Surface Electronic Structure Research Articles

Strained Au skin on Mesoporous Intermetallic AuCu3 Nanocoral for Electrocatalytic Conversion of Nitrate to Ammonia across a Wide Concentration Range.

Electrochemical nitrate reduction reaction (NitRR) uses nitrate from wastewater, offering a hopeful solution for environmental issues and ammonia production. Yet, varying nitrate levels in real wastewater greatly affect NitRR, slowing down its multi-step process. Herein, a multi-strategy approach was explored through the design of ordered mesoporous intermetallic AuCu3 nanocorals with ultrathin Au skin (meso-i-AuCu3@ultra-Au) as an efficient and concentration-versatile catalyst for NitRR. The highly penetrated structure, coupled with the compressive stress exerted on the skin layer, not only facilitates rapid electron/mass transfer, but also effectively modulates the surface electronic structure, addressing the concentration-dependent challenges encountered in practical NitRR process. As expected, the novel catalyst demonstrates outstanding NitRR activities and Faradaic efficiencies exceeding 95 % across a real and widespread concentration range (10-2000 mM). Notably, its performance at each concentration matched or exceeded that of the best-known catalyst designed for that concentration. Multiple operando spectroscopies unveiled the catalyst concurrently optimized the adsorption behavior of different intermediates (adsorbed *NOx and *H) while expediting the hydrogenation steps, leading to an efficient overall reduction process. Moreover, the catalyst also displays promising potential for use in ammonia production at industrial-relevant current densities and in conceptual zinc-nitrate batteries, serving trifunctional nitrate conversion, ammonia synthesis and power supply.

Construction of ZnAl LDH-Derived Sulfides with Etching Modification to Trigger Photocatalytic H2 Production and Degradation Oxidation.

Constructing novel functional photocatalysts represents a promising approach to optimize the energy band structure and facilitate the separation of photogenerated carriers. Layered double hydroxides (LDHs) exhibit notable advantages in photocatalysis due to the exceptional photoelectrochemical properties and elevated number of active surface atoms. However, an unsuitable band gap and limited carrier migration have inhibited their development in photocatalysis. Herein, we propose a novel in situ topological vulcanization strategy for optimizing the photocatalytic activity of ZnAl LDH-derived sulfides (ZnAlSx). The subsequent etching process via a 1 M NaOH solution was introduced to construct the ZnSx photocatalysts. Then, the crystallinity of the crystals was enhanced by etching to further improve the catalytic activity and stability of ZnSx. The as-synthesized ZnSx shows an excellent photocatalytic hydrogen production rate (11.89 mmol/g/h) and tetracycline degradation efficiency (91.94%) under light illumination, and its hydrogen evolution efficiency is approximately 176 and 2 times greater than that of ZnAl LDH and ZnAlSx, respectively. The characterization and density functional theory (DFT) analysis confirmed that the surface electronic properties and energy band structure of ZnAl LDH were significantly optimized after experimental treatment, resulting in enhanced carrier separation and photooxidative reduction capacity. Combining in situ topological vulcanization and etching to realize the functional conversion of ZnAl LDH provides promising insights into the construction of high-performance, low-cost photocatalysts.

Symbolic transform optimized convolutional neural network model for high-performance prediction and analysis of MXenes hydrogen evolution reaction catalysts

Two-dimensional MXenes materials are expected to be cost-effective and efficient catalysts for hydrogen evolution reaction (HER) due to their tunable surface electronic structure. To optimize its catalytic activity, this study proposes a data-driven framework (CROSST) to generate descriptors through feature engineering and integrate them into a convolutional neural network to predict the HER performance of transition-metal (TM) anchored bis-transition-metal carbon-nitride (TM-M′2M′′CNO2) catalysts. The STCNN model achieves a coefficient of determination of more than 0.93, showing the ability to predict the Gibbs free energy of hydrogen adsorption (ΔGH) with high accuracy. We explored the microscopic mechanisms of HER activity through density functional theory and machine learning analysis. It was found that TM anchoring altered the charge distribution of the MXenes material, elevated the atomic orbital occupancy of neighboring O sites, and weakened the O adsorption of H, thus affecting the HER activity. These results provide a theoretical basis for the design of high-performance MXenes HER catalysts and contribute new research perspectives.

