Inert Systems Research Articles

Precise photothermal treatment of bacterial infection mediated by charge-switchable nanoplatform with acylsulfonamide betaine surface

Photothermal therapy (PTT) offers a promising approach for the treatment of drug-resistant bacterial-infected wounds, yet it requires precise targeting of thermal damage to bacteria rather than healthy tissues. Herein, ultrasmall CuS NPs modified with polyzwitterion containing acylsulfonamide betaine (PCBSA@CuS), which provides a sensitive and reversible charge conversion around pH 6.8, are used to enhance the healing of bacteria-infected wounds. In the acidic infection microenvironment, the majority of PCBSA@CuS can electrostatically adsorb onto bacterial cells through cationic exposure, resulting in direct damage and death of bacteria upon NIR irradiation. Additionally, the photothermal NPs rapidly return to a zwitterionic nature in normal physiological environments, ensuring lower affinity and avoiding thermal damage to healthy tissues during continuous PTT. Compared to inert photothermal systems such as PEG-modified CuS NPs, the NPs used in this study exhibited higher bactericidal and wound healing efficacy. Therefore, this nano-antibacterial agent with highly sensitive thermal-targeting function provides a novel photothermal strategy for efficient and biosafe treatment of infected wounds.

Regulation of epithelial cell jamming transition by cytoskeleton and cell-cell interactions.

Multicellular systems, such as epithelial cell collectives, undergo transitions similar to those in inert physical systems like sand piles and foams. To remodel or maintain tissue organization during development or disease, these collectives transition between fluid-like and solid-like states, undergoing jamming or unjamming transitions. While these transitions share principles with physical systems, understanding their regulation and implications in cell biology is challenging. Although cell jamming and unjamming follow physics principles described by the jamming diagram, they are fundamentally biological processes. In this review, we explore how cellular processes and interactions regulate jamming and unjamming transitions. We begin with an overview of how these transitions control tissue remodeling in epithelial model systems and describe recent findings of the physical principles governing tissue solidification and fluidization. We then explore the mechanistic pathways that modulate the jamming phase diagram axes, focusing on the regulation of cell fluctuations and geometric compatibility. Drawing upon seminal works in cell biology, we discuss the roles of cytoskeleton and cell-cell adhesion in controlling cell motility and geometry. This comprehensive view illustrates the molecular control of cell jamming and unjamming, crucial for tissue remodeling in various biological contexts.

Synchronization of Chaotic Systems with Huygens-Like Coupling

One of the earliest reports on synchronization of inert systems dates back to the time of the Dutch scientist Christiaan Huygens, who discovered that a pair of pendulum clocks coupled through a wooden bar oscillate in harmony. A remarkable feature in Huygens’ experiment is that different synchronous behaviors may be observed by just changing a parameter in the coupling. Motivated by this, in this paper, we propose a novel synchronization scheme for chaotic oscillators, in which the design of the coupling is inspired in Huygens’ experiment. It is demonstrated that the coupled oscillators may exhibit not only complete synchronization, but also mixed synchronization—some states synchronize in anti-phase whereas other states synchronize in-phase—depending on a single parameter of the coupling. Additionally, the stability of the synchronous solution is investigated by using the master stability function approach and the largest transverse Lyapunov exponent. The Lorenz system is considered as particular application example, and the performance of the proposed synchronization scheme is illustrated with computer simulations and validated by means of experiments using electronic circuits.

How Enzyme Selectivity and Immobilization Affect Catalytic Yields in Lipase-Catalyzed Processes

Abstract: Herein, the influence of structural attributes, including the interactions of lipases with support systems, substrates, products/byproducts, and the media environment, on enzyme stability, selectivity and activity are discussed. Substrates/products, such as methanol, glycerol, phenolic acids and polyphenols, can inhibit lipase activity by influencing the mass flow of the reactants and products or by enzyme denaturation, which is also caused by extreme pH, high temperatures, and digestive action of most organic solvents. Immobilization techniques that involve chemical bonding between the functional groups of the support and the amino acids of the lipase maintain the enzyme’s active conformation via the formation of stable secondary structures. Functionalized metal nanoparticles and metal and covalent organic frameworks (COFs and MOFs) covalently bond to lipases, reducing the reliance of the active site conformation on hydrogen bonding and disulfide bonds. The crystallinity of COFand MOF-immobilized lipases allows them to be used in contrasting media environments and at high temperatures, which increases the reaction kinetics and improves the catalytic yield. On the other hand, inert support systems such as silica promote catalytic yields by minimizing protein leaching, which fairly maintains the amount of the preloaded lipase. The structure of substrates also plays a large role, whereas some lipases strictly prefer narrow substrates. In contrast, others, such as Candida species lipases, are liberal and allow substrates of varying bulkiness/steric hindrances.

