Materials For Solar Energy Conversion Research Articles

WS2–TiO2 hetero-photocatalysts for efficient hydrogen evolution via plasmon-induced resonance energy transfer

Lowering the cost and increasing the efficiency of photocatalysts for hydrogen (H2) evolution remain challenging, especially with eco-friendly materials. With these goals in mind, in this study we adopted tungsten disulfide (WS2) nanosheets, a nonmetallic surface plasmon resonance (SPR) material covering P25 TiO2, for plasmon-induced resonance energy transfer (PIRET) to improve the photocarrier response of H2 evolution. Under simulated solar light irradiation, the optimized 2.4W heterostructure provided a durable and outstanding H2 evolution rate (321 μmol g−1 h−1) that was approximately 55.3 times higher than that of TiO2. Raman spectra revealed the presence of dipole–dipole interactions within the WS2–TiO2 heterostructure, while UV–Vis optical absorption spectra indicated that the WS2 absorption range overlaid the band gap of TiO2. Under irradiation with light, the SPR of the WS2 nanosheets underwent near-field dipole-dipole coupling with the excitons of TiO2 to increase the number of excitons and inhibit charge recombination. This study suggests the possibility of using nonmetallic SPR materials for efficient solar energy conversion.

Engineering Graphdiyne for Solar Photocatalysis

AbstractGraphdiyne (GDY) with a direct band gap, excellent carrier mobility and uniform pores, is regarded as a promising photocatalytic material for solar energy conversion, while the research on GDY in photocatalysis is a less developed field. Herein, the distinctive structure, adjustable band gap, and electronic properties of GDY for photocatalysis is firstly summarized. The construction and progress of GDY‐based photocatalysts for solar energy conversion, including H2 evolution reaction (HER), CO2 reduction reaction (CO2RR) and N2 reduction reaction (NRR) are then elaborated. At last, the challenges and perspectives in developing GDY‐based photocatalysts for solar fuel production are discussed. It is anticipated that a timely Minireview will be helpful for rapid progress of GDY in solar energy conversion.

Engineering Graphdiyne for Solar Photocatalysis.

Graphdiyne (GDY) with a direct band gap, excellent carrier mobility and uniform pores, is regarded as a promising photocatalytic material for solar energy conversion, while the research on GDY in photocatalysis is a less developed field. Herein, the distinctive structure, adjustable band gap, and electronic properties of GDY for photocatalysis is firstly summarized. The construction and progress of GDY-based photocatalysts for solar energy conversion, including H2 evolution reaction (HER), CO2 reduction reaction (CO2 RR) and N2 reduction reaction (NRR) are then elaborated. At last, the challenges and perspectives in developing GDY-based photocatalysts for solar fuel production are discussed. It is anticipated that a timely Minireview will be helpful for rapid progress of GDY in solar energy conversion.

Near Field Scattering Optical Model-Based Catalyst Design for Artificial Photoredox Transformation

The sun offers a clean and renewable energy cornucopia, whereas how to utilize this inexhaustible yet decentralized energy with the assistance of appropriate media is an enduring topic. Plasmonic metal-based nanostructures (mainly Au and Ag) represent a class of fascinating materials for solar energy conversion due to their exclusive surface plasmon resonance (SPR)-enabled light-harvesting capability. In contrast to these plasmonic metals with characteristic SPR peaks, modulating the optical absorption peaks of nonplasmonic metals (e.g., small Pt nanoparticles) in the visible region but without size alteration is a grand challenge. Until recently, we demonstrated a near field scattering (NFS) optical model to manipulate the absorption peaks of Pt nanoparticles by adjusting their dielectric environment, sowing the seeds for tuning the optical absorption property of other metal nanoparticles and even semiconductor quantum dots. It is the purpose of the present Perspective to retrospect the history of NFS optical model and guide the function-oriented design of NFS-based nanostructures for artificial photoredox transformation.

Solution-Processed Cu2S Nanostructures for Solar Hydrogen Production.

