Efficient Solar Water Research Articles

Two-Dimensional Sb Modified TiO2 Nanorod Arrays as Photoanodes for Efficient Solar Water Splitting.

As one of the widely studied semiconductor materials, titanium dioxide (TiO2) exhibits high photoelectrochemical (PEC) water-splitting performance as well as high chemical and photo stability. However, limited by a wide band gap and fast electron-hole recombination rate, the low solar-to-hydrogen conversion efficiency remains a bottleneck for the practical application of TiO2-based photoelectrodes. To improve the charge separation and water oxidation efficiency of TiO2 photoanodes, antimonene, a two-dimensional (2D) material obtained by liquid-phase exfoliation, was assembled onto TiO2 nanorod arrays (TNRAs) by a simple drop-coating assembly process. PEC measurements showed that the resulting 2D Sb/TiO2 photoelectrode displayed an enhanced photocurrent density of about 1.32 mA cm-2 in 1.0 M KOH at 0.3 V vs. Hg/HgO, which is ~1.65 times higher than that of the pristine TNRAs. Through UV-Vis absorption and electrochemical impedance spectroscopy measurements, it was possible to ascribe the enhanced PEC performances of the 2D Sb/TiO2 photoanode to increased absorption intensity in the visible light region, and improved interfacial charge-transfer kinetics in the 2D Sb/TiO2 heterojunction, which promotes electron-hole separation, transfer, and collection.

Boosting charge separation and transfer at the boron-triggered BiVO4 interface for efficient and stable solar water splitting

Photoelectrochemical (PEC) water splitting is a promising strategy for solar energy conversion and storage. However, poor charge transfer and sluggish water oxidation reaction restrain the PEC performance. Herein, we propose a simple and effective interface etching strategy on the semiconductor surface to modulate the photoanode/cocatalyst interface, following by the decoration of NiFeBi oxygen evolution catalyst (OEC) for significantly improved oxygen evolution activity and stability of the BiVO4 photoanode. The resultant photoanode achieves a record photocurrent density of 6.33 mA cm−2 at 1.23 VRHE under one sun illumination, over approximately 3.63 times higher than that of the pristine BiVO4. The applied bias photon-to-current efficiency of 2.3% can be attained with showing a good durability of 40 h. Systematic studies have demonstrated that the introduction of electron-deficient state of B accelerates the surface trapping hole and the charge transfer, which enhances the interfacial coupling between BiVO4 and NiFeBi OEC, and strongly drives the hole from the BiVO4 to the NiFeBi surface for capable water oxidation. Density functional theory calculations prove that the surface B treatment increases the effective number of reaction paths of OER and the density of electronic states near the Fermi energy level, which improves the electrical conductivity of the BiVO4/OEC interface. This work provides a feasible strategy for tailoring the interface engineering to significantly enhance the PEC activity and stability of the photoanodes.

BC/GO-Ag composite aerogel with synergistic enhanced photothermal performance for efficient solar water evaporation

Solar water evaporation has great potential to alleviate the global freshwater crisis. Among them, photothermal materials have been widely studied as the core part of the solar water evaporation. However, its development is limited due to the complex preparation method and low evaporation efficiency. Herein, the composite aerogels based on graphene oxide (GO) and silver nanoparticles (Ag NPs) were developed by low-temperature-crosslinking method and in-situ reduction method and applied to solar interfacial evaporation. Due to the synergistic effect between the broadband light absorption of GO and the localized surface plasmon resonance effect of Ag NPs, the BC/GO-Ag composite aerogel has an optical absorption rate of 84.1%, an evaporation rate of 2.36 kg m-2h−1, and an evaporation efficiency of 94.5%, which is better than most of the previously reported photothermal materials. In addition, the material could be applied to various complex water environments. The BC/GO-Ag composite aerogel also showed good reusability. BC/GO-Ag composite aerogel is a promising material due to its simple and mild preparation method, environmental protection of raw materials, and high evaporation efficiency.