Quantitive HAZOP and D-S evidence theory-fault tree analysis approach to predict fire and explosion risk in inert gas system on-board tanker ship

Tanker ships carry volatile cargo, presenting inherent risks of fire and explosion. Inert gas systems (IGS) are pivotal in mitigating risks by displacing oxygen in cargo tanks. However, failure of IGS components may lead to fatal consequences such as loss of life and marine pollution. This paper prompts a systematic approach integrating Quantitative Hazard and Operability (HAZOP) analysis under D-S (Dempster–Shafer) evidence theory and Fault Tree Analysis (FTA) to predict and quantify the fire and explosion risk associated with IGS malfunction on tanker ships. The methodology systematically evaluates failure probabilities, and consequences using HAZOP to identify critical scenarios. D-S evidence theory is employed to address uncertainties and incorporate expert knowledge into the analysis. FTA is applied to model fault propagation and assesses the likelihood of fire and explosion events based on the identified failure scenarios. A case study is presented to demonstrate the application of the proposed methodology, illustrating effectiveness in identifying high-risk scenarios and providing insights for enhancing operational safety minimising the risk of IGS on tanker ships. The findings show that the risk of fire and explosion in the inert gas system due to the high concentration of oxygen entering the tank was found to be 2.86E-01. Besides its robust theoretical background, the findings of the paper provide the utmost contribution to ship crew, ship inspectors, HSEQ managers and safety professionals for proactive risk mitigation strategies, contributing to the advancement of safety management practices in the maritime industry.

The burning rate of wood cribs under forced flow and variable oxygen concentration: A B-number approach

Wood cribs are used in a multitude of fire testing and research capacities including the certification of inert gas extinguishing systems. In these standardized tests, a wood crib is subjected to the joint effects of a variable forced flow through the crib and a systematic reduction of oxygen concentration. These joint effects increase the wood crib burning rate, even at reduced oxygen concentrations, before extinction is achieved by oxygen depletion. Currently, no theoretical frameworks exist for studying these coupled effects simultaneously. To address this problem, the in-depth heat and mass transfer phenomena are examined, and a general mass transfer B-Number is proposed for wood cribs. The methodology presented in this work encapsulates the oxygen reduction effects through the B-Number and the forced flow effects through the heat transfer coefficient. The theoretical burning rate with inputs of experimental flow velocities and oxygen concentrations demonstrates that the initial increase in flow drives the observed burning rate increase in the experimental results. Following the initial increase, the reduction in the oxygen concentration dominates and leads to a decrease in the wood crib burning rate. The combined B-number and heat transfer coefficient approach provides a good representation of the competing flow and O2 depletion effects and correctly captures experimental trends. A more accurate wood crib Nusselt number correlation for the heat transfer coefficient is required to better account for the heat transfer in the complex crib geometry.

(Invited) Electrochemistry of Exceptionally Inert Systems: Determination and Speciation of Arsenic(III) and Arsenic(V)

