Surface Electronic Structure Research Articles

Probing electronic-structure pH-dependency of Au nanoparticles through X-ray Absorption Spectroscopy

Research on gold nanoparticles (Au NPs) remains a field of intense activity due to their broad range of applications in diverse fields like catalysis, renewable energy, environmental science, and medicine. Herein, the morphological and electronic structures investigation of Au NPs prepared at different pH values is reported. The dependence of the localized surface plasmon resonance wavelength and electronic structure with size was determined by combining transmission electron microscopy, and various spectroscopic methods led by X-ray absorption spectroscopy. The X-ray absorption experiments evidenced that the citrate-stabilized Au NPs bulk electronic structure remains intact over a broad range of pHs, and changes were detected resulting from differences in NPs surface terminations.

Hierarchical Reactions Involving Dynamic Structural Changes in Lithium-Ion Batteries during Overcharge Using Advanced Analytical Techniques

Abstract High-Ni cathode materials are promising for lithium-ion batteries compared to conventional cathode materials because of relatively high energy density and low cost. High-Ni cathodes are inherently thermally unstable, and when used in large scale batteries, they can cause serious problems such as thermal runaway and associated destruction of the internal structure. For practical use, it is necessary to understand the internal phenomena when they are incorporated into large scale batteries. We examined the stacked electrode structural change inside pouch cells with approximately 1 Ah capacity during over charging, which includes LiNi0.8Mn0.1Co0.1O2, LiNi0.6Mn0.2Co0.2O2, and LiCoO2 athodes, by using synchrotron-based operando X-ray radiography. In addition, the bulk crystalline, electronic, and local structures of these materials as well as surface electronic structure changes during overcharging were also analyzed. We found that as the amount of Ni-content in the cathodes increase, destabilization of surface oxygen and structural phase transitions occur at smaller state of charge, leading to faster and more severe collapse of the stacked electrode structure inside the pouch cells. This finding of a relationship of hierarchical structural changes from the cathode surface to the pouch cell is useful for the safe use of lithium-ion batteries with high energy density containing high-Ni cathodes.

Nitrogen substitution of bilayer penta-carbides: high solar-to-hydrogen conversion efficiency and excellent electrocatalytic activity for water splitting.

The shortage of fossil energy and environmental crises are two important issues in the 21st century, and the search for alternatives to fossil fuels, e.g. H2, is crucial. Herein, based on penta-germagraphene p-Ge2C4, bilayer penta-carbides of p-Ge4C8 and nitrogen substituted materials p-Ge4NnC8-n are proposed. The results indicate that gradually replacing the carbon atoms on the surface of p-Ge4C8 with nitrogen atoms can change the surface activities and electronic structures, and this is beneficial for both photocatalysis and electrocatalysis. The vertical intrinsic electric field in the two-dimensional materials can enhance photocatalytic water splitting of p-Ge2C4/Ge2N2C2 and break the conventional limitation of 1.23 eV for the band gap of photocatalysts. Therefore, solar energy conversion efficiency can reach 31%. The smaller effective mass and deformation potential of p-Ge2C4/Ge2N2C2 along the x and y directions lead to a huge electron mobility (425.64 × 103 cm2 V-1 s-1) at room temperature. Moreover, the overpotential for the hydrogen evolution reaction of p-Ge2C4/Ge2N2C2 is 0.074 V, which is beneficial for electrocatalysis. The external strain and electric field can also enrich the electronic properties. Surface modification achieved by introducing the nitrogen atoms can improve the catalytic performance of penta-carbides.

