Oxygen Electrode Research Articles

Oxygen Electrode Surface Constructing for Reversible Protonic Ceramic Electrochemical Cells

Reversible protonic ceramic electrochemical cells (R-PCECs) have great potential for energy conversion and storage at low-intermediate temperatures (400-700oC), which could enable the conversion of H2O into H2 in electrolysis (EL) mode, and inversely the production of electricity in fuel cell (FC) mode. However, the sluggish kinetics of oxygen reduction/evolution reaction (ORR/OER) at reduced temperatures, as well as undesired surface segregation and structural deterioration, have impeded the development of R-PCECs devices. In this presentation, we introduce a double-perovskite type oxygen electrode that has been optimized for enhanced reaction activity and surface stability using an efficient fluorite catalyst coating. Specifically, the oxygen electrode, PrBaCo2O5+δ (PBC), has been infiltrated with an active and durable shell, Pr0.1Ce0.9O2+δ (PCO). The obtained results show that PCO-PBC possess elevated oxygen vacancy concentration which would improve the surface exchange process, facilitate ion diffusion, and provide multiple active reaction sites, while simultaneously preventing Ba segregation during operation. Therefore, the fuel-electrode-supported single cell with a PCO-PBC oxygen electrode achieves high performance and a negligible degradation in EL and FC dual modes for 25 cycles and 100 h at 650 oC with 3vol.% H2O.

Effect of Backbone Selection on the Enhanced Electrocatalytic Activity of Pr2Ni0.6Cu0.4O4 Infiltrated Oxygen Electrodes

Infiltration is proved to be a highly efficient technique for increasing the electrocatalytic activity of oxygen electrodes in solid oxide fuel/electrolysis cells (SOFC/SOEC). One of the main advantages of this technique is the flexibility of choosing various backbone/surface-decoration combinations. The selection of correct backbone/surface-decoration combination is one of the challenges in developing the infiltrated oxygen electrodes. It is suggested that via choosing the correct combination, one can synergistically improve the electrochemical performance. Pr-based-Ruddlesden-Popper-nickelates such as Pr2Ni0.6Cu0.4O4 (PNCO) was recently demonstrated to be an efficient Cobalt-free and Alkaline earth-free electrocatalyst for oxygen reduction/evolution reaction (ORR/OER) when used as a surface decoration phases. Here, in this study, PNCO as a model electrocatalyst is infiltrated into various porous backbones of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), Ce0.9Gd0.1O2 (CGO), La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2 (LSCF/CGO) and LaNi0.6Fe0.4O3/Ce0.9Gd0.1O2 (LNF/CGO) with various levels of ionic and electronic conductivity, and effect of infiltration loading on polarization and series resistance of symmetrical cells was investigated. The results showed that to achieve high performances via surface decoration of ionic conductor backbones, such as CGO, usually very high infiltration loadings as high as 15-30 wt% is required. The reason behind such high loadings is the fact that the surface decoration phases are the only sources of electronic conduction, and therefore high infiltration loadings are necessary to attain sufficient percolation of the electronic conducting phase. However, if the surface decoration phase does not possess high electronic conduction, which is the case for oxides such as PNCO, then additional paths for electronic conduction must be created in the electrode network to prevent current constriction effects. This additional path can be generated via replacing some fraction of the ionic conductor phase in the backbone with the electronic conductor phases such as LNF and LSCF. The other common strategy for developing efficient infiltrated oxygen electrode is the surface decoration of a mixed-ionic-electronic-conductor MIEC backbone (such as LSCF) with another MIEC phase (PNCO). The best performances in these types of infiltrated electrodes are achieved with significantly less infiltration loading compared to infiltrated ionic conductor backbones with values as low as 10 wt%. In this study, marked performance improvements were achieved with 10 wt% infiltration loading of PNCO, including a reduction by a factor of 2 of the polarization resistance at 650 °C for both LSCF (0.22 Ω.cm2 to 0.1 Ω.cm2) and the LSCF/CGO (0.15 Ω.cm2 to 0.06 Ω.cm2) state of the art electrodes. In CGO as well as LNF/CGO composite backbone, infiltration with 30 wt% of PNCO led to enhanced electrode performance improvement, reaching 0.24 Ω.cm2 and 0.1 Ω.cm2 at 650 °C, faster than the state-of-the-art LSCF-CGO (0.15 Ω.cm2) at same temperature, which shows the potential of these highly efficient cobalt-free and alkaline earth-free oxygen electrodes for (SOFC/SOEC) application. Figure 1

