Oxygen Research Articles

Optimizing the Synthesis of Titanium Carbide-Bismuth Oxide for Enhanced Antimicrobial Properties.

Background The two-dimensional MXene, known as titanium carbide (Ti₃C₂), is characterized by its substantial interlayer spacing, extensive surface area, hydrophilic nature, exceptional thermal stability, and outstanding electrical conductivity. These distinctive attributes render Ti₃C₂ an ideal candidate for detecting target analytes and immobilizing biomolecules. Bismuth oxide (Bi₂O₃), an essential compound of bismuth, frequently acts as a foundational element in bismuth chemistry. Its applications are diverse, from fireworks to oxygen gas sensors and solid oxide fuel cells, with particular emphasis on its behaviour under elevated temperatures and pressures. Notably, phase transitions to various polymorphs, which remain metastable at room temperature, have been documented under these conditions, indicating potential for numerous applications. Integrating MXene with Bi₂O₃ composites holds significant promise for advancements in energy-related electronics, sensing technologies, and photocatalytic processes. Objective To optimize the synthesis of titanium carbide-bismuth oxide (Ti₃C₂-Bi₂O₃) nanoparticles to enhance their antimicrobial activity by identifying the best synthesis conditions and assessing their effectiveness against various microbial pathogens. Materials and methods The preparation of Ti₃C₂ MXene involves dissolving lithium fluoride in hydrochloric acid, followed by Ti₃AlC₂ and stirring at 40°C for 48 hours. The resulting pellet is then dispersed in ultrapure water and centrifuged to obtain the MXene dispersion. Bi₂O₃ nanoparticles are prepared by preparing bismuth nitrate pentahydrate in nitric acid and adding sodium hydroxide to adjust the pH. The resulting white precipitate is filtered, washed, and dried before being calcined at 400°C for two hours to produce Bi₂O₃ nanoparticles. The Ti₃C₂-Bi₂O₃ composite is synthesized by adding Bi(NO₃)₃ solution to a 5 mg/mL Ti₃C₂Tx MXene solution. The reaction solution is heated to 160°C, and the resulting black powder is labelled as x% Bi₂O₃/MXene. The antimicrobial efficacy of the nanoparticles is assessed using the disk diffusion method. The zones of inhibition are measured and analyzed as indicators of antimicrobial activity. Results The scanning electron microscopy (SEM) analysis revealed the presence of Bi₂O₃ particles alongside Ti₃C₂​​​​​​​ nanosheets, while the X-ray diffraction (XRD) analysis and energy-dispersive X-ray spectroscopy (EDS) confirmed the high crystallinity of the compound. Furthermore, the compound was determined to be impurity-free and demonstrated antimicrobial properties. Conclusion The XRDanalysis confirms the effective integration of various materials and the existence of crystalline phases. SEMprovides insights into the morphology and organization of particles within sheets, whereas EDSassesses the elemental composition and its uniform distribution. These studies demonstrate the synthesis of Ti₃C₂-Bi₂O₃​​​​​​​ composites, suggesting their potential for usage in applications involving antimicrobial action.

Is it oxygen, or electrons, that our respiratory system delivers?

Respiration involves the inspiration of atmospheric gases. Arguments are put forth that it is not oxygen gas that passes from the alveoli to the capillaries, but electrons extracted from the oxygen. Those electrons are theorized to bind to hemoglobin. They are then passed by the circulation directly to the tissues, where they support metabolism. Issues confronting the standard respiratory paradigm are identified, while various observations are put forth that seem consistent with the direct role of electrons in the respiratory process. If the hypothesis is validated, then a direct link will have been established between respiration and metabolism.

Long-term hypothermic storage of oocytes of the European common frog Rana temporaria at various pressure regimes in gas mixtures based on oxygen, carbon monoxide, and nitrous oxide

