La0.8Sr0.2Mn0.8Co0.2O3-δ perovskite as an efficient functional electrocatalyst for oxygen reduction reactions

The negative effects of the widespread and rough use of fossil energy have promoted the emergence of new energy technologies. Cost-effective electrocatalysts play an irreplaceable role in energy conversion and storage, especially oxygen reduction reactions (ORR) catalysts. While the reserves of precious metal catalysts are rare and expensive, it is of prime importance to develop catalysts that can replace precious metals. In the present work, La_0.8Sr_0.2Mn_0.8Co_0.2O_3-δ (LSMC) with Mn and Co is successfully prepared by sol-gel method and subsequent calcination. The characterizations of physical phase, microstructure, BET and valence state of elements demonstrate that LSMC material possesses ample mesoporous structure, large specific surface area, and multivalent elements, which can provide abundant active sites for ORR. The electrochemical tests reveal that the LSMC delivers outstandingly higher electrocatalytic activity for ORR, relatively lower overpotential and Tafel slope and a better long-term stability than the other perovskites (LSM, LSC) under alkaline condition. Furthermore, the coupling effects of high content of high-valence Co, multivalent Mn and large amounts of adsorbed oxygen endow the catalyst excellent ORR electrocatalytic activity. The present work investigating the effect of Mn and Co elements on the electrocatalysis of LSMC perovskite, will provide the possibility of developing a new type of perovskite electrocatalyst with excellent ORR electrocatalytic activity and low cost.     

High-performance anode-supported solid oxide fuel cells with co-fired Sm0.2Ce0.8O2-δ/La0.8Sr0.2Ga0.8Mg0.2O3−δ/Sm0.2Ce0.8O2-δ sandwiched electrolyte

In this study, intermediate-temperature solid oxide fuel cells (IT-SOFCs) with a nine-layer structure are constructed via a simple method based on the cost-effective tape casting-screen printing-co-firing process with the structure composed of a NiO-based four-layer anode, a Sm_0.2Ce_0·8O_2-δ(SDC)/La_0·8Sr_0.2Ga_0.8Mg_0·2O_3?δ (LSGM)/SDC tri-layer electrolyte, and an La_0·6Sr_0·4Co_0·2Fe_0·8O_3-δ (LSCF)-based bi-layer cathode. The resultant SDC (4.14 μm)/LSGM (1.47 μm)/SDC (4.14 μm) tri-layer electrolyte exhibits good continuity and a highly dense structure. The R_o and R_p values of the single cell are observed to be 0.15 and 0.08 Ω cm² at 800 °C, respectively, and the MPD of the cell is 1.08 Wcm-2. The high MPD of the cell appears to be associate with the significantly lower area-specific resistance and the reasonably high OCV. Compared to those with a similar electrolyte thickness reported in prior studies, the nine-layer anode-supported IT-SOFC with a tri-layer electrolyte developed by the study demonstrates superior cell properties.     

Ba0.5Sr0.5Fe0.8Sb0.2O3-δ- Sm0.2Ce0.8O2-δ bulk heterostructure composite: A cobalt free Oxygen Reduction Electrocatalyst for low-temperature SOFCs

Low-temperature operated ceramic fuel cells (LT-CFCs 350° to 550 °C) hold a great promise than high-temperature solid oxide fuel cells (HT-SOFCs ≥ 800 °C) for numerous large-scale real-application. If a suitable cathode should be developed to overcome the sluggish oxygen reduction activity at low temperatures, the low-temperature operation of ceramic fuel cells could be possible. In this study, we have developed a cobalt-free Ba_0.5Sr_0.5Fe_0.8Sb_0.2O_3-δ- Sm_0.2Ce_0.8O_2-δ (BSFSb- SDC) a bulk heterostructure composite for efficient ORR electrocatalyst for LT-SOFC cathode. The established BSFSb-SDC bulk heterostructure composite exhibits large lattice parameters, very low-area-specific resistance, and high oxygen reduction reaction (ORR) activity at low operating temperatures. The prepared fuel cell device has demonstrated high-power densities of 890 mW-cm-² at 550 °C for button-sized SOFC on H₂ and even possible operation at 400 °C. It is also found that BSFSb-SDC effectively facilitates small polaron hopping of valence electrons and diffusion of oxygen ions. Various spectroscopic measurements such as X-ray photoelectron, UV–visible, Raman, and Density Functional Theory (DFT) calculations were employed to understand the improved ORR electrocatalyst function of BSFSb-SDC bulk heterostructure composite SOFC cathode. The results can further help to develop functional cobalt-free electro-catalysts for LT-SOFCs and other related applications.     

