Oxygen Surface Exchange Research Articles

A New Method to Measure Oxygen Surface Exchange Kinetics On Porous Mixed Conducting Oxides With Simple Determination of Microstructure Parameters.

Oxygen exchange reaction on mixed conducting oxide is a critical reaction for many applications, yet measuring its rate constant remains poorly reliable by standard techniques. Here, a new technique that adapts the conductivity relaxation measurements on porous ceramics is proposed. Using a simple image analysis tool, it is possible to accurately determine the grain size distribution of the porous oxide, which is used in a new relaxation model that integrates relaxation times over that distribution. With such a model, it is possible to fit relaxation transients with the oxygen exchange reaction rate constant kchem as the only fitting parameter. With such rigidity, the output values of kchem are not sensitive to the fitting procedure, which does not require optimization. The model is proven to be applicable to various mixed conducting oxides and to a wide range of microstructures, yielding a remarkably low residual for all the porous ceramics considered. The procedure uses porous ceramics, therefore the derived kinetics are representative of ceramics used in real applications such as fuel cells, sensors, or catalysis.

Realizing extraordinary bifunctional electrocatalytic performance of layered perovskite through Ba-site Gd doping toward oxygen reduction and evolution reactions

Herein, we propose a Ba-site Gd doping protocol in layered perovskites, demonstrating highly active bifunctional PrBa1-xGdxCo2O5+δ electrocatalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Benefiting from enhanced oxygen surface exchange and chemical diffusion kinetics, resultant PrBa0.95Gd0.05Co2O5+δ (PBG0.05CO) exhibits an area-specific resistance (ASR) of 0.038 Ω cm2 at 700 °C, reduced by ∼46.5% relative to undoped PrBaCo2O5+δ (PBCO). When evaluated as the air electrode, the as-fabricated single coin fuel cell delivers a peak power density (PPD) of 1230 mW/cm2 at 700 °C. For the CO2-electrolysis at 750 °C, the large current density (J) of 2630 mA/cm2 is achieved in the PBG0.05CO anode-based electrolysis cell at a voltage (V) of 1.8 V. Furthermore, exceptional operating stability is realized in both ORR and OER manners. Our findings highlight an effective strategy to optimize the electrocatalytic properties of layered perovskites, endowing potential applications in energy storage and conversion aspects.

Multi-walled carbon nanotube wrapped rare earth tungstate nanosheet composites for selective and rapid detection of sulfadiazine

Multi-walled carbon nanotube wrapped rare earth tungstate nanosheet composites are developed for the ultrasensitive and selective electrochemical detection of sulfa drug, sulfadiazine (SAN) as they exhibit high levels of toxicity towards public health and ecosystem. Here, we synthesized Gadolinium tungstate decorated with multi-walled carbon nanotubes (Gd2WO6/MWCNT) though hydrothermal processing and characterized by XRD, SEM, EDX, TEM, and EIS measurement to investigate the phase purity, morphology, and interfacial property. Gd2WO6 is a double perovskite that has high oxygen surface exchange kinetics and the MWCNT possesses high catalytic capability and a larger surface area contributes to the efficient sensing ability. The Gd2WO6/MWCNT possessed a great electrical conductivity owing to the synergism between the Gd2WO6 and MWCNT. The synergistic effect increases the surface area, ionic and electrical conductivity which increases the current response of SAN. Under optimum conditions, the Gd2WO6/MWCNT/GCE displays a broad linear of 0.01 – 671 µM and a LOD level of 2 nM (S/N ratio: 3) with a sensitivity of 0.371 µA µM cm−1. The analytical applicability of the proposed electrode modifier leads to a promising sensor for SAN detection in human urine and water samples with appreciable results.