Exploring the low-index surfaces of D52-La2O3 from the first-principles calculations

The surface relaxations, surface stability, electronic structures, and equilibrium morphology of D52-La2O3 were analyzed by means of first-principles calculations. The stoichiometric surfaces of D52-La2O3 possess thermodynamic energies of the following order: (001) < (110) < (100). Changes in temperature and the partial pressure of oxygen were employed to determine the energy of the non-stoichiometric surfaces. The results indicated that the energies of the (ns-1La1O)-terminated (100) and (ns-1La)-terminated (001) surfaces increased with increasing oxygen partial pressures and decreased with temperatures, whereas the (ns-1O)-terminated (001) and (ns-1O)-terminated (100) surfaces exhibited the reverse rule. According to the calculated density of states, surface relaxations primarily impact the surface electronic structures. The Gibbs-Wulff model was used to forecast the equilibrium morphology of D52-La2O3, which followed in comparison with other’s experimental findings.

Controllable Regulation of MoS2 Surface Atomic Exposure for Boosting Interfacial Polarization and Microwave Absorption

AbstractAtomic‐level surface design of 2D materials, which benefits from their ultra‐high occupancy of surface atoms, has demonstrated significant potential for regulating electronic states. Despite efforts to explore heterojunctions on 2D surfaces, the stacking‐dominated surface electronic structures and their influences on dielectric polarization remain unclear. Herein, a confined growth strategy is proposed to accurately adjust the surface atom occupancy of MoS2 nanoflakes and thereby boost the polarization‐dominated microwave absorption (MA). By altering the stacking layer number from single layers to tens of layers of MoS2, the charge transfer from graphite substrate to MoS2 surface atoms, accompanied by the formation of local electric fields, reaches its highest intensity at two layers and then degrades dramatically with thicker MoS2 nanoflakes. The strengthened dielectric properties eventually enhance the MA performance, increasing the maximum absorption intensity (41.9 dB) by 346% and the effective absorption bandwidth (3 GHz) by 750%. These discoveries shed new light on the electronic modification of 2D materials and their electromagnetic functionalization.

Energy-Saving Ambient Electrosynthesis of Nylon-6 Precursor Coupled with Electrocatalytic Upcycling of Polyethylene Terephthalate.

Cyclohexanone oxime is an important intermediate in the chemical industry, especially for the manufacture of nylon-6. The traditional cyclohexanone oxime production strongly relies on cyclohexanone-hydroxylamine and cyclohexanone ammoxidation processes, which require harsh reaction conditions and consume considerable amounts of energy. Herein, direct electrosynthesis of cyclohexanone oxime is reported from environmental pollutants nitrite and cyclohexanone with almost 100% yield by using low-cost Cu2Se nanosheets as electrocatalysts. Combination of in situ Fourier transform infrared spectroscopy and theoretical calculations verifies that the p-d orbital hybridization between Cu and Se elements could synergistically optimize the surface electronic structure and enable improved adsorption and formation of the key active N intermediate NH2OH*, thereby enhancing cyclohexanone/nitrite-to-cyclohexanone oxime conversion over the Cu2Se nanosheets. Based on these, an efficient asymmetric co-electrolysis system is further demonstrated by coupling cyclohexanone/nitrite-to-cyclohexanone oxime conversion with the upcycling of polyethylene terephthalate plastics, achieveing energy-saving simultaneously production of value-added products (cyclohexanone oxime and glycolic acid).