Improved stability of nano-sized La0.6Sr0.4Co0.2Fe0.8O3-δ-Ce0.8Sm0.2O1.9 composite cathodes by substituting Sr2+ with Ca2+

The nano-sized composite cathodes prepared by infiltrating La_0.6Sr_{0. 4}Co_0.2Fe_0.8O_3-δ (LSCF) or La_0.6Ca_0.4Co_0.2Fe_0.8O_3-δ (LCCF) into the Ce_0.8Sm_0.2O_1.9 (SDC) scaffolds exhibit different electro-catalytic activity and microstructure evolution. Compared with LSCF-SDC nano-sized composite cathode, the LCCF-SDC composite cathode shows the higher microstructure stability. There is no observable coarsening or sintering and no diffraction peaks of other impurity phase are detected for both LSCF and LCCF after being aged at 600 °C for 500 h, but the lattice distortion is less if La³⁺ ions are substituted by Ca²⁺ ions instead of by Sr²⁺ in LaCo_0.2Fe_0.8O_3-δ (LCFO) lattice. The oxygen vacancy concentration is also less in LCCF than in LSCF. The less lattice distortion and oxygen vacancy concentration prohibit the Ca²⁺ ions segregation on the LCCF cathode surface because of less strain in the LCCF lattice and less electrostatic interactions between the negatively charge A-site dopants (Ca′_La) and the positively charged oxygen vacancies (V_o^··) on LCCF surface. The greater binding energy of Ca–O maybe also hinder the enrichment of Ca²⁺ ions on the cathode surface. After being aged in air at 600 °C for 500 h, more Sr²⁺ ions gather on the LSCF cathode surface to form a Sr-rich inert phase, which is detrimental to the oxygen reduction reaction on the cathode surface.     

Nanocomposite BaZr0.7Sm0.1Y0.2O3−δ–La0.8Sr0.2Co0.2Fe0.8O3−δ materials for single layer fuel cell

Single layer fuel cell (SLFC) is a novel breakthrough in energy conversion technology. This study is to realize the physical-electrochemical co-driving mechanism of a single component device composed of mixed ionic and semiconductor material. This paper is focused on investigating the mechanism and characterization of synthesized nanocomposite BaZr_0.7Sm_0.1Y_0.2O_3?δ (BZSY)–La_0.8Sr_0.2Co_0.2Fe_0.8O_3?δ (LSCF) in proportion 1:1 and 3:7 for SLFC. The crystallographic structure and morphology is studied with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The nano-particles lie in the range of 100–210 nm. Ultraviolet (UV) and electrochemical impedance spectroscopy (EIS) is used to analyze the semiconducting nature of nanocomposite (BZSY–LSCF). The performance of SLFC was carried out at different temperatures ranging between 400 and 650 °C. The mixed conductivity of the synthesized material was about 2.3 S cm^?1. The synergic effect of junction and energy band gap towards charge separation as well as the promotion of ion transport by junction built in field contributes to the working principle and high power output in the SLFC.     

