X-ray Photoemission Spectroscopy Research Articles

Ce3+/Ce4+–TiO2 Nano‐Octahedra as Active Photocatalysts for Ciprofloxacin Photodegradation Under Solar Light

AbstractCerium‐containing titania nano‐octahedra (CeTNOh) are obtained by ultrasonication‐hydrothermal synthesis of Ce‐containing titanate nanowires (0.35, 0.46, and 0.70 Ce mol %) from commercial TiO2 (Degussa P25). CeTNOh are tested as photocatalysts to degrade a target pollutant (ciprofloxacin) under simulated solar light and at mild conditions. CeTNOh are anatase polymorphs with increasing crystallite size as Ce content increases. Hydrothermal treatments enhance the specific surface area (SSA) compared to P25, although Ce addition slightly reduces SSA while increasing crystallite size. Electron Microscopy confirms the morphology, although higher Ce levels hinder a full transformation. X‐ray photoemission spectroscopy (XPS) shows the presence of Ce3+/Ce4+ redox pair, promoting electron mobility and Ti‐Ce interactions. Optical and electronic spectroscopy reveals that Ce loading reduces the bandgap from 3.20 to 2.74 eV, extending light absorption into the visible range, thus enhancing the photocatalytic activity. The best sample, CeTNOh0.35, achieved 83% degradation of ciprofloxacin after 360 minutes under solar irradiation, with poor adsorption in the dark period. Higher Ce loadings negatively affect photoactivity by partially covering titania active sites. Reusability tests confirm the stability and efficiency of CeTNOh0.35 over three cycles, highlighting the importance of octahedral morphology in Ce‐containing systems to boost the final photoactivity for water remediation.

Thin Ga-doped ZnO Film with Enhanced Dual Visible Lines Emission

Introduction: In this study, a simple and facile route was employed to prepare a highly transparent and luminescent ultra-thin gallium doped ZnO film (GZO). Methods: The thin GZO film has been deposited using the simultaneously ultrasonic vibration and sol-gel spin-spray coating technique. The structural and optical properties of pure and doped thin films were investigated by various methods, such as X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), scanning electron microscopy (SEM), UV-Vis, and PL spectroscopy. Results: XRD results indicated that both pure and doped ZnO films had a hexagonal wurtzite structure with (101) preferred orientation. XPS and EDX studies confirmed the incorporation and presence of Ga ions into the ZnO lattice structure. The doped sample showed nearly 90% of transparency, and a strong blue-green emission in the visible region. Conclusion: The obtained results proved that the prepared thin film could be a novel candidate for optoelectronic applications.

One-pot radiolytically synthesized reduced graphene oxide-gold nanoparticles composites and exploration in energy storage

Graphene and its composites are of primary importance, particularly in the field of energy storage. Numerous bottom-up and top-down methods have been proposed in the literature to produce these materials with enhanced physicochemical properties. Recently, an innovative and green methodology was developed based on ionizing radiation, allowing the quantitative synthesis of graphene oxide-based materials. With the aim to extend this strategy for the preparation of hybrid nanomaterials, the objective of this work was the one-pot synthesis of nanocomposites composed of reduced graphene oxide – gold nanoparticles (rGO-AuNPs) via gamma ray-induced radiolytic reduction. UV–Vis Absorption Spectroscopy, Fourier Transform Infrared Spectroscopy, Raman Spectroscopy and X-ray Photoemission Spectroscopy were utilized to comprehensively evaluate the reduction degree of graphene oxide and the formation of gold nanoparticles. Atomic Force Microscopy and Scanning Electron Microscopy were employed to obtain the morphological and topographical information on synthesized nanocomposites. Thermal properties were investigated by Thermogravimetric Analysis and electrical properties were investigated using Cyclic Voltammetry and Potentiostatic Charge and Discharge method. The results demonstrated the successful reduction of graphene oxide and gold ions through the drastic transformation of oxygen-containing functional groups and the formation of gold nanoparticles. Electrical characterization results highlighted the excellent electrical properties of radiosynthesized rGO-AuNPs composites and their great potential for supercapacitance application.