Anionic Disorder and Its Impact on the Surface Electronic Structure of Oxynitride Photoactive Semiconductors

Anionic Disorder and Its Impact on the Surface Electronic Structure of Oxynitride Photoactive Semiconductors

Economical iron-based catalyst electrode for highly stable catalytic industrial-scale overall seawater splitting

The development of economical and stable catalyst electrodes for industrial-scale seawater splitting is one of the current challenges in hydrogen production. The economical transition metals possess high electrical conductivity and offer the potential for designing electrodes with high intrinsic activity through appropriate modifications, thus holding promising applications in industrial contexts. Herein, a durable and economical self-supported bifunctional electrode (Fe@Ni) with high efficiency and large area is successfully constructed by one step in-situ deposition of iron on the porous structure of nickel foam (NF) via mild (298 K) electroplating method. Transition metals like iron and nickel offer high electrical conductivity and can be properly modified to achieve electrodes with high intrinsic activity. Due to the in-situ growth of cost-effective iron on the NF surface, the electrode surface morphology and electronic structure are reconstructed, which significantly improves the electrochemical activity surface area and electron transfer capability of the electrode. The hydrogen/oxygen evolution reaction (HER/OER) in simulated seawater (1 M KOH + 0.5 M NaCl) require only 129 mV and 323 mV overpotentials to achieve a current density of 100 mA cm−2. Overall seawater splitting (OWS) achieves 10 mA cm−2 at a low voltage of 1.49 V and with a faradaic efficiency of nearly 100%. More importantly, the bifunctional electrodes remain stable at industrial-level current density (1.0 A cm−2) for more than 50 days. More attractively, this work realizes the universal construction of large-area electrode for multiple metals (e.g., Fe, Cu, Al, etc.) with mild and simple process, which provides a new strategy for the current research of energy and materials.

Assessing the Effect of a Schwarz P Surface on the Oxygen Electroreduction Performance of Porous Single-Atom Catalysts.

The surface curvature of catalysts has a decisive impact on their catalytic performance. However, the influence of a negative-Gaussian-curvature surface on the catalytic performance of porous catalysts has remained unexplored due to the lack of suitable samples. Bicontinuous-structured porous structures can serve as ideal models, but they are known as "Plumber's nightmare" due to their highly difficult preparation. Here, using metal-organic frameworks as the precursor and polymer cubosomes as the template, a bicontinuous mesoporous Fe single-atom catalyst (named bmFeSAC) with a Schwarz P surface is synthesized. The bmFeSAC catalyst has a large specific surface area of 916m2g-1 and uniformly distributed Fe-N4 active sites with a 1.80wt.% Fe content. The continuous channels enabled high utilization efficiency of the Fe-N4 catalytic sites, while the negative-Gaussian-curvature surface enabled low reaction energy barrier. As an electrocatalyst of the oxygen reduction reaction, bmFeSAC delivered a high half-wave potential of 0.931V versus. RHE in alkaline electrolyte, reaching the leading level among those of the reported state-of-the-art electrocatalysts. Furthermore, the bmFeSAC-based Zn-air batteries exhibited excellent performance, demonstrating the potential application of bmFeSAC. This study revealed that a bicontinuous-structured porous structure can improve catalytic activity by increasing the utilization ratio of catalytic sites and, more importantly, by regulating the electronic structure of catalyst surfaces through the negative-Gaussian-curvature.

High-Entropy Metal Sulfide Promises High-Performance Carbon Dioxide Reduction.

The efficient conversion of carbon dioxide (CO2) requires the development of stable catalysts with high selectivity and reactivity within a wide potential range. Here, the high-entropy metal sulfide CuAgZnSnS4 is designed for CO2 reduction with excellent performance (FEcarbonproducts ≥ 90%) in whole test potential windows (600 mV) based on the synergistic effect of the high-entropy metal sulfide. In particular, CuAgZnSnS4 exhibits better single-product selectivity with the highest FEHCOOH/FECO value (29.03) at -1.28 versus reversible hydrogen electrode (RHE). In combination with in situ measurements and theoretical calculations, it is further revealed that the synergistic effect of CuAgZnSnS4 realizes the controllable regulation of the surface electronic structure at Sn active sites, strengthening orbital interactions between *OCHO and Sn active sites. As a result, the effective adsorption and activation of *OCHO instead of *H are obtained, improving the single-product selectivity of electrocatalytic CO2 reduction and inhibiting the competitive hydrogen evolution reaction significantly. Our findings may complete the understanding of the synergistic effect for high-entropy materials in catalysis and offer new insight into the design of efficient electrocatalysts with high catalytic activity.

