Growth of Size-Tunable Ag2O Polyhedra and Revelation of Their Bulk and Surface Lattices.

By primarily adjusting the reagent amounts, particularly the volume of AgNO3 solution introduced, Ag2O cubes with decreasing sizes from 440 to 79 nm, octahedra from 714 to 106 nm, and rhombic dodecahedra from 644 to 168 nm are synthesized. 733 nm cuboctahedra are also prepared for structural analysis. With in-house X-ray diffraction (XRD) peak calibration, shape-related peak shifts are recognizable. Synchrotron XRD measurements at 100 K reveal the presence of bulk and surface layer lattices. Bulk cell constants also deviate slightly. They show a negative thermal expansion behavior with shrinking cell constants at higher temperatures. The Ag2O crystals exhibit size- and facet-dependent optical properties. Bandgaps red-shift continuously with increasing particle sizes. Optical facet effect is also observable. Moreover, synchrotron XRD peaks of a mixture of Cu2O rhombicuboctahedra and edge- and corner-truncated cubes exposing all three crystal faces can be deconvoluted into three components with the bulk and the [111] microstrain phase as the major component. Interestingly, while the unheated Cu2O sample shows clear diffraction peak asymmetry, annealing the sample to 450 K yields nearly symmetric peaks even when returning the sample to room temperature, meaning even moderately high temperatures can permanently change the crystal lattice.

Electronic and Atomic Structural Properties Associated with Enhanced Photodegradation Activity in Mo-Doped TiO2 Nanoparticles.

The efficacy and structural evolution of Mo-doped titania nanoparticles (MTNPs) as advanced photocatalysts for degrading methyl blue (MB) are investigated by X-ray absorption spectroscopy (XAS). The 3 wt % MTNP, characterized by uniform size and anatase structure, exhibits higher efficiency. The spectral analyses unveiled structural variations in the TiO6 octahedral structure and revealed an active site of the distorted square pyramidal structure symmetry (C4v). The in situ XAS spectra illustrate that MTNPs, particularly at 3 wt % doping, effectively enhanced the hole carriers in Ti 3d orbitals with a charge transfer to Mo 4d orbitals and impeded electron-hole pair merging, significantly enhancing the photodegradation under light illumination. This study deepens our understanding of the crucial role of Mo doping in optimizing TiO2 nanoparticle performance for efficient environmental remediation, showcasing the potential of MTNPs as sustainable photocatalytic materials.

Lewis Acidic Support Boosts C-C Coupling in the Pulsed Electrochemical CO2 Reaction.

Copper-oxide electrocatalysts have been demonstrated to effectively perform the electrochemical CO2 reduction reaction (CO2RR) toward C2+ products, yet preserving the reactive high-valent CuOx has remained elusive. Herein, we demonstrate a model system of Lewis acidic supported Cu electrocatalyst with a pulsed electroreduction method to achieve enhanced performance for C2+ products, in which an optimized electrocatalyst could reach ∼76% Faradaic efficiency for C2+ products (FEC2+) at ∼-0.99 V versus reversible hydrogen electrode, and the corresponding mass activity can be enhanced by ∼2 times as compared to that of conventional CuOx. In situ time-resolved X-ray absorption spectroscopy investigating the dynamic chemical/physical nature of Cu during CO2RR discloses that an activation process induced by the KOH electrolyte during pulsed electroreduction greatly enriched the Cuδ+O/Znδ+O interfaces, which further reveals that the presence of Znδ+O species under the cathodic potential could effectively serve as a Lewis acidic support for preserving the Cuδ+O species to facilitate the formation of C2+ products, and the catalyst structure-property relationship of Cuδ+O/Znδ+O interfaces can be evidently realized. More importantly, we find a universality of stabilizing Cuδ+O species for various metal oxide supports and to provide a general concept of appropriate electrocatalyst-Lewis acidic support interaction for promoting C2+ products.

Description of Photodegradation Mechanisms and Structural Characteristics in Carbon@Titania Yolk-Shell Nanostructures by XAS.

