Loss Of Surface Area Research Articles

Room temperature sintering of polar ZnO nanosheets: III-Prevention

Abstract In this study, the coating of high specific surface area stainless steel wire mesh-supported ZnO with a monolayer of silica was investigated with the aim of preventing the room temperature sintering of the polar ZnO sample (75% specific surface area loss in two months in the presence of moisture, oxygen or light). This research study is the logical conclusion of previous works by the authors in which the room temperature sintering of polar ZnO was detected and analyzed for the first time ( https://doi.org/10.1039/c7cp02306e and https://doi.org/10.1039/c7cp02307c ). The ZnO surface was modified by inducing a substitution reaction between 3-aminopropyltriethoxysilane (APTES) and surface hydroxyls, followed by a low-temperature calcination step to produce a monolayer of silica (2 atom%) that would provide stability to the ZnO surface. The textural and structural characteristics of the protected material hardly differ from those of freshly calcined (unprotected) ZnO samples, and remain unchanged for long storage periods. This is due to the action of the silica coating, which causes an increase in the number of oxygen interstitials and a decrease in the amount of oxygen vacancies. The combination of these factors provokes the immobilization of the Zn interstitials, whose mobility is responsible for the room temperature sintering of unprotected ZnO. The efficiency of the polar ZnO as a sacrificial template remains unchanged in the presence of silica. Additionally, the photocatalytic activity of the protected ZnO sample in the continuous photodegradation of methylene blue shows a slight improvement compared to that of the unmodified sample calcined at the same temperature. Moreover, losses of Zn during the reaction diminished.

Performance of niobium catalysts in a one-pot system for selective methanol conversion to dimethoxymethane under mild conditions

In this work, the synthesis and application of catalysts based on niobium oxide were carried out in order to modify their acid and redox properties and make them active for the synthesis of dimethoxymethane (DMM), considered an excellent additive for diesel, in a single step. The materials were characterized by several techniques, where functionalization was confirmed by elemental analysis, infrared spectroscopy, XPS and TPR analysis. The functionalization with sulphate groups in the materials did not promote significant surface area losses. In addition, acid sites quantification showed that the modification of materials with sulfate groups led to increased acidity. Depending on the conditions used, such as 1 wt% catalyst and 10 wt% hydrogen peroxide, in relation to the methanol mass used (1.98 g), for 5 h at 100 °C the functionalized catalysts provided methanol conversion above 80% with almost 100% of DMM selectivity.

Salt stress effect on morphometrical and anatomical leaf traits of promising poplar biotypes

The purpose of the research was to determine the effect of short-term salt stress on the morphometric, anatomical and biochemical traits of fast-growing woody plants and to evaluate the promising poplar genotypes according to their degree of resistance. The experiments were conducted on five annual varieties in containers. The fourth leaf from the top of apical shoot, 80% of which corresponds to a maximum leaf area and high photosynthetic activity, was used in the experiment. The studies showed the nature of changes in the specific surface density and water content of the leaf of annual shoots. A short-term salt stress causes changes in leaf anatomy. Thus, the less stable genotype of poplar ‘Kitayskiy’ responds by the reduction of the leaf thickness. The changes in leaf anatomy of the experimental plants also include a decrease in height of the palisade and spongy parenchyma cells, which leads to the reduction of assimilation surface area and unproductive water loss. The study included analysis of changes in the proline concentration as a result of short-term salinization of the experimental plants. All samples showed a change in proline levels in response to stress, but most intense reaction was shown by genotypes ‘Veduga’ and ‘Hybrid e.s.-38’. In general, greater stability and plasticity at the initial stage of salinization is characteristic of poplars ‘Volosistoplodny’, ‘Sacrau-59’, ‘Hybrid e.s.-38’ and ‘Veduga’, which allows us to recommend them for reforestation and afforestation on irrigated soils.

