Oxygen Ions Research Articles

Plasma surface treatment of amorphous Ga2O3 thin films for solar-blind ultraviolet photodetectors

Recently, amorphous gallium oxide (a-Ga2O3) thin films are gaining more and more attention due to their advantages of low cost and low temperature growth. However, a-Ga2O3 solar-blind ultraviolet photodetectors are plagued by issues such as slow response speed and high dark current. In this work, radio frequency magnetron sputtering was used for a-Ga2O3 deposition, and a novel approach of plasma treatment (including oxygen, argon and hydrogen plasmas) was employed to tailor the device performance using a plasma-enhanced chemical vapor deposition system. It is demonstrated that: (i) the oxygen atoms and ions in the oxygen plasma effectively reduce the oxygen vacancy concentration and improve the respond speed of a-Ga2O3 photodetectors; (ii) the argon ions in the argon plasma create additional defects (such as dangling bonds and oxygen vacancies) and improve the responsivity of a-Ga2O3 photodetectors; (iii) the hydrogen atoms in the hydrogen plasma may incorporate into the film and form an ultra-thin passivation layer near the surface, which gives rise to a balance between responsivity and response speed. Finally, through the detailed analysis of the optical emission spectra and photoelectric performance, the underlying physical mechanism based on the energy band diagram has been proposed to interpret the obtained experimental results.

Current–voltage characteristics of Ag/Nb:SrTiO3/Ag and Au/Nb:SrTiO3/Ag heterostructures

Ag/Nb:SrTiO3(NSTO)/Ag and Au/NSTO/Ag structures were prepared and their current–voltage curves were studied in detail. The Ag/NSTO/Ag structure can demonstrate a pronounced resistive switching effect and the characteristics of its resistance change sequence as demonstrated in the I–V curves are significantly different from those of the Au/NSTO/Ag structure. Under a unipolar current, the Ag/NSTO/Ag structure translates first from a low-resistance state (LRS) to a high-resistance state (HRS) and then from the HRS to the LRS. However, the Au/NSTO/Ag structure only shows a transition from the HRS to the LRS. The phenomenon is analyzed taking into account the migration of oxygen ions and the electrochemical reaction of the Ag electrode, which lead to the formation of the Ag2O insulation layer as well as Ag conductive filaments in the Ag/NSTO/Ag structure and a change in the barrier height of the Au/NSTO interface.

High oxygen vacancy concentration and improved electrical conductivity in tetragonal LaNbO4 stabilized by Ga and Mo Co-doping on the Nb site

The LaNbO4-based materials were well documented to be good ionic conductors with the charge carriers of protons or interstitial oxygen ions. Herein, for the first time, we reported that the high oxide ion conduction, e.g. 3 × 10−3 S cm−1 at 900 °C, mediated by oxygen vacancies was achieved in LaNbO4 via equimolar Ga and Mo co-doping on the Nb site. Such a co-doping effectively stabilize the high temperature tetragonal structure of LaNbO4 to room temperature, and thus represents the first case of room temperature tetragonal LaNbO4 with high oxygen vacancy concentration, in contrast with the previously reported tetragonal LaNbO4 stabilized by isovalent doping free of oxygen vacancies or donor-doping with interstitial oxygen. The local structure and conducting mechanism of oxygen vacancy defects were thoroughly studied by computational simulations. The results revealed that the oxygen vacancy was accommodated by transforming two neighboring isolated NbO4 tetrahedrons into a corner-sharing Nb2O7 unit, and the oxygen ion migrated via a cooperative process involving the breaking and reforming of Nb2O7 units, assisted by synergic rotation and deformation of other neighboring NbO4 tetrahedra. These findings provided us a more comprehensive understanding for the LaNbO4-based materials and emphasized the possibility of developing LaNbO4 material as oxide-ion conductors mediated by high concentration of oxygen vacancies.