Carbon@titania yolk-shell nanostructures are successfully synthesized at different calcination conditions. These unique structure nanomaterials can be used as a photocatalyst to degrade the emerging water pollutant, acetaminophen (paracetamol). The photodegradation analysis studies have shown that the samples with residual carbon nanospheres have improved the photocatalytic efficiency. The local electronic and atomic structure of the nanostructures are analyzed by X-ray absorption spectroscopy (XAS) measurements. The spectra confirm that the hollow shell has an anatase phase structure, slight lattice distortion, and variation in Ti 3d orbital orientation. In situ XAS measurements reveal that the existence of amorphous carbon nanospheres inside the nano spherical shell inhibit the recombination of electron-hole pairs; more mobile holes are formed in the p-d hybridized bands near the Fermi surface and enables the acceleration of the carries that significantly enhance the photodegradation of paracetamol under UV-visible irradiation. The observed charge transfer process from TiO2  hybridized orbital to the carbon nanospheres reduces the recombination rate of electrons and holes, thus increasing the photocatalytic efficiency.

Site-Specified Two-Dimensional Heterojunction of Pt Nanoparticles/Metal-Organic Frameworks for Enhanced Hydrogen Evolution.

Heterojunction nanostructures usually exhibit enhanced properties in compariosn with their building blocks and are promising catalyst candidates due to their combined surface and unique interface. Here, for the first time we realized the oriented growth of ultrasmall metal nanoparticles (NPs) on metal-organic framework nanosheets (MOF NSs) by precisely regulating the reduction kinetics of metal ions with solvents. In particular, a rapid reduction of metal ions leads to the random distribution of metal NPs on the surface of MOF NSs, while a slow reduction of metal ions results in the oriented growth of NPs on the edge of MOF NSs. Impressively, the strong synergy between Pt NPs and MOF NSs significantly enhances the hydrogen evolution reaction (HER) performance, and the optimal catalyst displays HER activities superior to those of a composite with a random growth of Pt NPs and commercial Pt/C under both acidic and alkaline conditions. Moreover, the versatility of such oriented growth has been extended to other metal NPs, such as Pd, Ag, and Au. We believe this work will promote research interest in material design for many potential applications.

An Efficient Interfacial Synthesis of Two-Dimensional Metal-Organic Framework Nanosheets for Electrochemical Hydrogen Peroxide Production.

Two-dimensional (2D) metal-organic framework nanosheets (MOF NSs) play a vital role in catalysis, but the most preparation is ultrasonication or solvothermal. Herein, a liquid-liquid interfacial synthesis method has been developed for the efficient fabrication of a series of 2D Ni MOF NSs. The active sites could be modulated by readily tuning the ratios of metal precursors and organic linkers (RM/L ). The Ni MOF NSs display highly RM/L dependent activities towards 2e oxygen reduction reaction (ORR) to hydrogen peroxide (H2 O2 ), where the Ni MOF NSs with the RM/L of 6 exhibit the optimal near-zero overpotential, ca. 98 % H2 O2 selectivity and production rate of ca. 80 mmol gcat -1 h-1 in 0.1 M KOH. As evidenced by X-ray absorption fine structure spectroscopy, the coordination environment of active sites changed from saturation to unsaturation, and the partially unsaturated metal atoms are crucial to create optimal sites for enhancing the electrocatalysis.

Co-Induced Electronic Optimization of Hierarchical NiFe LDH for Oxygen Evolution.

Developing efficient and stable non-noble electrocatalysts for the oxygen evolution reaction (OER) remains challenging for practical applications. While nickel-iron layered double hydroxides (NiFe-LDH) are emerging as prominent candidates with promising OER activity, their catalytic performance is still restricted by the limited active sites, poor conductivity and durability. Herein, hierarchical nickel-iron-cobalt LDH nanosheets/carbon fibers (NiFeCo-LDH/CF) are synthesized through solvent-thermal treatment of ZIF-67/CF. Extended X-ray adsorption fine structure analyses reveal that the Co substitution can stabilize the Fe local coordination environment and facilitate the π-symmetry bonding orbital in NiFeCo-LDH/CF, thus modifying the electronic structures. Coupling with the structural advantages, including the largely exposed active surface sites and facilitated charge transfer pathway ensured by CF, the resultant NiFeCo-LDH/CF exhibits excellent OER activity with an overpotential of 249 mV at 10 mA cm-1 as well as robust stability over 20 h.