Role of particle size on the multicycle calcium looping activity of limestone for thermochemical energy storage

The calcium looping process, based on the reversible reaction between CaCO3 and CaO, is recently attracting a great deal of interest as a promising thermochemical energy storage system to be integrated in Concentrated Solar Power plants (CaL-CSP). The main drawbacks of the system are the incomplete conversion of CaO and its sintering-induced deactivation. In this work, the influence of particle size in these deactivation mechanisms has been assessed by performing experimental multicycle tests using standard limestone particles of well-defined and narrow particle size distributions. The results indicate that CaO multicycle conversion benefits from the use of small particles mainly when the calcination is carried out in helium at low temperature. Yet, the enhancement is only significant for particles below 15 μm. On the other hand, the strong sintering induced by calcining in CO2 at high temperatures makes particle size much less relevant for the multicycle performance. Finally, SEM imaging reveals that the mechanism responsible for the loss of activity is mainly pore-plugging when calcination is performed in helium, whereas extensive loss of surface area due to sintering is responsible for the deactivation when calcination is carried out in CO2 at high temperature.

Effects of reaction conditions and organic sulfur compounds on coke formation and HZSM-5 catalyst performance during jet propellant fuel (JP-8) cracking

Coke formation and catalytic performance under various conditions, such as reaction period, temperature, presence of carrier gas and organic sulfur compounds in the feed, were investigated for JP-8 cracking over HZSM-5 catalysts. The spent HZSM-5 catalysts were characterized by N2 adsorption/desorption, X-ray powder diffraction (XRD), Fourier-transform infrared spectroscope (FT-IR), Temperature programmed oxidation (TPO), and X-ray photoelectron spectroscopy (XPS). A significant loss of surface area and pore volume appeared in the initial period of the cracking reaction, owing to coke formation. Complex, aromatic structured coke formed and deposited on the surface the HZSM-5 catalyst. This resulted in high carbon content, carbon burn-off at higher temperatures, and a change in morphology to less well-defined shapes. As the reaction temperature increased, the aromaticity of the coke species increased, thereby resulting in the coke species having more carbon content and a lower H/C ratio. Furthermore, the absence of a carrier gas gave rise to faster catalyst deactivation and lower LPG yield. Surrogate JP-8 fuel experiments revealed that the aromatic sulfur compounds in the feed do not degrade the catalytic activity by sulfur poisoning, but rather by accelerated coke formation.

A gradient porous electrode with balanced transport properties and active surface areas for vanadium redox flow batteries

Enhancing the mass transport from the flow field side to the membrane side without sacrificing the active surface area is a critical strategy for the design of electrodes in flow-field structured vanadium redox flow batteries (VRFBs). In this work, we design and prepare a novel porous electrode with a gradient distribution in pores, enabling a gradual decrease in permeability but an increase in active surface areas from the flow field side to the membrane side. This design not only increases the electrode utilization due to the enhanced mass transport near the flow field side, but also avoids the loss of active surface area near the membrane side. Numerical modeling results show that compared to the conventional electrode design, the gradient electrode design can promote the uniform distribution of local reaction current density and overpotential, leading to a lower charge voltage and higher discharge voltage. Experimental results show that at the current density of 240 mA cm−2, the battery with the gradient electrode design delivers a 69% higher discharge capacity than that with the conventional electrode design, demonstrating the superiority of the gradient electrode design strategy.

Surface Hydrophobic Treatment of Water-Sensitive DUT-4 Metal–Organic Framework To Enhance Water Stability for Hydrogen Storage

Water stability in acidic, neutral, and basic aqueous solutions is quite important for the potential application of metal–organic frameworks. As evidenced by X-ray diffraction and scanning electron microscopy results, the pristine DUT-4 is extremely water sensitive to acidic, neutral, and basic aqueous solutions and undergoes crystal structure and morphology transformation. The pristine DUT-4 nearly loses its porosity and H2 uptake capacity after being exposed for 6 d. A facile solution-immersion approach was employed to deposit a hydrophobic layer on the DUT-4 surface without significant loss of surface area. This layer could effectively protect DUT-4 from water molecule attack and greatly enhance water stability. After the same exposure to aqueous solutions, the hydrophobic-treated DUT-4 could basically retain their crystal structure, morphology, surface area, and H2 uptake capacity. This approach could be explored to broaden the scope of practical applications of DUT-4 and other metal–organic frameworks under water-containing environments.

