Oxygen Research Articles

(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

Electronic Structure Investigation of BSCF Catalysts during Electrochemical Water Electrolysis by Using Time Zero Analysis and Advanced Operando X-Ray Absorption Spectroscopy

The rapid increase in global energy demands and environmental awareness regarding the excessive use of fossil fuel has spurred significant academic interest in the development of alternative energy conversion and storage technologies that prioritize both efficiency and environmental sustainability. Among all kinds of renewable energy, hydrogen energy holds the potential to create a carbon free clean society, and a possible solution to the environmental issues.1 Electrochemical water splitting is considered as a greener approach for pure H2, which involved cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). The anodic OER is kinetically sluggish and considered as a rate determining step of the water splitting reaction. Therefore, it is necessary to develop OER catalysts with high activities.Perovskite oxides knows as a promising oxygen electrode catalyst due to their low cost, flexibility, and tailorable properties. However, most perovskite oxides possess poor electrical conductivity at room temperatures, and this limits their oxygen catalytic activity. In our work Ba0.5Sr0.5CoxFe1-xO3-δ (BSCF) catalysts with different cobalt and iron amounts where X=0, 0.2, 0.8, 1 were synthesized and investigated by time zero analysis and flow rate infinitization analysis which are electrochemical testing method that uses pressure to remove generated oxygen gas bubbles and provides accurate activity of the catalyst.2We find the volcano plot of the Fe amount and the OER activities, showing samples with X=0.8 have the best OER activities as Figure 1. Electronic structure of B-Site transition metal elements, oxygen vacancies, crystal structures and electrical conductivity are the key factors for determining the activities of Perovskite catalysts in OER.3Also it is quite important to determine the real active sites during the OER process by using advance operando techniques.Therefore, in order to investigate the in-depth mechanism of OER activities of Perovskite catalysts, the newly designed operando soft X-ray Absorption Spectroscopy (XAS) cells was utilized to analyze the subtle change as shown in Figure 2 on the oxygen K-edge (531 eV - 532 eV). Ba0.5Sr0.5Co0.8Fe0.2O3-δ has the most obvious changes in integral surface area at the O K-edge pre-edge region, which leads to the best activity among other BSCF samples. According to the Energy Dispersive X-ray Spectroscopy and Lattice Oxygen Evolution Mechanism, ions on the A sites (Ba2+,Sr2+) tend to dissolve and ions on the B sites (Co, Fe) are forming hydroxides (BOOH).Keywords: oxygen evolution reaction, BSCF catalysts, Time zero analysis, operando X-ray absorption spectroscopy Acknowledgements This work is based on results obtained from a project (JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan. Reference: (1) Rose, P. K.; Neumann, F. Hydrogen refueling station networks for heavy-duty vehicles in future power systems. Transportation Research Part D: Transport and Environment 2020, 83, 102358.(2) Nagasawa, K.; Matsuura, I.; Kuroda, Y.; Mitsushima, S. A Novel Evaluation Method of Powder Electrocatalyst for Gas Evolution Reaction. Electrochemistry 2022, 90 (1), 017012-017012.(3) Zhu, Y.; Zhou, W.; Shao, Z. Perovskite/carbon composites: applications in oxygen electrocatalysis. Small 2017, 13 (12), 1603793. Figure 1

Selectivity Study of Anodic Seawater Electrolysis Catalysts Using the Rotating Ring-Disc Electrode Method

