Reduced Red Mud as the Solar Absorber for Solar-Driven Water Evaporation and Vapor-Electricity Generation

Solar-Driven Harvesting of Freshwater and Electricity Based on Three-Dimensional Hierarchical Cu2-xO@Cu Foam

The integration of solar steam generation and the hydrovoltaic effect is a promising strategy for simultaneously solving water scarcity and energy crises. However, it is still a challenge to attain a high water evaporation rate and a strong output of electricity in a single device. Here, we report a three-dimensional (3D) hierarchical Cu2-xO@Cu foam for solar-driven harvesting of freshwater and electricity efficiently. The 3D Cu2-xO@Cu foam synthesized by chemical etching shows a rough surface and porous structure, making it have a hydrophilic surface, high light absorption performance, and excellent photothermal effect. For deionized water, the evaporation rate is as high as 3.03 kg m-2 h-1; meanwhile, the output voltage is 0.37 V under 1 solar irradiation. For real seawater, the evaporation rate decreases to about 2.48 kg m-2 h-1, the output voltage increases to 0.41 V, and the maximum output power density is 9.47 μW cm-2. Both the water evaporation and power generation performance are very competitive. Outdoor experiments demonstrate that the 3D hierarchical Cu2-xO@Cu foam can desalinate seawater, while generating electricity continuously.

Dual-functional natural rubber latex foam composites for solar-driven clean water production and heavy metal decontamination

Solar steam generation (SSG) offers a sustainable approach to fresh water production. Herein, a novel dual-functional natural rubber/carbon black composite foam evaporator is presented for a cost-efficient SSG system that both produces fresh water and eliminates heavy metals present in the water. The composite foam is produced using the Dunlop process, and in its optimized form, it absorbed >96 % of sunlight. The foam evaporator exhibited a thermal conductivity of 0.052 W/m⋅K, a water evaporation rate of 1.40 kg/m2/h, converted 83.38 % of light to heat under 1 sun irradiation, and showed outstanding stability. The technology required to produce this composite foam is already available to make large-scale production feasible, while the natural raw materials are abundant. On the basis of its performance qualities, the rubber foam composite appears to be an excellent candidate for application as a viable solar absorber for SSG to produce fresh, clean water for commercial purposes.

High-efficiency and sustainable sodium humate aerogel evaporator for solar steam generation

The utilization of solar interface evaporation technology (SIET) for freshwater production from seawater and sewage is a sustainable, green, viable, and promising approach. However, the absorption rate of sunlight, evaporation rates, and high costs still pose large-scale solar steam generation. In this paper, a novel aerogel (named SAS) was prepared by graft copolymerization with sodium alginate (SA), acrylic acid (AA) and sodium humate (SH) in aqueous solution, using N, N'-Methylenebisacrylamide (MBA) as crosslinker and ammonium persulfate (APS) as initiator, which has high light absorption (90 %), high porosity (87.96 %), superhydrophilicity (35 ms), low thermal conductivity (0.23 W m-1 k-1). The evaporation rate of SAS aerogel can reach up to 1.66 kg m-2h-1 under 1 kW m-2 light intensity, and the reusability and reliability of SAS aerogel are verified by 10 cycles of experiments. The utilization of this SAS aerogel holds significant implications for the design and fabrication of cost-effective, high-performance solar steam evaporation systems, thereby offering promising solutions to address global freshwater shortages and enhance wastewater treatment efficiency.

A scalable and anti-fouling silver-nickel/cellulose paper with synergy photothermal effect for efficient solar distillation

Solar interfacial evaporation is one of the most efficient and environmentally-friendly clean freshwater production technologies. Plasma metal nanoparticles are excellent optical absorption materials, but their high cost and inherent resonance narrow bandwidth absorption limit their application. In this work, commercial cellulose papers are used as substrates to synthesize Ag-Ni/cellulose paper by the seed-mediated method. The Ag-Ni/cellulose paper exhibits high light absorption at the full wavelength (200-2500 nm) resulting from the synergistic effect of localized surface plasmon resonance (LSPR) of Ag NPs and the interband transitions (IBTs) of Ni. Under one-sun irradiation (1 kW m-2), the energy utilization efficiency of Ag-Ni/cellulose paper is as high as 93.8%, and the water evaporation rate is 1.87 kg m-2 h-1. Diffusion inhibition experiment results show that the Ag-Ni/cellulose paper exhibits excellent antibacterial performance, and the antibacterial performance is highly related with Ag NPs content. These provide new opportunities for commercial production of competitive cost, green, and portable solar evaporators for different application sceneries.