In recent years, the challenge of preserving amphibian biodiversity has increasingly been addressed through technologies for the short-term storage of unfertilized spawn at low positive temperatures. Previously the possibility of using a 6.5 atm gaseous mixture of carbon monoxide and oxygen for prolonged hypothermic preservation of unfertilized oocytes for more than 4 days was shown. This study aimed to investigate the viability of oocytes R. temporaria preserved under conditions of hypothermia at 2.5, 3 and 6.5 excess atm pressure in the various gas mixture compositions (CO, N2O, O2) and pure oxygen. The use of pressure up to 3 excess atmospheres was significantly beneficial compared to 6.5 atm at the 7 days storage period. The results indicate that oxygen pressure is a critical factor in maintaining oocyte viability. Admixing CO or N2O to oxygen reduced variability in the results but did not significantly affect the measured indicators (fertilization, hatching) in the experimental groups. The composition CO + O2 (0.5/3.5 ratio, 3 excess atm) reliably extended the shelf life of viable oocytes, indistinguishable from native controls by fertilization and hatching rates, to 4 days. After 7 days, oocytes exhibited fertilization and hatching rates that were 79 % and 48 % compared to native control. Reducing the pressure of the preserving gas mixture to 3 atm, as utilized in this study, simplifies the practical implementation of gas preservation technology for maintaining endangered amphibian species during breeding in laboratory conditions.

Unparalleled single-atom catalytic efficiency of TM@Al12P12 (TM = Fe, Co, Ni, Cu) nanoclusters toward oxygen evolution reaction (OER)

Global warming is an unparalleled challenge to the globe. The increased usage of fossil fuel has significantly increased the CO2 level in the environment. Thus, scientists have diversified their attention towards other energy resources. Hydrogen energy represents a sustainable resource of green energy, where hydrogen and oxygen gases are converted into high amounts of energy without emitting greenhouse gases. In this work, we evaluated the potential use of transition metal (TM) doped Al12P12 single atom catalysts (SACs) toward the oxygen evolution reaction (OER) on the basis of the density functional theory (DFT) calculations. Results have shown that the highest activity is realized by the Co@Al12P12 SAC. This study represents another milestone in our quest of exploring the applicability of different TM@Nanocage systems as SACs for water electrolysis. We hope that this study will assist in the full realization of the water splitting reaction to produce hydrogen energy fuel.

Engineering Oxygen-Independent NADH Oxidase Integrated with Electrocatalytic FAD Cofactor Regeneration.

An electrochemically mediated enzyme process for nicotinamide adenine dinucleotide (NADH) oxidation and biosensing has been developed in which the oxygen-dependent activities of wild-type NADH oxidase are replaced by electrochemical regeneration of the flavin adenine dinucleotide (FAD) cofactor in the active site. Consequently, the present bioelectrocatalysis does not rely on a continuous oxygen supply through bubbling air or pure oxygen in biosynthetic applications, which reduces enzyme stability. The coupled electrochemical and enzymatic catalysis is achieved through a combination of enzyme immobilization on the electrode and electrochemical oxidation of FADH2 in the active site mediated by the electron transfer mediator ferrocene carboxylic acid (FcCA). Furthermore, to minimize the effect of dissolved oxygen when the electrocatalytic process is exposed to air, we successfully designed mutations at the Leu40 and Cys42 sites of Leuconostoc mesenteroides (LmNOx) to block the oxygen passage into the active site and to eliminate the native FAD cofactor regeneration half-reaction. The engineered enzymes, whose activities are significantly reduced or inactive in solution, are electrocatalytically active toward conversion of NADH to NAD+, demonstrating successful FAD cofactor regeneration in the active site via electrochemistry. Finally, we developed two highly responsive electrochemical biosensors for NADH detection which has a superior substrate specific to standard detectors using metal electrodes, and comparable detection range and detection limit (1-3 μM).

Numerical investigation of liquid oxygen filling process in liquid rocket engine by a multi-dimensional co-simulation method

The liquid oxygen filling process in the thermal component downstream of the valve directly affects the starting performance and working reliability of the liquid rocket engine. The filling process is reproduced with a multi-dimensional co-simulation method including one-dimensional system simulation and three-dimensional component simulation, the former provides dynamic flow data for the latter to calculate the filling process. The characteristics of the flow and evaporation and the phenomenon of gaseous oxygen residue are investigated. The results indicate that the simulated pressure value and tendency in the thermal component agree well with the experiment. The flow and evaporation reach a temporary equilibrium due to the flash boiling of the superheated liquid oxygen in the thermal component. The pressure in the combustion chamber downstream of the thermal component plays an important role in breaking the equilibrium and promoting the transition from superheat to supercool state of liquid oxygen. Additionally, the volume proportion of residue gaseous oxygen is 35 % at ignition time, which is far from the ideal state and affects the temperature measurement in the experiment. 26 % of the gaseous oxygen has not been discharged in time, leading to the injection instability in the injection region away from the inlet.