Water electrolysis generating green hydrogen will play a vital role in achieving the net-zero 2050 goal; however, freshwater electrolysis will further strain an already strained supply of clean freshwater.1 If seawater electrolysis can be scaled successfully, it would provide an important source of green hydrogen. Current research on untreated, direct seawater electrolysis is limited, and only recently have studies emerged analyzing catalyst performance at near-neutral pH.2 At industrially-relevant current densities, the formation of corrosive hypochlorite must be considered as a secondary reaction.3 Hypochlorite forms through the chloride oxidation reaction (ClOR), which competes with the oxygen evolution reaction (OER) in seawater electrolysis.2 In this work, we discuss the limitations of the current methods for determining anodic catalyst selectivity between OER and ClOR. The short lifetime of hypochlorite can cause faradaic efficiency measurement methods such as titration or oxygen gas capture to become unreliable, as these tests require that the hypochlorite remain stable. Using a rotating ring-disc electrode (RRDE), we measure the selectivity of common OER catalysts in-situ (Figure 1a). Real-time hypochlorite sensing overcomes the challenge of measuring catalyst selectivity posed by the short lifetime of hypochlorite. Remarkably, a PtRu catalyst outperformed more common OER catalysts with the best in OER selectivity and low overpotential, a novel development in the field of near-neutral water electrolysis. We also determine that elevated heat and low chlorine concentration are conducive to improved OER selectivity on an IrO2 catalyst (Figure 1b). We hope this work will set the standard in catalyst benchmarking for seawater electrolysis catalysts and could lead to the development of catalysts for efficient, scalable, and sustainable hydrogen production from seawater. H. Jin et al., Sci Adv, 9, eadi7755 (2023) https://www.science.org/doi/10.1126/sciadv.adi7755.F. Dionigi, T. Reier, Z. Pawolek, M. Gliech, and P. Strasser, ChemSusChem, 9, 962–972 (2016) https://onlinelibrary.wiley.com/doi/full/10.1002/cssc.201501581.J. Guo et al., Nature Energy 2023, 1–9 (2023) https://www.nature.com/articles/s41560-023-01195-x. Figure 1. a) LSV profiles of common OER catalysts (solid line) and the corresponding faradaic efficiency (dashed line) for the OER, measured using the ring current of the rotating ring-disc electrode. Catalysts were tested in 0.5 M NaCl and buffered with KHCO3 to pH 8.5. b) A ternary plot depicting the effect of varying Cl concentrations and temperatures on the selectivity of an IrO2 catalyst at pH 8.5. Figure 1

Poly(3,4-ethylenedioxythiophene) (PEDOT) As an Electrocatalyst for Water Splitting: From Fundamental Insights to Practical Applications in Sustainable Hydrogen Production

Poly(3,4-ethylenedioxythiophene) (PEDOT) has recently emerged as a highly promising and versatile electrocatalyst for water splitting, a pivotal process in the realm of renewable energy conversion. This review comprehensively explores the multifaceted aspects of PEDOT's electrocatalytic prowess, covering its intrinsic properties, synthetic methodologies, catalytic mechanisms, and practical applications in the context of water electrolysis. PEDOT, [C2H4O2C4H2S]n a conductive polymer, exhibits unique features that render it particularly suitable for electrocatalysis. With its excellent electrical conductivity, notable stability, and facile synthesis, PEDOT stands out among its counterparts. These attributes make PEDOT an attractive candidate for addressing the challenges associated with the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), the two half-reactions constituting water splitting.One of the key advantages of PEDOT lies in its high surface area, which allows for increased active sites for catalysis. The tunable redox states of PEDOT further contribute to its electrocatalytic versatility, enabling tailored catalytic performance through controlled doping and modifications. The efficient charge transport properties of PEDOT are crucial for facilitating electron transfer during the electrocatalytic processes, ensuring high catalytic activity. This review delves into the simple fabrication of PEDOT-based electrocatalysts. Researchers have explored various strategies, including morphological control, doping with heteroatoms, and integration into composite materials, to enhance the catalytic performance of PEDOT. The rational design of PEDOT structures has demonstrated the potential to surpass the limitations of traditional electrocatalysts and unlock new avenues for efficient water splitting.In elucidating the mechanistic aspects of PEDOT's catalytic activity, the review investigates the intricate interplay of surface interactions, redox reactions, and mass transport phenomena. Understanding the fundamental principles governing PEDOT's electrocatalytic behavior is essential for optimizing its performance and guiding further developments in this burgeoning field. Simple electrodeposition method is carried out to polymerize EDOT. Cyclic voltammetry method was used for synthesizing PEDOT on nickel foam. Then the sample was heated at differnet temperatures.Hydrogen Evolution Reaction (HER) Overpotential:An overpotential of 170 mV at 10 mA/cm² is observed for the HER which indicates that PEDOT as an effective in catalyzing the reduction of protons to form hydrogen gas. A lower overpotential implies that PEDOT facilitates the electrochemical reaction at a lower energy input, showcasing its efficiency as an electrocatalyst for hydrogen production.Oxygen Evolution Reaction (OER) Overpotential:The PEDOT exhibits an overpotential of 300 mV at 10 mA/cm² for the OER which suggests its enhanced performance in catalyzing the oxidation of water to produce oxygen gas. While this overpotential is higher than that for the HER, it is still within a range that indicates good catalytic activity for the challenging OER.Surpassing Many Catalyst Behaviors:PEDOT's performance, as indicated by its low overpotentials, exceeds that of many other catalysts commonly used for water splitting reactions. This could include traditional metal-based catalysts or other conductive polymers, highlighting PEDOT's potential as a superior electrocatalyst. More electrochemical studies have been taken to prove practical application for PEDOT while the reported overpotentials are promising, and additional research and experimentation are being conducted to validate and understand PEDOT's practical application in real-world scenarios. This involve studying its stability over time, scalability, and compatibility with alkaline electrolyte systems and operational conditions. Figure 1

