Oxygen Electrode Research Articles

Facile anion engineering: A pathway to realizing enhanced triple conductivity in oxygen electrodes for reversible protonic ceramic electrochemical cells

Reversible proton ceramic electrochemical cells (R-PCECs) have emerged as a promising solution for sustainable energy conversion and storage at intermediate temperatures. However, the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics at the air electrodes of R-PCECs limit the cell performance. To achieve improved ORR/OER catalytic performance, we propose a practical approach of strategic anion engineering on the oxygen site of air electrode materials. Specifically, the popular triple H+/e−/O2− conducting oxide (TCO) Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) is selected to enhance the limiting H+/O2− generation and migration processes as an efficient air electrode for R-PCECs. By introducing different electronegative elements (F and Cl) to weaken metal-oxygen bonds (M-O), the oxygen chemical environment of the electrode material was optimized, thereby promoting surface oxygen exchange and O2−/H+ bulk migration. The resulting Ba0.5Sr0.5Co0.8Fe0.2O2.9-σF0.1 electrode exhibits enhanced proton uptake/mobility and catalytic activity for ORR and OER, as well as improved stability. This research offers a rational design strategy for engineering high-performance R-PCEC air electrodes with enhanced operating stability for efficient and sustainable energy conversion and storage.

Role of phosphorus impurities in decomposition of La2NiO4–La0.5Ce0.5O2-δ oxygen electrode in a solid oxide electrolysis cell

This study explored the decomposition mechanism of a La2NiO4 (LNO) phase in the La2NiO4–La0.5Ce0.5O2-δ (LNO-LDC) oxygen electrode in a solid oxide electrolysis cell (SOEC) after testing at 800 °C. Scanning electron microscopy and scanning transmission electron microscopy examinations of the LNO-LDC oxygen electrode before and after testing were undertaken. Other than phosphorus contamination in the form of P-rich grains and P-rich deposits along all grain boundaries (GBs), LNO and LDC phases were intact without degradation in the as-fabricated electrode. However, mild to aggressive LNO phase decomposition triggered by the phosphorus poisoned GBs was observed after testing at 800 °C for 900 h. The evolution of the LNO phase decomposition was noted beginning with the exsolution of Ni into the surrounding LNO matrix and GBs, forming La-rich and Ni-rich phases correspondingly, in the LNO. This study illustrates a detailed decomposition progress of the LNO phase at the atomic level under an SOEC operation condition, and sheds light on how to ameliorate the fabrication process of SOECs to enhance their performance and durability.

Pathway to high performance, low temperature thin-film solid oxide cells grown on porous anodised aluminium oxide

Reversible solid oxide cells (rSOCs) present a promising solution to future energy challenges through the efficient conversion between electrical and chemical energy. To date, the benefits of rSOC technology have been off-limits to portable power and electrolysis applications due to the excessive polarisation resistance of the oxygen electrode at low temperatures, characterised by high area specific resistance (ASR) values below 500 °C. In this work we demonstrate growth of symmetric and complete rSOC structures based on state-of-the-art vertically aligned nanocomposite (VAN) films grown by pulsed laser deposition (PLD) on porous Pt-coated anodised aluminium oxide (AAO) substrates. The symmetric rSOC structures give the first demonstration of an rSOC oxygen electrode with ASR below 0.1 Ωcm2 at temperatures less than 450 °C. This is achieved through oxygen vacancy tuning by annealing, as confirmed by Time-of-Flight Elastic Recoil Detection Analysis (ToF-ERDA) and Rutherford Backscattering Spectrometry (RBS) measurements. Thus, the present work describes a promising route towards future high-performance rSOC devices for portable power applications.

