Oxygen-enriched Surface Research Articles

The Assembly of Cerium(III)-Containing Silicotungstate with Lewis Acid-Base Sites Enables the Selective C3-Alkenylation of Oxindole.

A cerium(III)-containing silicotungstate, [H2N(CH3)2]10NaK[KCe(SiW11O39)2(H2O)]·18.5H2O (CeSiW), was successfully synthesized and characterized. Structure analysis reveals that CeSiW is composed of two {SiW11O39} units connected by one cerium(III) cation to form a typical 1:2 sandwich structure, which is further expanding into a 1D chain linked by K+ ions. The oxygen-enriched surfaces of {SiW11O39} units and open cerium sites provide abundant Lewis base and acid sites in CeSiW. As a result, CeSiW efficiently catalyzed the C3-alkenylation of oxindoles with aldehydes through the simultaneous activation of both reaction substrates on its crystal framework. Various 3-benzylidene-oxindoles are synthesized with excellent yields and high E-selectivity under solvent-free conditions.

Improving CO2 adsorption efficiency of an amine-modified MOF-808 through the synthesis of its graphene oxide composites

This research developed a novel composite of MOF-NH2 and graphene oxide (GO) for enhanced CO2 capture. Employing the response surface methodology-central composite design (RSM-CCD) for experiments design, various MOF-NH2/GO samples with GO loadings from 0 to 30 wt% were synthesized. The results of SEM, XRD, EDS, and BET analysis revealed that the materials maintained their MOF crystal structure, confirmed by X-ray diffraction, and exhibited unique texture, high porosity, and oxygen-enriched surface chemistry. The influence of temperature (25–65 °C) and pressure (1–9 bar) on CO2 adsorption capacity was assessed using a volumetric adsorption system. Optimum conditions were obtained at weight percent of 22.6 wt% GO, temperature of 25 °C, and pressure of 9 bar with maximum adsorption capacity of 303.61 mg/g. The incorporation of amino groups enhanced the CO2 adsorption capacity. Isotherm and kinetic analyses indicated that Freundlich and Fractional-order models best described CO2 adsorption behavior. Thermodynamic analysis showed the process was exothermic, spontaneous, and physical, with enthalpy changes of − 16.905 kJ/mol, entropy changes of − 0.030 kJ/mol K, and Gibs changes energy of − 7.904 kJ/mol. Mass transfer diffusion coefficients increased with higher GO loadings. Regenerability tests demonstrated high performance and resilience, with only a 5.79% decrease in efficiency after fifteen cycles. These findings suggest significant potential for these composites in CO2 capture technologies.

Water-Capture Filter Paper Separator Realizing Ambient Li-Air Battery.

Lithium-air battery (LAB) is regarded as one of the most promising energy storage systems. However, the challenges arising from the lithium metal anode have significantly impeded the progress of LAB development. In this study, cellulose-based filter paper (FP) is utilized as a separator for ambient Li-air batteries to suppress dendrite growth and prevent H2O crossover. Thermogravimetric analysis and molecular spectrum reveal that FP enables ambient Li-air battery operation due to its surface functional groups derived from cellulose. The oxygen-enriched surface of cellulose not only enhances ion conductivity but also captures water and confines solvent molecules, thereby mitigating anode corrosion and side reactions. Compared with commercial glassfiber (GF) separator, this cellulose-based FP separator is cheaper, renewable, and environmentally friendly. Moreover, it requires less electrolyte while achieving prolonged and stable cycle life under real air environment conditions. This work presents a novel approach to realizing practical Li-air batteries by capturing water on the separator's surface. It also provides insights into the exploration and design of separators for enabling practical Li-air batteries toward their commercialization.

Bioinspired polyoxometalates as light-driven water oxidation catalysts

The design of molecular systems with capabilities to carry out the water oxidation reaction and thereby overcome the bottleneck of artificial photosynthesis is one of the scientific fields of most significant interest and urgency due to its potential to address energy demand and climate change. Nevertheless, the search for efficient and robust catalysts has been limited by the degradation of carbon-based ligands under oxidative conditions, leading to the search for fully inorganic catalysts. Polyoxometalates (POMs), an emerging class of carbon-free ligands with oxygen-enriched surfaces, offer a unique alternative as inorganic scaffolds to self-assemble and stabilize transition-metal clusters with unique redox properties. Under catalytic working conditions, POMs can undergo electron transfer reactions coupled to O2 formation without modifying their parental structure. As a result, these materials have recently entered the scene as catalytic players in designing new artificial photosynthetic platforms for water oxidation. We focus on the methods used to create these compounds, their unique structural characteristics, and how effectively they function as catalysts. We also explore the proposed mechanisms behind their ability to produce O2 and their potential use in designing photosynthetic devices.