Corrosion Initiation on Reinforcing Steel with Mill Scale in Mortar

Corrosion of reinforcing steel rebar is the main cause of loss of the long-term reliability of concrete structures. When the rebar is corroded, the rust induces cracks and detachment of the cover concrete. The mill scale, a thick oxide film, is formed on the rebars when the rebar is hot rolled. The role of mill scale on the corrosion resistance of rebars in concrete has not been clarified, yet. This study studied the corrosion behavior of rebars with mill scale in mortar.The samples are commercial rebars with 19 mm diameter, which have a mill scale of several tens of micrometers in thickness. The rebars without mill scale prepared by the electrolytic polishing were used as the comparison samples. A Hyperbaric-oxygen accelerated corrosion test (HOACT) [1] was carried out using the rebars embedded in the mortar with a 5.5 mm cover thickness. To prompt the breakdown of passive film on the rebars, 2.1 M NaCl solution was mixed with the mortar. In the HOACT, pressurized oxygen gas is supplied to the sample, and the oxygen reduction reaction on the steel surface is enhanced, leading to the steel's corrosion acceleration. The oxygen pressure was 0.6 MPa and the test period was 14 days. The corrosion of the rebar with a mill scale was more significant than that without a mill scale. This result shows that the mill scale reduces the corrosion resistance of the steel rebar in concrete [2].To investigate the effect of the mill scale on the corrosion resistance of the rebar, anodic polarization measurements of the rebars with and without the mill scale were carried out in a saturated Ca(OH)2 solution containing Cl-. The pitting potential of the rebar with mill scale was more noble than that of the sample without mill scale. However, when the mill scale was scratched, the pitting potential was significantly shifted to the less noble direction, and it was below that of the rebar without the mill scale. These results show that the mill scale improves the corrosion resistance of the rebar in concrete, in contrast, the corrosion resistance of the rebar with a defective mill scale becomes even worse than that of the rebar without the mill scale [2].[1] K. Doi, S. Hiromoto, H. Katayama, E. Akiyama, J. Electrochem. Soc., 165(9), C582-C589 (2018).[2] K. Doi, S. Hiromoto, T. Shinohara, K. Tsuchiya, H. Katayama, E. Akiyama, Corrosion Science, 177, 108995 (2020).

Material Dynamics of Nickel (oxy)Hydroxide As an Alcohol Oxidation Electrocatalyst

