Loss Of Surface Area Research Articles

Identical Location Mapping of Pt in Polymer Electrolyte Fuel Cells before and after Heavy-Duty Accelerated Stress Test

Worldwide, governments and industries are pursuing the use of clean hydrogen to achieve zero emissions, especially for difficult to decarbonize sectors such as heavy-duty transportation, aviation, shipping and chemical manufacturing. Polymer electrolyte fuel cells (PEFCs) are an excellent candidate for heavy-duty vehicles (HDVs), particularly for their ability to scale range at a much smaller additional weight penalty1. However, initial system cost remains a significant challenge for large scale adoption mainly due to use of Platinum (Pt) electrocatalyst. Current approach to reduce initial cost by utilizing highly dispersed Pt nanoparticles (2-3 nm) adversely affects the system lifetime. The smaller nanoparticle size does result in improved Pt dispersion, which enhances performance and reduces Pt loading and cost. But smaller nanoparticles also tend to degrade faster due to higher surface energy, which negatively impacts durability1. During a HDV drive cycle, Pt nanoparticle surface undergoes repeated oxidation-reduction, which leads to dissolution of Pt ions causing loss in electrochemical surface area. The dissolved Pt ions can redeposit on nearby larger nanoparticles. This effect is known as electrochemical Ostwald ripening2. The Pt ions can also diffuse towards the anode and get reduced near the membrane-cathode interface by the crossover hydrogen to form a Pt band2. In addition, the Pt ions can leave the system via effluent water. The complex balance between cost, performance and durability of PEFCs makes understanding degradation mechanisms a priority.In this study, membrane electrode assemblies (MEAs) were subjected to accelerated stress tests (ASTs) to simulate heavy-duty lifetime. A simple method was developed to use micro-X-ray fluorescence spectroscopy to map identical locations of catalyst layer before and after the AST. The AST consisted of potential cycling between 0.6 V to 0.9 V (3s hold time each) for 90,000 cycles. Electrochemical characterization was performed at beginning of test, after 10k, 30k, 60k and 90k (end of test) AST cycles. The identical location maps revealed significant in-plane movement of Pt over the course of AST suggesting that electrochemical Ostwald ripening may not be a local effect. The in-plane movement of Pt led to development of local loading hotspots. A movement of Pt away from the cathode catalyst layer cracks was also observed. Such movement may be due to relative surface energy differences between the regions. A modified gas diffusion layer MEA was used to highlight the advantages and necessity of the method developed in this study. The modified MEA showed a ~13% change in/loss of Pt loading in the mapped region closer to the gas inlet. Identical location mapping allowed quantification of changes in the Pt loading caused by the AST. Lastly, identical location synchrotron micro-X-ray diffraction and florescence mapping was performed after the heavy-duty AST to identify correlation between Pt nanoparticle size growth and Pt loading. A direct correlation was observed, which developed only after the MEA was subjected to heavy-duty AST. References Cullen, D. A. et al. New roads and challenges for fuel cells in heavy-duty transportation. Nat. Energy 6, 462–474 (2021).Khedekar, K. et al. Probing Heterogeneous Degradation of Catalyst in PEM Fuel Cells under Realistic Automotive Conditions with Multi-Modal Techniques. Adv. Energy Mater. 11, (2021).

Quantitative Analysis of Fuel Cell Cathode Catalyst Layer Degradation Using Scanning Transmission Electron Microscopy and Energy Dispersive Spectroscopy

Proton exchange membrane fuel cells (PEMFCs) are a central technology for the electrification of the heavy-duty automotive fleet, ultimately enabling reduced carbon emissions. However, improvements in lifetime and cost are necessary before mass adoption of PEMFC vehicles is achieved. Significant research into analyzing and mitigating degradation of catalyst layers (CLs) is ongoing and this work highlights a transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) approach aimed at quantifying electrochemically active surface area (ECSA) loss through the thickness of CLs resulting from electrochemical-applied, catalyst-specific accelerated stress tests or ASTs.Several mechanisms contribute to degradation of the catalysts in PEMFCs, including Ostwald ripening, coalescence, and formation of a Pt band within the membrane, which result in decreased active surface area throughout the CL. TEM has often been used in conjunction with electrochemical testing to infer changes in the catalyst nanoparticle size, distribution, and changes to the support materials within the catalyst layer (CL) to investigate catalyst. Typically, high-magnification TEM with high-resolution are used to infer localized changes within the CL by examining shape and size to provide information concerning the degradation mechanism. Low-magnification TEM is typically used to observe changes in the support, ionomer, and catalyst distribution. Here we use a quantitative approach to show elemental differences within the CL by using scanning transmission electron microscopy and energy dispersive spectroscopy maps (STEM/EDS) for a given MEA that underwent catalyst-specific ASTs. This approach uses the fluorine to platinum ratio (F/Pt) from a fresh sample as a benchmark to track loss of Pt through the thickness of the CL of aged samples. This information can then be used to compare differences in various locations on the MEA in relationship to gas inlets and outlets as well as changes induced by different stressors during the catalyst ASTs. This analysis complements studies using bulk techniques, such as electrochemical ECSA via cyclic voltammetry and micro-X-ray diffraction (µ-XRD), to confirm trends in CL degradation.