The role of conduction band electrons in promoting O2 adsorption to silicon interfaces

Resonance enhanced Second Harmonic Generation (SHG) was employed to assess if conduction band electrons in silicon (Si) will promote molecular adsorption of ambient species and how such adsorption depends on temperature. Experiments were performed with three types of Si (n-doped or n-Si, p-doped or p-Si, and undoped Si) at temperatures between 18 and 260 °C and under atmospheres of dry N2 and dry (cylinder) air. All Si types were covered with a 2–4 nm thick native oxide layer. Under N2, all Si types behave similarly, with SHG intensity [I(2ω)] diminishing with increasing temperature. This effect was reversible and attributed to electron–phonon scattering. In the presence of O2, I(2ω) from n-Si at room temperature is enhanced significantly. Neither p-doped Silicon (p-Si) nor undoped Si show similar effects at room temperature, with I(2ω) being independent of gas phase composition. At temperatures ≥175 °C, all three Si types behaved similarly with no dependence on atmospheric O2 content. Varying the amount of O2 above n-Si at room temperature and measuring I(2ω) suggested that O2 adsorption to n-Si could be described with a Langmuir isotherm and an adsorption energy of −0.13 ± 0.05 eV. Increasing n-Si’s oxide thickness (to 600 nm) rendered the substrate insensitive to ambient gas phase composition. Taken together, these findings support a description of Si’s surface electronic structure that is controlled by n-Si conduction band electrons backbonding into the π* orbitals of adjacent O2 and imply that these conduction band electrons can affect adsorption despite the presence of a native oxide film.

An Angstrom-Scale Protective Skin Grown In Situ on Perovskite Oxide to Enhance Stability in Water.

The utilization of perovskite oxide as a catalyst for aqueous reactions is promising but challenging in stability. Here, we propose an in situ growth strategy that constructs an ultrathin protective skin on the Sr0.9Fe0.81Ta0.09Ni0.1O3-δ perovskite surface and thus effectively solves the stability issue. Using a spherical aberration-corrected transmission electron microscope, we observe the coexistence of an angstrom-scale (~7 Å) Fe2O3 protective skin and FeNi alloy nanoparticles. A number of alloy nanoparticles grow along with the skin and uniformly take root on the skin surface. Such a hierarchical structure can reconstruct the surface electronic structure and suppress the ion leaching of perovskite oxide in water. Benefiting from this unique structure, the catalyst has experienced a substantial increase (800 h, more than three orders of magnitude) in its stable operation time in water (for example, in a hydrogen evolution reaction). These results provide valuable insight into solid-solid phase transitions and have substantial implications for using structural defects at surfaces to modulate mass transport and transformation kinetics. Our strategy is sufficiently simple and can be used to subtly manipulate the catalyst structures to improve the performance of perovskite-based catalysts and potentially other oxide catalysts for a wide range of reactions.

An Angstrom‐Scale Protective Skin Grown In Situ on Perovskite Oxide to Enhance Stability in Water

AbstractThe utilization of perovskite oxide as a catalyst for aqueous reactions is promising but challenging in stability. Here, we propose an in situ growth strategy that constructs an ultrathin protective skin on the Sr0.9Fe0.81Ta0.09Ni0.1O3‐δ perovskite surface and thus effectively solves the stability issue. Using a spherical aberration‐corrected transmission electron microscope, we observe the coexistence of an angstrom‐scale (~7 Å) Fe2O3 protective skin and FeNi alloy nanoparticles. A number of alloy nanoparticles grow along with the skin and uniformly take root on the skin surface. Such a hierarchical structure can reconstruct the surface electronic structure and suppress the ion leaching of perovskite oxide in water. Benefiting from this unique structure, the catalyst has experienced a substantial increase (800 h, more than three orders of magnitude) in its stable operation time in water (for example, in a hydrogen evolution reaction). These results provide valuable insight into solid‐solid phase transitions and have substantial implications for using structural defects at surfaces to modulate mass transport and transformation kinetics. Our strategy is sufficiently simple and can be used to subtly manipulate the catalyst structures to improve the performance of perovskite‐based catalysts and potentially other oxide catalysts for a wide range of reactions.