Enhanced electrocatalytic activity of SrFe0.9Nb0.1O3-δ through in-situ synthesis of Sr3Fe1.8Nb0.2O7-δ coating

The influence of the heterogeneous interface is critical for the catalytic activity of the oxygen reduction reaction (ORR). This study demonstrates an enhancement of the electrocatalytic activity of the SrFe0.9Nb0.1O3-δ (SFN113) electrode through the construction of a SrFe0.9Nb0.1O3-δ-Sr3Fe1.8Nb0.2O7-δ (SFN113-SFN327) heterogeneous interface. By coating varying amounts of Sr(NO3)2 (0.1 g, 0.2 g and 0.3 g) on SFN113 (1 g), SFN113/327 composite electrodes with different amounts of triple conducting oxide SFN327 are in-situ synthesized by high temperature calcination. Electrical Conductivity Relaxation (ECR) tests show that SFN327 has superior oxygen surface exchange performance compared to SFN113, especially at lower temperatures. At 550 °C, the oxygen surface exchange parameter of SFN327 is 4.23 times higher than that of SFN113. Symmetric cell tests with SFN113/327||BaCe0.7Zr0.1Y0.1Yb0.1O3-δ (BCZYYb)||SFN113/327 configuration and single cell tests with Ni-BCZYYb||BCZYYb||SFN113/327 configuration indicate that the SFN113/327 composite electrode with a mass ratio of 1:0.2 displays the best electrocatalytic performance, achieving a power output of 502 mW cm−2 at 700 °C. The work not only in-situ synthesizes the SFN113/327 triple conducting composite electrode, but also introduces a novel method for developing proton conducting electrode materials.

A novel chemical composite strategy for synergistically enhancing the activity and stability of strontium-containing air electrode for protonic ceramic cells

Cation segregation on perovskite electrode surfaces usually leads to a decrease in the catalytic activity of electrodes and a shortened cell life. Herein, we have developed a simple and novel chemical composite strategy to achieve selectively surface reconstruction of the Sr-rich regions in perovskite Pr0.4Sr0.6Fe0.9Nb0.1O3-δ (PSFN), constructing strongly interacting interfaces between PSFN and Fe2O3 phases. The enhanced charge transfer between the two phases in PSFN/Fe2O3 is revealed by soft X-ray absorption spectroscopy. Meanwhile, fast surface oxygen exchange rate accelerates the migration and adsorption/desorption of oxygen species. The chemical composite electrode PSFN/Fe2O3 exhibits a smaller polarization resistance (0.35 Ω cm2) than that (0.61 Ω cm2) of the physical composite electrode PSFN + Fe2O3 at 600 °C in air. The distribution of relaxation time analyses demonstrate that enhanced reaction kinetics related to charge transfer and mass transfer are key factors in achieving stable operation of symmetric cell within 1000 h. Importantly, this study provides a simple and universal strategy for surface modification of perovskite oxides with cation separation issue, and highlights the crucial role of constructing strongly interacting interfaces in achieving high activity and stability of air electrodes.

A co-doped strategy for simultaneously improving oxygen permeability and stability of BaCoO3-δ ceramic membrane

Perovskite-type oxygen transport membrane (OTM) has considerable potential in the application of oxygen-enriched combustion, which can prepare low-cost, low-energy, and high-purity oxygen. BaCoO3-δ-based OTM, as a promising candidate, possesses high oxygen permeability, but poor stability limits its application. In this study, the strategy of Y3+ and W6+ co-doping BaCo0·8Y0.2-xWxO3-δ (BCYW-x) was proposed firstly to control the trade-off effect between oxygen permeability and stability by considering the radius and valence of ions. Y3+ and W6+ co-doping stabilize the perovskite cubic structure to room temperature of the BCYW-x, and the average bond energy of metal-oxygen increases with W6+ doping, enhancing the structure stability. Although oxygen vacancy concentration and critical radius decrease, the migration of oxygen ions is accelerated with the increase of W6+ content at high temperatures. The BCYW-0.1 shows the exceptional oxygen permeation flux of 1.90 mL･cm−2･min−1 at 900 °C and stably operates at 900 °C and 800 °C. Furthermore, the kinetic model calculation indicates that the permeation resistance decreases because of the acceleration of the oxygen surface exchange reaction as W6+ doping, contributing to the oxygen permeation process. This study provides a feasible and effective co-doping strategy to improve the oxygen permeability and stability of perovskite OTMs simultaneously.

