Exceptional Photocatalytic Hydrogen Peroxide Production from Sandwich-Structured Graphene Interlayered Phenolic Resins Nanosheets with Mesoporous Channels

Harnessing solar energy to produce hydrogen peroxide (H₂O₂) from water (H₂O) and dioxygen (O₂) via artificial photosynthesis is an attractive route. To achieve high solar-to-H₂O₂ conversion efficiency, herein, an interfacial self-assembly strategy is adopted to pattern mesoporous resorcinol-formaldehyde resin (MRF) onto reduced graphene oxide (rGO) to form sandwich-structured rGO@MRF polymeric photocatalysts. The internal graphene layer that mimics the electron transport chain of plant leaf, can effectively transfer electrons, and promote the two-electron reduction of O₂. Moreover, the mesoporous channels mimic the stomata, beneficially boost the fluid velocity, enrichment of O₂, and diffusion of H₂O₂. Consequently, the developed metal-free material can achieve an exceptional solar-to-chemical energy conversion efficiency of 1.23%. This ingenious interface engineering brings new opportunities for the design of efficient artificial photocatalysts.     

Enhanced Hydrogen Production by Photoreforming of Renewable Oxygenates Through Nanostructured Fe2O3 Polymorphs

Sunlight‐driven hydrogen production via photoreforming of aqueous solutions containing renewable compounds is an attractive option for sustainable energy generation with reduced carbon footprint. Nevertheless, the absence of photocatalysts combining high efficiency and stability upon solar light activation has up to date strongly hindered the development of this technology. Herein, two scarcely investigated iron(III) oxide polymorphs, β‐ and ε‐Fe₂O₃, possessing a remarkable activity in sunlight‐activated H₂ generation from aqueous solutions of renewable oxygenates (i.e., ethanol, glycerol, glucose) are reported. For β‐Fe₂O₃ and ε‐Fe₂O₃, H₂ production rates up to 225 and 125 mmol h^?1 m^?2 are obtained, with significantly superior performances with respect to the commonly investigated α‐Fe₂O₃.     

Interfacial Modulation with Aluminum Oxide for Efficient Plasmon-Induced Water Oxidation

Plasmon-induced photocatalysts hold great promise for solar energy conversion owing to their strong light-harvesting ability and tunable optical properties. However, the complex process of interfacial extraction of hot carriers and the roles of metal/semiconductor interfaces in plasmonic photocatalysts are still not clearly understood. Herein, the manipulation of the interface between a plasmon metal (Au) and a semiconductor (rutile TiO₂) by introducing an interfacial metal oxide (Al₂O₃) is reported. The resulting Au/Al₂O₃/TiO₂ exhibits remarkable enhancement in photocatalytic water oxidation activity compared with Au/TiO₂, giving an apparent quantum efficiency exceeding 1.3% at 520 nm for photocatalytic water oxidation. Such an interfacial modulation approach significantly prolongs the lifetime of hot carriers in the Au/TiO₂ system, which conclusively improves the utilization of hot carriers for plasmon-induced water oxidation reaction upon irradiation. This work emphasizes the essential role of the interfacial structure in plasmonic devices and provides an alternative method for designing efficient plasmonic photocatalysts for solar energy conversion.     

Black Phosphorus and Polymeric Carbon Nitride Heterostructure for Photoinduced Molecular Oxygen Activation

Metal‐free heterostructure photocatalysts composed of black phosphorus (BP) and polymeric carbon nitride (CN) are successfully synthesized via a one‐step liquid exfoliation method assisted by sonication. The combination of BP with CN strengthens the visible‐light harvesting ability, facilitates the charge separation in the photocatalytic process, and renders promoted activity of photoinduced molecular oxygen activation, such as superoxide radicals (·O₂^?) evolution and H₂O₂ production. This work highlights that coupling semiconductors with well‐matched band levels provide a flexible route to enhance the performance of photocatalysts for producing reactive oxygen species, and gives ideas for the design of highly active and metal‐free materials toward sustainable solar‐to‐chemical energy conversion and environmental remediation.     