Cu2S is a promising solar energy conversion material due to its suitable optical properties, high elemental earth abundance, and nontoxicity. In addition to the challenge of multiple stable secondary phases, the short minority carrier diffusion length poses an obstacle to its practical application. This work addresses the issue by synthesizing nanostructured Cu2S thin films, which enables increased charge carrier collection. A simple solution-processing method involving the preparation of CuCl and CuCl2 molecular inks in a thiol-amine solvent mixture followed by spin coating and low-temperature annealing was used to obtain phase-pure nanostructured (nanoplate and nanoparticle) Cu2S thin films. The photocathode based on the nanoplate Cu2S (FTO/Au/Cu2S/CdS/TiO2/RuO x ) reveals enhanced charge carrier collection and improved photoelectrochemical water-splitting performance compared to the photocathode based on the non-nanostructured Cu2S thin film reported previously. A photocurrent density of 3.0 mA cm-2 at -0.2 versus a reversible hydrogen electrode (V RHE) with only 100 nm thickness of a nanoplate Cu2S layer and an onset potential of 0.43 V RHE were obtained. This work provides a simple, cost-effective, and high-throughput method to prepare phase-pure nanostructured Cu2S thin films for scalable solar hydrogen production.

Designing Black Phosphorus and Heptazine-Based Crystalline Carbon Nitride Composites for Photocatalytic Water Splitting

Black phosphorus (BP) and heptazine-based crystalline carbon nitride (KPHI) composite photocatalysts were synthesized by molten salt and ultrasound-assisted liquid phase exfoliation methods. The structure, morphology and optical properties of the as-prepared BP/KPHI composites were evaluated by various characterization techniques. In addition, the photocatalytic performance of BP/KPHI composites for hydrogen production was investigated. The photocatalytic activity of BP/KPHI composite catalysts could be modulated by changing the loading mass ratio of BP. The BP/KPHI composite photocatalyst with a mass ratio of 10% exhibited the highest photocatalytic activity with the hydrogen production rate of 4.3 mmol g−1 h−1, about three times higher than that of pristine KPHI. Benefiting from the advantages of simplicity, rapidity, high yield and good controllability, this nanocomposite photocatalyst has the potential to serve as an excellent photocatalytic material for solar energy conversion.

Stable, Cost‐Effective TiN‐Based Plasmonic Nanocomposites with over 99% Solar Steam Generation Efficiency

AbstractPlasmonic nanoparticles (NPs), such as Au, Ag, and Cu, are considered as promising photothermal materials and attract extensive attention for freshwater production by solar steam generation. However, high cost, narrow absorption range and/or poor stability greatly limit their practical applications. Herein, a high‐efficiency solar energy conversion material consisting of low‐cost non‐metal, extremely thermally‐stable plasmonic TiN NPs and hydrophilic semi‐reduced graphene oxide (semi‐rGO), with broadband solar absorption capability, by a fast in situ microwave reduction method is prepared. The 2D semi‐rGO serves as a support for the loading of plasmonic NPs, and meanwhile accelerates the transport and evaporation of water due to its hydrophilicity. Then, decoration of plasmonic TiN NPs further enhances the solar photon absorption and hydrophilicity while suppressing the heat loss, thanks to the layered structure of TiN/semi‐rGO, improving overall solar energy utilization. Owing to the enhanced absorption and unique layered nanostructure with strong interfacial interaction, the optimal sample of TiN/semi‐rGO‐25% absorber achieves a high and stable water evaporation rate of ≈1.76 kg m−2 h−1 with an energy efficiency as high as 99.1% under 1 sun illumination. Furthermore, this plasmonic TiN/semi‐rGO absorber is capable of producing high‐quality freshwater from sustainable seawater desalination and wastewater purification processes.

Insights into conduction band flexibility induced by spin polarization in titanium-based metal-organic frameworks for photocatalytic water splitting and pollutants degradation.