Correlation between surface/bulk properties and electrochemical cycling performance of pure silicon anode materials

State-of-the-art lithium-ion batteries (LIBs) employ silicon (Si)-graphite composite anode with just a few percentages of Si active material, whose cycle-life relies on a stable solid electrolyte interphase (SEI) layer. As a number of various types of industrial Si active materials are currently available, an informative guideline based on the material properties and resultant cycling performance of different pure Si (i.e., without graphite) anode materials is strongly needed for material selection. The present study provides for the first time the correlation among material's surface and bulk properties, the SEI formation behavior, and cycling behavior of highly loaded pure Si anodes (2.3 mAh cm−2) prepared from four different industrial active materials, which are SiOx, carbon-coated Si, and bare Si with submicron and micron sizes. Commercial electrolyte with 10 wt% fluoroethylene carbonate additive is used for electrochemical performance evaluation. Based on solid-state NMR, XPS, and electrochemical analysis results, SiOx is determined to be relatively beneficial for practical applications beyond Si materials, in the aspects of high structural and particle morphology stability, cycling stability and suppressed interfacial resistance. This is mainly because of more effective accommodation of volume change of Si and oxygen-enriched surface (SEI) stability. The data give insight into the rational design of well-working Si-dominant or pure Si anodes for high energy density LIBs.

Unlocking the full potential of citric acid-synthesized carbon dots as a supercapacitor electrode material via surface functionalization.

This research paper investigates the effect of functionalizing the surfaces of citric acid-synthesized carbon dots (CDs) with hyperbranched bis(methylol)propionic acid (bis-MPA) polyester hydroxyl polymers (HBPs) on their performance as electrode materials in a supercapacitor. Two types of HBPs with 16 and 64 peripheral hydroxyl groups were used to functionalize the CDs' oxygen-enriched surface. Here, CDs were used as electrode materials for the first time in symmetric supercapacitors without a composite material, and how surface modification affects the capacitance performance of CDs was investigated. Our results showed that the functionalization of green-emitting CDs with HBP resulted in the successful passivation of surface defects, which improved their stability and prevented further oxidation. The CDs with HBP passivation exhibited excellent electrochemical performance, with a high specific capacitance of 32.08 F g-1 at 0.1 A g-1 and good rate capability, indicating a faster ion transport rate at high current densities. Experimental EPR spectra of functionalized and non-functionalized CDs reveal distinct changes in g-factor values and line widths, confirming the impact of dangling bonds and spin-orbit interactions. The observed broader linewidth indicates a wider range of electron spin resonances due to energy-level splitting induced by spin-orbit coupling. The excellent electrochemical performance of CDs with HBP passivation can be attributed to the presence of oxygen-containing surface functional groups such as hydroxyl and carboxyl groups on their surfaces, which enhance the conductivity and charge transfer reactions. These results suggest that functionalization with polar HBPs is a promising strategy to enhance the electrochemical performance of CDs in supercapacitor applications.

Targeted Grafting Metal-Organic Frameworks on Polyoxometalates for Efficient Water Oxidation

In recent years, due to the diverse and tunable microenvironment of metal centers, Metal-organic framework materials (MOFs) have shown great advantages in heterogeneous catalysis.[1,2] Studies have found that in some oxidation scenarios, taking water oxidation as an example, the instability of is framework limits its practical application under severe conditions. Therefore, many efforts have focused on improving the catalytic stability of MOFs materials. [3-5]The MOFs-based electro-catalytic systems developed for oxygen evolution under alkaline conditions in our work are discussed in the following three sections. First, based on the loss of active sites faced by MOFs during OER and the high oxidation potential due to insufficient electrical conductivity, a kind of nanoscale inorganic materials with oxygen-enriched surfaces --polyoxometalates (POMs), was selected as a composite modifier. Subsequently, a two-dimensional nanomaterial (MOFs@POMs) with high catalytic activity and ultra-high stability was synthesized on the basis of MOFs using a facile solvothermal method to immobilize the active sites of MOFs through the M-O ionic bond between POM and MOFs. Furthermore, we found that the structure of POMs plays a key role in the formation of this unique superstructure, which leads to a catalytic active site that can be persistently maintained during the OER process. Based on this, a scheme for the immobilization of MOFs active sites by POMs is proposed to synthesize MOFs composites with ultra-high OER stability based on both POMs and MOFs materials. The assembly mechanism of the composites during the synthesis process is proposed, and the intrinsic reason for the modulation of the active site of MOFs by POMs and its long-lasting immobilization is demonstrated, which enables the MOFs materials to maintain excellent catalytic activity throughout the great OER catalytic process. This study successfully demonstrates that the stability challenges faced in the OER process of MOFs can be solved, which may provide a helpful solution for the application of MOFs-related OER catalysts.

