Efficient Solar Evaporation by [Ni(Phen)3 ][V14 O34 Cl]Cl Hybrid Semiconductor Confined in Mesoporous Glass

Water Activation in Solar-Powered Vapor Generation

Solar-powered vapor evaporation (SVG), based on the liquid-gas phase conversion concept using solar energy, has been given close attention as a promising technology to address the global water shortage. At molecular level, water molecules escaping from liquid water should overcome the attraction of the molecules on the liquid surface layer to evaporate. For this reason, it is better to reduce the energy required for evaporation by breaking a smaller number of hydrogen bonds or forming weak hydrogen bonds to ensure efficient and convenient vapor production. Many novel evaporator materials and effective water activation strategies have been proposed to stimulate rapid steam production and surpass the theoretical thermal limit. However, an in-depth understanding of the phase/enthalpy change process of water evaporation is unclear. In this review, a summary of theoretical analyses of vaporization enthalpy, general calculations, and characterization methods is provided. Various water activation mechanisms are also outlined to reduce evaporation enthalpy in evaporators. Moreover, unsolved issues associated with water activation are critically discussed to provide a direction for future research. Meanwhile, significant pioneering developments made in SVG are highlighted, hoping to provide a relatively entire chain for more scholars who are just stepping into this field.

2D/2D Cs0.32 WO3 /CuS Nano-Heterojunctions for Simultaneous High-Efficiency Solar Desalination, Photocatalytic Decontamination, and Electricity Generation

Desalination and power generation through solar energy harvesting is a crucial technology that can effectively address freshwater shortages and energy crises. However, owing to the complexity of the actual water environment, the thermal output capability of the photothermal material and the functional integration of the evaporation system need urgent improvement, to obtain high-quality fresh water and sufficient electricity. Herein, a 2D/2D cesium tungsten bronze/copper sulfide (2D/2D Cs0.32 WO3 /CuS) nano-heterojunction is developed and it is loaded into a cellulose-based hybrid hydrogel to construct a multifunctional evaporator. Benefiting from the more nonradiative recombination centers from deep-level defects, as well as shorter carrier migration distances and higher redox potentials in the Cs0.32 WO3 /CuS nano-heterojunction, this evaporator has a significant improvement in thermal output capacity, enabling both super-efficient seawater evaporation (4.22 kg m-2 h-1 ) and photodegradation of organic pollutants (removal rate ≈ 99%). Moreover, the evaporator exhibits long-term stability and sustainable self-cleaning property against salt accumulation. Remarkably, the thermoelectric module based on the Cs0.32 WO3 /CuS nano-heterojunction shows promising electricity generation performance (4.85 W m-2 ), which can power small appliances durably and stably, exceeding previously reported similar devices. This 2D/2D heterojunction-based solar evaporation system will provide a more reliable solution for efficient and sustainable freshwater-electricity co-generation in resource-limited areas.

Soluble Hybrid Ionic Semiconductor and Its Photovoltaic Effect in Solution

Semiconductor materials were adopted in their solid states for photovoltaic applications owing to their nonsolubility and/or breaking of the photogenerated carrier transfer pathway in solution. The liquid-state photovoltaic device fills in a gap between currently prevailing full-solid-state and solid-liquid-state solar cells; however, reports on the photovoltaic effect from realistic semiconductor solution are absent so far. Herein, we report a hybrid inorganic-organic ionic semiconductor [Ni(Phen)3][V14O34Cl]Cl (Phen = 1,10-phenanthroline) and observe its photovoltaic effect in ionic liquid solution. This photovoltaic effect arises as a result of charge transfer between the coordination cation and inorganic polyoxovanadate in solution under illumination and subsequent transfer to electrodes. The liquid-state photovoltaic device (cell configuration: carbon cloth||[Ni(Phen)3][V14O34Cl]Cl in ionic liquid||Al foam) yields an open-circuit voltage of ca. 1.199 V and a photocurrent density of 3.268 mA cm-2 upon illumination using an air mass of 1.5 (100 mW cm-2) at 80 °C with a fill factor of 42.48% and an efficiency of 1.665%. This novel type of hybrid ionic semiconductor possesses great structural tunability for an optimized photovoltaic performance.