Annealing effects on 100 keV silicon negative ions implanted SiO2 thin films

SiO2 thin film of thickness 300 nm grown on p-type silicon substrate was implanted with 100 keV silicon negative ions for the fluences of 1 × 1016, 5 × 1016, and 1 × 1017 ions cm−2. The implanted samples were investigated using an energy-dispersive X-ray (EDX) spectroscopic technique, and the samples were annealed at a temperature of 900 oC under N2 ambient. Ultraviolet–visible near infrared (UV-Vis-NIR) spectroscopy has been used to investigate the implanted SiO2 thin film samples before and after thermal annealing. EDX results revealed an increase in the atomic percentage and weight percentage of silicon ions as compared to oxygen ions in SiO2 thin film. This may be due to the increase in the concentration of silicon ions with the increase of implanted ion fluences within the SiO2 thin film. UV-Vis-NIR studies showed higher transmittance for thermally annealed samples as compared to non-annealed samples. This may be attributed to the creation of a new SiOx phase in the SiO2 matrix at higher temperatures. UV-Vis-NIR studies also exhibited an increase in the energy band gap value after thermal annealing. This effect may be related to the formation of silicon nanoclusters in SiO2 thin film.

Populus trichocarpa EXPA6 Facilitates Radial and Longitudinal Transport of Na+ under Salt Stress.

Expansins are cell wall (CW) proteins that mediate the CW loosening and regulate salt tolerance in a positive or negative way. However, the role of Populus trichocarpa expansin A6 (PtEXPA6) in salt tolerance and the relevance to cell wall loosening is still unclear in poplars. PtEXPA6 gene was transferred into the hybrid species, Populus alba × P. tremula var. glandulosa (84K) and Populus tremula × P. alba INRA '717-1B4' (717-1B4). Under salt stress, the stem growth, gas exchange, chlorophyll fluorescence, activity and transcription of antioxidant enzymes, Na+ content, and Na+ flux of root xylem and petiole vascular bundle were investigated in wild-type and transgenic poplars. The correlation analysis and principal component analysis (PCA) were used to analyze the correlations among the characteristics and principal components. Our results show that the transcription of PtEXPA6 was downregulated upon a prolonged duration of salt stress (48 h) after a transient increase induced by NaCl (100 mM). The PtEXPA6-transgenic poplars of 84K and 717-1B4 showed a greater reduction (42-65%) in stem height and diameter growth after 15 days of NaCl treatment compared with wild-type (WT) poplars (11-41%). The Na+ accumulation in roots, stems, and leaves was 14-83% higher in the transgenic lines than in the WT. The Na+ buildup in the transgenic poplars affects photosynthesis; the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT); and the transcription of PODa2, SOD [Cu-Zn], and CAT1. Transient flux kinetics showed that the Na+ efflux of root xylem and leaf petiole vascular bundle were 1.9-3.5-fold greater in the PtEXPA6-transgenic poplars than in the WT poplars. PtEXPA6 overexpression increased root contractility and extensibility by 33% and 32%, indicating that PtEXPA6 increased the CW loosening in the transgenic poplars of 84K and 717-1B4. Noteworthily, the PtEXPA6-promoted CW loosening was shown to facilitate Na+ efflux of root xylem and petiole vascular bundle in the transgenic poplars. We conclude that the overexpression of PtEXPA6 leads to CW loosening that facilitates the radial translocation of Na+ into the root xylem and the subsequent Na+ translocation from roots to leaves, resulting in an excessive Na+ accumulation and consequently, reducing salt tolerance in transgenic poplars. Therefore, the downregulation of PtEXPA6 in NaCl-treated Populus trichocarpa favors the maintenance of ionic and reactive oxygen species (ROS) homeostasis under long-term salt stress.

Effects of oxygen volume fraction, temperature and diffusion layer thickness on the sensing characteristics of limiting current oxygen sensor

Oxygen sensors are prepared by Pt paddle bonding method with dense diffusion barrier of short-circuited yttria-stabilized zirconia (YSZ) solid electrolyte. Different from the previous normal diffusion and Knudsen diffusion mechanisms, the limiting current equation of this type oxygen sensor is derived based on the diffusion of oxygen ions in the dense diffusion barrier. The effects of oxygen volume fraction, temperature and diffusion layer thickness on the limiting current density are investigated. The relationship between the physical quantities in the experiment is consistent with the derived equation.

Monitoring the formation of infinite-layer transition metal oxides through in situ atomic-resolution electron microscopy.