Lanthanoid-containing polyoxometalate nanocatalysts in the synthesis of bioactive isatin-based compounds

Lanthanoid-containing polyoxometalates (Ln-POMs) have been developed as effective and robust catalysts due to their Lewis acid–base active sites including the oxygen-enriched surfaces of POM and the unique 4f. electron configuration of Ln. As an extension of our interest in Ln-POMs, a series of as-synthesized nanocatalysts K15[Ln(BW11O39)2] (Ln-B2W22, Ln = La, Ce, Nd, Sm, Gd, and Er) synthesized and fully characterized using different techniques. The Ln3+ ion with a big ionic radius was chosen as the Lewis acid center which is sandwiched by two mono-lacunary Keggin [BW11O39]9− units to form Ln-containing sandwiched type cluster. Consequently, the catalytic activity of nanocatalysts with different Ln was examined in the synthesis of bioactive isatin derivatives and compared under the same optimized reaction conditions in terms of yields of obtained products, indicating the superiority of the nano-Gd-B2W22 in the aforementioned simple one-pot reaction. The effects of different dosages of nanocatalyst, type of solvent, reaction time, and reaction temperature in this catalytic system were investigated and the best results were obtained in the presence of 10 mol% of nano-Gd-B2W22 in water for 12 min at the reflux condition.

Frontiers and applications of polyoxometalates-based porous ionic crystals

<p indent="0mm">Polyoxometalates (denoted as POMs) are discrete metal-oxide anions of V, Mo, W, etc., with variable structures and sub-nanometer sizes. Plenty of POMs and their derivatives have been reported due to their oxygen-enriched surface and abundant substitutional chemistry. However, few studies have focused on the modulation of the counter cations so far. Different from common cations, such as Na⁺, NH₄⁺ and other organic ammonium ions (tetramethylammonium, tetrabutylammonium, etc.), cation clusters with larger size can also be used as counter ions of POMs. They are arranged alternately through ionic bonds or hydrogen bonds to form the solid ionic crystal materials with special properties, which are named POM-based porous ionic crystals (PPICs). The use of cation clusters with different compositions greatly enriches the structure and type of PPICs, which further boosts the development of polyoxometalates chemistry. The POMs anions and large metal complex cations in PPICs are regularly arranged into a porous honeycomb or layered structure. Some PPICs also contain monovalent cations such as H⁺ and alkali metal ions to balance their extra negative charges. The use of ion clusters facilitates the formation of pore structures in the PPICs lattice because they can reduce the electrostatic interaction between cations and anions. Thus, the pore structure of PPICs is much larger than that of POMs. Note that the pore size in PPICs can be easily adjusted by changing the shape, size and charges of cation and anions. Apart from the electrostatic interaction, anisotropic π-π stacking and hydrogen bonding network among the components of PPICs also contribute to their assembly. All these interaction modes will affect the arrangement of anions and cations in the PPICs lattice, resulting in the formation of different hole sizes and various channels characteristics in the crystal lattice, such as hydrophilic, hydrophobic and amphiphilic pores. In addition, the long-range Coulomb interaction works isotropically, leading to the easy transformation of the flexible PPICs structure. Hence, the adjustment of the channel provides a useful strategy for constructing PPICs with unique structures. Most importantly, PPICs show better performance than individual components because they inherit the advantages from both anions and cations. Briefly, PPICs not only retain good redox reversibility, rich multi-electron transfer characteristics and strong Brønsted acidity of POMs, but also reserve the magnetic properties of large cation clusters. Therefore, the physical and chemical properties of PPICs can be modulated by the rational design of each component. The future research on PPICs should not be limited to expanding the categories of cations, and the innovative structural type of POMs is also an important aspect. In addition to the Keggin POMs, other POMs structures, such as Dawson, Anderson, and Preyssler, can also be used in PPICs, resulting in some unique properties. Besides, various POM-based materials (modified POMs or POM-based composites, etc.) can also be adopted to fabricate PPICs, which may bring unexpected performance. Thus, changing anions and cations makes PPICs have great potential in many interdisciplinary fields such as chemistry, materials science, and biomedicine. This review systematically summarizes the structural characteristics and composition of PPICs, which is essential for understanding the characteristics of PPICs, such as adjustable pore structure, unique redox behavior, strong acidity and magnetic properties. In general, PPICs with different properties can be constructed by using diverse POMs and distinct cation clusters, which will be widely applied in many fields such as guest adsorption, ion exchange, photoelectric catalysis, bioimaging and medical materials.