Improving Ruddlesden-Popper electrocatalysts through interstitial fluorination-driven rearrangements of local coordination environment

Anion-doping is an attractive strategy to regulate the local coordination environment of oxygen electrodes in solid oxide fuel cells (SOFCs), which is generally regarded as a substitution for O-sites. In this work, the interstitial fluorine anion-doping in Sr3Fe2O7-δ, a Ruddlesden-Popper oxide with a two-layered structure, has been observed for the first time. The X-ray absorption fine structure analysis and Rietveld refined X-ray diffraction results demonstrate that the fluorine anion dopants occupy the rock-salt layer forming the stronger metal-fluorine bonds to activate oxygen ions. Density functional theory calculations further verify fluorine anions' ability to insert into tetrahedral intervals consisting of four Sr2+ in the rock-salt layer. The elevated proportion of O22−/O− and Fe4+ are obtained, which are commonly deemed in favor of oxygen reduction reaction. The fluorine anion-doped oxygen electrode exhibits more than a 20% drop in area specific resistance measured from 600 to 750 °C. In addition, the symmetric cell with Sr3Fe2O7-δF0.1 single-phase cathode shows excellent durability within a 1000 h thermal cycling and long-term tests in air atmosphere. A high peak power density of 888 mWcm−2 is achieved at 700 °C, showing a 35% improvement.

Molecular cleavage strategy enabling optimized local electron structure of Co-based metal-organic framework to accelerate the kinetics of oxygen electrode reactions in lithium-oxygen battery

Metal-organic frameworks (MOFs) are considered as promising oxygen electrode materials for lithium-oxygen (Li-O2) batteries. However, their structure-activity relationship in catalyzing oxygen electrode reactions in Li-O2 battery is currently overlooked. Herein, molecular cleavage strategy is adopted to optimize local coordination structure of Co-MOF via introducing missing linkers. Theoretical calculation certifies that the introduction of monodentate ligand-benzoic acid (BA) as the missing linker causes the generation of defect state. Moreover, asymmetrically coordinated cobalt with surrounding oxygen caused by the introduction of BA optimizes electron coupling between Co 3d orbits and oxygen adsorbents, eventually promoting oxygen electrode reactions in Li-O2 batteries. However, excessive missing linkers can lead to the collapse of framework, covering active sites and thus deteriorating the catalytic activity of MOF. As a result, Li-O2 battery with Co-MOF containing 10 mol% BA (named as Co-MOF-BA0.1) delivers low overpotential of 0.86 V and large discharge capacity of 14011 mAh g−1.

Cycling tests of a reversible BaCe0.8Zr0.1Y0.1O3−δ electrolyte-based protonic ceramic cell with SmBa0.5Sr0.5Co1.5Fe0.5O5+δ oxygen electrode

Cells based on proton-conducting ceramics (PCC) working at intermediate temperatures have intrinsic properties that suggest promising potential applications. Currently, almost all the literature in the field of PCC has focused on hydrogen conversion (Protonic Ceramic Fuel Cell PCFC) and/or hydrogen production (Protonic Ceramic Electrolysis Cell PCEC). Very few studies have inspected the reversibility of these systems (RePCC) in order to understand their potential coupling to intermittent renewable energies. Despite the promising results achieved, the development of these technologies remains very challenging.The work presented here illustrates the fabrication and the characterization of a 32 mm–diameter hydrogen-electrode-supported cell. A double perovskite with general formula AA’BB’O5+δ is used as air electrode material (SmBa0.5Sr0.5Co1.5Fe0.5O5+δ, SmBSCF) exhibiting very good stability under water vapor- and carbon dioxide-containing atmosphere.The maximal power density of the Ni–BaCe0.8 Zr0.1Y0.1O3-δ (Ni-BCZY81)/BCZY81/SmBSCF cell corresponds to 0.58 W cm−2 at 600 °C in fuel cell mode and a current density of j = 0.8 A cm−2 is measured at 1.3 V and 600 °C in electrolysis mode. The results were collected over a total working time of 280 h. The cell was stressed with several complete shutdowns and restarting protocols exhibiting an overall remarkable reversibility and durability.

Uridine Diphosphate Glucose (UDP-G) Activates Oxidative Stress and Respiratory Burst in Isolated Neutrophils.