Amorphous NiB layer deposition and piezoelectric field assisted for efficient photocatalytic degradation of Sb2S3

The poor surface charge reaction efficiency and electrical conductivity limit the further application of Sb2S3 in photocatalytic degradation of pollutants. An amorphous NiB layer was deposited on the surface of Sb2S3 by photo-assisted electrodeposition, and the presence of the NiB layer accelerated the charge transport and catalytic reactivity, which greatly enhanced the degradation ability. The photocurrent density of NiB-Sb2S3 was about 0.12 mA/cm2, which was 6 times of that of pure Sb2S3. After increasing the applied mechanical site by ultrasonication, the photocurrent of NiB-Sb2S3 was further increased to 0.19 mA/cm2, which was almost 9.5 times that of pure Sb2S3 under photocatalytic conditions alone. The catalytic kinetic curves show that the degradation rate of RhB by NiB-Sb2S3 under piezoelectric-photocatalytic conditions is significantly increased, being 11.48 times of the degradation rate of Sb2S3 under photocatalytic conditions. The detailed experimental data indicate that the amorphous NiB layer not only changes the electronic structure of the catalyst surface, but also increases the number and activity of the catalyst active sites, and reduces the chance of electron and hole recombination after photoexcitation. The introduction of an applied piezoelectric field provided a driving force for carrier migration to the catalyst surface, which further improved the separation ability. This study provides a new strategy to further improve the photocatalytic degradation.

Se vacancies and interface engineering modulated bifunctionality prussian blue analogue derivatives for overall water splitting

It is a challenging task to design and synthesize stable, and high-performance non-precious metals bifunctional catalysts for water-splitting. Herein, the coupling between Se vacancy and interface engineering is highlighted to synthesize a unique CoFeSe hollow nanocubes structure on MXene-modified nickel foam (NF) by in-situ phase transition from bifunctionality prussian blue analogue (PBA) derivatives (VSe-CoFeSe@MXene/NF). DFT theory reveals that the Se vacancy and interface engineering modulate the surface electronic structure and optimize the surface adsorption energy of the intermediates. Experimental data also confirm that the as-prepared CoFeSe@MF catalyst exhibits advanced electrocatalytic properties, 283 mV (OER) and 67 mV (HER) are required to drive the current density of 10 mA cm−2. Notably, it is assembled into a two-electrode system for integral water decomposition, which only requires a low cell potential of 1.57 V at current of 10 mA cm−2, together with excellent durability for 48 h. The strategy is expected to provide a new direction for the design and construction of highly efficient collaborative integrated water decomposition electrocatalysts.

Controlled Electrode-Electrolyte Interphases (EEI) Formation Via Ex-Situ Interfacial Synthesis

The stability and electrochemical performance of energy storage systems are heavily influenced by their interfaces. The electrode-electrolyte interphases (EEIs) present at these interfaces are typically formed in-situ through the electrochemically induced complex interactions involving the electrode surface and bulk electronic structure, functional groups and chemical species present at the interface, and electrolyte. Given the importance of interface stability in energy storage, herein, multiple ex-situ approaches (electrochemical fluorination, ion-exchange metathesis, layer-by-layer coating) have been explored to form stable and controlled EEI that allow ion transport and limit the electron leakage. Such controlled EEI via ex-situ interfacial synthesis demonstrated significantly improved cycling stability compared to in-situ EEI formation.

Morphological and Surface Electronic Structure Design of Alloys Electrocatalyst for Alkaline HER

Among the various hydrogen production methods, water electrolysis provides numerous advantages, including high purity of the produced hydrogen and low carbon emission. In this context, one of the concerns is associated with the replacement, or partial replacement, of noble-metal electrocatalyst for hydrogen evolution reaction (HER) by low-cost, commercially viable ones. To achieve this objective, alloying provides a direct way to tailor the electronic structure of active site and hence is expected to effectively reduce the usage of noble metal. Furthermore, increasing the surface area through morphology design is considered a promising method for enhancing catalyst activity. Among the diverse strategies to increase the surface area, dealloying plays a unique role by generating porous structure, thereby offering advantages in terms of cost-effectiveness and controllable structure. In this study, we have synthesized various Zn-Ni based alloy electrocatalysts using a facile solvothermal method, followed by a dealloying process. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry are used to examine the morphology, composition, and electronic structure. The electrochemical performance is investigated using linear sweep voltammetry, electrochemical impedance spectroscopy, cyclic voltammetry, and electrochemical specific surface area analyses. We demonstrate that resulting HER alloy electrocatalyst exhibits a low overpotential and Tafel slope, and good stability over 200 hours.