Waste Egg Tray and Toner-Derived Highly Efficient 3D Solar Evaporator for Freshwater Generation

With the advancement of civilization, water purification, as well as management and disposal of ever-increasing municipal solid waste (MSW), and e-waste, have become global concerns. To address these issues in a sustainable way, a 3D solar evaporator has been proposed in this paper by repurposing recycled paper from MSW in the form of egg trays and waste dry toner (e-waste) using a facile fabrication method. The unique 3D porous structure, fibrous surface, superior water absorbing capability as well as low thermal conductivity of wastepaper-derived egg trays make them an excellent candidate for an efficient solar evaporator, while the waste toner powder coating significantly enhances the optical absorbance capacity. Under 1 sun illumination, the proposed solar evaporator demonstrates an excellent evaporation rate and efficiency of 1.3 kg/m² h and 78.5%, respectively. Moreover, the competitive advantage of the 3D structure in collecting solar irradiance at various light incident angles in comparison to a 2D structure, excellent cycle stability, low processing temperature, and the use of low-cost waste materials enable its use for large-scale water purification systems.

Efficient Photo-Thermo-Electric Conversion Using Polyoxovanadate in Ionic Liquid for Low-Grade Heat Utilization

A large fraction of energy, including solar energy, is dissipated into ambient atmosphere as low-grade waste heat. Efficient utilization of such energy is critical to address the current energy crisis and global warming issue. Herein, the efficient near-IR (NIR)-photothermal, thermoelectric, and thus photo-thermo-electric conversion of polyoxovanadate compound {[Ni(1,10-phenanthroline)₃ ][V₁₄ O₃₄ Cl]Cl, NiV₁₄ } in ionic liquid was achieved. The solution displayed a NIR-photothermal efficiency of 16.04 and 23.43 % at 808 and 1064 nm, respectively. Taking advantage of the synergetic thermodiffusive and thermogalvanic effects of various ion species in NiV₁₄ solution, an open circuit voltage of approximately 0.45 V was obtained at ΔT=70 K generated by physical heating or NIR irradiation, indicating a large Seebeck coefficient of 6.38 mV K^-1 and an optimized thermal power at 1.2 W m^-2 . The polyoxovanadate-ionic liquid system offers a new platform for efficiently utilizing not only low-grade thermal energy but also solar energy for electricity generation.

Microvessel-Assisted Environmental Thermal Energy Extraction Enabling 24-Hour Continuous Interfacial Vapor Generation

Interfacial solar evaporators have great potential for clean water production; however, their evaporation performance relies greatly on the solar illumination condition, which is restricted by daily sunshine time and climates. Here, a wood-based vapor generator in pyramid structure is fabricated to achieve efficient water evaporation under dark condition (0 kW m^-2 ) through efficient extraction of environmental thermal energy. The microvessels of wood provide fast water transportation whereas the tailored pyramid surface structure enables efficient evaporative cooling for extracting energy from the environment. The method enables fast water evaporation without the need of solar heat input. We demonstrate a vapor generation rate of up to 2.15 kg m^-2  h^-1 under dark condition (0 kW m^-2 ), which is even 1.4 times faster than the theoretical limit of conventional solar thermal evaporators working under 1 sun (1 kW m^-2 ) illumination condition. During the 24-h continuous evaporation test, the evaporator presented a daily vapor generation rate of up to 50.8 kg m^-2  day^-1 and 60.7 kg m^-2  day^-1 on cloudy and sunny day, respectively, offering a novel approach for the development of 24-h full-time water evaporators for seawater desalination and wastewater treatment.