A Review on Experimental Validation of Heat Pipe Solar Collector for Water Heating

Now a day’s climate of growing energy needs and increasing environmental concern, alternatives to the use of non -renewable and polluting fossil fuels have to be investigated. One such alternative is solar energy; solar water heating is the prime application of solar energy. The problem faced by the existing solar water heating system is periodic inspections, maintenance, time to time component may need repair or replacement and also sufficient quantity of hot water is not available during cloudy/rainy days. Hence to overcome these problem , the use of heat pipe concept which utilizes the low boiling temperature fluid to increase the heating efficiency, the objective of present work is to increase the heating efficiency solar water heater using low boiling temperature fluid. Key Words: Solar water heater, concept of heat pipe, low boiling temperature fluid (working fluid), thermosiphon.

In-situ cation-exchange strategy for engineering single-atomic Co on TiO2 photoanode toward efficient and durable solar water splitting

Single-atomic catalysts (SACs) have been emerging as one of potential candidates in catalysts, owing to their unique merits with extremely high specific surface area as well as remarkably exposed active sites. Herein, we develop an in-situ gas-phase cation exchange strategy for engineering single-atomic Co on the surface of TiO2 photoanode toward solar water splitting. It is verified that the atomically-dispersed Co with Co-O coordination could optimize the surface electronic structures, enhance the light absorption, promote the photoinduced charge transfer, lower the reaction barrier and accelerate the reaction kinetics, which consequently enable the overall improved photoelectrochemical (PEC) behaviors for photoanodes. As a proof of concept, the as-constructed TiO2-based photoanodes deliver robust stability up to 100 h and a photocurrent density up to 1.47 mA cm−2 at 1.23 V vs. RHE, which are superior to those of pristine TiO2, representing their significance for potential applications.

Assembly of a novel Fe2TiO5-impregnated donor-π-acceptor conjugated carbon nitride for highly efficient solar water splitting

Carbon nitride (CN) exhibits low photocatalytic performance for the energy conversion during photocatalytic water splitting (PWS) under visible light spectrum. Designing novel high-performance CN-based photocatalysts via providing advanced intrinsic characteristics to pristine CN material may further endorse the PWS process. Integrating organic molecules within the skeleton of CN is an interesting strategy to lessen the extent of charge recombination by promoting effective charge separation and transportation, thereby boosting light absorption and photocatalytic performances. Yet, limited progresses have been made along this line. We have carefully chosen and fused previously unexplored organic donor-π-acceptor-type 2,6-diaminopurine (DP) molecules within the skeleton of CN via a superficial organic molecular engineering. Moreover, the subsequent introduction of Fe2TiO5 with copolymerized CN-DP10.0 and pristine CN provide considerably more surface-active sites to form heterojunction material, synergistically extending both the optical absorption range and the lifetime of photoinduced electron. More importantly, with a typical type-II heterojunction formation, the CN and Fe2TiO5 energy levels are overlapped and compatible, thereby significantly accelerating both electron and hole transfer processes. These beneficial characteristics in turn lead to an outstanding apparent quantum yield (AQY) of 61.7% at a wavelength of 420 nm, together with highly efficient and greatly improved photocatalytic hydrogen (H2) (165.7 μmol/h) along with oxygen (O2) (6.2 μmol/h) evolution reactions in visible spectrum at 420 nm. These values are 15.7 and 11.4 times more than those of the pristine CN (9.9 μmol/h and 0.5 μmol/h). Consistent with these experimental findings, our computational simulations show that integration of Fe2TiO5 and DP molecules within the CN framework decreases the band gap from 3.25 to 2.55 eV, suggesting remarkable photocatalytic activities of Fe2TiO5/CN-DP10.0. As a result, it is anticipated that this work will offer a significant avenue for scientific investigation into the next generation of renewable energy employing improved heterostructure photocatalyst predicated on organic ligands.

