X-ray Photoelectron Spectroscopy Results Research Articles

Ultrafast Charge Transfer-Induced Unusual Nonlinear Optical Response in ReSe2/ReS2 Heterostructure.

Ultrafast charge transfer in van der Waals heterostructures can effectively engineer the optical and electrical properties of two-dimensional semiconductors for designing photonic and optoelectronic devices. However, the nonlinear absorption conversion dynamics with the pump intensity and the underlying physical mechanisms in a type-II heterostructure remain largely unexplored, yet hold considerable potential for all-optical logic gates. Herein, two-dimensional ReSe2/ReS2 heterostructure is designed to realize an unusual transition from reverse saturable absorption to saturable absorption (SA) with a conversion pump intensity threshold of approximately 170 GW/cm2. Such an intriguing phenomenon is attributed to the decrease of two-photon absorption (TPA) of ReS2 and the increase of SA of ReSe2 with the pump intensity. Based on the characterization results of X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, femtosecond transient absorption spectrum, Kelvin probe force microscopy, and density functional theory calculation, a type-II charge-transfer-energy level model is proposed combined with the TPA of ReS2 and SA of ReSe2 processes. The results reveal the critical role of ultrafast interfacial charge transfer in tuning the unusual nonlinear absorption and improving the SA of ReSe2/ReS2 under different excitation wavelengths. Our finding deepens the understanding of nonlinear absorption physical mechanisms in two-dimensional heterostructure materials, which may further diversify the nonlinear optical materials and photonic devices.

Unraveling Oxygen Vacancies Effect on Chemical Composition, Electronic Structure and Optical Properties of Eu Doped SnO2.

The influence of Eu doping (0.5, 1 and 2 mol.%) and annealing in an oxygen-deficient atmosphere on the structure and optical properties of SnO2 nanoparticles were investigated in relation to electronic structure. The X-ray diffraction (XRD) patterns revealed single-phase tetragonal rutile structure for both synthesized and annealed Eu-doped SnO2 samples, except for the annealed sample with 2 mol.% Eu. The results of X-ray photoelectron spectroscopy (XPS) emphasized that europium incorporated into the SnO2 host lattice with an oxidation state of 3+, which was accompanied by the formation of oxygen vacancies under cation substitution of tetravalent Sn. Moreover, XPS spectra showed the O/Sn ratio, which has been reduced under annealing for creating additional oxygen vacancies. The pulse cathodoluminescence (PCL) demonstrated the concentration dependence of Eu site symmetry. Combination of XRD, XPS and PCL revealed that Eu doping and following annealing induce strongly disordering of the SnO2 crystal lattice. Our findings provide new insight into the interaction of rare-earth metals (Eu) with host SnO2 matrix and new evidence for the importance of oxygen vacancies for optical and electronic structure formation.

A Novel Anion Receptor Additive for -40ºCSodium MetalBatteriesby Anion/Cation Solvation Engineering.

Sodium metal batteries, known for their high theoretical specific capacity, abundant reserves,and promisinglow-temperature performance, have garnered significant attention. However, the large ionic radius of Na+and sluggish transport kinetics across the interfacial structure hinder their practical application.Previous reviews have rarely regulated electrolyte performance from the perspective of anions; as important components of the electrolyte, the regulation mechanism is not well understood. Herein, a novel anion receptor additive, 4-aminophenylboronic acid pinalol ester (ABAPE), is proposed to weaken the coupling between anions and cations and accelerateNa+transport kinetics.The results of theoretical calculations and X-ray photoelectron spectroscopy with deep Ar-ion etching demonstrate thatthe introduction of this additive alters the solvation structure of Na+, reducesthe desolvation barrier and formsa stable and dense electrode-electrolyte interface. Moreover, ABAPE forms hydrogen bonds (-NH···O/F) with H2O/HF, effectively preventing the hydrolysis of NaPF6and stabilizing acidic species. Consequently, the Na||Na symmetric cell exhibits excellent long-cycle performance of 500 h at 1 mA cm-2 and 0.5 mAh cm-2. The Na||Na3V2(PO4)3(NVP) full cell with the addition of ABAPE maintains a capacity retention of 84.29% at 1 C after1200 cycles and presents no capacity decayover 150 cycles at -40°C.