Measurements of Dioxygen Formation in Catalytic Electrochemical Water Splitting

Water oxidation is a multielectron complex reaction that produces molecular oxygen as the final product. The article addresses the lack of confirmation of oxygen product formation in electrochemical oxygen evolution reaction (OER) studies, despite the extensive research conducted on catalysts for water splitting. It critically evaluates the trend observed in many studies that solely rely on electrochemical methods for OER quantification without confirming the oxygen product via complementary analytical techniques. The omission of measuring evolved oxygen gas leaves a crucial gap in the quantification of the OER process and raises concerns about the validity and accuracy of reported results. Analytical techniques, such as gas chromatography, Rotating Ring-Disk Electrode (RRDE), fluorescence oxygen probes, Clark electrode, and volumetry are critically analyzed and described to ensure the reliability and credibility of voltammetry and bulk electrolysis to provide a more accurate assessment of the OER process.

(Invited) Ruddlesden-Popper Oxides As Bi-Functional Oxygen Electrodes

Incorporating more renewables into our energy mix is a major challenge that confronts our transition to a carbon free economy. Solid oxide electrochemical cells when operated alternately in fuel cell and electrolysis modes, enable the incorporation and integration of far greater amounts of solar and wind energy into our power grid. As islanded systems, they can also function as distributed generation systems thereby decreasing our reliance on the power grid. In this talk, we present a recent survey of results on rSOCs based on rare earth nickelate – rare-earth doped ceria composite oxygen electrodes that exhibit excellent cycling behavior when operated alternately in solid oxide fuel cell (SOFC) and solid oxide electrochemical cell (SOEC) modes of operation. The degradation in such cells is significantly mitigated by mode-switching operation when compared to operating in single mode operation in electrolysis mode. By comparing distributed relaxation times (DRT) analysis of impedance spectra obtained from single-mode (electrolysis) operated cells, and cells operated in switched-modes, we obtain clues into cell degradation mechanisms.

Development of Durable Materials for Cost Effective Water Splitting

Saint-Gobain, a global leader in ceramic and polymer based materials and components has been developing solutions for fuel and electrolysis cells for over 20 years. These solutions include; electrode and electrolyte materials, innovative cell and stack designs, ceramic interconnects, seals (both glass-ceramic and polymer based) and hot box designs. Although high temperature electrolysis promises to be an efficient solution to the production of hydrogen, durability and performance improvements are still required to produce devices that are economically feasible. A promising material family for the air electrode are rare-earth nickelate oxides with the Ruddlesden-Popper structure. These oxides are known to have a point defect structure in which oxygen interstitials play a key role in the oxygen surface exchange and transport through the lattice. Although the performance of the rare-earth nickelates can be high, they unfortunately react and decompose when in contact with rare-earth doped ceria. Ceria is typically added as a second phase from the standpoint of buffering the coefficient of thermal expansion, providing additional oxygen ionic conducting paths, and for forming the buffer layer preventing adverse reactions between the oxygen electrode and the electrolyte which are typically yttrium or scandium doped zirconia.This work focuses on stabilizing the rare-earth nickelate electrodes through compositional modifications while developing cell-design agnostic material solutions using these materials. The driving force for nickelate decomposition was determined to be the high limits for cation solubility within typical ceria-based barrier layers. A solution to this problem is presented. In addition, towards improving the performance of cells the oxygen diffusion mechanism was modeled allowing the calculation of ionic conductivity for a variety of cation substitutions within the nickelate structure. Fundamental material properties such as exchange coefficient, oxygen incorporation into the lattice as a function of partial pressure, and electrode resistance over time were measured. Finally, an innovative processing technique for the simultaneous multilayer coating of highly loaded slurries was developed. This process provides a reduction in the number of processing steps required to produce cells while also allowing for good layer adhesion as well as thickness control at the 2.5 micron range.