Defect-rich spinel ferrites with improved charge collection properties for efficient solar water splitting

Spinel zinc ferrite (ZnFe₂O₄, ZFO) is a potential photoanode material for photoelectrochemical (PEC) water splitting because of its ideal bandgap (1.9–2.1 eV) and superior chemical stability in aqueous solutions. However, the low charge collection efficiency significantly hinders the improvement in PEC activity. Herein, we report an ultrafast and effective flame activation route to enhance the charge collection properties of ZFO. First, high-temperature flame (&gt; 1300 ℃) facilitated surface and grain boundary diffusions, increasing the grain size and connectivity of the ZFO nanoparticles. Second, the reducing atmosphere of the flame enabled the formation of surface defects (oxygen vacancy and Fe²⁺), thereby increasing the charge carrier density and surface adsorption sites. Significantly, these two factors promoted charge transport and transfer kinetics, resulting in a 10-fold increase in the photocurrent density over the unactivated ZFO. Furthermore, we deposited a thin Al₂O₃ overlayer to passivate the ZFO surface and then the NiFeO_<i>x</i> oxygen evolution catalyst (OEC) to expedite hole injection into the electrolyte. This surface passivation and OEC deposition led to a remarkable photocurrent density of ~1 mA/cm² at 1.23 V versus the reversible hydrogen electrode, which is the highest value among all reported ZFO photoanodes. Notably, the NiFeO_<i>x</i>/Al₂O₃/F-ZFO photoanode achieved excellent photocurrent stability over 55 h (96% retention) and superior faradaic efficiency (FE &gt; 94%). Our flame activation method is also effective in improving the photocurrent densities of other spinel ferrites: CuFe₂O₄ (93 times), MgFe₂O₄ (16 times), and NiFe₂O₄ (12 times).

Modulating Photothermal Properties of Carbon Dots through Nitrogen Incorporation Enables Efficient Solar Water Evaporation

As a new family in carbon nanomaterials, carbon dots (CDs) are potential candidates for solar water evaporator, owing to their cost-effectiveness, non-toxicity, high solubility, and tunable optical properties. Despite such potentials, however, CDs mainly absorb solar spectrum in the ultraviolet region while their absorption in the visible region is limited, the characteristics that hinder their functionality in generating steam from solar energy. Herein, the optical and photothermal properties of CDs, derived from urea and citric acid, can be modulated by controlling their surface stoichiometry through varying the molar ratio of the precursors. Our approach is simple, fast, and highly scalable by utilizing a microwave irradiation technique. We found that increasing the nitrogen content results in broadening of the absorption spectra into the visible region due to more functional groups introduced on the CD surface that reduce the band gap, as confirmed both by X-ray photoelectron spectroscopy and theoretical calculation. Employing the CDs as photothermal materials in the volumetric solar evaporator, we demonstrate a remarkable evaporation efficiency of up to 70% along with a volumetric evaporation rate of 1.11 kg m–2 h–1 under 1 sun illumination, superior to direct bulk water heating. Furthermore, the CDs show excellent durability and stability, as demonstrated by their stable evaporation rate for 10 days, with no significant decrease in the optical and photothermal properties. This finding provides a pathway to design and functionalize CDs with controllable optical and photothermal properties for an efficient solar evaporation system.

Pd/PdO and hydrous RuO2 difunction-modified SiO2@TaON@Ta3N5 nano-photocatalyst for efficient solar overall water splitting

A novel Pd/PdO and hydrous RuO2 difunction-modified SiO2@TaON@Ta3N5 core-shell structured nano-photocatalyst was synthesized successfully, which displayed excellent photocatalytic activity for overall water splitting into H2 (473.52 μmol−1·g−1·h−1), about 2.86 times higher than unmodified SiO2@TaON@Ta3N5 (165.74 μmol−1·g−1·h−1), under the visible-light irradiation with the wavelength ≥420 nm, without any sacrificial agent, as well as excellent stability against photocorrosion. The apparent quantum yield (AQY) reaches to 0.253% under irradiation intensity of 12 mW cm−2 at 420 nm. The spatially separated Pd, PdO and RuO2 clusters were decorated on the Ta3N5 surface to construct local multi-heterojunctions, which were confirmed to enhance the light absorption capability, drive efficient separation of charge carriers and directional transfer, and promote surface redox reaction kinetics of HER and OER. The trace modification of metallic Pd clusters and TaN could mainly contribute to the significant decrease in the HER overpotential, while PdO exhibited a stronger contribution than RuO2 for OER catalytic activity. The synergetic mechanism of enhanced photocatalytic overall water splitting for hydrogen production was discussed in detail. Thus the combination of core-shell heterojunction construction and surface difunction modification provides a promising strategy for develop efficient all-in-one photocatalysts for solar overall water splitting.