Comprehensive understanding of charge and mass transport in BaZr0.1Ce0.7Y0.1Yb0.1O3−δ

This work reports transport properties of BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb1711), studied during oxidation/reduction and hydration/dehydration using electrical conductivity relaxation (ECR) measurements. The oxidation/reduction displayed typical monotonic conductivity relaxation behavior, attributed to the ambipolar diffusion of oxygen vacancies (Vo∙∙) and electron-holes (h∙), and oxygen surface exchange coefficient (k) were >1 order of magnitude higher than bulk diffusivities (D˜), indicating a diffusion-controlled process. Whereas, hydration/dehydration displayed a temperature-dependent gradual transition from monotonic to non-monotonic relaxation profile. At lower temperatures, transient defect concentration profile indicated that overall hydration/dehydration involved an acid-base-type reaction, comprising the diffusion of oxygen vacancy (Vo∙∙) and proton (Hi∙) couples. However, at higher temperatures and high [h∙], it involved a combination of a hydrogenation reaction (comprising component H via diffusion of h∙ and Hi∙ couple) and an oxidation reaction (involving component O via diffusion of h∙ and Vo∙∙ couple), thus giving rise to a two-fold non-monotonic relaxation profile. The k and D˜ values for oxygen vacancies (kVO∙∙; DVO∙∙) were lower than those for protons (kHi∙;DHi∙) with the respective Ea being 57.51 ± 3.14 and 60.72 ± 1.48 kJ∙mol−1 for oxygen-vacancies and 68.78 ± 12.65 and 71.05 ± 13.87 kJ∙mol−1 for protons.

Construction of high performance fuel electrode in solid oxide electrolysis cells by tuning the surface oxygen defect to promote electrochemical reduction of CO2

B-site Co–Fe-based perovskite materials have shown potential as ceramic cathodes in solid oxide electrolysis cells (SOECs) for direct CO2 electrolysis. Nevertheless, their operational utilization is constrained by insufficient catalytic activity and durability in pure CO2. In this work, F− doping and A-site deficiency strategies are proposed and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), F-doped La0.6Sr0.4Co0.2Fe0.8F0.1O2.9 (LSCFF) and A-site deficiency combined with F-doped (La0.6Sr0.4)0.95Co0.2Fe0.8F0.1O2.9 (LSCFF95) are prepared as cathode materials for CO2 electrolysis. After doping with F−, the valence states of both Co and Fe elements decrease, while generating more oxygen vacancies. With the further introduction of A-site deficiency, the valence states further decrease, resulting in more oxygen vacancies. The enhancement of oxygen vacancies leads to an improvement in the oxygen surface exchange coefficient (kchem) and the bulk diffusion coefficient (Dchem) of LSCFF and LSCFF95 materials. At 800 °C, kchem of LSCFF and LSCFF95 reach 24.21 × 10−4 and 33.54 × 10−4 cm s−1, respectively, which are 51% and 110% higher than the value of 16.03 × 10−4 cm s−1 for LSCF. Meanwhile, the Dchem values of LSCFF and LSCFF95 are measured to be 37.52 × 10−5 and 47.81 × 10−5 cm2 s−1, respectively. These values are 49% and 90% higher than the value of 25.22 × 10−5 cm2 s−1 for LSCF. Consequently, F− doping and A-site deficiency significantly increase the electrochemical performance. For example, F− doping decreases the polarization resistance (Rp) value of the SOEC with LSCF cathode from 0.19 Ω cm2 to 0.13 Ω cm2 at 800 °C. Furthermore, when the A-site deficiency is introduced, the Rp value is further reduced to 0.11 Ω cm2. Therefore, the SOEC with the LSCFF95 cathode exhibits excellent performance. Specifically, it has demonstrated an impressively high current density of 2.85 A cm−2 at 800 °C and 1.5 V, and has exhibited exceptional durability over prolonged operation.