Degradation Issues in Solid Oxide Electrolysers

One of the crucial aspects to achieving long lifetime and high-efficient SOCs (Solid oxide cells) is to enhance durability of the current devices.Degradation issues are typically associated with problems in both electrodes. For example, nickel-yttria stabilized zirconia (Ni-YSZ) hydrogen electrodes present under extreme conditions of high steam partial pressures, a low durability due to Ni oxidation resulting in lowered electronic conductivity and catalytic activity of the electrode. Ni agglomeration, depleting and micro crack in Ni-containing hydrogen electrode can also occur leading to a lower activity of the Ni-based electrodes as an SOEC fuel electrode. Furthermore, carbon deposition and sulfur poisoning on the Ni surface are also lead to cell performance degradation and poor durability.In addition, the performance of the oxygen electrode is also particularly more important in electrolysis mode than in fuel cell mode, as it is well established that electrochemically induced oxygen pressure increase at the electrolyte-oxygen electrode interface and subsequent membrane failure have been theoretically predicted and experimentally observed in SOEC mode. For example, several examples in the literature reported the presence on voids at the YSZ electrolyte, leading to delamination of the oxygen electrode. In this sense, lanthanide nickelates (Ln = La, Nd, Pr) have received considerable interest as materials for IT-SOFC electrodes and oxygen separation membranes, and they seem to be very attractive for electrolysis applications. The hyperstoichiometry of some oxygen electrode materials such as these Ruddlesden-Popper phases is believed to be favourable for effective oxygen evolution, as performance of these electrodes is enhanced in SOEC mode.Different strategies to develop optimized electrode structures as well as controlled operating conditions will be discussed in order to improve the durability of SOCs.

Interaction of Catalysts for Unitized Regenerative Fuel Cells

There is a need for flexible and efficient storage facilities so that the integration of renewable energies and thus the energy transition can succeed. Intermediate storage of energy in the form of hydrogen by electrolysers and effective reconversion to electricity by fuel cells is a possibility. The unitized regenerative fuel cell (URFC) is a single-unit device that combines an electrolyser and a fuel cell, which makes the system costs much cheaper compared to two separate devices. Currently, the focus of URFC research, similar to proton exchange membrane (PEM) electrolysers, is on the development of new catalysts and electrodes with the aim of reducing costs through manufacturing and design optimization [1,2]. In this context, equally important is the increase of electrochemical activity on the oxygen side since oxygen evolution (OER) and oxygen reduction (ORR) are the speed-determining steps comparatively to their counter reactions on the hydrogen side. Due to high potentials and the corrosive oxygen atmosphere, there are additional requirements for electrode stability on the oxygen side. According to the current state of the art, the materials currently used as OER and ORR catalysts in single cell systems are resorted to and combined for the bifunctional oxygen electrode [3,4]. An effective working catalyst layer is crucial for high power densities in both operating directions and thus a research focus for URFCs.To further improve the stability and activity of the catalysts, support materials are used [5]. Important for support materials are good electrical conductivities and a high surface area, to allow a fine dispersion. This maximizes the relative electrochemical catalyst surface area (ECSA), thus leading to a reduction in costs and catalyst layer thickness, which in turn can lead to a reduction in mass transport resistances. A thin catalyst layer would also have advantages for alternating operation between electrolysis and fuel cell mode, since improved removal of liquid water from the catalyst layer can be ensured here.In this study we prepared supported and unsupported Ir and Pt catalysts. We investigated the distribution of catalyst particles on the support, measured by transmission electron microscope (TEM), and the crystallite sizes and structures by X-ray diffraction (XRD). Bifunctional electrodes consisting of supported and unsupported catalysts were investigated by rotating disk electrode (RDE) and single cell measurements. In this talk, we will take a closer look at interactions between Pt and Ir and their influence on OER and ORR.

