Symmetrical Electrode Material Research Articles

Efficient and stable symmetrical solid oxide fuel cell via A-site non-stoichiometry

Symmetrical solid oxide fuel cells (SSOFCs) with identical anode and cathode have many benefits compared with traditional SOFCs. However, it is still a challenge to find high performance electrode materials with excellent catalytic activity and preferable stability under both reducing and oxidizing atmosphere. Here, a novel Ba0.9La0.1Co0.7Fe0.2Nb0.1O3-δ (BLCFN) perovskite electrode has been developed as promising symmetrical electrode material for SSOFCs. The A-site non-stoichiometry introduced in BLCFN simultaneously enhances both the cathode and anode electrocatalytic performance. The cathode polarization resistance of BLCFN with 5% deficiency is decreased by 28.6% to 0.05 Ω·cm2 at 750°C in air, which can be mainly attributed to the increase of oxygen vacancy concentration via partial ionic defect. The BLCFN anode polarization resistance is reduced by 42.1% to 0.11 Ω·cm2 at 750°C in 5% H2/N2. The promoted hydrogen oxidation reaction activity of BLCFN is related to the exsolved homogeneous Co-Fe nanoparticles from BL95CFN substrate in reducing atmosphere. The full cell with BL95CFN symmetrical electrodes displays high redox stability through reversing the flow of wet hydrogen and ambient air. Additionally, this SSOFCs with strong anchor characteristic of exsolved Co-Fe nanoparticles shows excellent coking-tolerance using methane fuel compared with traditional Ni-SDC anode. This work provides a potential way towards the development of high-performance, excellent redox-stable and coking-tolerant SSOFCs.

Solid oxide cells with cermet of silver and gadolinium-doped-ceria symmetrical electrodes for high-performance power generation and water electrolysis

A cermet of silver and gadolinium-doped-ceria (Ag-GDC) is investigated as novel symmetrical electrode material for (ZrO2)0.92(Y2O3)0.08 (YSZ) electrolyte-supported solid oxide cells (SOCs) operated in fuel cell (SOFC) and electrolysis (SOEC) modes. The electrochemical performances are evaluated by measuring the current density-voltage characteristics and impedance spectra of the SOCs. The activity of hydrogen and air electrodes is investigated by recording overpotential versus current density in symmetrical electrode cells, respectively in hydrogen and air, using a three-electrode method. Conventional hydrogen electrode, Ni-YSZ, and oxygen electrode, LSCF (La0.6Sr0.4Co0.2Fe0.8O3-δ)-GDC, are tested as comparison. The results show that, as an oxygen electrode, Ag-GDC is more active than LSCF-GDC in catalyzing both oxygen reduction reaction (ORR) in an SOFC and oxygen evolution reaction (OER) in an SOEC. As a hydrogen electrode, Ag-GDC is more active than Ni-YSZ in catalyzing hydrogen oxidation reaction (HOR) in an SOFC and hydrogen evolution reaction (HER) in an SOEC, especially in high steam concentration. An SOC with symmetrical Ag-GDC electrodes operated in a fuel cell mode, with 3% H2O humidified H2 as the fuel, displays a peak power density of 395 mWcm−2 at 800 °C. Its polarization resistance at open circuit voltage is 0.21 Ω cm2. Ag-GDC electrode can be operated even at pure steam. An SOEC operated for electrolyzing 100% H2O, the current density reaches 720 mA cm−2 under 1.3 V at 800 °C.

Utilization of symmetric electrode materials in energy storage application: A review

The development of efficient energy storage systems is an important field of research in the modern era where fossil fuels are headed toward depletion. The invention of batteries is regarded as one of the most significant advancements in the field of energy storage. From its inception, a lot of research has been done and is still being carried out to develop novel and advanced materials that provide improved performance in terms of capacity, stability, and cost. In this context, symmetric or bipolar electrodes, which utilize the same material for the anode and the cathode, emerge as a suitable solution for battery technology. In this work, different types of symmetric electrode materials for batteries are subjected to review. The various structures, methods of synthesis, and characteristics are analyzed and presented. The Na3V2(PO4)3 (NVP) is the most widely analyzed symmetric material among all the symmetric materials. The Na-based systems are widely studied in symmetric configurations for their resource availability and price economics advantages. Aqueous and solid-state symmetric batteries are the emerging systems in symmetric batteries. This review will provide insights to battery researchers involved in bipolar material design and shed light on new emerging energy storage techniques.