Development of hard X-ray photoelectron spectroscopy in liquid cells using optimized microfabricated silicon nitride membranes.

We present first hard X-ray photoelectron spectroscopy (HAXPES) results of aqueous salt solutions and dispersions of gold nanoparticles in liquid cells equipped with specially designed microfabricated thin silicon nitride membranes, with thickness in the 15-25 nm range, mounted in a high-vacuum-compatible environment. The experiments have been performed at the HAXPES endstation of the GALAXIES beamline at the SOLEIL synchrotron radiation facility. The low-stress membranes are fabricated from 100 mm silicon wafers using standard lithography techniques. Platinum alignment marks are added to the chips hosting the membranes to facilitate the positioning of the X-ray beam on the membrane by detecting the corresponding photoemission lines. Two types of liquid cells have been used, a static one built on an Omicron-type sample holder with the liquid confined in the cell container, and a circulating liquid cell, in which the liquid can flow in order to mitigate the effects due to beam damage. We demonstrate that the membranes are mechanically robust and able to withstand 1 bar pressure difference between the liquid inside the cell and vacuum, and the intense synchrotron radiation beam during data acquisition. This opens up new opportunities for spectroscopic studies of liquids.

Achieving ultra-high energy storage performance in simple systems through minimal element substitution

Dielectric capacitors are essential components of modern advanced electronic devices and power systems based on their ultra-fast charging and discharging speeds and supreme power densities. Nevertheless, how to comprehensively boost their energy storage density and storage efficiency is still an insurmountable challenge. Here, we report a simple micro-chemical polarizability modulation strategy that enables SrTiO3-based dielectric materials to achieve excellent energy storage properties. The energy density and energy efficiency are increased to as high as 76 J∙cm−3 and 72 % from 0.4 J∙cm−3 and 46.7 % of pure STO, respectively, which is the largest value in micro-substitution (less than 3 %). Our results show that the introduction of trace amounts of elements with high ionic polarizabilities (Mn, V) facilitates the increase of chemical disorder and the formation of stable and highly dynamic polar nanoregions (PNRs), which reduces the hysteresis of the polarization switching and improves the polarization at the breakdown field strength, synergistically fostering the energy storage performance. The results of X-ray photoelectron spectroscopy and scanning electron microscopy reveal that the micro-substitution of Mn and V promote the reduction of oxygen vacancies and grain size, improving the breakdown resistance and stability of the capacitor. This present approach is expected to be widely used in the development of high-performance dielectrics.

Modulating the structural and electrical properties of SrFeO3–δ by a-site alkali metal ion doping

The electrical properties of perovskite structured SrFeO3–δ can be modulated by A site doping. The present work focuses on the influence of concentration and ionic radii of alkali metal cation on the structural and electrical properties of Sr1–xAxFeO3–δ (A = Ca, Ba and x = 0, 0.25, 0.50, 0.75). The x-ray diffraction studies confirm the phase change from cubic to orthorhombic with Ca content while orthorhombic to cubic structural translation was observed with Ba concentration. A lattice contraction and expansion were observed for doping depending on the ionic radii of dopant cation. The x-ray photoelectron spectroscopy results indicate the presence of Fe in mixed valence state of +2, +3, +4 state and adsorbed oxygen content was found to be higher upon Ba doping than that of Ca. A maximum conductivity of 1.82 × 10−3 S cm−1 (x = 0.25) and 5.31 × 10−3 S cm−1 (x = 0.5) was observed at 800 °C for Ca and Ba doped samples, respectively, one order higher than the base SrFeO3–δ .Thus, our results emphasise the importance of dopant addition on tailoring the electrode properties for SOFC application.

