Recent Advances in Self-Supported Semiconductor Heterojunction Nanoarrays as Efficient Photoanodes for Photoelectrochemical Water Splitting

Growth of semiconductor heterojunction nanoarrays directly on conductive substrates represents a promising strategy toward high-performance photoelectrodes for photoelectrochemical (PEC) water splitting. By controlling the growth conditions, heterojunction nanoarrays with different morphologies and semiconductor components can be fabricated, resulting in greatly enhanced light-absorption properties, stabilities, and PEC activities. Herein, recent progress in the development of self-supported heterostructured semiconductor nanoarrays as efficient photoanode catalysts for water oxidation is reviewed. Synthetic methods for the fabrication of heterojunction nanoarrays with specific compositions and structures are first discussed, including templating methods, wet chemical syntheses, electrochemical approaches and chemical vapor deposition (CVD) methods. Then, various heterojunction nanoarrays that have been reported in recent years based on particular core semiconductor scaffolds (e.g., TiO₂ , ZnO, WO₃ , Fe₂ O₃ , etc.) are summarized, placing strong emphasis on the synergies generated at the interface between the semiconductor components that can favorably boost PEC water oxidation. Whilst strong progress has been made in recent years to enhance the visible-light responsiveness, photon-to-O₂ conversion efficiency and stability of photoanodes based on heterojunction nanoarrays, further advancements in all these areas are needed for PEC water splitting to gain any traction alongside photovoltaic-electrochemical (PV-EC) systems as a viable and cost-effective route toward the hydrogen economy.

Uniform-embeddable-distributed Ni3S2 cocatalyst inside and outside a sheet-like ZnIn2S4 photocatalyst for boosting photocatalytic hydrogen evolution

The rational cocatalyst design is considered a significant route to boost the solar-energy conversion efficiency for photocatalytic H₂ generation. However, the traditional cocatalyst-loading on the surface of a photocatalyst easily leads to scarce exposed active sites induced by the agglomeration of cocatalysts and a hindrance of the light absorption of the photocatalyst, thus significantly limiting the enhancement of the photocatalytic H₂-generation performance. Herein, a new concept of uniform-embeddable-distributed cocatalysts is put forward. Consequently, uniform-embeddable-distributed cocatalysts of Ni₃S₂ were designed and constructed inside and outside of the nanosheet-like ZnIn₂S₄ photocatalyst to form a Ni₃S₂/ZnIn₂S₄ binary system (UEDNiS/ZIS). The unique uniform-embeddable-distributed Ni₃S₂ cocatalyst (UEDNiS) could provide abundant exposed active sites, facilitate the spatial separation and ordered transfer of charges inside and outside of ZnIn₂S₄ nanosheets, and reduce the hydrogen-adsorption free energy for photocatalytic H₂-generation reactions. As a result, UEDNiS/ZIS exhibited a high photocatalytic H₂-generation rate of 60 μmol h^-1 under visible-light irradiation, almost 7.8 and 2.8 times higher than pristine ZnIn₂S₄ and the traditional surface-loaded Ni₃S₂/ZnIn₂S₄ (TSLNiS/ZIS), respectively. This work represents a new cocatalyst-design approach to realize high-efficiency hydrogen evolution in binary heterostructured photocatalytic systems.

A fast curing assisted spray-coating method to fabricate a robust core-shell structured evaporator with stable solar vapor generation performance

Solar driven interfacial vapor generation is considered to be an effective strategy to alleviate the impact of water crisis on human activities. However, great efforts of researchers have been devoted to improving the solar steam generation efficiency, while less attention has been paid to the long-term stability of evaporators. Herein, we proposed a robust core-shell structured evaporator prepared by a simple fast curing assisted spray-coating method. Owing to the inherent superelasticity of melamine-formaldehyde (MF) sponge, the finely designed novel 3D core-shell structure, and the quick curing of branched polyethyleneimine (BPEI) and 5-pentaerythritol pentaacrylate (5Acl) induced special knot shaped photothermal coating, the as-obtained evaporator (CB/MF) performed well in vapor generation with a high water evaporation rate of 2.082 kg m^-2 h^-1 under 1 sun illumination, and the evaporation efficiency reached 123.5%, which is comparable to the state-of-the-art artificial solar evaporator. Even in strict application situations, such as long-term recycling testing for 40 h, 500 compression-release cycles (20%, 40% or 60%), sonication for 12 h, or shaking for 30 h, the water evaporation rate of the obtained evaporator remains at a high level of above 2.00 kg m^-2 h^-1. Additionally, the evaporator shows effective purification toward high-concentration brine, acid-base solutions, simulated seawater, dye wastewater, and heavy metal wastewater, as well as reliable pure water, providing an outdoor application. With the advantages of a high evaporation rate, stable long-term vapor generation, and effective purification toward various non-potable water sources, we believe that the fabricated core-shell structured CB/MF evaporator is a promising candidate for practical solar steam generation.