Degradation of core-shell Pt3Co catalysts in proton exchange membrane fuel cells (PEMFCs) studied by mathematical modeling

Understanding the degradation process of Pt-based catalysts is a crucial step to improve the durability of PEMFCs. A mathematical model is established to study the electrochemical surface area (ECA) loss and structural/compositional evolutions of core-shell Pt3Co catalysts along the cathode under a certain circumstance. Three major processes are included in this model: Pt dissolution and re-precipitation on the Pt shell, Co leaching from the bulk and deposition of Pt ions in the membrane due to crossover hydrogen. The results show that the significant ECA loss next to the membrane is mainly attributed to the severe particle corrosion rather than variation of the particle size distribution. The Pt shell thickness and Pt/Co atomic ratio decrease from gas diffusion layer (GDL)/CCL interface to the cathode catalysts layer (CCL)/membrane interface, while the Co mass loss shows an inverse trend. This work demonstrates that mathematical modeling is effective to predict the structural and compositional evolutions of the catalyst particles across the CCL, and therefore is useful to evaluate the complete performance degradation of Pt3M catalysts for PEMFCs in the future.

Platinum-Nickel Nanotubes Array as Cathode for PEMFC

Keywords: Electrocatalyst, PEMFC, PtNi alloy, Oxygen Reduction Reaction, Electrode The technology of polymer electrolyte membrane fuel cells (PEMFCs) have recently attracted much attention from both fundamental and applied point of views for their future potential as clean and mobile power sources. One of the barriers of their commercialization is the high cost of the catalyst [1]. In order to enhance their achievement on the market, it is mandatory to optimize the high costly catalyst and improve its durability and stability or to innovate a new structure of electrodes. Platinum nanoparticles supported on carbon is used due to its high surface area but has some limitations, namely insufficient activity and durability particularly at the cathode where the oxygen reduction reaction (ORR) occurs. The latter is limited by corrosion of the C and Pt dissolution/agglomeration through Electrochemical Ostwald ripening mechanism which is reflected by a fast and significant loss of electrochemical surface area (ECSA) over time during fuel cell operation [2]. This architecture can hardly be more optimized, it is for this reason that many researches have been lead to design new architectures of electrodes. Previous studies have demonstrated the benefits of Pt nanostructured electrodes showing high performances for low Pt loadings and stability such as NanoStructured Thin Film (NSTF) by 3M [3], Pt nanowires [4], unsupported Pt Aerogels [5], PtCu nanotubes [6].These architectures are highly desired to meet desirable performance to substitute the state-of-the-art Pt/C electrocatalysts architecture. The aim of this work is to develop and control a Pt-Based tubular nanostructure made only with catalyst without a carbon support. The vertically aligned tubes exibits less O2 loss because they are oriented parallel to the reactants flux [7]. Stamenkovic and co-workers reported that alloying Pt with Ni exhibits a higher ORR activity than with other transition metals [8]. Accordingly, combining the tubular structure and the higher activity of PtNi catalyst has the potential for overcoming the limitations of conventional Pt/C electrodes. In order to elaborate the PtNi nanotubes, porous anodic alumina template (PAAT) is used as a sacrificial mold in which Ni nanowires were electrodeposited. The PAAT allows the control of the geometry of the desired nanotubes. In terms of comparison, the theoretical Pt loading is fixed at 0,15 mg/cm² assuming that the tubes are made with Pt nanoparticles of 5 nm in diameter. Afterwards, Pt is deposited through spontaneous galvanic displacement process. The latter involves the control of a large set of parameters (Cation (K2PtCl6 and H2PtCl6), pH, annealing at different temperatures, concentrations, HCl addition at different concentrations, time, temperature) in order to transform NiNWs to PtNiNTs. Later, using the hot pressing process of Nafion® membrane on the synthetized nanotubes lead to their integration in a complete Membrane Electrode Assembly (MEA) in order to characterize their electrochemical and transport limitations in real operating conditions. Also, to the extent of optimizing the activity of the PtNiNTs, further studies to be done regarding the entire structure of nanotubes including their diameter, length, density and the introduction of Nafion® ionomer.