Electrochemical alcohol oxidation is an attractive reaction for renewable-energy driven production of value-added chemicals, like precursors for acrylic (acrolein from glycerol) and nylon (adipic acid from cyclohexanol). Implementing selective, earth-abundant catalysts for alcohol oxidation can improve electrolyzer efficiency and economics. For example, replacing the energy intensive oxygen evolution reaction (OER) in CO2 electrolyzers with alcohol oxidation can decrease operating voltage by about 0.85 V and reduce electricity requirements up to 53% while also reducing carbon emissions from chemical production.1 Electrochemical alcohol oxidation catalyzed by as synthesized nickel oxyhydroxide (NiOOH) is hypothesized to proceed through two pathways, a chemical, redox pathway preferred by aldehydes (geminal diols in alkaline electrolyte), and a potential dependent pathway preferred by alcohols.2 Many studies have focused on understanding reaction mechanisms and device performance, however, transition metal alcohol oxidation catalysts, such as NiOOH, are known to undergo reduction/oxidation, phase changes, and even dissolution in the same potential window as alcohol oxidation.3 It is still unclear how these processes affect catalyst material stability and electrochemical performance.In this work, we probe the performance stability and material stability of Ni(OH)2 for alcohol oxidation in alkaline media through electrochemical cycling and chronoamperometry. We use a rigorously Fe-free environment to mitigate performance impacts from Fe-contamination common in non-purified alkaline electrochemical studies.4 We show that the rate of change of alcohol oxidation current density (mA cm-2) depends on reaction pathway (redox vs. potential dependent), alcohol concentration, and side chain structure. Using EC-MS and NMR, we also probe changes in performance in yield and selectivity by quantifying oxidation products, including oxygen gas. These changes in performance are correlated to material changes through monitoring dissolution with on-line ICP-MS. Furthermore, to disentangle the role of potential and reactant (e.g. alcohol or water) on stability, we elucidate oxidation state and local structural changes using in situ X-ray Absorption Spectroscopy (XAS). Insights from this rigorous model system are directly translatable to the broader goal of developing efficient, long-lasting catalysts for industrial deployment of electrochemical organic reactions powered by clean energy. References. Verma, Sumit, Shawn Lu, and Paul JA Kenis. Nature Energy 4.6 (2019): 466-474.2.Bender, Michael T., and Kyoung‐Shin Choi. ChemSusChem 15.13 (2022): e202200675.Klaus, Shannon, et al. The Journal of Physical Chemistry C 119.13 (2015): 7243-7254Wei, Lingze, et al. ACS Catalysis 13.7 (2023): 4272-4282.

A cyclic trinuclear silver complex for photosynthesis of hydrogen peroxide.

The development of metal complexes for photosynthesis of hydrogen peroxide (H2O2) from pure water and oxygen using solar energy, especially in the absence of any additives (e.g., acid, co-catalysts, and sacrificial agents), is a worthwhile pursuit, yet still remains highly challenging. More importantly, the O2 evolution from the water oxidation reaction has been impeded by the classic bottleneck, the photon-flux-density problem of sunlight that could be attributed to rarefied solar radiation for a long time. Herein, we reported synthesis of boron dipyrromethene (BODIPY)-based cyclic trinuclear silver complexes (Ag-CTC), and they exhibited strong visible-light absorption ability, a suitable energy bandgap, excellent photochemical properties and efficient charge separation ability. The integration of BODIPY motifs as oxygen reduction reaction sites and silver ions as water oxidation reaction sites allows Ag-CTC to photosynthesize H2O2 either from pure water or from sea water in the absence of any additives with a high H2O2 production rate of 183.7 and 192.3 μM h-1, which is higher than that of other reported metal-based photocatalysts. The photocatalytic mechanism was systematically and ambiguously investigated by various experimental analyses and density functional theory (DFT) calculations. Our work represents an important breakthrough in developing a new Ag photocatalyst for the transformation of O2 into H2O2 and H2O into H2O2.

Poly(4-methyl-1-pentene)/ polypropylene alloy hollow fiber membrane with high rigidity for blood oxygenation