Organic Solar Cells Improved by Optically Resonant Silicon Nanoparticles

Silicon nanophotonics has become a versatile platform for optics and optoelectronics. For example, strong light localization at the nanoscale and lack of parasitic losses in infrared and visible spectral ranges make resonant silicon nanoparticles a prospect for improvement in such rapidly developing fields as photovoltaics. Here, we employed optically resonant silicon nanoparticles produced by laser ablation for boosting the power conversion efficiency of organic solar cells. Namely, we created colloidal solutions of spherical nanoparticles with a range of diameters (80-240 nm) in different solvents. We tested how the nanoparticles' position in the device, their concentration, silicon doping, and method of deposition affected the final device efficiency. The best conditions optimization resulted in an efficiency improvement from 6% up to 7.5%, which correlated with numerical simulations of nanoparticles' optical properties. The developed low-cost approach paves the way toward highly efficient and stable solution-processable solar cells.

Identifying the geometric catalytic active sites of crystalline cobalt oxyhydroxides for oxygen evolution reaction

Unraveling the precise location and nature of active sites is of paramount significance for the understanding of the catalytic mechanism and the rational design of efficient electrocatalysts. Here, we use well-defined crystalline cobalt oxyhydroxides CoOOH nanorods and nanosheets as model catalysts to investigate the geometric catalytic active sites. The morphology-dependent analysis reveals a ~50 times higher specific activity of CoOOH nanorods than that of CoOOH nanosheets. Furthermore, we disclose a linear correlation of catalytic activities with their lateral surface areas, suggesting that the active sites are exclusively located at lateral facets rather than basal facets. Theoretical calculations show that the coordinatively unsaturated cobalt sites of lateral facets upshift the O 2p-band center closer to the Fermi level, thereby enhancing the covalency of Co-O bonds to yield the reactivity. This work elucidates the geometrical catalytic active sites and enlightens the design strategy of surface engineering for efficient OER catalysts.

While cobalt-based electrocatalysts demonstrate promising performances for oxygen evolution, active site identification is complicated by concurrent structural changes. Here, authors examine crystalline, well-defined cobalt oxyhydroxide nanomaterials and identify the geometric active sites.

A Wave-Driven Piezoelectrical Film for Interfacial Steam Generation: Beyond the Limitation of Hydrogel

Solar interfacial vapor generation based on low evaporation energy requirements is an effective technology to speed up water purification under natural sunlight, offering great potential to alleviate the current global water crisis. The external electric field and hydrogel are two independent methods enabling low-energy water evaporation. However, the complicated external equipment for generating an electric field and the restricted activation area of hydrogels significantly limit their practical application in steam generation. Thus, a piezoelectric fiber membrane is embedded into a highly hydratable light-absorbing poly(vinyl alcohol) (PVA) hydrogel for synergistic water activation. The integrated evaporator is capable of continuously converting the wave energy reserved in the ocean into electrical energy, activating the water in the hydrogel. It is found that the activation effect leads to an improvement of over 23% compared to a non-piezoelectric hydrogel evaporator. This work provides an evaporation prototype based on the synergistic water activation of wave-triggered electricity and highly hydratable hydrogel.

Thermally-enhanced sono-photo-catalysis by defect and facet modulation of Pt-TiO2 catalyst for high-efficient hydrogen evolution

Sono-photo-catalysis (SPC) has been regarded as a promising route for hydrogen evolution from water splitting due to the sono-photo-synergism, whereas its current performance (∼μmol g^-1 h^-1) is yet far from expectation. Herein, we give the first demonstration that the intrinsically coupled thermal effects of light and ultrasound, which is normally underestimated or neglected, can simultaneously reshape the photo- and sono-catalytic activities for hydrogen evolution and establish a higher degree of synergy between light and ultrasound in SPC even on the traditional Pt-TiO₂ catalyst. A high-efficient hydrogen evolution rate of 225.04 mmol g^-1 h^-1 with light-to‑hydrogen efficiency of 0.89% has been achieved in thermally-enhanced SPC, which is an order of magnitude higher than that without thermal effects. More impressively, the increase of synergy index up to 53% has been achieved. Through experiments and theoretical calculations, the thermally-enhanced sono-photo-synergism is attributed to the sono-photo-thermo-modulated structural optimization of defect-rich TiO₂ support and deaggregated Pt species with functional complementary lattice facets, which optimizes not only the thermodynamic properties by enhancing light harvesting and the charge redox power, but also the kinetic properties by accelerating the net efficiency of charge separation and the whole processes of water splitting, including the dissociation of water molecules on high-index (200) Pt facets and production of H^∗ intermediates on defect-rich TiO_2-x support and low-index (111) Pt facets. This study exemplifies that coupling light- and ultrasonic-induced thermal effects in SPC system could enhance the synergy between light and ultrasound by modulating catalyst structure to achieve double optimization of thermodynamic and kinetic properties of SPC hydrogen evolution.