Electrochemical Performance of Na3V2(PO4)2F3 Electrode Material in a Symmetric Cell.

A NASICON-based Na3V2(PO4)2F3 (NVPF) cathode material is reported herein as a potential symmetric cell electrode material. The symmetric cell was active from 0 to 3.5 V and showed a capacity of 85 mAh/g at 0.1 C. With cycling, the NVPF symmetric cell showed a very long and stable cycle life, having a capacity retention of 61% after 1000 cycles at 1 C. The diffusion coefficient calculated from cyclic voltammetry (CV) and the galvanostatic intermittent titration technique (GITT) was found to be ~10−9–10−11, suggesting a smooth diffusion of Na+ in the NVPF symmetric cell. The electrochemical impedance spectroscopy (EIS) carried out during cycling showed increases in bulk resistance, solid electrolyte interphase (SEI) resistance, and charge transfer resistance with the number of cycles, explaining the origin of capacity fade in the NVPF symmetric cell. Finally, the postmortem analysis of the symmetric cell after 1000 cycles at a 1 C rate indicated that the intercalation/de-intercalation of sodium into/from the host structure occurred without any major structural destabilization in both the cathode and anode. However, there was slight distortion in the cathode structure observed, which resulted in capacity loss of the symmetric cell. The promising electrochemical performance of NVPF in the symmetric cell makes it attractive for developing long-life and cost-effective batteries.

Electrochemical performance of Sr1.9La0.1Fe1.5Mo0.5O6-δ symmetric electrode for solid oxide fuel cells with carbon-based fuels

La-doped Sr2-xLaxFe1.5Mo0.5O6-δ perovskite oxides are synthesized and used as a symmetric electrode to evaluate the effect of La on the crystal structure, conductivity, and catalytic activity for O2 reduction and H2 oxidation reaction. The electronic doping effect dominates the oversize effect in Sr2-xLaxFe1.5Mo0.5O6-δ oxide, resulting in unit cell volume expansion and decreased conductivity in air. In addition, the introduction of La increases the chemical structural stability of Sr2Fe1.5Mo0.5O6-δ in reducing condition due to the higher La–O bond compared with Sr–O bond, leading to high catalytic activity for the H2 oxidation reaction. At 800 °C, the Rp values of Sr1.9La0.1Fe1.5Mo0.5O6-δ symmetric cell in air and wet H2 are as low as 0.075 and 0.21 Ω cm2, respectively. Moreover, the peak power densities of 769, 561, 439, and 653 mW cm−2 at 850 °C are obtained when wet H2, CO, CH4, and C3H8 are used as fuels on Sr1.9La0.1Fe1.5Mo0.5O6-δ/LSGM/Sr1.9La0.1Fe1.5Mo0.5O6-δ cell. The symmetric cell also shows excellent stability (>100 h) in wet H2/air, implying Sr1.9La0.1Fe1.5Mo0.5O6-δ oxide is a promising symmetric electrode material.

Electrochemical performance and distribution of relaxation times analysis of tungsten stabilized La0·5Sr0·5Fe0·9W0·1O3-δ electrode for symmetric solid oxide fuel cells

W-doped La0·5Sr0·5Fe0·9W0·1O3-δ (LSFW) was prepared and evaluated as a symmetric electrode for solid oxide fuel cells (SSOFCs). Phase and structural stability of LSFW under both reducing and oxidizing atmospheres was studied. The oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) mechanisms were investigated by using electrochemical impedance spectra (EIS) and distribution of relaxation times (DRT). Electrode polarization resistance (Rp) of LSFW are 0.08 and 0.16 Ω cm2 in air and wet hydrogen at 800 °C, respectively. DRT results indicate that the rate-limiting step of LSFW at 800 °C in cathodic conditions and anodic conditions are related to oxygen diffusion and hydrogen adsorption/diffusion, respectively. A La0·8Sr0.2Ga0.8Mg0·2O3-δ (LSGM) electrolyte-supported single cell using LSFW electrodes shows a maximum power density of 617.3 mW cm−2 at 800 °C with considerable stability and reversibility, which enables LSFW a promising SOFCs symmetric electrode material.

