Highly Flexible and Efficient Solar Steam Generation Device.

Solar steam generation as a promising solar energy conversion technology has attracted considerable interest in achieving seawater desalination and water purification. Although wood with fast water transportation and excellent heat localization has drawn particular interest in regard to its application for solar steam generation, challenges still remain in terms of its complicated processing techniques and relatively low efficiency. Here, we propose a facile, cost-efficient, and scalable brushing method to prepare an aluminophosphate-treated wood (Wood@AlP) solar steam generation device. The aluminophosphate compound deposited on the wood surface can not only be considered as the Lewis acid catalyst capable of accelerating the formation of the carbon layer but also provide an aluminophosphate layer with a hierarchical porous structure, which is beneficial for broad solar absorption and vapor escape. On the other hand, benefiting from the natural hydrophilicity, low thermal conductivity, and excellent water transportation of wood, the obtained Wood@AlP device can float on seawater and exhibit a high solar thermal efficiency of 90.8% with a net evaporation rate of 1.423 kg m-2 h-1 under 1 sun illumination.

Thin film technology for solar steam generation: A new dawn

Solar steam generation is one of the most promising solar-energy-harvesting technologies to address the issue of water shortage. Despite intensive efforts to develop high-efficiency solar steam generation devices, challenges remain in terms of the relatively low solar thermal efficiency, complicated fabrications, high cost, and difficulty in scaling up. Herein, a double-network hydrogel with a porous structure (p-PEGDA-PANi) is demonstrated for the first time as a flexible, recyclable, and efficient photothermal platform for low-cost and scalable solar steam generation. As a novel photothermal platform, the p-PEGDA-PANi involves all necessary properties of efficient broadband solar absorption, exceptional hydrophilicity, low heat conductivity, and porous structure for high-efficiency solar steam generation. As a result, the hydrogel-based solar steam generator exhibits a maximum solar thermal efficiency of 91.5% with an evaporation rate of 1.40 kg m-2 h-1 under 1 sun illumination, which is comparable to state-of-the-art solar steam generation devices. Furthermore, the good durability and environmental stability of the p-PEGDA-PANi hydrogel enables a convenient recycling and reusing process toward real-life applications. The present research not only provides a novel photothermal platform for solar energy harvest but also opens a new avenue for the application of the hydrogel materials in solar steam generation.

The global fresh water shortage has driven enormous endeavors in seawater desalination and wastewater purification; among these, solar steam generation is effective in extracting fresh water by efficient utilization of naturally abundant solar energy. For solar steam generation, the primary focus is to design new materials that are biodegradable, sustainable, of low cost, and have high solar steam generation efficiency. Here, we designed a bilayer aerogel structure employing naturally abundant cellulose nanofibrils (CNFs) as basic building blocks to achieve sustainability and biodegradability as well as employing a carbon nanotube (CNT) layer for efficient solar utilization with over 97.5% of light absorbance from 300 to 1200 nm wavelength. The ultralow density (0.0096 g/cm3) of the aerogel ensures that minimal material is required, reducing the production cost while at the same time satisfying the water transport and thermal-insulation requirements due to its highly porous structure (99.4% porosity). Owing to its rationally designed structure and thermal-regulation performance, the bilayer CNF-CNT aerogel exhibits a high solar-energy conversion efficiency of 76.3% and 1.11 kg m-2 h-1 at 1 kW m-2 (1 Sun) solar irradiation, comparable or even higher than most of the reported solar steam generation devices. Therefore, the all-nanofiber aerogel presents a new route for designing biodegradable, sustainable, and scalable solar steam generation devices with superb performance.

Wood-based solar steam generation holds great promise in alleviating fresh water crises due to its advantages: light absorbability, thermal management, water transpiration, and water evaporation. Although tremendous efforts have been made to improve wood-based solar steam generation devices, they mainly have focused on the optimization of photothermal materials to optimize light absorbability and thermal management to enhance efficiency of steam generation. This research demonstrates that delignified wood (DL-wood) can further improve the efficiency of steam generation via increasing both the water transportation and water evaporation. The results show that after placing carbon nanotubes (CNTs) on DL-wood, the efficiency of steam production is higher than that of natural wood coated with CNTs by 20% under ambient sunlight conditions. DL-wood with CNTs has the following advantages: (1) it is stable, available, and easy to extend; (2) it does not pollute the environment and will not cause discoloration or dregs when used; and (3) it is a promising efficiency-enhancing solution for renewable and portable solar power generation.

Synergistic Tandem Solar Electricity-Water Generators

Carbon nanofibers enhanced solar steam generation device based on loofah biomass for water purification

Solar steam generation (SSG) is a promising technique that may find applications in seawater desalination, sewage treatment, etc. The core component for SSG devices is photothermal materials, among which biomass-derived carbon materials have been extensively attempted due to their low cost, wide availability, and diversified microstructures. However, the practical performance of these materials is not satisfactory because of the multifaceted structural requirements for photothermal materials in SSG scenarios. In this work, cactus stems, which possess abundant and multiscaled pores for simultaneous sunlight gathering and water evaporation, are applied as the photothermal structure for SSG devices after mild heat treatment. Consequently, the SSG device based on the carbonized cactus stems delivers high performance (an absorption rate of 93.7% of the solar spectrum, an evaporation rate of 2.02 kg m-2 h-1, and an efficiency of 91.4% under one solar irradiation). We anticipate that the material can be a potential candidate for efficient SSG devices and may shed light on the sustainable supply of water.