Highly Efficient and Salt-Rejecting Poly(vinyl alcohol) Hydrogels with Excellent Mechanical Strength for Solar Desalination

Interfacial solar steam generation (ISSG)-based solar desalination has recently emerged as a promising solution to tackle the global issue of fresh water scarcity. However, the energy-intensive process of conventional vapor generation techniques limits its practical applications. Hydrogels with three-dimensional (3D) structures have been reported to alleviate this energy demand, but their applications in sustainable solar desalination are hindered by their poor mechanical stability. Herein, we propose a 3D poly(vinyl alcohol) (PVA)-based hydrogel with excellent mechanical strength for effective solar desalination. The dual polymer network hydrogel (PVA-agar) incorporated with multi-walled carbon nanotubes (MWCNTs) achieved a noticeable evaporation rate of 3.1 kg m^-2 h^-1 under 1 sun irradiation, owing to its broadband light absorption, intrinsic water channels, and microporous structure that help reduce the latent heat of vaporization. More importantly, the application of kosmotropic ammonium sulfate ions was found to greatly improve the mechanical strength of the hydrogels using a facile Hofmeister-assisted soaking method. Finally, the PVA-agar-MWCNT hydrogel was able to desalinate seawater efficiently (2.5 kg m^-2 h^-1) with self-cleaning capability of salt crystals. The salinity level of the desalinated water was also comparable to drinking clean water. The present results would pave the way for fabricating mechanically strong, hydrophilic, and highly efficient hydrogels for effective and sustainable solar desalination.

Low-Loss, High-Transparency Luminescent Solar Concentrators with a Bioinspired Self-Cleaning Surface

Luminescent solar concentrators (LSCs) have emerged as a disruptive technology that can potentially enable carbon-neutral buildings. The issues with current LSCs, however, are low optical efficiencies and limited long-term outdoor stability. Here we simultaneously address them by developing an LSC with aggregation-induced-emission (AIE) molecules embedded in a polydimethylsiloxane (PDMS) matrix. The AIE-emitter displayed a near unity emission quantum yield when embedded in the PDMS and the apparent absorption-emission Stokes shift reached 0.59 eV, effectively suppressing the reabsorption loss of waveguided photons inside an LSC. Moreover, the surface texture of the PDMS matrix was engineered using a bioinspired nanolithography method with a natural lotus leaf as the template. This allowed the fabricated AIE-PDMS LSC to inherit the superhydrophobic, self-cleaning properties of the leaf and meanwhile to possess a light-trapping capability. Our 100 cm² LSC, when coupled with commercial Si PVs, delivered efficient solar power conversion, high visible transmittance, and high working stability.

An optimal molecule-matching co-sensitization system for the improvement of photovoltaic performances of DSSCs

Three biphenyl co-sensitizers (4OBA, 8OBA and 12OBA) with different terminal oxyalkyl chains were synthesized and co-sensitized respectively with the main dye (NP-1) in co-sensitized solar cells (co-DSSCs). The effects of the terminal oxyalkyl chains on the photophysical, electrochemical and photovoltaic properties of the co-DSSCs were systematically investigated. The optimal molecular matching relationship between the co-sensitizers and the main dye was obtained through density functional theory (DFT) calculations. Consequently, 4OBA has the most appropriate three-dimensional (3D) molecular structure, which could not only fill the gap between the large-size dyes but also plays a partial shielding role, inhibiting dye aggregation and electron recombination, therefore yielding the highest power conversion efficiency (PCE) for the co-DSSCs with NP-1@4OBA. This study suggests that adjusting the terminal oxyalkyl chains of the co-sensitizers can be used to enhance the intramolecular charge transfer efficiency and inhibit electron recombination, ultimately improving the photovoltaic performances of the co-DSSCs.

Rapid Solar Heating of Antimicrobial Ag and Cu2O Nanostructured Plasmonic Textile for Clean Water Production

Solar steam generation is an attractive method to produce clean water, and high steam generation rates have been achieved using nanostructured light absorbers. However, since it usually takes minutes to reach the temperature for steady-state steam generation under solar illumination, a material that responds quickly to intermittent sunlight is strongly desired. Here, we report an unprecedented heating rate in an ultralight freestanding textile consisting of interconnected Ag and Cu₂O nanoparticles. The textile demonstrated high solar absorption with low reflectance and transmittance, which were rationalized using our multiphysics simulations. A commercial polystyrene foam wrapped with this broadband light-absorbing textile showed the fastest response to sunlight together with a good steam generation rate compared to reported inorganic nanostructured steam generators. Furthermore, the textile exhibited antibacterial property, which might lower the risk of the vapor-induced transfer of bacteria during long-term intermittent use and the cost of subsequent water sanitization.