The extracellular purinergic agonist uridine diphosphate glucose (UDP-G) activates chemotaxis of human neutrophils (PMN) and the recruitment of PMN at the lung level, via P2Y14 purinergic receptor signaling. This effect is similar to the activation of PMN with N-formyl-methionyl-leucyl-phenylalanine (fMLP), a mechanism that also triggers the production of superoxide anion and hydrogen peroxide via the NADPH oxidase system. However, the effects of UDP-G on this system have not been studied. Defects in the intracellular phagocyte respiratory burst (RB) cause recurrent infections, immunodeficiency, and chronic and severe diseases in affected patients, often with sepsis and hypoxia. The extracellular activation of PMN by UDP-G could affect the RB and oxidative stress (OS) in situations of inflammation, infection and/or sepsis. The association of PMNs activation by UDP-G with OS and RB was studied. OS was evaluated by measuring spontaneous chemiluminescence (CL) of PMNs with a scintillation photon counter, and RB by measuring oxygen consumption with an oxygen Clark electrode at 37 °C, in non-stimulated cells and after activation (15 min) with lipopolysaccharides (LPS, 2 µg/mL), phorbol myristate acetate (PMA, 20 ng/mL), or UDP-G (100 μM). The stimulation index (SI) was calculated in order to establish the activation effect of the three agonists. After stimulation with LPS or PMA, the activated PMNs (0.1 × 106 cells/mL) showed an increase in CL (35%, p < 0.05 and 56%, p < 0.01, SI of 1.56 and 2.20, respectively). Contrariwise, the stimulation with UDP-G led to a decreased CL in a dose-dependent manner (60%, 25 μM, p < 0.05; 90%, 50-150 μM, p < 0.001). Nonetheless, despite the lack of oxidative damage, UDP-G triggered RB (SI 1.8) in a dose-dependent manner (38-50%, 100-200 μM, p < 0.0001). UDP-G is able to trigger NADPH oxidase activation in PMNs. Therefore, the prevention of OS and oxidative damage observed upon PMN stimulation with UDP-G indicates an antioxidant property of this molecule which is likely due to the activation of antioxidant defenses. Altogether, LPS and UDP-G have a synergistic effect, suggesting a key role in infection and/or sepsis.

Interface Diffusion and Compatibility of (Ba,La)FeO3-δ Perovskite Electrodes in Contact with Barium Zirconate and Ceria.

Ba1-xLaxFeO3-δ perovskites (BLF) capable of conducting electrons, protons, and oxygen ions are promising oxygen electrodes for efficient solid oxide cells (fuel cells or electrolyzers), an integral part of prospected large-scale power-to-gas energy storage systems. We investigated the compatibility of BLF with lanthanum content between 5 and 50%, in contact with oxide-ion-conducting Ce0.8Gd0.2O2-δ and proton-conducting BaZr0.825Y0.175O3-δ electrolytes, annealing the electrode-electrolyte bilayers at high temperature to simulate thermal stresses of fabrication and prolonged operation. By employing both bulk X-ray diffraction and synchrotron X-ray microspectroscopy, we present a space-resolved picture of the interaction between electrode and electrolyte as what concerns cation interdiffusion, exsolution, and phase stability. We found that the phase stability of BLF in contact with other phases is correlated with the Goldschmidt tolerance factor, in turn determined by the La/Ba ratio, and appropriate doping strategies with oversized cations (Zn2+, Y3+) could improve structural stability. While extensive reactivity and/or interdiffusion was often observed, we put forward that most products of interfacial reactions, including proton-conducting Ba(Ce,Gd)O3-δ and mixed-conducting (Ba,La)(Fe,Zr,Y)O3-δ, may not be very detrimental for practical cell operation.

High-performance screening of carbon-nitride single-atom catalysts for oxygen electrode reaction in rechargeable metal–air batteries

The sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which are the oxygen electrode reactions, impede further advancements in metal–air batteries technology. The main objective is to investigate the bifunctional catalytic activity of the VIIB, VIII, IB, and IIB groups transition metals doped carbon-nitride material (C9N4, C10N9, C13N3, C14N12, and C19N3) as bifunctional electrocatalysts for oxygen electrode reaction in metal–air batteries by density functional theory methods in this paper. C9N4, C13N3, and C19N3 are better doping substrates than C10N9 and C14N12 for all transition metals. For ORR, Co-C9N4, Cu-C13N3, Rh-C13N3, Co-C19N3, Ni-C19N3, and Cu-C19N3 exhibit the overpotential values of 0.36, 0.37, 0.40, 0.47, 0.48, and 0.48 V, respectively. These values are comparable to or even better those of Pt(111), indicating their exceptional ORR catalytic activity. For OER, Rh-C9N4, Pt-C9N4, Co-C13N3, Rh-C13N3, and Ni-C19N3 possess the overpotential values of 0.42, 0.40, 0.40, 0.33, and 0.41 V, respectively, showcasing a remarkable similarity to that of RuO2(110). Rh-C13N3 exhibits superior bifunctional catalytic activity (Bifunctional Index = 0.73 V). This study offers essential theoretical guidance for the utilization of carbon-nitride single-atom catalysts as bifunctional electrocatalysts in the oxygen electrode reaction of rechargeable metal-air batteries.