A novel fuel cell cathode hybrid intake structure design and control for integrated hydrogen energy utilization system

The typical Integrated Hydrogen Energy Utilization System (IHEUS) does not recycle oxygen. For maximizing the system's efficiency, this study proposes a method for recycling byproduct oxygen in a Fuel Cell (FC) hybrid cathode intake structure and its control. By introducing the pure oxygen produced as a byproduct of hydrogen production into the FC, a hybrid cathode intake structure is formed with the air branch. To control this structure, models of the oxygen and air branch, and the FC stack are established. Subsequently, using BiLSTM network to learn historical data and extract relevant features, the output power demand of the FC system is predicted. Based on the prediction results, the required gas flow is calculated, and a fuzzy PID control strategy is employed to adjust the opening of the solenoid valve to change the gas flow to meet the demand. Finally, comparative studies show that our FC system, operating in a pure oxygen state, outperforms conventional air intake design: heat production increases by 13 %, electric efficiency improves by 20 %, and pure water savings reach 65.57 %. The air compressor witnesses a substantial 37.63 % reduction in power consumption, contributing to an overall energy efficiency increase of 8.92 % for the IHEUS.

Hypoxic irreversible brain cells damage, associated risk factors and antihypoxants

It is reported that in the final stage of many diseases the immediate cause of biological death in humans and warm-blooded animals is hypoxic irreversible damage to brain cells. This explains the fact that to prevent biological death in all critical conditions without exception, inhalation with breathing gases containing oxygen has long been successfully used. This is also why oxygenation of the blood is considered one of the main conditions for preserving human life in all critical situations and forms the basis of emergency medical care in the intensive care unit. However, inhalation of oxygen gas and increasing blood oxygen saturation should be carried out as early as possible, and more precisely - before the onset of the stage of hypoxic irreversible damage in brain cells. The fact is that after the onset of irreversible damage brain cells die even in the presence of oxygen. In this connection, the mechanisms of adaptation of the organism to oxygen deficiency play a great role for longer preservation of brain cells viability and human life in conditions of hypoxemia. In order to increase resistance to hypoxemia, antihypoxants are traditionally used. But they can preserve the viability of brain cells not always, but only if they are introduced into the body before the onset of hypoxic irreversible damage to brain cells and in the case of unused reserves of adaptation to hypoxemia in the body. Risk factors of hypoxic irreversible damage of brain cells are indicated, among which excessively long duration of hypoxemia and hyperthermia are emphasized. It is shown that the most important circumstance for the development of hypoxic irreversible damage of brain cells is not so much the degree of hypoxemia as the degree of hypoxia of brain tissue and its duration, which exceeds the period of human resistance to hypoxia. It has been shown that human resistance to hypoxia can be assessed using the Stange test. It has been reported that fever and local cerebral hyperthermia decrease, and hibernation and local cerebral hypothermia increase, the resistance of brain cells to hypoxia. In this regard, recommendations not only to eliminate fever and local inflammatory processes in the head, but also recommendations to reduce brain temperature are highly appropriate to improve resistance to hypoxia. It is pointed out that among the methods of local therapeutic hypothermia, targeted temperature management is the most advanced. In addition, it is reported that in recent years a new group of promising antihypoxants - alkaline solutions of hydrogen peroxide - has been created. It is shown that hydrogen peroxide is able to decompose very quickly into water and oxygen gas under the action of catalase, which is found in all tissues. The peculiarities of using alkaline solutions of hydrogen peroxide as antihypoxants we all have to study in the future.

Ultrasound-assisted water oxidation: unveiling the role of piezoelectric metal-oxide sonocatalysts for cancer treatment