Oxygen Vacant Semiconductor Photocatalysts

Semiconductor photocatalysis acts as a sustainable green technology to convert solar energy for environmental purification and production of renewable energy. However, the current photocatalysts suffer from inefficient photoabsorption, rapid recombination of photogenerated electrons and holes, and inadequate surface reactive sites. Introduction of oxygen vacancies (OVs) in photocatalysts has been demonstrated to be an efficacious strategy to solve these issues and improve photocatalytic efficiency. This review systematically summarizes the recent progress in the oxygen vacant semiconductor photocatalysts. Firstly, the formation and characterizations of OVs in semiconductor photocatalysts are briefly introduced. Then, highlighted are the roles of OVs in the photocatalytic reactions of three types of typical oxygen-containing semiconductors, including metal oxides (TiO₂, ZnO, WO₃, W₁₈O₄₉, MoO₃, BiO_2-x, SnO₂, etc), hydroxides (In(OH)₃, Ln(OH)₃ (Ln=La, Pr, and Nd), Layered double hydroxides) and oxysalts (bismuth-based oxysalts and others) photocatalysts. Moreover, the advanced photocatalytic applications of oxygen vacant semiconductor photocatalysts, such as pollutant removal, H₂ production, CO₂ reduction, N₂ fixation and organic synthesis are systematically summarized. Finally, an overview on the current challenges and a prospective on the future of oxygen vacant materials is proposed.     

Versatile Graphene‐Promoting Photocatalytic Performance of Semiconductors: Basic Principles,Synthesis, Solar Energy Conversion,and Environmental Applications

Graphene‐semiconductor nanocomposites, considered as a kind of most promising photocatalysts, have shown remarkable performance and drawn significant attention in the field of photo‐driven chemical conversion using solar energy, due to the unique physicochemical properties of graphene. The photocatalytic enhancement of graphene‐based nanocomposites is caused by the reduction of the recombination of electron‐hole pairs, the extension of the light absorption range, increase of absorption of light intensity, enhancement of surface active sites, and improvement of chemical stability of photocatalysts. Recent progress in the photocatalysis development of graphene‐based nanocomposites is highlighted and evaluated, focusing on the mechanism of graphene‐enhanced photocatalytic activity, the understanding of electron transport, and the applications of graphene‐based photocatalysts on water splitting, degradation or oxidization of organic contaminants, photoreduction of CO₂ into renewable fuels, toxic elimination of heavy metal ions, and antibacterial applications.     

Covalent Furan-Benzimidazole-Linked Polymer Hollow Fiber Membrane for Clean and Efficient Photosynthesis of Hydrogen Peroxide

Photocatalytic H₂O₂ production by conversion of O₂ in aqueous solution is often challenged by the use of sacrificial agents, the separation of powdery photocatalysts, solution, and contaminants, and low activity of photocatalyst. Herein, a membrane of covalent furan-benzimidazole-linked polymer (Furan-BILP) with both O- and N-containing heterocycles bonded via O C CN is reported for the first time as a photocatalyst to harvest clean H₂O₂ in pure water with high-performance. A coordination-polymer hard template strategy is developed to produce Furan-BILP hollow microfibers that can be further assembled into membranes with desired sizes. The resultant Furan-BILP membrane directly delivers clean H₂O₂ solution as the product with a high H₂O₂ production rate of 2200 µmol g⁻¹ h⁻¹ in pure water. Density functional theory calculations and experiment results indicate that the C atom from Furan ring on the linkage binds to the adsorbed OOH^*, the H atom of OOH^* forms a hydrogen bond with the N atom in the benzimidazole ring, thus the intermediate six-membered ring structure stabilizes the OOH^* and favors 2e-ORR. The strategy using both molecular engineering to tune the electronic structure and macrostructural engineering to shape the morphology may be applied to design other coordination organic polymer photocatalysts with further improved performance.     

Optical and Electrical Enhancement of Hydrogen Evolution by MoS2@MoO3 Core–Shell Nanowires with Designed Tunable Plasmon Resonance