A Tetramethylurea-Electrolyte-Based Lithium-Oxygen Battery with High Performance and Alternative Mechanism

The electrolyte is a critical component in electrochemical energy storage devices as it creates the reaction environment for the electrode process. In lithium–oxygen (Li–O2) batteries, the oxygen electrode reaction involves a complex multiphase transition (e.g., gas, liquid, solid) and a variety of intermediates (e.g., O2 –, O2 2–, 1O2), making the role of the electrolyte system more prominent. As an ideal electrolyte for Li–O2 batteries, it should not only resist the attack of superoxide intermediate, but also provide a kinetically favorable O2 redox reaction mechanism. However, currently, no electrolyte solvent is perfectly suitable for Li–O2 batteries, which greatly limited their practical applications. Here, we present a new electrolyte solvent, 1,1,3,3-tetramethylurea, for Li–O2 batteries that exhibits high performance and an alternative mechanism. Specifically, it enables a kinetically favorable one-electron Li2O2 oxidation pathway upon charging. Furthermore, due to the absence of alpha-hydrogen atoms in its molecular structure, it also exhibits good stability in the presence of superoxide intermediates, significantly suppressing the related hydrogen extraction side reactions. Consequently, Li–O2 batteries utilizing this electrolyte show a much lower charge overpotential and a four-fold longer cycle life compared to those with the benchmark electrolyte. Acknowledgments X.L. acknowledges financial support from the Marie Skłodowska-Curie Actions (grant agreement No. 101064286) for his postdoctoral fellowship.

Poor Cycling Performance of Rechargeable Lithium–Oxygen Batteries Under Lean-Electrolyte and High-Areal-Capacity Conditions: Role of Carbon Electrode Decomposition

There has been considerable interest in developing rechargeable lithium oxygen batteries (LOBs) that have the potential to significantly exceed the energy density limit of a Li ion battery (approximately 300 Wh/kg). Although 500 Wh/kg LOB has been demonstrated and exhibited stable discharge/charge cycle at room temperature condition1, their cyclability remains less than 10 cycle. For realizing the LOB with practically high energy density and long cycle life, the deep understanding of complicated reaction in LOBs has been highly demanded. Especially, the problems specifically associated with the limited electrolyte (“lean-electrolyte”) conditions need to be taken into account in LOBs.Although the importance of investigating negative lithium electrodes in lean-electrolyte systems has been recognised in recent years2,3, specific problems associated with the negative lithium electrode in a LOB has not been investigated so far. In particular, chemical crossover from the positive electrode to the negative electrode is a crucial factor that needs to be taken into consideration. Actually, recent studies have shown that LiOH is formed on the surface of a lithium-metal electrode through reaction with H2O in the electrolyte4,5. This H2O is generated by the decomposition of the tetraethylene glycol dimethyl ether (TEGDME) solvent at the positive oxygen electrode, which then migrates to the negative electrode side to react with the lithium-metal electrode. Consequently, problems related to chemical crossover are prominent in lean-electrolyte LOBs, where the effective water concentration in the electrolyte is much higher than that in an excess electrolyte system.Despite the importance of investigating the reaction of negative lithium electrodes in LOB with appropriate technological parameters, mechanistic details remains unclear due to the technical difficulty for applying non-destructive analytical methods. In the present study, we investigated the reaction of a negative lithium electrode in a lean-electrolyte LOB operating under high areal capacity conditions. The use of advanced non-destructive analytical methods, including three-electrode electrochemical techniques and an in-situ analytical setup revealed that the reaction efficiency of the lithium electrode mostly decreases through chemical crossover from the positive oxygen electrode6. In particular, the H2O generated as a side-product at the positive oxygen electrode crosses over to the negative electrode side and reacts with the lithium-metal electrode to form a porous LiOH/Li2CO3 layer on the electrode surface. LiOH and Li2CO3 accumulates, and the porous layer thickens through repeated discharge/charge cycling, which supresses efficient Li-ion transport through the layer.Furthermore, using a solid-state ceramic-based separator to protect the lithium-metal negative electrode, the side reaction with the negative electrode was considerably suppressed, which helped exclusively assess the degradation phenomena occurring in the oxygen positive electrode. By series of in-situ and ex-situ analysis revealed the following points: (i) Although the electrolyte degradation intensified with increasing repeated discharge/charge cycling, the scarcity of the electrolyte minimally influenced the cycle life of the LOBs. (ii) Most of the Li2CO3-like solid-state side products decomposed during charging at voltages higher than 3.8 V. (iii) Severe decomposition of the carbon electrode occurred during cycling, and an equivalent amount of CO2 was generated during charging at voltages higher than 3.8 V. Because the carbon electrode used in these experiments merely decomposed via simple electrochemical oxidation at voltages up to 4.5 V, the carbon electrode was considered to deteriorate through the decomposition of its solid-state side products. The findings of this study are anticipated to guide future investigations on the advancement of LOBs. In particular, detailed understanding of the reaction at the interface between the carbon electrode and solid-state products is crucial for realizing practical high-energy-density LOBs with long cycle life.

