Efficient Photoelectrochemical Conversion of Methane into Ethylene Glycol by WO 3 Nanobar Arrays

Photoelectrochemical Conversion of Methane to Ethane and Hydrogen under Visible Light Using Functionalized Tungsten Trioxide Photoanodes with Proton Exchange Membrane

Developing methane utilization technologies is desired to convert abundant and renewable carbon resources, such as natural gas and biogas, into value-added chemical products. This study provides insights into emerging photoelectrochemical (PEC) technology for the photocatalytic transformation of methane to C2H6 and H2 using visible light at room temperature. The PEC conversion of methane to oxygenates has been investigated in aqueous electrolytes. Herein, we demonstrate the gas-phase PEC methane conversion using a proton exchange membrane (PEM) as a solid polymer electrolyte and a gas-diffusion photoanode for methane oxidation. Tungsten trioxide (WO3), a semiconductor photocatalyst responsive to visible light, is utilized as the photoanode material. Ultraviolet light (∼365 nm) excitation predominantly results in CO2 production with lower C2H6 selectivity in humidified methane. In contrast, visible light (∼453 nm) effectively promotes C2H6 production over the WO3 photoanode, attributed to preferential hydroxyl radical (•OH) formation compared to UV irradiation. Photogenerated holes formed near the valence band maximum of WO3 contribute to •OH formation through a single-electron water oxidation. The photogenerated •OH activates gaseous methane molecules to methyl radicals, subsequently coupled into C2H6 at the gas-electrolyte-semiconductor boundary. H2 is concurrently formed on the cathode electrocatalyst. Improving the selectivity for the dehydrogenative coupling of methane is pivotal for enhancing the energy efficiency in the PEM-PEC system.

Defect Engineering of WO3 by Rapid Flame Reduction for Efficient Photoelectrochemical Conversion of Methane into Liquid Oxygenates

Photoelectrochemical (PEC) conversion is a promising way to use methane (CH4) as a chemical building block without harsh conditions. However, the PEC conversion of CH4 to value-added chemicals remains challenging due to the thermodynamically favorable overoxidation of CH4. Here, we report WO3 nanotube (NT) photoelectrocatalysts for PEC CH4 conversion with high liquid product selectivity through defect engineering. By tuning the flame reduction treatment, we carefully controlled the oxygen vacancies of WO3 NTs. The optimally reduced WO3 NTs suppressed overoxidation of CH4 showing a high total C1 liquid selectivity of 69.4% and a production rate of 0.174 μmol cm-2 h-1. Scanning electrochemical microscopy revealed that oxygen vacancies can restrain the production of hydroxyl radicals, which, in excess, could further oxidize C1 intermediates to CO2. Additionally, band diagram analysis and computational studies elucidated that oxygen vacancies thermodynamically suppress overoxidation. This work introduces a strategy for understanding and controlling the selectivity of photoelectrocatalysts for direct conversion of CH4 to liquids.

Photocatalytic degradation performance of antibiotics by WO3/α-Fe2O3/zeolite type II heterojunction with core-shell structure

The accumulation of antibiotics in the environment can be harmful to human health, and research on their disposal technologies is of increasing interest. In this study, WO3/α-Fe2O3/zeolite (WFZ) type II heterojunction composites with core-shell structures were prepared by coupling WO3 semiconductors with visible-light photocatalytic activity with α-Fe2O3 via hydrothermal synthesis using zeolite as a carrier for the adsorption of synergistic photocatalytic degradation of antibiotics in wastewater. X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), specific surface, and porosity measurements were used to characterize the structure of WFZ type II heterojunction. The performance of WFZ heterojunction for the visible photocatalytic degradation of antibiotics (tetracycline hydrochloride (TCH), ciprofloxacin (CIP), and levofloxacin hydrochloride (LVF)) was investigated. Through four photocatalytic cycles, the catalyst exhibited excellent durability and stability. This was attributed to the core-shell structure and type II heterojunction promoting the effective separation of photogenerated carriers and the extended visible light response range, which resulted in the best photocatalytic activity of the catalyst under visible light irradiation. Radical trapping experiments showed that superoxide radicals (•O2-) and hydroxyl radical (•OH) were the main active species that played a major role in the photocatalytic degradation. These findings show that the synthesized WFZ type-II heterojunction can be used as a reliable visible-light-responsive photocatalyst for the treatment of antibiotics in wastewater.