Thermal Hydrogen Treatment of Electrodes for Performance and Stability Enhancement of Non-Aqueous Redox Flow Batteries

Vanadium acetylacetonate [(V(acac)3] is being used as model redox species for the study of non-aqueous redox flow battery (NAqRFB). The redox species present reversible redox reactions for both V+2/V+3 (i.e. the negolyte ca. -1.75 V vs Ag/Ag+) and V+3/V+4 (i.e. posolyte ca. 0.45 V vs Ag/Ag+). The same discharge state V+3 of this electrolyte can be used on both sides of the half cell. The latter and the fact it dissolves easily in an organic solvent, besides its commercial availability at a fair price makes it a promising candidate for future commercial versions of non-aqueous redox flow batteries.Nonetheless, merits are usually accompanied by some demerits. Vanadium has four valency states starting from V+2 to V+5; for the V-NAqRFB only three oxidations states are desirable V+2, V3+, and V4+ thus the formation of V5+ is unwanted. To avoid this oxidation state, typically the battery open circuit potential is kept below 2.27 V. Another downside of this electrolyte refers to its sensitivity towards a moisture/oxygen-enriched environment. The presence of moisture/oxygen in the environment triggers a non-reversible reaction which leads to the formation of VO(acac)2 at the positive electrode. VO(acac)2 irreversible formation causes rapid battery capacity loss due to its parasitic and increased concentration on the electrolyte. Therefore, the electrolyte must be kept in an inert atmosphere such as dry nitrogen. Nonetheless, it was observed that even by maintaining a strictly controlled saturation of the electrolyte with inert gas, the stability of the batteries was still rather negligible. Components such as the electrodes (carbon felts, CF) could also represent a major source for the oxygen-enriched surface. Many oxidation pre-treatments such as chemical exfoliation (H2SO4) and thermal oxidation under airflow at 450 °C are commonly performed on CFs to increase their wettability and performance in aqueous all vanadium redox flow cells. Nonetheless, these kind of pre-treatments might not be suitable for the system here in the study due to the beforehand mentioned reasons. The latter served as the main motivation for this study.Initially, cyclic voltammetry (CV) was performed using a three-electrode configuration cell and a glassy carbon as the working electrode. The addition of few DI water drop s (0.005% or 50 ppm) and the electrolyte saturation with O2 caused the immediate disappearance of redox species peaks (V2+/V3+ redox couple) and the appearance of additional peaks which indicated a strong influence for the reaction shift towards the formation of parasitic VO(acac)2. V+3/V+4 redox couple was also degraded significantly after 0.05% (500 ppm). Thus, keeping a dry and oxygen-free atmosphere is of utmost importance for maintaining a stable battery operation. Interestingly, it was found that the reversibility of species on top of the WE depends on the exposure time to oxygen. The effect is negligible up to 20 minutes of oxygen saturation but extremely critical over 4 hours as even upon saturating the electrolyte with an inert gas again, the adsorption of the active species was less effective and non-reversible (much lower anodic current peaks and much wider apart oxidation/reduction peaks).The carbon felt electrodes used for the aqueous vanadium redox flow battery, even with no treatment have already oxygen functional groups which serve as the reaction sites for the vanadium redox reaction in the aqueous electrolyte. Hydrogen is known as a powerful reducing agent and so might be employed to remove these oxygen functionalities. Therefore, the impact of different pre-treatments on the carbon felts morphology and performance for the V-NAqRFB was assessed. Mainly, the effect of solely adding a pre-oxygen heat treatment (referred to as PO) to a pristine carbon felt from SGL (4.6GFD), a hydrogen treatment (PH), and a combination of oxygen followed by a hydrogen treatment (POH) to completely remove all previously formed heteroatoms, were tested, each for 10 hours at 400 °C. For comparison purposes, a pristine electrode (P) was also used. Then upon, the electrochemical surface area of each CF was pre-screened by leading CV measurements and the hydrogen treatment followed by an oxygen heat treatment (POH) appeared to be the best solution to increase the number of active sites on the CF structure. Morphological characterization was performed on all electrodes using SEM and FTIR. Later, these CFs were used in NAqRFB-cell for battery cycling, impedance spectroscopy, and polarization measurements. The co-relation of the results highlighted that POH is performing better in the V(acac)3 based non-aqueous electrolyte. Besides, solely conducting a pre-oxygen heat treatment on the CFs condemns the performance of the battery, as expected. The results are shown in the attached figure. Figure 1