Enhanced Charge Separation for Efficient Photocatalytic H2 Production by Long-Lived Trap-State-Induced Interfacial Charge Transfer

Photogeneration of charge carriers in semiconductors provides the scientific fundamental for photocatalytic water splitting. However, an ongoing challenge is the development of a new mechanism promoting charge carrier separation. Here we propose a trap-state-induced interfacial charge-transfer transition mechanism (TSICTT), in which electrons in long-lived trap states recombine with holes on the valence band (VB) of the semiconductor, thus prolonging the electron lifetime. We demonstrate this concept in the Sr₄Al₁₄O₂₅:Eu²⁺, Dy³⁺/CdS (SAO/CdS) heterostructure, where trapped electrons with a lifetime of up to several hours in the SAO persistent luminescence phosphor (PLP) can continuously consume holes on the VB of CdS nanoparticles (NPs). We discover that the interfacial interaction and the work function difference between SAO and CdS are crucial for the TSICTT, which finally contributes to the improved H₂ production from 34.4 to 1212.9 μmol g_CdS^-1 h^-1 under visible-light irradiation. This model introduces a new strategy to manipulate charge carrier transport for the effective utilization of solar energy.

In Situ Engineering of the Cu+/Cu0 Interface to Boost C2+ Selectivity in CO2 Electroreduction

The Cu⁺/Cu⁰ interface in the Cu-based electrocatalyst is essential to promote the electrochemical reduction of carbon dioxide (ERCO₂) to produce multi-carbon hydrocarbons and alcohols with high selectivity. However, due to the high activity of the Cu⁺/Cu⁰ interface, it is easy to be oxidized in the air. How to control and prepare a Cu-based electrocatalyst with an abundant and stable Cu⁺/Cu⁰ interface in situ is a huge challenge. Here, combined with density functional theory (DFT) calculations and experimental studies, we found that the trace halide ions adsorbed on Cu₂O can slow the reduction kinetics of Cu⁺ → Cu⁰, which allowed us to in-situ well control the synthesis of the CuO-derived electrocatalyst with rich Cu⁺/Cu⁰ interfaces. Our Cu catalyst with a rich Cu⁺/Cu⁰ interface exhibits excellent ERCO₂ performance. Under the operation potential of -0.98 V versus RHE, the Faraday efficiency of C₂H₄ and C₂₊ products are 55.8 and 75.7%, respectively, which is about 16% higher than that of CuO-derived electrocatalysts that do not use halide ions. The high FEC2+ comes from the improvement of the coupling efficiency of reaction intermediates such as CO-CO, which is proved by DFT calculations, and the suppression of hydrogen evolution reaction. Therefore, we provide an in-situ engineering strategy, which is simple and effective for the design and preparation of high-performance ERCO₂ catalysts.

Enhancement in the photoelectrochemical performance of BiVO4 photoanode with high (040) facet exposure

Morphology and geometrical dimensions play crucial roles in the photoelectrochemical (PEC) performance of bismuth vanadate (BiVO₄) for water splitting. Decahedral BiVO₄ was synthesized through a facile hydrothermal process, which exhibited superior charge injection efficiency to the nanoporous counterpart prepared by the traditional method. More importantly, the crystal size and facet proportion of BiVO₄ decahedrons were facilely controlled. The charge separation efficiency can be significantly improved with a reduction in the crystal size and an increase in (040) facet exposure. A new method was developed for rate law analysis: illumination intensity-modulated oxygen evolution reaction rate versus open circuit potential difference, which suggested that the surface reaction kinetics was not affected by facet regulation. Furthermore, after decorating the FeOOH and NiOOH as dual oxygen evolution cocatalysts, an enhanced photocurrent density of 3.2 mA cm^-2 at 1.23 V versus reversible hydrogen electrode and interfacial charge injection efficiency of 97.0% can be reached. Our work inspires the development of facet-regulated BiVO₄ photoanodes with high charge injection efficiency in the PEC field and provides a feasible route to enhance its charge separation efficiency.