Ultrasound radiation has been widely used in biomedical application for both diagnosis and therapy. Metal oxides nanoparticles (NPs), like ZnO or TiO2 NPs, have been widely demonstrated to act as excellent sonocatalysts and significantly enhance cavitation at their surface, making them optimal for sonodynamic cancer therapy. These NPs often possess semiconductive and piezoelectric properties that contribute to the complex phenomena occurring at the water-oxide interface during sonostimulation. Despite the great potential in applied sonocatalysis and water splitting, the complex mechanism that governs the phenomenon is still a research subject. This work investigates the role of piezoelectric ZnO micro- and nano-particles in ultrasound-assisted water oxidation. Three metal oxides presenting fundamental electronic and mechanical differences are evaluated in terms of ultrasound-triggered reactive oxygen species generation in aqueous media: electromechanically inert SiO2 NPs, semiconducting TiO2 NPs, piezoelectric and semiconducting ZnO micro- and nanoparticles with different surface areas and sizes. The presence of silver ions in the aqueous solution was further considered to impart a potential electron scavenging effects and better evaluate the oxygen generation performances of the different structures. Following sonoirradiation, the particles are optically and chemically analyzed to study the effect of sonostimulation at their surface. The production of gaseous molecular oxygen is measured, revealing the potential of piezoelectric particles to generate oxygen under hypoxic conditions typical of some cancer environments. Finally, the best candidates, i.e. ZnO nano and micro particles, were tested on osteosarcoma and glioblastoma cell lines to demonstrate their potential for cancer treatment.

Overview of Strategic Supply Management of Oxygen for COVID- 19 Pandemic Patient Care in Sri Lanka

The immensurable COVID-19 pandemic has a ceaseless destabilizing effects on health systems, economies, and societies around the world. Total number of 671,756 positive cases have been reported in the country and 654,910 of them have recovered from the disease with 16,808 number of deaths out of the population of 21.8 million up to December 2022. Immense burden to the health system and heavy death rate was reported during the 3rd wave for which mainly the delta variant of COVID virus was responsible. Total number of 491,508 patients and 14375 number of deaths as well as nearly 3500 Oxygen dependent patients were managed per day in ICU, HDU, and inward set up using Oxygen concentrator, bi-pap and c -pap machine during 3rd wave. During this period, Ministry of Health had been urged to reassess its hospital surge capacity in relation to predicted COVID patient load. Based on that, the increasing COVID-19 surge has warranted the rapid hospital facilities expansion in every aspect especially in facilities for Oxygen therapy. Ministry of Health, Sri Lanka had to develop strategies for Medical Oxygen management to fulfill its rising demand. All those interventions were focused to improve the accessibility and availability of medical oxygen while preventing irrational use and wastage of Oxygen. The ultimate goal of spending such cost was to prevent morbidity and mortality due to poor access of oxygen. To improve the efficiency and effectiveness of medical oxygen gas utilization, it was important to monitor the capacity improvement and supply process.

Driving Pressure-guided Ventilation in the Intensive Care Unit and Operating Room

Mechanical ventilation is the cornerstone of management for critically ill patients and those undergoing general anesthesia. Currently, lung protective ventilation strategies primarily include low tidal volume, positive end-expiratory pressure, and limited pressure, combined with certain recruitment maneuvers. Recently, driving pressure has been proposed as a key parameter to optimize mechanical ventilation. This study reviewed the relevant literature and suggests that driving pressure may be correlated with improved survival in patients with acute respiratory distress syndrome, enhanced intraoperative pulmonary mechanics, reduced postoperative atelectasis, and better gas exchange and oxygenation, even in normal lungs. However, the correlation between driving pressure and postoperative pulmonary complications has also been described as controversial. These findings could serve as a reference for future clinical practice.

High-temperature corrosion mechanisms of a Ni-based alloy in simulated multi-source organic waste co-incineration environments

Due to the new trend of co-incinerating municipal solid waste (MSW) with sewage sludge, medical waste, or industrial organic waste to attain a “waste-free” status, mixing of multi-source organic wastes (MSOW) increases the complexity of solid waste, which fluctuates the composition of corrosive species in the boiler. The fluctuation of corrosive species alters the alkali metals/S/Cl ratios and increases the uncertainties of high-temperature corrosion of boiler key components. The corrosion behaviors and mechanisms in varying compositions of corrosive species are complex and remain elusive. To investigate the corrosion characteristics during the co-incineration of MSOW, this study examined the corrosion mechanisms of a nickel-based Ni59.08Cr24.31Al10.74W5.3B0.57 alloy in simulated co-incineration environments of MSOW. The environment contained either HCl, NaCl, or SO2 in wet oxygen at 600 °C. For each case experiment, the maximum possible value of each corrosive species expected in the actual incinerator and/or its absence was considered. HCl of either 0 or 1500 ppm, SO2 of 0 or 300 ppm, and NaCl of 0 or 50 mg/cm2 were systematically used in each experiment. The influence of each corrosive condition on the corrosion of the alloy was evaluated by mass gain measurements, and the corrosion mechanisms were elucidated through SEM, EDS mapping, XRD, XPS analyses, and thermodynamic equilibrium calculations. The results revealed that NaCl salt and HCl gas in wet oxygen have complementary effects, which accelerated the corrosion of alloy, reaching ∼ 65.6 mg/cm2 over one week. HCl enhanced the corrosion by affecting the chemical reactions that regenerated NaCl, which participated in prolonged corrosion processes. SO2 reduced the mass gain of the alloy to 38.4 mg/cm2. SO2 participated in the sulfation of NaCl, forming a mixed layer of Na2SO4 and (Al/Cr)2O3, reducing the mass gain by 1.71 times. In the environment without NaCl, SO2 helped in the formation of a protective oxide layer, which prevented HCl from reaching the alloy, reducing the corrosion impact by 23.5 times.

