Concentration Of Active Sites Research Articles

Mo-based bimetallic oxide catalysts for the reverse water gas shift reaction

The reverse water gas shift (RWGS) is of great significance to the resource utilization of CO2. In this paper, based on the features of MoO3, the Mo-based catalysts doped with Ga, Ti and Ce were prepared, and the effects of oxygen vacancies and basic sites on the RWGS reaction were studied. When the volume ratio of H2 and CO2 is 1 : 1, the yield of CO can reach 26.66%. Because it exposes higher concentration of Ce sites and moderate alkaline active sites on the surface. When the proportion of H2 in the reaction gas increases, the highest yield of CO can reach 54.53%, which is mainly attributed to a large number of oxygen vacancies on the surface of MoTi. This study can be used as a reference for the design of catalysts for RWGS reaction under different reaction conditions.

Understanding the mechanism of propane dehydrogenation over coordinatively unsaturated Co-O acid-base pairs and the inhibition effect of trace oxygen

High temperature and a reducing atmosphere are characteristic of propane dehydrogenation (PDH) reaction. Under such condition, the real surface structure of catalysts often differs from that in the ambient environment, particularly for CoOx species with multiple valence states and coordination. Here, a combination of in situ/operando Raman spectroscopy, in situ UV–Vis diffuse reflectance spectroscopy (DRS), and density functional theory (DFT) calculations reveal that coordinatively unsaturated Co-O (Cocu-O) acid-base pairs via lattice oxygen consumption are the PDH active sites of CoOx/Al2O3 catalysts. This highly dispersed Cocu-O species exhibit a C3H6 formation rate and C3H6 selectivity as high as 2 mmol‧gcat−1‧min−1 and 95 %, respectively, which is comparable to most state-of-the-art CoOx-based catalysts. However, industrial C3H8 raw gases typically contain 10–1000 ppm oxygen gas, and the complete eliminating oxygen increases costs. PDH catalytic performance of CoOx/Al2O3 catalysts is sensitive to the extremely low concentration of oxygen gas and is significantly inhibited by it. The fundamental reason is that the concentration of Cocu active sites is determined by the competitive reaction between the filling of trace oxygen on oxygen vacancies and lattice oxygen consumption. The reaction rate of the former is significantly higher than that of the latter. The higher reducibility of CoOx species leads to relatively weaken inhibition of trace oxygen for PDH activity. The oxygen content in the propane feed gas is a non-negligible factor in the development of new Co-based PDH catalysts, especially for their industrial applications.

Recommendations for improving rigor and reproducibility in site specific characterization

Heterogeneous catalysis is driven by the interaction of reactant molecules and the catalyst surface. The locus of this interaction as well as the surrounding ensemble of atoms is referred to as the catalyst active site. Active site characterization attempts to distinguish active catalytic sites from inactive surface sites, to elucidate the structural and chemical nature of active sites, and to quantify active site concentration. Numerous techniques have been demonstrated to provide compositional and structural information about the active sites within a catalyst. However, each technique has its own limitations and experimental pitfalls that can lead to data misinterpretation or irreproducible results. This work aims to provide an overview of the types of data that can be collected, to outline common experimental challenges and how to avoid them, and to assemble relevant references for the most used active site characterization techniques. More broadly, we aim to outline best practices for researchers to collect, interpret, and report active site characterization data in a way that provides the most benefit to the broader catalysis community. Increasing the rigor and reproducibility of active site characterization offers a strategy to better link properties with catalytic performance and to enable the community to develop consensus concerning these relationships.