MoS2 Nanosheets Decorated with Fe3O4 Nanoparticles for Highly Efficient Solar Steam Generation and Water Treatment.

The shortage of water resources has always been one of the most difficult problems that perplexes humanity. Solar steam generation (SSG) has been a new non-polluting and low-cost water purification method in recent years. However, the high cost of traditional photothermal conversion materials and the low efficiency of photothermal conversion has restricted the large-scale application of SSG technology. In this work, composite materials with Fe3O4 nanospheres attached to MoS2 nanosheets were synthesized, which increased the absorbance and specific surface area of the composite materials, reduced the sunlight reflection, and increased the photothermal conversion efficiency. During the experiment, the composite material was evenly coated on cotton. The strong water absorption of cotton ensured that the water could be transported sufficiently to the surface for evaporation. Under one sun irradiation intensity, the evaporation rate of the sample synthesized in this work reached 1.42 kg m-2 h-1; the evaporation efficiency is 89.18%. In addition, the surface temperature of the sample can reach 41.6 °C, which has far exceeded most photothermal conversion materials. Furthermore, the use of this composite material as an SSG device for seawater desalination and sewage purification can remove more than 98% of salt ions in seawater, and the removal rate of heavy metal ions in sewage is close to 100%, with a good seawater desalination capacity and sewage purification capacity. This work provides a new idea for the application of composite materials in the field of seawater desalination and sewage purification.

Hierarchically designed evaporators with dual-layered hydrogel/aerogel structure for efficient solar water evaporation

Solar water evaporation technology is now emerging rapidly as it realizes low-cost desalination by utilizing sunlight as energy source. However, many researches focused only on the performance of specific systems, while ignoring the universality and compatibility of their evaporator designs. Herein, molecular dynamic simulations were performed to select and predict the performance of photo-thermal conversion (PTC) materials before carrying out experiments. As MoS2 and TiN were predicted to have promising evaporation performance, hierarchical evaporators composed of upper hydrogel layers and ice-templated aerogel substrates were fabricated. By reducing water evaporation enthalpy, the highest evaporation rate of 1.61 kg m-2 h-1 was achieved in CSSA-TiN under 1.0 sun illumination. Owing to the hierarchical design and ice-templated substrate, local dual-layered hydrogel/aerogel structures and vertically aligned channels were constructed in the evaporators, which guarantees the structural integrity and the backflow of salts during evaporation. Our work provides comprehensive insights into the selection of PTC materials, the prediction of their performance, and the construction of evaporators.

Construction of Ti3C2 MXene based fire resistance nanocoating on flexible polyurethane foam for highly efficient photothermal conversion and solar water desalination.

In this work, a bilayer nanocoating was constructed on the surface of flexible polyurethane (FPU) foam with Ti3C2 MXene and polyethyleneimine-modified silica nanoparticles (mSiO2-NP@PEI) through layer-by-layer self-assembly technology, successfully obtaining modified flexible polyurethane composites (MFPU) with excellent flame retardancy, photothermal conversion and solar water desalination properties. The structure and morphology of MFPU foams were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Transmission electron microscope (TEM) and Scanning electron microscope (SEM). The MFPU with three coating cycles (MFPU3) had the best flame retardancy and smoke suppression performances, mainly in terms of decreased peak heat release rate (pHRR), peak smoke production rate (pSPR) and total smoke production (TSP) by 71.3%, 62.1% and 74.5%, respectively, compared to those of neat FPU. In addition, MFPU foams exhibited extraordinary light-to-heat conversion and solar water desalination capabilities. MFPU3 could reach 120°C in 138s and its steam conversion efficiency η was as high as 89.6%, which was 116.0% higher than that of unmodified foam and had a 262.8% increase over pure water. The flame retardant MFPU foams with excellent photothermal conversion efficiency will exhibit great application potential in solar water desalination and power generation.

