Ceria-based electrolyte reinforced by sol–gel technique for intermediate-temperature solid oxide fuel cells

High performance solid oxide fuel cells (SOFCs) based on gadolinia-doped ceria (GDC) electrolyte are demonstrated for intermediate temperature operation. The inherent technical limitations of the GDC electrolyte in sinterability and mechanical properties are overcome by applying sol–gel coating technique to the screen-printed film. When the quality of the electrolyte film is enhanced by the additional sol–gel coating, the OCV and maximum power density increase from 0.73 to 0.90 V and from 0.55 to 0.95 W cm⁻², respectively, at 650 °C with humidified hydrogen (3% H₂O) as fuel and air as oxidant. The impedance analysis reveals that the reinforcement of the thin electrolyte with sol–gel coating significantly reduces the polarization resistance. Elementary reaction steps for the anode and cathode are analyzed based on the systematic impedance study, and the relation between the structural integrity of the electrolyte and the electrode polarization is discussed in detail.     

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.     

High-performance NdSrCo2O5+δ–Ce0.8Gd0.2O2-δ composite cathodes for electrolyte-supported microtubular solid oxide fuel cells

NdSrCo₂O_5+δ (NSCO) is a perovskite with an electrical conductivity of 1551.3 S cm⁻¹ at 500 °C and 921.7 S cm⁻¹ at 800 °C and has a metal-like temperature dependence. This perovskite is used as the cathode material for Ce_0.8Gd_0.2O_2-δ (GDC)-supported microtubular solid oxide fuel cells (MT-SOFCs). The MT-SOFCs fabricated in this study consist of a bilayer anode, comprising a NiO–GDC composite layer and a NiO layer, and a NSCO–GDC composite cathode. Three cell designs with different outer tube diameters, GDC thicknesses, and NSCO/GDC ratios are designed. The MT-SOFC with an outer tube diameter of 1.86 mm, an electrolyte thickness of 180 μm, and a 5NSCO–5GDC composite cathode presents the best performance. The flexural strength of the aforementioned cell is 177 MPa, which is sufficient to confer mechanical integrity to the cell. Moreover, the ohmic and polarization resistance values of the cell are 0.22 and 0.09 Ω cm² at 700 °C, respectively, and 0.15 and 0.03 Ω cm² at 800 °C, respectively. These results indicate that the NSCO-GDC composite exhibits high electrochemical activity. The maximum power densities of the cell at 700 and 800 °C are 0.46 and 0.67 W cm⁻², respectively, exceeding those of existing electrolyte-supported MT-SOFCs with similar electrolyte thicknesses.     

Electrochemical and thermal properties of SmBa0.5Sr0.5Co2O5+δ cathode impregnated with Ce0.8Sm0.2O1.9 nanoparticles for intermediate-temperature solid oxide fuel cells

SmBa_0.5Sr_0.5Co₂O_5+δ (SBSC55) impregnated with nano-sized Ce_0.8Sm_0.2O_1.9 (SDC) powder has been investigated as a candidate cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The cathode chemical compatibility with electrolyte, thermal expansion behavior, and electrochemical performance are investigated. For compatibility, a good chemical compatibility between SBSC55 and SDC electrolyte is still kept at 1100 °C in air. For thermal dilation curve, it could be divided into two regions, one is the low temperature region (100–265 °C); the other is the high temperature region (265–850 °C). In the low temperature region (100–265 °C), a TEC value is about 17.0 × 10^?6 K^?1 and an increase in slope in the higher temperatures region (265–800 °C), in which a TEC value is around 21.1 × 10^?6 K^?1. There is an inflection region ranged from 225 to 330 °C in the curve of d(δL/L)/dT vs. temperature. The peak inflection point located about 265 °C is associated to the initial temperature for the loss of lattice oxygen and the formation of oxygen vacancies. For electrochemical properties, the polarization resistances (R_p) significantly reduced from 4.17 Ω cm² of pure SBSC55 to 1.28 Ω cm² of 0.65 mg cm^?2 of SDC-impregnated SBSC55 at 600 °C. The single cell performance of SBSC55∣SDC∣Ni-SDC loaded with 0.65 mg cm^?2 SDC exhibited the optimum power density of 823 mW cm^?2 at operating temperature of 800 °C. Based on above-mentioned properties, SBSC55 impregnated with an appropriate SDC is a potential cathode for IT-SOFCs.     