Stearic acid as a potential interlayer at the FAPI/hole transport layer interface

In this study, we explore the potential of using an ultra-thin film of stearic acid (SA) as an interlayer at the interface between the active material and the hole transport layer (HTL) in perovskite solar cells (PSCs). The FAPbI3 active material thin film was fabricated under ambient conditions using the antisolvent method, followed by the deposition of stearic acid overlayers of varying coverages/thicknesses. By adjusting the coverage/thickness of the SA overlayer, the electronic structure of the perovskite surface can be finely tuned, which may potentially lead to favorable energy level alignment at the perovskite/HTL interface. The interaction between the perovskite thin film and the stearic acid overlayer is expected to involve coordination between defects on the perovskite surface and the carboxyl group of stearic acid. The presence of the nonpolar alkyl chain of stearic acid on the perovskite surface enhances material stability by preventing water and oxygen ingress. Our findings suggest that introduction of SA interlayer at the perovskite/HTL interface may enhance operational stability and efficiency of PSCs by improving the charge transfer across the interface through optimization of energy level alignment and reduction of recombination sites, and protect the absorber from environmental factors like water and oxygen.

In-situ electrochemical interface of Cu@Ag/C towards the ethylene electrosynthesis with adequate *CO supply

The conversion of carbon dioxide to ethylene by electrochemical reduction (CO2RR) provides a new strategy for achieving carbon dioxide conversion. However, copper-based catalysts have the disadvantages of unsatisfactory selectivity and low current density, which limit the potential CO2RR industrial expansion. Researches have verified that the real reaction sites at the catalyst surface often undergo reconstruction during the reaction, therefore, understanding and utilizing this phenomenon is crucial for improving catalytic performance. In this work, we introduced additional Ag component into Cu@Ag/C tandem catalyst by in-situ electrochemical reconstruction of Cu2CO3(OH)2/AgCl/C precursor. This electro-reduced catalyst exhibits a C2H4 Faradaic efficiency of 50.41% in H-cell, and 58.03% in the flow cell, surpassing the counterparts of pure Cu and Ag, as well as the Cu-Ag homolog with separated interface. Moreover, it also provides a long-term stability of 21 h with the ethylene Faraday efficiency (FE) over 50%. The appropriate amount of Ag dopant into the Cu catalyst changes the electronic structure of Cu surface by the electron transfer from Cu to Ag, which distinctly enhances the binding energy of CO2 on the catalyst. Meanwhile, in-situ Raman results and theoretical calculation reveal that the introduction of silver increases the number of active sites and improves the coverage of *CO intermediate, thereby accelerating the kinetics of C–C coupling and reducing its energy barrier. The combination of cascade catalytic strategy and in-situ electroreduction interface provides potential applications for future artificial carbon balance.

Surface reconstructions and electronic structure of metallic delafossite thin films

Surface reconstructions and electronic structure of metallic delafossite thin films

Plasma-modified Co3O4 nanosheets for efficient CO detection: Insight into the structure-activity relationship

Exploring the correlation between crucial reactive sites and surface electron structure in the sensitive layer of gas sensors can achieve simultaneous optimization of kinetics and thermodynamics. In this work, Ar and O2 plasma sputtering are used to study how varying levels of Co3+ and oxygen vacancy affect the gas-sensitivity of Co3O4. The gas-sensing performance of Co3O4-O2PT (O2 plasma sputtering) is better than that of Co3O4-ArPT (Ar plasma sputtering), which exhibits a high response value (100 ppm-4.16) and quick response-recovery time (1.5 s/38 s). The enhancement of gas-sensing performance benefits from a high Co3+/Co2+ ratio, which provides strong CO-selective adsorption and oxidation capabilities. Therefore, the interfacial oxidation reaction reaches equilibrium rapidly. This work provides a straightforward and controllable modification approach and enhances the understanding of how oxygen vacancies and Co3+ affect Co3O4 gas sensors, which promotes the design and development of high-performance cobalt-based gas sensors.