Pt nanoparticles coupled with perylene-based small molecule deposited on Ti3+ self-doped TiO2 nanorods-An inorganic/organic type-II nanoheterostructure for efficient visible-light photoelectrochemical water oxidation

In the work reported in this article, we have coupled Ti³⁺-self-doped TiO₂ nanorods (NRs) with a newly synthesized tetrathiophene coupled perylene-based molecule (tThTMP) to form type-II inorganic/organic nanoheterostructures (NHs) for visible-light-driven water oxidation. The small organic molecule helps in better utilizing a wide range of the visible light spectrum, facilitates a faster delocalization of the photogenerated carriers at the inorganic/organic heterojunction, and exhibits improved photoelectrochemical performances. We have further decorated the NHs with platinum nanoparticles (NPs). The decoration of the Pt NPs significantly augments the various aspects of photoelectrochemical performances. The Pt NPs decorated NHs photoanode exhibits a photocurrent density of 0.83 mA/cm² at 1.23 V vs. RHE (@10 mV/s scan rate), a photoconversion efficiency of 0.26%, a substantial cathodic shift in the water oxidation onset potential and flat band potential, impressively reduced charge transfer resistance, improved photocarrier concentration, photovoltage, and stability.

Computational Analysis of Structure - Activity Relationships in Highly Active Homogeneous Ruthenium-based Water Oxidation Catalysts

Linear free energy scaling relationships (LFESRs) and regression analysis may predict the catalytic performance of heterogeneous and recently, homogenous water oxidation catalysts (WOCs). This study analyses twelve homogeneous Ru-based catalysts - some, the most active catalysts studied: the Ru(tpy-R)(QC) and Ru(tpy-R)(4-pic)2 catalysts, where tpy is 2,2:6,2-terpyridine, QC is 8-quinolinecarboxylate and 4-pic is 4-picoline. Typical relationships studied among heterogenous and solid-state catalysts cannot be broadly applied to homogeneous catalysts. This subset of structurally similar catalysts with impressive catalytic activity deserves closer computational and statistical analysis of energetics correlating with measured catalytic activity. We report general methods of LFESR analysis yield insufficiently robust relationships between descriptor variables. However, volcano plot-based analysis grounded in Sabatier's principle reveals ranges of ideal relative energies of the RuIV=O and RuIV-OH intermediates and optimal changes in free energies of water nucleophilic attack on RuV=O. A narrow range of RuIV-OH to RuV=O redox potentials corresponding with the highest catalytic activities suggests facile access to the catalytically competent high-valent RuV=O state, often inaccessible from RuIV=O. Our work introduces experimental oxygen evolution rates into approaches of LFESR and Sabatier principle-based analysis, identifying a narrow yet fertile energetic landscape to bountiful oxygen-evolution activity, leading future rational design.

Polymer Photoelectrodes for Solar Fuel Production: Progress and Challenges

Converting solar energy to fuels has attracted substantial interest over the past decades because it has the potential to sustainably meet the increasing global energy demand. However, achieving this potential requires significant technological advances. Polymer photoelectrodes are composed of earth-abundant elements, e.g. carbon, nitrogen, oxygen, hydrogen, which promise to be more economically sustainable than their inorganic counterparts. Furthermore, the electronic structure of polymer photoelectrodes can be more easily tuned to fit the solar spectrum than inorganic counterparts, promising a feasible practical application. As a fast-moving area, in particular, over the past ten years, we have witnessed an explosion of reports on polymer materials, including photoelectrodes, cocatalysts, device architectures, and fundamental understanding experimentally and theoretically, all of which have been detailed in this review. Furthermore, the prospects of this field are discussed to highlight the future development of polymer photoelectrodes.

Modularly Integrated System for Spatiotemporally Separated Solar Energy Storage and Release

The sun is regarded as an endless source of clean energy. However, the intermittent supply and dynamically changeable demand of solar energy, as well as its uneven regional distribution, have been continually motivating the technological research of practical strategies to realize the spatiotemporally separated solar energy harvest and utilization. Accordingly, we here developed an integrated system for efficient solar energy capture, stable storage, and on-demand release, which corresponds to the intricate design of three distinct modules, namely, a photothermal conversion module, a latent heat storage module, and a mechanical trigger module. Moreover, efficient heat transfer and long-term supercooled stability necessitate interfacial passivation to coordinate the physical coupling of different modules. In addition to providing an integrated prototype that demonstrates a closed energy cycle in practice, this study may further inspire a new paradigm for advanced solar utilization in both theory and methodology.

Self-Assembled Supercrystals Enhance the Photothermal Conversion for Solar Evaporation and Water Purification

Photothermal materials can convert renewable solar energy into thermal energy and have great potential for solar water evaporation. Copper sulfide (Cu_{2- x} S) is an easily available and inexpensive plasmonic material with a high photothermal conversion efficiency and can be applied to solar evaporation and water purification. Monodispersed Cu₇ S₄ nanoparticles (NPs) and supercrystalline self-assembled superparticles are obtained via wet chemical synthesis and micelle self-assembly. The photothermal properties of the superstructures are investigated using the finite difference time domain method and laser radiation photothermography. The results show that the electromagnetic field intensity and photothermal efficiency of the self-assembly are significantly higher than those of isolated NPs, which is due to the plasmonic coupling of the NPs. The evaporation efficiency of the superstructure is significantly higher than that of isolated NPs, the metal salt ion and total organic carbon concentrations in the waterbody significantly decrease after evaporation, and the water polluted by high salt and organic dye concentrations is purified. The water quality significantly improves after the lake water from Fuxian Lake in the Yunnan-Guizhou Plateau of China is used for solar evaporation. The color changes from pale yellow to colorless and the ion and total organic carbon contents significantly decrease.