Covalent organic frameworks bearing Ni active sites for free radical-mediated photoelectrochemical organic transformations

Photoelectrochemical (PEC) organic transformations occurring at anodes are a promising strategy for circumventing the sluggish kinetics of the oxygen evolution reaction. Here, we report a free radical-mediated reaction instead of direct hole transfer occurring at the solid/liquid interface for PEC oxidation of benzyl alcohol (BA) to benzaldehyde (BAD) with high selectivity. A bismuth vanadate (BiVO4) photoanode coated with a 2,2'-bipyridine-based covalent organic framework bearing single Ni sites (Ni-TpBpy) was developed to drive the transformation. Experimental studies reveal that the reaction at the Ni-TpBpy/BiVO4 photoanode followed first-order reaction kinetics, boosting the formation of surface-bound ·OH radicals, which suppressed further BAD oxidation and provided a nearly 100% selectivity and a rate of 80.63 μmol hour-1 for the BA-to-BAD conversion. Because alcohol-to-aldehyde conversions are involved in the valorizations of biomass and plastics, this work is expected to open distinct avenues for producing key intermediates of great value.

Mild Methane Electrochemical Oxidation Boosted via Plasma Pre-Activation

Obtaining partial methane oxidation reaction (MOR) with various oxygenates via a mild electrochemical method is practically difficult because of activation of stable C─H bond and consequent reaction pathway regulation. Here, a real-time tandem MOR with cascaded plasma and electrocatalysis to activate and convert the methane (CH4 ) synergistically is reported for the first time. Boosted CH4 conversion is demonstrated toward value-added products including, alcohols, carboxylates, and ketone via use of commercial Pd-based electrocatalysts. Compared with hash industrial processes, a mild condition, that is, anode potential < 1.0 V versus RHE (reversible hydrogen electrode) is used that mitigates overoxidation of oxygenates and obviates competing reaction(s). One evidence that Pd(II) sites and surface adsorbed hydroxyls are important in facilitating activated-CH4 species conversion, and establish a reaction mechanism for conversion(s) that involves coupling reactions between adsorbed hydroxyls, carbon monoxide and C1 /C2 alkyls. One conclude that pre-activation is important in boosting electrochemical partial MOR under mild conditions and will be of benefit in the development of sustainable CH4 conversion technology.

Electron-Delocalization-Stabilized Photoelectrocatalytic Coupling of Methane by NiO-Polyoxometalate Sub-1 nm Heterostructures

The oxidative coupling of methane to C2 oxygenates merits great scientific and technological potential yet remains a challenge due to its inferior selectivity. Subnanomaterials (SNMs) with "p-n-p-n"-type heteroconstructions feature enhanced external field coupling properties and tunable electronic structures, serving as promising catalysts for the selective partial oxidation of methane. Here we develop NiO-polyoxometalate (POM) subnanocoils with a thickness of 1.8 nm, showing excellent catalytic activity toward photoelectrochemical coupling of methane into a C2 product under mild conditions (1 bar, 25 °C) with a notable productivity (up to 4.48 mmol gcat-1 h-1) and a high selectivity (>99%). Under photoelectrochemical coupling, C-H bonds can be activated by NiO, and the resulted *COOH intermediates are stabilized by the delocalized electrons in POM clusters. The contiguous active sites of NiO and POM at the molecular level allow the in situ coupling of *COOH into oxalate. This work points out an economic way for the oxidation of methane under mild conditions and may enlighten the design of functional SNMs from fundamental standpoints.

Photocatalytic Conversion of Methane: Current State of the Art, Challenges, and Future Perspectives

With 28-34 times the greenhouse effect of CO2 over a 100-year period, methane is regarded as the second largest contributor to global warming. Reducing methane emissions is a necessary measure to limit global warming to below 1.5 °C. Photocatalytic conversion of methane is a promising approach to alleviate the atmospheric methane concentrations due to its low energy consumption and environmentally friendly characteristics. Meanwhile, this conversion process can produce valuable chemicals and liquid fuels such as CH3OH, CH3CH2OH, C2H6, and C2H4, cutting down the dependence of chemical production on crude oil. However, the development of photocatalysts with a high methane conversion efficiency and product selectivity remains challenging. In this review, we overview recent advances in semiconductor-based photocatalysts for methane conversion and present catalyst design strategies, including morphology control, heteroatom doping, facet engineering, and cocatalysts modification. To gain a comprehensive understanding of photocatalytic methane conversion, the conversion pathways and mechanisms in these systems are analyzed in detail. Moreover, the role of electron scavengers in methane conversion performance is briefly discussed. Subsequently, we summarize the anthropogenic methane emission scenarios on earth and discuss the application potential of photocatalytic methane conversion. Finally, challenges and future directions for photocatalytic methane conversion are presented.