Transparent Flexible Heteroepitaxy of NiO Coated AZO Nanorods Arrays on Muscovites for Enhanced Energy Storage Application.

Transparent flexible energy storage devices are considered as important chains in the next-generation, which are able to store and supply energy for electronic devices. Here, aluminum-doped zinc oxide (AZO) nanorods (NRs) and nickel oxide (NiO)-coated AZO NRs on muscovites are fabricated by a radio frequency (RF) magnetron sputtering deposition method. Interestingly, AZO NRs and AZO/NiO NRs are excellent electrodes for energy storage application with high optical transparency, high conductivity, large surface area, stability under compressive and tensile strain down to a bending radius of 5 mm with 1000 bending cycles. The obtained symmetric solid-state supercapacitors based on these electrodes exhibit good performance with a large areal specific capacitance of 3.4 mF cm-2 , long cycle life 1000 times, robust mechanical properties, and high chemical stability. Furthermore, an AZO/NiO//Zn battery based on these electrodes is demonstrated, yielding a discharge capacity of 195 mAh g-1 at a current rate of 8 A g-1 and a discharge capacity of over 1000 cycles with coulombic efficiency to 92%. These results deliver a concept of opening a new opportunity for future applications in transparent flexible energy storage.

Structural and Electronic Optimization of MoS2 Edges for Hydrogen Evolution.

The activity and accessibility of MoS2 edge sites are critical to deliver high hydrogen evolution reaction (HER) efficiency. Here, a porous carbon network confining ultrasmall N-doped MoS2 nanocrystals (N-MoS2/CN) is fabricated by a self-templating strategy, which realizes synergistically structural and electronic modulations of MoS2 edges. Experiments and density functional theory calculations demonstrate that the N dopants could activate MoS2 edges for HER, while the porous carbon network could deliver high accessibility of the active sites from N-MoS2 nanocrystals. Consequently, N-MoS2/CN possesses superior HER activity with an overpotential of 114 mV at 10 mA cm-2 and excellent stability over 10 h, delivering one of best MoS2-based HER electrocatalysts. Moreover, this study opens a new venue for optimizing materials with enhanced accessible catalytic sites for energy-related applications.

Novel iron oxyhydroxide lepidocrocite nanosheet as ultrahigh power density anode material for asymmetric supercapacitors.

A simple one-step electroplating route is proposed for the synthesis of novel iron oxyhydroxide lepidocrocite (γ-FeOOH) nanosheet anodes with distinct layered channels, and the microstructural influence on the pseudocapacitive performance of the obtained γ-FeOOH nanosheets is investigated via in situ X-ray absorption spectroscopy (XAS) and electrochemical measurement. The in situ XAS results regarding charge storage mechanisms of electrodeposited γ-FeOOH nanosheets show that a Li(+) can reversibly insert/desert into/from the 2D channels between the [FeO6 ] octahedral subunits depending on the applied potential. This process charge compensates the Fe(2+) /Fe(3+) redox transition upon charging-discharging and thus contributes to an ideal pseudocapacitive behavior of the γ-FeOOH electrode. Electrochemical results indicate that the γ-FeOOH nanosheet shows the outstanding pseudocapacitive performance, which achieves the extraordinary power density of 9000 W kg(-1) with good rate performance. Most importantly, the asymmetric supercapacitors with excellent electrochemical performance are further realized by using 2D MnO2 and γ-FeOOH nanosheets as cathode and anode materials, respectively. The obtained device can be cycled reversibly at a maximum cell voltage of 1.85 V in a mild aqueous electrolyte, further delivering a maximum power density of 16 000 W kg(-1) at an energy density of 37.4 Wh kg(-1).

Photoelectrochemical activity on Ga-polar and N-polar GaN surfaces for energy conversion.