Freestanding 2D NiFe Metal-Organic Framework Nanosheets: Facilitating Proton Transfer via Organic Ligands for Efficient Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is crucial to electrochemical hydrogen production. However, designing and fabricating efficient electrocatalysts still remains challenging. By confinedly coordinating organic ligands with metal species in layered double hydroxides (LDHs), an innovative LDHs-assisted approach is developed to facilely synthesize freestanding bimetallic 2D metal-organic framework nanosheets (2D MOF NSs), preserving the metallic components and activities in OER. Furthermore, the research has demonstrated that the incorporation of carboxyl organic ligands coordinated with metal atoms as proton transfer mediators endow 2D MOF NSs with efficient proton transfer during the electrochemical OH_ads  → O_ads transition. These freestanding NiFe-2D MOF NSs require a small overpotential of 260 mV for a current density of 10 mA cm^-2 . When this strategy is applied to LDH nanosheets grown on nickel foam, the overpotential can be reduced to 221 mV. This outstanding OER activity supports the capability of multimetallic organic frameworks for the rational design of water oxidation electrocatalysts. This strategy provides a universal path to the synthesis of 2D MOF NSs that can be used as electrocatalysts directly.

Enhanced H2O2 Production via Photocatalytic O2 Reduction over Structurally-Modified Poly(heptazine imide)

Solar H₂O₂ produced by O₂ reduction provides a green, efficient, and ecological alternative to the industrial anthraquinone process and H₂/O₂ direct-synthesis. We report efficient photocatalytic H₂O₂ production at a rate of 73.4 mM h^-1 in the presence of a sacrificial donor on a structurally engineered catalyst, alkali metal-halide modulated poly(heptazine imide) (MX → PHI). The reported H₂O₂ production is nearly 150 and >4250 times higher than triazine structured pristine carbon nitride under UV-visible and visible light (≥400 nm) irradiation, respectively. Furthermore, the solar H₂O₂ production rate on MX → PHI is higher than most of the previously reported carbon nitride (triazine, tri-s-triazine), metal oxides, metal sulfides, and other metal-organic photocatalysts. A record high AQY of 96% at 365 nm and 21% at 450 nm was observed. We find that structural modulation by alkali metal-halides results in a highly photoactive MX → PHI catalyst which has a broader light absorption range, enhanced light absorption ability, tailored bandgap, and a tunable band edge position. Moreover, this material has a different polymeric structure, high O₂ trapping ability, interlayer intercalation, as well as surface decoration of alkali metals. The specific C≡N groups and surface defects, generated by intercalated MX, were also considered as potential contributors to the separation of photoinduced electron-hole pairs, leading to enhanced photocatalytic activity. A synergy of all these factors contributes to a higher H₂O₂ production rate. Spectroscopic data help us to rationalize the exceptional photochemical performance and structural characteristics of MX → PHI.

How the Way a Naphthalimide Unit is Implemented Affects the Photophysical and -catalytic Properties of Cu(I) Photosensitizers

Driven by the great potential of solar energy conversion this study comprises the evaluation and comparison of two different design approaches for the improvement of copper based photosensitizers. In particular, the distinction between the effects of a covalently linked and a directly fused naphthalimide unit was assessed. For this purpose, the two heteroleptic Cu(I) complexes CuNIphen (NIphen = 5-(1,8-naphthalimide)-1,10-phenanthroline) and Cubiipo (biipo = 16H-benzo-[4′,5′]-isoquinolino-[2′,1′,:1,2]-imidazo-[4,5-f]-[1,10]-phenanthroline-16-one) were prepared and compared with the novel unsubstituted reference compound Cuphen (phen = 1,10-phenanthroline). Beside a comprehensive structural characterization, including two-dimensional nuclear magnetic resonance spectroscopy and X-ray analysis, a combination of electrochemistry, steady-state and time-resolved spectroscopy was used to determine the electrochemical and photophysical properties in detail. The nature of the excited states was further examined by (time-dependent) density functional theory (TD-DFT) calculations. It was found that CuNIphen exhibits a greatly enhanced absorption in the visible and a strong dependency of the excited state lifetimes on the chosen solvent. For example, the lifetime of CuNIphen extends from 0.37 µs in CH2Cl2 to 19.24 µs in MeCN, while it decreases from 128.39 to 2.6 µs in Cubiipo. Furthermore, CuNIphen has an exceptional photostability, allowing for an efficient and repetitive production of singlet oxygen with quantum yields of about 32%.