Intolerance of Ruddlesden-Popper La2NiO4±δ Structure to a-Site Cation Deficiency

Mixed ionic-electronic conductors derived from Ruddlesden-Popper Ln2NiO4+δ (Ln = La, Pr, Nd) attract significant attention as oxygen electrode materials for solid oxide fuel and electrolysis cells. However, literature data on the impact of A-site deficiency on the phase relationships and functional properties of Ln2NiO4+δ-based phases are contradictory. While some works report an accommodation of A-site vacancies up to x = 0.15 in La2-x NiO4±δ, others indicate difficulties in the synthesis of single-phase La2-x NiO4+δ even for low x values. The present work explores the impact of the nominal A-site deficiency on the phase composition and electrical transport properties of La2-x NiO4±δ ceramics.Ceramics with the nominal composition La2-x NiO4±δ (x = 0, 0.02, 0.05, 0.10) were synthesized by the glycine-nitrate technique and sintered at 1350-1450°C. While XRD analysis suggested the formation of single-phase materials with orthorhombic K2NiF4-type structure, the lattice parameters remained independent of composition within the experimental uncertainty. Neutron diffraction studies of x = 0 and 0.05 samples revealed that the lattice parameters, La:Ni atomic ratio (2:1) and oxygen sites occupancy remain identical for both samples, while the presence of impurity NiO phase (0.4 wt.%) was detected for La1.95NiO4±δ. SEM/EDS inspection of ceramic samples confirmed the presence of nickel-rich inclusions for x ≥ 0.02, which could not be eliminated by increasing the temperature and time of sintering. The volume fraction of inclusions increased with x. The experimental observations are supported by the atomistic simulations showing that the coexistence of cation-stoichiometric La2NiO4+δ with nickel-rich La4Ni3O10 or NiO is more favorable compared to cation-deficient La1.95NiO4±δ. Molecular dynamics simulations of La1.95NiO4±δ lattice demonstrated that the introduction of La vacancies leads formation of instability zone in the rock-salt-type layer and destabilization of the crystal lattice. The intolerance of La2NiO4+δ lattice to A-site vacancies and coexistence of La2NiO4+δ with traces of Ni-rich secondary phase in the samples with the nominal composition La2-x NiO4±δ results in an insignificant variation of electrical transport properties with x. Acknowledgements This work was developed within the scope of the project CARBOSTEAM (POCI-01-0145-FEDER-032295) funded by FEDER through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) and by national funds through FCT/MCTES, and the project CICECO-Aveiro Institute of Materials (UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020) financed by national funds through the FCT/MCTES (PIDDAC). A.B. acknowledges the PhD scholarship by the FCT (grant SFRH/BD/150704/2020). This work was partially supported by the National Science Centre, Poland, grant UMO-2020/37/B/ST8/02097.

