Achieving exceptional activity and durability toward oxygen reduction based on a cobalt-free perovskite for solid oxide fuel cells

In response to the shortcomings of cobalt-rich cathodes, iron-based perovskite oxides appear as promising alternatives for solid oxide fuel cells (SOFCs). However, their inferior electrochemical performance at reduced temperatures (<700 ℃) becomes a major bottleneck for future progress. Here, a novel cobalt-free perovskite Ba_(0.75)Sr_(0.25)Fe_(0.875)Ga_(0.125)O_(3−δ) (BSFG) is developed as an efficient oxygen reduction electrode for SOFCs, featuring cubic-symmetry structure, large oxygen vacancy concentration and fast oxygen transport. Benefiting from these merits, cells incorporated with BSFG achieve exceptionally high electrochemical performance, as evidenced by a low polarization area-specific resistance of 0.074 Ω cm^(2) and a high peak power density of 1145 mW cm^(−2) at 600 ℃. Meanwhile, a robust short-term performance stability of BSFG cathode can be ascribed to the stable crystalline structure and favorable thermal expansion behavior. First-principles computations are also conducted to understanding the superior activity and durability toward oxygen reduction reaction. These pave the way for rationally developing highly active and robust cobalt-free perovskite-type cathode materials for reduced-temperature SOFCs.

A defective iron-based perovskite cathode for high-performance IT-SOFCs:Tailoring the oxygen vacancies using Nb/Ta co-doping

The sluggish kinetics of the electrochemical oxygen reduction reaction(ORR)in intermediatetemperature solid oxide fuel cells(IT-SOFCs)greatly limits the overall cell performance.In this study,an efficient and durable cathode material for IT-SOFCs is designed based on density functional theory(DFT)calculations by co-doping with Nb and Ta the B-site of the SrFeO_(3-δ)perovskite oxide.The DFT calculations suggest that Nb/Ta co-doping can regulate the energy band of the parent SrFeO_(3-δ)and help electron transfer.In symmetrical cells,such cathode with a SrFe_(0.8)Nb_(0.1)Ta_(0.1)O_(3-δ)(SFNT)detailed formula achieves a low cathode polarization resistance of 0.147Ωcm^(2) at 650℃.Electron spin resonance(ESR)and X-ray photoelectron spectroscopy(XPS)analysis confirm that the co-doping of Nb/Ta in SrFeO_(3-δ)B-site increases the balanced concentration of oxygen vacancies,enhancing the electrochemical performance when compared to 20 mol%Nb single-doped perovskite oxide.The cathode button cell with NiSDC|SDC|SFNT configuration achieves an outstanding peak power density of 1.3 W cm^(-2)at 650℃.Moreover,the button cell shows durability for 110 h under 0.65 V at 600℃ using wet H_(2) as fuel.

Effect of H_2S Flow Rate and Concentration on Performance of H_2S/Air Solid Oxide Fuel Cell

A solid state H2S/air electrochemical cell having the configuration of H2S, (MoS2+NiS+Ag)/YSZ/Pt, air has been examined with different H2S flow rates and concentrations at atmospheric pressure and 750-850 ℃. Performance of the fuel cell was dependent on anode compartment H2S flow rate and concentration. The cell open-circuit voltage increased with increasing H2S flow rate. It was found that increasing both H2S flow rate and H2S concentration improved current-voltage and power density performance. This is resulted from improved gas diffusion in anode and increased concentration of anodic electroactive species. Operation at elevated H2S concentration improved the cell performance at a given gas flow rate. However, as low as 5% H2S in gas mixture can also be utilized as fuel feed to cells. Highest current and power densities, 17500mA·cm-2 and 200mW·cm-2, are obtained with pure H2S flow rate of 50ml·min-1 and air flow rate of 100ml·min-1 at 850℃.

The Effect of Fabrication Conditions for GDC Buffer Layer on Electrochemical Performance of Solid Oxide Fuel Cells

A Gd-doped ceria（GDC） buffer layer is required between a conventional yttria-stabilized zirconia（YSZ） electrolyte and a La-Sr-Co-Fe-O3（LSCF） cathode to prevent their chemical reaction. In this study,the effect of varying the conditions for fabricating the GDC buffer layer, such as sintering temperature and amount of sintering aid, on the solid oxide fuel cell（SOFC） performance was investigated. A finer GDC powder（i.e., ultra-high surface area）, a higher sintering temperature（1290℃）, and a larger amount of sintering aid（12%） resulted in improved densification of the buffer layer; however, the electrochemical performance of an anode-supported cell containing this GDC buffer layer was poor. These conflicting results are attributed to the formation of（Zr, Ce）O2 and/or excess cobalt grain boundaries（GBs） at higher sintering temperatures with a large amount of sintering aid（i.e., cobalt oxide）. A cell comprising of a cobalt-free GDC buffer layer, which was fabricated using a low-temperature process, had lower cell resistance and higher stability. The results indicate that electrochemical performance and stability of SOFCs strongly depend on fabrication conditions for the GDC buffer layer.