Comparing low-temperature NH3-SCR activity, operating temperature window and kinetic properties of the Mn-Fe-Nb/TiO2 catalysts prepared by different methods

In order to overcome the shortcomings of traditional V-based catalysts, such as poor low-temperature activity, narrow temperature window, and toxicity. Therefore, the Mn-Fe-Nb/TiO2 catalysts were prepared using impregnation (IM), citric acid complexation (CA), co-precipitation (CP), hydrothermal synthesis (HY), and sol–gel (SG) methods to develop novel NH3 selective catalytic reduction (NH3-SCR) catalysts with excellent low-temperature activity, a wide temperature window, and environmental friendliness. Their NH3-SCR catalytic activity was evaluated, followed by a detailed analysis of their morphology, structure, specific surface area, chemical state, redox properties, acidity, and interactions using X-ray diffraction (XRD), Bruaner-Emmet-Teller (BET), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD), and Fourier transform infrared spectroscopy (FTIR) techniques. The 5Mn-7Fe-4Nb/TiO2-SG catalyst, prepared via sol–gel, exhibited the highest denitrification (de-NOx) activity and the widest operating temperature window, achieving over 80% Nitric oxide (NO) conversion at 180–350 °C and a peak conversion of 97% at 250 °C. The XRD, BET, SEM, and HR-TEM characterization results showed that the catalyst prepared using the sol–gel method had the smallest particles, the highest specific surface area, and the greatest dispersion. XPS and NH3-TPD results revealed that the catalyst prepared using the sol–gel method possessed the highest surface adsorbed oxygen (Oα) content and the largest number of acidic sites. H2-TPR and FTIR analyses indicated that the catalyst prepared using the sol–gel method enhanced the reduction capacity and possessed the strongest interaction forces among support-active-promoter components. Steady-state kinetic tests confirmed that in the NH3-SCR reaction, the rate-determining step was the adsorption activation of NO on the catalyst surface. The sol–gel method reduced the activation energy for de-NOx reactions, enhancing the low-temperature activity of the catalyst.

Improved-Performance Amorphous Ga2O3 Photodetectors Fabricated by Capacitive Coupled Plasma-Assistant Magnetron Sputtering

Ga2O3 has received increasing interest for its potential in various applications relating to solar-blind photodetectors. However, attaining a balanced performance with Ga2O3-based photodetectors presents a challenge due to the intrinsic conductive mechanism of Ga2O3 films. In this work, we fabricated amorphous Ga2O3 (a-Ga2O3) metal–semiconductor–metal photodetectors through capacitive coupled plasma assisted magnetron sputtering at room temperature. Substantial enhancement in the responsivity is attained by regulating the capacitance-coupled plasma power during the deposition of a-Ga2O3. The proposed plasma energy generated by capacitive coupled plasma (CCP) effectively improved the disorder of amorphous Ga2O3 films. The results of X-ray photoelectron spectroscopy (XPS) and current-voltage tests demonstrate that the additional plasma introduced during the sputtering effectively adjust the concentration of oxygen vacancy effectively, exhibiting a trade-off effect on the performance of a-Ga2O3 photodetectors. The best overall performance of a-Ga2O3 photodetectors exhibits a high responsivity of 30.59 A/W, a low dark current of 4.18 × 10−11, and a decay time of 0.12 s. Our results demonstrate that the introduction of capacitive coupled plasma during deposition could be a potential approach for modifying the performance of photodetectors.