Zinc blende ZnS (001) surface structure investigated by XPS, LEED, and DFT

The formation and stability of the zinc blende ZnS (001) single crystal surface have been examined by x-ray photoemission spectroscopy (XPS), low-energy electron diffraction (LEED), and density-functional theory (DFT) calculations. LEED patterns obtained from the ZnS (001) surface prepared in ultrahigh vacuum conditions at 1420 K reveal the formation of a (1 × 2) reconstructed structure. Surface chemical characterization performed by XPS indicates that the surface region consists of a Zn-deficient (sulfur-rich) phase. Our DFT theoretical calculations confirm that the ZnS (001) (1x2) surface structure is energetically favorable and consists of a Zn-terminated topmost surface layer stabilized by Zn-vacancies. The calculations also suggest that the remaining Zn-cations on the surface are displaced inward, driven by surface energy minimization related to zinc-blend ZnS (001) polar nature. Notably, the observed surface structural modifications have potential implications for the ZnS physical and chemical properties.

Formation of highly stable interfacial nitrogen gas hydrate overlayers under ambient conditions

Surfaces (interfaces) dictate many physical and chemical properties of solid materials and adsorbates considerably affect these properties. Nitrogen molecules, which are the most abundant constituent in ambient air, are considered to be inert. Our study combining atomic force microscopy (AFM), X-ray photoemission spectroscopy (XPS), and thermal desorption spectroscopy (TDS) revealed that nitrogen and water molecules can self-assemble into two-dimensional domains, forming ordered stripe structures on graphitic surfaces in both water and ambient air. The stripe structures of this study were composed of approximately 90 % and 10 % water and nitrogen molecules, respectively, and survived in ultra-high vacuum (UHV) conditions at temperatures up to approximately 350 K. Because pure water molecules completely desorb from graphitic surfaces in a UHV at temperatures lower than 200 K, our results indicate that the incorporation of nitrogen molecules substantially enhanced the stability of the crystalline water hydrogen bonding network on graphitic surfaces. Additional studies on interfacial gas hydrates can provide deeper insight into the mechanisms underlying formation of gas hydrates.

Copper benzene-1,3,5-tricarboxylate based metal organic framework (MOF) derived CuO/TiO2 nanofibers and their use as visible light active photocatalyst for the hydrogen production

Photocatalytic hydrogen generation through water splitting offers a sustainable and renewable approach to producing green and clean hydrogen fuel. However, it is crucial to explore low-cost semiconductor photocatalysts that can effectively capture a broad range of solar radiation. The present study aims to develop photocatalytic CuO/TiO2 nanofibers (NFs) with homogeneity of copper with titanium in the heterostructures through the metal–organic framework (MOF) assisted strategy via the electrospinning and subsequent calcination approach. The new methodology enables the fabrication of CuO-modified TiO2 NFs based on HKUST-1 (copper benzene-1,3,5-tricarboxylate, Hong Kong University of Science and Technology-1) as Cu-MOF varying the amounts of HKUST-1. Ultraviolet–visible light diffuses reflectance spectroscopy (DRS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), photoluminescence spectroscopy (PL), X-ray photoemission spectroscopy (XPS) and Raman spectroscopy are employed to assess the structural and morphological characteristics of the prepared NFs. The characterization revealed that the CuO-TiO2 NFs heterostructure was uniform. The bandgaps of the CuO-TiO2 NFs ranged from 3.08 to 2.83 eV based on the Kubelka–Munk function, which is considerable for improving the light-harvesting capacity. The photocurrent technique is used to confirm efficiency in charge separation and transfer, as well as a longer lifetime of photo-generated charge carriers effect in photocatalytic activity. In addition, density functional theory calculations were performed to analyze the impact of CuO on the geometric, electronic structure and photocatalytic properties of TiO2. The CuO/TiO2 photocatalyst containing 1.5 mol% of CuO exhibited the highest photocatalytic activity. The hydrogen production rate was exceptional at 45.6 mmol·g−1·h−1, which was a remarkable 400 times higher than that achieved with pure TiO2 nanofibers. Owing to the one-dimensionality of nanostructures, the prepared CuO-based TiO2 NFs had high recyclability without lessening the efficiencies of photocatalytic activity.

Predicting Sodium-Ion Battery Performance through Surface Chemistry Analysis and Textural Properties of Functionalized Hard Carbons Using AI.