A Case Study of a Solid Oxide Fuel Cell Plant on Board a Cruise Ship

The work is a case study of a cruise ship supplied by liquefied natural gas(LNG)and equipped with a solid oxide fuel cell(SOFC).It is supposed that a 20 MW SOFC plant is installed on-board to supply hotel loads and assisting three dual-fuel(DF)diesel/LNG generator sets.LNG consumption and emissions are estimated both for the SOFC plant and DF generator sets.It results that the use of LNG-SOFC plant in comparison to DF generator sets allows to limit significantly the SO_(x),CO,NO_(x),PM emissions and to reduce the emission of CO_(2)by about 11%.A prediction of the weight and volume of the SOFC plant is conducted and a preliminary modification of the general arrangement of the cruise ship is suggested,according to the latest international rules.It results that the SOFC plant is heavier and occupies more volume on board than a DF gen-set;nevertheless,these features do not affect the floating and the stability of the cruise ship.

Review： Perspectives on the metallic interconnects for solid oxide fuel cells

The various stages and progress in the development of interconnect materials for solid oxide fuel cells (SOFCs )over the last two decades are reviewed. The criteria for the application of materials as interconnects are highlighted. Interconnects based on lanthanum chromite ceramics demonstrate many inherent drawbacks and therefore are only useful for SOFCs operating around 1000℃. The advance in the research of anode-supported flat SOFCs facilitates the replacement of ceramic interconnects with metallic ones due to their significantly lowered working temperature. Besides, interconnects made of metals or alloys offer many advantages as compared to their ceramic counterpart. The oxidation response and thermal expansion behaviors of various prospective metallic interconnects are examined and evaluated. The minimization of contact resistance to achieve desired and reliable stack performance during their projected lifetime still remains a highly challenging issue with metallic interconnects. Inexpensive coating materials and techniques may play a key role in promoting the commercialization of SOFC stack whose interconnects are constructed of some current commercially available alloys. Alternatively, development of new metallic materials that are capable of forming stable oxide scales with sluggish growth rate and sufficient electrical conductivity is called for.

Data-driven nonlinear control of a solid oxide fuel cell system

Solid oxide fuel cells (SOFCs) are considered to be one of the most important clean,distributed resources. However,SOFCs present a challenging control problem owing to their slow dynamics,nonlinearity and tight operating constraints. A novel data-driven nonlinear control strategy was proposed to solve the SOFC control problem by combining a virtual reference feedback tuning (VRFT) method and support vector machine. In order to fulfill the requirement for fuel utilization and control constraints,a dynamic constraints unit and an anti-windup scheme were adopted. In addition,a feedforward loop was designed to deal with the current disturbance. Detailed simulations demonstrate that the fast response of fuel flow for the current demand disturbance and zero steady error of the output voltage are both achieved. Meanwhile,fuel utilization is kept almost within the safe region.

LSM-infiltrated LSCF cathodes for solid oxide fuel cells

Mixed ionic-electronic conductors in the family of LaxSr1-xCoyFe1-y O3-δ have been widely studied as cathode materials for solid oxide fuel cells （SOFCs）. However, the long-term stability was a concern. Here we report our findings on the effect of a thin film coating of La0.85Sr0.15MnO3-δ （LSM） on the performance of a porous La0.6Sr0.4Co0.2Feo.8O3-δ（LSCF） cathode. When the thicknesses of the LSM coatings are appropriate, an LSM-coated LSCF electrode showed better stability and lower polarization （or higher activity） than the blank LSCF cathode without LSM infiltration. An anode-supported cell with an LSM-infiltrated LSCF cathode demonstrated at 825 ℃ a peak power density of -1.07 W/cm2, about 24% higher than that of the same cell without LSM infiltration （-0.86 W/cm2）. Further, the LSM coating enhanced the stability of the electrode; there was little degradation in performance for the cell with an LSM-infiltrated LSCF cathode during 100 h operation.