Microscopic Insights into the Inhomogeneous Degradation of Pt Alloy Catalysts in PEM Fuel Cells

Fuel cell electric vehicles (FCEVs) powered by proton exchange membrane fuel cells (PEMFCs) offer a sustainable, low-carbon alternative to the world’s current energy structure based on fossil fuels. Recently, application of PEMFC to heavy-duty vehicles (HDVs) has attracted significant interest for reducing greenhouse gas emissions in this market. Relative to passenger vehicles, HDVs require extended lifetimes and high operating costs, leading to an increased emphasis on the durability and efficiency of membrane electrode assembly components [1].Degradation of the oxygen reduction reaction (ORR) cathode catalyst is one of the main challenges for heavy duty applications. Several degradation mechanisms have been identified, such as Ostwald ripening, particle coalescence/migration, and particle detachment, the observation of which relies on transmission electron microscopy (TEM) [2,3]. Through TEM, inhomogeneous degradation at the micro- and nanoscale during operation have been observed: (1) the Pt loading decreases toward the cathode/membrane interface and creates a depletion zone adjacent to the interface [2,4] and (2) different rates of electrochemical surface area loss of PtCo supported on various porous carbons,[5] leading to the speculation of different degradation rates for particles at the exterior vs. interior carbon surfaces.To elucidate these inhomogeneous degradation mechanisms, we employ high-throughput image analysis and electron tomography methods to analyze fuel cell cathodes before and after accelerated stress tests (ASTs) performed in both nitrogen and air environments. An automated, high-throughput method was developed that provides statistically relevant analysis of PtCo particle size, shape, and loading distribution. This method combines automated image or energy-dispersive spectroscopy (EDS) map acquisition using a commercial software (MAPS, Thermo Fisher Scientific) and custom Python codes to analyze high-angle annular dark field (HAADF) and EDS spectrum images. With the high-throughput method, we reveal the inhomogeneous distribution of PtCo particle size, Pt loading, and Co content across the entire electrode. In addition, an electron tomography workflow is under development to measure PtCo particle size and composition on the exterior and interior of the porous carbon support. The effect of cathode gaseous environment on the distribution of particle size, loading, and composition is discussed at the microscale across the electrode and at the nanoscale for exterior and interior surfaces of primary carbon particles. Findings from this study will provide new mitigation strategies and design principles to enable durable fuel cell catalysts.[6]References[1] DA Cullen et al., Nat. Energy. 6 (2021), p. 462.[2] PJ Ferreira et al., J. Electrochem. Soc. 152 (2005), p. A2256.[3] R Borup et al., Chem. Rev. 107 (2007), p. 3904.[4] H Yu et al., Electrochim. Acta 247 (2017), p. 1169.[5] M Ko et al., J. Electrochem. Soc. 168 (2021), p. 24512.[6] This material is based on work performed by the Million Mile Fuel Cell Truck (M2FCT) Consortium, technology managers Greg Kleen and Dimitrios Papageorgopoulus, which is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office, and by U.S. Department of Energy, Office of Nuclear Energy, Fuel Cycle R&D Program, and the Nuclear Science User Facilities. Electron microscopy research was supported by the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

Evaluation of scrap metallic waste electrode materials for the application in electrocoagulation treatment of wastewater