Infinite-layer transition metal oxides with two-dimensional oxygen coordination exhibit intriguing electronic and magnetic properties due to strong in-plane orbital hybridization. The synthesis of this distinctive structure has primarily relied on kinetically controlled reduction of oxygen-rich phases featuring three-dimensional polyhedral oxygen coordination. Here, using in situ atomic-resolution electron microscopy, we scrutinize the intricate atomic-scale mechanisms of oxygen conduction leading to the transformation of SrFeO2.5 to infinite-layer SrFeO2. The oxygen release is highly anisotropic and governed by the lattice reorientation aligning the fast diffusion channels towards the outlet, which is facilitated by cooperative yet shuffle displacements of iron and oxygen ions. Accompanied with the oxygen release, the three-dimensional to two-dimensional reconfiguration of oxygen is facilitated by the lattice flexibility of FeOx polyhedral layers, adopting multiple discrete transient states following the sequence determined by the least energy-costing pathways. Similar transformation mechanism may operate in cuprate and nickelate superconductors, which are isostructural with SrFeO2.

Construction of Pillared-Layer Metal-Organic Frameworks as an All-Visible-Light Switchable Photocatalyst for Aqueous Cr(VI) Reduction.

Recently, two-dimensional metal-organic frameworks that are photoactive have shown great potential for efficiently converting solar energy into chemical energy. In this work, we successfully synthesized and designed two M2-MOFs ([Cu(L1)((CH3)2NH)]n (Cu-MOF) and [Zn(L1)(CH3)2NH)]n (Zn-MOF), H2L1 = 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzoic acid). Structural analysis suggests that the five-coordinated M(II) ion is surrounded by four oxygen ions from two ligands and one nitrogen atom from one dimethylamine molecule. The ligand spacer acts as a bridge between two SBUs and forms a 2D layer with rhomboid windows. These moieties are arranged in a staggered ABAB pattern, which likely aids in exfoliation. The UV-vis diffuse reflectance spectra (DRS) test shows that when the metal center in the MOF framework is replaced with Cu(II) ions, the light absorption range covers 200-1100 nm, which is much larger than the light absorption range of Zn-MOF. Moreover, the photoelectric current, electrochemical impedance spectra (EIS), and Mott-Schottky tests all indicate that Cu-MOF has better photoelectric properties. When applied to the photocatalytic reduction of Cr(VI), Cu-MOF and Zn-MOF can completely reduce Cr(VI) within 100 min under 450 nm LED light irradiation. Under sunlight irradiation, Cu-MOF can completely reduce Cr(VI) within 40 min, achieving the removal of Cr(VI) ions, which is much faster than the rate of Cr(VI) removal by Zn-MOF.

A new insight on surface chemistry and redox species of transition metal (Fe, Mn) doped CeO2-SnO2/Al2O3 nanocomposites for automobile emission control

The ceria-tin/alumina mixed metal oxides (Ce/Sn =1) with different proportions of Fe & Mn dopants were synthesized and investigated in detailed approach for diesel emission reduction. The dopants created structural defects enhancing the oxygen ion mobility for exhaust treatment. The existence of surface-active oxygen sites and oxygen ion vacancy sites generated for charge compensation due to reduction of Ce4+, Sn4+ and dopants incorporation evidenced from XPS analysis. The Mn doped sample holds better physicochemical properties than Fe doped sample. The Mn doped sample with higher surface area of about 101.32 m2 g−1 exhibits greater active sites for better catalytic activity. The redox couples in the Mn-doped sample Ce4+/Ce3+, Sn4+/Sn2+, and Mn3+/Mn2+ helps in oxygen regeneration to contribute to exhaust treatment by oxygen ion conduction from bulk to the surface. This sample exhibited the 92 % of NOx reduction and proved to be a dynamic candidate for diesel emission reduction.