Janus β-Te2X (X = S, Se) monolayers for efficient excitonic solar cells and photocatalytic water splitting

In this work, we have investigated the novel 2D allotropes i.e., β-Te2X (X = S, Se) using first-principles calculations and study their potential applications in light harvesting devices.

Charge transfer enhancement at the CZTS photocathode interface using ITO for efficient solar water reduction

The study employs an ITO layer to enhance CZTS photocathodes for water splitting, resulting in improved photocurrent, onset potential, and stability through phosphate ion removal and In–Pt/Sn–Pt interactions on the ITO surface.

Improved Photo-Excited Carriers Transportation of WS2 -O-Doped-Graphene Heterostructures for Solar Steam Generation.

Two-dimensional (2D) transition metal dichalcogenides and graphene have revealed promising applications in optoelectronic and energy storage and conversion. However, there are rare reports of modifying the light-to-heat transformation via preparing their heterostructures for solar steam generation. In this work, commercial WS2 and sucrose are utilized as precursors to produce 2D WS2 -O-doped-graphene heterostructures (WS2 -O-graphene) for solar water evaporation. The WS2 -O-graphene evaporators demonstrate excellent average water evaporation rate (2.11kgm-2 h-1 ) and energy efficiency (82.2%), which are 1.3- and 1.2-fold higher than WS2 and O-doped graphene-based evaporators, respectively. Furthermore, for the real seawater with different pH values (pH 1 and 12) and rhodamine B pollutants, the WS2 -O-graphene evaporators show great average evaporation rates (≈2.08 and 2.09kgm-2 h-1 , respectively) for producing freshwater with an extremely low-grade of dye residual and nearly neutral pH values. More interestingly, due to the self-storage water ability of WS2 -O-graphene evaporators, water evaporation can be implemented without the presence of bulk water. As a result, the evaporation rate reaches 3.23kgm-2 h-1 , which is ≈1.5 times higher than the regular solar water evaporation system. This work provides a new approach for preparing 2D transition metal dichalcogenides and graphene heterostructures for efficient solar water evaporation.

Dibenzo[b,f][1,5]Diazocines/ZnO Organic/Inorganic Hybrid Photoanodes for Efficient Photo Electrochemical Water Splitting

In this study, we propose dibenzo[b,f][1,5]diazocine/ZnO organic/inorganic hybrid photoanode for application in the photoelectrochemical water splitting. The electrode consisting of inorganic ZnO nanorod (ZnO NR) array structures and organic diazocine derivative film with or without platinum nanoparticle (Pt NP) cocatalyst was examined. The morphology characterization was performed by FESEM. UV-vis absorbance spectra showed enhanced absorbance in the visible light spectrum for the hybrid sample. Photoluminescence analysis of a hybrid sample showed a significant decrease in charge recombination and enhanced charge separation. Photoelectrochemical measurements revealed an increase in current density for the organic/inorganic hybrid photoanode reaching 1.256 mA/cm2 at 1.23 V vs. RHE which is almost two times higher than bare ZnO NR arrays (0.716 mA/cm2 at 1.23 V vs. RHE). The addition of the Pt NP cocatalyst further enhanced the photocurrent density up to 1.636 mA/cm2. Therefore, proposed organic/inorganic hybrid photoelectrode is a promising candidate for the efficient solar water splitting.