Understanding Electrochemical Degradation of Polymer Electrolyte Fuel Cell Catalysts Using Time-Resolved Measurements

The catalysts of choice in polymer electrolyte fuel cells (PEFCs) remain Pt-based nanoparticles on high-surface-area carbon support. One critical challenge facing commercialization of this fuel cell is the gradual decline in performance during operation, mainly caused by the loss of electrochemical surface area (ECA) of the Pt or Pt alloy nanoparticles at the cathode and, if an alloy, loss of the base metal alloying component (e.g., Co, Ni, or Fe). In this respect, the understanding of the dominant mechanisms of the loss of ECA and loss of oxygen reduction activity, such as the electrochemical dissolution of Pt or the base metal, is of vital importance. Several mechanisms for dissolution of platinum have been proposed including direct Pt dissolution and electrochemical oxidation of the Pt surface atoms followed by chemical dissolution of the resulting Pt surface oxide. Our previous measurements on PtCo catalyst showed that degradation of PtCo/C catalysts due to Pt dissolution is greatly accelerated by the reduction of PtOx species formed at potentials >0.9 V and that accelerated Co loss is also associated with reduction of the oxides formed at >0.9 V. 1 This presentation will outline effects of type of Pt alloy catalyst (e.g., solid solution, ordered intermetallic, shape-controlled) on Pt and alloying element dissolution rates as a function of number of accelerated stress test cycles. Studies are performed to quantify the amount of dissolved base metal and Pt during potentiodynamic conditions in an electrochemical flow cell system connected to an inductively-coupled plasma-mass spectrometer (ICP-MS) capable of detecting trace concentrations (<ppb) of dissolved elements in solution. The electrochemical data combined with the ICP-MS data are used to evaluate the influence of various factors such as potential, potentiodynamic profile parameters (e.g., scan rate, upper and lower potential limits), atomic structure, and base metal content on the dissolution processes of alloy catalysts in acidic electrolytes at room temperature. Fundamental models will be developed to explain the mechanisms of degradation process for the various catalyst types under various potential conditions. References K. Ahluwalia, D. D. Papadias, N. Kariuki, J. K. Peng, X. P. Wang, Y. Tsai, D. Graczyk, and D. J. Myers, J Electrochem Soc, 165, F3024 (2018) This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Fuel Cell Performance and Durability Consortium (FC-PAD). Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.

Measurement of Protonic Conductivity of PEM Water Electrolyzer Electrodes

Polymer electrolyte membrane water electrolyzer (PEMWE) performance mostly depends on the catalyst layer (CL) composition and microstructure. The CL microstructure is influenced by catalyst ink composition and fabrication process [1]. Due to the use of an unsupported catalyst (IrOx) in PEMWE, the porosity of the CL is low, resulting in a low CL surface area and high activation loss. By increasing the porosity of the CL, it is hypothesized that more catalyst surface area will be exposed to the reactant and electrolyte. One method to increase the CL porosity is to use pore formers: sacrificial particles that are added to the ink and then removed after CL fabrication, leaving additional pores. Limited work has been done on the use of pore formers in fuel cell applications [2–6] which resulted in an increase of the porosity [3,5] and the surface area [2–4]. No work has been done using pore formers in PEMWE application. In this study, a pore former is used to study the effect of pore former addition on PEMWE microstructure and performance. In order to fabricate the catalyst coated membranes (CCMs), an anode catalyst ink was prepared by dispersing iridium oxide powder (Tanaka Kikinzoku Kogyo, ELC-0110) and pore former in a dispersion media as described in ref. [7]. The pore former to IrOx volume ratio was varied between 0 to 0.25 (Table 1). The ionomer content was kept constant at 35 wt.%. The cathode ink was prepared using the method and material described in ref. [8]. The CCMs were prepared by inkjet printing method as described in ref. [7] with catalyst loading as shown in Table 1. Two CCMs for each pore former to IrOx volume ratio were tested and the results are reported. The effect of the pore former on the electrochemical surface area (ECSA) was studied using cyclic voltammetry (CV). ECSA was estimated, after conditioning and obtaining a polarization curve, using the method developed by Tan et al. [9]. The average ECSA of CCM-0.1 is increased by 38 % compared to the CCM-0 as shown in Figure 1b and Table 1. While CCM-0.1 shows the highest ECSA, a similar improvement is not seen from CCM-0.25, indicating that the removal of pore former is having an impact beyond increasing the ECSA. To study the electrode performance without the effect of varying loading between electrodes, the normalized electrochemical performance with respect to IrOx loading are compared in Figure 1a. CCM-0.1 exhibits the highest performance and shows an average improvement of 30 mV at 2 A/mg, compared to the CCM-0. CCM-0.25 shows an improved performance in the kinetic region, however, the performance in the ohmic region is significantly worse than the other two CCMs. This is despite having a similar high frequency resistance (HFR) to the other CCMs. The pore former has a complex impact on the CL microstructure. These preliminary results indicate that the PEMWE performance can be improved by using pore formers, and that there might be an optimal pore former content. References K.-H. Kim, K.-Y. Lee, H.-J. Kim, E. Cho, S.-Y. Lee, T.-H. Lim, S. P. Yoon, I. C. Hwang and J. H. Jang, Int. J. Hydrog. Energy, 35, 2119 (2010). Y. Song, Y. Wei, H. Xu, M. Williams, Y. Liu, L. J. Bonville, H. R. Kunz and J. M. Fenton, J. Power Sources, 141, 250 (2005). T. V. Reshetenko, H.-T. Kim and H.-J. Kweon, J. Power Sources, 171, 433 (2007). Q. Huang, J. Jiang, J. Chai, T. Yuan, H. Zhang, Z. Zou, X. Zhang and H. Yang, J. Power Sources, 262, 213 (2014). A. Fischer, J. Jindra and H. Wendt, J. Appl. Electrochem., 28, 277 (1998). Y.-H. Cho, N. Jung, Y. S. Kang, D. Y. Chung, J. W. Lim, H. Choe, Y.-H. Cho and Y.-E. Sung, Int. J. Hydrog. Energy, 37, 11969 (2012). M. Mandal, A. Valls, N. Gangnus and M. Secanell, J. Electrochem. Soc., 165, F543 (2018). S. Shukla, K. Domican, K. Karan, S. Bhattacharjee and M. Secanell, Electrochimica Acta, 156, 289 (2015). X. Tan, J. Shen, N. Semagina and M. Secanell, J. Catal., 371, 57 (2019). Figure 1