Highly dispersed g-C3N4 on one-dimensional W18O49/carbon nanofibers for constructing well-connected S-scheme heterojunctions with synchronous H2 evolution and pollutant degradation performance

Synchronous dual-functional photocatalytic reaction can simultaneously consume photogenerated electrons and holes, leading to redox reaction, which is a promising photocatalytic reaction system model. However, the severe recombination of photogenerated charge carriers in photocatalysts limits their photocatalytic performance. In this work, W18O49/C@g-C3N4 S-scheme heterojunctions nanofibers with core-shell structure were prepared through electrospinning combined with the vapor deposition method, for high-performance synchronous photocatalytic H2 evolution and pollutant degradation. The X-ray photoelectron spectroscopy and Mott-Schottky results demonstrated that the S-scheme heterojunctions effectively separate charges while maintaining high redox capacity. The UV-vis-NIR absorption spectra results revealed the LSPR effect in W18O49, which can generate “hot electrons”. The scanning electron microscope images showed that the unique core-shell structure independently consumes electrons and holes, thereby enhancing charge separation and accelerating carrier kinetics. Specifically, the synchronous H2 evolution and RhB degradation efficiency of W18O49/C@g-C3N4 nanofibers were approximately 5.60 and 3.51 times higher than that of W18O49/C, and 2.45 and 22.55 times higher than that of C@g-C3N4 nanofibers, respectively. Furthermore, the ultra-long one-dimensional network structure of W18O49/C@g-C3N4 nanofibers enables easy recycling after liquid reactions. This study presents a novel approach for customizing band structures and unique surface morphology to improve synchronous dual-functional photocatalytic activity.

Zr-based conversion film fabricated on cold rolled steel by separately providing zirconium and fluorine ions: Performance and mechanism study

Controlling the concentrations of Zr4+ and F− in traditional Zirconium (Zr)-based film-formation solution is challenging due to their dependence on the hydrolytic equilibrium of H2ZrF6. In this study, Zr-based films were prepared on cold rolled steel surface through the film-formation solution prepared by mixing Zr(NO3)4 and different amount of HF. The electrochemical results demonstrated that the Zr-based film prepared by Zr(NO3)4 and HF exhibited superior corrosion resistance compared to H2ZrF6. Under optimal film formation conditions, the protective efficiency of the prepared film reached 74.4 % which was higher than that of film fabricated in H2ZrF6. The electrochemical results concurrently demonstrated the self-reinforcing anti-corrosion performance of the prepared films. Scanning electron microscopy revealed that the Zr film, prepared in Zr(NO3)4 and HF, exhibited excellent corrosion resistance attributed to its high film density. The X-ray photoelectron spectroscopy and energy dispersive spectroscopic results indicated the presence of a fluoride layer on the surface of the Zr film. The F− ions can chelate with the corrosion products and selectively deposit onto the damaged areas of the film, thereby effectively contributing to the repair of the film layer. The results of density functional theory calculations demonstrated that Zr4+ readily forms Zr(OH)4 rather than ZrF62−. The present study offers an enhanced approach for regulating the properties of films prepared via H2ZrF6 by separately providing zirconium and fluorine ions.

Constructing high efficient carrier channels in double ternary compounds MoSSe/CdSSe heterojunction for photoelectrochemistry and electrocatalytic hydrogen production

Here is a demonstration of constructing MoSSe/CdSSe heterojunction catalyst from bimetallic selenium sulfides. CdSSe has a high conduction band position of −0.65 eV, resulting in a strong reduction potential of photogenerated electrons. However, the high resistance of CdSSe affects the transport of charge carriers. In addition, experiments have confirmed that the presence of S and Se in MoSSe and CdSSe enhances their chemical activity and facilitates bonding. A better connection can be formed between MoSSe and CdSSe, resulting in high carrier transport efficiency. In the X-ray photoelectron spectroscopy results, the Mo and Se signals showed a large shift nearly 1 eV which confirms the strong binding between MoSSe and CdSSe. In the photoelectrochemical tests, the MoSSe/CdSSe heterojunction demonstrated a photocurrent density of 3.097 mA/cm2 at 0 V (RHE) which is 2.7 and 2.9 times that of MoSSe (1.227 mA/cm2) and CdSSe (1.127 mA/cm2) respectively with a low resistance of 161 Ω. Moreover, the MoSSe/CdSSe also has good electrocatalytic hydrogen evolution performance with an overvoltage of 180 mV and Tafel slope of 69 mV/dec. Fluorescence and photocurrent response tests confirmed its higher carrier separation efficiency. This work demonstrates the application of ternary metal selenium sulfide heterojunctions in catalytic energy materials.