Understanding the Electrochemical Carbon Dioxide Reduction Reaction Mechanism of Lattice Tuning of Copper by Silver Single-Crystal Surface.

Intermolecular interactions and adsorbate coverage on a metal electrode's surface/interface play an important role in CO2 reduction reaction (CO2RR). Herein, the activity and selectivity of CO2RR on bimetallic electrode, where a full monoatomic Cu layer covers on Ag surface (CuML/Ag) are investigated by using density functional theory calculations. The surface geometric and electronic structure results indicate that there is high electrocatalytic activity for CO2RR on the CuML/Ag electrode. Specifically, the CuML/Ag surface can accelerate the H2O and CO2 adsorption and hydrogenation while lowering the reaction energy of the rate-determining step. The structure parameters of chemisorbed CO2 with and without H2O demonstrate that activated H2O not only promotes the C-O dissociation but also provides the protons required for CO2RR on the CuML/Ag electrode surface. Furthermore, the various reaction mechanism diagrams indicate that the CuML/Ag electrode has high selectivity for CO2RR, and the efficiency of products can be regulated by modulating the reaction's electric potential.

Topological material in the III–V family: Heteroepitaxial InBi on InAs

InBi(001) is formed epitaxially on InAs(111)-A by depositing Bi onto an In-rich surface. Angle-resolved photoemission measurements reveal topological electronic surface states, close to the M¯ high symmetry point. This demonstrates a heteroepitaxial system entirely in the III–V family with topological electronic properties. InBi shows coexistence of Bi and In surface terminations, in contradiction with other III–V materials. For the Bi termination, the study gives a consistent physical picture of the topological surface electronic structure of InBi(001) terminated by a Bi bilayer rather than a surface formed by splitting to a Bi monolayer termination. Theoretical calculations based on relativistic density functional theory and the one-step model of photoemission clarify the relationship between the InBi(001) surface termination and the topological surface states, supporting a predominant role of the Bi bilayer termination. Furthermore, a tight-binding model based on this Bi bilayer termination with only Bi–Bi hopping terms, and no Bi–In interaction, gives a deeper insight into the spin texture. Published by the American Physical Society 2024

Elaboration of a new 4-(4-nitrophenyl)piperazin-1-ium tetrakis(thiocyanato)-cobalt hydrate: Crystal structure, optical properties, quantum computational investigation, electrical and biological study

The preparation, spectroscopic, biological, and electrical characterization, in addition to the X-ray crystal structure investigation of a novel three-dimensional compound (C10H14N3O2)2 [Co(NCS)4].H2O ((NPP)2[Co(NCS)4].H2O) is reported. The synthesized compound crystallizes in the Pna21 space group. The structure comprises layers of cobalt (II) bridged by terminally bound thiocyanate-N ligand achieving distorted MN4 tetrahedron surroundings around the metal center. The vibrational modes of the functional groups were investigated using FT-IR measurements. Hirshfeld surface (HS) analysis and electronic structures calculations reveal the excellent reactivity and intermolecular interactions in stabilizing complex. The change transfer and NLO parameters were also computed using the DFT method. The study of the optical behavior reveals a high optical property. Explorations of impedance spectroscopy on (NPP)2[Co(NCS)4].H2O reveals fascinating electrical behavior which reveals that the Co complex component can be used as an electronic chip under certain conditions. The thermal analysis was used to confirm the crystal’s thermal stability. The compound’s antimicrobial activity suggested that the Cobalt complex acts as an inhibitor Agent against different types of bacteria.