There has been growing interest in development of new methods for the determination of arsenic oxo species due to their high toxity and increasing population in the environment. Electrochemical methods for the determination of arsenic can be considered as complimentary to spectroscopic and chromoatographic ones because they are fairly simple, and they are subject to different selectivity criteria. In this respect, various stripping voltammetric procedures are becoming popular. The actual stripping voltammetric measurement consists of two steps in which preconcentration of an analyte at the electrode surface is followed by the so called „stripping” step involving electrode reaction recorded in a form of the voltammetric peak. A representative approach involves reduction of the analyte anions upon application of the sufficiently negative potential to form As(0) on the electrode (e.g. gold) surface; this step is followed by voltammetric oxidation (anodic stripping) of the deposit (to As(III)). In a case of so called cathodic stripping voltammetry, the stationary Hanging Mercury Drop Electrode (HMDE) is often used. During the preconcentration step, an insoluble salt (e.g. Cu3As2) is produced on the electrode surface. There is also a need to differentiate between As(III) and As(V) oxo-species, which are relatively more and less toxic, respectively.Because sensitivity and detection limit in electroanalytical determinations strongly depend on the current densities measured, there is a need to search for specific catalytic materials that would induce otherwise highly slow and irreversible redox processes of As(III) (oxidation) and, in particular, As(V) (reduction). Our research interests concern development of highly specific catalytic systems leading to the enhancement of the electrooxidation of arsenic (III). We explore here the capability of various noble metals nanoparticles (Pt, Rh, Pd) of inducing the arsenic(III) oxidation in acidic medium. The recorded currents have been compared to those observed previously at the electrodes modified with oxocyanoruthenates, the most potent system for the electrocatalytic oxidation of AsIII(OH)3. Reduction of arsenic (V) is even the more inert reaction. Network films of bimetallic (PtRu) nanoparticles (bare and derivatized) permit preconcentration of arsenic(V) species on their surfaces. The stripping step would allow determination of low concentrations of arsenic (10-6 mol/dm-3 or lower).

Impact of a Weather Predictive Control Strategy for Inert Building Technology on Thermal Comfort and Energy Demand

The sun’s total radiation alone exceeds the world population’s entire energy consumption by 7.500 times and ignites secondary renewable energy sources. The end energy consumption buildings use for heating amounts to 28% of Germany’s total energy consumption. With the ongoing trend of digitalization and the transition of the German energy supply away from fossil fuels and the consequent political dependency, electric heat pumps and photovoltaic (PV) systems have become increasingly important to the discussion. This has led to an increasing demand for smart control strategies, especially for inert systems such as thermally activated building systems (TABS). This paper presents and analyses a weather predictive control (WPC) strategy using a validated thermodynamic simulation model. The literature review of this paper outlines that the current common control strategies are data intense and complex in their implementation into the built environment. The simple approach of the WPC uses future ambient temperature and solar radiation to optimize the control of the heating, cooling, ventilation, and sun protection system. The thermal comfort and energy demand evaluate the concept. We show that with a WPC for TABS, thermal comfort can improve without increasing the energy demand for the office building in the moderate climate of Munich. Furthermore, this paper concludes that the WPC works more effectively with more thermal mass. This simplified building control strategy promotes the European roadmap goal of climate neutrality in 2050, as it bridges the phenomenon of the performance gap.

"PERFORMANCE ANALYSIS OF INERT GAS PLANT WITH SCRUBBER USING ANSYS FOR A VLCC SHIP"

"Through the 1978 SOLAS Protocol and then through the introduction of amendments from 1981 and 1983, new specifications are brought regarding the design, operation, maintenance, verification of inert gas systems intended for both oil tanks and bulk chemical tanks, and, in general, the systems of safety on board ships carrying dangerous goods. The inerting method using a gas system with generator and scrubber involves a continuous and very efficient process, with a low level of supervision and maintenance, that is why this type of installation was chosen in this study. Installations with a scrubber type unit require the installation of an inert gas generator that operates at a pressure of 8-10 bar and releases nitrogen at 7-9 bar. The quality of the air will depend on the type of generator used, scrubber type unit, but air without impurities with the best possible quality is recommended. Nitrogen quality for a given unit varies with production rate and is generally 95-97% pure. By connecting high-quality scrubbers, nitrogen can be brought to 99% purity, but at lower production rates and much higher energy consumption rates of any system on board ship is specifically identified with its reliability. So as to get the best out of marine motors, it is critical to screen their performances and take measures to accomplish productive combustion. As a result of heat gains on board ships from engine rooms and crew, the increase in humidity as well as due to the various releases of gases from on board systems, room air deteriorates, requiring replacement and its processing through the HVAC (heat, ventilation and air conditioning) system. The combustion process in diese."