Study on durability of novel core-shell-structured La0.8Sr0.2Co0.2Fe0.8O3-δ@Gd0.2Ce0.8O1.9 composite materials for solid oxide fuel cell cathodes

Core-shell-structured La_0.8Sr_0.2Co_0.2Fe_0.8O_3-δ@Gd_0.2Ce_0.8O_1.9 (LSCF@GDC) composite materials are synthesized and sintered as the SOFC cathodes by screen-printing method. The durability of core-shell-structured LSCF@GDC composite cathodes are evaluated through constant current polarizations (CCP) process at 750 °C and the results indicate that the core-shell-structured LSCF@GDC composite cathode (nanorod, 0.6) possesses an excellent long-term stability. In addition, molecular dynamics (MD) model is developed and applied to simulate the interaction between LSCF and GDC particles. According to the simulation results, compressive stress is generated at the cathode-electrolyte interface by the coated GDC layer. Combining with the X-ray diffraction (XRD) refinement results, it's revealed that the lattice strains are introduced in LSCF lattices because of the compressive stress. Furthermore, XPS results show that the core-shell-structured LSCF@GDC composite cathode (nanorod, 0.6) possess a better inhibition ability for Sr surface segregation. This study provides a possible way to suppress Sr surface segregation.     

La0.4Sr0.6Co0.7Fe0.2Nb0.1O3-δ perovskite prepared by the sol-gel method with superior performance as a bifunctional oxygen electrocatalyst

The advancement of efficient noble-metal-free electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is crucially important for energy storage devices such as fuel cells and metal-air batteries. This paper reports the development of a novel bifunctional perovskite, La_0.4Sr_0.6Co_0.7Fe_0.2Nb_0.1O_3-δ (LSCFN). The crystal structure, morphology, adsorption, valence, and oxygen catalytic activity of LSCFN were systematically studied. In addition, an investigation of the influence of the synthetic method on the oxygen catalytic activity was performed. Sol-gel and solid-phase methods were applied for the synthesis of LSCFN, and the resulting perovskites were denoted as LSCFN-SG and LSCFN-SP, respectively. The catalyst LSCFN-SG exhibited excellent bifunctional catalytic activity, with a low overpotential (360 mV) and superior stability in the OER. Subsequently, LSCFN-SG was used as the cathode catalyst in an aluminum-air battery and exhibited a high power density. The results of this study indicate that LSCFN-SG is a promising bifunctional oxygen electrocatalyst for metal-air batteries.     

Single layer low-temperature SOFC based on Ce0.8Sm0.2O2-δ- La0.25Sr0.75Ti1O3-δ-Ni0.8Co0.15Al0.05LiO2-δ composite material

This study reports a kind of single layer solid oxide fuel cell (SLSOFC) based on semiconductor-ionic conductor composite material which consists of Ce_0.8Sm_0.2O_2-δ (SDC, ionic conductor), La_0.25Sr_0.75Ti₁O_3+δ (LST, n-type semiconductor) and Ni_0.8Co_0.15Al_0.05LiO_2-δ (NCAL, p-type semiconductor). It was found that the LST-SDC-NCAL composite based SLSOFC exhibited open circuit voltage (OCV) of more than 1 V and maximum power density of 222 mW cm^?2 under 550 °C. In-situ Schottky junction in the device helps to prevent short circuiting as well as promote ion transport. Electrochemical impedance spectroscopy (EIS) analysis revealed that the ionic conductivity of the SLSOFC was about 0.09 S cm^?1, and the corresponding activation energy is 0.7 eV. The cell performance was stable during 65 h without any significant degradation. Moreover, the SLSOFC possessed higher tolerance for temperature change than traditional three-layer SOFC due to the well match of thermal expansion coefficient between electrodes and electrolyte. This device is of great significance in preventing fuel cell delamination, simplifying manufacturing process and promoting its commercialization.     