Traditionally, the performance of sodium-ion batteries has been predicted based on a single characteristic of the electrodes and its relationship to specific capacity increase. However, recent studies have shown that this hypothesis is incorrect because their performance depends on multiple physical and chemical variables. Due to the above, the present communication shows machine learning as an innovative strategy to predict the performance of functionalized hard carbon anodes prepared from grapefruit peels. In this sense, a three-layer feed-forward Artificial Neural Network (ANN) was designed. The inputs used to feed the ANN were the physicochemical characteristics of the materials, which consisted of mercury intrusion porosimetry data (SHg and average pore), elemental analysis (C, H, N, S), ID/IG ratio obtained from RAMAN studies, and X-ray photoemission spectroscopy data of the C1s, N1s, and O1s regions. In addition, two more inputs were added: the cycle number and the applied C-rate. The ANN architecture consisted of a first hidden layer with a sigmoid transfer function and a second layer with a log-sigmoid transfer function. Finally, a sigmoid transfer function was used in the output layer. Each layer had 10 neurons. The training algorithm used was Bayesian regularization. The results show that the proposed ANN correctly predicts (R2 > 0.99) the performance of all materials. The proposed strategy provides critical insights into the variables that must be controlled during material synthesis to optimize the process and accelerate progress in developing tailored materials.

Novel mixed self-assembled monolayers of L-cysteine and methanol on gold surfaces under ambient conditions.

In this work, we carried out an experimental and theoretical study on the formation of self-assembled monolayers of L-cysteine molecules on gold surfaces in the presence of methanol as a solvent. We report for the first time L-cysteine and methanol ordered structures forming a mixed self-assembled mono-layer on Au(100) surfaces under ambient conditions. Finger-like ordered structures with a relative height of 0.10-0.20 nm, average width of 2.0 nm and variable lengths were observed using scanning tunneling microscopy under room temperature and ambient pressure conditions. Using X-ray photoemission spectroscopy, it was determined that L-cysteine molecules bind to the gold surface through the sulfur atom of their thiol group in two molecular configurations: neutral and zwitterionic. We found that the finger-like structures are the result of complex interactions of L-cysteine molecules with gold surfaces and L-cysteine molecules with methanol molecules and among all three components of the system (L-cysteine + methanol + gold surfaces). These interactions were detected through attenuated total reflectance-Fourier transform infrared spectroscopy. Furthermore, adsorbate/substrate interactions were studied by employing ab initio calculations using density functional theory, resulting in molecular arrangements formed by chains of L-cysteine pairs surrounded by physisorbed methanol molecules.

Fabrication of silver-doped titanium vanadium nitride (TiVN) coatings for biomedical applications

The term "silver-doped vanadium titanium nitride" refers to a class of composite biomaterial that combines the characteristics of vanadium titanium nitride with silver's antibacterial and bioactive capabilities. Using the physical vapor deposition (PVD) technique, the coating was applied by first depositing a single layer of Titanium on a titanium substrate, followed by a layer of TiVN(Ag), with fixed power for the Titanium (450W) and vanadium (350W), and variable power for the silver (25–100W). Atomic force microscopy (AFM) was used to evaluate surface morphology, transmission electron microscopy (TEM) was used to evaluate cross-sectional microstructural analysis of coatings, X-ray diffraction (XRD) was used to evaluate the phase formation of the coating, X-ray photoemission spectroscopy (XPS) was used to evaluate composition and atomic bonding, and finally, the biocompatibility test was conducted individually to evaluate the viability of MG-63 cells. Our results showed that the fluctuation of the silver concentration in the system impacts the microstructural and biological characteristics of the coating. The best balance between cell viability and microstructure was obtained using a sample of TiVN(Ag) and 50W of electricity.

Tuning Ceramic Surface to Minimize the Ionic Resistance at the Interface between PEO- and LATP-Based Ceramic Electrolyte.

New battery technologies are currently under development, and among them, all-solid-state batteries should deliver better electrochemical performance and enhanced safety. Composite solid electrolytes, combining a solid polymer electrolyte (SPE) and a ceramic electrolyte (CE), should then provide high ionic conductivity coupled to high mechanical stability. To date, this synergy has not yet been reached due to the complexity of the Li-ion transport within the hybrid solid electrolyte, especially at the SPE/CE interface currently considered the limiting step. Yet, there is no proper kinetic model to elucidate the parameters influencing this interfacial barrier. The limited understanding of the SPE/CE interface can be partly explained by scattered SPE/CE interface resistances reported in the literature as well as the lack of systematic studies. Herein, we propose a systematic study of the effect on the SPE/CE interfacial resistance of chemical and thermal treatments of a model LATP-based ceramic based on a methodology relying on electrochemical impedance spectroscopy (EIS) and X-ray photoemission spectroscopy (XPS). The results provide different levers for the optimization of this interface and valuable insights into experimental precautions needed to obtain more reproducible results.

