The CO2 electrolysing mechanism in single-phase mixed-conducting cathode of solid oxide cell.

In the field of solid oxide cells (SOC), unveiling the electrochemical reaction and transfer mechanisms in mixed ionic and electronic conducting (MIEC) electrodes is of great importance. Due to the chemical capacitance effects of MIEC materials, SOC often shows large capacitance current during electrochemical tests, which might interfere with the polarization behaviors. This work presents a numerical multiphysical model based on the transport of oxygen species, which accurately and concisely replicates the current-voltage curves of a solid oxide electrolysis cell (SOEC) with MIEC electrodes under various scanning rates. The scanning IV and electrochemical impedance spectra measurement under different SOEC working conditions are combined to enable the separation of Faradic and charging currents. Thus, both the bulk diffusion and surface gaseous diffusion of the oxygen species are encompassed, which explains how the current being generated due to intertwined chemical capacitance effects and chemical reactions in the MIEC electrodes.

Reduced Surface Area for the Oxygen Reduction Reaction in Porous Electrode via Electrical Conductivity Relaxation.

Oxygen reduction reaction (ORR) performance of porous electrode is critical for solid oxide fuel cells (SOFCs). However, the effects of gas diffusion on the ORR in porous media need further investigation, although some issues, such as nonthermal surface oxygen exchange, have been attributed to gas diffusion. Herein, La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) with various porosity, pore radii and gas permeability were investigated via the electrical conductivity relaxation method and analysed using the distributed of characteristic time (DCT) model. The ORR is revealed with three characteristic times, which are gas diffusion, oxygen exchange via the surface corresponding to small pores, and oxygen exchange to large pores. Gas diffusion delays the oxygen surface exchange reaction, resulting in very low chemical oxygen surface exchange coefficient compared with that obtained with dense sample under the assumption that all the surfaces are active for the ORR. Reduced surface area is thus defined to quantitatively represent the gas diffusion effects. The reduced surface area increases with increasing gas permeability, demonstrating the importance of electrode engineering for fast gas transport. Moreover, reduced surface area is suggested for replacing the specific surface area to calculate the electrode polarization resistance using the ALS model.

Disruption of the intestinal barrier by avermectin in carp involves oxidative stress and apoptosis and leads to intestinal inflammation.

Avermectin (AVM) is a widely used insecticide. Due to its sensitive toxicity to aquatic organisms, the toxicology of AVM on fish intestines remains unclear. Here, we established a 96 h AVM acute toxicity model to explore the effects of AVM on the intestinal tract of carp. The 96 h LC50 of carps exposed to AVM was 24.04 µg/L, 12.02 µg/L was selected as the high-dose group and 3.005 µg/L was selected as the low-dose group. After 96 h of exposure, intestinal tissues were collected and subsequently analyzed for histopathology, the activities of antioxidant oxidases (CAT, SOD, GSH-Px), and the expression of mRNA associated with oxidative stress, inflammation, and apoptosis. Our study showed that AVM exposure caused intestinal damage in carp, decreased the expression of the tight junction protein gene, activated oxidative stress, induced apoptosis, and induced intestinal inflammation in carp. Therefore, we demonstrated that AVM exposure compromised the integrity of the intestinal barrier in carp, activated oxidative stress, induced endogenous apoptosis, and induced intestinal inflammatory responses. These results indicate that AVM, as a drug-sensitive to aquatic organisms, has a much more complex toxic effect on the fish intestinal tract, which provides a new perspective for studying the toxicology of AVM on the fish intestinal tract.

Difenoconazole disrupts carp intestinal physical barrier and causes inflammatory response via triggering oxidative stress and apoptosis.

As a common fungicide, difenoconazole (DFZ) is widespread in the natural environment and poses many potential threats. Carp makes up a significant proportion of China's freshwater aquaculture population and are vulnerable to the DFZ. Therefore, this study investigated the effects of DFZ (0.488 mg/L and 1.953 mg/L) exposure for 4 d on the intestinal tissues of carp and explored the mechanisms. Specifically, DFZ exposure caused pathological damage to the intestinal tissues of carp, reducing the expression levels of intestinal tight junction proteins, and leading to damage to the intestinal barrier. In addition, DFZ exposure activated the NF-κB signaling pathway, increasing the levels of pro-inflammatory factors (TNF-α, IL-1ß, IL-6) and decreasing the levels of anti-inflammatory factors (IL-10, TGF-ß1). As disruption of the intestinal barrier is closely linked to oxidative stress and apoptosis, we have conducted research in both areas for this reason. The results showed that DFZ exposure elevated reactive oxygen species in carp intestines, decreased antioxidant enzyme activity, and suppressed the expression of oxidative stress-related genes. TUNEL results showed that DFZ induced the onset of apoptosis. In addition, the expression levels of apoptosis-related genes and proteins were examined. Western blotting results showed that DFZ could upregulate the protein expression levels of Bax, Cytochrome C and downregulate the protein levels of Bcl-2. qPCR results showed that DFZ could upregulate the transcript levels of Bax, Caspase-3, Caspase-8 and Caspase-9 and downregulate the transcript levels of Bcl-2 transcript levels. This suggests that DFZ can induce apoptosis of mitochondrial pathway in carp intestine. In conclusion, DFZ can induce oxidative stress and apoptosis in carp intestine, leading to the destruction of intestinal physical barrier and the occurrence of inflammation. Our data support the idea that oxidative stress and apoptosis are important triggers of pesticide-induced inflammatory bowel illness.