Surface functional modification of Nb2CTx MXene for high performance capacitive deionization

MXene, show a promising electrode material for capacitive deionization (CDI) due to their elevated conductivity and hydrophilic surface characteristics. Despite optimal electrochemical reaction conditions, MXene still exhibits unsatisfactory capacity. Enhancing capacitance in Nb2CTx MXene poses a key challenge, and addressing this involves leveraging pseudocapacitance through increased active site concentration. This study reports a method to notably improve the capacitance by incorporating cation intercalation and surface modification. After alkali treatment and thermal annealing, the obtained 400-KOH-Nb2C as a cathode in capacitive deionization, exhibiting notable salt adsorption capacity of 104.2 mg g−1 at 1.6 V and an efficient removal rate of 1.73 mg g−1 min−1, cyclic stability maintained over 200 cycles. This optimized electrochemical and desalination performance is due to the large interlayer spaces of Nb2CTx and the surface with lowest termination of -F and –OH group, promoting the delicate surface of Nb2CTx MXene and accelerating ion transport. Furthermore, the derivation of KNbO3 nanowires on 400-KOH-Nb2C surface further expands the layer spacing of MXene and enhances the active sites, and also acts as a protective layer to improve the stability of Nb2C, this effectively addressing challenges associated with desalination. This study offers a novel solution for improving Nb2CTx MXene electrochemical properties in CDI.

Synthesis and evaluation of mono(phenoxy-imine) titanium complexes attached to a single polystyrene chain end for ethylene polymerization

Monodisperse polystyrene (PS) chains with different lengths are synthesized by atom transfer radical polymerization (ATRP), serving as soluble supports for attaching mono(phenoxy-imine) metal complexes in the chain end. For ethylene polymerization, the PS chain-supported titanium (Ti) complexes exhibit unique catalytic features such as higher activity. Their performance in ethylene polymerization and kinetic examination is extensively investigated to uncover the influence mechanism of support chain length. Initially, the catalytic activity of the supported catalysts increases with the support chain length, but then decreases. Effective preservation by the support prevents catalyst deactivation and enhances the concentration of active sites [C*], leading to increased activity. However, the decline in activity is attributed to the exceptionally long support chain, impeding ethylene diffusion and leading to a reduction in ethylene concentration [M] around active sites. As the support chain length increases, the molecular weight (Mw) of the produced polyethylene (PE) decreases. The nascent polyethylene obtained from supported catalysts displays a uniform petal-like and shish-kebab morphology. The well-defined nature of these PS chain-supported catalysts provides a powerful tool for studying interactions between active centers and supports, offering insights that can guide the design of catalysts.

Cu3P Nanoarrays Derived from 7,7,8,8-Tetracyanoquinodimethane for High-Rate Electrocatalytic Oxygen Reactions of Lithium-Oxygen Batteries

Efficient electrocatalysis at the cathode is crucial for addressing the challenges faced by lithium-oxygen batteries (LOBs), including limited stability and low-rate capability. To develop an efficient cathode for aprotic LOBs, self-supported copper phosphide nanoarrays on carbon cloth are prepared at different heating rates via a phosphidation process using CuTCNQ nanoarrays. Different ramping rates have effects on particle size and intrinsic interaction, which in turn affect their catalytic properties. When phosphidation is carried out at a slow rate, it results in the formation of smaller, evenly distributed Cu3P particles on the nanoarrays (SG-Cu3P NAs/CC) compared to fast rate phosphidation (FG-Cu3P NAs/CC). As a result, SG-Cu3P NAs/CC exhibits lower resistance and a higher concentration of active sites than FG-Cu3P NAs/CC. The SG-Cu3P NAs/CC demonstrates LOBs with a low overpotential of 1.51 V at a high current rate of 1 mA cm−2 and a long cycle life of 115 cycles at 0.1 mA cm-2. The in situ Raman spectroscopy supports that Li2O2 is uniformly formed and decomposed on the SG-Cu3P NAs/CC surface. This study provides a compelling approach for the precise fabrication and analysis of binder-free, self-supported copper phosphides as highly efficient and stable materials for bifunctional oxygen electrocatalysis.