Solar energy is becoming the most promising option to mitigate the energy crisis in the future and can be applied in renewable and economical technologies such as water splitting and pollutants degradation. The promotion of the electronic energetic level is considered an efficient method to enhance the photocatalytic performance of semiconductor materials for solar energy conversion. The highly energetic electrons exhibit a remarkable reduction ability by virtue of the electronic spin polarization, which is associated with the conduction band (CB) position. Thus, the regulation of the CB position due to the redistribution of electrons by means of defect engineering presents potential. Here, a series of titanium-based metal-organic frameworks (Ti-based MOFs) named MIL-125-m% containing different extents of defects are reported to enable photocatalytic activity under simulated sunlight and visible light illumination for remarkably enhanced photocatalytic hydrogen evolution and pollutant degradation. The experimental results illustrated that MIL-125-5% exhibited a superior photocatalytic hydrogen evolution rate (16507.27μmol·g-1·h-1), much higher than that of MIL-125-0% (1.444μmol·g-1·h-1). The excellent photocatalytic performance was attributed to upshift of d-band center, which strengthened the adsorption of H*, facilitating the H2 evolution reaction. In addition, the degradation rate of MIL-125-5% was up to twice the original rate, for the highly energetic electrons induced by the CB flexibility alleviated the photoinduced electron recombination in defective MIL-125. The strategy of defect engineering provides a new path to control the flexibility of the CB position by electronic spin polarization on adjustable metal-organic frameworks (MOFs), and the photocatalytic effect is changed accordingly.

Upcycling Waste Poly(ethylene terephthalate) into a Porous Carbon Cuboid through a MOF-Derived Carbonization Strategy for Interfacial Solar-Driven Water–Thermoelectricity Cogeneration

Converting plastics into functional carbonaceous materials for solar energy conversion and storage has emerged as a prospective solution to concurrently advanced waste plastics upcycling and solar energy exploitation. However, synthesizing efficient carbon-based photothermal materials with well-defined shapes from waste plastics remains challenging. Herein, we propose metal–organic framework-derived carbonization strategy to upcycle waste poly(ethylene terephthalate) into a porous carbon cuboid (PCC) for interfacial solar-driven water–thermoelectricity cogeneration. PCC with well-controlled shapes is readily prepared from carbonization of a Ca-metal–organic framework cuboid derived from recycled poly(ethylene terephthalate). The size and porous structure of the PCC are facilely regulated by changing the carbonization temperature (700–900 °C). Owing to abundant hierarchical micro-/meso-/macropores, unique cuboid morphology, and many oxygen-containing groups of the PCC, the PCC-based solar evaporator reveals high light absorptivity, reduced evaporation enthalpy, low heat conductivity, and superior photothermal conversion capability. Thanks to these advantages, it displays an ultra-high evaporation rate (2.49 kg m–2 h–1) under 1 sun illumination, surpassing many recent evaporators. Besides, an outdoor solar-driven desalination apparatus achieves the freshwater generation amount per unit area of 7.1 kg. Significantly, the evaporator combined with a thermoelectric module generates a voltage of 201 mV at the illumination intensity of 1 kW m–2, with a maximum power density of 0.8 W m–2. This work not merely offers new opportunities for sustainable electricity and freshwater supply from renewable solar energy but also contributes to upcycling waste plastics and achieving carbon neutrality.

Phenothiazine-Based Donor-Acceptor Polymers as Multifunctional Materials for Charge Storage and Solar Energy Conversion.

The increasing energy demand for diverse applications requires new types of devices and materials. Multifunctional materials that can fulfill different roles are of high interest as they can allow fabricating devices that can both convert and store energy. Herein, organic donor-acceptor redox polymers that can function as charge storage materials in batteries and as donor materials in bulk heterojunction (BHJ) photovoltaic devices are investigated. Based on its reversible redox chemistry, phenothiazine is used as the main building block in the conjugated copolymer design and combined with diketopyrrolopyrrol and benzothiadiazole as electron-poor comonomers to shift the optical absorption into the visible region. The resulting polymers show excellent cycling stability as positive electrode materials in lithium-organic batteries at discharge potentials of 3.6-3.7V versus Li/Li+ as well as good performances in BHJ solar cells with up to 1.9% power conversion efficiency. This study shows that the design of such multifunctional materials is possible, however, that it also faces challenges, as essential properties for good device function can lead to diametrically opposite requirements in materials design.