Multicomponent doping realized superior triple-conducting within cobalt-free Ruddlesden-Popper-type perovskite for Proton-conducting fuel cells cathode

Proton-conducting solid oxide fuel cells (H-SOFCs) are appealing for low-to-intermediate temperature operation due to their intrinsic lower activation energy and better ionic conductivity. Unfortunately, there are currently few acceptable and high-performing cathode materials available for H-SOFCs. Herein, we present a novel high performance multicomponent Ruddlesden-Popper (RP) type cathode Pr3Ni1.5Cu0.3Nb0.05Ta0.05Zr0.05Y0.05O7-δ (PNCNTZY) with superior triple conducting property. The multicomponent co-doping of Nb, Ta, Zr, and Y brings about the enhancement of configurational entropy and cocktail effect for improving H+/O2-/e- triple conductivity and oxygen vacancy concentration. Naturally, the ORR activity is improved by facilitated charge transfer and oxygen surface exchange, exhibiting reduced polarization resistance to just 0.24 Ω cm2 at 550 °C. When used as the cathode in H-SOFC single cells, excellent power production is demonstrated at 550 °C, with a peak power density of up to 0.84 W cm-2. Furthermore, the PNCNTZY sample shows adequate thermal compatibility with proton conductor electrolytes BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) and then appropriate endurance durability (0.8 A cm-2 at 550 °C for about 250 h) due to their match of thermal expansion coefficient (TEC) brought about by the Co-free and partial replacement of larger-size elements. This extremely promising Co-free RP perovskite cathode for H-SOFCs produced by this work might provide a new type candidate and novel strategy for the commercialization of H-SOFCs.

An active bifunctional Pd-doped double perovskite air electrode for reversible protonic ceramic electrochemical cells

Reversible protonic ceramic electrochemical cells (R-PCECs) have a good application prospect as the energy conversion and storage devices. The electrode surface kinetics (i.e., oxygen reduction reaction (ORR) and water oxidation reaction (WOR)) are major technical obstacles to developing the R-PCECs. Here, we report a phase-pure Pd-doped double perovskite with a PrBa0.8Ca0.2Co1.95Pd0.05O5+δ (PBCCPd) formula. The PBCCPd air electrode displays a polarization resistance (Rp) of 0.056 Ω cm2 in the BZCYYb-based symmetrical cell at 700 °C, and also performs a peak power density (PPD) of 2.08 W cm−2 using the fuel cell mode, and a current density of -4.42 A cm−2 at 1.3 V using the electrolysis cell mode at 700 °C. Moreover, R-PCECs with PBCCPd air electrodes show excellent stability in fuel and electrolysis cells, and cycling modes with reasonable Faradaic efficiency. It is shown that Pd doping can effectively increase the oxygen vacancy, improve the oxygen surface exchange, bulk diffusion capabilities, and electrocatalytic activity and stability in the air electrode of R-RCECs, indicated by the X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectra (EIS), electrical conductivity relaxation (ECR), and distribution of relaxation time (DRT).

Cross-Validation of the Remarkably High Surface Oxygen Exchange Kinetics of PrBa0.5Sr0.5Co1.5Fe0.5O5+δ: A Combined Thin-Film Mass Relaxation and Bulk Electrical Conductivity Relaxation Study.

In this work, we measure the oxygen kinetic properties of double perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF), a material widely used as the air electrode in solid oxide electrochemical cells, by mass relaxation (MR) and electrical conductivity relaxation (ECR) experiments. MR studies are carried out using thin films deposited on a gallium phosphate piezocrystal microbalance, and ECR studies are performed using a bulk bar sample with 97% theoretical density. Measurements are performed at 600 °C over the temperature oxygen partial pressure range from 10-4 to 0.21 atm. Despite the differences in experimental formats and surface microstructural features, the ks values extracted from the two methods are found to be in good agreement with one another. The rate constant is found to increase with oxygen partial pressure with a power law dependence, rising from 1.0 × 10-6 cm/s at 3.2 × 10-4 atm to 1.2 × 10-4 cm/s at 0.24 atm, as averaged over the oxidation and reduction directions. The rates in the oxidation direction are observed to be slightly higher than those in the reduction direction for a given pair of pO2 values, suggesting that the final pO2 value controls the overall relaxation behavior. The power law exponent describing the dependence of ks on pO2 is found to be 0.74 ± 0.01. The ECR study of the bulk sample reveals that even with a diffusion length of 1.8 mm, the relaxation process is largely free of diffusion limitations, indicating that PBSCF has the high bulk transport properties required for a double-phase boundary oxidation/reduction pathway.