Effect of hetero-structured nano-particulate coating on the oxygen surface exchange properties of La0.6Sr0.4Co0.2Fe0.8O3-δ

In this study, dense La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) electrodes decorated with the novel hetero-structured ceramic oxide mixture in four different ratios of Ce_0.8Gd_0.2O_2-δ (GDC) and La₂Mo₂O₉ (LMO). The time-dependent conductivity transients were acquire using electrical conductivity relaxation (ECR) technique at a chosen conditions of temperature in the range of 650–850 °C and instantaneous pO₂ step change between 0.2 and 0.8. Fitting of time-dependent conductivity to the appropriate non-equilibrium solutions of Fick's diffusion equation has yielded the chemical diffusion coefficient, D_chem, and oxygen surface exchange coefficient, k_chem. As expected, the D_chem of the coated samples remained invariant, whilst the k_chem is found to vary with the change in GDC-LMO coating mixture ratio. Substantial increase of a factor of 10 in the surface exchange coefficient is noticed for the LSCF coated with a 1:0.75 mixing ratio as compared to bare sample at 850 °C. The enhancement in k_chem is attributed to the optimal triple-phase boundary (TPB) regions which promotes oxygen surface exchange kinetics. Thus, coating of selective ratio of hetero-structured oxide in a form of nano-particulate layer over the LSCF surface is considered to be a promising candidate for solid oxide fuel cell (SOFC) cathode.     

La0.6Ca0.4Fe0.8Ni0.2O3−δ – Sm0.2Ce0.8O1.9 composites as symmetrical bi-electrodes for solid oxide fuel cells through infiltration and in-situ exsolution

Symmetrical solid oxide fuel cells (SOFCs) have more attractive benefits such as a simplified fabrication procedure and enhanced stability and reliability compared to conventional SOFC. In this study, we fabricated a La_0.6Ca_0.4Fe_0.8Ni_0.2O_3?δ (LCFN) – Sm_0.2Ce_0.8O_1.9 (SDC) composite via infiltration and simple mixing methods and evaluated it as both anode and cathode for symmetrical SOFCs (S-SOFC). X-ray diffraction (XRD) and scanning electron microscope (SEM) results demonstrated that Fe-Ni bimetallic nanoparticles were exsolved in-situ from LCFN perovskite and distributed on the surface of LCFN backbone after H₂ reduction at high temperature. The electro-activity towards oxygen reduction reaction (ORR) at the cathode side could be further improved by infiltration of SDC nanoparticles. A combined effect of in-situ ex-solution of Fe-Ni as well as infiltration of SDC nanoparticles synergistically promoted the hydrogen oxidation reaction at the anode and ORR activity at the cathode. Furthermore, the S-SOFC showed good stability in H₂ at 800 °C for 140 h and reliable redox stability undergoing a repeated H₂-air cycles. These recent results indicate that the LCFN-SDC composite electrodes were promising bi-electrode materials for high performance and cost-effective S-SOFCs.     

Characteristics of La0.6Sr0.4Co0.2Fe0.8O3–Cu2O mixture as a contact material in SOFC stacks

La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF), a cathode material for solid oxide fuel cells, is mixed with six weight percentages (2.46–21.74 wt%) of more conductive Cu₂O powder for use as a cathode contact material. Electrical conductivity change is measured at 800 °C for 600 h. Conductivity first increases with the Cu₂O weight percentage to reach a peak value 30.67 S/cm at 7.18 wt%, then decreases with further more Cu₂O content. Microstructural examination reveals that Cu₂O oxidizes as CuO in the high temperature environment with a loose matrix, which can raise the electrical resistance. LSCF–Cu₂O paste with three weight percentages of Cu₂O is also applied in steel/paste/steel assemblies. The area specific resistance is measured at 800 °C for 200–300 h. It is found that LSCF-7.18 wt% Cu₂O exhibits the lowest resistance. Additionally, stack performance is compared between two single-cell stacks with Ag mesh and LSCF-4.9 wt% CuO as the contact layer respectively. It shows that the LSCF-4.9 wt% CuO stack yields comparable power output with a lower degradation rate. Experimental results indicate that LSCF with 7.18 wt% Cu₂O addition can serve as a potential contact material.     