Effect of SO_2 on Performance of Solid Oxide Fuel Cell Cathodes

Effects of SO2 in ambient air on the performance and durability of solid oxide fuel cell（SOFC） cathode were evaluated by galvanostatic measurement. Comparison between two cathode materials was made to consider the cathode degradation mechanisms. The degradation performance is associated with a slow decomposition of the La0.6Sr0.4Co0.2Fe0.8O3（LSCF） due to the segregation of strontium oxide. Negligible deterioration for （La0.7Sr0.3）MnO3 （LSM） cathode was caused by SO2 poisoning under a current density of 200 mA/cm2. Metal sulphate formation may explain a slight deterioration under increasing high the concentration of SO2. It was verified that the poisoning mechanism for the two cathode materials resulted from the gradual decomposition of the cathode materials.

Efficiency and Size Optimization of a General Solid Oxide Fuel Cell System

An irreversible model of high temperature solid oxide fuel cells( SOFCs) working at steady-state is developed,devoted to performing the optimization with regard to two objectives:minimization of the fuel cell size and maximization of the system efficiency. The performance characteristics of the system are analyzed in details, illustrated by the curves of power density,efficiency and voltage. Genetic algorithm is used to perform the multi-objective optimization with four decision variables: the operating pressure, the fuel stoichiometric ratio, the air stoichiometric ratio and the current density. A Pareto set giving a quantative description of the trade-off between the two objectives is used to analyze the results. Optimization results prove the existence of optimal designs region for a 50 kW system with efficiency from 43% corresponding to a 14. 6 m2 electrolyte area to 48% corresponding to a 25.4 m2 electrolyte area. The SOFC model used is general and the optimization results could be applied to the practical SOFC design.

Performance test of a 5 kW solid oxide fuel cell system under high fuel utilization with industrial fuel gas feeding

As the demand for green energy with high efficiency and low carbon dioxide(CO2)emissions has increased,solid oxide fuel cells(SOFCs)have been intensively developed in recent years.Integrated gasification fuel cells(IGFCs)in particular show potential for large-scale power generation to further increase system efficiency.Thus,for commercial application of IGFCs,it is important to design reliable multi-stacks for large systems that show long-term stability and practical fuel gas for application to industrial equipment.In this work,a test rig(of a 5 kW SOFC system,with syngas from industrial gasifiers as fuel)was fabricated and subjected to long-term tests under high fuel utilization to investigate its performance.The maximum steady output power of the system was 5700 W using hydrogen and 5660 W using syngas and the maximum steady electrical efficiency was 61.24%while the fuel utilization efficiency was 89.25%.The test lasted for more than 500 h as the fuel utilization efficiency was larger than 83%.The performances of each stack tower were almost identical at both the initial stage and after long-term operation.After 500 h operation,the performances of the stack towers decreased only slightly under lower current and showed almost no change under high current.These results demonstrate the reliability of the multi-stack design and the prospect of this SOFC power-generation system for further enlarging its application in a MWth demonstration.

LSM-YSZ nano-composite cathode with YSZ interlayer for solid oxide fuel cells

Low temperature prepared(La;Sr;);MnO;-δ-Y;Zr;O;（LSM-YSZ） nano-composite cathode has high three-phase boundary（TPB） density and shows higher oxygen reduction reaction（ORR） activity than traditional LSM-YSZ cathode at reduced temperatures. But the weak connection between cathode and electrolyte due to low sintering temperature restrains the performance of LSM-YSZ nano-composite cathode. A YSZ interlayer, consisted of nanoparticles smaller than 10 nm, is introduced by spinning coating hydrolyzed YSZ sol solution on electrolyte and sintering at 800 °C. The thickness of the interlayer is about 150 nm. The YSZ interlayer intimately adheres to the electrolyte and shows obvious agglomeration with LSM-YSZ nano-composite cathode. The power densities of the cell with interlayer are 0.83, 0.46 and 0.21 W/cm;under 0.7 V at 800, 700 and 600 °C, respectively, which are 36%, 48% and 50% improved than that of original cell. The interlayer introduction slightly increases the ohmic resistance but significantly decreases the polarization resistance. The depressed high frequency arcs of impedance spectra suggest that the oxygen incorporation kinetics are enhanced at the boundary of YSZ interlayer and LSM-YSZ nanocomposite cathode, contributing to improved electrochemical performance of the cell with interlayer.