The oxygenator with hollow fiber membranes (HFMs) is the key component of the extracorporeal membrane oxygenation which allows the blood to be oxygenated and the carbon dioxide to be removed. The poly(4-methyl-1-pentene) (PMP) is recognized as the optimal oxygenated membrane material with high gas permeability coefficient, and the oxygenated membrane fabricated from it has an asymmetric structure that can resist plasma leakage for a long period of time. However, the relatively low rigidity of PMP oxygenated membrane makes it difficult to be processed in subsequent weaving and applications, during which deformation and fracture of HFMs often happen. In this work, the polymer alloy oxygenated membranes are fabricated by blending polypropylene (PP) as a high rigidity reinforcement agent with PMP via thermally induced phase separation (TIPS). Firstly, the effect of the PP content on phase separation structure and crystallization of alloy flat sheet membrane are investigated. When the PP content is 15 wt%, the rigidity of the alloy membrane reinforces dramatically. The elastic modulus and tensile strength of the PMP-PP-15 alloy membrane is 288.5 ± 12.4 MPa and 8.3 ± 0.4 MPa, respectively, which is 275.7 % and 96.7 % higher than that of the PMP membrane. Furthermore, PMP-PP-15 alloy HFM are fabricated under the optimum polymer composition. The elastic modulus of the PMP-PP-15 alloy HFM is 312.6 ± 16.0 MPa, which is 679.6 % higher than that of the PMP HFM and 40.1 % higher than that of the commercial PMP HFM. Meanwhile, the tensile strength and fracture stress are 15.4 ± 0.7 MPa and 186 ± 12.2 cN, respectively, which are both higher than those of the PMP and commercial PMP HFM. In addition, the PMP-PP-15 alloy HFM shows high gas permeability and oxygenation performance. This study might provide a convenient method to achieve rigidity reinforcement of PMP-based oxygenated membranes with great potential for application.

Influence of the atmosphere on the phosphorescence of a brominated diphenylphosphine oxide-ethyl naphthaleneimide dyad.

The molecular dyad diphenylphosphine-ethyl bromine naphthaleneimide (Br-DPPENI) emits strong fluorescence and phosphorescence. We studied the intensity and lifetime of the phosphorescence of Br-DPPENI embedded in PMMA films in atmospheres of air, He, Ar, N2, and O2 as a function of pressure between vacuum and ambient pressure (1 bar). The experiment was performed in the frequency domain with a two-channel lock-in amplifier, and the data were analyzed with the polar plot or phasor technique. Reversible shortening of the lifetime due to triplet-triplet annihilation was found in the presence of atmospheric or pure oxygen. With small modulation frequencies, an additional slow component of the phosphorescence dynamics is observed, which is ascribed to the diffusion of oxygen into the sample films.

Photodynamic Therapy of Atherosclerotic Plaque Monitored by T1 and T2 Relaxation Times of Magnetic Resonance Imaging

Atherosclerosis, marked by plaque accumulation within arteries, results from lipid dysregulation, inflammation, and vascular remodeling. Plaque composition, including lipid-rich cores and fibrous caps, determines stability and vulnerability. Photodynamic therapy (PDT) has emerged as a promising treatment, leveraging photosensitizers to induce localized cytotoxicity upon light activation. PDT targets plaque components selectively, reducing burden and inflammation. Challenges remain in optimizing PDT parameters and translating preclinical success to clinical efficacy. Nonetheless, PDT offers a minimally invasive strategy for atherosclerosis management, promising personalized interventions for cardiovascular health. The objective of the current study was to present the findings from quantitative non-contrast MRI of atherosclerosis post-PDT by assessing relaxation times. The study aimed to utilize and optimize a 1.5T MRI system. Clinical scanners were used for MRI examinations. The research involved analyzing T1 and T2 relaxation times. Following treatment of the samples with Rose Bengal and exposure to pure oxygen, PDT irradiation was administered. The results indicated that the therapy impacted the crus, evidenced by a significant decrease in relaxation times in the MRI data.

Two-dimensional nanocontainers with sheet structure endow epoxy resin with triple effects of oxygen barrier, anti-corrosion and corrosion inhibition

Previous coatings or barrier films have failed to focus on the combined application of oxygen barrier and long-term corrosion protection. In this paper, a two-dimensional sheet filler KCB with triple functions of anti-corrosion, oxygen barrier and corrosion inhibition was prepared by growing cerium dioxide (CeO2) on the surface of natural nanocontainer kieselguhr and adsorbing benzotriazole (BTA). Then applied KCB to epoxy resin (EP) to obtain EP/KCB composite coating. The hydroxyl group of CeO2 improves the compatibility of EP with KCB. The hydrogen bonding between BTA and KC, and the adsorption at the Ce3+ defect sites turn KCB into an impermeable physical barrier, which can form an inert protective film at the interface after the BTA later release. The experimental data show that the O2 GTR value of the EP/KCB5 composite coating is reduced by 35.88 % compared with that of the PET film. The |Z|0.01 Hz value both are as high as 1011 Ω·cm2 after immersed in 3.5 wt% NaCl solution for four months and with 3.0 MPa pure oxygen for 7 days, showing excellent potential for long-term oxygen resistance and corrosion protection. EP/KCB5 composite coating has an adhesion up to 11.63 MPa. Moreover, the BTA released in KCB chelates with the metal substrate to form an inert protective film, which further improves the anti-corrosion performance of the composite coating and has a certain self-healing ability. In summary, the EP/KCB5 composite coating shows excellent comprehensive properties, providing a new solution for long-term oxygen barrier and corrosion protection.