The constant need for sacrificial electrodes is one of the limitations of applying the EC in wastewater treatment. Accordingly, this study proposes a sustainable alternative in reusing scrap metallic wastes as electrode materials. Four different types of metallic wastes (beverage cans, used aluminum (Al) foil, scrap iron, and scrap mild steel) are proposed as sacrificial electrodes for grey water (GW) treatment using the EC technique. At electrical current densities (CD) ranging between 5 and 20 mA/cm2, the treatment performance was evaluated for a reaction time of 10 min in terms of the removal efficiency of some key parameters such as color, turbidity, chemical oxygen demand (COD), and electrical conductivity, energy and material consumption, and metal contamination of GW from electrodes. The results demonstrated that using metallic wastes as sacrificial electrodes can achieve a considerable reduction in color, turbidity, COD, and electric conductivity of about 97.2%, 99%, 88%, and 89%, respectively. However, their reuse as electrodes revealed some important concerns. Al foil undergoes quick and substantial perforation and loss of surface area during electrolysis. The scrap iron and scrap mild steel were found to cause metal contamination by increasing Fe ions in the treated GW. Generally, metal scrap wastes can serve effectively as alternative sustainable electrodes. However, further research is recommended regarding the operating costs, which are considered crucial aspects of the EC process in terms of energy consumption and the most efficient method of fabricating the metallic wastes into a form suitable for reuse in the EC technique.

Epithelial cells sacrifice excess area to preserve fluidity in response to external mechanical stress

Viscoelastic properties of epithelial cells subject to shape changes were monitored by indentation-retraction/relaxation experiments. MDCK II cells cultured on extensible polydimethylsiloxane substrates were laterally stretched and, in response, displayed increased cortex contractility and loss of excess surface area. Thereby, the cells preserve their fluidity but inevitably become stiffer. We found similar behavior in demixed cell monolayers of ZO-1/2 double knock down (dKD) cells, cells exposed to different temperatures and after removal of cholesterol from the plasma membrane. Conversely, the mechanical response of single cells adhered onto differently sized patches displays no visible rheological change. Sacrificing excess surface area allows the cells to respond to mechanical challenges without losing their ability to flow. They gain a new degree of freedom that permits resolving the interdependence of fluidity β on stiffness {K}_{{{{{{{{rm{A}}}}}}}}}^{0}. We also propose a model that permits to tell apart contributions from excess membrane area and excess cell surface area.

Mitigating Pt Loss in Polymer Electrolyte Membrane Fuel Cell Cathode Catalysts Using Graphene Nanoplatelet Pickering Emulsion Processing

AbstractCarbon‐supported Pt nanoparticles are the leading catalysts for the cathode oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells. However, these ORR catalysts suffer from poor electrochemical durability, particularly the loss of electrochemical surface area (ECSA) due to Pt nanoparticle dissolution and agglomeration. Here, Pt loss is mitigated through a Pickering emulsion‐processing strategy that employs graphene nanoplatelet dispersions stabilized by the polymer ethyl cellulose. The resulting graphene‐Pt/Vulcan carbon (Pt/C) catalysts exhibit superior durability and ECSA retention throughout an accelerated stress test compared with a commercial Pt/C standard catalyst, both in a diagnostic‐rotating disc electrode setup and in a membrane electrode assembly full cell. These graphene‐Pt/C catalysts also improve durability at high‐voltage conditions, providing further evidence of their exceptional electrochemical stability. Consistent with density functional theory calculations, postelectrochemical characterization reveals that Pt nanoparticles localize at graphene defects both on the basal plane and especially at the edges of the graphene nanoplatelets. Since this Pt nanoparticle localization suppresses Pt nanoparticle dissolution and agglomeration without hindering accessibility of the reactant species to the catalyst surface, the ORR performance under both idealized and practical experimental conditions shows significantly improved durability while maintaining high electrochemical activity.

Therapeutic Potential of GLP-2 Analogs in Gastrointestinal Disorders: Current Knowledge, Nutritional Aspects, and Future Perspectives.