The design of transition‐metal chalcogenides (TMCs) photocatalysts for water splitting is highly important, in which both light absorption and interfacial engineering play vital roles in photoexcited electron generation, electron transport, and ultimately speeding up water splitting. To this end, plasmonic metal nanomaterials with surface plasmon resonances are promising candidates. However, it is very difficult to enhance the light absorption and manage the interfacial engineering simultaneously, thus, resulting in suboptimal photocatalytic performance. Here, a doped semiconductor plasmon is proposed to optically and electrically enhance TMCs hydrogen evolution. With the tunability of plasmon resonance in a doped MoO₃ semiconductor via hydrogen reduction, the broadband absorption and good interfacial engineering are simultaneously demonstrated in flexible MoS₂@MoO₃ core–shell nanowire photocatalysts. Better energy‐band alignment with MoS₂ can also be realized, thereby achieving improved photoinduced electron generation. More importantly, the defects at the interface between MoO₃ and MoS₂ are effectively reduced because of precise tunability of plasmon resonance, which enhances electron transport. As a proof of concept, this optimized hybrid nanostructure exhibits outstanding H₂ evolution characteristics (841.4 μmol h^?1 g^?1), excellent stability, and good flexibility. The value is also one of the highest hydrogen evolution activity rates to date among the two dimensional‐layered visible‐light photocatalysts.     

Covalent Organic Frameworks Based Heterostructure in Solar-To-Fuel Conversion

Photocatalytic reactions for fuel generation are crucial for the world's energy needs. Covalent-Organic-Frameworks (COFs) have been extensively studied as promising designable photocatalysts for these reactions due to their efficient visible-light absorption, suitable energy-band structure, facilitated intramolecular charge separation, and fast mass transfer. However, the activities of pristine COFs remain unsatisfactory, due to intermolecular charge recombination. Recently, COF-based heterostructures, which combine COFs with metal-sulfides, metal-oxides, carbon materials, or MOFs, have attracted increasing attention for enhancing solar-to-fuel conversion efficiency by facilitating interfacial photo-generated carrier separation, sensitizing wide-gap semiconductors, and promoting surface redox reactions. Thus, a review of the state-of-the-art progress of COF-based heterostructure photocatalysts in reactions such as H₂ evolution, CO₂ reduction, O₂ evolution, H₂O splitting and CO₂ splitting is crucial for the design of new photocatalysts to promote solar-to-fuel conversion. In this review, the COF-based heterostructures photocatalysts are highlighted based on their synthesis, properties, and reasons for enhanced activities. Moreover, design principles are raised for such photocatalysts for each fuel generation reaction, based on insights into related research. Finally, this review is concluded by proposing future trends for COF-based heterostructures photocatalysts, with attention to the design of COFs and supports, analyzing the photocatalytic reaction dynamics, together with considering practical applications.     

Defective Photocathode: Fundamentals,Construction, and Catalytic Energy Conversion

The development of a long-term and sustainable energy economy is one of the most significant technological challenges facing humanity. Photoelectrochemical (PEC) technology is considered as the most attractive route for converting solar energy into chemical energy. However, the slow reaction kinetics of PEC oxidation and reduction greatly hinder its practical application. To address this issue, engineering photoelectrodes with various defects can significantly improve their catalytic performance, which can not only regulate catalyst electronic structure but also promote charge transfer/separation by serving as an active/adsorption/energy storage site. Herein, the defect engineering strategies for photoelectrodes are systematically summarized, focusing on the latest progress in defective photocathode for energy conversion. First, an overview of defect types, basic principles of photocathode, and the positive role of defects in the photocathode are provided. Second, the construction strategies and characterization methods of defective photocathode are summarized. Then, the progress of typical energy conversion applications, including hydrogen production, CO₂ reduction, and nitrogen reduction over defective photocathode, is reviewed, highlighting the crucial role of defects in high catalytic performance. Finally, the challenges and future prospects of defective photocathode are discussed, aiming to bring new opportunities for the development of photocathode through defect engineering.     

Atomistic Structural Engineering of Conjugated Microporous Polymers Promotes Photocatalytic Biomass Valorization

Polymer photocatalysts have great promise for solar fuel production due to their flexible structural and functional designability. However, their photocatalytic efficiencies are still unsatisfactory, limited by their intrinsically large exciton binding energy and fast charge recombination. Herein, the atomistic structural engineering of donor–acceptor (D−A) polymer photocatalysts for enhanced charge separation and photocatalytic hydrogen production is proposed. By changing the electron affinity of the acceptor units, the electron delocalization and exciton binding energy of the polymeric networks can be readily tuned, resulting in enhanced charge separation efficiency and photocatalytic activity. The optimal sample shows the highest H₂ production rate of 3207 µmol g⁻¹ h⁻¹ in the presence of ascorbic acid as the sacrificial agent. Moreover, the photocatalytic H₂ production can be coupled with almost stoichiometrical conversion of 5-hydroxymethyl furfural to 2,5-diformylfuran.     