Morphological, structural and optical properties of dye-doped graphene-supported TiO2 nanotubes for solar water splitting applications

Solar water splitting has attained much attention in recent years for renewable and clean production of hydrogen from water under irradiation by sunlight. Solar water splitting has been progressively at the forefront of chemical research and also provides a promising path for sustainable hydrogen production. TiO2 has a wide range of applications and is considered as one of the most propitious semiconductors due to its photo-stability, low price and chemical stability. TiO2 nanotubes have been prepared by using electrochemical anodization method followed by organic dye deposited onto the TiO2 nanotubes. rGO-supported TiO2 nanotubes and dye-doped graphene-supported TiO2 nanotubes show more efficient behavior for water splitting as compared to pure TiO2 nanotubes. The surface morphology, elemental composition, structure and size of the nanocrystalline TiO2 nanotubes and dye-doped graphene-supported TiO2 nanotubes were examined by using SEM, XRD, EDX and UV/Visible spectroscopy, respectively. Dye-doped graphene-supported TiO2 nanotubes have been utilized for efficient solar water splitting.

Facile fabrication of Ni5P4-NiMoOx nanorod arrays with synergistic thermal management for efficient interfacial solar steam generation and water purification

Interfacial steam generation by harnessing renewable solar energy has been recognized as a sustainable solution to global freshwater crisis. A promising evaporator with key components of high spectral absorption, efficient thermal management and adequate water transport is highly desired. In the present study, an integrated design for three-in-one functionality is achieved by simply loading Ni5P4-NiMoOx (P-NMO) on a macroporous nickel foam (NF) carrier. In situ embedding broadband Ni5P4 absorber into insulating NiMoOx enables efficient photothermal conversion and heat localization. Benefiting from proper thermal management and abundant water transmission, P-NMO/NF exhibits the excellent performance for interfacial steam generation with a high evaporation rate of 1.49 kg m−2h−1 and evaporation efficiency of 93.0 % under one sun irradiation. Furthermore, the obtained P-NMO/NF is proven to be applicable for high-efficiency freshwater production in seawater desalination and wastewater purification, showing great potential for practical solar evaporator under natural environmental conditions.

Multifunctional hydrophilic MXene/Gelatin composite aerogel with vertically aligned channels for efficient sustainable solar water evaporation and Oil/Water separation

Solar-driven water evaporation has emerged as a sustainable approach for water purification and desalination, helping to relieve the long-standing water scarcity issues. However, achieving strong mechanical structure and superior light absorption simultaneously in an evaporator for various realistic conditions in marine environment remains challenging. Here, we prepared a hydrophilic and oleophobic Ti3C2Tx MXene/gelatin (M&G) composite aerogel with vertically aligned channels which are propitious to water transport, light absorption and vapor release for clean water generation. Simultaneously, the composite aerogel has excellent dry compression resistance and wet resilience due to the addition of gelatin, which are benefit to resist shear forces caused by water surface fluctuations. Acting as solar evaporator, M&G composite aerogel demonstrates high evaporation rate (1.7 kg m-2h−1, 1 sun) and preferable wastewater purification abilities. Furthermore, the hydrophilic and oleophobic properties of the composite aerogel is critical to extract water from oil/water mixture to adapt to the application of diverse water environments. Therefore, the designed composite aerogels show great potential for water treatment in a variety of water sources.

Surface modification of CuInS2 photocathodes with ruthenium co-catalysts for efficient solar water splitting

In this work, the photoelectrochemical H2 production activity of CuInS2 photocathodes is investigated after sequential surface modification with a-MoSx, Pt, or Ru. Although Ru has much inferior electrocatalytic activity to Pt for hydrogen evolution reaction (HER), a Ru-modified CuInS2/a-MoSx photocathode shows higher photoelectrochemical (PEC) activities than a Pt-modified one. X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and other (photo)electrochemical characterizations were carried out for the surface-modified CuInS2 photocathode to reveal the origin of the high PEC activity. The energy level of Ru on CuInS2/a-MoSx photocathodes is more suitable for the electron transfer between semiconductor–metal-electrolytes, and it leads to a fast electron transient time during PEC reaction by the improved carrier lifetime. This result implies that the Ru modification of photocathodes can be one of potential strategies for tuning band alignment and improving PEC activities.