Ultrafast laser spectroscopy uncovers mechanisms of light energy conversion in photosynthesis and sustainable energy materials

The invention of the laser in 1960 gave us the ruby laser, which generally produced chaotic pulses of light. Six years later, in 1966, a concept called passive mode-locking applied to neodymium-glass lasers produced reasonably well-behaving picosecond pulses. This triggered an intense activity, with respect to developing improved laser pulse sources, measurement techniques, and application to chemistry, physics, and biology. Initially, only ∼10 –ps-long pulses at a few wavelengths were available. Nevertheless, insight into the function of complex biological systems, like photosynthetic proteins, and molecules of chemical interest was gained in very early studies. Today, both duration and color of ultrashort pulses can be tuned to almost any value. This has of course opened up possibilities to study almost any atomic, molecular, or solid-state system and any dynamic process. This review focuses on the use of laser spectroscopy to investigate light energy conversion mechanisms in both natural photosynthesis and a topical selection of novel materials for solar energy conversion. More specifically, in photosynthesis we will review light harvesting and primary electron transfer; materials for solar energy conversion that we discuss include sensitized semiconductors (dye sensitized solar cells), polymer:fullerene and polymer:polymer bulk heterojunctions (organic solar cells), organometal halide perovskites, as well as molecular and hybrid systems for production of solar fuel and valuable chemicals. All these scientific areas, and in particular photosynthesis and the solar cell materials, have been extensively studied with ultrafast spectroscopy, resulting in a vast literature; a comprehensive review of the individual materials is, therefore, not feasible, and we will limit our discussion to work that we think has been of particular importance for understanding the function of the respective systems.

Photophysical Properties of Linear, Net-structured and Branched Polybenzimidazoles.

Polybenzimidazoles with three different network structures are synthesized by condensation polymerization between the conventional monomer 3,3'-Diaminobenzidine and three different acid monomers. The synthesised polymer networks are characterized using several characterization techniques such as FT-IR, powder XRD, HR-SEM and TG-DTA analyses. The polybenzimidazoles are amorphous in nature with excellent thermal stability up to 450 ºC. The photophysical properties of polybenzimidazoles are studied using UV-visible absorption and Emission spectral techniques. Further, the excited state photoluminescence decay time measurement shows a functional group dependant decay behaviour. All the three polymers display narrow optical band gap energy and could be applied as a material for solar energy conversion and semiconductors.

Organic radicals stabilization above 300 °C in Eu-based coordination polymers for solar steam generation

Organic radicals feature unpaired electrons, and these compounds may have applications in biomedical technology and as materials for solar energy conversion. However, unpaired electrons tend to pair up (to form chemical bonds), making radicals unstable and hampering their applications. Here we report an organic radical system that is stable even at 350 °C, surpassing the upper temperature limit (200 °C) observed for other organic radicals. The system reported herein features a sulfur-rich organic linker that facilitates the formation of the radical centers; on the solid-state level, the molecules are crystallized with Eu(III) ions to form a 3D framework featuring stacks of linker molecules. The stacking is, however, somewhat loose and allows the molecules to wiggle and transform into sulfur-stabilized radicals at higher temperatures. In addition, the resulting solid framework remains crystalline, and it is stable to water and air. Moreover, it is black and features strong broad absorption in the visible and near IR region, thereby enhancing both photothermal conversion and solar-driven water evaporation.

Enhanced solar-driven hydrogen evolution over ultrathin g-C3N4/ReSe2 heterojunction-like nanosheets with surface selenium vacancies

The design of composite photocatalytic materials is essential for efficient photocatalytic hydrogen production. In the present work, we have successfully designed a simple synthetic process to ultrathin ReSe2 nanosheets using an ultrasound-assisted liquid-phase synthetic route through self-assembling ReSe2 onto g-C3N4 (shortened as g-C3N4/ReSe2 nanosheets) to improve photocatalytic performance. Based on density functional theory (DFT) estimation along with experimental characterization, it is found that the integrated heterojunction-like ultrathin g-C3N4/ReSe2 nanosheets possess more edge active sites, enhanced electron transfer efficiency and conductivities, which significantly accelerates the dissociation and migration of photogenerated electron-hole pairs. Meanwhile, selenium vacancies could be introduced into nanosheets via controlling the synthetic procedure with a reduced Se source that will favor to enhance the photocatalytic efficiency. The ultrathin g-C3N4/ReSe2 heterojunction with Se vacancies performed highly improved photocatalytic hydrogen production. In typical, the H2 production of the g-C3N4/ReSe2 nanosheets under visible light is 1055.50 μmol g−1 h−1, which is 21 times higher than that of bare g-C3N4, indicating that it overcomes the high charge complexation rate of g-C3N4. These results do not only provide insight into the application of two-dimensional ReSe2 nanosheets in photocatalysis, but also open up new avenues for the rational design of two-dimensional hybrid materials in solar energy conversion.