Voltage Cycling Degradation Dependence on O2 Pressure: A Comparative Voltage-Loss Analysis

Polymer-electrolyte-membrane fuel cells (PEMFCs) have proven their applicability as a clean energy conversion technology. At the same time, a clear understanding of their degradation under dynamic operation is critical to project and ultimately improve long-term durability. In order to mimic real-life operation stressors, accelerated stress tests (ASTs) are used to enhance a particular type of degradation mechanism. After the AST application, various physico- and electrochemical diagnostic tools aid to understand and catalogue the observed performance losses. Since the ultimate goal is to develop in situ mitigation and recovery strategies for automotive applications, a comprehensive voltage loss study describing the degradation effects on performance losses is desired. Particularly inside ASTs, voltage cycling tests reproduce conditions that mimic the dynamic operation of a fuel cell stack, and which are directly linked to the degradation of catalyst layers1 in a membrane electrode assembly (MEA). In a semi-empirical study, voltage cycling tests were applied by Kneer et al. 2 to promote electrochemical surface area (ECSA) losses of a carbon-supported platinum catalyst (Pt/C) for the oxygen reduction reaction (-ORR), establishing an ECSA loss semiempirical model for a wide range of voltage cycling conditions. Subsequently, this model was used to project performance losses in H2/air curves based on a theoretical relationship between ECSA evolution and the ORR observed kinetic and transport losses. However, the authors observed that their model prediction resulted in a substantial unaccounted voltage loss (compared to experimental data), suggesting that deeper analyses are required to understand voltage cycling induced performance losses, with the ultimate goal to develop in situ mitigation and recovery strategies. Therefore, our study will make use of voltage cycling ASTs, which will correlate voltage losses to degradation phenomena measured by various diagnostic tests3. These include the ORR mass activity (via H2/O2 measurements), proton transport resistance through the membrane and catalyst layer (via impedance analyses), and O2 transport resistance (via limiting current measurements). By performing a standardized protocol, the differences in MEA aging during voltage cycling tests conducted with H2/air vs. the more frequently used H2/N2 (anode and cathode, respectively) will be separately studied. Furthermore, as observed in Figure 1a, lowering the relative humidity (RH) of the reactants significantly reduces ECSA losses during voltage cycling tests, in comparison to the same protocol performed at 100% RH. More importantly, the H2/air performance losses are substantially lowered after low RH testing (in comparison to 100% RH) (Figure 1b). The unaccounted voltage losses vs. specific current density (ispec ) (the difference between the theoretical 70 mV/dec. line (black line in Figure 1c) and the corrected experimental cell voltages) are lowered, as well. Therefore, the effect of further operational stressors (e.g. cell temperature) on voltage cycling aging for H2/N2 vs. H2/air will be presented. Ultimately, we will seek to correlate the observed losses to those under automotive operating conditions. This insight leads to a better understanding of catalyst degradation and its subsequent suppression via appropriate mitigation strategies through the correct application of operating conditions as described by single cell experiments. Figure 1: a) ECSA losses vs. number of cycles. The insert depicts the used voltage profile (1 cycle equals to 8s at the lower voltage limit (LVL) followed by 8s at the higher voltage limit (HVL), voltage ramp >4V/s). Voltage cycling tests were performed as described by Harzer et. al. in a single-cell PEMFC with 5 cm2 active area (loading: 0.1 and 0.4 mgPt cm-2 in the anode and cathode, respectively; 100 kPaabs, 80°C and H2/N2 flows of 200 nccm/75 nccm on anode/cathode, respectively)3. b) H2/air performance curves (conditions: differential flow, 80°C, 170 kPaabs inlet-controlled pressure, anode: 2000 nccm of H2, cathode: 5000 nccm of air). c) Tafel representation of I-V curves after voltage cycling AST at 30% RH (20k cycles) and 100% RH (10k cycles). Ecell was corrected for HFR, H+ resistance through the catalyst layer, and O2 mass transport resistance; specific current density (ispec ) is corrected for cell shorting resistance and H2 crossover current. References Kneer, A.; Wagner, N.; Sadeler, C.; Scherzer, A. C.; Gerteisen, D., Effect of Dwell Time and Scan Rate during Voltage Cycling on Catalyst Degradation in PEM Fuel Cells. J Electrochem Soc 2018, 165 (10), F805-F812. Kneer, A.; Wagner, N., A Semi-Empirical Catalyst Degradation Model Based on Voltage Cycling under Automotive Operating Conditions in PEM Fuel Cells. J Electrochem Soc 2019, 166 (2), F120-F127. Harzer, G. S.; Schwämmlein, J. N.; Damjanovic, A. M.; Ghosh, S.; Gasteiger, H. A., Cathode Loading Impact on Voltage Cycling Induced PEMFC Degradation: A Voltage Loss Analysis. J Electrochem Soc 2018, 165 (6), F3118-F3131. Figure 1