Hydrogen generation through direct photoelectrolysis of water was studied using photoelectrochemical cells made of different facets of free-standing polar GaN system. To build the fundamental understanding at the differences of surface photochemistry afforded by the GaN {0001}and {000-1}polar surfaces, we correlated the relationship between the surface structure and photoelectrochemical performance on the different polar facets. The photoelectrochemical measurements clearly revealed that the Ga-polar surface had a more negative onset potential relative to the N-polar surface due to the much negative flat-band potential. At more positive applied voltages, however, the N-polar surface yielded much higher photocurrent with conversion efficiency of 0.61% compared to that of 0.55% by using the Ga-polar surface. The reason could be attributed to the variation in the band structure of the different polar facets via Mott-Schottky analyses. Based on this work, understanding the facet effect on photoelectrochemical activity can provide a blueprint for the design of materials in solar hydrogen applications.

Silver-decorated hierarchical cuprous oxide micro/nanospheres as highly effective surface-enhanced Raman scattering substrates.

A facile and simple route to manufacture active surface-enhanced Raman scattering (SERS) substrate based on Ag-decorated Cu2O micro/nanospheres on Cu foil was systematically investigated. Hierarchical Cu2O micro/nanostructure transfers from CuO nanosheets and Cu(OH)2 nanowires by means of thermally reducing the oxides from Cu2+ to Cu1+ at temperature of 500 °Cunder nitrogen atmosphere. The subsequent decoration of Ag on Cu2O nanostructural substrate was carried out by means of thermal evaporator deposition. Using 4-aminothiophenol (4-ATP) as probing molecules, the SERS experiments showed that the Ag-decorated Cu2O micro/nanospheres exhibit excellent detecting performance, which could be used as effective SERS substrate for ultrasensitive detection. Additionally, these novel hierarchical SERS substrates showed good reproducibility and a linear dependence between analyte concentrations and intensities, revealing the advantage of this method for easily scale-up production.

Dual-Vacancy-Engineered ZnIn2S4 Nanosheets for Harnessing Low-Frequency Vibration Induced Piezoelectric Polarization Coupled with Static Dipole Field to Enhance Photocatalytic H2 Evolution.

This study investigates the impact of In- and S-vacancy concentrations on the photocatalytic activity of non-centrosymmetric zinc indium sulfide (ZIS) nanosheets for the hydrogen evolution reaction (HER). A positive correlation between the concentrations of dual In and S vacancies and the photocatalytic HER rate over ZIS nanosheets is observed. The piezoelectric polarization, stimulated by low-frequency vortex vibration to ensure the well-dispersion of ZIS nanosheets in solution, plays a crucial role in enhancing photocatalytic HER over the dual-vacancy engineered ZIS nanosheets. The piezoelectric characteristic of the defective ZIS nanosheets is confirmed through the piezopotential response measured using piezoelectric force microscopy. Piezophotocatalytic H2 evolution over the ZIS nanosheets is boosted under accelerated vortex vibrations. The research explores how vacancies alter ZIS's dipole moment and piezoelectric properties, thereby increasing electric potential gradient and improving charge-separation efficiency, through multi-scale simulations, including Density Functional Theory and Finite Element Analysis, and a machine-learning interatomic potential for defect identification. Increased In and S vacancies lead to higher electric potential gradients in ZIS along [100] and [010] directions, attributing to dipole moment and the piezoelectric effect. This research provides a comprehensive exploration of vacancy engineering in ZIS nanosheets, leveraging the piezopotential and dipole field to enhance photocatalytic performances.

Direct Capturing and Regulating Key Intermediates for High-Efficiency Oxygen Evolution Reactions.