Thickness effect of thin-film barrier layers for enhanced long-term operation of solid oxide fuel cells

Highly efficient solid oxide cells are one of the most promising technologies for a sustainable future based on renewable hydrogen. The diffusion barrier layer employed between zirconia-based electrolytes and state-of-the-art oxygen electrodes aims to limit the formation of electrically insulating secondary phases that dramatically reduce the cells’ performance. Conventional barrier layers manufactured by screen-printing technology lead to porous microstructures that enable the formation of insulating SrZrO3, partially blocking the active area of the cells. Opposite, homogeneous and dense barrier layers have proven to be the ultimate solution to limit interdiffusion, substantially improving the cells’ performance. Despite the relevance of this solution, the impact of the barrier layer thickness on the final performance of the cells is still unknown. In this work, gadolinia-doped ceria barrier layers with thicknesses between 200 and 800 nm made by pulsed laser deposition were studied in button cells. Excellent electrochemical performance was obtained for all the cells, improving 45% of the power output of the reference counterparts. Moreover, durability tests performed on the cell with the thinnest layer (200 nm) did not show any measurable degradation for 3500 h of continuous operation under high current densities of 0.77 A cm−2 (∼0.87 V) at 750 °C. Post-mortem characterization by synchrotron nano-x-ray fluorescence of a pristine cell and the aged cell allowed us to observe that some spots of SrZrO3 were present at the cathode/electrolyte interface since the cell manufacturing step without increasing during long-term operation. Indeed, the discontinuity of this insulating phase seems not to be critical for cell operation.

Quantifying individual electrode polarization and unraveling the interactive phenomenon in solid oxide fuel cells

In electrochemically active systems, such as fuel cells, electrolyzers, and batteries, researchers often modify the material chemistry or operating variables at one of the electrodes (e.g., the cathode) to investigate its properties. This approach assumes that changes in measured polarization and cell performance result solely from the modifications made to the selected electrode, while the conditions at the other electrode (e.g., the anode) remain constant. However, the potential interactions between the polarizations of these two electrodes have remained unclear. In our study, we utilize a voltage probe capable of precisely determining electrode polarization. Our findings reveal three key insights:1.The quantification of electrode polarization becomes feasible through the implementation of a voltage probe.2.The fuel electrode plays a pivotal role in the performance of state-of-the-art solid oxide cells, with its influence being comparable to that of the oxygen electrode.3.A reciprocal interaction exists between the two electrodes within a solid oxide cell. Consequently, when there are changes in the chemistry or operational conditions at one electrode, the polarization of the other electrode changes simultaneously.

Effect of temperature on the electrode overpotential of molten carbonate electrolysis and fuel cells with inert-gas step addition method

This study explores molten carbonate electrolysis and fuel cell behaviour across temperatures from 823 to 973 K using steady-state polarization (SSP), electrochemical impedance spectroscopy (EIS), and inert-gas step addition (ISA) techniques. The findings reveal that total voltage loss decreases with rising temperature in fuel cell (FC) and electrolysis (EC) modes. The ohmic loss similarly declines as temperature increases. The ISA method determines the gas-phase mass transfer-induced overpotential, which increases as temperature increases in both modes at the hydrogen electrode (HE). This indicates that pore diffusion resistance strongly affects the HE in both modes. The liquid-phase mass transfer-induced overpotential at the oxygen electrode (OE) exhibits a much smaller value in EC mode than in FC mode at all temperatures. The increased O2 and CO2 partial pressures and decomposition of sufficient amounts of carbonate electrolytes to generate O2 in EC mode would reduce the liquid-phase resistance and its induced overpotential at the OE in the temperature range.