Mechanistic understanding of oxygen spillover enables efficient propane combustion over Pt/AlSOx catalyst

Understanding of the mechanism of saturated alkanes catalytic combustion is crucial for the petrochemical industrial exhaust elimination. Noble metals are commonly proposed to be the active sites for C–H bond activation of saturated alkanes, whereas the critical role of support is largely underestimated. Herein, we reveals a novel pathway for propane activation and combustion on acidic support of Pt catalyst, driven by oxygen spillover, which differs significantly from previously reported reaction mechanisms. Specifically, the Pt/AlSOx-I catalyst was prepared by pyrolyzing the Al2(SO4)3 sol–gel to obtain the acidic micro-mesoporous AlSOx support, followed by loading the Pt active sites using wetness impregnation. In comparison to Pt catalysts supported by Al2O3 nanoparticles (10 nm) or commercially available common γ-Al2O3, the Pt/AlSOx-I catalyst demonstrates superior catalytic activity for propane combustion. It is found that gaseous oxygen species activated on Pt active sites spillovers to acidic support of Pt/AlSOx-I and then drives propane to activation and further oxidation on acidic support, thereby remarkably decreasing the apparent activation energies (Ea) from 112.4 to 72.0 kJ·mol−1. Kinetic results suggest that the negative effect of oxygen competitive adsorption is weakened because propane can be activated on the acidic AlSOx support. Additionally, high proportion of metallic Pt species benefits to gaseous oxygen activation as observed on Pt/AlSOx-R, leading to the further increased catalytic activity with highest specific mass reaction rate of 170.2 μmol gPt−1 s−1 and TOFPt of 0.289 s−1 at 220 °C. Our primary results provide novel insights into revealing the reaction mechanism of saturated alkanes combustion on dual active sites.

Carbon and oxygen recycling strategies in CO2-to-sustainable synthetic fuel production: Recycling route, techno-economics and carbon intensity

Anthropogenic carbon utilization and recycling into fuel using renewably sourced or nuclear energy and water is a potentially valuable strategy for replacing fossil fuels. The high-level elemental balance of the CO2-to-Fuel system involves oxygen rejection, with CO2 and H2O reduction dependent on crucial process steps that determine performance metrics such as energy efficiency, element utilization, economics, and carbon footprint. This study elaborates on carbon and oxygen recycling strategies for producing sustainable synthetic hydrocarbon fuels. It covers electrolysis routes, internal recycling pathways, and additional processes to increase synfuel yield. An element balance was derived for four process schemes with systematic recycling route variations, facilitating a comparison of elemental efficiencies: (1) carbon utilization (80.7–90.6 %), (2) hydrogen efficiency (4.8–30.8 %), and (3) oxygen gas rejection rate (56.8–63.1 %). A process flow diagram was proposed to discuss techno-economics through the existing route via the Fischer-Tropsch process. The energy intensity ranged from 118.5 to 177.4 GJ per tonne of synfuel, and the energy conversion efficiency varied from 0.24 to 0.36. We further evaluated the carbon intensity, considering the primary energy efficiency to show the different energy supply scenarios, including (i) 100 % fossil-based (506–1416 kgCO2eq/GJFuel), (ii) grid power with fossil fuel (246–687 kgCO2eq/GJFuel), (iii) hybridization of renewable sources (biomass and wind power) (42–78 kgCO2eq/GJFuel), and (iv) nuclear energy (7–18 kgCO2eq/GJFuel). This work considers the interplay between oxygen rejection, syngas conversion, and combustion, undertaking a novel analysis to bridge the high-level elemental analysis with detailed metrics calculations.