From Lab to Clinic: The Potential of Nanobubble Ozone Stored in Liposome with Pantothenic Acid (NOSLIP) in Treating Vaginal Infections with Long-lasting Effectiveness

Every year, 5-10 million women apply to various centers for sexually transmitted diseases due to infectious vaginitis (1). The three most notable causes of infectious vaginitis are bacterial vaginosis (BV), trichomoniasis, and vulvovaginal candidiasis (VVC). BV and VVC, which are endogenous genital infections, are the agents most responsible for the etiology of vaginal discharge (2). The most common symptoms of infectious vaginitis are vaginal discharge, itching, and a burning sensation. However, some cases are asymptomatic and are untreated (3). Group B streptococci (Streptococcus agalactiae; GBS) are gram-positive encapsulated bacteria that can colonize the intestinal and vaginal flora in 10-30% of healthy adults (4). Streptococcus agalactiae causes serious infections such as meningitis, sepsis, skin and soft tissue infections, pneumonia, urinary tract infections, and postpartum endometritis in newborns, pregnant women and adults with underlying diseases (4-6). Ozone is a highly reactive form of oxygen composed of three oxygen atoms. It is generated through the interaction of UV light and high-pressure diatomic oxygen. Ozone is widely acknowledged for its potent antibacterial properties due to its strong oxidative nature. Ozone therapy has garnered growing interest in recent years and is widely recognized for its beneficial impact on infection, reperfusion injury, cancer, and dental caries (7-8). At present, ozone therapy is an emerging approach in the clinical management of vaginitis. The medical ozone therapy device utilizes an ozone generator to produce a specific concentration of ozone, which is subsequently combined with filtered tap water to create ozonated water. Ozone and reactive chemicals exist in a liquid state and have a significant impact on vaginal sterilization (9).

Oxygen Ion Pumping across Atomically Designed Oxide Heterointerfaces

AbstractComplex oxide heterointerfaces and heterostructures have demonstrated enormous emergent phenomena over the last decades, attributed to the reconstructions of mis‐matched crystalline structure, polarity, and spin ordering across the heterointerfaces. This work employs the heterostructures of La0.7Sr0.3MnO3 and CaFeO2.5 as model system to demonstrate an interface‐specific oxygen migration/reconstruction across the interfaces due to the mismatched chemical potential, which dramatically influences the ferromagnetic and electronic states of La0.7Sr0.3MnO3 layer. Specifically, the alternative stacking of octahedral (Oh) and tetrahedral (Td) layers in CaFeO2.5 are used to form two distinct heterointerfaces, namely the Oh‐Td and the Oh‐Oh interfaces with the adjacent La0.7Sr0.3MnO3 layer. Interestingly, the oxygen ion migrates toward opposite directions across the interface for these two cases, in which the CaFeO2.5 layer acts as an “oxygen pump” and manipulates the oxygen contents of its adjacent La0.7Sr0.3MnO3 layers. Such manipulation leads to a dramatically changed ferromagnetic transition temperature for the heterostructure with the Oh‐Td and Oh‐Oh interface. This work establishes a feasible and efficient strategy to control the oxygen ionic distribution through atomic‐scale interface design and opens up new opportunities to exploit emergent states at the complex oxide heterostructures through selective oxygen ion evolution.

Field-Driven Solid-State Defect Control of Bilayer Switching Devices.

We develop a framework for controlling and investigating reversible ionic transfer between two solid metal oxides layers by examining field-driven changes in electrical properties of the thin film bilayer oxide system Pr0.1Ce0.9O2/La1.85Ce0.15CuO4 (PCO/LCCO). We show that we can reversibly redistribute oxygen ions by applied voltage in a highly controlled and reversible fashion near ambient temperatures over large oxygen ion activity limits, which, for the first time, is directly interpretable by defect chemical models. This allowed us to determine how defect concentrations in each layer systematically varied with voltage and the subsequent impact on each film's conductance. These results showcase the relevance and applicability of defect chemical models, traditionally considered only at elevated temperatures, to the development of bilayer devices of importance to neuromorphic memory applications. This allows for a more systematic approach for studying and understanding the solid-solid exchange process in electrochemically controlled microelectronic devices. Moreover, our work sets the foundation for the development of large-area field-driven defect-controlled bilayer switching devices with potential application to a broad array of functionally modulated devices.