Fabrication of Black In2O3 with Dense Oxygen Vacancy through Dual Functional Carbon Doping for Enhancing Photothermal CO2 Hydrogenation

Photothermocatalytic CO₂ reduction as the channel of the energy and environmental issues resolution has captured persistent attention in recent years. In₂O₃ has been prompted to be a potential photothermal catalyst in this sector on account of its unique physicochemical properties. However, different from the metal-based photothermal catalyst with the nature of efficient light-to-thermal conversion and H₂ dissociation, the wide-bandgap semiconductor needs to be modified to possess wide-wavelength-range absorption and the active surface. It remains a challenge to achieve the two aims simultaneously via a single material modulation approach. In this study, one strategy of carbon doping can empower In₂O₃ with two advantageous modifications. Carbon doping can reduce the formation energy of oxygen vacancy, which induces the generation of oxygen-vacancy-riched material. The introduction of oxygen defect levels and carbon doping levels in the bandgap of In₂O₃ significantly reduces this bandgap, which endows it full-spectral and intensive solar light absorption. Therefore, the carbon doped In₂O₃ achieves effective light-to-thermal conversion and delivers a 123.6 mmol g^–1 h^–1 of CO generation rate with near-unity selectivity, as well as prominent stability in photothermocatalytic CO₂ reduction.     

Photosystem I‐based Biophotovoltaics on Nanostructured Hematite

The electronic coupling between a robust red algal photosystem I (PSI) associated with its light harvesting antenna (LHCI) and nanocrystalline n‐type semiconductors, TiO₂ and hematite (α‐Fe₂O₃) is utilized for fabrication of the biohybrid dye‐sensitized solar cells (DSSC). PSI‐LHCI is immobilized as a structured multilayer over both semiconductors organized as highly ordered nanocrystalline arrays, as evidenced by FE‐SEM and XRD spectroscopy. Of all the biohybrid DSSCs examined, α‐Fe₂O₃/PSI‐LHCI biophotoanode operates at a highest quantum efficiency and generates the largest open circuit photo­current compared to the tandem system based on TiO₂/PSI‐LHCI material. This is accomplished by immobilization of the PSI‐LHCI complex with its reducing side towards the hematite surface and nanostructuring of the PSI‐LHCI multilayer in which the subsequent layers of this complex are organized in the head‐to‐tail orientation. The biohybrid PSI‐LHCI‐DSSC is capable of sustained photoelectrochemical H₂ production upon illumination with visible light above 590 nm. Although the solar conversion efficiency of the PSI‐LHCI/hematite DSSC is currently below a practical use, the system provides a blueprint for a genuinely green solar cell that can be used for molecular hydrogen production at a rate of 744 μmoles H₂ mg Chl^?1 h^?1, placing it amongst the best performing biohybrid solar‐to‐fuel nanodevices.     

Hierarchical NiCo2S4 Nanowire Arrays Supported on Ni Foam: An Efficient and Durable Bifunctional Electrocatalyst for Oxygen and Hydrogen Evolution Reactions

A recent approach for solar‐to‐hydrogen generation has been water electrolysis using efficient, stable, and inexpensive bifunctional electrocatalysts within strong electrolytes. Herein, the direct growth of 1D NiCo₂S₄ nanowire (NW) arrays on a 3D Ni foam (NF) is described. This NiCo₂S₄ NW/NF array functions as an efficient bifunctional electrocatalyst for overall water splitting with excellent activity and stability. The 3D‐Ni foam facilitates the directional growth, exposing more active sites of the catalyst for electrochemical reactions at the electrode–electrolyte interface. The binder‐free, self‐made NiCo₂S₄ NW/NF electrode delivers a hydrogen production current density of 10 mA cm^–2 at an overpotential of 260 mV for the oxygen evolution reaction and at 210 mV (versus a reversible hydrogen electrode) for the hydrogen evolution reaction in 1 m KOH. This highly active and stable bifunctional electrocatalyst enables the preparation of an alkaline water electrolyzer that could deliver 10 mA cm^–2 under a cell voltage of 1.63 V. Because the nonprecious‐metal NiCo₂S₄ NW/NF foam‐based electrodes afford the vigorous and continuous evolution of both H₂ and O₂ at 1.68 V, generated using a solar panel, they appear to be promising water splitting devices for large‐scale solar‐to‐hydrogen generation.     