A promising Bi-doped La0.8Sr0.2Ni0.2Fe0.8O3-δ oxygen electrode for reversible solid oxide cells

Reversible solid oxide cells (RSOCs) are clean and effective electrochemical conversion devices that require highly active electrodes and stable electrochemical performance for the practical application. Herein, we investigate a series of La_0.8-xBi_xSr_0.2Ni_0.2Fe_0.8O_3-δ (LBSNF-x, x = 0.0, 0.05, 0.1, 0.15) oxides as the potential oxygen electrode material for RSOCs. The properties of electrical conductivity, thermal expansion coefficient, and chemical compatibility with the Ce_0.9Gd_0.1O_1.95 (GDC) barrier layer of LBSNF-x oxides are evaluated. When LBSNF-0.1 and GDC forms a composite oxygen electrode with the ratio of 7:3, it shows the lowest polarization resistance with fastest oxygen reduction reaction activity in the symmetrical cell test. Then the cell with the configuration of Ni-YSZ/YSZ/GDC/LBSNF-0.1-GDC was prepared and evaluated both in fuel cell (FC) and electrolysis cell (EC) mode. The maximum power density of 824 mW cm⁻² is obtained at 800 °C in FC mode, and current density of 1.20 A cm⁻² is achieved under 50% steam content at 1.3 V in EC mode. Additionally, the cell exhibits good stability both in FC and EC mode after 80 h test at 700 °C. The results of this work provide a strong support for application of the LBSNF-0.1-GDC oxygen electrode for reversible solid oxide cells.     

Effects of Gd0.8Ce0.2O1.9−δ coating with different thickness on electrochemical performance and long-term stability of La0.8Sr0.2Co0.2Fe0.8O3-δ cathode in SOFCs

The commercialization of Solid oxide fuel cells (SOFCs) has always been limited by the poor catalytic activity and the severe degradation of cathode in the intermediate and low operating temperature. Here we report a Gd_0.8Ce_0.2O_1.9?δ (GDC) coated La_0.8Sr_0.2Co_0.2Fe_0.8O_3-δ (LSCF) composite cathode material, which can significantly improve the electrochemical performance and durability of LSCF cathode. The effects of different GDC coating thickness on the electrochemical performance and long-term working stability of LSCF cathode are investigated, and the optimal coating thickness is established. The polarization impedance of GDC coated LSCF (LSCF@GDC) cathode with 9 nm of GDC coating is 0.08 Ω cm² at 800 °C, which is only one quarter of that of the raw LSCF cathode, and the degradation rate of constant current polarization with 100 mA cm^?2 is only 0.42%/100 h at 700 °C, which is far less than that of the raw LSCF cathode. The X-ray photoelectron spectroscopy (XPS) results show that the degree of Sr segregation decreases with the increase of the thickness of the coated GDC layer. The potential LSCF@GDC composite material is expected to increase the operability of SOFCs and accelerate its commercialization.     

Electrochemical performance of La0.65Sr0.35MnO3 oxygen electrode with alternately infiltrated Sm0.5Sr0.5CoO3-δ and Sm0.2Ce0.8O1.9 nanoparticles for reversible solid oxide cells

La_1-xSr_xMnO₃ is a well-known oxygen electrode for reversible solid oxide cells (RSOCs). However, its poor ionic conductivity limits its performance in redox reaction. In this study, we selected Sm_0.5Sr_0.5CoO_3-δ (SSC) as catalyst and Sm_0.2Ce_0.8O_1.9 (SDC) as ionic conductor and sintering inhibitor to co-modify the La_0.65Sr_0.35MnO₃ (LSM) oxygen electrode through an alternate infiltration method. The infiltration sequence of SSC and SDC showed an influence on the morphology and performance of LSM oxygen electrode, and the influence was gradually weakened with the increasing infiltration time. The polarization resistance of the alternately infiltrated LSM-SSC/SDC electrode was 0.08 Ω cm² at 800 °C in air, which was 3.36% of the LSM electrode (2.38 Ω cm²). The Ni-YSZ/YSZ/LSM-SSC/SDC single cell attained a maximum power density of 1205 mW cm^?2 in SOFC mode at 800 °C, which was 8.73 times more than the cell with LSM electrode. The current density achieved 1620 mA .cm^?2 under 1.5 V at 800 °C in SOEC mode and the H₂ generation rate was 3.47 times of the LSM oxygen electrode.     