Electrospun Lignin-Based Phase-Change Nanofiber Films for Solar Energy Storage

Functional materials for solar energy collection, conversion, and storage need to be developed to address the global energy crisis. In this study, phase-change nanofiber films [PCNFs, sodium lignosulfonate (SLS)/polyvinyl alcohol (PVA)/polyethylene glycol (PEG)], which maintain their shape, were developed for solar-to-thermal energy conversion and storage. The films were constructed by electrospinning with PEG as the phase-change material, SLS/PVA mixture as the supporting matrix, and SLS as the photothermal material. SLS effectively improved the supporting property of the PCNFs owing to sturdy hydrogen bonds and electrostatic entanglement between its macromolecule chains and PVA/PEG, which prevented the leakage and transfer issue for PEG. Moreover, the PCNFs showed excellent solar-to-thermal energy conversion and storage ability, attributed to the π–π stacking of SLS molecules and the phase-change process, respectively. The SLS/PVA/PEG film with a PEG content of 32.43% exhibited a diameter of 465 ± 109 nm and a latent heat of fusion of 42.16 J·g–1, with a phase-change temperature of 45.20 °C. The film showed favorable stability over 50 heating–cooling cycles, thermal stability below 220 °C, good shape stability, and a solar-thermal energy conversion and storage efficiency of 18.03%. This study demonstrates a potential route to improve the utilization of lignin and solar energy and promotes the development of sustainable energy.

Optoelectronic properties and ion diffusion mechanism in 2D perovskites Cs3BX5 (B = Ge, Sn, and Pb; X = Cl, Br, and I): A first–principles investigation

Mitigating ion migration is a big challenge for optoelectronic perovskite materials. In this work, we investigate a novel family of layered halide perovskites Cs3BX5 (B = Ge, Sn, and Pb; X = Cl, Br, and I) by first–principles calculations. These compounds exhibit direct bandgap and small effective masses of electrons and holes. The optical absorption and spectroscopic limited maximum efficiency suggest the promising potential for these materials in solar energy conversion. The suppressed ionic conductivity has also been demonstrated by the higher energy barriers of halide ions migrations, which would be conducive to mitigate the hysteresis in perovskite solar cells.

Construction of CuS/ZnS heterostructures with enhanced photocatalytic activities on dye degradation and Cr (VI) reduction

The CuS/ZnS nanocomposites with particle morphology were prepared by ion exchange method. The systemically characterizations were used to study the phase structure, morphology, heterojunction, surface chemical components and optical properties. Furthermore, photocatalytic properties were researched by using 20 mg/L methylene blue and 40 mg/L of potassium dichromate solution as photocatalytic ox-red indicators, respectively. The results showed that the ZnS/CuS composites degraded 86.1% methylene blue solution within 50 min, which was 2.2 times higher than that of bare CuS nanoparticles. Significantly, the degradation rate of Cr (VI) reached 96.6% only within 8 min, which was greatly higher than that of each single component. Therefore, selecting appropriate semiconductors to construct type I-type hetero-structured composite materials could also take into account the three aspects’ efficiency of photo-quantum absorption, photogenerated charge transfer separation and surface chemical reaction for modifying the photocatalytic property, which provided a reliable experimental basis for the design and development of efficient solar energy conversion materials.

Effects of Mono- and Bifunctional Surface Ligands of Cu-In-Se Quantum Dots on Photoelectrochemical Hydrogen Production.