Surface Oxygen Species in Metal Oxide Photoanodes for Solar Energy Conversion

Converting and storing solar energy directly as chemical energy through photoelectrochemical devices are promising strategies to replace fossil fuels. Metal oxides are commonly used as photoanode materials, but they still encounter challenges such as limited light absorption, inefficient charge separation, sluggish surface reactions, and insufficient stability. The regulation of surface oxygen species on metal oxide photoanodes has emerged as a critical strategy to modulate molecular and charge dynamics at the reaction interface. However, the precise role of surface oxygen species in metal oxide photoanodes remains ambiguous. The review focuses on elucidating the formation and regulation mechanisms of various surface oxygen species in metal oxides, their advantages and disadvantages in photoelectrochemical reactions, and the characterization methods employed to investigate them. Additionally, the article discusses emerging opportunities and potential hurdles in the regulation of surface oxygen species. By shedding light on the significance of surface oxygen species, this review aims to advance our understanding of their impact on metal oxide photoanodes, paving the way for the design of more efficient and stable photoelectrochemical devices.

Hierarchical triphase diffusion photoelectrodes for photoelectrochemical gas/liquid flow conversion

Photoelectrochemical device is a versatile platform for achieving various chemical transformations with solar energy. However, a grand challenge, originating from mass and electron transfer of triphase-reagents/products in gas phase, water/electrolyte/products in liquid phase and catalyst/photoelectrode in solid phase, largely limits its practical application. Here, we report the simulation-guided development of hierarchical triphase diffusion photoelectrodes, to improve mass transfer and ensure electron transfer for photoelectrochemical gas/liquid flow conversion. Semiconductor nanocrystals are controllably integrated within electrospun nanofiber-derived mat, overcoming inherent brittleness of semiconductors. The mechanically strong skeleton of free-standing mat, together with satisfactory photon absorption, electrical conductivity and hierarchical pores, enables the design of triphase diffusion photoelectrodes. Such a design allows photoelectrochemical gas/liquid conversion to be performed continuously in a flow cell. As a proof of concept, 16.6- and 4.0-fold enhancements are achieved for the production rate and product selectivity of methane conversion, respectively, with remarkable durability.

Temperature-Controlled Transformation of WO3 Nanowires into Active Facets-Exposed Hexagonal Prisms toward Efficient Visible-Light-Driven Water Oxidation

A unique transformation of WO₃ nanowires (NW-WO₃) into hexagonal prisms (HP-WO₃) was demonstrated by tuning the temperature of the (N₂H₄)WO₃ precursor suspension prepared from tungstic acid and hydrazine as a structure-directing agent. The precursor preparation at 20 °C followed by calcination at 550 °C produced NW-WO₃ nanocrystals (ca. <100 nm width, 3-5 μm length) with anisotropic growth of monoclinic WO₃ crystals to (002) and (200) planes and a polycrystalline character with randomly oriented crystallites in the lateral face of nanowires. The precursor preparation at 45 °C followed by calcination at 550 °C produced HP-WO₃ nanocrystals (ca. 500-1000 nm diameter) with preferentially exposed (002) and (020) facets on the top-flat and side-rectangle surfaces, respectively, of hexagonal prismatic WO₃ nanocrystals with a single-crystalline character. The HP-WO₃ electrode exhibited the superior photoelectrochemical (PEC) performance for visible-light-driven water oxidation to that for the NW-WO₃ electrode; the incident photon-to-current conversion efficiency (IPCE) of 47% at 420 nm and 1.23 V vs RHE for HP-WO₃ was 3.1-fold higher than 15% for the NW-WO₃ electrode. PEC impedance data revealed that the bulk electron transport through the NW-WO₃ layer with the unidirectional nanowire structure is more efficient than that through the HP-WO₃ layer with the hexagonal prismatic structure. However, the water oxidation reaction at the surface for the HP-WO₃ electrode is more efficient than the NW-WO₃ electrode, contributing significantly to the superior PEC water oxidation performance observed for the HP-WO₃ electrode. The efficient water oxidation reaction at the surface for the HP-WO₃ electrode was explained by the high surface fraction of the active (002) facet with fewer grain boundaries and defects on the surface of HP-WO₃ to suppress the electron-hole recombination at the surface.