Oxygen-enriched surface modification for improving the dispersion of iron oxide on a porous carbon surface and its application as carbon molecular sieves (CMS) for CO2/CH4 separation.

The separation of CO2/CH4 can be enhanced by impregnating porous carbon with iron oxide. Dispersion of iron oxide is one of the critical factors which supports the separation process performance. Iron oxide dispersion can be enhanced by enriching the oxygen functional groups on the carbon surface. This study investigates three distinct oxidation processes: oxidation with a 10% H2O2 solution, ozonation with distilled water, and ozonation with a 10% H2O2 solution. The research steps included the following: (i) oxidation, (ii) impregnation of iron oxide followed by calcination, (iii) material characterization, and (iv) material performance analysis. Materials were characterized using N2 sorption analysis, X-ray diffraction analysis (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy analysis (SEM-EDX), and Fourier transform infrared analysis (FT-IR). Iron oxide was well dispersed on the carbon surface, as evidenced by the elemental mapping of materials. In addition, the oxygen functional groups increased significantly in the range of 28.6–79.7% following the oxidation process, as indicated by the elemental component using SEM-EDX analysis. The impregnation of iron oxide on oxidized carbon ozonated with distilled water (COA–Fe) obtained a maximum CO2 uptake capacity of 3.0 mmol g−1 and CO2/CH4 selectivity increased by up to 190% at a temperature of 30 °C and pressure of 1 atm. Furthermore, the enhancement of CO2/CH4 separation up to 1.45 times was the best performance achieved by COA–Fe. Thus, improving iron oxide dispersion on oxidized carbon surfaces has a potential application in CO2/CH4 separation.

Tuning Pb(II) Adsorption from Aqueous Solutions on Ultrathin Iron Oxychloride (FeOCl) Nanosheets.

Structural tunability and surface functionality of layered two-dimensional (2-D) iron oxychloride (FeOCl) nanosheets are critical for attaining exceptional adsorption properties. In this study, we combine computational and experimental tools to elucidate the distinct adsorption nature of Pb(II) on 2-D FeOCl nanosheets. After finding promising Pb(II) adsorption characteristics by bulk FeOCl sheets (B-FeOCl), we applied computational quantum mechanical modeling to mechanistically explore Pb(II) adsorption on representative FeOCl facets. Results indicate that increasing the exposure of FeOCl oxygen and chlorine sites significantly enhances Pb(II) adsorption. The (110) and (010) facets of FeOCl possess distinct orientations of oxygen and chlorine, resulting in different Pb(II) adsorption energies. Consequently, the (110) facet was found to be more selective toward Pb(II) adsorption than the (010) facet. To exploit this insight, we exfoliated B-FeOCl to obtain ultrathin FeOCl nanosheets (U-FeOCl) possessing unique chlorine- and oxygen-enriched surfaces. As we surmised, U-FeOCl nanosheets achieved excellent Pb(II) adsorption capacity (709 mg g-1 or 3.24 mmol g-1). Moreover, U-FeOCl demonstrated rapid adsorption kinetics, shortening adsorption equilibration time to one-third of the time for B-FeOCl. Extensive characterization of FeOCl-Pb adsorption complexes corroborated the simulation results, illustrating that increasing the number of Pb-O and Pb-Cl interaction sites led to the improved Pb(II) adsorption capacity of U-FeOCl.