Developing efficient oxygen evolution reaction (OER) electrocatalysts can greatly advance the commercialization of proton exchange membrane (PEM) water electrolysis. However, the unclear and disputed reaction mechanism and structure-activity relationship of OER pose significant obstacles. Herein, the active site and intermediate for OER on AuIr nanoalloys are simultaneously identified and correlated with the activity, through the integration of in situ shell-isolated nanoparticle-enhanced Raman spectroscopy and X-ray absorption spectroscopy. The AuIr nanoalloys display excellent OER performance with an overpotential of only 246 mV to achieve 10 mA cm-2 and long-term stability under strong acidic conditions. Direct spectroscopic evidence demonstrates that *OO adsorbed on IrOx sites is the key intermediate for OER, and it is generated through the O-O coupling of adsorbed oxygen species directly from water, providing clear support for the adsorbate evolution mechanism. Moreover, the Raman information of the *OO intermediate can serve as a universal "in situ descriptor" that can be obtained both experimentally and theoretically to accelerate the catalyst design. It unveils that weakening the interactions of *OO on the catalysts and facilitating its desorption would boost the OER performance. This work deepens the mechanistic understandings on OER and provides insightful guidance for the design of more efficient OER catalysts.

Atomically dispersed iron sites from eco-friendly microbial mycelium as highly efficient hydrogenation catalyst.

Iron, one of the most abundant elements on earth and an essential element for living organisms, plays a crucial role in our daily metabolism. In the field of catalysis, the development of high-performance catalysts based on less toxic iron element is also of significant importance for green chemistry and a sustainable future. To construct Fe-based heterogeneous catalysts with excellent hydrogenation performance, precise modulation of the atomic coordination structure is a key strategy for enhancing catalytic activity. In this study, we present an in-situ coating method for applying a zeolitic imidazolate framework (ZIF) onto the surface of fungal hyphae. The asymmetric coordination structure of Fe1-N3P1 was precisely tailored by utilizing the phosphorus source from the fungus and the nitrogen source in the ZIFs. Detailed characterizations and density functional theory calculations revealed that the incorporation of ZIFs not only increased the specific surface area of catalysts, but also facilitated the dispersion of Fe2P nanoparticles into the Fe1-N3P1 center, making the lowest reaction energy barrier and resulting in the best performance for nitrobenzene hydrogenation when compared to the Fe2P nanoparticles and clusters. This research introduces a novel design concept for constructing asymmetric monoatomic configuration based on the inherent characteristics of natural microorganisms and the exogenous porous coordination polymers.

Dual-plasmonic Au@Cu7S4 yolk@shell nanocrystals for photocatalytic hydrogen production across visible to near infrared spectral region.

Near infrared energy remains untapped toward the maneuvering of entire solar spectrum harvesting for fulfilling the nuts and bolts of solar hydrogen production. We report the use of Au@Cu7S4 yolk@shell nanocrystals as dual-plasmonic photocatalysts to achieve remarkable hydrogen production under visible and near infrared illumination. Ultrafast spectroscopic data reveal the prevalence of long-lived charge separation states for Au@Cu7S4 under both visible and near infrared excitation. Combined with the advantageous features of yolk@shell nanostructures, Au@Cu7S4 achieves a peak quantum yield of 9.4% at 500 nm and a record-breaking quantum yield of 7.3% at 2200 nm for hydrogen production in the absence of additional co-catalysts. The design of a sustainable visible- and near infrared-responsive photocatalytic system is expected to inspire further widespread applications in solar fuel generation. In this work, the feasibility of exploiting the localized surface plasmon resonance property of self-doped, nonstoichiometric semiconductor nanocrystals for the realization of wide-spectrum-driven photocatalysis is highlighted.

Growth of ß-Ga2O3 and GaN nanowires on GaN for photoelectrochemical hydrogen generation.

Enhanced photoelectrochemical (PEC) performances of Ga(2)O(3) and GaN nanowires (NWs) grown in situ from GaN were demonstrated. The PEC conversion efficiencies of Ga(2)O(3) and GaN NWs have been shown to be 0.906% and 1.09% respectively, in contrast to their 0.581% GaN thin film counterpart under similar experimental conditions. A low crystallinity buffer layer between the grown NWs and the substrate was found to be detrimental to the PEC performance, but the layer can be avoided at suitable growth conditions. A band bending at the surface of the GaN NWs generates an electric field that drives the photogenerated electrons and holes away from each other, preventing recombination, and was found to be responsible for the enhanced PEC performance. The enhanced PEC efficiency of the Ga(2)O(3) NWs is aided by the optical absorption through a defect band centered 3.3 eV above the valence band of Ga(2)O(3). These findings are believed to have opened up possibilities for enabling visible absorption, either by tailoring ion doping into wide bandgap Ga(2)O(3) NWs, or by incorporation of indium to form InGaN NWs.