Functionalization of graphene oxide via chromium complexes coordinated on 5-aminopyridine-2-carboxylic acid as a symmetric supercapacitor electrode materials in energy storage devices

In the present study, the functionalization of graphene oxide (GO) via 5-Aminopyridine-2-carboxylic acid Cr (ш) complex (FGO-Ap/Cr) was fulfilled using a one-pot hydrothermal method. Then, the synthesized FGO-Ap/Cr was evaluated through Fourier transform infrared (FT-IR) spectrometry and X-ray photoelectron spectroscopy (XPS). The electrochemical functionality of the given electrodes was then analyzed using cyclic voltammetry (CV), chronopotentiometry, and electrochemical impedance spectrometry (EIS). A high specific capacitance of 461.5 F g−1 is achieved at a current density of 1 A g−1 for the FGO-Ap/Cr in three electrodes electrochemical measurement. These electrodes show remarkable electrochemical behaviors for supercapacitors (SCs) with regard to incredible rate capacity, elevated specific capacitance, and superb cycle stability. A high energy and power density symmetric supercapacitor was also successfully designed using FGO-Ap/Cr and GO, as the anode and cathode electrodes in a neutral 3 M KNO3 electrolyte. Due to the desired poriferous construct, the elevated specific capacitance, the rated capacity, and the complemental potential of the three electrodes, the asymmetrical supercapacitor is capable of revolving in a full potential window of 0–1.7 V with an energy density of 523.3 W h kg−1 at a power density of 98111.3 W kg−1 for FGO-Ap/Cr//GO. Besides, the symmetrical supercapacitor showed steady cycling functionality for FGO-Ap/Cr//GO capacitance retention at 8 A g−1 following 5000 cycles, with 96.2%. These encouraging results demonstrate a high potential for practical applications in the development of energy-storing equipment with elevated energy and power concentrations.

Hierarchical porous nitrogen-doped graphite from tissue paper as efficient electrode material for symmetric supercapacitor

Hierarchical porous nitrogen-doped graphite from tissue paper (N-ATG) is synthesized and used as symmetric supercapacitor electrode material. Electrochemical characterizations show that the N-ATG has an ultrahigh capacitance of 696 F g−1 (473 F cm−3) at 0.5 A g−1 and mass loading of 1 mg cm−2, in 6 mol L−1 KOH solution. The capacitance retention rate is 49.6% at 80 A g−1 from mass loading of 1 mg cm−2 to 20 mg cm−2. The energy densities of the N-ATG are 24.2 and 9.8 Wh kg−1 (i.e. 16.5 and 6.7 Wh L−1) at power densities of 320 and 39831 W kg−1 (i.e. 218 and 27085 W L−1), respectively, which rank the highest performances especially at high power densities among heteroatom-doped carbon electrodes. The N-ATG possesses ultrahigh specific surface area of 2327 m2 g−1, large average pore diameter of 10.3 nm, high contents of doped N (6.5 at.%), graphitized structure with 1–5 graphene layers and widened lattice distance, dense defects, and high packing density (0.68 g cm−3), which account for the excellent gravimetric and volumetric capacitances as well as the high rate capacity.

Highly active and novel A-site deficient symmetric electrode material (Sr0.3La0.7)1−x (Fe0.7Ti0.3)0.9Ni0.1O3−δ and its effect on electrochemical performance of SOFCs