Sustainable methane utilization technology via photocatalytic halogenation with alkali halides

Methyl halides are versatile platform molecules, which have been widely adopted as precursors for producing value-added chemicals and fuels. Despite their high importance, the green and economical synthesis of the methyl halides remains challenging. Here we demonstrate sustainable and efficient photocatalytic methane halogenation for methyl halide production over copper-doped titania using alkali halides as a widely available and noncorrosive halogenation agent. This approach affords a methyl halide production rate of up to 0.61 mmol h^-1 m^-2 for chloromethane or 1.08 mmol h^-1 m^-2 for bromomethane with a stability of 28 h, which are further proven transformable to methanol and pharmaceutical intermediates. Furthermore, we demonstrate that such a reaction can also operate solely using seawater and methane as resources, showing its high practicability as general technology for offshore methane exploitation. This work opens an avenue for the sustainable utilization of methane from various resources and toward designated applications.

Emerging catalysts for the ambient synthesis of ethylene glycol from CO2 and its derivatives

Ethylene glycol (EG), a useful chemical raw material, has been widely applied in many aspects of modern society. The conventional preparation of ethylene glycol mainly uses the petroleum route at high temperatures and pressure. More and more approaches have been developed to synthesize EG from CO₂ and its derivatives under mild conditions. In this review, the ambient synthesis of EG from thermocatalysis, photocatalysis, and electrocatalysis is highlighted. The coal-to-ethylene glycol technology, one of the typical thermal catalysis routes for EG preparation, is relatively mature. However, it still faces some problems to be solved in industrialization. The recent progress in the development of coal-to-ethylene glycol technology is introduced. The main focus is on how to realize the preparation of EG under mild conditions. The strategies include doping promoters, modification of supports, design of catalysts with special structures, etc. Furthermore, the emerging technological progress of photocatalytic and electrocatalytic ethylene glycol synthesis under ambient conditions is introduced. Compared with the thermal catalytic reaction, the reaction conditions are milder. However, there are still many problems in large-scale production. Finally, we propose future development issues and related prospects for the ambient synthesis of EG using different catalytic routes.

Dynamic semiconductor-electrolyte interface for sustainable solar water splitting over 600 hours under neutral conditions

Photoelectrochemical (PEC) water splitting that functions in pH-neutral electrolyte attracts increasing attention to energy demand sustainability. Here, we propose a strategy to in situ form a NiB layer by tuning the composition of the neutral electrolyte with the additions of nickel and borate species, which improves the PEC performance of the BiVO₄ photoanode. The NiB/BiVO₄ exhibits a photocurrent density of 6.0 mA cm^-2 at 1.23 V_RHE with an onset potential of 0.2 V_RHE under 1 sun illumination. The photoanode displays a photostability of over 600 hours in a neutral electrolyte. The additive of Ni²⁺ in the electrolyte, which efficiently inhibits the dissolution of NiB, can accelerate the photogenerated charge transfer and enhance the water oxidation kinetics. The borate species with B─O bonds act as a promoter of catalyst activity by accelerating proton-coupled electron transfer. The synergy effect of both species suppresses the surface charge recombination and inhibits the photocorrosion of BiVO₄.

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), H₂ O₂ 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 CO₃ ^2- . Our results demonstrate that the IFE favors the adsorption of CO₃ ^2- 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.

Multiple roles for LaFeO3 in enhancing the Photoelectrochemical performance of WO3

For photoelectrochemical (PEC) water splitting, constructing heterojunctions and loading co-catalysts are effective means to realizing sufficient light absorption, effective photogenerated carrier separation and fast charge transport. However, during implementation, the PEC performance of the catalyst is affected by both parasitic light absorption and reflection and the change in energy band structure due to the creation of new interfaces. Herein, in order to minimize the effect of recombination of photogenerated electron-hole pairs on the catalyst PEC performance due to the nascent interface arising from the co-catalyst compounding, WO3 and Ni/Co co-doped LaFeO3 (LFO) are constructed as heterojunctions, in which NiCo-LFO acts both as a part of the heterojunction to enhance photogenerated carrier separation and a co-catalyst to enhance the conductivity and modulate the surface state density at the catalyst-electrolyte interface. The current density of NiCo-LFO/WO3 reaches 3.92 mA cm-2, which is more than 7 times that of LFO/WO3. This work provides a reference for the efficient water splitting of B-site doped, especially the co-doped perovskite oxide as multifunctional roles integrated with conventional photoelectrodes.