Crystal chemical investigations on TiU8S17 and U36Lu21S93I3 - ordered and disordered multinary uranium sulfides

The crystal chemistry of uranium sulfides is characterized by a large diversity in composition, crystal structures, oxidation states and physical properties. This holds also for TiU8S17 and U36Lu21S93I3, of which large single crystals up to several mm in length were grown by chemical vapor transport using iodine as a transport agent. TiU8S17 crystallizes with the monoclinic CrU8S17 structure type (C2/m, a = 13.3477(2) Å, b = 8.4927(2) Å, c = 10.4836(2) Å, β = 101.207(2)°) featuring distorted octahedra [TiS6] and bicapped trigonal prisms [US8]. Interatomic distances and X-ray photoelectron spectra indicate tetravalent uranium. Disordered U36Lu21S93I3 represents a new structure type (R3¯m, 13.3841(2) Å, 20.6447(2) Å) with an average crystal structure exhibiting square antiprisms [LuS8], bi- and tricapped trigonal prisms [US8] and [US9] and distorted octahedra [IU6]. Lutetium and sulfur atoms are disordered similar to Ce53Fe12S90X3, La53Fe12S90X3 (X = Cl, Br, I) and La52Fe12S90. This might be caused by positional shifts of iodine atoms away from the center of the polyhedron, thus avoiding unusually long U–I distances and severely disrupting the order of neighboring lutetium and sulfur atoms. The results of chemical analyses (ICP-MS, EDX), electron microscopy (TEM) and X-ray photoelectron spectroscopy support the composition and crystal structure of U36Lu21S93I3 and indicate mixed valency of uranium and charge balance according to the crystal chemical formula (U+III)18(U+IV)18(Lu+III)21(S-II)93(I–I)3.

Green synthesis of carbon dots from Hakka yellow wine lees: Characterization and applications for Fe3+ and NaFeEDTA sensing

In this study, Hakka yellow wine lees carbon dots (HYWL-CDs) with an average diameter of 1.75 nm are synthesized from Hakka yellow wine lees (HYWL) via a one-pot hydrothermal method. Results of X-ray photoelectron spectroscopy and FTIR reveal the presence of C=C and –OH in the HYWL-CDs. Additionally, the HYWL-CDs present excitation-wavelength dependence, with maximum excitation and emission wavelengths of 360 and 440 nm, respectively. The fluorescence of the HYWL-CDs can be quenched by Fe3+. The Fe3+ concentration is correlated linearly with the quenching rate over a linear range of 0.6–1.1 mg/mL, and the limit of detection is 0.18 μg/mL. And phenols have been shown to be present in HYWL-CDs, and the color reaction between phenols and FeCl3 is most likely the mechanism by which FeCl3 causes fluorescence burst in HYWL-CDs. Moreover, the HYWL-CDs demonstrate significant potential for detecting NaFeEDTA in iron-fortified soy sauces, the linear-fit equation was y = 185.38x + 1024.6 (R2 = 0.9995) The HYWL-CDs are loaded onto paper strips, iron-fortified straw mushroom dark soy sauce showed noticeable color changes, which allows one to differentiate normal soy sauce from iron-fortified soy sauce more conveniently and provides a new perspective for the high-value utilization of yellow wine lees.