Impact of Shut-Down Procedures on Performance Recovery of Proton Exchange Membrane Fuel Cells

It has been noticed that after intentional or unintentional interruption of fuel cell operation or durability testing, such as due to equipment maintenance, normal start-up/shutdown procedure, system failure, overnight rest, continuous electrochemical in situ testing, etc., its performance often improves. This indicates that some of the performance loss is recoverable. The goal of this study is to investigate the impact of shutdown procedure and duration of the shutdown period on PEM fuel cell rejuvenation. An already conditioned standard 50 cm2 (single) fuel cell was exposed to an accelerated stress test (AST) protocol consisting of voltage cycling, designed to target electrocatalyst degradation, but with the intentional recovery periods (so-called soak time steps) every 2500 voltage cycles. Before and after every intentional soak time, a series of diagnostic methods (namely polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry, linear sweep voltammetry) were performed. Different shutdown procedures, as well as different duration of the soak time period were tested and their impact on performance recovery evaluated. Figure 1 shows degradation as calculated electrochemical surface area loss during AST and recovery after each shutdown period. The results suggest that cause of the reversible degradation could be accumulated water within the cell and/or presence of oxygen within the catalyst layer leading to formation of Pt oxides on the catalyst surface. The prolonged soak time step reduces recovery effect, while rapid reduction of the cell temperature with ice proved to be counterproductive for performance recovery. Shutdown procedure without shortly-connected resistor has shown no effect on recovery. Shutdown procedure without nitrogen purge proved to be the most effective for performance recovery. Figure 1

Nanoscopic Porous Iridium/Iridium Dioxide Superstructures (15 nm): Synthesis and Thermal Conversion by In Situ Transmission Electron Microscopy.