Interfacial solar-driven steam generation is one of the most promising techniques used to produce clean water. However, achieving rapid water evaporation using solar steam generation devices is challenging because of their two-dimensional (2D) planar structures and confined evaporation areas. The three-dimensional (3D) structural design of evaporation devices improves water evaporation rates, thereby enhancing solar-driven steam generation. This study developed a 3D wood-based evaporator through 3D structure shaping and the flexible treatment of wood that involved coating photothermal materials with tannic acid. Because of the ampliative evaporation area and outstanding absorption, the water evaporation rate of the prepared 3D wood-based evaporator was as high as 2.5 kg m−2 h−1, and the efficiency of energy transformation was up to 101 % under simulated 1-sun irradiation; the evaporation rate and efficiency of energy transformation were considerably higher than those of 2D planar wood evaporators. Furthermore, the effective seawater desalination performance and good durability of the 3D wood-based evaporator were demonstrated. This study provides different insights into the fabrication of high-efficiency wood-based solar steam generators with high prospects for application in seawater desalination.

Solar steam generation is regarded as one of the most sustainable techniques for desalination and wastewater treatment. However, there has been a lack of scalable material systems with high efficiency under 1 Sun. A solar steam generation device is designed utilizing crossplane water transport in wood via nanoscale channels and the preferred thermal transport direction is decoupled to reduce the conductive heat loss. A high steam generation efficiency of 80% under 1 Sun and 89% under 10 Suns is achieved. Surprisingly, the crossplanes perpendicular to the mesoporous wood can provide rapid water transport via the pits and spirals. The cellulose nanofibers are circularly oriented around the pits and highly aligned along spirals to draw water across lumens. Meanwhile, the anisotropic thermal conduction of mesoporous wood is utilized, which can provide better insulation than widely used super‐thermal insulator Styrofoam (≈0.03 W m−1 K−1). The crossplane direction of wood exhibits a thermal conductivity of 0.11 W m−1 K−1. The anisotropic thermal conduction redirects the absorbed heat along the in‐plane direction while impeding the conductive heat loss to the water. The solar steam generation device is promising for cost‐effective and large‐scale application under ambient solar irradiance.

Three-dimensional multimodal porous graphene-carbonized wood for highly efficient solar steam generation

Although solar‐driven water evaporation technology is promising for desalination of seawater and purification of wastewater, it is still an issue to enhance the solar steam generation performances by efficient utilization of sustainable solar energy. Herein, 2D ferrous ion‐crosslinked Ti3C2Tx MXene‐based aerogel films (MAFs) are fabricated as efficient solar steam generation devices by vacuum‐assisted filtration of aqueous dispersions of MXene with FeCl2 followed by freeze‐drying. The strong interaction of ferrous ions with –OH groups of MXene sheets and the freeze‐drying process are crucial for constructing structurally stable porous films with rough surfaces. Benefiting from the strong solar light absorption capacity and high solar‐thermal energy conversion efficiency of MXene sheets, along with the hydrophilic and structurally stable porous architecture of MAFs, the average evaporation rates of an optimal MAF evaporator are as high as 1.67 and 14.52 kg m−2 h−1 with evaporation efficiencies of 94.3% and 91.7% under solar light irradiations of 1 and 10 kW m‐2, respectively. As a promising solar steam generation device, the 2D porous and hydrophilic MAF evaporator is highly efficient in generating clean water from both natural seawater and organic wastewater with satisfactory ion rejection efficiencies of close to 100%.

Copper sulfide-macroporous polyacrylamide hydrogel for solar steam generation

Solar steam generation (SSG) has garnered significant attention for its potential in water purification applications. While composites with physically combined structures based on semiconductors or biomass have been developed for SSG, there remains a critical need for low-cost, high-efficiency devices. In this study, TiO2 composites exhibiting excellent stability, high solar absorption, porous microstructure, and hydrophilic surfaces were identified as effective materials for SSG and water purification for the first time. A novel SSG device was designed by decorating TiO2 onto three-dimensional carbonized Osmanthus fragrans leaves (TiO2/carbonized OFL). Compared to directly carbonized OFL (without TiO2) and Osmanthus fragrans leaves with templated TiO2 (OFL-templated TiO2), the TiO2/carbonized OFL carbon composites demonstrated enhanced solar absorption, achieving over 99% in the visible region and more than 80% in the near-infrared region. Under solar illumination of 1 kW·m-2, the TiO2/carbonized OFL device achieved a high water evaporation rate of 2.31 kg·m-2·h-1, which is 1.6 times higher than that of carbonized OFL and 3.45 times higher than OFL-templated TiO2. Additionally, the TiO2/carbonized OFL system exhibited remarkable efficiency in treating pharmaceutical wastewater, with a chemical oxygen demand (COD) removal efficiency of 98.9% and an ammonia nitrogen removal efficiency of 90.8% under solar radiation.

Omnidirectionally irradiated three-dimensional molybdenum disulfide decorated hydrothermal pinecone evaporator for solar-thermal evaporation and photocatalytic degradation of wastewaters