Microphase separation of living cells

Self-organization of cells is central to a variety of biological systems and physical concepts of condensed matter have proven instrumental in deciphering some of their properties. Here we show that microphase separation, long studied in polymeric materials and other inert systems, has a natural counterpart in living cells. When placed below a millimetric film of liquid nutritive medium, a quasi two-dimensional, high-density population of Dictyostelium discoideum cells spontaneously assembles into compact domains. Their typical size of 100 μm is governed by a balance between competing interactions: an adhesion acting as a short-range attraction and promoting aggregation, and an effective long-range repulsion stemming from aerotaxis in near anoxic condition. Experimental data, a simple model and cell-based simulations all support this scenario. Our findings establish a generic mechanism for self-organization of living cells and highlight oxygen regulation as an emergent organizing principle for biological matter.

Study of the Unstable Rotational Dynamics of a Tor-Fullerene Molecular System

This work is devoted to modeling the dynamics of large molecules. The key issue in modeling the dynamics of real molecular systems is to correctly represent the temperature of the system using the available theoretical tools. In most works on molecular dynamics, vibrations of atoms inside a molecule are modeled with enviable persistence, which has nothing to do with physical temperature. These vibrations represent the energy internal to the molecule. Therefore, it should not be present in problems in the dynamics of inert molecular systems. In this work, by means of classical mechanics, it is shown that the simplest system containing only three molecular bodies, due to multiple acts of pair interactions of these bodies, reproduces the temperature even in an extremely complex unstable motion of the system. However, at the same time, it is necessary to separate the stochastic part of the movement from the deterministic one. Calculations also show that translational fluctuations in the motion of molecules make the greatest contribution to temperature. The contribution of rotational energy to the total energy of fluctuation motions is small. It follows from these results that the thermal state of the system is determined only by the translational temperature. The latter, in turn, opens up possibilities for a simplified description of many complex systems composed of carbon molecules such as fullerenes and nanotori.

Experimental methods in chemical engineering: Computational fluid dynamics/finite volume method—CFD/FVM

AbstractComputational fluid dynamics (CFD) applies numerical methods to solve transport phenomena problems. These include, for example, problems related to fluid flow comprising the Navier–Stokes transport equations for either compressible or incompressible fluids, together with turbulence models and continuity equations for single and multi‐component (reacting and inert) systems. The design space is first segmented into discrete volume elements (meshing). The finite volume method, the subject of this article, discretizes the equations in time and space to produce a set of non‐linear algebraic expressions that are assigned to each volume element—cell. The system of equations is solved iteratively with algorithms like the semi‐implicit method for pressure‐linked equations (SIMPLE) and the pressure implicit splitting of operators (PISO). CFD is especially useful for testing multiple design elements because it is often faster and cheaper than experiments. The downside is that this numerical method is based on models that require validation to check their accuracy. According to a bibliometric analysis, the broad research domains in chemical engineering include: (1) dynamics and CFD‐DEM, (2) fluid flow, heat transfer, and turbulence, (3) mass transfer and combustion, (4) ventilation and the environment, and (5) design and optimization. Here, we review the basic theoretical concepts of CFD and illustrate how to set up a problem in the open‐source software OpenFOAM to isomerize n‐butane to i‐butane in a notched reactor under turbulent conditions. We simulated the problem with 1000, 4000, and 16 000 cells. According to the Richardson extrapolation, the simulation underestimates the adiabatic temperature rise by 7% with 16 000 cells.

Reduced pressure laser weld comparison to electron beam welds in Ti-6Al-4 V

Reduced pressure laser welds were made using a 6-kW commercial fiber-laser system on Ti-6Al-4 V and compared to electron beam welds of the same beam diameters as measured by beam diagnostics. The laser welds showed keyhole characteristics under easily achievable mechanical pumped vacuum levels of 1 mbar pressure that nearly matched the electron beam weld penetrations made at 9 × 10–5 mbar vacuum. Ti-6Al-4 V alloys were used to represent refractory metals such as vanadium, tantalum, zirconium, or molybdenum that require vacuum or highly protective inert gas protection systems to prevent adverse interactions with air and can be difficult to weld under non-vacuum conditions. Results show that laser weld depths of 20 mm with aspect ratios of 17:1 can be made under what appears to be stable keyhole behavior as the result of reduced pressure. The effect of fiber diameter was examined using 0.1-, 0.2-, and 0.3-mm fibers, showing that small spot sizes can easily be achieved at long focal length lenses of 400 and 500 mm. The 0.1- and 0.2-mm fibers produced keyhole welds with minimal amounts of porosity, which was only present at 2 kW or higher, while the 0.3-mm fiber produced keyhole welds with more rounded roots that were porosity free as shown by radiography up to the maximum power of 6 kW. Correlations between weld depth and processing conditions are presented for the reduced pressure laser. These results are directly compared to electron beam welds, facilitating design of future reduced pressure laser systems targeted for deep weld penetrations historically developed for electron beams.