Although Glucagon-like peptide (GLP)-1 receptor agonists have been used for almost two decades in the treatment of diabetes mellitus type 2 and, lately, in obesity, recent years have seen an increasing interest in the pharmacological agonism of other proglucagon-derived peptides, including GLP-2. Herein, we aimed to review the available evidence on the effects of GLP-2 agonism from animal and clinical studies. Furthermore, we summarize the current clinical applications of GLP-2 agonists among patients with intestinal failure associated with short bowel syndrome (SBS-IF) as well as potential future expansion of their indications to other intestinal disorders. Evidence from preclinical studies has highlighted the cellular trophic and functional beneficial actions of GLP-2 on small intestinal and colonic mucosa. Subsequently, pharmacologic agonism of GLP-2 has gathered interest for the treatment of patients with conditions pertaining to the loss of intestinal anatomical and/or functional integrity to a degree requiring parenteral support, collectively referred to as intestinal failure. GLP-2 analogs positively influence nutrient absorption in animal models and humans, although continued therapy is likely needed for sustained effects. The degradation-resistant GLP-2-analog teduglutide has received approval for the treatment of SBS-IF, in which it may decisively reduce patient dependency on parenteral support and improve quality of life. Another two longer-acting analogs, glepaglutide and apraglutide, are currently undergoing phase III clinical trials. The use of GLP-2 analogs is effective in the management of SBS-IF and may show promise in the treatment of other severe gastrointestinal disorders associated with loss of effective intestinal resorptive surface area.

Modeling the Performance Degradation of a High-Temperature PEM Fuel Cell

In this paper, the performance of a high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) was modeled using literature data. The paper attempted to combine different sources from the literature to find trends in the degradation mechanisms of HT-PEMFCs. The model focused on the activation and ohmic losses. The activation losses were defined as a function of both Pt agglomeration and loss of catalyst material. The simulations revealed that the loss of electrochemical active surface area (ECSA) was a major contributor to the total voltage loss. The ohmic losses were defined as a function of changes of acid doping level in time. The loss of conductivity increased significantly on a percentage basis over time, but its impact on the overall voltage degradation was fairly low. It was found that the evaporation of phosphoric acid caused the ohmic overpotential to increase, especially at temperatures above 180 °C. Therefore, higher temperatures can lead to shorter lifetimes but increase the average power output over the lifetime of the fuel cell owing to a higher performance at higher temperatures. The lifetime prognosis was also made at different operating temperatures. It was shown that while the fuel cell performance increased linearly with increasing temperature at the beginning of its life, the voltage decay rate increased exponentially with an increasing temperature. Based on an analysis of the voltage decay rate and lifetime prognosis, the operating temperature range between 160 °C and 170 °C could be said to be optimal, as there was a significant increase in performance compared to lower operating temperatures without too much penalty in terms of lifetime.

Tuning of surface structure of porous glass-supported titania with fibrous silica for efficient coupling adsorption‒catalysis‒resorption desulfurization scheme

A core-shell porous catalyst of porous glass coated with TiO2-fibrous silica (KCC-1) was prepared. The fibrous structure of KCC-1 can load a large quantity of titanium dioxide with minimum loss of surface area. Effects of the reaction time, quantity of TiO2 coated, initial concentration of sulfide, and reaction temperature on the desulfurization rate were investigated, and the prepared catalysts showed excellent catalytic desulfurization performance. The desulfurization rate of the composite catalyst with 35 wt% TiO2 coating in simulated fuel with 50 mg/L DBT concentration can reach 94.91% at 293.15 K within 160 min. Compared with other studies, the unit desulfurization rate is improved significantly without introducing any additional oxidants. In addition, in order to verify the effectiveness of the adsorption‒catalysis‒resorption desulfurization system, the adsorption kinetics and thermodynamics were studied, and the surface binding energy between the catalyst and the sulfide was calculated using Material Studio software. Experiments and simulations revealed that good adsorption performance of the catalyst on the reactants will greatly enhance the heterogeneous reaction rate for the enrichment of reactants on the surface of the catalyst, and the products can be selectively adsorbed on the catalyst surface via strong polar interaction to achieve coupling desulfurization of adsorption-catalysis-resorption in the initial position. In addition, spent TiO2-KCC-1/PG can be regenerated by simple thermal treatment and no visible decrease will be observed in the desulfurization rate after three regeneration cycles.

Enhancing the energy and exergy performance of a photovoltaic thermal system with [formula omitted]-shape collector using porous metal foam

The use of porous media in heat transfer systems leads to a rise in the heat transfer surface area and pressure loss of the working fluid, the first of which is desirable and the second is undesirable. The effect of porous metal foam positioning on the energy and exergy performances of an air-based photovoltaic thermal system with ∇-shape collector is investigated in this research. For this purpose, porous foam is placed once in the channel between the photovoltaic panel and the collector (system II), again in the channel between the collector and the back insulation wall (system III), and finally in both channels (system IV). The results are compared with each other and with those of the system without porous metal foam (system I). The energy balance equation is written for each part of the system, and the resulting system of equations is solved with a code written in MATLAB. The mathematical modeling was performed for several values of air mass flow rate. The results showed that the maximum overall energy efficiency (61.53–111.49%) and overall exergy efficiency (14.18–17.46%) belong to systems II and IV.