A Universal Descriptor for Complicated Interfacial Effects on Electrochemical Reduction Reactions

Supported catalysts have exhibited excellent performance in various reactions. However, the rational design of supported catalysts with high activity and certain selectivity remains a great challenge because of the complicated interfacial effects. Using recently emerged two-dimensional materials supported dual-atom catalysts (DACs@2D) as a prototype, we propose a simple and universal descriptor based on inherent atomic properties (electronegativity, electron type, and number), which can well evaluate the complicated interfacial effects on the electrochemical reduction reactions (i.e., CO₂, O₂, and N₂ reduction reactions). Based on this descriptor, activity and selectivity trends in CO₂ reduction reaction are successfully elucidated, in good agreement with available experimental data. Moreover, several potential catalysts with superior activity and selectivity for target products are predicted, such as CuCr/g-C₃N₄ for CH₄ and CuSn/N-BN for HCOOH. More importantly, this descriptor can also be extended to evaluate the activity of DACs@2D for O₂ and N₂ reduction reactions, with very small errors between the prediction and reported experimental/computational results. This work provides feasible principles for the rational design of advanced electrocatalysts and the construction of universal descriptors based on inherent atomic properties.

Small practical cluster models for perovskites based on the similarity criterion of central location environment and their applications

Developing universal theoretical models for perovskites (often denoted as ABX₃) can contribute to the rational design of novel perovskite photovoltaic materials. However, few models can be successfully applied to study the intrinsic electronic structure due to the poor accuracy and unaffordable computational cost. Herein, we report the innovative construction of small practical cluster models through the similarity criterion of the central location environment, which retains only the central A-site as the original cation while the others are substituted by Cs to keep the clusters electrically neutral. The central cation has a chemical environment similar to that of the bulk perovskite. The binding energy between A and the BX framework, geometric structures (B-X distances and B-X-B angles), and the electronic structures (the gap and the spatial distribution of HOMO and LUMO, electron distribution) of these clusters have been investigated and compared with the corresponding properties of bulk materials. The results suggest that the cluster model with twelve B-atoms suitably describes these properties. The geometric structures and gaps are closer to the bulk situations than the quasi-one-dimensional and quasi-two-dimensional cluster models with all-primitive cations, respectively. Other organic cations, such as NH₃(CH₂)_nCH₃ (n = 1, 2, and 3 for EA, PA, and BA, respectively), and (NH₂)₂CH (FA) can, therefore, mimic perovskite materials. Clusters with different sizes of A indicate that PA and BA will distort the quasi-cubic structures, which is consistent with the judgment of the tolerance factor of bulk materials. The reliable cluster model provides the research foundation for some basic issues of perovskites, such as vibrational spectroscopy and hydrogen bonding strength, to gain detailed insight into the interactions between A and the BX framework.

A water supply tunable bilayer evaporator for high-quality solar vapor generation

Interfacial heating is the most obvious feature that distinguishes the novel solar driven interfacial heating from the traditional solar heating technology, and it is also a key factor in promoting solar energy utilization and vapor generation performance. However, the inherent trade-off between water supply and the interfacial heating performance of photothermal materials has rarely been investigated. Herein, an all-in-one designed bilayer evaporator consisting of a top solar absorber (Fe₃O₄@PDA-SA) and a bottom water transport layer (SA) is reported. This bilayer structured aerogel can provide good thermal insulation, effective water transmission channels, and reliable light absorbance, and perform well as a high-quality solar steam evaporator with the evaporation rate of approximately 1.517 kg m^-2 h^-1 and the evaporation efficiency of approximately 98.27% under 1 kW m^-2 solar illumination. Most importantly, we can control the pore size of the bottom layer by a simple free water evaporation method, so as to manipulate the water transport capacity of materials. There is flexibility to change the water content of the light-absorbing structure and further explore the influence of water supply on the interfacial heating performance of the evaporator, which provides more possibilities for the design and preparation of high-quality solar steam evaporators.

Photocatalytic Material-Microorganism Hybrid System and Its Application—A Review

The photocatalytic material-microorganism hybrid system is an interdisciplinary research field. It has the potential to synthesize various biocompounds by using solar energy, which brings new hope for sustainable green energy development. Many valuable reviews have been published in this field. However, few reviews have comprehensively summarized the combination methods of various photocatalytic materials and microorganisms. In this critical review, we classified the biohybrid designs of photocatalytic materials and microorganisms, and we summarized the advantages and disadvantages of various photocatalytic material/microorganism combination systems. Moreover, we introduced their possible applications, future challenges, and an outlook for future developments.