Polysulfone membranes decorated with Fe–Mn binary oxide nanoparticles and polydopamine for enhanced arsenate/arsenite adsorptive removal

Arsenic contamination of water is a global environmental concern, and membrane technology combined with nanotechnology contributes to more efficient removal of arsenic. In this study, Fe–Mn oxide (FM), Polydopamine (PDA), and PDA-modified FM (PFM) were incorporated into polysulfone (PSF) to prepare adsorption membranes (PFMP) for arsenic removal. The prepared nanoparticles and membranes were characterized using TEM, SEM, FTIR, TGA, contact angle, and pure water flux. The introduction of particles enhanced the hydrophilicity of the membranes and significantly enhanced the pure water flux of the membranes. Adsorption experiments indicated that the PFMP membrane exhibited the best arsenic removal performance, with maximum adsorption capacities for As(III) and As(V) were 11.57 mg/g and 12.39 mg/g, respectively. The Langmuir model fitted the adsorption isotherms well, and the kinetics followed the pseudo-second-order model. The filtration experiment revealed that the PFMP membrane was capable of reducing As(III) solution (915 L/m2) and As(V) solution (1075 L/m2) from a concentration of 100 μg/L to the safe limit of As (＜10 μg/L). The As-loaded membrane was regenerated using NaOH solution (pH = 11), and the filtration experiment was repeated. FTIR and XPS demonstrated that the mechanism of the reaction between the membrane and arsenic was ligand exchange, where the arsenic ions were bonded to the oxygen ions to form Mn–O–As and Fe–O–As.

First-principles calculations to investigate the impact of fluorine doping on electrochemical properties of Li-rich Li2MnO3 layered cathode materials.

Li-rich layered oxides are promising candidates for high-capacity Li-ion battery cathode materials. In this study, we employ first-principles calculations to investigate the effect of F doping on Li-rich Li2MnO3 layered cathode materials. Our findings reveal that both Li2MnO3 and Li2MnO2.75F0.25 exhibit significant volume changes (greater than 10%) during deep delithiation, which could hinder the cycling of more Li ions from these two materials. For Li2MnO3, it is observed that oxygen ions lose electrons to compensate for charge during the delithiation process, leading to a relatively high voltage plateau. After F doping, oxidation occurs in both the cationic (Mn) and anionic (O) components, resulting in a lower voltage plateau at the beginning of the charge, which can be attributed to the oxidation of Mn3+ to Mn4+. Additionally, F doping can somewhat suppress the release of oxygen in Li2MnO3, improving the stability of anionic oxidation. However, the increase of the activation barriers for Li diffusion can be observed after F doping, due to stronger electrostatic interactions between F- and Li+, which adversely affects the cycling kinetics of Li2MnO2.75F0.25. This study enhances our understanding of the impact of F doping in Li2MnO3 based on theoretical calculations.

Deciphering the enhanced oxygen reduction reaction activity of PrBa0.5Sr0.5Co1.5Fe0.5O5+δ via constructing negative thermal expansion offset for high-performance solid oxide fuel cell

Solid oxide fuel cells (SOFCs) are one of the most efficient energy conversion devices. However, the sluggish oxygen reduction reaction (ORR) kinetics at low temperatures significantly challenge the performance and commercialization of SOFCs. Introducing negative expansion coefficient materials has been recognized as an effective approach to enhancing the ORR catalytic properties, but a clear understanding of this enhanced electrochemical performance is still lacking. In this work, the composite cathode of PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) with different amounts of negative-thermal-expansion material Sm0.85Zn0.15MnO3 (SZM) is prepared, and in-depth analysis the effect of SZM on the catalytic activity of cathodic ORR is systematically investigated. Simultaneously, the mechanistic studies verify that the enhanced ORR activity might be attributed to the constructed compression strain during sintering, which significantly improves the adsorption, dissociation, and oxygen ion exchange process of the PBSCF cathode.

Enhanced Hg(II) removal by polyethylenimine-modified fly ash-based tobermorite

The polyethylenimine (PEI)-modified fly ash based tobermorite (PTFA) was prepared from fly ash (FA) by hydrothermal synthesis of fly ash-based tobermorite (TFA) and PEI grafting. The TFA and PTFA were systematically characterized, and their Hg(II) removal properties from aqueous solutions were investigated. The influences of pH, adsorbent dosage, contact time, initial concentration, and coexisting ions on removing Hg(II) by PTFA were systematically investigated. The results showed that PTFA had good adsorption capacity and adsorption selectivity towards Hg(II). The optimum dosage of PTFA was 1 g/L, and the preferred pH range was 3 ∼ 5. The adsorption of Hg(II) on PTFA was found to follow the pseudo-second-order and Langmuir model, indicating chemical adsorption and monolayer adsorption between Hg(II) ions and PTFA. The thermodynamic results suggested that the adsorption of Hg(II) on PTFA was spontaneous, heat-absorbing, and entropy-increasing. The maximum adsorption capacity of PTFA for Hg(II) was 43.89 mg/g, which was higher than that of TFA and other reported FA-based adsorbents. The main removal mechanisms involved chemical chelation with oxygen and nitrogen atoms and ion exchange with Ca(II). This study shows that PTFA has good application prospects in treating wastewater containing Hg(II).