Innovative process for sulphur recovery from waste incineration flue gases: production of marketable sodium bisulphite solution

ABSTRACT This study presents an innovative process for recovering sulphur from hazardous waste incineration flue gases, designed to produce a marketable sodium bisulphite solution while ensuring complete SO2 removal. This new process is characterized by a double absorption strategy at two different pH levels. The first step, at an acidic pH, generates the desired bisulphite solution, while the second step, at a basic pH, produces the sulphite solution for recycling into the first step and ensures total SO2 removal. The process’s performance and feasibility were evaluated on a laboratory scale using a batch reactor with synthetic gas. The parametric study focused on the initial sulphite concentration in the absorption solution and the reactor temperature. A removal efficiency exceeding 95% was achieved across all initial sulphite concentrations and temperature ranges, when the pH was maintained above 6. At pH 5, where bisulphites are the predominant sulphur species, the removal efficiency remained substantial at approximately 70%. The oxidation of sulphites/bisulphites by oxygen in the flue gases was minimal, with less than 5% conversion to sulphate. Additionally, pH-controlled experiments were conducted to optimize plant start-up procedures. For the basic reactor, starting with water and adjusting the pH to 8 during SO2 absorption effectively minimized sodium hydroxide consumption. In contrast, for the acidic reactor at pH 5, initiating the process with a concentrated sulphite solution resulted in more stable absorption rates. These findings underscore the process's potential for efficient sulphur recovery and highlight the importance of pH management in optimizing operational stability and chemical consumption.

Improving polymer electrolyte membrane fuel cell performance and preventing flooding by exciting gas flow

Effective water management is necessary to prevent the performance degradation of polymer electrolyte membrane fuel cells (PEMFCs). In this study, acoustic pressure waves (AWs) are superimposed on an oxygen gas flow passing through a cathode to evaluate its potential to mitigate the flooding issue in flow channels. The goal is to expedite droplet removal by exciting droplets at frequencies close to their natural frequency. In-situ experiments are conducted to investigate the influence of AWs on two-phase flows in the cathode channel and the corresponding PEMFC performance. When AWs are applied, the frequency of water discharge from the cathode channel increases, and reduces the internal accumulated water, resulting in the pressure drop decreases. The internal flooding is also decreased, resulting in the reduction of the high frequency resistance attributed to decreased contact resistance. The external excitation improves the PEMFC performance owing to the effective and frequent water discharge induced by the increase in the local inertial force related to the droplet oscillation. The water management method propose in this study is considered to be an efficient method not only for PEMFC systems but also for other systems requiring water management.

Performance estimation of hybrid rocket by varying the flow rate at multi-location swirl injector

This study attempts to evaluate the effect of varying the oxidizer mass flow rate through the secondary mid-location swirl injector on the performance of a hybrid rocket motor (HRM). The hybrid fuel used in this study was paraffin wax along with commercially available gaseous oxygen as oxidizer. Utilizing a swirl injector is crucial as it adds a tangential velocity component alongside the axial one. Introducing a secondary mid-location swirl injector heightens this effect, leading to noticeably improved performance in HRM. An increase in the oxidizer mass flow rate through the secondary mid-location swirl injector is associated with a reduction in the regression rate. This is attributed to the blowing away of wax melt layer and flame from the solid hybrid fuel grain. Furthermore, an overall increase in the oxidizer mass flow rate corresponds to a rise in combustion efficiency, closely linked to pressure development, which, in turn, correlates with the mass flowing out of the rocket nozzle. Peak thrust was observed and also maximum fuel was burnt in case where highest gaseous oxygen (GOX) rate of 50 g/s was utilized. The multi-location swirl injector assembly maintains swirling flow towards the nozzle end, presenting an optimal scenario for enhancing HRM performance.