Modified La0.6Sr0.4Co0.2Fe0.8O3-δ cathodes with the infiltration of Er0.4Bi1.6O3 for intermediate-temperature solid oxide fuel cells

Aiming to lower the activation energy and expedite the oxygen reduction reaction (ORR) process of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) cathodes for application in intermediate-temperature solid oxide fuel cells (IT-SOFCs), Er_0.4Bi_1.6O₃ (ESB) modified LSCF was prepared by infiltrating using organic solvents. The infiltration of ESB dramatically reduces the polarization resistances of LSCF cathodes (from 0.27 to 0.11 Ω cm² at 700 °C, from 0.58 to 0.25 Ω cm² at 650 °C), and lowers their activation energy (from 100.28 to 97.15 kJ mol^?1). Also, ESB makes the rate-limiting step of LSCF cathodes at high frequency change from the charge transfer process on the cathode to the adsorption and diffusion of oxygen on cathode surface. The single cell with ESB infiltrated LSCF cathodes shows a peak power density of 469 mW cm^?2 at 700 °C using humid hydrogen and air as fuels and oxidants, respectively, as well as a good short-term stability for 50 h.     

Self-assembled Fe-doped PrBaCo2O5+δ composite cathodes with disorder transition region for intermediate-temperature solid oxide fuel cells

PrBa(Co_1-xFe_x)₂O_5+δ polymorphs (0.1 < x < 0.4, denoted as PBCF-x with Fe-doping level x) are reported and dual phase of cubic phase Pr_0.5Ba_0.5Co_1−xFe_xO_3−δ and tetragonal phase PrBa(Co_1-xFe_x)₂O_5+δ are co-produced through an common sol–gel method. The co-generation of the dual-phases leads to the formation of abundant hetero-interfaces between the neighboring crystal phases and the synergic effect demonstrates remarkably high oxygen adsorption and dissociation ability in the air. The density functional theory (DFT) calculation establishes that the existence of hetero-interfaces promotes oxygen reduction reaction activity (ORR) which is crucial to improve cathode performance of proton-conducing solid oxide fuel cells (H–SOFCs). Moreover, an outstanding electrochemical performance is obtained for the single cell with a PBCF03 cathode and the research demonstrates that a self-assemble dual phase cathode can be an effective approach for developing high-performing H–SOFCs.     

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.     

Synthesis and electrochemical characterization of La0.6Sr0.4Co0.2Fe0.8O3–δ / Ce0.9Gd0.1O1.95 co-electrospun nanofiber cathodes for intermediate-temperature solid oxide fuel cells

Synthesis and electrochemical characterization of composite cathodes, formed from a mixture of La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ (LSCF) and Ce_0.9Gd_0.1O_1.95 (GDC) nanofibers, is reported. The electrodes are obtained by simultaneous electrospinning of the two precursor solutions, using apparatus equipped with two spinnerets working in parallel. Results of electrochemical testing carried out through electrochemical impedance spectroscopy (EIS) are presented and discussed. The results suggest that the electrochemical reaction takes place in an electrode region close to the electrode/current collector interface and that the oxygen ions then flow along the ionic conducting path of the GDC fibers. At 650 °C, the polarization resistance is R_p = 5.6 Ω cm^?2, in line with literature values reported for other IT-SOFC cathodes.     

