Nanoscale compositional changes and modification of the surface reactivity of Pt3Co/C nanoparticles during proton-exchange membrane fuel cell operation

This study bridges the structure/composition of Pt-Co/C nanoparticles with their surface reactivity and their electrocatalytic activity. We show that Pt₃Co/C nanoparticles are not stable during PEMFC operation (H₂/air; j = 0.6 A cm⁻², T = 70 °C) but suffer compositional changes at the nanoscale. In the first hours of operation, the dissolution of Co atoms at their surface yields to the formation of a Pt-enriched shell covering a Pt-Co alloy core (“Pt-skeleton”) and increases the affinity of the surface to oxygenated and hydrogenated species. This structure does not ensure stability in PEMFC conditions but is rather a first step towards the formation of “Pt-shell/Pt-Co alloy core” structures with depleted Co content. In these operating conditions, the Pt-Co/C specific activity for the ORR varies linearly with the fraction of Co alloyed to Pt present in the core and is severely depreciated (ca. −50%) after 1124 h of operation. This is attributed to: (i) the decrease of both the strain and the ligand effect of Co atoms contained in the core (ii) the changes in the surface structure of the electrocatalyst (formation of a multilayer-thick Pt shell) and (iii) the relaxation of the Pt surface atoms.     

Influence of technological parameters on the structure of the batter and the texture of frankfurter type sausages

The aim of the study was, on the one hand, to determine the relationships between various technological factors, the structure of the batters and the texture characteristics of frankfurter type sausages, and, on the other, to define the possibilities of realizing a reference scale for texture. The addition of sodium chloride in the 0-2% range induces a large increase (60%) in the cooking yield, a decrease in the specific gravity and an increase in the viscosity of the batter determined indirectly through the evolution of the product temperature during chopping. These variations together, give a 30% decrease in the mechanical firmness and a 100% and 90% increase in the juiciness and elasticity of the final products, respectively. However, beyond 2%, sodium chloride does not induce any significant effect on these characteristics. The addition of caseinate in a 1-3% range induces a degassing of the batter and a 10-37% decrease in the water losses during cooking. The higher the caseinate content in the 0-6% range, the larger the rise in the batter temperature during chopping. Sausages are also considered harder (+22%) and less juicy and elastic (-50%) when caseinate content increases. Addition of 0·1-0·5% polyphosphates and chopping under vacuum (0·2 atm) induce variations in the cooking yield, +3% and -1%, respectively, but have no influence on the texture of the final products. Modifications of all these technological parameters induced variations by a factor of 2 in the different mechanical parameters and in parallel differences of 1-2 points on a 6 point scale for sensory characteristics.     

Effects of poloxamer 407 on transfection time and percutaneous adenovirus-mediated gene transfer in native and stented vessels

Reduction in transfection time and the ability to perform gene transfer in conjunction with endovascular stent implantation constitute two important challenges for percutaneous adenovirus-mediated gene transfer to vessel walls. Studies have suggested that the use of biocompatible polyol poloxamer 407 could be useful. We first evaluated the use of poloxamer 407 for percutaneous gene transfer in nonstented rabbit iliac arteries. A 200-microl mixture of Ad-RSVbetagal or Ad-CMVLuc in either phosphate-buffered saline (PBS) or 20% poloxamer was delivered. After 3 days, gene transfection was evaluated by X-Gal staining or measurement of luciferase activity. Poloxamer use resulted in a 3- to 15-fold increase in the percentage of transfected cells (X-Gal, p = 0.001) and a 16-fold increase in protein product (luciferase activity, p = 0.03), and allowed a decrease in transfection time from 30 to 5 min with minimal reduction in transfection efficiency. We then evaluated the feasibility of percutaneous gene transfer, using Ad-RSVbetagal diluted in pure PBS or 20% poloxamer, in conjunction with stent implantation. Gene delivery was performed either immediately before (pre-) or after (post-) stent implantation. When adenoviruses were diluted in PBS, gene transfer had a low efficiency (prestent, 0.3%; poststent, 0.2%; NS). With poloxamer, the efficacy was much higher (p = 0.0001) and similar "pre" (2.2%) or "post" (1.7%) stent delivery (NS). CONCLUSIONS: (1) The use of poloxamer, rather than PBS, as a vehicle increases the efficacy of percutaneous adenovirus-mediated gene transfer and reduces transfection time; (2) gene transfer performed during stent implantation with poloxamer is feasible and achieves a significant level of gene expression. Thus percutaneous gene delivery is applicable to conventional stents and could present an attractive method by which to achieve local biological effects in a stent environment.     

Biomaterial‐Induction of a Transplantable Angiosome

Creating transplantable vascular networks (angiosomes) that are fed and drained by vessels large enough to be surgically reconnected is key to harnessing the potential of regenerative medicine and advancing reconstructive surgical techniques. Currently, the only way to create a new angiosome is nontrivial and involves pressurizing a vein graft by its surgical attachment to an artery forming an arteriovenous loop (AVL). Material induction of a venous angiosome is reported, by placement of a 3D printed microporous monetite scaffold around a vein and its transplantability is further demonstrated. When the transplanted venosome is cut, it bleeds, illustrating potential reconstructive functionality. The volume of blood vessels generated by biomaterial‐induction is as great as by AVL. Direct contact of the material with the vein does not appear to be critical to luminal sprouting, and wrapping the implant in a silicone membrane significantly reduces sprouting. Pilot studies with microporous polymeric scaffolds induce far less vascular invasion. After 4 weeks, monetite scaffolds are extensively vascularized and can be transplanted to an arterial vessel. This report is significant since a lack of tools to control vascular generation is an impediment to the treatment of several conditions that give rise to tissue ischemia and tissue reconstruction.     