A Strategy for Drastic Improvement in the Durability of Pt/C and PtCo/C Alloy Catalysts for the Oxygen Reduction Reaction by Melamine Surface Modification

A strategy for drastic improvement in the durability of a Pt/C catalyst and a PtCo/C alloy catalyst for the oxygen reduction reaction (ORR) by melamine surface modification was demonstrated. The durability of the catalysts was evaluated by an accelerated durability test (ADT) using a square wave potential cycling of 0.6–1.0 V vs RHE performed in Ar-saturated 0.1 mol dm–3 HClO4 containing a very small amount of melamine (10 μmol dm–3) at 80 °C for 10,000 cycles. Transmission electron microscopy (TEM) observations showed that melamine addition suppressed a size increase in the catalyst nanoparticles (NPs) during the ADT caused by the Ostwald ripening and/or migration-coalescence, which mitigated a loss in the electrochemical surface area of the catalysts. More importantly, TEM-EDX compositional analysis revealed that melamine addition suppressed Co dealloying of the PtCo NPs during the ADT and the alloy catalyst retained a high ORR mass activity of 1019 A g–1-Pt at 0.9 V vs RHE even after the ADT. The durability improvement is considered to arise from the suppression of Pt-oxygenated species formation caused by destabilization of a stable water molecule network formed on the catalyst surface and selective adsorption of melamine molecules at low-coordination surface Pt sites. Our results open up an alternative avenue for drastic improvement in the durability of the Pt-based catalysts for the ORR in polymer electrolyte fuel cells.

Soil refinement accelerates in-field degradation rates of soil-biodegradable mulch films

Soil-biodegradable mulch films are a promising solution to replace conventional polyethylene-based mulch films, the use of which has led to negative environmental impacts. Soil-biodegradable mulch films are specifically designed to be incorporated into the soil at the end of the cropping cycle, and are expected to be biodegraded by soil microorganisms. The biodegradability of such products must be tested under laboratory-controlled conditions following international standards, although these can fail to represent real environmental conditions where mulch films are used. The objective of this study was to evaluate the effects of soil refinement on the degradation rates of three different commercial soil-biodegradable mulch films after their incorporation into the soil. The hypotheses were that: (i) soil refinement (i.e., ploughing followed by grubbing) creates more favourable conditions for film biodegradation compared to ploughing alone; and (ii) different mulch films show different degradation rates. An open-field completely randomised design was applied to test the effects of soil refinement by ploughing to 0.35 m depth without and with subsequent grubbing to 0.15 m depth twice. Three commercially available soil-biodegradable mulch films were sampled in 2020 (i.e., two Mater-bi-based, one Ecovio-based) at the end of a zucchini growing season (~3 months) when films were still lying above ground, and were later buried at 0.2 m depth inside mesh bags. Biodegradation rates of the sampled films were assessed with the indirect indicators of film weight loss and surface area loss at ~2-month intervals over 314 days. The results showed that soil refinement significantly accelerated degradation of the three tested mulch films by 14% and 17% according to the loss of weight and surface area indicators, respectively. One Mater-bi-based film showed higher degradation rates compared to the other two films. Future studies are needed to quantify the time needed for these different mulch films to be completely biodegraded. Such studies should be carried out following standards for laboratory incubation and/or in-field quantification of residual polymers in the soil over time. Highlights- Degradation rates of three biodegradable mulch films were evaluated in the open-field.- Soil refinement accelerates the degradation of film weight (14%) and surface (17%).- Highest degradation rates were observed for one Mater-bi-based film.- Fastest degradation rates were observed in spring for all the tested films.- Weight and surface area loss indicators showed positive relationship.