A-site deficient (Sr0.3La0.7)1-x (Fe0.7Ti0.3)0.9Ni0.1O3-δ ((SL)1-xFTN) symmetrical electrodes with compositions x = 0.1, 0.2 and 0.3 denoted as SLFTN-01, SLFTN-02, and SLFTN-03 respectively were synthesized via modified Pechini method. The as prepared samples were further coated on LGSM electrolyte through screen-printing technique. Electrochemical performance was significantly improved for A-site deficient (SL)1-xFTN due to increased concentration of oxygen vacancy. XRD patterns revealed better reversibility for (SL)1-xFTN with rhombohedral structure. Low polarization resistance (Rp) ~0.210, 0.195 and 0.165 Ωcm2 (in dry H2) and 0.069, 0.046 and 0.043 Ωcm2 (in air) was measured for SLFTN-01, SLFTN-02, and SLFTN-03 respectively at a temperature of 750 °C. Highest conductivities ~326, 338 and 342 Scm−1 were calculated in air and the conductivities obtained in dry H2 were ~0.64, 0.81 and 1.01 Scm−1 at 700 °C. It was observed that small polaron mechanism was responsible for the decreased conductivity with the increased temperature range. The fabricated symmetrical cell ((SL)1-xFTN/LDC|LSGM|LDC/(SL)1-xFTN), maintained good stability without any degradation during the test time ~500 h (in air) and 100 h (in dry H2). The detailed investigations categorized the fabricated cells well suited as anode and cathode with improved performance and excellent stability both in oxidizing and reducing atmospheres.

Preparation and characterization of a redox-stable Pr0.4Sr0.6Fe0.875Mo0.125O3-δ material as a novel symmetrical electrode for solid oxide cell application

In this work, to simultaneously meet the requirements of good electrochemical performance and redox stability, perovskite oxide Pr0.4Sr0.6Fe0.875Mo0.125O3-δ (PSFM) material has been developed as a novel redox-stable electrode for symmetrical cell application. The experimental results obtained by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy show that metallic Fe nanoparticles will exsolve from the parent oxide PSFM through in-situ exsolution method when treating in 97% H2–3% H2O atmosphere, and then completely re-incorporate into the parent oxide in air, demonstrating excellent redox stability for PSFM material. In addition, the redox stability in electrochemical performance is also studied by recording the electrochemical impedance spectra and distribution of relaxation times (DRT) analysis. It is demonstrated that a constant electrode polarization resistance (Rp) of ~0.60 Ωcm2 is achieved for the symmetrical cell with PSFM electrode in air at 800 °C after activation, and Rp value is significantly increased to 1.59 Ωcm2 when exposing the symmetrical cell to 97% H2–3% H2O, which is possibly ascribed to the significantly decreased electrical conductivity form 71.0 Scm−1in air to 3.8 Scm−1 in 97% H2–3% H2O. Moreover, it is shown that Rp value recorded in air is effectively decreased to ~0.33 Ωcm2, and keeps constant during the following 200-h redox stability testing, while Rp value measured in 97% H2–3% H2O atmosphere is gradually decreased to 0.82 Ωcm2, which can be explained by the enhanced electro-catalytic properties of PSFM electrode induced by the gradually exsolved Fe nanocatalysts from parent PSFM electrode. At the same time, DRT analysis demonstrates that the sub-electrode process including oxygen/hydrogen adsorption, dissociation ionization and surface diffusion to triple phase boundaries occurred at the electrode/electrolyte interfacial is the predominant rate-limiting step, which can be effectively accelerated by surface modification and exsolved Fe nanoparticles. These results indicate that PSFM is a promising symmetrical electrode material for symmetrical cell application because of its good electrochemical performance and excellent long-term redox stability.

Effects of cobalt and iron proportions in Pr0.4Sr0.6Co0.9-xFexNb0.1O3-δ electrode material for symmetric solid oxide fuel cells

Abstract Pr0.4Sr0·6Co0.9-x FexNb0.1O3-δ (PSCFxN) (x = 0, 0.2, 0.4, 0.6 and 0.9) oxides are evaluated as symmetric electrode materials for solid oxide fuel cells (SOFCs). Both the thermal expansion coefficient (TEC) and conductivity decrease with the increasing of Fe amount. With the increase in Fe content, more Fe4+ species are reduced to Fe3+, generating more oxygen vacancies. It effectively promotes the oxygen incorporation kinetics, and lowers the polarization resistance (Rp). As a result, the PSCF0·6N exhibits the lowest polarization resistance of 0.028 and 0.077 Ωm2 at 900 °C in air and hydrogen, respectively, and the highest electrical conductivity of 258.90 Scm−1 at 650 °C among all the prepared PSCFxN materials. Meanwhile, with the doping of Fe, the TEC decreases near to the electrolyte TEC value. As such, the peak power densities of the electrolyte supported PSCF0.6N-based symmetric SOFCs with different electrolyte thicknesses of 500, 400 and 300 μm are 0.642, 0.713 and 0.891 Wcm−2, respectively. Meanwhile, the output voltage of the obtained PSCF0·6N/LSGM/PSCF0·6N symmetric SOFC decreases only 5% in 50 h stability test under a current density of 0.5 Acm−2. These results indicate that the PSCF0·6N material should be a promising electrode material for the symmetric SOFCs.