Observation of the multiple magnetic phases in double perovskite Pr1.8La0.2CoFeO6

The structural and magnetic properties of the double perovskite Pr1.8La0.2CoFeO6 have been investigated. The X-ray diffraction study shows that the system acquires room-temperature orthorhombic phase with the Pnma space group. The X-ray photoemission spectroscopy (XPS) measurement confirmed that the B-site ions are present in mixed valence states i.e. Co has been found in Co2+ and Co3+ valance states whereas Fe has been found in Fe3+/Fe4+. Magnetic measurements of the system confirm the existence of several fascinating magnetic behaviors, such as long-range canted antiferromagnetism withTN ∼ 271 K, giant exchange bias, and re-entrant cluster glass phase (TG ∼ 33 K). Field-dependent magnetization shows a large spontaneous exchange bias; HSEB∼ 1.8 kOe and giant conventional exchange bias, HCEB∼ 2.4 kOe at 5 K. Antiferromagnetic materials with large exchange bias can be utilized in high-density spintronic devices. Temperature-dependent Raman study demonstrates that the observed phonon mode exhibits anomalous behavior close to the magnetic transition temperature. Analysis of anomalous softening of phonon mode below TN, clarifies the presence of significant spin-phonon coupling while the magnetostriction effect does not play any significant role in the observed phonon anomaly.

Ohmic Contact Formation to β-Ga2O3 Nanosheet Transistors with Ar-Containing Plasma Treatment

Effective Ohmic contact between metals and their conductive channels is a crucial step in developing high-performance Ga2O3-based transistors. Distinct from bulk materials, excess thermal energy of the annealing process can destroy the low-dimensional material itself. Given the thermal budget concern, a feasible and moderate solution (i.e., Ar-containing plasma treatment) is proposed to achieve effective Ohmic junctions with (100) β-Ga2O3 nanosheets. The impact of four kinds of plasma treatments (i.e., gas mixtures SF6/Ar, SF6/O2/Ar, SF6/O2, and Ar) on (100) β-Ga2O3 crystals is comparatively studied by X-ray photoemission spectroscopy for the first time. With the optimal plasma pre-treatment (i.e., Ar plasma, 100 W, 60 s), the resulting β-Ga2O3 nanosheet field-effect transistors (FETs) show effective Ohmic contact (i.e., contact resistance RC of 104 Ω·mm) without any post-annealing, which leads to competitive device performance such as a high current on/off ratio (>107), a low subthreshold swing (SS, 249 mV/dec), and acceptable field-effect mobility (μeff, ~21.73 cm2 V−1 s−1). By using heavily doped β-Ga2O3 crystals (Ne, ~1020 cm−3) for Ar plasma treatments, the contact resistance RC can be further decreased to 5.2 Ω·mm. This work opens up new opportunities to enhance the Ohmic contact performance of low-dimensional Ga2O3-based transistors and can further benefit other oxide-based nanodevices.

Electrolyte-Induced Fe-Doping of LaNiO3 Model Surfaces for Water Electrolysis

Renewable energy needs to be store in different energy forms for the energy transition away from fossil fuels. One of most promising forms is chemicals such as H2 and C-based fuels obtained via electrochemical reactions. The common hinderance in such reactions is the sluggish oxygen evolution reaction (OER), which causes low energy efficiency in conversion devices. Developing highly active, earth-abundant OER electrocatalysts in alkaline media is necessary to boost the performance of such devices. Fe ion content in electrolyte is known to influence the OER-activity of metal oxide electrocatalysts. For example, the Fe incorporation in NiOOH is a well-established and important effect for OER.[1] Here, we present the effect of absorbed Fe on the OER activity of the epitaxial Ni-surface terminated LaNiO3 thin films. The correlation between surface species and OER activity of electrocatalysts was investigated using surface-sensitive low-energy ion scattering and X-ray photoemission spectroscopies. We observe more than an order-of-magnitude boost in OER activity during initial cycling, from 0.15 mAcm-2 to 3.40 mAcm-2 at 1.60 V vs. reversible hydrogen electrode. The activity increase was mainly caused by the incorporation of up to 5 % Fe at the top surface of LaNiO3 film (less than ~1 nm) even though only a very trace amount of Fe ion, 30 ppb, is present in the 0.1 M electrolyte of high purity KOH 99.99 %. Our results demonstrate that the disordered active surface phase, which develops even on single crystalline surfaces, is a complex interplay between the as-prepared (surface) crystalline structure, composition of the solid electrocatalyst and the liquid electrolyte, and has strong impact on the final OER activity, implying that we need to think differently about the crystalline electrocatalysts: crystalline bulk and dynamically changing surface layer.[1] L. Trotochaud, S.L. Young, J.K. Ranney, S.W. Boettcher, Nickel–Iron Oxyhydroxide Oxygen-Evolution Electrocatalysts: The Role of Intentional and Incidental Iron Incorporation, J. Am. Chem. Soc. 136 (2014) 6744–6753.