Porous particle superstructures of about 15 nm diameter, consisting of ultrasmall nanoparticles of iridium and iridium dioxide, are prepared through the reduction of sodium hexachloridoiridate(+IV) with sodium citrate/sodium borohydride in water. The water-dispersible porous particles contain about 20 wt % poly(N-vinylpyrrolidone) (PVP), which was added for colloidal stabilization. High-resolution transmission electron microscopy confirms the presence of both iridium and iridium dioxide primary particles (1-2 nm) in each porous superstructure. The internal porosity (≈58 vol%) is demonstrated by electron tomography. In situ transmission electron microscopy up to 1000 °C under oxygen, nitrogen, argon/hydrogen (all at 1 bar), and vacuum shows that the porous particles undergo sintering and subsequent compaction upon heating, a process that starts at around 250 °C and is completed at around 800 °C. Finally, well-crystalline iridium dioxide is obtained under all four environments. The catalytic activity of the as-prepared porous superstructures in electrochemical water splitting (oxygen evolution reaction; OER) is reduced considerably upon heating owing to sintering of the pores and loss of internal surface area.

The way to enhance the thermal stability of V2O5-based catalysts for NH3-SCR

Abstract A series of V2O5/WO3-TiO2 and V2O5/SiO2-WO3-TiO2 catalysts containing 2 wt%, 3.5 wt% and 5 wt% V2O5, respectively, were prepared by impregnation method. The NH3-SCR activity and thermal stability of the catalysts were investigated. It is noted that both V2O5 loading and SiO2 modification could affect the thermal stability of the V2O5/WO3-TiO2 catalysts. Increasing V2O5 loading improved the low temperature SCR activity of the catalysts in fresh state, but high V2O5 loading aggravated the deactivation of the catalysts upon aging. With relatively high V2O5 loading (3.5 wt% and 5 wt% V2O5), V2O5/SiO2-WO3-TiO2 showed remarkably improved thermal stability than V2O5/WO3-TiO2 NH3-SCR catalysts. The catalysts were characterized by BET, XRD, SEM, Raman, XPS, H2-TPR and NH3-TPD. The results indicated that high V2O5 loading on V2O5/WO3-TiO2 catalyst can accelerate the phase transition of anatase TiO2 to rutile TiO2 upon thermal aging, which resulted in the loss of surface area and consequently led to the deactivation, while introduction of silica prevented the phase transition of TiO2, therefore enhancing the thermal stability of the catalysts.

Freeze–Thaw Pre-Treatment of Cassava Tubers to Improve Efficiency of Mechanical Peeling

The effect of a freeze–thaw pre-treatment (FTP) on the peeling process of cassava tubers was investigated in this study. The length and weight of the cassava tubers varied from 200 to 280 mm and 500 to 900 g, respectively. A prototype abrasive cassava peeling machine was used. The operational parameters were the rotational speed of the brushes (550–1150 rpm), peeling time (1–5 min), thawing temperature (50–90 °C), and incubation time of the thawing treatment (0–120 s). Response surface methodology was applied to optimize FTP to improve the peeling process of cassava tubers. Peeled surface area and peel loss were measured as the responses. Results revealed that the peeled surface area and peel loss were significantly influenced by the rotational speed of the brushes, peeling time, and the incubation time of the thawing treatment (p &lt; 0.05). Under optimal peeling conditions, with a rotational speed of 1000 rpm, a peeling time of 3.4 min, a thawing temperature of 59 °C, and an incubation time of 90 s, the peeled surface and the peel loss were approximately 99.5 and 19%, respectively. The results show that the use of FTP can improve cassava peeling by softening the peels and increasing the peeled surface area.

Acid washed lignite char supported bimetallic Ni-Co catalyst for low temperature catalytic reforming of corncob derived volatiles

Acid washed Shengli lignite (AWSL) supported Ni, Co and Ni-Co catalysts were prepared, characterized and evaluated in catalytic reforming (CR) of corncob pyrolysis volatiles at a relatively low catalytic temperature of 450 °C. Moreover, the production and selectivity of H2 were also investigated. Amongst the catalysts studied, bimetallic Ni-10%Co/AWSL exhibited the most remarkable activity, yielding 36.3 mmol H2/g corncob and 710 μmol min−1 g−1 formation rate of syngas (H2 + CO + 4CH4) with trace of tar. It also tuned the gas composition and showed the greatest selectivity of H2 due to the promotion of the water gas shift reaction (with H2 accounting for the maximum 50.3% and 63% under Ar and steam atmosphere, respectively). Regardless of the loss of specific surface area, the superior performance of Ni-Co based catalysts under mild circumstance was attributed to the better reducibility and electronic properties along with a high dispersion of active metal. Additionally, the synergy of Ni and Co contributed to the combined and enlarged activity for CR of corncob volatiles and great selectivity for H2-rich syngas under moderate condition.