Co-free La0.6Sr0.4Fe0.9Nb0.1O3-δ symmetric electrode for hydrogen and carbon monoxide solid oxide fuel cell

Co-free La0.6Sr0.4FeO3-δ (LSFNb0) and La0.6Sr0.4Fe0.9Nb0.1O3-δ (LSFNb0.1) perovskite oxides were prepared by a standard solid-state reaction method. The structural stability and electrochemical performance of La0.6Sr0.4Fe0.9Nb0.1O3-δ as both cathode and anode were studied. Nb dopant in LSFNb0 significantly enhances the structural and chemical stability in anode condition. At 800 °C, the polarization resistances (Rp) of LSFNb0.1 symmetric electrode based on YSZ electrolyte are 0.5 and 0.05 Ω cm2 in H2 and air, respectively. The peak power densities of LSFNb0.1 based on LSGM electrolyte-supported SSOFCs are 934 and 707 mW cm−2 at 850 °C in H2 (3% H2O) and dry CO, respectively. Moreover, the symmetric cell exhibits reasonable stability in both H2 and CO fuel, suggesting that La0.6Sr0.4Fe0.9Nb0.1O3-δ may be a potential symmetric electrode material for hydrogen and carbon monoxide SOFCs.

A Hollow‐Shell Structured V2O5 Electrode‐Based Symmetric Full Li‐Ion Battery with Highest Capacity

AbstractThe symmetric batteries with an electrode material possessing dual cathodic and anodic properties are regarded as an ideal battery configuration because of their distinctive advantages over the asymmetric batteries in terms of fabrication process, cost, and safety concerns. However, the development of high‐performance symmetric batteries is highly challenging due to the limited availability of suitable symmetric electrode materials with such properties of highly reversible capacity. Herein, a triple‐hollow‐shell structured V2O5 (THS‐V2O5) symmetric electrode material with a reversible capacity of >400 mAh g−1 between 1.5 and 4.0 V and >600 mAh g−1 between 0.1 and 3.0 V, respectively, when used as the cathode and anode, is reported. The THS‐V2O5 electrodes assembled symmetric full lithium‐ion battery (LIB) exhibits a reversible capacity of ≈290 mAh g−1 between 2 and 4.0 V, the best performed symmetric energy storage systems reported to date. The unique triple‐shell structured electrode makes the symmetric LIB possessing very high initial coulombic efficiency (94.2%), outstanding cycling stability (with 94% capacity retained after 1000 cycles), and excellent rate performance (over 140 mAh g−1 at 1000 mA g−1). The demonstrated approach in this work leaps forward the symmetric LIB performance and paves a way to develop high‐performance symmetric battery electrode materials.

Highly Stable and Efficient Perovskite Ferrite Electrode for Symmetrical Solid Oxide Fuel Cells

Here, we report a new perovskite oxide with formula Sm0.8Sr0.2Fe0.8Ti0.15Ru0.05O3-δ (SSFTR), which exhibits a great potential as a symmetrical electrode material with satisfying stability in both reducing and oxidizing environments. Moreover, SSFTR exhibits good redox and thermal cycle stability. The electrolyte-supported (Sm0.2Ce0.8O1.9, SDC) symmetrical cell with SSFTR electrodes possesses a peak power density of 271 mW·cm-2 at 800 °C in wet H2. Moreover, the peak power density is remarkably improved to 417 mW·cm-2 when applying A-site-deficient perovskite oxide Sm0.7Sr0.2Fe0.8Ti0.15Ru0.05O3-δ as the symmetrical electrode, benifiting by the in situ-exsolved Ru nanoparticles with excellent electrocatalytic activity, since A-site deficiency can provide additional driving force for the exsolution of B-site cations upon reduction. As an ingenious approach, this exsolution of electrocatalytically active nanoparticles on the surface of electrode may be applicable to the development of other excellent performance electrodes for symmetrical SOFCs and other electrochemical systems.