In-situ doped and activated N, S co-doped porous carbon derived from organic salt for application in high-performance potassium-ion batteries

Owing to its abundance in nature and low cost, potassium has attracted considerable attention as a substitute for lithium in the manufacture of secondary-ion batteries. However, developing amorphous carbon materials that show fast K+ ion kinetics for application in high-performance potassium-ion battery (PIB) anodes remains challenging. In this study, we designed and synthesized a 3-D hierarchical nitrogen and sulfur co-doped porous carbon electrode via in-situ doping and activation using acesulfame potassium. Owing to its prominent structural advantages, the as-prepared N, S co-doped electrode showed a high reversible capacity (459.8 mAh g−1 at 0.05 A g−1) and long-term cycle stability (205 mAh g−1 after 1000 cycles at 0.5 A g−1). Further, the results of ex-situ Raman spectroscopy and X-ray photoelectron spectroscopy verified the advantages of N and S co-doping with respect to K+ ion intercalation and adsorption/desorption properties within the carbon matrix. Therefore, our findings enhance understanding regarding the advantages of the dual-doped system with respect to K+ ion storage and highlight an efficient strategy for developing high-performance and durable carbon anode materials for PIBs.

Phase-Engineered MoSe2/CeO2 Composites for Room-Temperature Gas Sensing with a Drastic Discrimination of NH3 and TEA Gases.

Detecting and distinguishing between hazardous gases with similar odors by using conventional sensor technology for safeguarding human health and ensuring food safety are significant challenges. Bulky, costly, and power-hungry devices, such as that used for gas chromatography-mass spectrometry (GC-MS), are widely employed for gas sensing. Using a single chemiresistive semiconductor or electric nose (e-nose) gas sensor to achieve this objective is difficult, mainly because of its selectivity issue. Thus, there is a need to develop new materials with tunable and versatile sensing characteristics. Phase engineering of two-dimensional materials to better utilize their physiochemical properties has attracted considerable attention. Here, we show that MoSe2 phase-transition/CeO2 composites can be effectively used to distinguish ammonia (NH3) and triethylamine (TEA) at room temperature. The phase transition of nanocomposite samples from semimetallic (1T) to semiconducting (2H) prepared at different synthesis temperatures is confirmed via X-ray photoelectron spectroscopy (XPS). A composite sensor in which the 2H phase of MoSe2 is predominant lacks discrimination capability and is less responsive to NH3 and TEA. An MoSe2/CeO2 composite sensor with a higher 1T phase content exhibits high selectivity for NH3, whereas one with a higher 2H phase content (2H > 1T) shows more selective behavior toward TEA. For example, for 50% relative humidity, the MoSe2/CeO2 sensor's signal changes from the baseline by 45% and 58% for 1 ppm of NH3 and TEA, respectively, indicating a low limit of detection (LOD) of 70 and 160 ppb, respectively. The composites' superior sensing characteristics are mainly attributed to their large specific surface area, their numerous active sites, presence of defects, and the n-n type heterojunction between MoSe2 and CeO2. The sensing mechanism is elucidated using Raman spectroscopy, XPS, and GC-MS results. Their phase-transition characteristics render MoSe2/CeO2 sensors promising for use in distributed, low-cost, and room-temperature sensor networks, and they offer new opportunities for the development of integrated advanced smart sensing technologies for environmental and healthcare.