Insights into the Surface Electronic Structure and Catalytic Activity of InOx/Au(111) Inverse Catalysts for CO2 Hydrogenation to Methanol

Insights into the Surface Electronic Structure and Catalytic Activity of InO_<i>x</i>/Au(111) Inverse Catalysts for CO₂ Hydrogenation to Methanol

Surface‐Interface Engineering of Electrocatalysts for Two‐Electron Water Oxidation Reaction to Produce H2O2

AbstractElectrochemical two‐electron water oxidation reaction (2e− WOR) driven by renewable energy offers an attractive route to produce H2O2, while the corresponding electrocatalyst still requires further improvement for the activity, selectivity, and the resulting H2O2 yield. Surface‐interface engineering of electrocatalysts has great potential to advance 2e− WOR performance. This review provides a succinct yet comprehensive insight into the functional mechanisms of surface‐interfacial properties affecting 2e− WOR performance on electrocatalyst. The Gibbs free energy theoretical framework related to surface electronic structure and interfacial reactive kinetics mechanism related to electrolyte, electrode–electrolyte interface structure, and interfacial microenvironment properties are firstly discussed. Afterward, various surface‐interface engineering strategies toward high performance electrocatalysts including the regulation of surface electronic structure, the electrode–electrolyte interface structure, and the interfacial microenvironment have been overviewed. Rational manipulations of the above surface‐interfacial engineering strategies are critical to design highly efficient 2e− WOR electrocatalysts, leading to the development of the green H2O2 production.

Self-consistent quasiparticle GW and hybrid functional calculations for Al/InAs/Al heterojunctions: Band offset and spin-orbit coupling effects

The electronic structure of surfaces and interfaces plays a key role in the properties of quantum devices. Here, we study the electronic structure of realistic Al/InAs/Al heterojunctions using a combination of density functional theory with hybrid functionals and state-of-the-art quasiparticle GW (QSGW) calculations. We find a good agreement between QSGW calculations and hybrid functional calculations, which themselves compare favorably well with angle-resolved photoemission spectroscopy experiments. Our paper confirms the need for well-controlled quality of the interfaces to obtain the needed properties of InAs/Al heterojunctions. A detailed analysis of the effects of spin-orbit coupling on the spin splitting of the electronic states shows a linear scaling in k space, related to the two-dimensional nature of some interface states. The good agreement by QSGW and hybrid functional calculations opens the door towards trustable use of an effective approximation to QSGW for studying very large heterojunctions. Published by the American Physical Society 2024

Time-resolved photoelectron spectroscopy at surfaces

Light is still an important spectroscopic tool for investigating the electronic structure of surfaces. Time-resolved photoelectron spectroscopy has mainly been developed in the last 30 years. It is therefore not surprising that the topic was hardly mentioned in the last issue on “The first thirty years” of surface science. In the second thirty years, however, we have seen tremendous progress in the development of time-resolved photoelectron spectroscopy on surfaces. Femtosecond light pulses and advanced photoelectron detection schemes are increasingly being used to study the electronic structure and dynamics of occupied and unoccupied electronic states and dynamic processes such as the energy and momentum relaxation of electrons, charge transfer at interfaces and collective processes such as plasmonic excitation and optical field screening. Using spin- and time-resolved photoelectron spectroscopy, we were able to study ultrafast spin dynamics, electron-magnon scattering and spin structures in magnetic and topological materials. Light also provides photon energy as well as electric and magnetic fields that can influence molecular surface processes to steer surface photochemistry and hot-electron-driven catalysis. In addition, we can consider light as a chemical reagent that can alter the properties of matter by creating non-equilibrium states and ultrafast phase transitions in correlated materials through the coupling of electrons, phonons and spins. Electric fields have also been used to temporarily change the electronic structure. This opened up new methods and areas such as high harmonic generation, light wave electronics and attosecond physics. This overview certainly cannot cover all these interesting topics. But also as a testimony to the cohesion and constructive exchange in our ultrafast community, a number of colleagues have come together to share their expertise and views on the very vital field of dynamics at surfaces. Following the introduction, the interested reader will find a list of contributions and a brief summary in Section 1.3.

