A Metal-Organic-Framework-Derived g-C3N4/α-Fe2O3 Hybrid for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Evolution

As one of the most efficient systems for photocatalytic hydrogen evolution, the Z-Scheme system, consisting of different semiconductors with a reversible donor–acceptor pair, has attracted great attention. Considering the non-toxicity and low cost of photocatalysts, a series of g-C₃N₄/α-Fe₂O₃ hybrids were rationally constructed based on the Z-Scheme mechanism for the first time, using a metal-organic framework template approach that can fine tune the compositions and properties of the hybrids. An optimized hybrid, g-C₃N₄/α-Fe₂O₃-2, exhibited prominent photocatalytic water splitting performance with a visible light response. Under irradiation of visible light (λ>420 nm), the hybrid shows a high durability and superior hydrogen production rate of 2066.2 μmol g⁻¹ h⁻¹ from water splitting, which is approximately three times greater than that of bulk g-C₃N₄ because of the effective separation of photo-excited charge carriers by two narrow band gap semiconductors, tightly coupled with the Z-Scheme structural feature.     

Solar-Driven CO2 Conversion via Optimized Photothermal Catalysis in a Lotus Pod Structure

Photothermal CO₂ reduction is one of the most promising routes to efficiently utilize solar energy for fuel production at high rates. However, this reaction is currently limited by underdeveloped catalysts with low photothermal conversion efficiency, insufficient exposure of active sites, low active material loading, and high material cost. Herein, we report a potassium-modified carbon-supported cobalt (K⁺−Co−C) catalyst mimicking the structure of a lotus pod that addresses these challenges. As a result of the designed lotus-pod structure which features an efficient photothermal C substrate with hierarchical pores, an intimate Co/C interface with covalent bonding, and exposed Co catalytic sites with optimized CO binding strength, the K⁺−Co−C catalyst shows a record-high photothermal CO₂ hydrogenation rate of 758 mmol g_cat⁻¹ h⁻¹ (2871 mmol g_Co⁻¹ h⁻¹) with a 99.8 % selectivity for CO, three orders of magnitude higher than typical photochemical CO₂ reduction reactions. We further demonstrate with this catalyst effective CO₂ conversion under natural sunlight one hour before sunset during the winter season, putting forward an important step towards practical solar fuel production.     

Directional and Ultrafast Charge Transfer in Oxygen-Vacancy-Rich ZnO@Single-Atom Cobalt Core-Shell Junction for Photo-Fenton-Like Reaction

In photosynthesis, solar energy is harvested by photosensitizers, and then, the excited electrons transfer via a Z-Scheme mode to enzymatic catalytic centers to trigger redox reactions. Herein, we constructed a core–shell Z-scheme heterojunction of semiconductor@single-atom catalysts (SACs). The oxygen-vacancy-rich ZnO core and single-atom Co−N₄ sites supported on nitrogen-rich carbon shell (SA-Co-CN) act as the photosensitizer and the enzyme-mimicking active centers, respectively. Driven by built-in electric field across the heterojunction, photoexcited electrons could rapidly (2 ps) transfer from the n-type ZnO core to the p-type SA-Co-CN shell, finally boosting the catalytic performance of the surface-exposed single-atom Co−N₄ sites for peroxymonosulfate (PMS) activation under light irradiation. The synergies between photocatalysis and heterogeneous Fenton-like reaction lead to phenomenally enhanced production of various reactive oxygen species for rapid degradation of various microcontaminants in water. Experimental and theoretical results validate that the interfacial coupling of SA-Co-CN with ZnO greatly facilitates PMS adsorption and activation by reducing the adsorption energy and enhancing the cascade electron transfer processes for the photo-Fenton-like reaction.     

Production of Hydrogen Peroxide by Photocatalytic Processes

Hydrogen peroxide (H₂O₂) has received increasing attention because it is not only a mild and environmentally friendly oxidant for organic synthesis and environmental remediation but also a promising new liquid fuel. The production of H₂O₂ by photocatalysis is a sustainable process, since it uses water and oxygen as the source materials and solar light as the energy. Encouraging processes have been developed in the last decade for the photocatalytic production of H₂O₂. In this Review we summarize research progress in the development of processes for the photocatalytic production of H₂O₂. After a brief introduction emphasizing the superiorities of the photocatalytic generation of H₂O₂, the basic principles of establishing an efficient photocatalytic system for generating H₂O₂ are discussed, highlighting the advanced photocatalysts used. This Review is concluded by a brief summary and outlook for future advances in this emerging research field.     