Perspective on high-temperature surface oxygen exchange in a porous mixed ionic-electronic conductor for solid oxide cells.

The surface exchange coefficient (k) of porous mixed ionic-electronic conductors (MIECs) determines the device-level electrochemical performance of solid oxide cells. However, a great difference is reported for k values, which are measured using presently available technologies of electrical conductivity relaxation (ECR), electrochemical impedance spectroscopy (EIS), and oxygen isotope exchange (OIE). In terms of this issue, this perspective paper estimates the possible physiochemical processes for the oxygen reduction reaction (ORR) in porous MIECs by comparing the oxygen supply/consumption fluxes through calculation. Then, the potential problems associated with ECR, EIS, and OIE for application in porous materials are discussed regarding theory, assumptions, sample requirements, and data processing. Finally, gas diffusion effects are revealed by comparing the simulated and measured ECR profiles, which show that the ORR process can be significantly delayed by gas diffusion. This perspective aims to recommend a reasonable method to characterize the true ORR kinetics of porous electrodes and quantify the effect of gas diffusion.

Cobalt-Free Double Perovskite Oxide as a Promising Cathode for Solid Oxide Fuel Cells.

Double perovskite oxide PrBaFe2O5+δ is a potential cathode material for intermediate-temperature solid oxide fuel cells. To improve its electrochemical performance, the trivalent element Ga is investigated to partially replace Fe, forming PrBaFe2-xGaxO5+δ (PBFGx, x = 0.05, 0.1, and 0.15). The doping effects on physicochemical properties and electrochemical properties are analyzed regarding the phase structures, element valence states, amount of oxygen vacancies, content of oxygen species, oxygen surface exchange coefficients (kchem), electrochemical polarization resistance, and single-cell performance. Specifically, PBFG0.1 exhibits improved kchem, such as a 19% improvement from 4.09 × 10-4 to 4.86 × 10-4 cm s-1 at 750 °C, due to the increased concentration of reactive oxygen species and oxygen vacancies. Consequently, the interfacial polarization resistance is decreased by 28% from 0.057 to 0.041 Ω cm2 at 800 °C. The subreaction steps of the oxygen reduction reaction in the PBFG0.1 cathode are further investigated, which suggests that the oxygen dissociation process is greatly enhanced by doping Ga. Meanwhile, doping Ga increases the peak power density of the anode-supported single cell by 36% from 629 to 856 mW cm-2 at 800 °C. The single cell with the PBFG0.1 cathode also exhibits good stability in 100 h of long-term operation at 750 °C.

Surface Self-Assembly Protonation Triggering Triple-Conductive Heterostructure with Highly Enhanced Oxygen Reduction for Protonic Ceramic Fuel Cells.

Triple-conducting (H+ /O2- /e- ) cathodes are a vital constituent of practical protonic ceramic fuel cells. However, seeking new candidates has remained a grand challenge on account of the limited material system. Though triple conduction can be achieved by mechanically mixing powders uniformly consisting of oxygen ion-electron and proton conductors, the catalytic activity and durability are still restricted. By leveraging this fact, a highly efficient strategy to construct a triple-conductive region through surface self-assembly protonation based on the robust double-perovskite PrBaCo1.92 Zr0.08 O5+δ , is proposed. In situ exsolution of BaZrO3 -based nanoparticles growing from the host oxide under oxidizing atmosphere by liberating Ba/Zr cations from A/B-sites readily forms proton transfer channels. The surface reconstructing heterostructures improve the structural stability, reduce the thermal expansion, and accelerate the oxygen reduction catalytic activity of such nanocomposite cathodes. This design route significantly boosts electrochemical performance with maximum peak power densities of 1453 and 992 mW cm-2 at 700 and 650 °C, respectively, 86% higher than the parent PrBaCo2 O5+δ cathode, accompanied by a much improved operational durability of 140 h at 600 °C.

Perovskite Oxyfluoride Ceramic with In Situ Exsolved Ni-Fe Nanoparticles for Direct CO2 Electrolysis in Solid Oxide Electrolysis Cells.

Solid oxide electrolysis cell (SOEC) is a potential technique to efficiently convert CO2 greenhouse gas into valuable fuels. Thus, there is significant interest in developing highly active and stable electrocatalysts for the CO2 reduction reaction (CO2RR). Herein, a Ni and F co-doping strategy is proposed to facilitate the exsolution reaction and form a new cathode, Ni-Fe alloy nanoparticles embedded in ceramic Sr2Fe1.5Mo0.5O6-δ (SFM) doped with fluorine. F-doping and Ni-Fe exsolution enhance CO2 adsorption by a factor of 2.4 and increase the surface reaction rate constant (kchem) for CO2RR from 6.79 × 10-5 to 18.1 × 10-5 cm s-1, as well as the oxygen chemical bulk diffusion coefficient (Dchem) from 9.42 × 10-6 to 19.1 × 10-6 cm2 s-1 at 800 °C. Meanwhile, the interfacial polarization resistance (Rp) decreases by 52%, from 0.64 to 0.31 Ω cm2. At 800 °C and 1.5 V, an extremely high current density of 2.66 A cm-2 and a stability test over 140 h are achieved for direct CO2 electrolysis in the SOEC.