Microwave synthesis of hierarchically porous activated carbon from lignite for high performance supercapacitors

A hierarchically porous activated carbon (HPAC) with high surface area (3064 m2/g) and large pore volume (2.319 cm3/g) was prepared from lignite using KOH as activation agent by microwave heating. Nitrogen adsorption–desorption at −196 °C, X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy were used to characterize the HPAC. Because of its high surface area, macro–meso–micro hierarchically porous structure and oxygen-enriched surface, the HPAC exhibits excellent electrochemical performance in terms of specific capacitance, energy density and cycling stability as electrode material for supercapacitors. The HPAC showed a high specific capacitance of 390 F/g in aqueous electrolyte at a current density of 50 mA/g and 94.1 % of the initial specific capacitance was retained after 2000 cycles. Furthermore, this HPAC displayed a high specific capacitance of 198 F/g in an organic electrolyte.

Lignite-derived high surface area mesoporous activated carbons for electrochemical capacitors

Mesoporous activated carbons (ACs) were successfully prepared from lignite using KOH as activation agent at the temperature above 700°C. The pore structure and surface chemistry of the as-prepared ACs were characterized by means of nitrogen adsorption–desorption, X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy. The results show that such prepared mesoporous ACs have a high specific surface area (~3036m2·g−1) with a hierarchical macro–meso–micro-pore structure and oxygen-enriched surface. The electrochemical performances of the ACs as electrode materials for electrochemical capacitors (ECs) were assessed by galvanostatic charge–discharge, cyclic voltammetry and cycling durability tests. It was demonstrated that the mesoporous ACs produced in this study possessed a maximum specific capacitance of 355F·g−1 and 196F·g−1 in 3M KOH aqueous and 1M (C2H5)4NBF4/PC organic electrolytes, respectively, at a current density of 50mA·g−1, and exhibited a desirable energy and power density with a superior cycling performance. The excellent capacitive behavior of the prepared mesoporous ACs in aqueous system is attributed to their unique macro–meso–micro-hierarchical pore structure with high surface area and oxygen-containing surface. Their superb electrochemical performance in the organic electrolyte is attributed to their well-developed mesoporous structure.

The adsorption of NO on YSZ(1 1 1) and oxygen-enriched YSZ(1 1 1) surfaces

The reaction of NOx gases with yttria-stabilised zirconia (YSZ) surfaces, and in particular the oxygen enriched surfaces, is complex and of importance for gas sensing applications. In this letter the binding energy, vibrational frequencies, density of states, magnetic moments, electron localization, and charge transfer are presented for all stable configurations of NO on YSZ(111) and oxygen-enriched YSZ+O(111) surfaces, determined using density functional theory calculations. Complementary ab initio molecular dynamics simulations revealed the adsorption characteristics of NO at 298 and 773K. Our findings can be used to assist in explaining the reactions of NOx gases that occur on electrochemical gas sensors.

Photoelectrooxidation of Water on Hematite Thin Films

Hematite photoanodes for the oxygen evolution reaction (OER) were prepared by a cost-efficient sol-gel procedure. We show that annealing and plasma post-treatments improve significantly the photoelectrochemical properties for the OER. Annealing steps lead to a reorganization of the crystal structure and thereby to a pronounced shift of the photocurrent to negative potentials. Surface photovoltage measurements (SPV) indicate an enhanced separation of charge carriers originated from the band gap photoabsorption. Nevertheless a more pronounced effect on the catalytic efficiency was gained by a surface-treatment in oxygen plasma. X-ray photoelectron spectroscopy (XPS) analysis reveals an oxygen enriched surface layer with new oxygen species which might be responsible for the improved electrochemical activity. SPV measurements identify an increased fraction of transferred charge carriers from this newly produced surface defects. The combination of these post-treatments leads finally to an efficient hematite photoanode for the OER.

Surface aspects of sol–gel derived hematite films for the photoelectrochemical oxidation of water

α-Fe(2)O(3) (hematite) photoanodes for the oxygen evolution reaction (OER) were prepared by a cost-efficient sol-gel procedure. Due to low active photoelectrochemical properties observed, it is assumed that the sol-gel procedure leads to hematite films with defects and surface states on which generated charge carriers are recombined or immobilized in trap processes. Electrochemical activation was proven to diminish unfavourable surface groups to some extent. More efficiently, a plasma treatment improves significantly the photoelectrochemical properties of the OER. X-ray photoelectron spectroscopy (XPS) analysis reveals an oxygen enriched surface layer with new oxygen species which may be responsible for the improved electrochemical activity. Due to surface photovoltage an increased fraction of transferred charge carriers from these newly produced surface defects are identified.