Processing and characterization of novel Ce0.8Sm0.1Bi0.1O2-δ-BaCe0.8Sm0.1Bi0.1O3-δ (BiSDC-BCSBi) composite electrolytes for intermediate-temperature solid oxide fuel cells

Ce_0.8Sm_0.1Bi_0.1O_2-δ-BaCe_0.8Sm_0.1Bi_0.1O_3-δ (BiSDC-BCSBi) composites are fabricated as novel electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Both dramatically enhanced sinterability and electrical performance are obtained due to the Bi doping. BiSDC-BCSBi composites are densified at as low as 1200 °C, allowing a decrease of 350 °C compared with Ce_0.8Sm_0.2O_2-δ-BaCe_0.8Sm_0.2O_3-δ (SDC-BCS) composites. The optimal electrical conductivity of BiSDC-BCSBi electrolytes measured at 600 °C in humid air reaches up to 27.97 mS cm^?1, almost 6 times higher than that of SDC-BCS electrolytes (3.91 mS cm^?1 in humid air), which is mainly attributed to their lower sintering temperature, more uniform microstructure, larger tensile strains, and higher concentrations of O–H groups and oxygen vacancies. The electrolyte-supported single cell with BiSDC-BCSBi electrolyte displays a peak power density of 397 mW cm^?2 at 600 °C using humid hydrogen as fuel and ambient air as oxidant. These results imply that BiSDC-BCSBi composites have a great application prospect for IT-SOFCs.     

Investigation of the Fe doping effect on the B-site of the layered perovskite PrBa0.8Ca0.2Co2O5+δ for a promising cathode material of the intermediate-temperature solid oxide fuel cells

Layered perovskites can be considered as promising cathode materials for intermediate-temperature solid oxide fuel cell because of their fast oxygen kinetics compared to simple perovskites. Among them, the cobalt-based layered perovskites are considered as very promising cathode materials due to its high conductivity and fast oxygen kinetics, but they are unstable under operating condition. Doping other transition metal such as Fe, Mn, Cu, and Ni can be considered to solve the instability of the cobalt-based layered perovskites.In this paper, we investigated Fe doped cobalt-based layered perovskite, PrBa_0.8Ca_0.2Co_2-xFe_xO_5+δ (x = 0, 0.5, and 1.0), as prospective cathode materials in terms of their crystal structures, thermal expansion behavior, electro- and electro-chemical properties. The PrBa_0.8Ca_0.2Co_1.5Fe_0.5O_5+δ shows improved maximum power density of 1.89 W cm⁻² and polarization resistance of 0.080 Ω cm² at 600 °C as compared with un-doped PrBa_0.8Ca_0.2Co₂O_5+δ while maintaining suppressed thermal expansion. Based on these results, PrBa_0.8Ca_0.2Co_1.5Fe_0.5O_5+δ can be considered as a promising cathode material for intermediate-temperature solid oxide fuel cell.     

LaBa0.8Ca0.2Co2O5+δ cathode with superior CO2 resistance and high oxygen reduction activity for intermediate-temperature solid oxide fuel cells

The development of highly efficient cathode materials with durable performance and high resistance toward environmental impurity is crucial for realizing the practical applications of intermediate temperature - solid oxide fuel cells (SOFCs). Since CO₂ as the oxidation product of hydrocarbons is unavoidable in the surrounding air atmosphere for SOFCs operating on hydrocarbon fuels, CO₂ tolerance of the air electrode is a big concern. Herein, LaBa_0.8Ca_0.2Co₂O_5+δ (LBCC) double perovskite is proposed as a promising cathode with superior CO₂ tolerance and favourable oxygen reduction activity. It shows a relatively low area specific resistance of 0.128 Ω cm² at 600 °C in a CO₂-free synthetic air atmosphere, tested based on a symmetrical cell configuration (LBCC | Gd_0.2Ce_0.8O_1.9 | LBCC). In addition, under open-circuit voltage condition, it can run stably for more than 120 h in the air containing 1% CO₂ (1% CO₂, 21% O₂ and 78% N₂) at 650 °C. More attractively, the LBCC shows high reversibility in performance by removing CO₂ from air. An anode-supported single SOFC with thin film doped ceria electrolyte (～25 μm) and LBCC cathode shows a favourable peak power density of 1063 mW cm^?2 at 700 °C by using ambient air as the cathode atmosphere and hydrogen as the fuel.     

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.     