Enhanced Peroxide Fluxes and Radiosensitization in Colorectal Tumors but Not Normal Enterocytes from the Combination of Superoxide Dismutase Mimetics and Pharmacological Ascorbate

Selective superoxide dismutase mimetics (DMs), including GC4419 and GC4711, are radiation (RT) modulators which induce opposite effects in tumors and normal tissues and may be ideally suited for locally advanced rectal cancer. However, their tumor radiosensitization effect is limited at RT doses relevant to rectal cancer (2-5 Gy). Over this dose range, they protect normal mucosal tissues, but we and others have shown they do not reliably enhance tumor radiosensitization at doses < 8-15 Gy. We hypothesize that combining DMs and other therapies which also target redox metabolism may effectively sensitize tumors to clinically relevant RT doses for rectal cancer while maintaining their normal tissue sparing effects. Like DMs, pharmacological ascorbate (P-AscH) selectively increases lethal hydrogen peroxide (H2O2) fluxes in tumors, but it does so through distinct mechanisms which are potentially complimentary with DMs (particularly at low RT doses). Human HCT116, SW480, and HT29 colorectal tumor models and non-malignant FHs74 intestinal epithelial cells were used. Clonogenic survival was assessed following single-fraction RT (2-5 Gy) +/- P-AscH (5 pmol/cell) +/- GC4711 (20 µM). Dependency on H202 fluxes was tested by adding bovine catalase with drug and RT treatments. Oxygen consumption in culture media was measured using a Clark electrode. Rectal toxicity was assessed in vivo using IHC in fixed rectal tissues following fractionated, image-guided rectal RT (5-9 Gy x 3). Tumor growth delay was assessed following RT (5 Gy x 3) +/- P-AscH (4 g/kg) +/- GC4419 (10 mg/kg) in animals with unilateral HCT116 flank tumors. Combination therapy with P-AscH and GC4711 potently radiosensitized all tumor lines in vitro whereas neither agent significantly decreased clonogenic survival as a monotherapy. Neither drug nor combination treatment sensitized FHs74 epithelial cells. P-AscH increased oxygen consumption and H2O2 production in culture media and the addition of GC4711 significantly increased both more than P-AscH alone. Co-treatment with exogenous catalase inhibited cancer cell killing with combination therapy +/- RT. In vivo, combination therapy significantly enhanced tumor growth delay and survival. Both agents significantly decreased markers of acute rectal RT injury as monotherapies. Co-treatment with DMs and P-AscH selectively enhanced tumor radiosensitization by increasing oxygen consumption and H202 fluxes even in tumor models which are known to be resistant to oxidative stressors (HT29). In contrast, each agent conferred a radioprotective effect in the rectum. Combination therapy with DMs and P-AscH may represent a novel, potent approach to target dysregulated redox metabolism in colorectal tumors.

Reversed charge transfer induced by nickel in Fe-Ni/Mo2C@nitrogen-doped carbon nanobox for promoted reversible oxygen electrocatalysis

The interaction between metal and support is critical in oxygen catalysis as it governs the charge transfer between these two entities, influences the electronic structures of the supported metal, affects the adsorption energies of reaction intermediates, and ultimately impacts the catalytic performance. In this study, we discovered a unique charge transfer reversal phenomenon in a metal/carbon nanohybrid system. Specifically, electrons were transferred from the metal-based species to N-doped carbon, while the carbon support reciprocally donated electrons to the metal domain upon the introduction of nickel. This led to the exceptional electrocatalytic performances of the resulting Ni-Fe/Mo2C@nitrogen-doped carbon catalyst, with a half-wave potential of 0.91 V towards oxygen reduction reaction (ORR) and a low overpotential of 290 mV at 10 mA cm−2 towards oxygen evolution reaction (OER) under alkaline conditions. Additionally, the Fe-Ni/Mo2C@carbon heterojunction catalyst demonstrated high specific capacity (794 mA h gZn−1) and excellent cycling stability (200 h) in a Zn-air battery. Theoretical calculations revealed that Mo2C effectively inhibited charge transfer from Fe to the support, while secondary doping of Ni induced a charge transfer reversal, resulting in electron accumulation in the Fe-Ni alloy region. This local electronic structure modulation significantly reduced energy barriers in the oxygen catalysis process, enhancing the catalytic efficiency of both ORR and OER. Consequently, our findings underscore the potential of manipulating charge transfer reversal between the metal and support as a promising strategy for developing highly-active and durable bi-functional oxygen electrodes.