Nitrogen-doped carbonaceous electrode modified by biological metal-organic framework for vanadium redox flow batteries

The biological metal-organic framework (Bio-MOF) is utilized to modify the carbonaceous electrode for the vanadium redox flow batteries. The microwave solvothermal method prepared the cobalt-based Bio-MOF on a graphite felt (GF) surface. Then, the nitrogen-doping graphite and porous structure formation were completed simultaneously during the carbonization process. Finally, electrochemical activation was conducted to remove cobalt metal from the GF electrode and raise the concentration of oxygen-containing functional group active sites. By in-situ Raman spectroscopy, the increase of disordered graphitic lattices could be observed by raising the potential from 0.6 V to 1.6 V. The microwave solvothermal method and electrochemical activation can effectively shorten the treatment time compared with the traditional solvothermal method and acidic etching processes. Among the carbonization parameters for Bio-MOF-covered GFs, maintaining the temperature at 900 °C for 2 h under an argon atmosphere is the most suitable. The annealed sample after electrochemical activation (BMDGF-900EA) displays 73.7 % energy efficiency at 120 mA cm−2 and possesses a 90 % retention rate of efficiency after 250 cycles at 180 mA cm−2. The superior performance results from more catalytic active sites, hydrophilic surface features, and larger specific surface area prove that this modification method derived from Bio-MOF indeed provides a novel and potential way to improve the VRFB performance.

Impact of Sr Addition on Zirconia-Alumina-Supported Ni Catalyst for COx-Free CH4 Production via CO2 Methanation.

Zirconia-alumina-supported Ni (5Ni/10ZrO2+Al2O3) and Sr-promoted 5Ni/10ZrO2+Al2O3 are prepared, tested for carbon dioxide (CO2) methanation at 400 °C, and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, surface area and porosity, infrared spectroscopy, and temperature-programmed reduction/desorption techniques. The CO2 methanation is found to depend on the dispersion of Nickel (Ni) sites as well as the extent of stabilization of CO2-interacted species. The Ni active sites are mainly derived from the reduction of 'moderately interacted NiO species'. The dispersion of Ni over 1 wt % Sr-promoted 5Ni/10ZrO2+Al2O3 is 1.38 times that of the unpromoted catalyst, and it attains 72.5% CO2 conversion (against 65% over the unpromoted catalyst). However, increasing strontium (Sr) loading to 2 wt % does not affect the Ni dispersion much, but the concentration of strong basic sites is increased, which achieves 80.6% CO2 conversion. The 5Ni4Sr/10ZrO2+Al2O3 catalyst has the highest density of strong basic sites and the highest concentration of active sites with maximum Ni dispersion. This catalyst displays exceptional performance and achieves approximately 80% CO2 conversion and 70% methane (CH4) yield for up to 25 h on steam. The unique acidic-basic profiles composed of strong basic and moderate acid sites facilitate the sequential hydrogenation of formate species in the COx-free CH4 route.

Creating Remarkably Moisture‐ and Air‐Stable Macromolecular Lewis Acid by Integrating Borane within the Polymer Chain: A Highly Active Catalyst for Homo(co)polymerization of Epoxides

AbstractBorane‐based Lewis acids (LA) play an indispensable role in the Lewis pair (LP) mediated polymerization. However, most borane‐based LPs are moisture‐ and air‐sensitive. Therefore, development of moisture and air‐stable borane‐based LP is highly desirable. To achieve this goal, the concept of “aggregation induced enlargement effects” by chemically linking multiple borane within a nanoscopic confinement was conceived to create macromolecular LA. Accordingly, an extremely moisture and air stable macromolecular borane, namely, PVP‐1B featuring poly(4‐vinylphenol) backbone, was constructed. The concentration of borane active site is greatly higher than average concentration due to local confinement. Therefore, an enhanced activity was observed. Moreover, the local LA aggregation effects allow its tolerance to air and large amount of chain transfer agent. Consequently, PVP‐1B showed remarkable efficiency for propylene oxide (PO) polymerization at 25 °C (TOF=27900 h−1). Furthermore, it enables generation of well‐defined telechelic poly (CHO‐alt‐CO2) diol (0.6–15.3 kg/mol) with narrow Đs via copolymerizing cyclohexene oxide and CO2 at 80 °C. This work indicates unifying multiple borane within a polymer in a macromolecular level shows superior catalytic performance than constructing binary, bi(multi)functional systems in a molecular level. This paves a new way to make functional polyethers.

