Enhanced Photothermal Conversion by Hot-Electron Effect in Ultrablack Carbon Aerogel for Solar Steam Generation

Abstract

Ecofriendly, highly effective, and low-cost solar steam generation has great potential in the applications of power generation, seawater desalination, and industry wastewater treatment. Solar steam generation requires an evaporator that has strong light absorption over a wide-frequency band (200–3000 nm), high photothermal conversion efficiency, and good thermal insulation to avoid excessive heat loss. Herein, foam-strengthened ultrablack carbon aerogels (CAs) with micropores, mesopores, and macropores were prepared using freeze drying. The small-size conductor effect in ultrablack CAs could increase the surface electron concentration, leading to the increase of light absorption and ultimately enhancing photothermal conversion efficiency. Consequently, under 1 sun illumination, dried CA-5 exhibited a fast temperature rise rate and the highest thermal equilibrium temperature of 87.6 °C among CAs, the equilibrium temperature is 20.8 °C higher than that of the foam. Besides, CA-5 exhibited a high water evaporation rate of 1.29 kg m–2 h–1 under only 1 sun illumination. To further increase the hot-electron effect, CO2 activation was implemented. The highest water evaporation rate among activated CAs (ACAs) was 1.37 kg m–2 h–1, which is about 2.85 times higher than that of pure water. The highest water evaporation efficiency was 87.51%, which is better than most of the previously reported evaporation efficiencies. Besides the hot-electron enhancement effect, ACAs with thermal insulation, mechanical strength, and thermal stability show great potential for producing fresh water from seawater, industrial wastewater, and even concentrated acidic or alkaline solutions.

A versatile platform of poly(acrylic acid) cryogel for highly efficient photothermal water evaporation

“…7,8 They should have full-spectrum light absorbance and high light-to-heat conversion efficiency but their actual performance varies from each other, being dependent on the mechanism of photothermal conversion and light absorption capacity. 9,10 Among them, carbon materials such as carbon nanotubes, 11 graphene, 12,13 carbon black, 14 carbon aerogels as well as conjugated polymers such as polypyrrole (PPy) and polyaniline (PANI) [15][16][17] have broadband absorption spectrum, high photothermal stability, and low density, making them ideal candidates. In addition, many carbon materials and conjugated polymers are of low cost and can be well incorporated into polymeric matrices to produce photothermal evaporation systems through various routes including in situ polymerization.…”

Ultra‐Black Pinecone for Efficient Solar Steam Generation under Omnidirectional Illumination

“…The photo‐thermal conversion efficiency, η, is the sum of the heat efficiency (sensible heat) and evaporation efficiency (latent heat). The most frequently used equation for calculating the photo‐thermal conversion efficiency is as following: [ 38,57 ] where is the water evaporation rate subtracted the dark evaporation rate; C is the specific heat capacity of water, which is a constant (4.18 kJ kg −1 K −1 ); Δ T is the water temperature difference after and before solar illumination; C opt is the optical concentration; I is the solar intensity of 1 sun (1 kW m −2 ); and ΔH vap is the latent heat of vaporization based on the measured vapor temperature (surface temperature of the evaporator).…”

“…), semiconductors (Cu x S, [ 20,21 ] MoS 2 , [ 22,23 ] TiO x , [ 24,25 ] etc. ), polymers, [ 26–31 ] MXene, [ 11,32 ] carbon materials, [ 2,7,8,33–44 ] and composite materials [ 45–48 ] have been developed. However, there are still many challenges, including material cost, industrial scale‐up, and outdoor performance degradation, that need to be overcome.…”

“…[ 51,56,57 ] We have found that the SSG performances of evaporators could be improved by designing microstructure and macrostructure. [ 38,57 ] Transpiration of plants provides an ideal solution for SSG because the hierarchical scales and vertically arrayed microchannels are natural and minimized the water transport resistance and follow Murray's law. [ 43 ] By inheriting the moisture‐sensitive deployable structure and porous structures of pinecones and combining the advantages of the transpiration of plants, it is possible to achieve efficient SSG under omnidirectional illumination.…”

Preparation and application of sunlight absorbing ultra-black carbon aerogel/graphene oxide membrane for solar steam generation systems

“…Fig. 11b displays the efficiency of aerogel-and porous carbon-based absorbents reported in literatures, 5,[33][34][35][36][58][59][60][61] and this work. In comparison to the other absorbents, higher efficiency was achieved in this work due to the employment of ultra-black nanoporous CA, superhydrophilic GO, and superhydrophilic modied substrate (MCF) with micron sized pores.…”