Liquid-Metal-Induced Hydrogen Insertion in Photoelectrodes for Enhanced Photoelectrochemical Water Oxidation

Fast charge separation and transfer (CST) is essential for achieving efficient solar conversion processes. This CST process requires not only a strong driving force but also a sufficient charge carrier concentration, which is not easily achievable with traditional methods. Herein, we report a rapid hydrogenation method enabled by gallium-based liquid metals (GBLMs) to modify the prototypical WO₃ photoelectrode to enhance the CST for a PEC process. Protons in solution are controllably embedded into the WO₃ photoanode accompanied by electron injection due to the strong reduction capability of GBLMs. This process dramatically increases the carrier concentration of the WO₃ photoanode, leading to improved charge separation and transfer. The hydrogenated WO₃ photoanode exhibits over a 229% improvement in photocurrent density with long-term stability. The effectiveness of GBLMs treatment in accelerating the CST process is further proved using other more general semiconductor photoelectrodes, including Nb₂O₅ and TiO₂.

Cu and Si co-doping on TiO2 nanosheets to modulate reactive oxygen species for efficient photocatalytic methane conversion

In this study, we successfully construct Cu and Si co-doped ultrathin TiO₂ nanosheets. As confirmed by comprehensive characterizations, Cu and Si co-doping can rationally tailor the electronic structure of TiO₂ to maneuver reactive oxygen species for effective photocatalytic methane conversion. In addition, this co-doping greatly enhances the utilization efficiency of photogenerated charges. Furthermore, it is revealed that Cu and Si co-doping can significantly boost the adsorption and activation of methane on TiO₂ nanosheets. As a result, the optimized catalyst achieves a C₂H₆ production rate of 33.8 μmol g^-1 h^-1 with a selectivity of 88.4%. This work provides insights into nanocatalyst design toward efficient photocatalytic methane conversion into value-added compounds.

Multi-Function of the Ni Interlayer in the Design of a BiVO4-Based Photoanode for Photoelectrochemical Water Splitting

BiVO₄ with an appropriate band structure is considered to be an ideal candidate for photoanodes. However, slow water oxidation kinetics and low charge separation efficiency seriously restrict its application. To address these issues, an NF/N/BVO photoanode with a hierarchical network structure was successfully constructed by direct-current magnetron sputtering of Ni followed by electrochemical deposition of nickel-iron layered double hydroxide (NiFe-LDH) on BiVO₄. A photocurrent density of 4.50 mA/cm² was obtained for NF/N/BVO, which was 2.4 times that for pristine BiVO₄. The introduction of the Ni layer contributed to the following growth of NiFe-LDH nanosheets with larger size, which acted as active sites and speeded up water oxidation kinetics. Furthermore, surface photovoltage microscopy revealed that Ni and NiFe-LDH acted as the electron collector and hole reservoir, respectively. The co-existence of the two components constituted a highly efficient surface charge separation structure, which was one of the important issues for the excellent water oxidation activity.

Crystal Facet-Modulated WO3 Nanoplate Photoanode for Photoelectrochemical Glyoxal Semi-oxidation into Glyoxylic Acid

Transforming glyoxal to value-added glyoxylic acid (GA) is highly desirable but challenging due to the uncontrollable over-oxidation. In this work, we report on a first demonstration of semi-oxidation of glyoxal with high selectivity (86.5%) and activity on WO₃ nanoplate photoanode through the photoelectrochemical strategy. The optimization of reactivity was achieved via crystal facet regulation, showing a satisfactory GA production rate of 308.4 mmol m^-2 h^-2, 84.0% faradaic efficiency, and 4.3% total solar-to-glyoxylic acid efficiency on WO₃ with enriched {200} facets at 1.6 V versus RHE. WO₃ with a high {200} facet ratio exhibits more efficient electron-hole transfer kinetics, resulting in the facilitated formation of hydroxyl radicals (^•OH) and glyoxal radicals. Meanwhile, the theoretical calculation results indicate that the high selectivity and activity come from the strong adsorption ability for glyoxal and the low reaction energy for glyoxal radical generation on the (200) facets of WO₃. Moreover, the high energy demand toward oxalic acid production on WO₃ leads to the exciting semi-oxidation process.