A Multifunctional Asymmetric Fabric for Sustained Electricity Generation from Multiple Sources and Simultaneous Solar Steam Generation

Harvesting electrical energy from water and moisture has emerged as a novel ecofriendly energy conversion technology. Herein, a multifunctional asymmetric polyaniline/carbon nanotubes/poly(vinyl alcohol) (APCP) that can produce electric energy from both saline water and moisture and generate fresh water simultaneously is developed. The constructed APCP possesses a negatively charged porous structure that allows continuous generation of protons and ion diffusion through the material, and a hydrophilicity-hydrophobic interface which results in a constant potential difference and sustainable output. A single APCP can maintain stable output for over 130 h and preserve a high voltage of 0.61 V, current of 81 µA, and power density of 82.4 µW cm-3 with 0.15 cm3 unit size in the water-induced electricity generation process. When harvesting moisture energy, the APCP creates dry-wet asymmetries and triggers the spontaneous development of electrical double layer with a current density of 1.25 mA cm-3 , sufficient to power small electronics. A device consisting of four APCP can generate stable electricity of 3.35 V and produce clean water with an evaporation rate of 2.06 kg m-2  h-1 simultaneously. This work provides insights into the fabrication of multifunctional fabrics for multisource energy harvesting and simultaneous solar steam generation.

3D Tea-Residue Microcrystalline Cellulose Aerogel with Aligned Channels for Solar-Driven Interfacial Evaporation Co-generation

Solar-driven interfacial evaporation co-generation (SIE-CG) technology is of great significance in solving the problem of water and energy shortage. Herein, we report the ionic liquid-assisted alignment of waste biomass tea residue-based microcrystalline cellulose for aerogels (abbreviated as TPPA-5) with aligned channels for solar-driven interfacial evaporation co-generation. In the ionic liquid, strong H-bonding is formed between the pyranoid rings of cellulose combined with the slow freezing technique, resulting in the microcrystalline cellulose being reoriented, which allowed TPPA-5 to form abundant aligned channels after solvent replacement and freeze-drying. These aligned channels enable the brine to form a localized circulating flow, which is conducive to the improvement of the TPPA's evaporation rate and salt resistance. The salinity gradient is naturally formed in the channel of TPPA, which enables TPPA-5 to show excellent power generation performance. The evaporation rate of TPPA-5 can reach 3.39 kg m-2 h-1 under 1 kW m-2. With methanol as a highly polar proton solvent, the maximum output voltage obtained was 67.534 mV due to the overlapping electric double-layer effect formed by hydrogen protons on the TPPA surface, and the energy utilization efficiency is 95.95%. Moreover, TPPA-5 can purify pesticide-containing wastewater, which has the advantages of being recyclable and environmentally friendly, showing potential application value in the field of seawater desalination and steam co-generation.

Enhancing Freshwater Production via Customizable and Highly Efficient Solar-Driven Seawater Desalination

Solar-powered water generation is an appealing strategy for cost-effective and energy-sustainable seawater purification/desalination, where rational material selection and device design is crucial. Nevertheless, prevailing carbon-based photothermal materials in such systems still suffer from mediocre steam-to-water efficiency, failing to satisfy an adequate freshwater supply. Herein, we demonstrate a biomimetic corrugated evaporator (CE) affording carbon nanotube (CNT) encapsulated Fe nanocluster-decoration in the pursuit of high-efficiency seawater purification. The thus-customized CE demonstrates a maximum evaporation rate of 4.2 kg m-2 h-1 with a refraction angle of 60° and a water-lifting height of 5.5 cm, outperforming most state-of-the-art carbon-based counterparts. By employing a tailored architectural design and optimized condensing volume, the steam-to-water efficiency increases from 65.8 to 88.2% as the volume enlarges from 0.8 to 5.3 L, further harvesting a peak value of 91% under negative pressure. Light intensity simulation and experimental mechanistic investigation disclose the dual property-performance relationships between evaporator microstructure and evaporation rate, as well as between condensing device volume and steam-to-water efficiency. The universality of the theoretical guidance of this work will offer insight into the development of solar-driven evaporator construction toward simultaneous seawater desalination and clean water generation.