High-performance Bi2O3 nanoflakes for advanced energy storage applications

In this work, Bi2O3 nanoflakes (NFs) were synthesized using the co-precipitation method. To understand the crystal structure-surface morphology and their functional properties such as optical band-gap energy, specific capacitance and magnetic properties are examined by various analytical techniques including X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), High-Resolution Transmission Electron Microscopy (HRTEM), Vibrating Sample Magnetometer (VSM), UV–Visible Diffuse Reflectance Spectroscopy (UV-DRS), X-ray Photoelectron Spectroscopy (XPS), Raman Spectroscopy, and Cyclic Voltammetry (CV). FE-SEM confirmed the formation of the nanoflakes, while HRTEM verified their monoclinic crystal structure and provided details on the orientation of the lattice planes. XRD result showed distinctive peaks corresponding to the α-phase, indicating a crystallite size of 8.21 nm. Raman and XPS results are also demonstrated formation of the Bi2O3 NFs with their signature bands. VSM analysis revealed the presence of both magnetic and nonmagnetic phases in the Bi2O3 NFs. Optical studies indicated a promising band gap of 1.9 eV, suggesting potential for optoelectronic applications. Surface analysis confirmed the composition of Bi+ and O2− in the NFs. Additionally, electrochemical assessments through CV demonstrated a significant specific capacitance of 537 F/g at 20 mV/s. Nyquist plot analysis suggested an equivalent circuit R(CR)(CR), indicating an optimal fit. Furthermore, we have made the systematic comparison of optical band gap energy of Bi2O3 with reported different nanostructures such as Peanut, needles, rod and flakes and found that the present study nanoflakes offer much lower band energy compared to above mentioned all other morphologies. Due to the obtained lower energy band gap and specific capacitance performance of the Bi2O3 NFs, it is strongly suggested to the advanced energy storage applications.

Unveiling the role of silicon in boosting electrochemical carbon dioxide reduction via carbon nanotubes@bismuth silicates

Electrochemical CO2 reduction reaction (CO2RR) is one of the most attractive measures to achieve the carbon neutral goal by converting CO2 into high-value chemicals such as formate. Si in Bi silicates is promising to enhance CO2 adsorption and activation due to its strong oxygenophilicity. Whereas, its role in boosting CO2RR via the cheap Bi-based catalysts is still not clear. Herein, we design CNT@Bi silicates catalyst, demonstrating the highest FEHCOOH of 96.3 % at −0.9 V vs. reversible hydrogen electrode with good stability. Through X-ray photoelectron spectroscopy (XPS), in-situ Attenuated Total Reflectance-Fourier Transform Infrared (In-situ ATR-SEIRAS) experiments, and Density Functional Theory (DFT) calculations, the role of Si in Bi silicates was unveiled: tuning the electronic structure of Bi, weakening the Bi-O bond, and strengthening electron transfer from Bi to CO2, thereby promoting the generation of CO2*− and *OCHO intermediates. Additionally, carbon nanotubes (CNTs) promote not only the conductivity but also the generation of abundant oxygen vacancies in CNT@Bi silicates evidenced by the electron transfer from CNT to Bi silicates from XPS results. Further, the CNT@Bi silicates endows it with the highest electrochemical activation area. These findings suggest the effectiveness of Si in Bi silicates and structure tuning to design highly selective CO2RR catalyst for HCOOH production.

Combined experimental and density functional theory approaches to address different mechanisms of nitrogen and sulfur doping on the enhancement of capacitive performance of hierarchical porous biochars

Activated carbon derived from biomass as hierarchical porous biochars (HPB) has been developed as electrode materials for supercapacitors. Nitrogen is known as the doping element that enhances quantum capacitance, but the mechanisms of sulfur doping on the quantum capacitance enhancement remain ambiguous. In this study, conventional approaches to assess the characteristics and capacitive performance of biochars were combined with density functional theory (DFT) calculations to assess different mechanisms of nitrogen and sulfur doping. The Bbiochar samples were prepared from the pyrolyzed fish bone powder at 800 °C without additional doping possessed a specific capacitance of 240 F g−1 at 1 A/g within 1 M H2SO4. Interestingly, additional nitrogen doping through urea mixing and additional sulfur doping through thiosulfate mixing prior to the pyrolysis enhanced the specific capacitance of biochar samples to exceed 400 F g−1 under the same condition. The urea mixed sample possessed low porosity but high charge transfer resistance, while the thiosulfate mixed sample possessed high porosity but low charge transfer resistance. The different underlying mechanisms were discussed through DFT calculations on graphene models designed based on the x-ray photoelectron spectroscopy (XPS) results. Nitrogen-doped configurations with topological defects mainly stored charge at the dangling atoms and possessed a relatively high quantum capacitance. Meanwhile, doped configurations of oxidized sulfur groups required relatively low formation energy and possessed large bond dipoles, corresponding to larger pore size and surface area of the thiosulfate mixed biochars. Understanding the contrary between effects of nitrogen and sulfur doping could resolve the bottleneck on enhancing the performance of electronic double layer supercapacitors.