Cold ironing: modelling the interdependence of terminals and vessels in their choice of suitable systems

Cold ironing has the potential to reduce the impact of ship exhausts in densely populated areas. However, especially for tankers, the implementation of this concept is almost non-existent. Still, these vessels have a relatively high port energy use, despite relatively short port visits, as they provide power to both pumps and inert gas systems during unloading and loading. A key factor in the reluctance, besides the fact that a sparkless connection is required, is the lack of a standard and the uncertainty from both tanker owners visiting a berth and terminal owners on which shore power systems to apply. This paper investigates the interdependency between ship and terminal owner choices for systems and establishes the overall most economical solution. Cold ironing was reviewed to identify existing systems and solutions and analyse the tanker fleet and terminals. The insights were combined in an integrated economic model consisting of two sub-models; one relating terminal decisions to a cold ironing price and one establishing the vessel side costs and savings. By using fuel price as an input and acceptance rates (for both terminals and vessels) for cold ironing systems as key variables to determine. The models have been used to identify the potential of cold ironing for shortsea and parcel tankers against different fuel prices and % of fleet and terminals that have shore power equipment. In all cases, shore power was not economical, which was caused by the high costs of the fixed costs of electricity, due to the high powers required. Interesting avenues for further research would be to increase the individuality of the model using e.g. an agent based model. Also extending the model with a battery pack on the terminal to allow for peak-shaving could lead to much lower costs and higher economic potential.

Blood compatibility of widely used central venous catheters; an experimental study

An inserted central venous catheter (CVC) is considered foreign material by the inert host defence systems and induce inflammation and thrombus formation. The objective of this study was to evaluate blood compatibility of six commonly used CVCs. Three coated and three uncoated CVC materials were tested in a modified Chandler loop model. Each catheter material circulated in blood from ten different healthy volunteers for 1 h. Blood cell counts and measurements of the inert host defence systems were performed on blood samples from the loop. All the tested catheters demonstrated impact on blood cells, contact coagulation, the complement system, or inflammatory markers, although the impact varied significantly. Of the catheters we evaluated, the most unfavourable blood compatibility profile was found for the polyurethane CVC coated with chlorohexidine and silver sulfadiazine. The greatest variation in blood compatibility between test runs was noted for the silicone dialysis catheter. Poor blood compatibility should be taken seriously but given the experimental design of the current study the clinical significance remains to be evaluated.

Assessing the suitability of new film laminates for sustainable insect eradication by modified atmosphere in museums

The increasing demand for applying modified inert atmosphere systems for insect eradication in museums has led to the desire for lower-cost consumable materials, particularly laminated plastic films. An ultra-low oxygen-permeable laminate is required for creating successful systems of modified inert atmosphere to keep the oxygen concentration lower than 0.3%. A range of ultra-high barrier laminates is commercially available but at a high cost, which could affect the sustainability of applying these systems in museums of limited budgets. The wide use of local laminates for food preservation makes them a perfect target for testing and improvement as alternatives. However, a laboratorial test method for evaluating their oxygen permeability is required to assess their suitability for insect eradication using modified atmospheres. Therefore, the present work investigates the potential of using two laminates (one local and one imported) to create a successful modified atmosphere system. A laboratory easy-to-use test method was used to assess the oxygen permeability of each laminate and calculate its oxygen transmission rate. The test method is a sealed static chamber separated in the middle by a known area of the laminate to be tested. The test relies on monitoring the change of oxygen concentration overtime on either side of the laminate membrane within the sealed system to assess its oxygen transmission rate. The specifications and design of the test chamber are adopted from the ASTM Designation: E2945 − 14. Results indicated that the new method is useful for an unlimited number of tests of an unlimited number of laminates. The conducted tests proved that the local laminate normally used for food packaging showed good results in terms of its oxygen transmission rate.