Hydrogen activation on organometallic complexes and H2 production, utilization, and storage for future energy

This perspective article serves to highlight the contributions to this special volume of Journal of Organometallic Chemistry entitled “Organometallics for Energy Conversion”. The key features of dihydrogen coordination to transition metal complexes are discussed in the context of the challenge of producing and utilizing hydrogen as the energy carrier of the future. Ultimately, production of H₂ fuel from water will be needed rather than its current production principally from natural gas. Schemes involving use of solar energy to split water are currently of high interest, and a massive research effort is underway worldwide to accomplish this goal. This is primarily a chemistry problem (rather than engineering or materials), and it can then be assumed that organometallic chemistry will play an important role for both hydrogen production and storage.     

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 (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.     

Decoupling Hydrogen and Oxygen Production in Acidic Water Electrolysis Using a Polytriphenylamine‐Based Battery Electrode

Hydrogen production through water splitting is considered a promising approach for solar energy harvesting. However, the variable and intermittent nature of solar energy and the co‐production of H₂ and O₂ significantly reduce the flexibility of this approach, increasing the costs of its use in practical applications. Herein, using the reversible n‐type doping/de‐doping reaction of the solid‐state polytriphenylamine‐based battery electrode, we decouple the H₂ and O₂ production in acid water electrolysis. In this architecture, the H₂ and O₂ production occur at different times, which eliminates the issue of gas mixing and adapts to the variable and intermittent nature of solar energy, facilitating the conversion of solar energy to hydrogen (STH). Furthermore, for the first time, we demonstrate a membrane‐free solar water splitting through commercial photovoltaics and the decoupled acid water electrolysis, which potentially paves the way for a new approach for solar water splitting.     

Boosting Reactive Oxygen Species Generation Using Inter-Facet Edge Rich WO3 Arrays for Photoelectrochemical Conversion

Water oxidation reaction leaves room to be improved in the development of various solar fuel productions, because of the kinetically sluggish 4-electron transfer process of oxygen evolution reaction. In this work, we realize reactive oxygen species (ROS), H₂O₂ and OH⋅, formations by water oxidation with total Faraday efficiencies of more than 90 % by using inter-facet edge (IFE) rich WO₃ arrays in an electrolyte containing CO₃²⁻. Our results demonstrate that the IFE favors the adsorption of CO₃²⁻ while reducing the adsorption energy of OH⋅, as well as suppresses surface hole accumulation by direct 1-electron and indirect 2-electron transfer pathways. Finally, we present selective oxidation of benzyl alcohol by in situ using the formed OH⋅, which delivers a benzaldehyde production rate of ≈768 μmol h⁻¹ with near 100 % selectivity. This work offers a promising approach to tune or control the oxidation reaction in an aqueous solar fuel system towards high efficiency and value-added product.     

Surface modification of semiconductor photoelectrodes for better photoelectrochemical performance

The present paper describes the modification and solar hydrogen production studies employing a new semiconductor-septum (SC-SEP) photoelectrode ns-TiO₂/In₂O₃ based photoelectrochemical solar cell. The current-voltage characteristics of the above SC-SEP cell revealed that an enhancement in short-circuit current (I_SC) up to three times (5 ～ 14.6 mA cm^?2). The optimum hydrogen production rate was found to be 11.8 lh^?1 m^?2 for 5M H₂SO₄ and with a further increase in H₂SO₄ concentration, the hydrogen production rate was found to be invariant. In yet another part of our study instead of using new SC-SEP solar cell design, we used another new oxide material form such as ns-TiO₂/WO₃. The ns-TiO₂/WO₃ exhibited a high photocurrent and photo-voltage of 15.6 mA cm^?2, 960 mV, respectively. The ns-TiO₂/WO₃ electrode exhibited a higher hydrogen gas evolution rate of 13.8 lh^?1 m^?2. Evidences and arguments are put forward to show that, whereas for the bare ns-TiO₂ electrode, the improvement in the performance of this photo-electrode compared with its original form was due to the higher quantum yield. In the case of ns-TiO₂/In₂O₃ and ns-TiO₂/WO₃ photo-electrodes, the improvement is due to the improved spectral response resulting from decrease of energy band gap.     

Inorganic Photocatalysts for Overall Water Splitting

Photocatalytic water splitting using semiconductor photocatalysts has been considered as a “green” process for converting solar energy into hydrogen. The pioneering work on electrochemical photolysis of water at TiO₂ electrode, reported by Fujishima and Honda in 1972, ushered in the area of solar fuel. As the real ultimate solution for solar fuel‐generation, overall water splitting has attracted interest from researchers for some time, and a variety of inorganic photocatalysts have been developed to meet the challenge of this dream reaction. To date, high‐efficiency hydrogen production from pure water without the assistance of sacrificial reagents remains an open challenge. In this Focus Review, we aim to provide a whole picture of overall water splitting and give an outlook for future research.     