Constructing oxygen vacancies by selective anion doping in high entropy perovskite oxide for water splitting

High entropy perovskite oxide (HEPO) is a potential electrocatalyst for the oxygen evolution reaction (OER), but insufficient activity remains a problem. Oxygen vacancies can activate the lattice oxygen to induce the lattice oxygen-mediated mechanism (LOM), which can avoid the kinetic limitation present in adsorbate evolution mechanism (AEM), thereby improving the OER activity. Herein, we select the appropriate doping element (S) through analysis of ionic radius, electronegativity, and oxygen vacancy formation energy, and report an effective two-step oxygen vacancy strategy for introducing oxygen vacancies into HEPO through electrospinning and sulfurization treatment. This strategy optimizes the eg orbital filling electron number and significantly increases the active area, oxygen vacancy content and electroconductivity. Furthermore, the apparent pH dependence and the TMA+ inhibition phenomenon suggest the involvement of the LOM. Consequently, the resulting S/LMO-E has a lower overpotential (314 mV at 10 mA cm−2) and faster kinetics, and shows excellent stability. Meanwhile, the water splitting is achieved at 1.59 V to afford 10 mA cm−2 current density for S/LMO-E⎪⎢Pt/C, which is smaller than that of RuO2⎪⎢Pt/C (1.62 V). This work provides an attractive OER electrocatalyst for efficient water splitting to produce renewable hydrogen and opens a new way for the design of effective and stable high entropy material electrocatalysts.

Insights from Ab Initio Molecular Dynamics on the Interface Reaction between Electrolyte and Li2MnO3 Cathode during the Charging Process.

The complex interface reactions are crucial to the performance of the Li2MnO3 cathode material. Here, the interface reactions between the liquid electrolyte and the typical surfaces of Li2MnO3 during the charging process are systematically investigated by ab initio molecular dynamics (AIMD) simulation and first-principles calculation. The results indicate that these interface reactions lead to the formation of hydroxide radicals, oxygen, carbon dioxide, carbonate radicals, and other products, which are consistent with the experimental findings. These processes primarily result from the conversion of the stable closed-shell O2- into reactive oxygen ions by electron loss. All surfaces exhibit some degree of layered- and spinel-like phase transitions during the AIMD simulations, consistent with the experiment. This is mainly attributed to the decrease in the Mn-O bond strength and the increase in the Li/O ion vacancy concentration. This study offers valuable theoretical insights into the interface reaction between lithium-rich cathode materials and liquid electrolytes.

Influence of Water Vapor on the Oxidation of Pure Titanium

Titanium and titanium alloys are extensively used in the aerospace, automotive, and medical industries due to their high chemical and mechanical stability. In a previous study, the influence of water vapor on the growth of the oxide scale and the formation of the oxygen diffusion zone (ODZ) for Ti-6Al-4V was investigated using a 6-zone furnace. To elucidate the effect of water vapor on the oxide scale growth and ODZ, without the effect of alloying elements on diffusion, a systematic comparative study at 500, 600, and 700 °C for up to 500 h was carried out on pure Ti. Inert marker experiments showed that outward scale growth and diffusion of Ti4+ were promoted by water vapor. Additionally, the extent of oxygen enrichment in the subsurface zone (ODZ) as a function of temperature and time was determined for pure Ti by nanoindentation profiles and compared with results obtained for Ti-6Al-4V. The thickness of the ODZ increased with increasing temperature and time for dry air and humid air. The diffusion of oxygen ions within pure Ti and Ti-6Al-4V was not significantly affected by the presence of water vapor in the oxidizing environment. The effect of water vapor on the oxide scale spallation was found to be less critical for pure Ti when compared to Ti-6Al-4V.

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.