Car-Following Dynamics, Characteristics, and Model Based on Interaction Potential Function

To model the car-following behavior more accurately, we carried out the molecular similarity analysis between the vehicles on the road and the inert gas system, comparing vehicles with microscopic particles in long and narrow pipes. The complex car-following interaction behavior is simplified into a dynamic process of the follower car that is constantly seeking to maintain the required safety distance from the leading vehicle. Through mathematical derivation of the Lennard–Jones potential function suitable for thermodynamic analysis of inert gas systems, the influence of each variable on the potential energy is clarified, and the existing problems of the existing molecular car-following model are analyzed, referring to the general Lennard–Jones potential function to build the vehicle interaction potential function. Considering the impact of the road wall potential generated by the lane boundary, a car-following model based on Lennard–Jones interaction potential is presented. The simulation test results show that compared with the existing molecular car-following model and IDM model, the average absolute error and root mean square error of the vehicle acceleration results obtained by this model and the actual data are lower, which proves that the vehicle is based on the Lennard–Jones interaction potential. The vehicle-following model based on Lennard–Jones interaction potential has a better fitting effect on the real vehicle-following behavior.

Selection of an Inert Gas System for the Transportation of Direct Reduced Iron

Direct reduced iron (DRI) can create significant risks such as ignition, explosion, and fire because of the oxidation reaction in case when DRI undergoes spontaneously heating and comes in contact with oxygen or water. For this reason, the transportation of DRI is classified as a dangerous task of which the inert process should be done in the ship’s holds. Many studies have been conducted on the production and production stages of DRI and other areas of use of inert gas, but no studies have been conducted on the safe transportation of this cargo by ships. This study analyzes the criteria and alternatives for selecting the inert gas system for the benefits of investors and shipowners in the shipping industry. The intuitionistic fuzzy TOPSIS (IF-TOPSIS) method is implemented to conduct the decision-making process. As a result of this study, preferences for candidate inert gas systems are modelled. Port facility nitrogen generator is selected as the most suitable inert gas system among alternative inert gas systems based on predetermined criteria.

Computational Model for Electrochemical Gas Separation and Inerting System

In July 1996, TWA flight 800 crashed into the Atlantic Ocean only 12 minutes after takeoff killing all 230 people on board. After a 4-year investigation into this catastrophe, the National Transportation Safety Board concluded that the accident was probably caused by the explosion of flammable fuel vapor in the Boeing 747’s center fuel tank. Following this landmark incident new regulations for aircraft fuel tank inerting were developed to prevent such explosions. Fuel tank inerting is the process of reducing the flammability of the fuel vapor by restricting the oxygen concentration in the ullage (air volume above the fuel) to a safe value – 12% for commercial aircraft and 9% for military aircraft. Generally, inerting is carried out by driving oxygen out the ullage using an inert gas like nitrogen.Existing inerting technologies include systems like liquid nitrogen, explosion suppressant foam, halon extinguishment, and on-board inert gas generation systems (OBIGGS). Compared to other techniques, OBIGGS is seen as viable option since nitrogen enriched air (NEA) can be produced during flight by supplying pressurized air into separation modules that preferentially retain nitrogen while allowing oxygen to escape. However, such systems are expensive and consume substantial amounts of energy, while also undergoing premature failure. Additionally, the NEA generation rate is fixed in such systems, whereas the actual NEA requirement depends on the aircraft’s flight stage. Thus, incumbent technologies are designed based on the highest demand making them overweight and expensive.Here, we propose a novel on-board electrochemical gas separation and inerting system (EGSIS) to overcome such problems. EGSIS is an electrically powered system that can be used to produce and supply NEA to the fuel tank. It combines a polymer electrolyte membrane (PEM) electrolyzer anode wherein water is dissociated to generate oxygen, and a PEM fuel cell cathode where oxygen from the inlet air inlet is reduced to produce humidified NEA as the output gas. After proper dehumidification, the NEA can be supplied directly to the ullage to reduce its oxygen concentration. Unlike current technologies, the NEA production rate in EGSIS can be easily varied with demand just by controlling the voltage applied to the system. Experimental investigations of EGSIS have been previously conducted by our group. This paper represents the first attempt to model and simulate EGSIS.We present a two-dimensional mathematical model of a single cell EGSIS that provides a foundation for the simulation and analysis of a full-scale EGSIS module. A single phase, two-dimensional, steady state, isothermal model is implemented in an EGSIS cell using COMSOL. Various EGSIS performance parameters such as current densities, reactant concentration distributions, and polarization curves are investigated as a function of operating voltage and temperature. The model involves the material properties of the various components including the polymer electrolyte membrane, the catalyst later and gas diffusion media; the transport of water vapor and air in the anode and cathode flow field channels, respectively; the transport of protons and water in the catalyst layer and the membrane; and the transport of electrical charge in the solid phase. The governing equations include continuity and steady-state incompressible Navier-Stokes equations. Additionally, species transport is modeled using the generalized Stefan-Maxwell equations whereas the Butler-Volmer equation is employed for charge transport. All of these coupled model equations are solved by the finite element method using the COMSOL Multi physics software package. The results from the computational model are then compared and validated with our experimental results for various operating conditions. Different operating strategies are explored with the goal of improving system performance. The simulated results reveal the influence of temperature, reaction flowrate, and optimized material properties on EGSIS performance. This model also provides a base for future research into the effect of alternate catalysts and gas diffusion media. It also serves as a foundation for the analysis of a practical EGSIS stack.