Piezo-Flexocatalysis of Single-Atom Pt-Loaded Graphitic Carbon Nitride.

This study develops a single-atom Pt-loaded graphitic carbon nitride (SA-Pt/CN) and evaluates its piezo-flexocatalytic properties by conducting a hydrogen evolution reaction (HER) and Rhodamine B (RB) dye degradation test under ultrasonic vibration in the dark. SA-Pt/CN has a hydrogen gas yield of 1283.8 µmol g-1  h-1 , which is 23.3 times higher than that of pristine g-C3 N4 . Moreover, SA-Pt/CN enhances the dye degradation reaction rate by ≈2.3 times compared with the pristine sample. SA-Pt/CN exhibits lattice distortion and strain gradient enlargement caused by the single atom Pt at the N sites of g-C3 N4 , which disrupts the symmetric structure and contributes to the enhancement of piezoelectric and flexoelectric polarization. As far as it is known, this is the first study to investigate the piezo-flexocatalytic reaction of SA-Pt/CN without light irradiation and provides new insights into single-atom piezocatalysts.

Carbon-Free Conversion of SiO2 to Si via Ultra-Rapid Alloy Formation: Toward the Sustainable Fabrication of Nanoporous Si for Lithium-Ion Batteries.

Silicon has the potential to improve lithium-ion battery (LIB) performance substantially by replacing graphite as an anode. The sustainability of such a transformation, however, depends on the source of silicon and the nature of the manufacturing process. Today's silicon industry still overwhelmingly depends on the energy-intensive, high-temperature carbothermal reduction of silica─a process that adversely impacts the environment. Rather than use conventional thermoreduction alone to break Si-O bonds, we report the efficient conversion of SiO2 directly to Mg2Si by a microwave-induced Mg plasma within 2.5 min at merely 200 W under vacuum. The underlying mechanism is proposed, wherein electrons with enhanced kinetics function readily as the reductant while the "bombardment" from Mg cations and electrons promotes the fast nucleation of Mg2Si. The 3D nanoporous (NP) Si is then fabricated by a facile thermal dealloying step. The resulting hierarchical NP Si anodes deliver stable, extended cycling with excellent rate capability in Li-ion half-cells, with capacities several times greater than graphite. The microwave-induced metal plasma (MIMP) concept can be applied just as efficiently to the synthesis of Mg2Si from Si, and the chemistry should be extendable to the reduction of multiple metal(loid) oxides via their respective Mg alloys.

Oxygen-Bridged Stabilization of Single Atomic W on Rh Metallenes for Robust and Efficient pH-Universal Hydrogen Evolution.

Highly efficient and durable electrocatalysts are of the utmost importance for the sustainable generation of clean hydrogen by water electrolysis. Here, we present a report of an atomically thin rhodium metallene incorporated with oxygen-bridged single atomic tungsten (Rh-O-W) as a high-performance electrocatalyst for pH-universal hydrogen evolution reaction. The Rh-O-W metallene delivers ascendant electrocatalytic HER performance, characterized by exceptionally low overpotentials, ultrahigh mass activities, excellent turnover frequencies, and robust stability with negligible deactivation, in pH-universal electrolytes, outperforming that of benchmark Pt/C, Rh/C and numerous other reported precious-metal HER catalysts. Interestingly, the promoting feature of -O-W single atomic sites is understood via operando X-ray absorption spectroscopy characterization and theoretical calculations. On account of electron transfer and equilibration processes take place between the binary components of Rh-O-W metallenes, fine-tuning of the density of states and electron localization at Rh active sites is attained, hence promoting HER via a near-optimal hydrogen adsorption.