Effects of Ni-NCAL and Ni–Ag electrodes on the cell performances of low-temperature solid oxide fuel cells with Sm0.2Ce0·8O2-δ electrolyte at various temperatures

Three low-temperature solid oxide fuel cells are built using Sm_0.2Ce_0·8O_2-δ (SDC) as the electrolyte. Cell A is symmetrical and features Ni–LiNi_0.8Co_0·15Al_0·05O₂ (Ni–NCAL) electrodes, Cell B comprises a Ni–NCAL anode and a Ni–Ag cathode, and Cell C is fabricated using a Ni–NCAL cathode and a Ni–Ag anode. The ohmic resistance and polarization resistance (R_p) of Cells B and C are significantly higher than those of Cell A. The reduction of NCAL at the anodes of Cells A and B yields LiOH and Li₂CO₃ phases, and the Ni particles generated on the surfaces of the NCAL particles improve the catalytic activity of the cells. Li₂CO₃–LiOH melts at temperatures >450 °C and penetrates the porous SDC electrolyte layer, causing its densification and abnormal grain growth and increasing its ionic conductivity to >0.2 S/cm at low temperatures. The high open-circuit voltages (OCVs) (0.970–1.113 V) of the cells during electrochemical measurements are ascribed to the Li₂CO₃–LiOH phase which serves as an electron-blocking layer for the SDC electrolytes. As the reduction of NCAL approaches completion, the anode comprises only Ni phase, which hinders the charge transfer process. The triple-phase-boundary (TPB) area at cathode of Cell B is significantly lower than that of Cell A; therefore, the catalytic activity of Cell B for the oxygen reduction reaction is lower than that of Cell A. Consequently, the maximum power density (MPD) of Cell B is less than half of that of Cell A. The large R_p value of Cell C is ascribed to its low TPB area at Ni–Ag anode which has no reaction with H₂ during operation. No visible sintering of the SDC electrolyte layer is observed for Cell C; therefore, its ionic conductivity is considerably smaller than those of the electrolyte layers of Cells A and B. The OCVs of Cell C (0.281–0.495 V) are significantly lower than the typical OCVs of ceria-based SOFCs. This is attributed to the porous SDC electrolyte layer of Cell C. The large R_p values and the low OCVs contribute to the low MPDs of Cell C at various temperatures.     

In-situ strategy to suppress chromium poisoning on La0.6Sr0.4Co0.2Fe0.8O3-δ cathodes of solid oxide fuel cells

The surface segregation of strontium in the La_0.6Sr_0.4Co_0.8Fe_0.2O_3-δ (LSCF) electrode interacts with volatile contaminants such as chromium in the solid oxide fuel cell (SOFC) interconnect, causing deterioration in cell performance. A simple in-situ reaction strategy has been exploited to synergistically improve oxygen reduction reaction (ORR) activity in air and anti-chromium stability of LSCF electrode via infiltration and calcination of nickel nitrate and ferrite nitrate (NF) precursor on the LSCF backbone. The chemical compatibility, electrochemical performance, interfacial element distribution and stability in chromium-containing atmosphere of the as-prepared hybrid electrodes were systematically investigated. At a calcination temperature of 1100 °C, Sr(Co,Ni)O_3-δ layer was formed owing to Co diffusion and Sr precipitation from LSCF and the reaction with Ni atoms at the surface of LSCF. This will promote anti-chromium ability for the hybrid LSCF@NF cathode material. After the symmetrical cells were operated at 750 °C for 400 h under Cr contamination, the polarization resistance of LSCF@NF was only half of that of blank LSCF electrode with much less Cr species. This strategy via in-situ reaction may be extended to other high temperature energy conversion systems such as anti-sulfur and anti-carbon deposition of SOFC anodes and CO₂ resistance of cathodes.     