Beyond Water Oxidation: Hybrid, Molecular-Based Photoanodes for the Production of Value-Added Organics

The political and environmental problems related to the massive use of fossil fuels prompted researchers to develop alternative strategies to obtain green and renewable fuels such as hydrogen. The light-driven water splitting process (i.e., the photochemical decomposition of water into hydrogen and oxygen) is one of the most investigated strategies to achieve this goal. However, the water oxidation reaction still constitutes a formidable challenge because of its kinetic and thermodynamic requirements. Recent research efforts have been focused on the exploration of alternative and more favorable oxidation processes, such as the oxidation of organic substrates, to obtain value-added products in addition to solar fuels. In this mini-review, some of the most intriguing and recent results are presented. In particular, attention is directed on hybrid photoanodes comprising molecular light-absorbing moieties (sensitizers) and catalysts grafted onto either mesoporous semiconductors or conductors. Such systems have been exploited so far for the photoelectrochemical oxidation of alcohols to aldehydes in the presence of suitable co-catalysts. Challenges and future perspectives are also briefly discussed, with special focus on the application of such hybrid molecular-based systems to more challenging reactions, such as the activation of C–H bonds.

Solar-Driven Soil Remediation along with the Generation of Water Vapor and Electricity

As a renewable energy source, solar energy has become an important part of human energy use. However, facilities utilizing solar energy are often complex and technically difficult, and preparation equipment and materials are expensive, while these equipment and materials often cause new environmental pollution. Soil, which exists in large quantities on the earth’s surface, is an inexhaustible natural material with loose and stable properties. Due to the specificity of its composition and microscopic form, the soil has an inherent advantage as a medium for solar thermal and photovoltaic conversion. Here, we built an integrated solar energy utilization system, the Integrated Soil Utilization Module (ISUM), integrating multi-functions into one hybrid system, which enables solar-driven water vapor and electricity generation and soil remediation. The evaporation rate of the soil represented by the rocky land was 1.2 kg·m⁻²·h⁻¹ under 1-sun irradiation with evaporation induced voltage of 0.3 V. With only seven days of continuous exposure to sunlight, the removal of heavy metal ions from the soil reached 90%, while the pH was raised to near neutral. The combined application of readily available natural soil with solar energy not only demonstrates the potential of a soil for solar desalination and power generation, but in addition, solar-driven interfacial evaporation provides an energy-efficient, environmentally friendly, and sustainable method for purifying heavy metal and acid-contaminated soil.

Robust photothermal anti-icing/deicing via flexible CMDSP carbon nanotube films

Photothermal anti-icing/deicing technology is an environmentally friendly surface technology that can be applied to the surface of aircraft, vehicles or ships. However, it is still a huge challenge to develop a strong and stable flexible film that can efficiently convert light to heat. Here, based on a simple electrochemical method to construct a zinc oxide (ZnO) nanoneedles structure on the surface of the carbon nanotube film, a film with the function of condensed micro-droplet self-propelling (CMDSP) was successfully prepared. The prepared film has excellent light absorption capacity and high energy transfer efficiency (76.71%). The film has strong photothermal anti-icing/deicing performance. Under 4406 Lux light irradiation, even under low temperature conditions of -5 °C, the icing delay time exceeds 4 h. This novel characteristic is attributed to the CMDSP function on the surface and the ultra-fast evaporation mechanism, which can remove water droplets on the surface as quickly as possible. This function helps to design energy-saving equipment that requires high-power heating and deicing.

Enhancing the Photocatalytic Hydrogen Evolution Performance of the CsPbI3/MoS2 Heterostructure with Interfacial Defect Engineering

Developing highly efficient photocatalysts for the hydrogen evolution reaction (HER) by solar-driven water splitting is a great challenge. Here, we study the atomistic origin of interface properties and the HER performance of all-inorganic iodide perovskite β-CsPbI₃/2H-MoS₂ heterostructures with interfacial vacancy defects using first-principles calculations. Both CsI/MoS₂ and PbI₂/MoS₂ heterostructures have strong binding and dipole moment, which are enhanced by interfacial iodine vacancies (V_I). Because of the nature of type II heterojunctions, photogenerated electrons on the CsPbI₃ side are promptly transferred to the MoS₂ side where HER occurs, and sulfur vacancies (V_S) spoil this process, acting as surface traps. The formation energies of various defects are calculated by applying atomistic thermodynamics, identifying the growth conditions for promoting V_I and suppressing V_S formation. The HER performance is enhanced by forming interfaces with lower ΔG_H values for hydrogen adsorption on the MoS₂ side, suggesting PbI₂/MoS₂ with V_I to be the most promising photocatalyst.