Benzyl viologen dichloride as a novel ligand for CdSe CQDs in hybrid QDs/organic photodiodes

The use of colloidal quantum dots (CQDs) in advanced optoelectronic devices requires the substitution of bulky long ligands with short organic ligands. The search for a short-ligand that can create stable quantum solids without compromising the confinement of the CQDs is of paramount importance.Within this context, we present a novel surface passivation ligand, benzyl viologene dichloride (BVD-Cl), as a replacement for the conventional trioctylphosphine oxide (TOPO) capping of CdSe CQDs. BVD-Cl enables the creation of a CdSe quantum solid while retaining quantum confinement. To demonstrate the efficacy of this ligand-exchange process, we utilised Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectrometry (EDX), high-resolution transmission electron microscopy (HR-TEM), and X-ray photoemission spectroscopy (XPS). We then implanted the new BVD-Cl:CdSe quantum film as the main inorganic QDs layer into a hybrid photodiode combined with poly 3-hexylthiophene (P3HT) as the organic layer. The photodiode demonstrated high sensitivity to light stimuli and rectifying behaviour, with a responsivity of 70 mA/W at 550 nm. Our observations imply that using BVD-Cl as a surface passivation ligand for CQDs has significant implications for the development of advanced optoelectronic devices.

Effect of Film Thickness on the Electrical Resistivity and Optical Functions Distribution of Iron Tris(8-hydroxyquinoline) Thin Films

Iron tris(8-hydroxyquinoline) (Feq3) was synthesized and investigated by X-ray photoemission spectroscopy. It crystalizes in triclinic polycrystalline structure in powder form, whereas the Feq3 films, with different thickness values (12, 20, 35, and 42 nm), have an amorphous structure. The influence of film thickness on the electrical resistivity and the optical properties is reported. The morphology of Feq3 was investigated in terms of field-emission scanning electron microscope. Electrical resistivity measurements indicate an inverse proportionality to the film thickness. The optical properties of Feq3 films were investigated in terms of photoluminescence spectra and spectrophotometric measurements of transmittance and reflectance. The optical functions such as absorption coefficient and refractive index of the films were calculated. The dependence of the Feq3 film thickness on the optical energy band gap and dispersion parameters was studied. The outcomes indicate that the Feq3 films are of great importance for applications in organic solar cells and light emitting diodes.

Orientation-dependent electronic structure of Li2WO4 films epitaxial grown on LiCoO2 by spontaneous lithiation

Understanding and modulating the properties of materials requires a deep knowledge of their electronic structures. However, analysis of the electronic structure of a single material can be challenging, particularly for modified electrode materials, due to the complexity of mixed interface structures. In this study, we employ pulsed laser deposition (PLD) to epitaxially synthesize Li₂WO₄ (LWO) films on LiCoO₂ (LCO) layers with different orientations. Based on a series of high-resolution synchrotron-based techniques including X-ray absorption spectroscopy (XAS) and X-ray photoemission spectroscopy (XPS), the electronic structure of LWO is carefully scrutinized where a higher main energy level of W5d(eg)-O2p orbitals hybridization in LWO/LCO(104) as compared to LWO/LCO(003) has been observed. This experimental finding is further validated by a comprehensive set of density of states calculations. Furthermore, detailed polarized XAS characterization unveils distinct anisotropy between the two oriented LWO configurations. This comprehensive scientific investigation, harnessing the capabilities of synchrotron-based techniques, provides invaluable insights for future studies, offering guidance for the optimized utilization of LWO as a solid-state electrolyte or modification layer for LCO cathodes in high-powered Li-ion batteries.