Contribution of numerical modelling to design oxygen electrode for micro-solid oxide cells: A case study of high-performance nano-columnar La2NiO4 thin films

This article presents a numerical study that aims to guide the development of nano-columnar La2NiO4 thin films as high performing oxygen electrodes for micro-Solid Oxide Cell (μSOC). La2NiO4 thin films were deposited by Pulsed Injection Metal Organic Chemical Vapor Deposition (PI-MOCVD) and their performance is characterized by Electrochemical Impedance Spectroscopy (EIS) and Electrical Conductivity Relaxation (ECR). Excellent performance is obtained for 1 μm thick film with an Area Specific Resistance (ASR) of 0.12 Ω cm2 at 600 °C, making them suitable for low-temperature μSOCs. A Finite Element Method (FEM) model has been implemented and used to predict the ASR and impedance spectra in order to guide further optimization of the film thickness and morphology. After experimental validation of the model using various electrode thicknesses, the optimal value is estimated to be between 3 and 4 μm for the temperature range of 450–650 °C. For each temperature and thickness, the model can clearly predict whether the electrode is limited by the surface exchange reactions or the bulk diffusion. The simulations revealed that the gas diffusion process is not rate-limiting when the electrode thickness is below 5 μm and the temperature is below 650 °C. Furthermore, a geometrical parameters analysis study allowed to determine the ideal nano-columnar morphology for this promising electrode composition.

Recent Development in Reversible Solid Oxide Fuel Cells: Theory, Integration and Prospective

AbstractReversible solid oxide fuel cell (RSOC) has gained widespread attention due to their potential for high efficiency in implementing multi‐energy distributed systems. When high power demand is required, RSOC can operate in the solid oxide fuel cell (SOFC) mode, directly converting the chemical energy from hydrogen or other renewable fuels into electricity. When excess electricity is available, RSOC can operate in the solid oxide electrolysis cell (SOEC) mode, producing fuels through the electrolysis of water or co‐electrolysis of water and carbon dioxide. The reversible operation of RSOC enables the direct conversion between chemical energy and electricity, offering a promising solution for clean and sustainable energy with low cost and high round‐trip efficiency. This paper introduces the research background and working principles of RSOC, provides a detailed overview of the current research status of electrolyte, fuel electrode, and oxygen electrode materials, discusses the optimization design of RSOC stacks and energy utilization strategies in the system. In addition, the future development directions of RSOC were also explored, which is of significant importance for the commercialization of RSOC.

Co2MnO4/Ce0.8Tb0.2O2−δ Dual-Phase Membrane Material with High CO2 Stability and Enhanced Oxygen Transport for Oxycombustion Processes

Co₂MnO₄/Ce_0.8Tb_0.2O_2−δ Dual-Phase Membrane Material with High CO₂ Stability and Enhanced Oxygen Transport for Oxycombustion Processes

Novel Perovskite Structured Nd0.5Ba0.5Co1/3Ni1/3Mn1/3O3-δ as Highly Efficient Catalyst for Oxygen Electrode in Solid Oxide Electrochemical Cells.

Developing catalytic materials with highly efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for lower-temperature solid oxide fuel cell (SOFC) and electrolysis cell (SOEC) technologies. In this work, a novel triple perovskite material, Nd0.5Ba0.5Co1/3Ni1/3Mn1/3O3-δ, has been developed and employed as a catalyst for both ORR and OER in SOFC and SOEC operations at relatively lower temperatures, showing a low polarization resistance of 0.327 Ω cm2, high-power output of SOFC up to 773 mW cm-2 at 650 °C, and a high current density of 1.57 A cm-2 from SOEC operation at 1.5 V at 600 °C. The relaxation time distribution reveals that Nd0.5Ba0.5Co1/3Ni1/3Mn1/3O3-δ could maintain a slow polarization process at the relatively low operating temperature, offering a significant antipolarization advantage over other perovskite electrode materials. The Nd0.5Ba0.5Co1/3Ni1/3Mn1/3O3-δ electrode provides a low energy barrier of about 0.36 eV in oxygen ion mobility, which is beneficent for oxygen reduction/evolution reaction processes.