Effect and investigating of oxygen / nitrogen on modified glassy carbon electrode chitosan/carbon nanotube and best detection of nicotine using Cyclic voltammetry measurement technique

Nicotine, a component of tobacco smoke, is a neurotoxin. It exerts its effects by stimulating nicotine-containing acetylcholine receptors. Nicotine, one of over 4,700 components in tobacco smoke, was previously used as an insecticide in agriculture. Although the use of nicotine in agriculture has been banned in many countries, nicotine poisoning due to accidental or intentional ingestion of nicotine products remains a problem for smoking workers as well as children and adults. Understanding the mechanisms of nicotine poisoning is important for both prevention and treatment, as well as for appropriate regulatory approaches. We study the pharmacological properties of nicotine and the cellular mechanisms underlying acute and persistent nicotine addiction that appear to be related to the central and peripheral nervous systems. The electrochemical properties of nicotine were studied using a glassy carbon-chitosan/multiwalled carbon nanotubes-COOH electrode. Nicotine-COOH via chitosan/multiwalled carbon nanotubes was irreversibly reduced in the presence of oxygen and nitrogen gas. Oxidation signals at lower potentials and higher currents were obtained for nicotine via the modified electrode compared to the glassy carbon electrode. This condition proliferated in the presence of oxygen gas, suggesting that nanotubes, including carbon nanotubes, facilitate electron transfer and form the basis for electrocatalytic nicotine applications. Under optimal conditions, cyclic voltammetry (CV) shows oxidation of nicotine in the presence of oxygen at 0.74 V and nitrogen at 0.81 V in phosphate buffer solution at pH = 7.4. Linear calibration curves range from 0.1 to 200 μM for oxygen and 0.05 to 200 μM for nitrogen conditions, both with R2 = 0.99, and detection limits of 7.1 for oxygen and 9.2 nM for nitrogen.

Improving plasma uniformity in the inductively coupled plasma by external magnetic field

To enhance etching efficiency and uniformity in process production, in this work, a two-dimensional fluid model was used to study the modulation effect of an external magnetic field on the argon–oxygen inductively coupled plasma (ICP). The study found that as the magnetic coil current increases, the electron density changes from center-high to uniform to edge-high distribution. The best plasma uniformity degree is 94%, obtained at a magnetic coil current of 10 A, which represents a 39% improvement over the unmagnetized ICP. The electric field reversal occurs during the transition from weak magnetization to strong magnetization. The electron temperature shows a single-peak to dual-peak to single-peak distribution during this period. In addition, we also found that gas pressure and oxygen ratio also impact magnetized plasma, where the effect of gas pressure on magnetized plasma is more significant than that of oxygen ratio. The results show that introducing an external magnetic field can significantly improve the plasma density and radial uniformity. This finding has contributed to enhancing plasma etching uniformity and optimizing etching processes.

Experimental investigation of an electronegative cylindrical capacitively coupled geometrically asymmetric plasma discharge with an axisymmetric magnetic field

In this study, we have investigated the production of negative ions by mixing electronegative oxygen gas with electropositive argon gas in a geometrically asymmetric cylindrical capacitively coupled radio frequency plasma discharge. The plasma parameters such as density (electron, positive, and negative ion), negative ion fraction, and electron temperature are investigated for fixed gas pressure and increasing axial magnetic field strength. The axisymmetric magnetic field creates an E × B drift in the azimuthal direction, leading to the confinement of high-energy electrons at the radial edge of the chamber, resulting in decreased species density and negative ion fraction in the plasma bulk. However, the electron temperature increases with the magnetic field. It is concluded that low magnetic fields are better suited for negative ion production in such devices. Furthermore, in addition to the percentage ratio of the two gases, the applied axial magnetic field also plays a vital role in controlling negative ion fraction.

A comprehensive study of oxygenator gas transfer efficiency and thrombosis risk

A comprehensive study of oxygenator gas transfer efficiency and thrombosis risk