Improved La0.8Sr0.2MnO3-δ oxygen electrode activity by introducing high oxygen ion conductor oxide for solid oxide steam electrolysis

The limited oxygen ion conductivity of conventional La0.8Sr0.2MnO3-δ (LSM) electrode has hindered the development of high-performance solid oxide cells. To address this issue, the electrode interface structure of LSM electrode is regulated by incorporating oxides with high oxygen ion conductivity. Specifically, the addition of Dy and Y co-doped Bi2O3-δ oxide (DBY) with a conductivity of 0.34 S cm−1 at 700 °C, which is almost 9 and 20 times higher than conventional SDC and YSZ oxides, has found to substantially reduce the electrode sintering temperature and enhance the transport ability of ion and electron at the interface. As a result, the interface polarization resistance of the LSM/DBY composite electrode is as low as 0.096 Ω cm2 at 700 °C. Finally, a solid oxide cell equipped with an LSM/DBY electrode attains a high power density of 1.78 Wcm−2 in fuel cell mode at 800 °C and 3%H2O–H2, as well as a current density of −1.58 Acm−2 in electrolysis mode under 1.50 V and 50% H2O–H2 condition.

Substrate‐Driven Catalyst Reducibility for Oxygen Evolution and Its Effect on the Operation of Proton Exchange Membrane Water Electrolyzers

To increase the efficiency of hydrogen production by proton exchange membrane water electrolyzers (PEMWEs), the relationships between the specific activity and stability of the membrane–electrode assembly (MEA) must be clarified. Ir oxide electrodeposited on Ti substrate is used as an oxygen electrode, and its electronic properties and electrochemical behavior in PEMWE operation are observed. The electrode, fabricated through a facile strategy based on annealing in the air atmosphere, enhances the specific oxygen evolution reaction (OER) activity and stability in PEMWE operation. Furthermore, the electronic catalyst–substrate interactions associated with different reducibilities in the heteroatom system are studied. The morphology, electronic properties, and chemical state of the oxygen electrode are investigated through X‐ray spectroscopy, microscopy techniques, and computational analyses. Thermal treatment of the catalyst‐coated substrate decreases the bulk oxidation state of Ir and increases the surface oxidation state. According to the electrochemical and physical behavior analyses of PEMWEs, the oxygen content in the Ir oxide structure, which defines the OER activity and its stability, is influenced by the crystalline structure and formation of a stable interface between the catalyst and substrate. The outcomes can facilitate the development of strategies for enhancing the performance of PEMWEs and designing rational MEAs.

Theoretical insights on oxygen electrode reactions of YNxC4-x@Gra with hydroxylation effect

The oxygen electrode reactions (ORR/OER) are the key to electrochemical storage and conversion technologies. In this study, the bifunctional electrocatalytic mechanisms of YNxC4-x@Gra with hydroxylation effect were discussed extensively. Firstly, the configurations with N coordination have good stability. Secondly, YN1C3/N2C2hex@Gra with unstable coordination environment break the scale relationships between adsorption intermediates and exhibit outstanding OER performance with ηOER of 0.45 V and 0.46 V. Thirdly, YN2C2oppo/N2C2pen/N3C1OH@Gra with stable coordination environment demonstrate excellent bifunctional activity with ηORR of 0.48 V, 0.54 V, and 0.53 V and ηOER of 0.71 V, 0.73 V, 0.63 V. Forth, for catalysts with stable coordination environments, there are scale relationships between the adsorption of intermediates, and thus volcanic curves were constructed. Finally, the d-electron number was introduced to predict catalytic performance, saving time and computative costs for screening potential catalyst configurations. All in all, YNxC4-x@Gra catalysts are potential oxygen electrode bifunctional electrocatalysts.