Chromium deposition and poisoning of cathodes of solid oxide fuel cells – A review

Intermediate temperature solid oxide fuel cells (IT-SOFCs) using chromia-forming alloy interconnect requires the development of cathode not only with high electrochemical activity but also with the high resistance or tolerance towards Cr deposition and poisoning. This is due to the fact that, at SOFC operating temperatures, volatile Cr species are generated over the chromia scale, poisoning the cathodes such as (La,Sr)MnO₃ (LSM) and (La,Sr)(Co,Fe)O₃ (LSCF) and causing a rapid degradation of the cell performance. Thus, a fundamental understanding of the interaction between the Fe–Cr alloys and SOFC cathode is essential for the development of high performance and stable SOFCs. The objective of this paper is to critically review the progress and particularly the work done in the last 10 years in this important area. The mechanism and kinetics of the Cr deposition and Cr poisoning process on the cathodes of SOFCs are discussed. Chromium deposition at SOFC cathodes is most likely dominated by the chemical reduction of high valence Cr species, facilitated by the nucleation agents on the electrode and electrolyte surface and/or at the electrode/electrolyte interface, i.e., the nucleation theory. The driving force behind the nucleation theory is the surface segregation and migration of cationic species on the surface of perovskite oxide cathodes. Overwhelming evidences indicate that the surface segregation plays a critical role in the Cr deposition. The prospect of the development in the Cr-tolerant cathodes for SOFCs is presented.     

Cobalt-free perovskite SrTa0.1Mo0.1Fe0.8O3-δ as cathode for intermediate-temperature solid oxide fuel cells

Ta⁵⁺ and Mo⁶⁺ substituted SrFeO_3-δ perovskites were researched as cathodes of intermediate-temperature solid oxide fuel cells (IT-SOFCs). The samples were synthesized with three components, e.g. mono-doped SrTa_0.2Fe_0.8O_3-δ, SrMo_0.2Fe_0.8O_3-δ and co-doped SrTa_0.1Mo_0.1Fe_0.8O_3-δ. Their phase structure, thermal stability, electrical conductivity and electrochemical catalytic property were researched comparatively. Ta⁵⁺ and Mo⁶⁺ co-doped SrTa_0.1Mo_0.1Fe_0.8O_3-δ possesses better electrochemical catalytic activity than that of the mono-doped SrFeO_3-δ. The performance difference between the mono-doped and co-doped SrFeO_3-δ has a close relation with the different contents of oxygen vacancy in the materials. The synergistic effect derived from Ta⁵⁺ and Mo⁶⁺ co-doping enhances the amount of oxygen vacancies in material, thus resulting in its better electrochemical property. The cells with SrTa_0.1Mo_0.1Fe_0.8O_3-δ as cathode deliver a R_p of 0.085 Ω·cm² and an output of 931 mW·cm^-2 at 800 °C.     

Demonstrating the dual functionalities of CeO2–CuO composites in solid oxide fuel cells

Nowadays, lowering the operating temperature of solid oxide fuel cells (SOFCs) is a major challenge towards their widespread application. This has triggered extensive material studies involving the research for new electrolytes and electrodes. Among these works, it has been shown that CeO₂ is not only a promising basis of solid oxide electrolytes, but also capable of serving as a catalytic assistant in anode. In the present work, to develop new electrolytes and electrodes for SOFCs based on these features of CeO₂, a new type of functional composite is developed by introducing semiconductor CuO into CeO₂. The prepared composites with mole ratios of 7:3 (7CeO₂–3CuO) and 3:7 (3CeO₂–7CuO) are assessed as electrolyte and anode in fuel cells, respectively. The cell based on 7CeO₂–3CuO electrolyte reaches a power outputs of 845 mW cm^?2 at 550 °C, superior to that of pure CeO₂ electrolyte fuel cell, while an Ce_0.8Sm_0.2O_2-δ electrolyte SOFC with 3CeO₂–7CuO anode achieves high power density along with open circuit voltage of 1.05 V at 550 °C. In terms of polarization curve and AC impedance analysis, our investigation manifests the developed 7CeO₂–3CuO composite has good electrolyte capability with a hybrid H⁺/O^2? conductivity of 0.1–0.137 S cm^?1 at 500–550 °C, while the 3CeO₂–7CuO composite plays a competent anode role with considerable catalytic activity, indicative of the dual-functionalities of CeO₂–CuO in fuel cell. Furthermore, a bulk heterojunction effect based on CeO₂/CuO pn junction is proposed to interpret the suppressed electrons in 7CeO₂–3CuO electrolyte. Our study thus reveals the great potential of CeO₂–CuO to develop functional materials for SOFCs to enable low-temperature operation.     