Cardiorespiratory and muscle oxygenation responses to voluntary hypoventilation at low lung volume in upper body repeated sprints.

To investigate the impact of voluntary hypoventilation at low lung volumes (VHL) during upper body repeated sprints (RS) on performance, metabolic markers and muscle oxygenation in Brazilian Jiu-Jitsu (BJJ) athletes. Eighteen male well-trained athletes performed two randomized RS sessions, one with normal breathing (RSN) and another with VHL (RS-VHL), on an arm cycle ergometer, consisting of two sets of eight all-out 6-s sprints performed every 30s. Peak (PPO), mean power output (MPO), and RS percentage decrement score were calculated. Arterial oxygen saturation (SpO2), heart rate (HR), gas exchange, and muscle oxygenation of the long head of the triceps brachii were continuously recorded. Blood lactate concentration ([La]) was measured at the end of each set. Bench press throw peak power (BPPP) was recorded before and after the RS protocol. Although SpO2 was not different between conditions, PPO and MPO were significantly lower in RS-VHL. E, HR, [La], and RER were lower in RS-VHL, and VO2 was higher in RS-VLH than in RSN. Muscle oxygenation was not different between conditions nor was its pattern of change across the RS protocol influenced by condition. [La] was lower in RS-VHL than in RSN after both sets. Performance was significantly lower in RS-VHL, even though SPO2 was not consistent with hypoxemia. However, the fatigue index was not significantly affected by VHL, nor was the neuromuscular upper body power after the RS-VHL protocol. Additionally, [La] was lower, and oxygen consumption was higher in RS-VHL, suggesting a higher aerobic contribution in this condition.

(Invited) Understanding Photo-Driven Water Oxidation Mechanisms

Water oxidation is an important reaction that produces electrons and protons, which are important for downstream reactions such as hydrogen production and carbon dioxide reduction. Presently, the slow water oxidation is a key limiting factor for the development of hydrogen production and/or carbon dioxide reduction into practical solar energy storage technologies. An important reason for the slow progress in solve water oxidation problems is the lack of knowledge on the detailed mechanisms by which water is oxidized. As a multi-step process, the reaction involves at least 4 protons and 4 holes (when the desired product is oxygen gas). Intuitively, the coordination of charges and protons plays a critical role, but the details remain unknown. In this talk, we report our recent progress in understanding how water oxidation is influenced by surface hole behaviors. Using an Ir-based catalyst that features atomically defined structures, we were able to systematically vary a number of parameters, including the hole concentration, the density of active sites, as well as the properties of the supporting substrate that determines hole accumulation. It was found that matching the concentrations of surface holes and active site densities is critical. It was also revealed that the support substrate could have a profound influence on the reaction kinetics, even though they do not directly participate in the reactions. This knowledge is expected to propel the development of catalysts for improved water oxidation under photochemical conditions.

Limiting Current Density in Water Vapor-Fed Polymer Electrolyte Membrane Electrolyzers

Polymer electrolyte membrane water electrolyzers (PEMWE) are a critical technology in development for addressing the need for efficient hydrogen production. In order to make hydrogen a cost-effective fuel or industrial feedstock, the overpotentials across the cell needs to be decreased and platinum-group metal loading reduced. Devising novel electrode structures that enable ultra-high current densities at low oxygen evolution reaction (OER) catalyst (e.g. Iridium oxide) loadings is one approach to achieving efficiency and cost targets. One of the overpotentials that needs to be addressed is due to mass transport limitations within the porous transport layer (PTL) and anode catalyst layer, which could be a limiting factor at ultra-high current densities. When operating at ultra-high current densities, the rate of the OER may reach a point at which oxygen gas bubbles fill the pores of the anode catalyst layer PTL, blocking access of liquid water to the anode catalyst layer. Because of this, there is a possibility that the cell will rely on water vapor diffusion through the evolving oxygen gas to deliver the water reactant to the OER catalyst. To assess the limitation of a PEMWE while relying on water vapor diffusion, a commercially manufactured membrane electrode assembly (MEA) was tested by flowing water vapor into the anode as the reactant. With the aim of identifying a limiting current density (LCD) of the electrolyzer under these conditions, potentiostatic polarization curves were obtained for a range of relative humidities (RH) and back pressures. The RH was varied to assess the impact of reactant concentration on the LCD, while the back pressure was varied to identify the impact of the molecular gas diffusion coefficient on the LCD. In this presentation, we will present our analysis of the significance of the water vapor diffusion transport resistance through the pressure-dependent resistance evaluation. Furthermore, we will discuss application of this approach to evaluating the impact of vapor operation on membrane water transport and OER reaction kinetics.