Creating Remarkably Moisture- and Air-Stable Macromolecular Lewis Acid by Integrating Borane within the Polymer Chain: A Highly Active Catalyst for Homo(co)polymerization of Epoxides.

Borane-based Lewis acids (LA) play an indispensable role in the Lewis pair (LP) mediated polymerization. However, most borane-based LPs are moisture- and air-sensitive. Therefore, development of moisture and air-stable borane-based LP is highly desirable. To achieve this goal, the concept of "aggregation induced enlargement effects" by chemically linking multiple borane within a nanoscopic confinement was conceived to create macromolecular LA. Accordingly, an extremely moisture and air stable macromolecular borane, namely, PVP-1B featuring poly(4-vinylphenol) backbone, was constructed. The concentration of borane active site is greatly higher than average concentration due to local confinement. Therefore, an enhanced activity was observed. Moreover, the local LA aggregation effects allow its tolerance to air and large amount of chain transfer agent. Consequently, PVP-1B showed remarkable efficiency for propylene oxide (PO) polymerization at 25 °C (TOF=27900 h-1 ). Furthermore, it enables generation of well-defined telechelic poly (CHO-alt-CO2 ) diol (0.6-15.3 kg/mol) with narrow Đs via copolymerizing cyclohexene oxide and CO2 at 80 °C. This work indicates unifying multiple borane within a polymer in a macromolecular level shows superior catalytic performance than constructing binary, bi(multi)functional systems in a molecular level. This paves a new way to make functional polyethers.

Synergistic effects of interface and valence state on boosting electrochemical CO2 reduction activity of La2CuO4

The electrochemical CO2 reduction reaction (CER) to methane (CH4) has received great attention. Here, we proposed an efficient method to facilitate the conversion of CO2-to-CH4 by creating a two-phase interface over urea-modified La2CuO4 catalyst. The most optimized one exhibits the highest selectivity (22%) for CH4 and the best activity (14 mA cm−2) and stability (5 h) at the potential of −1 V vs. reversible hydrogen electrode. The enhanced CER performance can be attributed to the establishment of interfacial effect within the two-phase, which facilitates the reduction of Cu2+ and promotes the active sites concentration.

Graphene nanosheet-supported ultrafine RuO2 quantum dots as electrochemical energy materials

Ruthenium oxide (RuO2) shows great promise as an electrode material for supercapacitors, which are energy storage devices that have large power densities. However, RuO2 materials suffer low surface area, poor electrical conductivity and a tendency to aggregate after reactions, limiting their rate capability and cycle stability and can lead to inadequate redox reactions with electrolytes. To address these problems, this work synthesized homogeneous ultrafine-RuO2 quantum dots (QDs) materials with a size of around 2 nm on the surface of graphene nanosheets (GNS) via a facile hydrothermal method. The small size and uniform distribution of RuO2 QDs in the composite electrode material allowed for a high concentration of active adsorption sites for ions in the electrolyte while also facilitating efficient electrochemical redox reactions. The resulting RuO2/GNS composite exhibited a large specific area of 177.34 m2g‐1 and demonstrated an excellent capacitance performance of 1138.5 Fg‐1 at a current density of 0.5 Ag‐1. Additionally, a retention rate of 91.4 % when applying current densities from 0.5 to 10 Ag‐1 and cycling stability with 94.5 % retention after 20000 cycles, demonstrates the occurrence of a rapid and reversible faradaic redox reaction on the electrode surface. The symmetrical supercapacitor configuration with two identical RuO2/GNS electrodes was fabricated and demonstrated a high capacity (309.16 Fg‐1 at a current density of 0.5 Ag‐1) and an outstanding retention rate of 91.2 % at a current density of 10 A g−1). A device operated within a 1.8 V potential window showed high energy density from 126 Whkg‐1 to 139.2 Whkg‐1 and a power density from 440.1 Wkg‐1 to 8494.4 Wkg‐1 at current densities ranging from 0.5 Ag‐1 to 10 Ag‐1, respectively. This ultrafine-RuO2 quantum dots composite is a potentially promising advanced functional electrode material for electrochemical applications beyond supercapacitors and may be suitable for a broader range of energy storage and conversion applications.