Artificial Mn4Ca Clusters with Exchangeable Solvent Molecules Mimicking the Oxygen‐Evolving Center in Photosynthesis

The natural Mn₄Ca cluster in photosystem II serves as a blueprint to develop artificial water‐splitting catalysts for the generation of solar fuel in artificial photosynthesis. Although significant advances have recently been achieved, it remains a great challenge to prepare robust artificial Mn₄Ca clusters that precisely mimic the structure and function of the biological catalyst. Herein, we report the isolation and structural characterization of two Mn₄CaO₄ complexes with polar solvent molecules, acetonitrile or N,N‐dimethylformamide, which closely mimics the two water molecules on the calcium ion, as well as the oxidation states of the four manganese ions and the main geometric structure of the natural Mn₄Ca cluster. These new artificial Mn₄Ca complexes provide important chemical clues to understand the structure and mechanism of the biological system.     

Well‐Defined Palladium Nanoparticles Supported on Siliceous Mesocellular Foam as Heterogeneous Catalysts for the Oxidation of Water

Herein, we describe the use of Pd nanoparticles immobilized on an amino‐functionalized siliceous mesocellular foam for the catalytic oxidation of H₂O. The Pd nanocatalyst proved to be capable of mediating the four‐electron oxidation of H₂O to O₂, both chemically and photochemically. The Pd nanocatalyst is easy to prepare and shows high chemical stability, low leaching, and recyclability. Together with its promising catalytic activity, these features make the Pd nanocatalyst of potential interest for future sustainable solar‐fuel production.     

Enhancement of Solar Fuel Production Schemes by Using a Ru,Rh,Ru Supramolecular Photocatalyst Containing Hydroxide Labile Ligands

Polyazine‐bridged Ru^IIRh^IIIRu^II complexes with two halide ligands, Cl^? or Br^?, bound to the catalytically active Rh center are efficient single‐component photocatalysts for H₂O reduction to H₂ fuel, with the coordination environment on Rh impacting photocatalysis. Herein reported is a new, halide‐free Ru^IIRh^IIIRu^II photocatalyst with OH^? ligands bound to Rh, further enhancing the photocatalytic reactivity of the structural motif. H₂ production experiments using the photocatalyst bearing OH^? ligands at Rh relative to the analogues bearing halides at Rh in solvents of varying polarity (DMF, CH₃CN, and H₂O) suggest that ion pairing with halides deactivates photocatalyst function, representing an exciting phenomenon to exploit in the development of catalysts for solar H₂ production schemes.     

Engineering a Copper Single-Atom Electron Bridge to Achieve Efficient Photocatalytic CO2 Conversion

Developing highly efficient and stable photocatalysts for the CO₂ reduction reaction (CO₂RR) remains a great challenge. We designed a Z-Scheme photocatalyst with N−Cu₁−S single-atom electron bridge (denoted as Cu-SAEB), which was used to mediate the CO₂RR. The production of CO and O₂ over Cu-SAEB is as high as 236.0 and 120.1 μmol g⁻¹ h⁻¹ in the absence of sacrificial agents, respectively, outperforming most previously reported photocatalysts. Notably, the as-designed Cu-SAEB is highly stable throughout 30 reaction cycles, totaling 300 h, owing to the strengthened contact interface of Cu-SAEB, and mediated by the N−Cu₁−S atomic structure. Experimental and theoretical calculations indicated that the SAEB greatly promoted the Z-scheme interfacial charge-transport process, thus leading to great enhancement of the photocatalytic CO₂RR of Cu-SAEB. This work represents a promising platform for the development of highly efficient and stable photocatalysts that have potential in CO₂ conversion applications.     

Boosting charge separation of BiVO4 photoanode modified with 2D metal-organic frameworks nanosheets for high-performance photoelectrochemical water splitting

Water splitting by photoelectrochemical (PEC) processes to convert solar energy into hydrogen energy using semiconductors is regarded as one of the most ideal methods to solve the current energy crisis and has attracted widespread attention. Herein, Co-based metal-organic framework (Co(bpdc)(H₂O)₄ (Co-MOF) nanosheets as passivation layers were in-situ constructed on the surface of BiVO₄ films through an uncomplicated hydrothermal method (Co-MOF/BiVO₄). Under AM 1.5G illumination, synthesized Co-MOF/BiVO₄ electrode exhibited a 4-fold higher photocurrent than bare BiVO₄, measuring 6.0 mA/cm² at 1.23 V vs. RHE in 1 mol/L potassium borate electrolyte (pH 9.5) solution. Moreover, the Co-MOF/BiVO₄ film demonstrated a 96% charge separation efficiency, a result caused by an inhibited recombination rate of photogenerated electrons and holes by the addition of Co-MOF nanosheets. This work provides an idea for depositing inexpensive 2D Co-MOF nanosheets on the photoanode as an excellent passivation layer for solar fuel production.     

