflection coated spectrally selective carbon nanotube solar absorbers

“…The preparation procedure of MWCNT solar absorber samples has been reported in the authors' previous work [10], where functionalized MWCNTs (Nanocyl, Belgium) were dispersed and stabilized in aqueous solution with the addition of an ionic surfactant. The stable MWCNT suspension was applied for EPD on aluminium substrates (Oudifu, China).…”

Dual use of carbon nanotube selective coatings in evacuated tube solar collectors

“…Abendroth et al (2016), deposited single-walled CNT solutions on top of a quartz substrate by ultrasonic spraying and found that film thickness influenced the optical properties. Others have demonstrated that multi-walled CNTs electrophoretic deposited on top of aluminum substrates can achieved high absorbance (90%) and low thermal emissivity (0.13) with 1.7µm thick CNT film [16]. With CNT solutions the observed trend is that high absorbance and low reflectance in the visible spectrum and high reflectance in the infrared region can be achieved with thicker films, but at the cost of increased thermal emissivity [16].…”

“…Although CNT forest and solutions have shown interesting results as SSCs, they are not suitable for use in SWHs. In many cases, the SSC required the deposition of a reflective surface made of expensive metals, such as gold, titanium or aluminum on top of quartz or stainless steel by sputtering techniques [16][17][18]. Thus, the production at large scale is limited by cost and deposition technique.…”