Unraveling the poisoning effects of different K salts exerted on phosphotungstic acid-modified MnOx for NH3-SCR of NOx

The inevitable presence of various K species in real flue gas may deactivate catalysts used for NH3-SCR of NOx. Herein, the poisoning effects of several K salts (KNO3, K2SO4, KCl) on catalytic performance of phosphotungstic acid-modified MnOx (Mn-HPW) were studied. The extent of deactivation follows the sequence of KC/Mn-HPW > KN/Mn-HPW ≈ KS/Mn-HPW. Especially, KCl decreases significantly SCR activity of Mn-HPW at 90–300 °C, whereas K2O or K2SO4 exerts the negative effect only below 210 °C. The characterization results show that the presence of K species leads to worse reducibility as well as fewer amounts of Mn4+, Mn3+, and chemisorbed oxygen of the Mn-HPW catalyst. The decrease in the quantity and reactivity of active NH3-Lewis and active bridged nitrate is another critical reason for inhibiting NOx elimination at low temperatures on poisoned catalysts. Especially, SO42− in KS/Mn-HPW acts as the spectators in the reaction between active NH3-Lewis with NOx or between active bridged nitrate with NH3, so de-NOx activity of KS/Mn-HPW is comparable to that of KN/Mn-HPW. For KCl/Mn-HPW, the reducibility and relative concentrations of active sites as well as chemisorbed oxygen are the worst. Furthermore, Cl− further restrains the adsorption of active NH3-Lewis, undermining the NOx removal by E-R route; Cl− also hinders the formation of active bridged nitrate, cutting off the reaction through the L-H route. Therefore, KCl exerts the most serious deactivation of Mn-HPW.

Characterization of Ag/α-Al2O3 olefin epoxidation catalysts containing promoters and co-promoters using pulse hydrogen titration methods

A series of Cs and Cs + Re promoted 12 wt% Ag/α-Al2O3 catalysts were prepared and characterized by H2 pulse titration of O-precovered Ag to measure active Ag site concentrations. Temperature programmed reduction (TPR) at temperatures up to 500 °C was performed on α-Al2O3 supported 3–4 wt% Cs, Re, or Mo only catalysts to confirm the metal–oxygen bonds of the promoters were not reactive during titration of Ag-O surface at 170 °C; absence of H2 uptake during H2 titration for these samples confirmed the TPR results. H2 pulse titration results of 0 to 7.5 μmol Cs promoted, 12 wt% Ag/α-Al2O3 catalysts showed non-preferential deposition of Cs on Ag and α-Al2O3 surfaces. However, when Cs (2.6 μmol)–12 wt% Ag/α-Al2O3 catalyst was promoted with ≥1.3 μmol of Re, titration results showed preferential deposition of Re on Ag sites, presumably to lower overall surface free energy of the Re-Ag-Al2O3 system.