Self-adaptive reconstructed high-entropy sulfide catalysts with optimized surface electronic structure for lithium-oxygen batteries

Nonaqueous lithium-oxygen batteries have attracted immense attention owing to their high theoretical energy density. High-entropy based materials, encompassing both high-entropy alloys and high-entropy oxides (sulfides), have emerged as promising candidates for cathode catalysts. However, current fabrication methods for high-entropy materials, particularly high-entropy sulfides, remain complex and expensive. And the catalytic mechanism of high-entropy sulfides under oxygen-mediated reactions remains elusive and warrants further investigation. Herein, we propose a novel synthesis method for high-entropy sulfides, involving a hydrogel-xerogel conversion followed by a duplex treatment (low-temperature sulfuration and high-temperature calcination) processes. The synthesized (CoFeNiMnCu)9S8 high-entropy sulfide catalyst achieves elemental equilibrium and exhibits an optimized surface charge distribution. During oxygen-based battery reactions, the catalyst undergoes self-adaptive surface reconstruction, resulting in the formation of a nanoscale polycrystalline layer. This surface modification facilitates charge transfer between Co and Ni elements, and further modulates the localized electronic structure. Benefiting from the reconstructed (CoFeNiMnCu)9S8 cathode catalysts, lithium-oxygen batteries exhibit high reversible specific capacity (15100 mAh g−1), good rate capability, and enhanced long-term cycling stability.

Waste derived 0D nanomaterials for the catalysis reduction of p-nitrophenol: A technological progress and developments

The global concern regarding the persistence of p-nitrophenol (p-NP) in environmental matrices has intensified research efforts toward developing effective remediation strategies. Among these strategies, zero-dimensional nanomaterials (0D NMs) have emerged as highly promising candidates for the removal of p-NP due to their high surface area, tunable physicochemical properties, and versatile functionalization capabilities. This comprehensive review examines green synthesis methods for 0D NMs, utilizing various waste materials, in alignment with the principles of Sustainable Development Goals (SDGs) and circular economy. The mechanistic pathways that contribute to the efficacy of different 0D NMs in p-NP remediation were systematically investigate. By critically analyzing the extant literature, the key factors influencing the catalytic activity of these nanomaterials, such as surface morphology, electronic structure, and functional group interactions systematically were also investigated. Additionally, the current challenges and potential future directions for the large-scale application of 0D NMs in environmental remediation were also discussed. This review offers novel insights into developing sustainable, nanotechnology-based platforms for the efficient removal of p-nitrophenol, highlighting the significance of green chemistry and waste valorization in advancing environmental remediation technologies.

Efficient and Ultrastable Seawater Electrolysis at Industrial Current Density with Strong Metal-Support Interaction and Dual Cl--Repelling Layers.

Direct seawater electrolysis is emerging as a promising renewable energy technology for large-scale hydrogen generation. The development of Os-Ni4Mo/MoO2 micropillar arrays with strong metal-support interaction (MSI) as a bifunctional electrocatalyst for seawater electrolysis is reported. The micropillar structure enhances electron and mass transfer, extending catalytic reaction steps and improving seawater electrolysis efficiency. Theoretical and experimental studies demonstrate that the strong MSI between Os and Ni4Mo/MoO2 optimizes the surface electronic structure of the catalyst, reducing the reaction barrier and thereby improving catalytic activity. Importantly, for the first time, a dual Cl- repelling layer is constructed by electrostatic force to safeguard active sites against Cl- attack during seawater oxidation. This includes a strong Os─Cl adsorption and an in situ-formed MoO4 2- layer. As a result, the Os-Ni4Mo/MoO2 catalyst exhibits an ultralow overpotential of 113 and 336mV to reach 500mA cm-2 for HER and OER in natural seawater from the South China Sea (without purification, with 1m KOH added). Notably, it demonstrates superior stability, degrading only 0.37 µV h-1 after 2500 h of seawater oxidation, significantly surpassing the technical target of 1.0 µV h-1 set by the United States Department of Energy.