Boosting the electrochemical performance of oxygen electrodes via the formation of LSCF-BaCe0.9–xMoxY0.1O3–δ triple conducting composite for solid oxide fuel cells: Part II

This research is the continuation of our previous work, in which we introduced novel proton-conducting electrolytes BaCe0.9–xMoxY0.1O3–δ (BCMxY; x = 0.025, 0.05). In this study, we explore the potential of the proton-conducting BCM0.025Y electrolyte by creating a composite with La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF) to form triple conducting electrodes for solid oxide fuel cells (SOFC). The formation of the LSCF-BCM0.025Y composite enhances both the three-phase reaction interface length and the concentration of oxygen vacancies, contributing to improved dissociation rates and enhanced oxygen adsorption. The desired characteristics, including density, structure, composition, electrochemical performance, and thermal stability, have been confirmed through a comprehensive set of analyses including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS), and thermogravimetric analysis (TGA) coupled with differential scanning calorimetry (DSC), respectively. The cell configuration of Ni-YSZ | BCZY | LSCF-BCM0.025Y exhibited a remarkable maximum power density (MPD) of 418.7 mW cm−2, which is approximately 29 % higher than that achieved with a typical LSCF cathode (325.6 mW cm−2) at an operating temperature of 600 °C. The outstanding performance and enduring stability of the LSCF-BCM0.025Y composite over a 500 h period demonstrate its potential as a promising cathode material for intermediate-temperature SOFCs.

High-Energy-Density Solid-State Metal-Air Batteries: Progress, Challenges, and Perspectives.

Next-generation batteries have long been considered a transition to more sustainable storage technologies. Among them, metal-air batteries (MABs) with low cost, high safety, and environmental friendliness have shown great potential for future large-scale applications. Motivated by the desirable characteristics, significant progress is made in suppressing serious parasitic reactions, improving electrochemical performance, and increasing the energy density in MABs. Compared to the widely reported liquid electrolyte strategy, solid-state electrolytes (SSEs)can thoroughly solve the volatilization challenges of liquid electrolytes and protect the oxygen electrodes without the formation of diffusion-blocking oxide phases. Notably, SSEs for MABsare still in their infancy, and many thorny challenges still need to be solved. In this review, the main electrochemical mechanism, key challenges, and some important progress are sorted out for solid-state MABs, such as lithium-air, zinc-air, aluminum-air, and magnesium-air batteries. Besides their fundamental significance, these configurations are further compared in terms of energy density, cost, carbon footprint, energy consumption, rate performance, cycle performance, safety, and air stability of prevailing electrolytes.

Bifunctional activity of NiCo on carbon nanotube catalyst for oxygen reduction and evolution on anion exchange membrane-unitized regenerative fuel cells (AEM-URFCs)

Cobalt or nickel/cobalt on carbon nanotube (Co@CNT, NiCo@CNT) catalysts were synthesized by heat treatment of the metal-organic framework, ZIF-67. The X-ray patterns of the synthesized ZIF-67 and the catalysts confirmed their crystalline structures. The field-emission scanning electron microscopy (FESEM) images of ZIF-67 after pyrolysis showed that the dodecahedral crystalline structure of ZIF-67 was retained, and the organic ligands were converted into CNTs and graphitic carbon in an H2 gas environment. The transmission electron microscopy images of the synthesized catalysts confirm the presence of the Ni or Co atoms at the tips of the carbon nanotubes. The NiCo@CNT catalyst exhibited a higher surface area and larger pore volume than those of Co@CNT. X-ray photoelectron spectroscopy confirmed the presence of pyridinic nitrogen, which forms Co-Nx and Ni-Nx, active groups. In anion exchange membrane-unitized regenerative fuel cells (AEM-URFC), NiCo@CNT as a bifunctional oxygen electrode (BOE) catalyst showed a higher current density and lower Tafel slope compared to that of Co@CNT. The cell with the NiCo@CNT catalyst in BOE exhibits the highest current density of 130.0 mA cm−2 at 0.3 V (fuel cell mode) and 32.5 mA cm−2 at 2.0 V (water electrolyzer mode) among all catalysts. This cell exhibited a maximum 38.90 % round trip efficiency, which was comparable to that of the benchmark noble metal (Ir-black) catalyst (38.40 %).