A Cleaner Approach for Controllable Synthesis of Au/TiO2 Nanocomposite as an Efficient Catalyst for 4‐Nitrophenol Reduction

AbstractSupported metal catalysts have attracted considerable attention because of their remarkably high catalytic activity and thermal stability. In this work, we report a facile and eco‐friendly method to synthesize porous Au/TiO2 nanocomposites with tunable size and different loading of Au nanoparticles. Porous TiO2 particles with average size of 20 nm were obtained using deep eutectic solvent‐assisted solvothermal method, in which Au NPs were immobilized by citrate reduction process. By adjusting the molar ratio of citrate and gold precursor, the size and loading of Au particles could be effectively controlled. The optimized nanocomposite with maximum Au loading and smallest particle size of 9 nm manifested the best catalytic activity in the 4‐nitrophenol reduction and excellent reusability. The superior catalytic performance can be ascribed to the strong interfacial interaction between small Au NPs and porous TiO2 support together with the high concentration of active sites at the interface.

Synthesis of 2D zeolitic imidazolate frameworks based on Co(II) and Pd(II): Effect of Pd(II) addition on the CO2 cycloaddition with epichlorohydrin

Carbon dioxide (CO2) cycloaddition with epoxide can yield value-added cyclic carbonates with 100 % atom efficiency. Moreover, zeolitic imidazolate frameworks (ZIFs) have emerged as promising catalysts for this reaction as their basic and acidic sites can effectively activate CO2 and epoxide molecules. Here, novel mixed-metal ZIFs containing Pd and Co ions (PdCo-ZIFs) that are linked by benzimidazole ligands were synthesized, after which their structures were comprehensively characterized. Despite the inherent two-dimensional nanosheet structure of Co-ZIF, PdCo-ZIFs exhibited a large surface area, with a hierarchical porous structure and profoundly increased active site concentrations (10–20 times higher than those of Co-ZIFs), exhibiting significantly increased catalytic activity toward CO2 cycloaddition. Additionally, the relationship between the catalytic activity and structural characteristics of ZIFs correlated, and the representative Pd2Co8-ZIF catalyst achieved a maximum product yield of 97.3 %, with a high turnover number (5754) and turnover frequency (479 h−1) for cyclic carbonates, attributed to the well-developed porous structure and defect sites that could not be observed in single-metal ZIF materials.

Modification of Al Surface via Acidic Treatment and its Impact on Plating and Stripping.

Amorphous Al2 O3 film that naturally exists on any Al substrate is a critical bottleneck for the cyclic performance of metallic Al in rechargeable Al batteries. The so-called electron/ion insulator Al oxide slows down the anode's activation and hinders Al plating/stripping. The Al2 O3 film induces different surface properties (roughness and microstructure) on the metal. Al foils present two optically different sides (shiny and non-shiny), but their surface properties and influence on plating and stripping have not been studied so far. Compared to the shiny side, the non-shiny one has a higher (~28 %) surface roughness, and its greater concentration of active sites (for Al plating and stripping) yields higher current densities. Immersion pretreatments in Ionic-Liquid/AlCl3 -based electrolyte with various durations modify the surface properties of each side, forming an electrode-electrolyte interphase layer rich in Al, Cl, and N. The created interphase layer provides more tunneling paths for better Al diffusion upon plating and stripping. After 500 cycles, dendritic Al deposition, generated active sites, and the continuous removal of the Al metal and oxide cause accelerated local corrosion and electrode pulverization. We highlight the mechanical surface properties of cycled Al foil, considering the role of immersion pretreatment and the differences between the two sides.

Chlorphenamine adsorption on commercial activated carbons: Effect of Operating Conditions and Surface Chemistry.