Preparation of three-dimensional Fe–N co-doped open-porous carbon networks as an efficient ORR electrocatalyst in both alkaline and acidic media

It is of significant importance to construct the low-cost, efficient, and stable carbon-based non-noble metal to replace the noble metal electrocatalyst for oxygen reduction reaction in both alkaline and acidic media. In this work, a straightforward and cost-efficient strategy is reported to synthesize the Fe–N co-doped open-porous carbon materials with three-dimensional (3D) carbon networks structure, high surface areas and multiple actives sites including iron carbide nanoparticles, pyridinic N, and graphitic N using a new kind of Fe-Imace coordinated complex as the precursor and melamine as nitrogen sources by direct pyrolysis. The obtained Fe–N–C 900 catalyst shows excellent oxygen reduction performance in both alkaline (E_onset, 1.014 vs. RHE) and acidic (E_onset, 0.982 V vs. RHE) media, which are better than those of the Pt/C in alkaline (E_onset, 0.986 vs. RHE) and acidic media (E_onset, 0.979 V vs. RHE). Even more important, the stability and methanol tolerance of the Fe–N–C 900 catalyst are much better than that of the Pt/C catalyst in both alkaline and acidic media. All the results demonstrate that the present facile and universal one-step pyrolytic strategy can be used to synthesize catalyst materials as one of the superior non-precious cathode electrocatalysts for fuel cells.     

High-performance La0.5(Ba0.75Ca0.25)0.5Co0.8Fe0.2O3-δ cathode for proton-conducting solid oxide fuel cells

La_0.5(Ba_0.75Ca_0.25)_0.5Co_0.8Fe_0.2O_3-δ, a simple perovskite cathode material with high electrical conductivity (940 S cm^?1 at 600 °C) and impressive surface catalytic activity, was prepared and used in proton-conducting solid oxide fuel cells. As its thermal expansion coefficient is higher than that of the electrolyte material BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ, they were combined and used as a composite cathode. The crystal structure, chemical compatibility, electrical conductivity, cell performance, and the oxygen reduction reaction of the cathode material were explored, and we found that the single fuel cell developed with the composite cathode achieved excellent electrochemical performance, with both a low polarization resistance and high peak power density (0.044 Ω cm² and 1102 mW cm^?2 at 750 °C, respectively). Outstanding stability was also achieved, as indicated by a long-term 100-h test. Additionally, the rate-limiting steps of the oxygen reduction reaction were the oxygen adsorption, dissociation, and diffusion processes.     

Kinetics of oxygen reaction in porous La0.6Sr0.4Co0.2Fe0.8O3–δ-Ce0.8Gd0.2O1.9 composite electrodes for solid oxide cells

Kinetics of oxygen reaction in porous La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ (LSCF) and La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ-Ce_0.8Gd_0.2O_1.9 (LSCF-GDC) electrodes are systematically studied. Normally, there are two pathways of oxygen reaction in porous LSCF: in reaction region with oxygen exchanging at electrode/air interface, and around electrode/electrolyte interface with oxygen exchanging at electrode/electrolyte/air triple-phase boundary (TPB). GDC in porous LSCF-GDC accelerates oxygen transport and oxygen gas diffusion during oxygen reaction. In addition, because the formation of LSCF/GDC interface increases the length of TPB and affects the geometry of reaction region, oxygen reaction in LSCF-GDC tends to proceed in the TPB pathway. The performance and oxygen reactions of LSCF-GDC are evaluated at 650 °C and 850 °C. Oxygen reaction in LSCF-GDC is suppressed by CO₂, but increasing GDC content is able to improve the CO₂ tolerance of electrode. Though the performance reduction by H₂O is unobvious, H₂O can aggravate CO₂ degradation at low temperature.     