Freeing the Polarons to Facilitate Charge Transport in BiVO4 from Oxygen Vacancies with an Oxidative 2D Precursor

The BiVO₄ photoelectrochemical (PEC) electrode in tandem with a photovoltaic (PV) cell has shown great potential to become a compact and cost‐efficient device for solar hydrogen generation. However, the PEC part is still facing problems such as the poor charge transport efficiency owing to the drag of oxygen vacancy bound polarons. In the present work, to effectively suppress oxygen vacancy formation, a new route has been developed to synthesize BiVO₄ photoanodes by using a highly oxidative two‐dimensional (2D) precursor, bismuth oxyiodate (BiOIO₃), as an internal oxidant. With the reduced defects, namely the oxygen vacancies, the bound polarons were released, enabling a fast charge transport inside BiVO₄ and doubling the performance in tandem devices based on the oxygen vacancy eliminated BiVO₄. This work is a new avenue for elaborately designing the precursor and breaking the limitation of charge transport for highly efficient PEC‐PV solar fuel devices.     

Modification strategies of TiO2 for potential applications in photocatalysis: a critical review

TiO₂ has received tremendous attention owing to its potential applications in the field of photocatalysis for solar fuel production and environmental remediation. This review mainly describes various modification strategies and potential applications of TiO₂ in efficient photocatalysis. In past few years, various strategies have been developed to improve the photocatalytic performance of TiO₂, including noble metal deposition, elemental doping, inorganic acids modification, heterojunctions with other semiconductors, dye sensitization and metal ion implantation. The enhanced photocatalytic activities of TiO₂-based material for CO₂ conversion, water splitting and pollutants degradation are highlighted in this review.     

Integration of Nine Steps into One Membrane Reactor To Produce Synthesis Gases for Ammonia and Liquid Fuel

The synthesis of ammonia and liquid fuel are two important chemical processes in which most of the energy is consumed in the production of H₂/N₂ and H₂/CO synthesis gases from natural gas (methane). Here, we report a membrane reactor with a mixed ionic‐electronic conducting membrane, in which the nine steps for the production of the two types of synthesis gases are shortened to one step by using water, air, and methane as feeds. In the membrane reactor, there is no direct CO₂ emission and no CO or H₂S present in the ammonia synthesis gas. The energy consumption for the production of the two synthesis gases can be reduced by 63 % by using this membrane reactor. This promising membrane reactor process has been successfully demonstrated by experiment.     

Photosynthetic hydrogen production

Among various technologies for hydrogen production, the use of oxygenic natural photosynthesis has a great potential as can use clean and cheap sources—water and solar energy. In oxygenic photosynthetic microorganisms electrons and protons produced from water and redirected by the photosynthetic electron-transport chain via ferredoxin to the hydrogen-producing enzymes hydrogenase or nitrogenase. By these enzymes, e^? and H⁺ recombine and form molecular hydrogen. Hydrogenase activity can be very high but is extremely sensitive to the photosynthetically evolved O₂ that leads to reduced and unstable H₂ production. However, presently, several approaches are developed to improve the energetic efficiency to generate H₂. This review examines the main available pathways to improve the photosynthetic H₂ production.     

Prolonged Hot Electron Dynamics in Plasmonic‐Metal/Semiconductor Heterostructures with Implications for Solar Photocatalysis

Ideal solar‐to‐fuel photocatalysts must effectively harvest sunlight to generate significant quantities of long‐lived charge carriers necessary for chemical reactions. Here we demonstrate the merits of augmenting traditional photoelectrochemical cells with plasmonic nanoparticles to satisfy these daunting photocatalytic requirements. Electrochemical techniques were employed to elucidate the mechanics of plasmon‐mediated electron transfer within Au/TiO₂ heterostructures under visible‐light (λ>515 nm) irradiation in solution. Significantly, we discovered that these transferred electrons displayed excited‐state lifetimes two orders of magnitude longer than those of electrons photogenerated directly within TiO₂ via UV excitation. These long‐lived electrons further enable visible‐light‐driven H₂ evolution from water, heralding a new photocatalytic paradigm for solar energy conversion.