Ultrathin Ti-doped WO3 nanosheets realizing selective photoreduction of CO2 to CH3OH

Arduous CO₂ activation and sluggish charge transfer retard the photoreduction of CO₂ to CH₃OH with high efficiency and selectivity. Here, we fabricate ultrathin Ti-doped WO₃ nanosheets possessing approving active sites and optimized carrier dynamics as a promising catalyst. Quasi in situ X-ray photoelectron spectroscopy and synchrotron-radiation X-ray absorption near-edge spectroscopy firmly confirm that the true active sites for CO₂ reduction are the W sites rather the Ti sites, while the Ti dopants can facilitate charge transfer, which accelerates the generation of crucial COOH* intermediates as revealed by in situ Fourier-transform infrared spectroscopy and density functional theory calculations. Besides, the Gibbs free energy calculations also validate that Ti doping can lower the energy barrier of CO₂ activation and CH₃OH desorption by 0.22 eV and 0.42 eV, respectively, thus promoting the formation of CH₃OH. In consequence, the Ti-doped WO₃ ultrathin nanosheets show a superior CH₃OH selectivity of 88.9% and reach a CH₃OH evolution rate of 16.8 μmol g^-1 h^-1, about 3.3 times higher than that on WO₃ nanosheets. This work sheds light on promoting CO₂ photoreduction to CH₃OH by rational elemental doping.

Revealing *OOH key intermediates and regulating H(2)O(2) photoactivation by surface relaxation of Fenton-like catalysts

Hydrogen peroxide (H₂O₂) molecules play important roles in many green chemical reactions. However, the high activation energy limits their application efficiency, and there is still huge controversy about the activation path of H₂O₂ molecules over the presence of *OOH intermediates. Here, we confirmed the formation of the key species *OOH in the heterogeneous system, via in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), isotope labeling, and theoretical calculation. In addition, we found that compared with *H₂O₂, *OOH was more conducive to the charge transfer behavior with the catalyst and the activation of an O-O bond. Furthermore, we proposed to improve the local coordination structure and electronic density of the YFeO₃ catalyst by regulating the surface relaxation with Ti modification so as to reduce the activation barrier of H₂O₂ and to improve the production efficiency of •OH. As a result, the kinetics rates of the Fenton-like (photo-Fenton) reaction had been significantly increased several times. The •OH free radical activity mechanism and molecular transformation pathways of 4-chloro phenol (4-CP) were also revealed. This may provide a clearer vision for the further study of H₂O₂ activation and suggest a means of designing catalysts for efficient H₂O₂ activation.

Synergy of Pd atoms and oxygen vacancies on In2O3 for methane conversion under visible light

Methane (CH4) oxidation to high value chemicals under mild conditions through photocatalysis is a sustainable and appealing pathway, nevertheless confronting the critical issues regarding both conversion and selectivity. Herein, under visible irradiation (420 nm), the synergy of palladium (Pd) atom cocatalyst and oxygen vacancies (OVs) on In2O3 nanorods enables superior photocatalytic CH4 activation by O2. The optimized catalyst reaches ca. 100 μmol h-1 of C1 oxygenates, with a selectivity of primary products (CH3OH and CH3OOH) up to 82.5%. Mechanism investigation elucidates that such superior photocatalysis is induced by the dedicated function of Pd single atoms and oxygen vacancies on boosting hole and electron transfer, respectively. O2 is proven to be the only oxygen source for CH3OH production, while H2O acts as the promoter for efficient CH4 activation through ·OH production and facilitates product desorption as indicated by DFT modeling. This work thus provides new understandings on simultaneous regulation of both activity and selectivity by the synergy of single atom cocatalysts and oxygen vacancies.