Plasma-modified viscose rayon activated carbon felt (VR-ACF) for Cu(II) and Cd(II) decontamination-mechanism and continuous-flow column operation

This study investigates the enhanced removal of Cu(II) and Cd(II) heavy metal ions from water using viscose rayon based activated carbon felt (VR-ACF). Employing a synergistic approach involving oxidant (KMnO4) and plasma treatment, the surface modification process was meticulously examined. Key findings demonstrate the superior efficacy of KMnO4 over H2O2 and Na2S2O8 in coating. The synergy between plasma modification and 0.1 M KMnO4 enhances VR-ACF’s adsorption capacity, ensuring effective metal ion removal. Fine-tuning plasma parameters aids a comprehensive understanding of the modification process, guiding successful metal ion removal. Adsorption complexities are evidenced by prolonged kinetics of 720 min at pH 5 with high Qmax of 175.43 mg/g for Cu(II) and 223.22 mg/g for Cd(II), and extended column experiments, affirming the efficacy of modified VR-ACF. Thermodynamic analyses underscore the spontaneity and variability of Cu(II) and Cd(II) adsorption. X-ray photoemission spectroscopy (XPS), Scanning electron microscopy (SEM), X-ray Diffraction (XRD) investigations endorse complexation, ion-exchange, co-precipitation, and solvation interactions. Recyclability tests reveal maintenance of 60% removal efficiency for five cycles, with reduced efficiency in the presence of phosphates and divalent cations. The 50% breakthrough time for adsorption of Cu(II) and Cd(II) was found to be 58 days and 62 days, respectively. This underscores the efficacy of modified VR-ACF in sustainable water purification, particularly in extended column setups, offering a hopeful path for advanced materials in eliminating heavy metal ions.

Review of actinide core-level photoemission

Photoelectron spectroscopy allows for the investigation of the electronic structure and chemical bonding of actinide elements and their compounds, providing insights into oxidation states, chemical environments, and electronic configurations. This knowledge can aid in comprehending reactivity, stability, and other properties of actinide materials, which is essential for ensuring safe handling, storage, and disposal in nuclear applications. We have reviewed a number of results in actinide core-level photoemission studies, with a particular focus on x-ray photoemission spectroscopy (XPS) techniques. Actinides, due to their inherent radioactivity, have not been as well studied with XPS as have other segments of the periodic table. Given the inherent safety concerns, equipment requirements, and short isotopic lifetimes associated with actinide research, we outline the strategies and precautions necessary for conducting successful and safe XPS experiments on these elements. Core-level photoemission can be a powerful proven tool for investigating the electronic structure, chemical bonding behaviors, and physical properties of actinides, providing valuable insights into an incredibly complex behavior of these systems. We highlight key findings from recent studies that demonstrate the potential of core-level photoemission in uncovering the unique properties of actinides and their compounds. Finally, we identify current knowledge gaps and future research directions that could enhance our understanding of actinide chemistry and physics.

Correlation analysis in X-ray photoemission spectroscopy

X-ray photoelectron spectroscopy (XPS) is a powerful technique for surface analysis, but its application can be hindered by uncertainty in modelling spectra. Often, many spectral models have a similar goodness of fit, and distinguishing between them can be impossible without additional information. A further challenge is found in interpreting spectra from samples consisting of multiple chemical compounds. We show here how correlation analysis can be used to interpret large XPS datasets. Correlations in atomic concentrations and binding energies of core lines can be interpreted within a framework of an underlying chemical model and this can yield additional information compared with analysis of each spectrum individually. We give examples of the usage of this analysis on some simple systems, and discuss the potential and limitations of the technique.

Influence of Oxygen Vacancies Introduced via Acceptor (Gadolinium) Doping to the Pseudocapacitive Properties of Nano-Sized Cerium Oxide.

The voluntary introduction of defects can be considered an effective strategy for enhancing the electrochemical properties of metal oxide electrodes. In this study, the enhanced pseudocapacitive properties of an acceptor (Gd) doped cerium oxide nanoparticle-a sustainable metal oxide with low environmental and human toxicity-are investigated in depth using ex situ X-ray photoemission spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Interestingly, with 15at% Gd doping (15GDC), the specific capacitance of the nanoparticles measured at 1Ag-1 enhanced to 547.8Fg-1, which is fivefold higher than undoped CeO2 (98.7Fg-1 at 1Ag-1). The rate-dependent capacitance is also improved for 15GDC, which showed a 31.0% decrease in the specific capacitance upon a tenfold increase in the current density, while CeO2 showed a 49.9% decrease. The enhanced electrochemical properties are studied in depth via ex situ XPS and EIS analysis, which revealed that the oxygen vacancies at the surface of the nanoparticles played important roles in enhancing both the specific capacitance and the high-rate performance of 15GDC by acting as the active site for pseudocapacitive redox reaction and allowing fast diffusion of oxygen ions at the surface of 15GDC nanoparticles.