Study of hydrothermal aging impact on Na- and P-modified diesel oxidation catalyst (DOC)

The effects of hydrothermal aging (HT-aging), of a biodiesel oxidation catalyst in presence of Na and P impurities were studied. The synthesized reference-PtPd/CeZrO2/La-Al2O3 and Na-, P-modified-PtPd/CeZrO2/La-Al2O3 catalysts were HT-aged, characterized by several techniques and catalytically tested. The characterization results showed the loss of specific surface area due to the sintering of the catalyst. H2-TPR results evidenced the decrease of the catalytic redox activity. TEM results indicated that sodium impurities did not modified the catalyst structure while phosphates were formed. In general, lower reaction rates were found for CO, C3H6 and NO involved reactions after HT-aging. The electronic changes induced by sodium species were attenuated after HT-aging due to the sintering of the catalyst. The lower metal-adsorbates charge transfer enhanced CO oxidation while had a negative effect for C3H6 and NO involved reactions. Diffuse Reflectance Infrared Fourier Transform Spectroscopy experiments indicated that phosphates inhibited the intermediates adsorption on the catalyst surface.

Surfactant dysfunction and alveolar collapse are linked with fibrotic septal wall remodeling in the TGF-β1-induced mouse model of pulmonary fibrosis

In human idiopathic pulmonary fibrosis (IPF), collapse of distal airspaces occurs in areas of the lung not (yet) remodeled. Mice lungs overexpressing transforming growth factor-β1 (TGF-β1) recapitulate this abnormality: surfactant dysfunction results in alveolar collapse preceding fibrosis and loss of alveolar epithelial type II (AE2) cells' apical membrane surface area. Here we examined whether surfactant dysfunction-related alveolar collapse due to TGF-β1 overexpression is linked to septal wall remodeling and AE2 cell abnormalities. Three and 6 days after gene transfer of TGF-β1, mice received either intratracheal surfactant (Surf-groups: Curosurf®, 100 mg/kg bodyweight) or 0.9% NaCl (Saline-groups). On days 7 (D7) and 14 (D14), lung mechanics were assessed followed by design-based stereology at light and electron microscopic level to quantify structures. Compared with Saline, Surf showed significantly improved tissue elastance, increased numbers of open alveoli, as well as reduced alveolar size heterogeneity on D7. Deterioration in lung mechanics was highly correlated to the loss of open alveoli. On D14, lung mechanics, number of open alveoli, and alveolar size heterogeneity remained significantly improved in the Surf-group. Volumes of extracellular matrix and collagen fibrils in septal walls were significantly reduced, whereas the apical membrane surface area of AE2 cells was increased in Surf compared with Saline. In remodeled tissue with collapsed alveoli, three-dimensional reconstruction of AE2 cells based on scanning electron microscopy array tomography revealed that AE2 cells were trapped without contact to airspaces in the TGF-β1 mouse model. Similar observations were made in human IPF. Based on correlation analyses, the number of open alveoli and of alveolar size heterogeneity were highly linked with the loss of apical membrane surface area of AE2 cells and deposition of collagen fibrils in septal walls on D14. In conclusion, surfactant replacement therapy stabilizes alveoli and prevents extracellular matrix deposition in septal walls in the TGF-β1 model.

Facile synthesis of hierarchically structured manganese oxides as anode for lithium-ion batteries

Developing high-performance lithium ion batteries (LIBs) using manganese oxides as anodes is attractive due to their high theoretical capacity and abundant resources. Herein, we report a facile synthesis of hierarchical spherical MnO2 containing coherent amorphous/crystalline domained by a simple yet effective redox precipitation reaction at room temperature. Further, flower-like CoMn2O4 constructed by single-crystalline spinel nanosheets has been fabricated using MnO2 as precursor. This mild methodology avoids undesired particle aggregation and loss of active surface area in conventional hydrothermal or solid-state processes. Moreover, both MnO2 and CoMn2O4 nanosheets manifest superior lithium-ion storage properties, rendering them promising applications in LIBs and other energy-related fields.