Strain Effects in the Work Function and Charge Transfer of the Au(111) Surface.

Work function (WF) is one of the most fundamental physical parameters of metal surfaces, which can not only reflect the electronic structure of metal surfaces but is also very sensitive to the surface microstructure. In this paper, we use first-principles calculations to systematically study the strain effects on the vacuum level, Fermi level, and WF of the Au(111) surface. We find that the vacuum level and Fermi level of the Au(111) surface increase under compressive strain and decrease under tensile strain, and the effects of biaxial strain on the vacuum level and Fermi level can be equivalent to the superposition of two perpendicular uniaxial strains. These strain effects are attributed to the charge transfer induced by the strain. However, the change of WF with strain is the result of the competition between the strain effects of the vacuum level and Fermi level. That leads to the WF increasing with compressive uniaxial strain and decreasing with tensile uniaxial strain. Moreover, because the Fermi level is more responsive to compressive uniaxial strain, the Fermi level changes faster than the vacuum level under compressive biaxial strain. Consequently, the WF decreases with increasing tensile biaxial strain and slightly increases before decreasing with increasing compressive biaxial strain.

Decreased Metal Dusting Resistance of Ni-Cu Alloys by Fe and Mn Additions

AbstractNi-Cu alloys are promising for application at temperatures between 400–900 °C and reducing atmospheres with high C-contents. Typically, under such conditions, metallic materials in contact with the C-rich atmosphere are degraded by a mechanism called metal dusting (MD). Ni-Cu-alloys do not form protective oxide scales, but their resistance is attributed to Cu, which catalytically inhibits the C-deposition on the surface. Adding other alloying elements, such as Mn or Fe, was found to enhance the MD attack of Ni-Cu alloys again. In this study, the effect of the Mn and Fe is divided into two affected areas: the surface and the bulk. The MD attack on binary Ni-Cu alloys, model alloys with Fe and Mn additions, and commercial Monel Alloy 400 is experimentally demonstrated. The surface electronic structure causing the adsorption and dissociation of C-containing molecules is investigated for model alloys. Analytical methods such as scanning electron microscopy combined with energy-dispersive X-ray spectroscopy, electron probe microanalysis combined with wavelength-dispersive X-ray spectroscopy, X-ray diffraction analysis, and near-edge X-ray absorption fine structure measurements were used. The results are correlated to CALPHAD calculations and atomistic simulations combining density functional theory calculations and machine learning. It is found that the Cu content plays a significant role in the surface reaction. The effect of Mn and Fe is mainly attributed to oxide formation. A mechanism explaining the enhanced attack by adding both Fe and Mn is proposed.

Electronic perturbation of Cu nanowire surfaces with functionalized graphdiyne for enhanced CO2 reduction reaction

Abstract Electronic perturbation of Cu catalysts surface is crucial for optimizing electrochemical CO2 reduction activity, yet still poses great challenges. Herein, nanostructured Cu nanowires (NW) with fine-tuned surface electronic structure are achieved via surface encapsulation with electron-withdrawing (–F) and -donating (–Me) group-functionalized graphdiynes (R-GDY, R = –F and –Me), and the resulting catalysts, denoted as R-GDY/Cu NW, display distinct CO2 reduction performances. In-situ electrochemical spectroscopy revealed that the *CO (a key intermediate of the CO2 reduction reaction) binding affinity and consequent *CO coverage positively correlate to the Cu surface oxidation state, leading to the favorable C–C coupling on F-GDY/Cu NW over Me-GDY/Cu NW. Electrochemical measurements corroborate the favorable C2H4 production with an optimum C2+ selectivity of 73.15% ± 2.5% observed for F-GDY/Cu NW, while the predominant CH4 production is favored by Me-GDY/Cu NW. Furthermore, leveraging the *Cu–OH/*CO ratio as a descriptor, mechanistic investigation reveals that the protonation of distinct adsorbed *CO facilitated by *Cu–OH is crucial for the selective generation of C2H4 and CH4 on F-GDY/Cu NW and Me-GDY/Cu NW, respectively.