Universal Correlation between the Roughness Factor and PEMFC Performance Losses in Voltage Cycling Based Accelerated Stress Tests

During operational lifetime, proton exchange membrane fuel cells (PEMFCs) suffer from high performance losses. For the year 2025, the U.S. Department of Energy (DoE) set the durability target for PEMFC light-duty transportation applications at 5,000 hours.1 To meet the automotive target, different aging protocols were established in order to simulate load cycle variations.2 It is well known that load or voltage cycling induces substantial catalyst degradation due to an increasing loss of electrochemically active surface area (ECSA), which is known to be a main driver for the resulting performance penalties.3 Thus, an increasing interest exists in developing accelerated stress test (AST) protocols that can sufficiently describe the degradation of the different components of a membrane electrode assembly (MEA) during automotive application using shorter measurement times.In this study, we report on a strategy to predict the performance degradation of an MEA, making use of a strongly accelerated voltage cycling based ASTs. For this, voltage cycling based ASTs were performed using 5 cm2 MEAs with a 0.1 mgPt cmMEA -2 loaded Pt/C catalyst (TEC10V20E, Tanaka) for both cathode and anode. Voltage cycling was done under H2/N2 (200/75 nccm) at 80 °C, 95% RH, and ambient pressure using square wave profiles with a constant lower potential limit (LPL) of 0.6 V and different upper potential limits (UPLs) of 0.85, 0.95, and 1.0 V, with LPL/UPL hold times of 1, 2, or 8 s. Full characterization of the MEA at beginning-of-life and after each set of voltage cycling intervals was performed by: i) measuring H2/O2 and H2/air polarization curves; ii) determining the ECSA by cyclic voltammetry and CO stripping; iii) conducting limiting current measurement to calculate the O2 transport resistance (R O2 total); and, iv) conducting electrochemical impedance spectroscopy (EIS) measurements under blocking conditions to quantify the proton conduction resistance in the cathode catalyst layer (R H+ cath).When the ECSA loss ranges between ≈20-85%, it was found that the ECSA decreases approximately linearly when plotted against the logarithm of the number of cycles (see fig. 1), exhibiting higher slopes for procedures with higher UPLs and longer hold times, in agreement with the results from previous studies.3, 4 In addition, a direct and AST protocol independent correlation between the loss in total available surface area, i.e., the roughness factor (rf ≡ ECSA × Pt-loading), and the individual loss contributions in H2/air performance curves, namely kinetic (mass/specific activity for the oxygen reduction reaction (ORR)) and O2 transport resistance contributions, was shown. This is due to the fact, that these individual voltage losses are not only highly affected by the cathode rf,3, 5 but that the Pt dissolution/redeposition mechanism seems to be identical for all of the here investigated voltage cycling ASTs, despite the largely varying UPLs and hold times. As a result, a universal correlation between the H2/air performance losses and the rf deterioration was found throughout all ASTs. The important corollary of this finding is that the data from quickly degrading voltage cycling ASTs (i.e., with high UPL) can be used to project the H2/air performance losses when cycling under less degrading conditions.

Novel silica-modified boehmite aerogels and fiber-reinforced insulation composites with ultra-high thermal stability and low thermal conductivity

Alumina–silica composite aerogels have drawn vast attention due to their enhanced thermal stability compared to pristine alumina aerogels. However, they are generally weakly-crystallized and tend to experience inevitable sintering and significant surface area loss especially above 1200 °C. In this study, we developed a hydrothermal treatment and supercritical drying strategy for synthesizing novel, well-crystallized, silica-modified boehmite aerogels and fiber-reinforced composites. For the prepared aerogel, network coarsening was significantly hindered and the α-Al2O3 transition was completely prevented even at 1400 °C. As a result, the aerogel exhibits extremely high surface area maintenance (87 % and 53 % after 1300 °C and 1400 °C calcination, respectively) and low linear shrinkage (14 % after 1300 °C calcination) at elevated temperatures. The composite with good toughness shows excellent heat resistance and thermal insulating performance up to 1500 °C. These findings provide a general, direct new idea to improve the thermal tolerance of alumina-based aerogels and extend their applications to higher temperatures.

Alkali poisoning of Fe-Cu-ZSM-5 catalyst for the selective catalytic reduction of NO with NH3

Fe (2 wt%)-Cu (1.5 wt%)-ZSM-5 SCR catalyst contacted 1.5 wt% of Na and 1.8 wt% of K in order to simulate poisoning by species more specifically contained in exhaust gases from exhaust gases of diesel engines and power plants. Poisoning agents do not cause loss of surface area nor pore occlusion. XRD and SEM results showed that alkali metals introduction did not deteriorate the crystallinity and morphology of zeolite crystals. However, a significant loss of surface acidity was observed upon alkali-poisoned catalysts causing a dramatic deactivation of the NH3-SCR of NO reaction. Na-doped catalyst showed higher low-temperature SCR activity, while potassium has a stronger deactivation effect on Fe-Cu-ZSM-5 than sodium beyond 400 °C.