Chlorphenamine (CPA) adsorption onto three activated carbons (ACs), namely, Megapol M (MM), Micro 10 (M10), and GAMA B (GB), was studied in this work. The textural properties, concentrations of active sites, surface charge and point of zero charge of the ACs were assessed. The surface areas (SBET) of MM, GB and M10 were 1107, 812 and 766 m2/g, respectively. The MM surface had an acidic character, while the surfaces of M10 and GB were basic. The adsorption capacity of MM, M10, and GB towards CPA was studied at pH 7 and 11, and the adsorption capacity decreased in the order MM > M10 ≈ GB, which was ascribed to the magnitude of SBET and the concentration of acidic sites. The solution pH significantly increased the adsorption capacity of MM towards CPAby raising the solution pH from 5 to 9, and this behavior was attributed to the electrostatic attraction between the negatively charged surface of MM and the cationic species of CPA. The maximum uptake of CPA adsorbed on MM was 574.6mg/g at pH = 11 and T = 25°C. The adsorption capacity of MM was slightly raised by incrementing the temperature. Lastly, the zeta potential measurements of pristine MM and MM saturated with CPA confirmed that the electrostatic attraction predominated in the pH range of 5-9, and the π-π stacking interactions were the principal mechanism of CPA adsorption on MM at pH 11.

Engineering of Micro-mesoporous two-dimensional CeO2-based heterojunction oxides for energy storage applications

With growing demands on energy supply and storage, there is a need for advanced devices that can meet the high power and energy requirements. One such device is a supercapacitor, which is classified into two types, namely the electrical double-layer capacitor (EDLC) and the pseudocapacitor. Pseudocapacitors show energy storage properties that are between EDLCs and batteries and generally, transition metal oxides are used for these applications. Recent work has demonstrated that CeO2 is a potential material for such applications owing to its reversible charge-switching capabilities and good stability in different environments. In the present work, novel ultrathin nanosheets of CeO2-x and a composite of ruthenium (Ru)-CeO2-x, with the Ru in the form of mixed heteroatoms and dopants were synthesised using a Ce-based coordination polymer (Ce-CP) as the precursor using modified anodic chronoamperometric electrodeposition (MACE) technique. The ready exfoliation of Ce-CP in triethanolamine, which was the exfoliation medium, followed by solvent removal and annealing at 300 °C resulted in the formation of ultrathin 2D CeO2 nanosheets that are partially stacked, resulting in the formation of flower-like 3D nanostructures. The ultrathin 2D CeO2 formed 3D flower-like nanostructures with high concentrations of defects, active sites, and mesopores, which increased with the concentration of Ru in the CeO2-x nanostructure. Additionally, the specific surface area of the Ru-CeO2-x samples was higher, increasing to 354 m2·g−1 compared to the value of 146 m2·g−1 for pristine CeO2-x. The cyclic voltammetry analysis revealed that the introduction of Ru increased the capacitance of pristine CeO2-x from 665 F·g−1 to 923 F·g−1 at a scan rate of 5 mV·s−1. These findings suggest that Ru-CeO2-x nanosheets have potential for use in supercapacitor applications.

Modifying electronic and physical properties of Fe-NSC catalyst for oxygen reduction reaction via sulfur doping process

The primary challenge in the large-scale production of metal-air batteries or fuel cells is the high cost of Pt, which is used in the oxygen reduction reaction. To address this issue, we synthesized non-precious metal catalysts by doping Fe, N, and S in various sequences. X-ray diffraction and Raman spectroscopy proved that these catalysts had a higher degree of graphitization than carbon black. While the Fe3C phase was found in the catalyst without S, it was absent in all Fe-NSC catalysts. Imaging and X-ray absorption near edge structure (XANES) studies showed atomically dispersed Fe metal in the S-doped non-precious metal catalysts. X-ray photoelectron spectroscopy (XPS) and XANES reveal that the active site concentrations, inactive Fe-S bond, and oxidation number of the Fe species vary according to the N and S doping sequences. Fe-NSC-1 showed fast kinetics and high selectivity, with an onset potential of 0.96 V. Even after 10,000 potential cycles between 0.6 and 1.0 V, the half-wave potential for Fe-NSC-1 decreased by only 3%. Additionally, the Fe-NSC-1 catalyst showed a negligible decrease in current density during the methanol tolerance tests. Overall, this study found that the doping sequence plays a vital role in enhancing the electrochemical performance and stability of these catalysts under suitable operating conditions by influencing their chemical and electronic structures.