Comprehensive study of O2 and H2O interaction with La0.9Sr0.1ScO3–δ oxide

In this paper we study the processes of O2 and H2O interaction with La0.9Sr0.1ScO3−δ. Using high temperature neutron powder diffraction (HT-NPD), the evolution of crystal structure and water uptake was investigated in the temperature range 25–700 °C at 21.3 kPa in O2 and O2 + D2O atmospheres. The results of HT-NPD show the influence of the water uptake by La0.9Sr0.1ScO3–δ bulk on the thermal expansion of the material. The kinetics of oxygen surface exchange was studied using pulsed isotope exchange technique. The measurements were carried out in the temperature range 300−900 °C at pO2 = 5.1, 12.2 and 21.3 kPa in dry and humid (pH2O = 2.6 kPa) conditions. For the first time the physical model describing the kinetics of oxygen surface exchange between the mixture of oxygen and water in the gas phase and a solid oxide has been suggested. The model includes following steps: oxygen dissociative adsorption, oxygen incorporation, hydrogen surface diffusion, water adsorption and dissociation. The rate-determining step of the exchange is considered. The influence of O2 humidification on the oxygen surface exchange is discussed.

Enhancing Sr-deficient Sr(Ti0.3Fe0.7)O3–δ Cathode Performance through Sm0.5Sr0.5CoO3–δ Infiltration

The development of cathodes with improved polarization, aimed at reducing the operating temperature of solid oxide fuel cells (SOFCs), is an important avenue of research toward more efficient SOFCs. Sr(Ti0.3Fe0.7)O3–δ recently emerged as an active and stable cathode material; although its oxygen transport capability was shown to be further improved by introducing a Sr deficiency, the accompanying increased sinterability creates challenges in optimizing cathode microstructure. One facile approach may be single-step infiltration with highly active materials, such as Sr0.5Sm0.5CoO3–δ (SSC). However, there is limited knowledge regarding the impact of SSC on the electrochemical mechanisms within Sr-deficient Sr(Ti0.3Fe0.7)O3–δ . In this study, we systematically investigate the electrochemical characteristics of SSC-infiltrated Sr0.95(Ti0.3Fe0.7)O3–δ (STF) cathodes. Transmission line model-based impedance analysis provides a mechanistic understanding of STF and the role of SSC infiltrants in polarization improvement. The results reveal that SSC effectively reduces the resistance associated with key electrode processes, including oxygen diffusion, surface exchange, and dissociative adsorption/desorption. Consequently, using SSC infiltration, the power density of a Ni–Zr0.84Y0.16O2–δ (YSZ) anode-supported full cell with thin (∼2.5 μm) electrolyte increased from ∼1.88 to ∼2.47 W cm–2 at 800 °C.

Spontaneous Growth of Perovskite‐Derived Oxide over Double Perovskite Surface for Enhancing Cathodic Performance in Protonic Ceramic Fuel Cells

AbstractRobust catalytic materials with high activity and stability play important roles in energy conversion and storage devices such as protonic ceramic fuel cells (PCFCs), in which a favourable cathode should possess high oxygen ion, proton and electron triple conductivities, and superior surface oxygen exchange kinetics. Herein, a thermal‐driven self‐construction phenomenon in cation‐nonstoichiometric Ba1+xGd1‐xCo2O6‐δ is reported, accordingly developing a new type of nanocomposite, that is, double perovskite BaGdCo2O6‐δ (DP‐BGCO) anchored by perovskite‐derived BaCoO3‐δ (P‐D‐BCO) nanoparticles, which, used as the cathode of PCFCs, demonstrates low area‐specific resistances of 0.053 and 0.026 ohm cm−2 respectively at 650 and 700 °C over BaZr0.3Ce0.5Y0.1Yb0.1O3‐δ protonic electrolyte and attractive peak power densities of 0.87 (650 °C) and 1.15 W cm−2 (700 °C) with outstanding stability, much superior to the similar cell with single‐phase BCO or BGCO cathodes. The synergy between the two components brings the outstanding performance with the mixed oxygen ion and electronic conducting perovskite‐derived oxide showing superior catalytic activity for oxygen reduction reaction while the double perovskite provides good bulk protonic conductivity to enlarge reaction sites. Such selective self‐construction, well manipulated through the A‐site cation stoichiometry engineering, provides a facile way for developing new high‐performance electrocatalysts with broad application potential.