Revealing M (M = Cu, Co and Zr) oxides doping effects on anti-PbCl2 poisoning over Mn-Ce/AC catalysts in low-temperature NH3-SCR reaction

Lead salts poisoning was a great challenge for the catalysts application in selective catalytic reduction (SCR) reaction of NOx with NH3 in stationary sources. Herein, several typical transition metal (Cu, Co and Zr) oxides modified Mn-Ce/AC catalysts were prepared by impregnation method, and the effects of Cu, Co and Zr doping on resistance PbCl2 poisoning for the catalyst were investigated. The addition of three transition metal oxides improved the PbCl2 resistance of Mn-Ce/AC catalyst and maintained excellent low-temperature denitrification activity of the catalyst. The lead resistance performance of the three metal oxides followed: Cu > Co > Zr oxides. The NO conversion of Cu-doping catalyst after PbCl2 poisoning was only ca. 10% lower than that of fresh Mn-Ce/AC catalyst at 225 °C. Cu, Co and Zr doping could decrease the loss of specific surface area caused by poisoning, while Cu-doped catalyst showed lowest crystallinity of active components. Meanwhile, the contents of Mn4+ and chemisorbed oxygen in Cu-doped catalyst were higher than those in Co- or Zr-doped catalysts. Cu, Co and Zr doping improved the surface acidity and redox performance of the poisoned catalysts, with Cu-doped poisoned catalyst exhibiting nearly the same surface acidity and redox performance as the fresh Mn-Ce/AC catalyst. Furthermore, Cu doping could also improve NO adsorption and was in favor to the SCR process. Besides, in situ DRIFTS results showed that the catalytic reaction pathways of all the poisoned or modified catalysts were in accordance with both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms. Finally, a possible anti-PbCl2 poisoning mechanistic model of (Cu, Co and Zr) oxides modified on Mn-Ce/AC catalyst was proposed.

Glenoid Bone Loss Directly Affects Hill-Sachs Morphology: An Advanced 3-Dimensional Analysis

Background: While the glenoid track concept presents a useful prediction for recurrent glenohumeral instability, little is known about the humeral head bony architecture as it relates to glenoid erosion in the setting of bipolar bone loss. Purpose: To (1) qualitatively and quantitatively analyze the interplay between glenoid bone loss (GBL) and Hill-Sachs lesions (HSLs) in a cohort of patients with anterior instability using 3-dimensional imaging software and (2) assess the relationships between GBL and HSL characteristics. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Patients were identified who had anterior shoulder instability with a minimum 5% GBL and evidence of HSL confirmed on computed tomography. Unilateral 3-dimensional models of the ipsilateral proximal humeral head and en face sagittal oblique view of the glenoid were reconstructed using MIMICS software (Materialise NV). GBL surface area, width, defect length, and glenoid track width were quantified. The volume, surface area, width, and depth of identified HSLs were quantified with their location (medial, superior, and inferior extent) on the humeral head. Severity of GBL was defined as percentage glenoid bone surface area loss and categorized as low grade (5%-10%), moderate grade (>10% to 20%), high grade (>20% to 30%), and extensive (>30%). Analysis of variance was then computed to determine significance (P < .05) between severity of GBL and associated HSL parameters. Results: In total, 100 patients met inclusion criteria (mean age, 27.9 years; range, 18-43 years), which included 58 right shoulders and 42 left shoulders (84 male, 16 female). Among groups, there were 32 patients with low-grade GBL (mean GBL = 6.1%), 38 with moderate grade (mean GBL = 16.2%), 17 with high grade (mean GBL = 23.7%), and 13 with extensive (mean GBL = 34.0%), with an overall mean GBL of 18.1% (range, 5%-39%). Patients with 5%-10% GBL had significantly narrower HSLs (average and maximum width; P < .03) and deeper HSLs (average depth; P = .002) as compared with all other GBL groups, while greater GBL was associated with wider and shallower HSLs. GBL width, percentage width loss, defect length, and glenoid track width all significantly differed across the 4 GBL groups (P < .05). Conclusion: HSLs had significantly different morphological characteristics depending on the severity of GBL, indicating that GBL was directly related to the characteristics of HSLs. Patients presenting with smaller glenoid defects had significantly narrower and deeper HSLs with less humeral head surface area loss, while greater GBL was associated with wider and shallower HSLs.