Ruthenium Oxide Hydrogen Evolution Catalysis on Composite Cuprous Oxide Water‐Splitting Photocathodes

Photocathodes based on cuprous oxide (Cu₂O) are promising materials for large scale and widespread solar fuel generation due to the abundance of copper, suitable bandgap, and favorable band alignments for reducing water and carbon dioxide. A protective overlayer is required to stabilize the Cu₂O in aqueous media under illumination, and the interface between this overlayer and the catalyst nanoparticles was previously identified as a key source of instability. Here, the properties of the protective titanium dioxide overlayer of composite cuprous oxide photocathodes are further investigated, as well as an oxide‐based hydrogen evolution catalyst, ruthenium oxide (RuO₂). The RuO₂‐catalyzed photoelectrodes exhibit much improved stability versus platinum nanoparticles, with 94% stability after 8 h of light‐chopping chronoamperometry. Faradaic efficiencies of ～100% are obtained as determined by measurement of the evolved hydrogen gas. The sustained photocurrents of close to 5 mA cm^?2 obtained with this electrode during the chronoamperometry measurement (at 0 V vs. the reversible hydrogen electrode, pH 5, and simulated 1 sun illumination) would correspond to greater than 6% solar‐to‐hydrogen conversion efficiency in a tandem photoelectrochemical cell, where the bias is provided by a photovoltaic device such as a dye‐sensitized solar cell.     

Manipulation of light harvesting for efficient dye‐sensitized solar cell by doping an ultraviolet light‐capturing fluorophore

An organic fluorophore is doped into a mesoporous TiO₂ photoelectrode to absorb ultraviolet light and convert it to green light for more efficient light harvesting of N719 dye. This fluorescence conversion enables the absorption of additional green light by dye molecules by means of Förster resonance energy transfer between fluorescent compound donor and N719 dye acceptor. Owing to close fit between the emission peak of fluorophore and the absorption peak of N719 dye, the Förster resonance energy transfer effect enhances the incident photon to current conversion efficiency of the dye‐sensitized solar cells based on fluorophore‐doped TiO₂ photoelectrodes. Improved power conversion efficiency (8.03–8.13%) is also achieved for the fluorophore‐doped (10⁻⁴ M) dye‐sensitized solar cells compared with a cell without the doping of fluorophore (7.63%). Copyright © 2013 John Wiley & Sons, Ltd.     

CdIn2S4 Nanotubes and “Marigold” Nanostructures: A Visible‐Light Photocatalyst

Nanostructured photocatalysts with high activity are sought for solar production of hydrogen. Spinel semiconductors with different nanostructures and morphologies have immense importance for photocatalytic and other potential applications. Here, a chemically stable cubic spinel nanostructured CdIn₂S₄ prepared by a facile hydrothermal method is reported as a visible‐light driven photocatalyst. A pretty, marigold‐like morphology is observed in aqueous‐mediated CdIn₂S₄, whereas nanotubes of good crystallinity, 25 nm in diameter, are obtained in methanol‐mediated CdIn₂S₄. The aqueous‐ and methanol‐mediated CdIn₂S₄ products show excellent photocatalytic activity compared to other organic mediated samples, and this is attributed to their high degree of crystallinity. The CdIn₂S₄ photocatalyst gives quantum yields of 16.8 % (marigold‐like morphology) and 17.1 % (nanotubes) at 500 nm, respectively, for the H₂ evolution reaction. The details of the characteristics of the photocatalyst, such as crystal and band structure, are reported. Considering the importance of hydrogen energy, CdIn₂S₄ will be an excellent candidate as a catalyst for “photohydrogen” production under visible light. Being a nanostructured chalcogenide semiconductor, CdIn₂S₄ will have other potential prospective applications, such as in solar cells, light‐emitting diodes, and optoelectronic devices.     