Ni-doped Fe-based perovskite to obtain multifunctional and highly efficient electrocatalytic active IT-SOFC electrode

This paper systematically studies Ni doping at Fe sites in La0.6Sr0.4Co0.3Fe0.7O3-δ (LSCF) as an intermediate temperature solid oxide fuel cell (IT-SOFC) electrode. The electrocatalytic activity of Ni-doped electrodes in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) modes was analyzed, rather than individual cathode or anode. The results indicate that Ni doping increases the internal vacancies, ORR activity, and charge transfer ability of La0.6Sr0.4Co0.3Fe0.6Ni0.15O3-δ (LSCFN15). In addition, compared to LSCF, LSCFN15 also reduces the energy barriers for surface oxygen exchange and bulk diffusion, thereby increasing the overall ORR kinetic rate. Combined with the distribution of relaxation time (DRT) analysis, it was confirmed that Ni-doped LSCFN15 increased the adsorption and dissociation rates of oxygen. At 750 ℃, the area-specific resistance (ASR) of LSCFN15 reached 0.045 Ω cm2, which is only 58.4 % of LSCF (0.077 Ω cm2). As a SOFC cathode, the peak power density (PPD) reached 1175 mW cm−2, 1.31 times that of LSCF (898 mW cm−2). As a SOFC anode, the current exchange density of LSCFN15 in OER mode reaches 164 mA cm−2, which is higher than the 125 mA cm−2 of LSCF, indicating that LSCFN15 also has the potential to serve as an anode for SOFC. In addition, Ni doping reduces the thermal expansion coefficient of the electrode and improves its thermal compatibility with traditional electrolytes. As an electrode, LSCFN15 exhibits excellent long-term stability in both SOFC and SOEC modes. Overall, Ni-doped Fe-based perovskite can improve the ORR and OER activities while enhancing the stability of cell operation and is expected to obtain multifunctional SOFC electrode materials.

Machine Learning Design of Perovskite Catalytic Properties

AbstractDiscovering new materials that efficiently catalyze the oxygen reduction and evolution reactions is critical for facilitating the widespread adoption of solid oxide fuel cell and electrolyzer (SOFC/SOEC) technologies. Here, machine learning (ML) models are developed to predict perovskite catalytic properties critical for SOFC/SOEC applications, including oxygen surface exchange, oxygen diffusivity, and area specific resistance (ASR). The models are based on trivial‐to‐calculate elemental features and are more accurate and dramatically faster than the best models based on ab initio‐derived features, potentially eliminating the need for ab initio calculations in descriptor‐based screening. The model of ASR enables temperature‐dependent predictions, has well calibrated uncertainty estimates and online accessibility. Use of temporal cross‐validation reveals the model to be effective at discovering new promising materials prior to their initial discovery, demonstrating the model can make meaningful predictions. Using the SHapley Additive ExPlanations (SHAP) approach, detailed discussion of different approaches of model featurization is provided for ML property prediction. Finally, the model is used to screen more than 19 million perovskites to develop a list of promising cheap, earth‐abundant, stable, and high performing materials, and find some top materials contain mixtures of less‐explored elements (e.g., K, Bi, Y, Ni, Cu) worth exploring in more detail.

A-site and B-site co-doped PrBaFe2O5+δ double perovskite as a symmetrical electrode of solid oxide fuel cell with potential of CO2 electrolysis

In this study, PrBa0.5Sr0.5Fe1.9Ge0.1O5+δ (PBSFG), the Sr and Ge doped PrBaFe2O5+δ (PBF), is investigated as a symmetrical electrode of solid oxide cells (SOCs). PBSFG has the potential to be a promising symmetrical electrode in SOCs owing to its high catalytic performance with redox stability. The concentration of oxygen vacancies and surface exchange coefficient of PBSFG are better than that of PBF. The results indicate that PBSFG exhibits not only adequate performance in the fuel cell, with a maximum power density of 1.05 W cm−2 at 800 °C, but also enhanced CO2 electrolysis performance, compared to the PBF. Specifically, in the CO2-electrolysis mode, a maximum current density of 825 mA cm−2 is measured at 850 °C and 1.5 V, which is substantially higher than that of 370 mA cm−2 measured for undoped PBF. These results demonstrate the effectiveness of Sr and Ge doping in PBF to improved CO2 electrolysis performance and notable fuel cell performance.