Co-doped bismuth vanadate/zinc tungstate heterojunction with dual internal electric fields for efficient photocatalytic reduction of carbon dioxide

Enhanced carriers separation on photocatalysts is crucial for improving photocatalytic activity. In this paper, the Co-doped BiVO4/ZnWO4 S-scheme heterojunctions were constructed to induce double internal electric fields (IEFs) for enhancing charges separation and transfer for efficient photocatalytic reduction of CO2. The photocatalytic CO2 reduction efficiencies of the heterojunctions were significantly enhanced as compared with the counterparts. The optimized Co-doped BiVO4/ZnWO4 exhibited the highest CO yield of 138.4 μmol·g−1·h−1, which were 86.5 and 1.4 folds of the BiVO4 and Co-doped BiVO4. Results of X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and work function demonstrated that charge transfer path of Co-doped BiVO4/ZnWO4 conformed to S-scheme heterojunction mechanism. The kelvin probe force microscopy (KPFM) and density functional theory (DFT) calculations of the differential charge distributions confirmed the existence of double IEFs, which accelerated carrier separation and improved CO2 adsorption and activation. In addition, in-situ Fourier transform infrared spectroscopy (ISFT-IR) revealed that HCOO− was the major intermediate during the CO2 reaction. This study provides a feasible means to develop composite photocatalysts with dual IEFs for effective photocatalytic CO2 reduction.

Effect of Al doping on structural and optical properties of atomic layer deposited ZnO thin films

In this work, zinc oxide (ZnO) and aluminum-doped ZnO (AZO) thin films with varying Al contents were grown via atomic layer deposition on Si and glass substrates. The structural and optical properties of ZnO and AZO thin films were investigated using X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), photoluminescence (PL), and ultraviolet-visible spectroscopy. While undoped ZnO had a wurtzite crystal structure, Al2O3 layers altered the crystal structure depending on the Al content. With the increasing number of Al2O3 monolayers, the γ- Al2O3 structure became more prominent, and ZnO peaks were completely suppressed when the Zn ratio reached 10:1 and beyond. SEM images revealed that the thin films homogeneously covered the entire substrate surface. EDS mapping showed a uniform distribution of Zn, Al, and O in the structure. According to the XPS results, the thin films displayed significant peak intensities corresponding to the main components Zn, O, and Al. Zinc atoms were present only in their oxidized state, not as interstitial atoms. The O 1 s peak could be deconvoluted into three components: the oxygen-zinc bond, the oxygen-aluminum bond, and chemisorbed or OH species. In the AZO samples, a direct correlation was observed between the intensity of the Al 2p peak and the number of Al2O3 layers. Additionally, the calculated elemental ratio of Al increased from 2.582 to 23.955 at.% with more Al2O3 layers. Optical measurements revealed that ZnO and AZO thin films exhibit high transmittance in the visible region. Moreover, introducing Al2O3 layers into the supercycle led to an increasing trend in transmittance. Another improvement in the optical properties was observed as a blue shift in the absorption edge with Al doping, indicating band gap widening. The optical band gap of the ZnO thin films increased from 3.2 to 3.5 eV with Al doping. The origin and concentration of defects were evaluated by deconvoluting the PL spectra. A comparative investigation of the PL spectrum and XPS results revealed variations in defect concentration with deposition parameters and defect formation mechanism was discussed.