A molecular dynamics study of radiation induced diffusion in uranium dioxide

The nuclear oxide fuels are submitted ‘in-pile’ to strong structural and chemical modifications due to the fissions and temperature. The diffusion of species is notably the result of a thermal activation and of radiation induced diffusion. This study proposes to estimate to what extent the radiation induced diffusion contributes to the diffusion of lattice atoms in UO₂. Irradiations are simulated using molecular dynamics simulation by displacement cascades induced by uranium primary knock-on atoms between 1 and 80 keV. As atoms are easier to displace when their vibration amplitude increases, the temperature range which have been investigated is 300-1400 K. Cascade overlaps were also simulated. The material is shown to melt at the end of cascades, yielding a reduced threshold energy displacement. The nuclear contribution to the radiation induced diffusion is compared to thermally activated diffusion under in-reactor and long-term storage conditions.     

Impact of ultra-low Pt loadings on the performance of anode/cathode in a proton-exchange membrane fuel cell

This study focuses on the elaboration of PEMFC electrodes containing ultra-low platinum (Pt) loadings by direct liquid injection metal organic chemical vapor deposition (DLI-MOCVD). DLI-MOCVD offers a large number of advantages for the elaboration of model PEMFC electrodes. First, by using different metal precursors or elaboration temperature, the size of the Pt nanoparticles and thus the intrinsic catalytic activity can easily be tailored in the nanometer range. In this work, Pt nanoparticles (1-5 nm) with remarkable low degree of agglomeration and uniform distribution were deposited onto the microporous side of a commercial gas-diffusion layer (GDL). Second, reduction of the Pt loading is made possible by varying the Pt deposition time and its influence of the cell performance can be extracted without variation of the thickness of the catalytic layer (in previous studies, a decrease of the catalyst utilization was observed when increasing the Pt loading, i.e. the thickness of the catalytic layer (CL)). The electrocatalytic activity of home-made Pt nanoparticles elaborated by DLI-MOCVD was measured in liquid electrolyte or in complete fuel cell operating on H₂/O₂ or H₂/air and compared vs. that of a commercially available electrode containing 500 μg_Pt cm⁻² (Pt_Ref500). At the cathode, the performance of the electrodes containing 104-226 μg of Pt per cm² of electrode compares favorably with that of the Pt_Ref500 in H₂/O₂ conditions. In H₂/air conditions, additional mass-transport losses are detected in the low-current density region but the high effectiveness of our electrodes improves the performance in the high-current density region. At the anode, the Pt loading can be reduced to 35 μg_Pt cm⁻² without any voltage loss in agreement with previous observations.     

Effect of the structure of Pt-Ru/C particles on COad monolayer vibrational properties and electrooxidation kinetics

In this paper, we combined FTIR spectroscopy and CO_ad stripping voltammetry to investigate CO_ad adsorption and electrooxidation on Pt-Ru/C nanoparticles. The Pt:Ru elemental composition and the metal loading were determined by ICP-AES. The X-ray diffraction patterns of the Pt-Ru/C indicated formation of a Pt-Ru (fcc) alloy. HREM images revealed an increase in the fraction of agglomerated Pt-Ru/C particles with increasing the metal loading and showed that agglomerated Pt-Ru/C nanoparticles present structural defects such as twins or grain boundaries. In addition, isolated Pt-Ru/C nanoparticles have similar mean particle size (ca. 2.5 nm) and particle size distributions whatever the metal loading. Therefore, we could determine precisely the effect of particle agglomeration on the CO_ad vibrational properties and electrooxidation kinetics. FTIR measurements revealed a main CO_ad stretching band at ca. , which we ascribed to a-top CO_ad on Pt domains electronically modified by the presence of Ru. As the metal loading increased, the position of this band was blue shifted by ca. 5 cm⁻¹ and a shoulder around 2005 cm⁻¹ developed, which was ascribed to a-top CO_ad on Ru domains. The reason for this was suggested to be the increasing size of Ru domains on agglomerated Pt-Ru/C particles, which lifts dipole-dipole coupling and allows two vibrational features to be observed (CO_ad/Ru, CO_ad/Pt). This is evidence that FTIR spectroscopy can be used to probe small chemical fluctuations of the Pt-Ru/C surface. Finally, we comment on the CO_ad electrooxidation kinetics. We observed that CO_ad was converted more easily into CO₂ as the metal loading, i.e. the fraction of agglomerated Pt-Ru/C nanoparticles, increased.     

Five-substrate cocktail as a sensor array for measuring enzyme activity fingerprints of lipases and esterases

Substrate arrays for measuring enzyme activity fingerprints can be conveniently formulated as cocktails designed such that the reaction products can be separated and quantified by analytical high-performance liquid chromatography (HPLC). Fingerprinting of lipases and esterases, an important class of microbial enzymes, is reported with a cocktail of only five substrates as a practical fingerprinting reagent. An unusually strong C4-esterase activity was thus revealed in a recently discovered microbial esterase.