Chemical Trends of the Bulk and Surface Termination-Dependent Electronic Structure of Metal-Intercalated Transition Metal Dichalcogenides.

The addition of metal intercalants into the van der Waals gaps of transition metal dichalcogenides has shown great promise as a method for controlling their functional properties. For example, chiral helimagnetic states, current-induced magnetization switching, and a giant valley-Zeeman effect have all been demonstrated, generating significant renewed interest in this materials family. Here, we present a combined photoemission and density-functional theory study of three such compounds: , , and , to investigate chemical trends of the intercalant species on their bulk and surface electronic structure. Our resonant photoemission measurements indicate increased hybridization with the itinerant NbS2-derived conduction states with increasing atomic number of the intercalant, leading to pronounced mixing of the nominally localized intercalant states at the Fermi level. Using spatially and angle-resolved photoemission spectroscopy, we show how this impacts surface-termination-dependent charge transfers and leads to the formation of new dispersive states of mixed intercalant-Nb character at the Fermi level for the intercalant-terminated surfaces. This provides an explanation for the origin of anomalous states previously reported in this family of compounds and paves the way for tuning the nature of the magnetic interactions in these systems via control of the hybridization of the magnetic ions with the itinerant states.

Efficient photoreduction of CO2 to tunable syngas by Zn-doped Co3O4: Tuning binding strength to versatile reaction intermediates simultaneously

Photochemical reduction of CO2 (CO2RR) to syngas is an attractive approach for carbon–neutral recycling. Manipulating binding strength to reactive species on catalyst surfaces is challenging but essential for achieving efficient syngas production with a desired CO/H2 ratio. Here, we demonstrate that the binding strength to key reaction intermediates (*CO2, *H and *CO) on the Co3O4 surface can be fine-tuned by incorporating varying amount of Zn atoms. Dedicated experiments and theoretical simulations unveil that Zn doping allows for simultaneous control of both CO2 adsorption/activation and the adsorption affinity of *CO on Zn-Co3O4 catalysts, resulting in a significant enhancement in CO2 to CO conversion. Moreover, Zn doping can alter the hydrophilicity of the catalyst surface, affecting the water adsorption behavior and adjusting the hydrogen evolution reaction (HER) activity. As a result, the CO/H2 ratio can be readily tuned via varying the Zn doping level. This study presents an effective and economical method approach to manipulate the electronic structure of catalyst surfaces for controlling the kinetics of CO2RR and HER reactions, providing valuable insight into the design of highly active transition metal oxides (TMOs) based photocatalysts for syngas production with a tailored CO/H2 ratio.

Interface engineering assisted La1-xSrxCoO3/FeOOH heterostructure as a high-performance electrocatalyst for oxygen evolution reaction

Perovskite oxides play a crucial role as catalysts in the oxygen evolution reaction (OER) owing to their distinctive structure and diverse physical and chemical characteristics. Currently, enhancing the electronic structure and specific surface area of the perovskite surface through strategic regulation poses a significant challenge in the advancement of perovskite catalyst development. Here, we propose a novel method for enhancing the OER activity of LaCoO3 (LCO) perovskite through atomic doping and interface engineering. The La0.6Sr0.4CoO3–FeOOH (Fe-LSCO) composite exhibits a notable enhancement in electrocatalytic performance, manifesting a low overpotential of 296.3 mV for the oxygen evolution reaction (OER) at a current density of 10 mA cm−2, while maintaining a high level of activity for a duration of 120 h. The enhanced activity of Fe-LSCO can be attributed to oxygen vacancy defects and the increase of the active site caused by A-site-doping and amorphous nanosheets of FeOOH, which synergistic effect reduces the energy barrier for water dissociation. The highly disordered surface and high surface energy of amorphous FeOOH render it highly active. This study presents a viable interface engineering approach for manipulating the reconstruction of the active phase in high-performance perovskite-based electrocatalytic materials.