Boosting Water Evaporation by Construction of Photothermal Materials with a Biomimetic Black Soil Aggregate Structure

Solar-driven interfacial evaporation is considered an efficient way to get fresh water from seawater. However, the low evaporation rate, surface salt crystallization, and low energy collection of the photothermal evaporation layer limit its further application in an outdoor freshwater field. And the aggregate structure design of the material itself is often ignored in solar-driven water evaporation. Black soil (BS), with a unique soil aggregate structure, is rich in tubular pores, which can be used for multilevel sunlight utilization and good capillary water transport. Based on the extraordinary photothermal properties and pumping capacity of BS, a reasonable unidirectional salt-collecting device is designed, which can realize long-term collection of mineral salts and continuous evaporation of seawater and generate electric energy in the continuous evaporation. Inspired by the unique aggregate structure, the photothermal material doping of halloysite and nigrosin will simulate the generation of this aggregate structure and retain a good water transport effect while obtaining multistage utilization of sunlight. The solar-driven evaporation rate of a nigrosin-halloysite solar steam generator is 1.75 kg m-2 h-1 under 1 kW m-2 mimic solar radiation; it can achieve stable salt leaching-induced voltage generation of 240 mV. This work demonstrates not only a solar evaporator that can continuously achieve desalination but also the design strategy of BS-like aggregate photothermal materials, which promotes the development of low-cost resource recovery and energy generation for practical outdoor seawater desalination.

Microfluidic Salinity Gradient-Induced All-Day Electricity Production in Solar Steam Generation

Synergistic generation of freshwater and electricity using solar light would be an ideal solution for global freshwater challenges and energy demands. Recently, interface solar steam generation has been considered one of the promising cost-effective alternatives for freshwater generation. Here, we have systematically maintained the salinity gradient within two-legged paper-based microfluidic channels to transport wastewater from the reservoir to the evaporator surface and generate electricity all-day-long. Flowing seawater (3.5 wt % NaCl) on one leg and tap water on the other of the water-conducting channels connected to a conical evaporator, we achieved an average open-circuit voltage (V_OC) of 150 mV and a short-circuit current of 6.5 μA across each channel along with a water evaporation efficiency of 88%. As the V_OC depends only on the ion concentration gradient within the channel in the direction perpendicular to the water flow, the electricity generation persists throughout the day and can be tuned by varying the salinity. Increasing the salt concentration of the seawater to 20 wt %, the V_OC increased to 250 mV in a single channel. In an evaporator connected with four such channels, we achieved a maximum output power density of 9.9 mW m^-2 in a series combination without sacrificing the evaporation rate. Furthermore, removing agglomerated salt from the evaporator surface, we harvested salt at a rate of 0.33 kg m^-2 h^-1. Therefore, our approach provides an alternative way of freshwater generation, salt harvesting, and all-day-long electricity production simultaneously.

Bifunctional polypyrrole-based conductive paper towards simultaneous efficient solar-driven water evaporation and electrochemical energy storage

The thriving solar-driven water evaporation (SDWE) technology is considered the ideal candidate for next-generation water treatment because of its high efficiency, environment-friendliness, and low cost. The irresistible trend of diversified energy demand presents multi-functional requirements for a successful SWDE. However, the current SDWE technology rarely breaks through this technical dilemma. Here, we have designed a bifunctional polypyrrole-based capacitor to achieve water purification and energy storage. The hydrophilicity of the filter paper and the high light absorptance of polypyrrole (96.18%) promote the generation of solar steam. The evaporation rate of the PPy-200 (Polypyrrole-200) filter paper reached 1.54 kg m^-2 h^-1 under 1 kW m^-2. Interestingly, the symmetric supercapacitor assembled with PPy-based filter paper electrodes could simultaneously realize efficient evaporation (1.94 kg m^-2 h^-1) and electrochemical energy storage. As a single electrode, the PPy-200 filter paper exhibited ultra-high specific capacitance (4129.50 mF cm^-2) and favorable cycling stability (71.16% after 4000 cycles). More importantly, the capacitance of PP-PPy-200 (Polyvinyl alcohol/Polyethylene glycol-Polypyrrole-200) increased to 2.55 times under one sun illumination. This work not only points out a direction for solar thermal utilization, but also provides new design inspiration for high-efficiency flexible electrochemical energy storage devices.