Uniform and scalable Sm3+ and Nd3+ doped ceria nanocatalysts decorating bifunctional oxygen electrodes for high performing reversible solid oxide electrochemical cells

Surface modification with nanoparticles has been widely studied to promote catalytic activity and stability of the oxygen electrode in solid oxide electrochemical cells (SOCs). However, attaining uniformity and scalability of the nanoparticles remains a challenging endeavor. Herein, we developed a highly conductive nano-sized Sm3+ and Nd3+ double-doped ceria decorated La0.6Sr0.4Co0.2Fe0.8O3-δ -Gd0.1Ce0.9O2- δ (SNDC@LSCF-GDC) oxygen electrode via an ultrasonic spray infiltration technique. The uniform SNDC infiltrates promote oxygen catalytic activity by increasing oxygen vacancies and reaction sites on the surface of the electrode. The SOC with the SNDC@LSCF-GDC oxygen electrode shows high performance in fuel cell (1.97 W/cm2 at 750 °C) and electrolysis cell (1.72 A/cm2 at 750 °C) modes. Moreover, ultrasonic infiltration-based SNDC nanoparticles were successfully demonstrated in a large-size commercial cell (10 cm × 10 cm effective area), showing increased power output and remarkable stability for 960 h. This work presents a scalable and feasible way to decorate large area electrodes with uniform infiltrates for energy storage and conversion applications.

Optimizing d-orbital occupation on interfacial transition metal sites via heterogeneous interface engineering to accelerate oxygen electrode reaction kinetics in lithium-oxygen batteries

Aprotic lithium-oxygen batteries (LOBs) possess extremely high theoretical energy density of about 3500 Wh kg-1, which is superior to state-of-the-art lithium-ion batteries. However, the poor energy efficiency and cyclability originated from sluggish kinetics of oxygen electrode reactions in LOBs severely restrict their development and practical application. The solution to these challenges is closely related to the construction of electrocatalysts with both high catalytic activity and stability for oxygen redox reactions in LOBs. In this work, Co3O4 @NiFe2O4 composite with modified heterogeneous interface is fabricated and studied as oxygen electrode catalyst for LOBs. It is theoretically predicted that the electron transfer at the heterogeneous interface in Co3O4 @NiFe2O4 is capable of reducing the occupation of eg electrons in the interfacial Ni sites, leading to the rearrangement of electrons with enhanced spin polarization in the d orbital and the upshift of the d-band center toward Fermi level, eventually enabling the smooth electron transfer between Co3O4 @NiFe2O4 and oxygenated species due to the facile formation of Ni-O bond. This endows Co3O4 @NiFe2O4 based LOBs with high specific capacity of 12697 mAh g-1 and extremely low overpotential of 0.68 V at 100 mA g-1, as well as long cycle life of 274 times at a high current density of 500 mA g-1. This work provides a new strategy for adjusting the surface electronic structure of oxygen electrode catalysts to accelerate oxygen redox kinetics in LOBs.

Study of Ca3Co4O9+δ oxygen electrode with La0.6Sr0.4FeO3-δ interlayer in YSZ-based reversible solid oxide cells

The electrochemical performance of Ca3Co4O9+δ (CCO) oxygen electrode with La0.6Sr0.4FeO3-δ (LSF) interlayer in YSZ-based reversible solid oxide cells (RSOCs) was investigated in present work. Results proved that CCO oxygen electrode with LSF interlayer had a superior stability under alternating anodic and cathodic polarization. Both the polarization resistance and overpotential of the CCO electrode with LSF interlayer were significantly reduced compared to that with Ce0.9Gd0.1O1.95 (GDC) interlayer, which confirmed the improvement of the redox reactivity of the oxygen electrode. The maximum power density of Ni-YSZ/YSZ/LSF/CCO fuel cell was 1276 mW cm−2 at 800 °C. An electrolysis current density of 1695 mA cm−2 was achieved at 1.5 V and 50% H2O. The hydrogen production rate of the electrolysis cell improved by 2 times than that with the GDC interlayer. Results made clear reliability of LSF as an interlayer in YSZ-based RSOCs.