Ta/Nb doping motivating cubic phase stability and CO2 tolerance of Sr2Co1.6Fe0.4O6-δ double perovskite for high-performing SOFC cathode

Developing cathodes that are both phase-stable and tolerant to carbon dioxide (CO2) is a crucial and challenging task for solid-oxide fuel cells (SOFCs) operating at reduced temperatures. The activity of oxygen reduction reaction (ORR) in SOFC cathodes is typically influenced by factors such as geometric features and oxygen vacancies. In this study, new and robust cathodes for SOFCs, Sr2Co1.5Fe0.4Ta0.1O5+δ (SCFT) and Sr2Co1.5Fe0.4Nb0.1O5+δ (SCFN) are developed by doping a small amount of niobium (Nb) and tantalum (Ta) into Sr2Co1.6Fe0.4O5+δ (SCF) using a simple solid-state reaction technique. The effects of Nb/Ta doping on the crystal structure, oxygen vacancies, electrical conductivity, and electrochemical properties of SCFT and SCFN are investigated. The results reveal that these materials possess a fully cubic structure in the Fm-3m space group, with improved oxygen vacancy and electrical conductivity. They also exhibit good chemical compatibility with electrolytes at 1100 °C for 8 h and remain thermally stable when exposed to air and CO2 at 700 °C, without any additional phase formation. The area-specific resistance (ASR) of the SCFT cathode is found to be only 0.06 Ω cm2, whereas the SCFN cathode has an ASR of 0.10 Ω cm2. The superior performance of SCFT can be attributed to the higher oxygen vacancy, which enhances oxygen surface exchange kinetics and diffusivity compared to SCFN. When tested in a single cell using humidified H2 as the fuel and ambient air as the oxidant, the SCFT cathode achieves a power density of 656 mW cm−2 at 700 °C, while the SCFN cathode reaches 559 mW cm−2, indicating the potential of SCFT as a promising cathode material for SOFCs. The excellent performance of these materials can be attributed to their mixed electronic-ionic conduction properties, unique structural features, and high observed oxygen vacancy, which contribute to their remarkable electronic conductivity and significant ionic mobility.

Oxygen surface exchange kinetics of La1−xSrxCoO3–δ thin-films decorated with binary oxides: links between acidity, strontium doping, and reaction kinetics

Recent study shows the enhancement of oxygen exchange kinetics of oxygen electrodes using oxides selected using Smith acidity. However, what are the limits to this approach?

Pr2Ni0.8Co0.2O4+δ impregnated La0.6Sr0.4CoO3-δ oxygen electrode for efficient CO2 electroreduction in solid oxide electrolysis cells.

The solid oxide electrolysis cell (SOEC) is an advanced electrochemical device with a promising future in reducing CO2 emissions. Currently, the insufficient oxygen evolution reaction activity in conventional anode materials severely restricts the development of electrolytic CO2. Herein, the PNCO-LSC composite oxygen electrode was exploited by impregnating Pr2Ni0.8Co0.2O4+δ (PNCO) on the surface of La0.6Sr0.4CoO3-δ (LSC) oxygen electrode. The results of electrochemical tests and various physicochemical characterizations indicate that the infiltration of PNCO can lead to a significant improvement in the performance of the cell for CO2 electroreduction by increasing the surface oxygen exchange. The current density of the PNCO-LSC oxygen electrode infiltrated twice at 800 °C and 1.5 V reaches 0.917 A cm-2, which is about 40% higher than that of the bare LSC oxygen electrode. In addition, the single cell did not show significant degradation in a long-term stability test at a current density of 0.4 A cm-2 for 100 h of electrolysis. Therefore, the PNCO-LSC composite oxygen electrode material is effective in enhancing electrolytic CO2 performance.