Electrochemical performance and stability of La0·5Sr0·5Fe0·9Nb0·1O3-δ symmetric electrode for solid oxide fuel cells

Symmetric solid oxide fuel cells (SSOFCs) based on the Co-free La0·5Sr0·5Fe0·9Nb0·1O3-δ (LSFNb) perovskite oxide are prepared by the sol-gel method. The structural stability and catalytic activity of LSFNb as an electrode for both the hydrogen oxidation reaction and oxygen reduction reaction are studied. We show that Nb substitution in La0·5Sr0·5FeO3-δ greatly improves its chemical and phase stability under reducing atmosphere. At 800 °C, the area specific polarization resistances (ASRp) of La0·5Sr0·5Fe0·9Nb0·1O3-δ symmetric cells are as low as 0.06 and 0.24 Ω cm2 in air and wet H2 (3% H2O), respectively. LSFNb based electrolyte-supported SSOFCs deliver peak power densities of 1000 mW cm-2 at 850 °C in wet H2/air. In addition to high performance, the symmetric cell shows stable power output under load (measured for 140 h at a current density of 520 mA cm−2, 800 °C) under air/humidified H2 operation, indicating that LSFNb may be a particularly promising new symmetric electrode material for solid oxide fuel cells.

Evaluation of PrNi0.4Fe0.6O3-δ as a symmetrical SOFC electrode material

Symmetrical Solid Oxide Fuel Cell has identical electrode material on both electrodes, of which the most outstanding advantage is the ability to remove the deposited carbon and other deposits from anode. Owing to the working conditions of electrodes, there are more requirements for electrode materials than normal ones. In this study, we evaluate the traditional cathode material PrNi0.4Fe0.6O3-δ as a symmetrical solid oxide fuel cell electrode material. Unstable as most traditional cathode materials are in fuel gas, however, the result here exhibits PrNi0.4Fe0.6O3-δ has good performance. The peak power density of the cell with PrNi0.4Fe0.6O3-δ electrode in wet methane at 800 °C is 663 mWcm−2 with observable decomposition on anode. After switching the fuel gas on anode to air, the structure recovers quickly. In terms of the recyclable performance, PrNi0.4Fe0.6O3-δ seems suitable for symmetrical solid oxide fuel cell.

Novel nanocomposite of MnFe2O4 and nitrogen-doped carbon from polyaniline carbonization as electrode material for symmetric ultra-stable supercapacitor

In this work, direct carbonization of polyaniline manganese ferrite (Mn-PANI) nanocomposite was employed to prepare a novel N-doped carbon material decorated with manganese ferrite (Mn-CPANI) and implemented as an ultra-stable symmetric supercapacitor electrode material. The surface morphology of as-prepared samples is investigated with field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Also, uniform distribution of manganese ferrite (MnFe2O4) on PANI surface and the N-doped carbon material is confirmed through EDX analysis. Carbonized nanocomposite contains about 8 wt% of nitrogen. The obtained Mn-CPANI nanocomposite shows a high specific capacitance of 329 F g−1 and exhibits excellent capacitance retention of 83.2% from 1 to 10 A g−1, which is more stable compared to Mn-PANI nanocomposite. Moreover, the symmetric Mn-CPANI supercapacitor cell possesses a specific capacitance of about 246 F g−1 (at 1 A g−1) and an excellent stable cyclability (only 3% of specific capacitance decreases after 10000 cycles). The excellent enhanced electrochemical performance of Mn-CPANI nanocomposite could be originated from the combination and synergism of N-doped carbon material as an electrical double-layer capacitor with pseudocapacitive MnFe2O4. As a result, a novel electrode material is developed for high-performance ultra-stable energy storage devices.