Designing Ceria/Alumina for Efficient Trapping of Platinum Single Atoms

Cerium oxide (ceria) has been shown to be very effective at trapping platinum atoms due to formation of stable surface complexes at step edges, where coordinatively unsaturated cerium cations are present. But ceria loses its effectiveness when heated to high temperatures due to loss of surface area and growth in particle size associated with sintering of the oxide. Being a rare earth, and with limited supplies worldwide, it is important to develop methods to improve the effectiveness of ceria as a catalyst support. Here, we explore the performance for trapping Pt atoms when the ceria is supported on a high surface area alumina carrier. This helps create a more sustainable catalyst formulation, especially if we can retain the high dispersion of Pt seen on ceria supports. For this work, we studied the atom trapping efficacy of ceria/alumina samples with increasing ceria content (8–50 wt %) and contrasted the behavior with pure ceria. Electron microscopy reveals that when dispersed on alumina, ceria is present in the form of crystalline nanoparticles and isolated cerium ions. These two forms of ceria differ markedly in their ability to trap Pt atoms. Atomically dispersed cerium is present in the form of Ce3+ cations on alumina; however, this form of ceria is not effective for trapping Pt atoms. Our results show that the atom-trapped Pt resides primarily on crystalline ceria nanoparticles. CO oxidation was used as a probe reaction to evaluate the performance of these PtAT/ceria-alumina catalysts. We conclude that over the range of ceria loadings we investigated, 50% ceria/alumina represents the optimal catalyst support for achieving high surface area and atom trapping efficiency while helping reduce the total ceria content in this catalyst system.

Three-Dimensional Printed MoS2/Graphene Aerogel Electrodes for Hydrogen Evolution Reactions.

In this work, we demonstrate the use of direct ink writing (DIW) technology to create 3D catalytic electrodes for electrochemical applications. Hybrid MoS2/graphene aerogels are made by mixing commercially available MoS2 and graphene oxide powders into a thixotropic, high concentration, viscous ink. A porous 3D structure of 2D graphene sheets and MoS2 particles was created after post treatment by freeze-drying and reducing graphene oxide through annealing. The composition and morphology of the samples were fully characterized through XPS, BET, and SEM/EDS. The resulting 3D printed MoS2/graphene aerogel electrodes had a remarkable electrochemically active surface area (>1700 cm2) and were able to achieve currents over 100 mA in acidic media. Notably, the catalytic activity of the MoS2/graphene aerogel electrodes was maintained with minimal loss in surface area compared to the non-3D printed electrodes, suggesting that DIW can be a viable method of producing durable electrodes with a high surface area for water splitting. This demonstrates that 3D printing a MoS2/graphene 3D porous network directly using our approach not only improves electrolyte dispersion and facilitates catalyst utilization but also provides multidimensional electron transport channels for improving electronic conductivity.

Dynamic modeling of Pt degradation and mitigation strategies in polymer electrolyte membrane fuel cells

The durability issue of polymer electrolyte membrane fuel cells must be resolved before their widespread commercialization in transportation. A central issue in fuel cell durability is the loss of Pt electrochemical active surface area (ECSA) during automotive conditions, which is induced primarily by the Pt mass loss and Pt particle growth mechanisms. A comprehensive Pt degradation model to study the evolution of the ECSA distribution, induced mechanisms and mitigation strategies is developed. After validation with experimental results, the importance of the Pt mass loss and particle growth mechanisms is studied. Results reveal that the Pt mass loss mechanism occurs primarily near the proton-exchange-membrane/catalyst-layer (PEM/CL) interface and becomes more critical with improved electrode potential. The ECSA loss by the particle growth (Ostwald ripening) mechanism is, for the most part, uniformly distributed along the thickness direction, whereas it is suppressed near the PEM/CL interface by the Pt mass loss mechanism. The model also studies possible mitigation strategies for ECSA loss by suppressing the mass loss mechanism. Both the graded PEM structure and reduced Pt 2+ ion diffusivity can help mitigate the ECSA loss process. • Modeling of Pt degradation in the membrane electrode assembly is developed. • The model distinguishes Pt ECSA loss by mass loss and particle growth types. • Pt mass loss mechanism distributes nonuniformly and increases with cell voltage. • Pt growth mechanism distributes uniformly and increases with voltage cycling. • The model proposes mitigation strategies for ECSA loss by reducing Pt mass loss.