WO3 Photoanode with Predominant Exposure of {202} Facets for Enhanced Selective Oxidation of Glycerol to Glyceraldehyde

The photoelectrocatalytic (PEC) oxidation of glycerol into highly value-added products is attractive, but it is extremely challenging to limit the oxidation products to the valuable C3 chemicals. The hole concentration and surface atomic arrangement of a photoanode can be modulated by controlling facet exposure, thus tuning the activity and selectivity. Herein, we report for the first time the formation of a WO3 photoanode with predominant exposure of {202} facets by a secondary hydrothermal method. The photoanode exhibits superior PEC glycerol conversion efficiency, giving an 80% selectivity to glyceraldehyde with a production rate of 462 mmol h-1 m-2. Also, the faraday efficiency for the C3 product reaches 98.6%. We made comparison between the {202} facets and the commonly studied {200} facets using experimental and theoretical methods. It is disclosed that the former enhances not only the adsorption and activation of glycerol via the terminal hydroxyl groups but also the desorption of glyceraldehyde.

Governing Interlayer Strain in Bismuth Nanocrystals for Efficient Ammonia Electrosynthesis from Nitrate Reduction

Electrochemical ammonia (NH₃) synthesis from nitrate (NO₃^-) reduction offers an intriguing approach for both sustainable ammonia synthesis and environmental denitrification, yet it remains hindered by a complicated reaction pathway with various intermediates. Here we present that the interlayer strain compression in bismuth (Bi) nanocrystals can contribute to both activity and selectivity improvement toward NH₃ electrosynthesis from NO₃^- reduction. By virtue of comprehensive spectroscopic studies and theoretical calculations, we untangle that the interlayer lattice compression shortens Bi-Bi bond to broaden the 6p bandwidth for electron delocalization, promoting the chemical affinities of nitrogen intermediates. Such a manipulation facilitates NO₃^- activation to reduce the energy barrier for activity improvement, and also alleviates *NO₂ desorption to suppress nitrite generation. As a result, a strain-compressive Bi electrocatalyst yields a maximal Faradaic efficiency of 90.6% and high generation rate of 46.5 g h^-1 g_cat^-1 with industrially scalable partial current density up to 300 mA cm^-2 for NH₃ product at the optimized conditions, respectively.

Operando Photo-Electrochemical Catalysts Synchrotron Studies

The attempts to develop efficient methods of solar energy conversion into chemical fuel are ongoing amid climate changes associated with global warming. Photo-electrocatalytic (PEC) water splitting and CO₂ reduction reactions show high potential to tackle this challenge. However, the development of economically feasible solutions of PEC solar energy conversion requires novel efficient and stable earth-abundant nanostructured materials. The latter are hardly available without detailed understanding of the local atomic and electronic structure dynamics and mechanisms of the processes occurring during chemical reactions on the catalyst–electrolyte interface. This review considers recent efforts to study photo-electrocatalytic reactions using in situ and operando synchrotron spectroscopies. Particular attention is paid to the operando reaction mechanisms, which were established using X-ray Absorption (XAS) and X-ray Photoelectron (XPS) Spectroscopies. Operando cells that are needed to perform such experiments on synchrotron are covered. Classical and modern theoretical approaches to extract structural information from X-ray Absorption Near-Edge Structure (XANES) spectra are discussed.

Engineering Catalytic Interfaces in Cuδ+/CeO2-TiO2 Photocatalysts for Synergistically Boosting CO2 Reduction to Ethylene

Photocatalytic CO₂ conversion into a high-value-added C₂ product is a highly challenging task because of insufficient electron deliverability and sluggish C-C coupling kinetics. Engineering catalytic interfaces in photocatalysts provides a promising approach to manipulate photoinduced charge carriers and create multiple catalytic sites for boosting the generation of C₂ product from CO₂ reduction. Herein, a Cu^δ+/CeO₂-TiO₂ photocatalyst that contains atomically dispersed Cu^δ+ sites anchored on the CeO₂-TiO₂ heterostructures consisting of highly dispersed CeO₂ nanoparticles on porous TiO₂ is designedly constructed by the pyrolytic transformation of a Cu²⁺-Ce³⁺/MIL-125-NH₂ precursor. In the designed photocatalyst, TiO₂ acts as a light-harvesting material for generating electron-hole pairs that are efficiently separated by CeO₂-TiO₂ interfaces, and the Cu-Ce dual active sites synergistically facilitate the generation and dimerization of *CO intermediates, thus lowering the energy barrier of C-C coupling. As a consequence, the Cu^δ+/CeO₂-TiO₂ photocatalyst exhibits a production rate of 4.51 μmol^-1·g_cat^-1·h^-1 and 73.9% selectivity in terms of electron utilization for CO₂ to C₂H₄ conversion under simulated sunlight, with H₂O as hydrogen source and hole scavenger. The photocatalytic mechanism is revealed by operando spectroscopic methods as well as theoretical calculations. This study displays the rational construction of heterogeneous photocatalysts for boosting CO₂ conversion and emphasizes the synergistic effect of multiple active sites in enhancing the selectivity of C₂ product.