Strategic Design and Refinement of Lewis Acid–Base Catalysis by Rare-Earth-Metal-Containing Polyoxometalates

Efficient polyoxometalate (POM)-based Lewis acid-base catalysts of the rare-earth-metal-containing POMs (TBA(6)RE-POM, RE = Y(3+), Nd(3+), Eu(3+), Gd(3+), Tb(3+), or Dy(3+)) were designed and synthesized by reactions of TBA(4)H(4)[γ-SiW(10)O(36)] (TBA = tetra-n-butylammonium) with RE(acac)(3) (acac = acetylacetonato). TBA(6)RE-POM consisted of two silicotungstate units pillared by two rare-earth-metal cations. Nucleophilic oxygen-enriched surfaces of negatively charged POMs and the incorporated rare-earth-metal cations could work as Lewis bases and Lewis acids, respectively. Consequently, cyanosilylation of carbonyl compounds with trimethylsilyl cyanide ((TMS)CN) was efficiently promoted in the presence of the rare-earth-metal-containing POMs via the simultaneous activation of coupling partners on the same POM molecules. POMs with larger metal cations showed higher catalytic activities for cyanosilylation because of the higher activation ability of C═O bonds (higher Lewis acidities) and sterically less hindered Lewis acid sites. Among the POM catalysts examined, the neodymium-containing POM showed remarkable catalytic performance for cyanosilylation of various kinds of structurally diverse ketones and aldehydes, giving the corresponding cyanohydrin trimethylsilyl ethers in high yields (13 substrates, 94-99%). In particular, the turnover frequency (714,000 h(-1)) and the turnover number (23,800) for the cyanosilylation of n-hexanal were of the highest level among those of previously reported catalysts.

Template-Free Synthesis and Supercapacitance Performance of a Hierachically Porous Oxygen-Enriched Carbon Material

A hierarchically porous carbon material (HPCM) with plentiful pores from 0.5 to 700 nm and oxygen-enriched surfaces has been prepared starting from sodium alginate by using a sustainable and green process in which neither porous templates nor additional activation agents are utilized. While the macropores originate from the dissolution of in situ formed Na2CO3 particles during the carbonization of sodium alginate, the micropores and mesopores derive from the chemical activation process of Na ions in sodium alginate and the interspaces between the packed carbon nanoparticles, respectively. Raman spectrum and X-ray photoelectron spectroscopy reveal its nature of partial graphitization and oxygen-enriched functionalities. Electrochemical tests for electrochemical capacitors show that the present HPCM could deliver both higher energy and higher power densities than commercial activation carbon. The high energy density can be ascribed to the oxygen-enriched surfaces as well as the plentiful micropores of HPCM. While the former could provide large pseudocapacitance, the latter would strengthen the electric double layer capacitance. On the other hand, the high power density could be attributed to the excellent meso/macroporosity of HPCM.

Effects of Solvent and Doping Acid on the Morphology of Polyaniline Prepared with the Ice-Templating Method

Various morphologies of polyaniline (PANI), such as microflakes stacked by 1D nanofiberes, porous microwebs, hemispheres, and nests piled by nanoparticles, were prepared through an ice-templating method, using different doping acids assisted by secondary solvent. The structure and morphology of these PANI were characterized by Fourier transform infrared (FT-IR) spectra, X-ray diffraction (XRD) patterns, and scanning electron microscope images (SEM). Although the ice-templating method has been used for preparing conducting polymer materials with unique structures in recent years, to the best our knowledge, this is the first report on synthesizing PANI doped with polyoxometalates (POMs) using the ice-templating method assisted by secondary solvent to direct the polymerization of aniline. In this paper, the effects of doping acid and the secondary solvent on the morphology of PANI were investigated in detail. All the results showed that just the doping acids, POMs with unique nucleophilic oxygen-enriched surfaces, multi-hydrogen proton, and the binding capacity with the secondary solvent play a major role in determining the formation of various morphologies of PANI. A possible mechanism for the formation of the different morphologies of PANI was proposed. The gas-responses to ammonia were examined at room temperature. Compared with PANI porous microwebs, hemispheres, or nests piled by nanoparticles, the PANI microflakes stacked by nanofibers showed the best performance in both sensitivity and time response due to their small nanofiber diameter, high surface area, and porous nature, which will have potential application in the area of chemical sensors.