Highly Efficient, Redox-Stable, La0.5Sr0.5Fe0.9Nb0.1O3- δ Symmetric Electrode for Both Solid-Oxide Fuel Cell and H2O/CO2 Co-Electrolysis Operation

Co-free La0.5Sr0.5Fe0.9Nb0.1O3-δ (LSFNb) perovskite oxide is synthesized by the sol-gel method. LSFNb oxide exhibits good chemical and structural stability in both oxidizing and reducing atmospheres. Therefore, symmetric cells with the configuration LSFNb/LSGM/LSFNb are prepared and the electrochemical performance is evaluated for both solid oxide fuel cell (SOFC) and solid oxide electrolysis (SOEC) applications. The LSFNb symmetric electrode presents excellent catalytic activity in both SOFC and SOEC modes. At 850°C, the peak power density of the symmetric cell reaches 1157 mW cm−2 in SOFC mode, while the current density exceeds 1460 mA cm−2 at 1.3 V in SOEC mode. Under H2O/CO2 co-electrolysis at 800°C, the H2 and CO production rates reach 2.19 and 2.77 mL min−1 cm−2 at −708 mA cm−2 with nearly 100% faradaic efficiency. Moreover, the symmetric cell displays good stability under CO2 and H2O co-electrolysis, indicating that LSFNb oxide is a promising symmetric electrode material for steam and CO2 co-electrolysis as well as for regenerative fuel cells.

Reduced-temperature redox-stable LSM as a novel symmetrical electrode material for SOFCs

Based on its reduced-temperature redox-stable phenomenon, the state-of-the-art perovskite oxide La0.8Sr0.2MnO3-δ (LSM) is proposed as a novel symmetrical electrode material for solid oxide fuel cells (SOFCs) at intermediate temperatures. LSM exhibits redox instability at high temperatures (≥850 °C) in agreement with the literature, whereas LSM is stable in both fuel and air conditions at intermediate temperatures (≤800 °C). The electrical conductivity of LSM in both air and humidified H2 (3% H2O) exhibit a semiconductor behavior, and the maximum values are 123.8 S cm−1 and 2.01 S cm−1 at 800 °C, respectively. LSM-Gd0.2Ce0.8O2-δ (LSM-GDC) composite electrode was used to improve the electrochemical performance. The area specific resistance of LSM-based electrode decrease from 3.03 Ω cm2 to 1.44 Ω cm2 in air and from 10.49 Ω cm2 to 5.19 Ω cm2 in H2 at 800 °C by adding mixed ionic-electronic conducting GDC, respectively. The electrochemical performance of symmetrical SOFCs with LSM-based electrodes are dramatically enhanced by more than 120 percent at 800 °C. The LSM-GDC composite electrode delivered optimum electrochemical properties with 140 h long-term stability, demonstrating its potential as both anode and cathode for symmetrical SOFCs at intermediate temperatures.

Characterization of Sr/Ru co-doped ferrite based perovskite as a symmetrical electrode material for solid oxide fuel cells

Abstract The perovskite Sm0.9Sr0.1Fe0.9Ru0.1O3-δ (SSFR) is synthesized and investigated as a new type of symmetrical electrode material for solid oxide fuel cells (SOFCs). X-ray diffraction analysis indicates that SSFR exhibits an orthorhombic structure with a space group of Pnma (62). There are no significant changes in polarization resistance (Rp) after a series of experiments in hydrogen and oxygen atmospheres at 800 °C, implying that SSFR has a good redox stability. To get an insight into the rate-limiting steps of SSFR electrode, behavior of Rp is investigated in different oxygen partial pressures (pO2). Generally, the relationship between Rp and pO2 follows the equation Rp = k(pO2)−n and different n values correspond to different rate-limiting steps. In this study, the n value of 0.5 is obtained for SSFR cathode at high temperature, relating to the diffusion of oxygen atom. In high pO2, SSFR presents a p-type conducting behavior, with decreasing pO2, a p–n transition occurs in the range 10−17 to 10−18 atm. Additionally, peak power density of the Sm0.2Ce0.8O1.9 (SDC, ∼0.6 mm) electrolyte-supported symmetrical cell SSFR|SDC|SSFR achieves 119.69 mW cm−2 at 800 °C using humidified hydrogen (∼3% H2O) as fuel.