A La0.8Sr0.2MnO3/La0.6Sr0.4Co0.2Fe0.8O3−δ core–shell structured cathode by a rapid sintering process for solid oxide fuel cells

A La_0.8Sr_0.2MnO₃ (LSM)/La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF) core–shell structured composite cathode of solid oxide fuel cells (SOFCs) has been fabricated by wet infiltration followed by a rapid sintering (RS) process. The RS is carried out by placing LSCF infiltrated LSM electrodes directly into a preheated furnace at 800 °C for 10 min and cooling down very quickly. The heating and cooling step takes about 20 s, substantially shorter than 10 h in the case of conventional sintering (CS) process. The results indicate the formation of a continuous and almost non-porous LSCF thin film on the LSM scaffold, forming a LSCF/LSM core–shell structure. Such RS-formed infiltrated LSCF–LSM cathodes show an electrode polarization resistance of 2.1 Ω cm² at 700 °C, substantially smaller than 88.2 Ω cm² of pristine LSM electrode. The core–shell structured LSCF–LSM electrodes also show good operating stability at 700 °C and 600 °C over 24–40 h.     

Composite ceramic cathode La0.9Ca0.1Fe0.9Nb0.1O3-δ/Sc0.2Zr0.8O2−δ towards efficient carbon dioxide electrolysis in zirconia-based high temperature electrolyser

In this paper, a novel composite La_0.9Ca_0.1Fe_0.9Nb_0.1O_3-δ/Sc_0.2Zr_0.8O_2?δ (LCFNb/ScSZ) is developed and investigated as a fuel electrode candidate for direct electrolyzing carbon dioxide (CO₂) in solid oxide electrolysis cells (SOECs). XRD patterns of LCFNb powder sintered in CO₂ at 850 °C for 10 h indicate that no secondary phases are found during the heat treatment and linear thermal expansion results prove that the LCFNb is compatible with ScSZ electrolyte used in this work. The electrolyser with porous LCFNb membrane cathode fabricated by infiltration method shows impressive electrochemical performance. The current density of 1.97 A/cm² at 2.0 V at 800 °C is obtained. The polarization resistance Rp of the SOEC decreases with the increase of the applied voltage between the electrodes. The obtained lowest Rp is as low as 0.113 Ω cm² at 2.0 V and this value is much lower than its many other perovskite and nickle-based counterparts. Besides, the LCFNb/ScSZ cathode shows excellent stability in pure CO₂ at different applied voltage, especially at 2.0 V. Furthermore, the LCFNb/ScSZ electrode exhibits the current efficiencies close to theoretical ones for CO₂ electrolysis, indicating that the LCFNb/ScSZ composite ceramic is an excellent cathode for zirconia-based high temperature electrolyser.     

The electrolyte-layer free fuel cell using a semiconductor-ionic Sr2Fe1.5Mo0.5O6-δ – Ce0.8Sm0.2O2-δ composite functional membrane

Commercial double Perovskite Sr₂Fe_1.5Mo_0.5O_6-δ (SFM), a high performance and redox stable electrode material for solid oxide fuel cell (SOFC), has been used for the electrolyte (layer) -free fuel cell (EFFC) and also as the cathode for the electrolyte based SOFC in a comprehensive study. The EFFC with a homogeneous mixture of Ce_0.8Sm_0.2O_2-δ (SDC) and SFM achieved a higher power density (841 mW cm^?2) at 550 °C, while the SDC electrolyte based SOFC, using the SDC-SFM composite as cathode, just reached 326 mW cm^?2 at the same temperature. The crystal structure and the morphology of the SFM-SDC composite were characterized by X-ray diffraction analysis (XRD), and scanning electron microscope (SEM), respectively. The electrochemical impedance spectroscopy (EIS) results showed that the charge transfer resistance of EFFCs were much lower than that of the electrolyte-based SOFC. To illustrate the operating principle of EFFC, we also conducted the rectification characteristics test, which confirms the existence of a Schottky junction structure to avoid the internal electron short circuiting. This work demonstrated advantages of the semiconductor-ionic SDC-SFM material for advanced EFFCs.