Tungsten oxide polymorphs and their multifunctional applications

Owing to the natural abundance, easy availability, high stability, non-stoichiometry, and chemical diversity, considerable interest has been devoted to tungsten oxide (WO_3-x) nanomaterials, and many advances have been achieved ranging from traditional catalysts and electronics to emerging artificial intelligence. This review focuses on recent progress of WO_3-x polymorphs and their multifunctional applications. The structural diversity and crystal phase transitions of WO_3-x and recent advances on the general synthesis of various WO_3-x nanostructures are first summarized, since the crystal structure and morphology adjustment obviously affect the physiochemical merits of WO_3-x materials. Then, their applications and related mechanisms in different fields are demonstrated, such as gas sensing, chromogenic (electro-, photo-, gaso-, and thermochromic), photocatalytic (pollutant degradation and water splitting), and emerging applications (biomedical, antibiotic, and artificial intelligence). With the advances highlighted here and the ongoing research efforts, the continuous breakthrough in functionalized WO_3-x nanostructure and their attractive applications is foreseeable in the future.

Photoelectrochemical Conversion of Methane into Value-Added Products

Methane has been reported to be directly converted into value-added products through various methods. Among them, photoelectrochemical (PEC) methane conversion is considered an eco-friendly method because it utilizes solar light and is able to control the selectivity to different products by means of application of an external bias. Recently, some PEC methane conversion systems have been reported, but their performance efficiencies are relatively lower than those of other existing thermal, photocatalytic, and electrochemical systems. The detailed mechanism of methane activation is not clear at this stage. In this review, various catalytic materials and their roles in the reaction pathways are summarized and discussed. Furthermore, promising semiconductor materials, co-catalysts, and oxidants have also been proposed. Finally, direct and indirect pathways in the design of the PEC methane conversion system have been discussed.

Synthesis and applications of WO3 nanosheets: the importance of phase, stoichiometry, and aspect ratio

Tungsten trioxide (WO₃) is an abundant, versatile oxide that is widely explored for catalysis, sensing, electrochromic devices, and numerous other applications. The exploitation of WO₃ in nanosheet form provides potential advantages in many of these fields because the 2D structures have high surface area and preferentially exposed facets. Relative to bulk WO₃, nanosheets expose more active sites for surface-sensitive sensing/catalytic reactions, and improve reaction kinetics in cases where ionic diffusion is a limiting factor (e.g. electrochromic or charge storage). Synthesis of high aspect ratio WO₃ nanosheets, however, is more challenging than other 2D materials because bulk WO₃ is not an intrinsically layered material, making the widely-studied sonication-based exfoliation methods used for other 2D materials not well-suited to WO₃. WO₃ is also highly complex in terms of how the synthesis method affects the properties of the final material. Depending on the route used and subsequent post-synthesis treatments, a wide variety of different morphologies, phases, exposed facets, and defect structures are created, all of which must be carefully considered for the chosen application. In this review, the recent developments in WO₃ nanosheet synthesis and their impact on performance in various applications are summarized and critically analyzed.

Photo-driven Oxygen Vacancies Extends Charge Carrier Lifetime for Efficient Solar Water Splitting

A photocharge/discharge strategy is proposed to initiate the WO₃ photoelectrode and suppress the main charge recombination, which remarkably improves the photoelectrochemical (PEC) performance. The photocharged WO₃ surrounded by a 8-10 nm overlayer and oxygen vacancies could be operated more than 25 cycles with 50 h durability without significant decay on PEC activity. A photocharged WO₃ /CuO photoanode exhibits an outstanding photocurrent of 3.2 mA cm^-2 at 1.23 V_RHE with a low onset potential of 0.6 V_RHE , which is one of the best performances of p-n heterojunction structure. Using nonadiabatic molecular dynamics combined with time-domain DFT, we clarify the prolonged charge carrier lifetime of photocharged WO₃ , as well as how electronic systems of photocharged WO₃ /CuO semiconductors enable the effective photoinduced electrons transfer from WO₃ into CuO. This work provides a feasible route to address excessive defects existed in photoelectrodes without causing extra recombination.