(Invited) Past, Present and Future for Electrochemical Gas Sensors in Energy Applications

The markets for modern low-cost electrochemical gas sensors have been growing for longer than sensors have been around. Energy markets for gas sensors include the oil, gas and electricity industries as well as the new developing and fast growing green energy sectors. The primary gases to detect include combustible hydrocarbons, oxygen, and toxic gases. Specifically, we are interested in methane (blue and green), ammonia, and H2 for the renewable energy sectors but include hydrocarbon fuels and CO2 as a greenhouse gas emission. The reasons for monitoring crosscut all areas of the energy business and include applications in production, transport, storage and use. Primary sensor uses include: 1) health and safety (people and assets), 2) leak detection and isolation to help mitigate product losses, 3) monitoring to protect the environment and 4) measurements for process control and efficacy. Each of these areas of sensing have special requirements and demand cost-effective and time efficient sensor performance in many and varied real world scenarios.Electrochemical gas sensors have a long and rich history starting with the commercialization of the first practical potentiometric CO2 gas sensor by Severinghaus in 1954 and the O2 amperometric sensor by Clark in 1956 that launched the modern blood gas analysis industry. Additional milestones include the introduction of the “diffusion electrode” in 1968 creating the modern amperometric sensor which has produced a large array of sensors for toxic and hazardous gases including H2, ammonia, and other energy gases. Progress has been made in the field of electrochemical gas sensors, not only in improving performance, sensitivity, selectivity, response time, and stability, but also in logistical properties including miniaturization, lower power consumption, low cost as well as communication and computation to make automated-operational systems. New high-volume production has contributed to lower costs commensurate with a chip-based sensor mentality. The evolution of one of the gas sensor technologies is given below (the room temperature AGS or amperometric gas sensor) and similar progress has been seen in mixed potential and solid state gas sensors.The growing understanding of the sensor’s fundamental electrocatalytic reactions has led to tailored designs of electrode-electrolyte combinations and packages for the various applications. Often ignored in sensor publications of performance, the fundamental electrocatalytic studies are poised to make significant advances in energy gas sensor selectivity and sensitivity. The additional implementation of intelligent algorithms (AI/ML) to make “smart” sensors and sensor arrays complements advanced nano-materials and designs for improving sensor performance. One major improvement is our understanding of the sensor response mechanisms at the electrocatalytic level. This new research will enable new electrochemical sensor advances that are poised to impact the health and wellbeing of both people and the planet. Ideas and concepts that significantly contribute to the safe and efficient rollout of the newest green energy platforms are presented. Figure 1

Theoretical Understanding of Stability of the Oxygen Electrode in a Proton-Conductor Based Solid Oxide Electrolysis Cell

The oxygen electrode in a proton-conductor based solid oxide cells is often a tripleconducting material that enables the transport and exchange of electrons (e), oxygen ions (O2), and protons (H+), thus expanding active areas to enhance the oxygen electrode activity. In this work, a theoretical model was developed to understand stability of triconducting oxygen electrode by studying chemical potentials of neutral species (i.e., μO2 , μH2 , and μH2O) as functions of transport properties, operating parameters, and cell geometry. Our theoretical understanding shows that (1): In a conventional oxygen-ion based solid oxide cell, a high μO2 (thus high oxygen partial pressure) exists in the oxygen electrode during the electrolysis mode, which may lead to the formation of cracks at the electrode/electrolyte interface. While in a proton-conductor based solid oxide cell, the μO2 is reduced significantly, suppressing the crack formation, and resulting in improved performance stability (2). In a typical proton-conductor based solid oxide electrolyzer, the dependence of μO2 on the Faradaic efficiency is negligible. Hence, approaches to block the electronic current can improve the electrolysis efficiency while achieving stability (3). The difference of the μO2 (thus pO2 ) between the oxygen electrode and gas phase can be reduced by using higher ionic conducting components and improving electrode kinetics, which lead to further improvement of electrode stability.