Optimization of Pt infiltrated Sr2Fe2-xMoxO6-δ-Ce0.8Sm0.2O1.9 oxygen electrode for reversible solid oxide cell and CH4-assisted electrolysis process

Sr2Fe2-xMoxO6-δ-Ce0.8Sm0.2O1.9 (SFM-SDC) is a promising composite oxygen electrode for reversible solid oxide cells. In this study, well-dispersed Pt nanoparticles are prepared by one-cycle infiltration method using H2PtCl6 aqueous solution in SFM-SDC scaffold, to form high electrocatalytic activity Pt-SFM-SDC electrode for fuel cell, steam electrolysis and CH4-assisted steam electrolysis processes. Systematic studies in concentration variation of H2PtCl6 solution demonstrate that the discharge current of the 3.14 cm2 cell infiltrated by 0.040 M solution is significantly increased from 0.4 to 1.32 A (>3 times) at 0.5 V at 800 °C while the electrolysis current is effectively enhanced from 0.8 to 3.28 A (>4 times) at 1.5 V. Moreover, cells with Pt-SFM-SDC electrode applied in CH4-assisted electrolysis process realized a remarkable reduction of power consumption. Impedance analysis and morphological observation results suggest that appropriate H2PtCl6 concentration has a positive effect on surface exchange and gas diffusion process at oxygen electrode side.

In-situ reconstruction of rock-like 3D hierarchical MIL-53(Fe) self-supporting electrode with oxygen vacancy induced ultra-long stable and efficient water oxidation

The exploitation of efficient, stable and cheap electrocatalyst for oxygen evolution reaction (OER) is very significant to the development of energy technology. In this study, Fe-based metal–organic frameworks (MIL-53(Fe)) self-supporting electrode with a 3D hierarchical open structure was developed through a semi-sacrificial strategy. The self-supporting electrode exhibits an excellent OER performance with an overpotential of 328 mV at 100 mA cm−2 in 1 M KOH, which is superior than that of IrO2 catalyst. Importantly, the optimized self-supporting electrode could operate at 100 mA cm−2 for 520 h without visible decrease in activity. It was also found that the structure of MIL-53(Fe) was in-situ self-reconstructed into oxyhydroxides during OER process. However, the 3D hierarchical open structure assembled with nano-microstructures kept well, which ensured the long-term stability of our self-supporting electrode for OER. Furthermore, density functional theory (DFT) calculations reveal that the FeOOH with rich oxygen vacancy transformed from MIL-53(Fe) plays a key role for the OER catalytic activity. And, the uninterrupted formation of oxygen vacancy during OER process ensures the continuous OER catalytic activity, which is the original source for the ultra-long stability of the self-supporting electrode toward OER. This work explores the way for the construction of efficient self-supporting oxygen electrodes based on MOFs.

Electrochemical Biosensors for Express Analysis of the Integral Toxicity of Polymer Materials.

Biosensors based on an oxygen electrode, a mediator electrode, and a mediator microbial biofuel cell (MFC) using the bacteria Gluconobacter oxydans B-1280 were formed and tested to determine the integral toxicity. G. oxydans bacteria exhibited high sensitivity to the toxic effects of phenol, 2,4-dinitrophenol, salicylic and trichloroacetic acid, and a number of heavy metal ions. The system "G. oxydans bacteria-ferrocene-graphite-paste electrode" was superior in sensitivity to biosensors formed using an oxygen electrode and MFC, in particular regarding heavy metal ions (EC50 of Cr3+, Mn2+, and Cd2+ was 0.8 mg/dm3, 0.3 mg/dm3 and 1.6 mg/dm3, respectively). It was determined that the period of stable functioning of electrochemical systems during measurements was reduced by half (from 30 to 15 days) due to changes in the enzyme system of microbial cells when exposed to toxicants. Samples of the products made from polymeric materials were analyzed using developed biosensor systems and standard biotesting methods based on inhibiting the growth of duckweed Lemna minor, reducing the motility of bull sperm, and quenching the luminescence of the commercial test system "Ecolum". The developed bioelectrocatalytic systems were comparable in sensitivity to commercial biosensors, which made it possible to correlate the results and identify, by all methods, a highly toxic sample containing diphenylmethane-4,4'-diisocyanate according to GC-MS data.