Status and prospects of intermediate temperature solid oxide fuel cells

Compared with conventional electric power generation systems, the solid oxide fuel cell （SOFC） has many advantages because of its unique features. High temperature SOFC has been successfully developed to its commercial applications, but it still faces many problems which hamper large-scale commercial applications of SOFC. To reduce the cost of SOFC, intermediate temperature solid oxide fuel cell （IT-SOFC） is presently under rapid development. The status of IT-SOFC was reviewed with emphasis on discussion of their component materials. 2008 University of Science and Technology Beijing. All rights reserved.

A dynamic infiltration technique to synthesize nanolayered cathodes for high performance and robust solid oxide fuel cells

Solution infiltration is a popular technique for the surface modification of solid oxide fuel cell(SOFC)cathodes.However,the synthesis of nanostructured SOFC cathodes by infiltration is a tedious process that often requires several infiltration and high temperature(≥500℃)calcination cycles.Moreover,fabricating large-area nanostructured cathodes via infiltration still requires serious attention.Here,we propose a facile and scalable urea assisted ultrasonic spray infiltration technique for nanofabrication of SOFC cathodes.It is demonstrated that by using urea as a precipitating agent,the calcination after each infiltration cycle can be omitted and the next infiltration can be performed just after a drying step(≤100℃).Finally,the precipitates can be converted into a desired catalyst phase in single calcination thus,a nanostructured cathode can be fabricated in a much faster manner.It is also shown that the low calcination temperature of the cathode(≤900℃)can produce highly durable SOFC performance even without employing a Ce_(0.9)Gd_(0.1)O_(2)(GDC)diffusion barrier layer which provides the ease of SOFC fabrication.While coupling with an ultrasonic spray technique,the urea assisted infiltration can be scaled up for any desired cathode area.La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3) nanolayered cathode was fabricated and it was characterized by scanning electron microscope(SEM),X-ray diffraction(XRD),and transmission electron microscopy(TEM)techniques.SEM showed the formation of a nanolayer cathode just after 5 cycles of the urea assisted infiltration while the XRD and TEM confirmed the phase and stoichiometric uniformity of the 100 nm cathode nanolayer.The effectiveness of the newly developed technique was further verified by the stable operation of a GDC buffer layer free SOFC having an active cathode area of 25 cm^(2) during a 1200 h durability test.The research outcomes propose urea assisted ultrasonic spray infiltration as a facile,scalable,and commercially viable method for the fabrication of durable nanostructured SOFC cathodes.

Composite Cathode Bi_(1.14)Sr_(0.43)O_(2.14)-Ag for Intermediate-temperature Solid Oxide Fuel Cells

Composites consisting of strontium stabilized bismuth oxide （Bi1.14Sr0.43O2.14, SSB） and silver were investigated as cathodes for intermediate-temperature solid oxide fuel cells with doped ceria electrolyte. There were no chemical reactions between the two components. The microstructure of the interfaces between composite cathodes and Ce0.8Sm0.2O1.9 （SDC） electrolytes was examined by scanning electron microscopy （SEM）. Impedance spectroscopy measurements show that the performance of cathode fired at 700 ℃ is the best. When the content of Ag2O is 70 wt%, polarization resistance values for the SSB-Ag cathodes are as low as 0.2 Ωcm^2 at 700℃ and 0.29 Ωcm^2 at 650℃. These results are much smaller than some of other reported composite cathodes on doped ceria electrolyte and indicate that SSB-Ag composite is a potential cathode material for intermediate temperature SOFCs.

Interface engineering of an electrospun nanofiber-based composite cathode for intermediate-temperature solid oxide fuel cells

Sluggish oxygen reduction reaction(ORR)kinetics are a major obstacle to developing intermediate-temperature solid-oxide fuel cells(IT-SOFCs).In particular,engineering the anion defect concentration at an interface between the cathode and electrolyte is important for facilitating ORR kinetics and hence improving the electrochemical performance.We developed the yttria-stabilized zirconia(YSZ)nanofiber(NF)-based composite cathode,where the oxygen vacancy concentration is controlled by varying the dopant cation(Y2O3)ratio in the YSZ NFs.The composite cathode with the optimized oxygen vacancy concentration exhibits maximum power densities of 2.66 and 1.51 W cm^(−2)at 700 and 600℃,respectively,with excellent thermal stability at 700℃ over 500 h under 1.0 A cm^(−2).Electrochemical impedance spectroscopy and distribution of relaxation time analysis revealed that the high oxygen vacancy concentration in the NF-based scaffold facilitates the charge transfer and incorporation reaction occurred at the interfaces between the cathode and electrolyte.Our results demonstrate the high feasibility and potential of interface engineering for achieving IT-SOFCs with higher performance and stability.