Hybridized Nanowires and Cubes: A Novel Architecture of a Heterojunctioned TiO2/SrTiO3 Thin Film for Efficient Water Splitting

A unique morphology of SrTiO₃ nanocubes precipitated on TiO₂ nanowires is successfully synthesized in the form of a thin‐film heterojunctioned TiO₂/SrTiO₃ photocatalyst using facile hydrothermal techniques. The formation mechanisms of the synthesized photocatalysts are meticulously studied and described. Growth of SrTiO₃ single crystal nanocubes (≈50 nm in width) on anatase polycrystalline nanowires follows an in situ dissolution‐precipitation pathway. This is consonant with the classic LaMer model. By analyzing the results of field emission scanning electron microscopy (FESEM), field emission transmission electron microscopy (FETEM), X‐ray diffraction (XRD), energy dispersive X‐ray (EDX) spectroscopy, X‐ray photoelectron spectroscopy (XPS), and UV‐vis spectrophotometry, a comprehensive structural and morphological characterization of the photocatalysts is established. FESEM images reveal that the anatase film comprises mainly of nanowires bristles while the tausonite film is primarily made up of nanocube aggregations. In comparison to the respective pristine semiconductor photocatalysts, the heterostructured photocatalyst demonstrates the highest efficiency in photocatalytic splitting of water to produce H₂, 4.9 times that of TiO₂ and 2.1 times that of SrTiO₃. The enhanced photocatalytic efficiency is largely attributed to the efficient separation of photogenerated charges at heterojunctions of the two dissimilar semiconductors, as well as a negative redox potential shift in the Fermi level.     

Novel Composites of α‐Fe2O3 Tetrakaidecahedron and Graphene Oxide as an Effective Photoelectrode with Enhanced Photocurrent Performances

Novel composites composed of α‐Fe₂O₃ tetrakaidecahedrons and graphene oxide have been easily fabricated and demonstrated to be efficient photoelectrodes for photoelectrochemical water splitting reaction with superior photocurrent response. α‐Fe₂O₃ tetrakaidecahedrons are facilely synthesized in a green manner without any organic additives and then modified with graphene oxide. The morphological and structural properties of α‐Fe₂O₃/graphene composite are intensively investigated by several means, such as X‐ray diffraction, field‐emission scanning electron microscope, transmission electron microscope, X‐ray photoelectron spectroscopy, Fourier Transform infrared spectroscopy, and Raman spectroscopy. The tetrakaidecahedronal hematite particles have been indicated to be successfully coupled with graphene oxide. Systematical photoelectrochemical and impedance spectroscopy measurements have been carried out to investigate the favorable performance of α‐Fe₂O₃/graphene composites, which are found to be effective photoanodes with rapid, steady, and reproducible feature. The coupling of graphene with α‐Fe₂O₃ particles has greatly enhanced the photoelectrochemical performance, resulting in higher photocurrent and lower onset potential than that of pure α‐Fe₂O₃. This investigation has provided a feasible method to synthesize α‐Fe₂O₃ tetrakaidecahedron and fabricate an efficient α‐Fe₂O₃/graphene photoelectrode for photoelectrochemical water oxidation, suggesting a promising route to design noble metal free semiconductor/graphene photocatalysts.     

Facile “Spot‐Heating” Synthesis of Carbon Dots/Carbon Nitride for Solar Hydrogen Evolution Synchronously with Contaminant Decomposition

The use of solar energy to produce the clean hydrogen (H₂) energy from water splitting is a promising means of renewable energy conversion. High activation barriers for O₂ generation associated with the rate‐limiting steps require utilization of noble metal‐based cocatalysts, which complicates the fabrication procedure and compromises the stability of the catalyst. Here, a homogenous “spot heating” approach is designed via the ultrasonic cavitation effect for evenly embedding highly crystalline carbon quantum dots (CQDs) on 2D C₃N₄ nanosheets. Based on density functional calculations and electrochemical experiments, the optimal introduction of CQDs into C₃N₄ not only extends light absorption spectrum, but also reduces effective mass of electrons (e^?), facilitating photocarrier transport from excited sites. And, more importantly, the well‐organized CQDs with superior peroxidase mimetic activity can increase catalytic H₂ production through the process of (i) 2H₂O → H₂O₂ + H₂; (ii) H₂O₂→2 ? OH; (iii) ?OH + bisphenol A→ Final Products, with H₂ production rate (152 µmol g^?1 h^?1) several times higher than that for pure C₃N₄. This work demonstrates an ideal platform for efficient H₂ production with synergetic organic contaminant degradation, thereby opening possibilities for coupling energy conversion with environmental remediation.