Semiconductor nanocrystal quantum dots (QDs) are promising materials for solar energy conversion because of their bandgap tunability, high absorption coefficient, and improved hot-carrier generation. CuInSe2 (CISe)-based QDs have attracted attention because of their low toxicity and wide light-absorption range, spanning visible to near-infrared light. In this work, we study the effects of the surface ligands of colloidal CISe QDs on the photoelectrochemical characteristics of QD-photoanodes. Colloidal CISe QDs with mono- and bifunctional surface ligands are prepared and used in the fabrication of type-II heterojunction photoanodes by adsorbing QDs on mesoporous TiO2. QDs with monofunctional ligands are directly attached on TiO2 through partial ligand detachment, which is beneficial for electron transfer between QDs and TiO2. In contrast, bifunctional ligands bridge QDs and TiO2, increasing the amount of QD adsorption. Finally, photoanodes fabricated with oleylamine-passivated QDs show a current density of ~8.2 mA/cm2, while those fabricated with mercaptopropionic-acid-passivated QDs demonstrate a current density of ~6.7 mA/cm2 (at 0.6 VRHE under one sun illumination). Our study provides important information for the preparation of QD photoelectrodes for efficient photoelectrochemical hydrogen generation.

Noble-metal free plasmonic nanomaterials for enhanced photocatalytic applications—A review

Plasmonic nanomaterial catalysis is currently at the frontier of photocatalysis, overcoming the limitations of wide bandgap semiconductors for light absorption. Its localized surface plasmon resonance (LSPR) properties allow broad ultraviolet—visible—near infrared ray (UV—vis—NIR) absorption, making it an ideal material for solar energy conversion. Most plasmonic nanostructures rely on precious metals. Although noble metal plasmonic nanomaterials have proven to be one of the strategies for enhancing photocatalytic activity, their expensive cost and limitations in light absorption range have hindered their practical application. As a result, noble-metal free plasmonic nanomaterials have risen to the top of the research priority list. Therefore, this paper reviews the fundamental principles and classification of the LSPR effect of noble-metal free plasmonic nanomaterials in photocatalytic and their recent applications in hydrogen generation, carbon dioxide reduction, and pollutant degradation. Specific cases elucidate the possible working mechanism of enhanced photocatalysis by noble-metal free plasmonic nanomaterials. Finally, the challenges and future opportunities for noble-metal free plasmonic nanomaterials in energy conversion and storage are discussed and envisioned.

NiO Modified CN Film As Photoanodes for Photoelectrochemical Water Oxidation

The utilization of solar energy, by far the most promising renewable energy resource, remains one of the hottest topics in the 21st century. Metal-free carbon nitride (CN) material emerged as a promising water splitting photocatalyst in 2009 due to its appropriate visible light absorption, suitable optical band gap energy (2.7 eV), and facile synthesis. Though CN is one of the leading materials for solar energy conversion, this material is limited by light absorption, rapid charge recombination, and low charge carrier mobility. Metal oxide are thus investigated for counterbalancing CN’s inherent drawbacks. Interfacial CN/metal oxide heterostructures facilitate charge transportation, resulting in improved sunlight-driven water splitting process. In this work, low-cost NiO transition-metal oxide material was applied to speed up the sluggish kinetics of the oxygen evolution reaction (OER). Typically, CN modification is achieved by traditional hydrothermal approach, while its disadvantages such as uneven coating particle size and heterogenous distribution are becoming increasingly apparent. Aiming at a conformal morphology, atomic layer deposition (ALD) is developed as the state-of-the-art technique. It has boosted the depositing accuracy by achieving precisely depositing thickness and extremely homogenous surface. In our process, a uniform CN film was deposited on FTO substrates using a dipping-drying technique with a hot saturated thiourea aqueous solution followed by a thermal treatment. Then plasma-enhanced atomic layer deposition (PEALD) was used to modify the CN film with a thin layer of NiO. PEALD controls the NiO modification on a fine-scale, allowing to with deposit a nanoscale NiO layer on the CN surface while exposing adequate CN photoreactive sites. According to our results, the modified NiO/CN heterostructure has the potential to improve photoelectrochemical water oxidation as a photoanode in alkaline solution. From the morphology side, the NiO loaded flake-like CN creates relatively high specific area for OER. Then we investigated the photo-process kinetic using a series of optical and spectroelectrochemcial techniques. Optical absorption is enhanced, showing stronger visible light absorption up to 700 nm. Fast charge separation is suggested in photoluminescence (PL) characterization. Superior (photo)electrochemical (PEC) activity is foreseen through PEC and EC measurements. To conclude, this is the first time we succeed to modify the CN film with the ALD technique for solar-driven water oxidation, and has the highly possibility of reaching the photo(electro)chemical performance new level.