Effects of PdO modification on the performance of La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes for solid oxide fuel cells: A first principle study

Effects of palladium (Pd) impregnation on the performance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF) cathodes are investigated with density functional theory plus U (DFT + U) and experimental methods. In-situ high temperature X-ray diffractometer results show that the impregnated Pd species exist at states of palladium oxide (PdO) at 700 °C. The measured electrochemical impedance spectroscopy at 700 °C indicates PdO modification promotes the catalytic activity of LSCF cathodes. The modification structure of PdO on LSCF surfaces and effects of PdO modification on the performance of LSCF cathodes are investigated with DFT + U methods. The results show that B-8 with PdO molecule modification by a parallel posture on LSCF surface is the most stable structure. O₂ prefers to be adsorbed on AO-terminated surfaces rather than that on BO₂-terminated ones. The oxygen surface adsorption activity of LSCF surface is improved by PdO modification. The calculated partial densities of states (PDOS) and Fermi level of O₂ adsorption on LSCF surfaces imply that the charge transfer is easier with PdO modification than that without PdO modification because PdO acts as a metal-like modification. The PdO modification on LSCF surface leads to a better oxygen surface adsorption activity of LSCF cathodes.     

Electrochemical properties of LiNi0.8Co0.2−xAlxO2 prepared by a sol–gel method

Prospective positive-electrode (cathode) materials for a lithium secondary battery, viz., LiNi_0.8Co_0.2−xAl_xO₂ (x = 0.00, 0.01, 0.03, and 0.05), were synthesized using a sol–gel method and the structural and electrochemical properties are examined by means of X-ray diffraction, cyclic voltammetry, and charge–discharge tests. The LiNi_0.8Co_0.2−xAl_xO₂ maintains the α-NaFeO₂-type layered structure regardless of the aluminium content in the range x ≤ 0.05. On the other hand, as the aluminium content is increased, the capacity retention of LiNi_0.8Co_0.2−xAl_xO₂ is improved while initial discharge capacity is slightly decreased. Results also show that the current peaks on the cyclic voltammograms are diminished and merged on aluminium addition. This suggests that the improved cycle stability of LiNi_0.8Co_0.2−xAl_xO₂ is due to suppression of the phase transition.     

Investigating the electrochemical performance of Nd1-xSrxCo0.8Fe0.2O3−δ (0 ≤ x ≤ 0.85) as cathodes for intermediate temperature solid oxide fuel cells

Perovskite-type structure oxides with the nominal chemical composition Nd_1-xSr_xCo_0.8Fe_0.2O_3−δ (0 ≤ x ≤ 0.85) (NSCF) were synthesized by solid-state method to investigate the effect of Sr-doping on the crystal structure and electrochemical performance in the intermediate temperature range of 600 °C–750 °C. The electrical conductivity of the sintered NSCF pellets was found to be in the range of 300–1000 S cm⁻¹. All the NSCF compositions showed a transition from semiconducting to metallic behavior with an increase in temperature. NSCF showed reactivity with the La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte. The electrochemical performance was tested by preparing the symmetrical cells with the configuration 70 wt% NSCF +30 wt% LSGM using LSGM electrolyte in the temperature range of 650–800 °C. AC-impedance results showed a decrease in polarization resistance (Rp) of the cathode with increase in Sr-doping due to increase in electrical conductivity. Among the samples studied, composite electrode of Nd_0.3Sr_0.7Co_0.8Fe_0.2O_3−δ – LSGM showed the lowest area specific resistance (ASR) of 0.1 Ω cm² at 750 °C in air. It was chosen to investigate the effect of pO₂ on the electrochemical performance of the cathode to determine the rate determining step (RDS) in oxygen reduction reaction (ORR). Dissociation of molecular oxygen into oxygen atoms seems to be the RDS in the ORR.