(Invited) Electrocatalytic Reduction of Highly Inert Redox Probes: Arsenates, Nitrates, Chlorates, As Well As Carbon Dioxide and Nitrogen in Acid Medium

Arsenates(V), nitrites(III), nitrates(V), chlorates(V), as well as carbon dioxide (CO2) and nitrogen (N2) are electrochemically highly inert systems during reductions. There is also a problem of the competitive hydrogen evolution reaction in acid media, particularly when noble metal electrocatalysts are considered. But arsenates, nitrates, chlorates and CO2 (but not N2) can adsorb and undergo activation on noble metal (platinum group metal and alloyed) catalytic nanoparticles. Among important issues is the presence of monoatomic hydrogen highly active centers and/or the feasibility of adsorptive activating interactions with metallic or metal oxide sites.On electrochemical grounds, noble metal nanoparticles (Pt, Rh, Ir, Pd, as well as bimetallic PtRu or PtSn), when deposited on an inert electrode substrates, exhibit electrocatalytic properties during reduction of arsenates, nitrates and chlorates in acid medium (e.g. 0.5 mol dm-3 H2SO4). For example, upon application of the appropriate potential, both As(III) and As(V) are preconcentrated and activated on surfaces of Pt-type nanoparticles. Consequently, the presence of respective adsorbates can monitored under voltammetric conditions. Population of protons does affect the systems’ electrochemical characteristics. The nature of the voltammetric reduction peaks of the adsorbates of arsenates(V), nitrates(III,V), chlorates(V), and even CO2 is strongly dependent on the preconcentration or activation potential. While the reduction and deposition of arsenite(III) and nitrate(III) is induced by adsorbed hydrogen on Pt formed at potentials lower than 0.25 V (vs. RHE), the adsorption, preconcentration and activation of arsenate(V) and chlorate(V) can be readily achieved at Pt oxides generated at Pt nanoparticles at potentials higher than 0.85 V (vs. RHE). The dynamics of the electroreduction of chlorates can be significantly enhanced through utilization of bimetallic PtRu or PtSn catalysts, in which specific interaction between Pt catalytic sites and the alloying metal (e.g. Ru or Sn) affect the electronic structure, chemisorptive properties and activity of platinum. Carbon dioxide is strongly adsorbed on surfaces of Pt-based catalysts and, subsequently, reduced to CO adsorbate; obviously it can be re-oxidized in the reverse positive-going voltammetric potential scan. While nitrogen does not interact specifically with noble metal catalytic centers, and its reduction is practically hindered by hydrogen evolution, immobilization of noble metal (e.g. Pd) nanostructures within polynuclear oxometallate networks leads to better selectivity and permits some electroreduction of nitrogen parallel to hydrogen evolution. A unique feature of the adsorbed As(III) and As(V) oxo species is the ability to agglomerate and form stable polynuclear electroactive conducting-polymer-like films on noble metal nanoparticles thus modifying their catalytic reactivity. Electrochemical experiments are supported by the data from scanning and transmission electron microscopies and Raman spectroscopy.