Dynamic Oxygen Collection Efficiency: Unraveling the Effects of Perovskites on Carbon Corrosion As Composite Catalysts for Oxygen Electrode

Introduction The composite catalyst comprising perovskite and carbon has been extensively studied as a catalyst for the oxygen evolution reaction (OER) at the oxygen electrode in alkaline media. However, the competitive corrosion of carbon under harsh OER potential necessitates additional caution when determining OER activity from the overall oxidation current. The use of a rotating ring-disk electrode (RRDE) is acknowledged for its ability to quantitatively determine the faradaic efficiency of the OER. [1] However, for practical applications, the generation of oxygen bubbles can cause unpredictable disturbance, leading to the erroneous collection efficiency. In this study, we aim to establish a dynamic current-response collection efficiency during the generation of oxygen bubbles. This was achieved by modelling with an Au/Au RRDE, well-known for its electrochemical stability under harsh conditions. In addition, using this calibrated collection efficiency, we investigate the influence of perovskite catalysts on the degradation behaviors of carbon materials at OER potentials in alkaline media. Materials and electrochemical measurements Measurements of oxygen gas collection efficiency were conducted using a modeled RRDE comprising an Au disk electrode and an Au ring electrode. The RRDE served as the working electrode, with a Pt wire as the counter electrode, a reversible hydrogen electrode (RHE) as the reference electrode, and a solution of Ar-saturated 1 mol dm-3 KOH as the electrolyte. The disk electrode underwent a 5-minute chronopotentiometry with varied oxidation currents, while the ring electrode underwent chronoamperometry at 0.3 V (vs. RHE). The collection efficiency was calculated from the ring current attributed to the oxygen 2-electron reduction reaction.Two kinds of perovskite catalysts, namely Sr2Co0.8Fe0.2O3Cl[2] (hereafter SCFOC) and LaCoO3 (hereafter LCO), and two carbonaceous materials, namely graphitized carbon black (TOKABLACK#3845, hereafter TB) and ketjen black (EC-600JD, hereafter KB), were used to evaluate the influence of perovskite on the carbon degradation behavior. Four composite catalysts, each comprising perovskite and carbon with a weight ratio of 5:1, were loaded on a disk electrode of the glassy carbon disk/Au ring RRDE. A cell analogous to the aforementioned design was assembled. Electrochemical measurements were conducted through chronoamperometry, employing various potentials at the disk electrode, and maintaining a potential of 0.3 V vs. RHE at the ring electrode, for a duration of 5 minutes. Results and discussion Figure 1 illustrates a three-dimensional representation of the oxygen gas collection efficiency of the Au/Au RRDE as two functions of disk current density and measurement time. It was evident that the oxygen gas collection efficiency varied significantly from the theoretical value (25.6 %) and was dependent on the disk current density and measurement time. The constrained solubility of oxygen in aqueous solution and the hydrophobic nature of the PTFE between the ring and the disk might cause a decrease in the collection efficiency due to the partial retention of oxygen bubbles on the electrode as the oxygen generation current increased and the measurement time elapsed. This suggests that, unlike typical solution reactions, the dynamic determination of the oxygen gas collection efficiency is essential, considering current density and measurement time.Figure 2 illustrates the computation of faradaic oxygen efficiency, utilizing dynamic oxygen collection efficiency. The composite catalyst composed of TB and SCFOC was taken as an illustrative example. The variation in collection efficiency, synchronized with the shape of disk current density, was employed in determining the faradaic oxygen efficiency. This dynamic collection efficiency yielded a comparatively smooth faradaic oxygen efficiency.Utilizing the calibrated faradaic oxygen efficiency, we proceeded to assess the capacity of carbon degradation by integrating the current density of the carbon oxidation reaction (COR) calculated by subtracting the OER current from the overall current. As depicted in Figure 3, the COR capacity as a function of the potential suggested that the components of the composite catalysts had distinct impacts on carbon degradation. Specifically, SCFOC appears to enhance degradation, whereas LCO exhibits a comparatively less pronounced effect.A more comprehensive discussion of these findings will be presented at the upcoming meeting.[1] I.S. Filimonenkov et al., Electrochim. Acta 321, 134657 (2019).[2] Y. Miyahara et al., Chem. Mater. 32, 8195 (2020). Figure 1