Numerical simulation of a direct internal reforming solid oxide fuel cell using computational fluid dynamics method

A detailed mathematical model of a direct internal reforming solid oxide fuel cell(DIR-SOFC) incorporating with simulation of chemical and physical processes in the fuel cell is presented. The model is developed based on the reforming and electrochemical reaction mechanisms,mass and energy conservation,and heat transfer. A computational fluid dynamics(CFD) method is used for solving the complicated multiple partial differential equations(PDEs) to obtain the numerical approximations. The resulting distributions of chemical species concentrations,temperature and current density in a cross-flow DIR-SOFC are given and analyzed in detail. Further,the influence between distributions of chemical species concentrations,temperature and current density during the simulation is illustrated and discussed. The heat and mass transfer,and the kinetics of reforming and electrochemical reactions have significant effects on the parameter distributions within the cell. The results show the particular characteristics of the DIR-SOFC among fuel cells,and can aid in stack design and control.

Exploitation of Waste Heat from a Solid Oxide Fuel Cell via an Alkali Metal Thermoelectric Converter and Electrochemical Cycles

In order to employ the waste heat effectively,a novel three-stage integrated system based upon a solid oxide fuel cell(SOFC),an alkali metal thermoelectric converter(AMTEC)and thermally regenerative electrochemical cycles(TRECs)is put forward.Considering the main electrochemically and thermodynamically irreversible losses,the power output and the efficiency of the subsystems and the integrated system are compared,and optimally operating regions for the current density,the power output,and the efficiency of the integrated system are explored.Calculations demonstrate that the maximum power density of the considered system is up to 7466 W/m2,which allows 18%and 74%higher than that of the conventional SOFC-AMTEC device and the stand-alone fuel cell model,respectively.It is proved that the considered system is an efficient approach to boost energy efficiency.Moreover,the influence of several significant parameters on the comprehensive performance of the integrated system is expounded in detail,including the electrolyte thickness of the SOFC,the leakage resistance of the SOFC,and the area ratio between the SOFC electrode and the AMTEC subsystem.

Application of Solid Oxide Fuel Cell-Auxiliary Power Unit on Different Trucks in Northeast China

A diesel engine of conventional trucks has a low efficiency under the idling condition,leading to a high cost for heating or cooling in the cab during night. The solution to this problem will have great significance on energy conservation and emission reduction. A new auxiliary power unit of solid oxide fuel cell( SOFCAPU) with high efficiency solves this problem perfectly. Heat pump air conditioner is considered as a promising device for the application of SOFC-APU with a high cooling and heating efficiency. To make a quantitative analysis for the application of SOFC-APU,a model is built in Matlab / Simulink. The diesel engine model and SOFC-APU model are fitted based on some experimental data of SOFC-APU and diesel engine during the idling operation. An analysis of the application of SOFC-APU on different trucks in Northeast China is comprehensively made,including efficiency and emission.

LaNi_(0.6)Fe_(0.4)O_(3)阴极接触材料导电特性调控及其对SOFC电化学性能的影响

鉴于平板式固体氧化物燃料电池(SOFC)电堆对低面电阻、高稳定性阴极接触材料的需求,本研究阐明了LaNi_(0.6)Fe_(0.4)O_(3)(LNF)颗粒尺寸调控对导电和SOFC单电池性能演变的影响机制,优化了LNF预处理工艺,降低了接触组件面电阻,提升了SOFC单电池性能及热循环稳定性。结果表明:预压造粒的样品(LNF-2)与高温烧结预处理的样品(LNF-3)的面电阻更小,分别为0.074和0.076Ω·cm^(2);在750℃施加1 A/cm^(2)电流负载后,能够更快地进入稳态,并保持颗粒尺寸稳定。其中,LNF-2单电池在750℃下的峰值功率密度0.94 W/cm^(2)较未处理的LNF的0.66 W/cm^(2)高,但在热循环过程中性能衰减较大,下降了20%;而LNF-3单电池在20次热循环后峰值功率密度仅下降了4%。本研究对高可靠SOFC电堆装配及其长寿命稳定运行具有指导及参考价值。