Composite Cathode Powders Research Articles

Fabrication and Characterisation of La<sub>0.6</sub>Sr<sub>0.4</sub>Co<sub>0.2</sub>Fe<sub>0.8</sub>O<sub>3-δ</sub>-SDC Composite Cathode

Composite cathode is a promising material to be used as electrodes in fuel cells. The fabricated composite cathode materials in this study are comprised of a mixture of submicron La0.6Sr0.4Co0.2Fe0.8O3- (LSCF6428) powders with two types of nanoscale ionically conducting ceramic electrolyte materials, samarium-doped ceria (SDC) and SDC-carbonate (SDCc). 30 – 50 wt% of electrolyte materials are added to the LSCF6428 cathode via the solid state method. The composite powders were ball-milled in ethanol and calcined at the temperature range of 800°C to 900°C for 2 hours in air. The composite cathode powders are characterised in terms of morphology and crystal structure. It is found that after calcining, the LSCF and the electrolyte materials retained their original structures as there was no chemical reaction between the two components. In addition, the LSCF-SDC composite cathode powders were found to exhibit a narrower distribution in size compared to the LSCF-SDC carbonate powders.

Surface Exchange Coefficients of Composite Cathode Materials Using In Situ Isothermal Isotope Exchange

Isothermal isotope exchange (IIE) was used to evaluate the surface kinetics of the oxygen reduction reaction on composite cathode materials. With IIE, powder materials can be tested to ensure surface exchange behavior is isolated. Macroscopic diffusion coefficients and surface exchange coefficients were extracted from composite cathode powders (LSCF/GDC), (LSM/YSZ), and (LSM/GDC) using IIE, and characteristic thicknesses were calculated from the ratio of . Mixed ionic and electronic conductor LSCF/GDC was shown to have the highest values between 500 and and values above . Adding an ionically conducting phase to LSM significantly improved the magnitude of , which below were highest for LSM/YSZ of the three composites. In addition, LSM/YSZ and LSM/GDC exhibited an apparent negative activation energy, which can be explained by a precursor-mediated mechanism for dissociative adsorption. Sample thicknesses (particle size) were shown to be well below characteristic thicknesses , ensuring that samples were in a surface exchange controlled regime and validating the accuracy of the extracted values.

Preparation of Pr 0.35Nd 0.35Sr 0.3MnO 3− δ/YSZ composite cathode powders for tubular solid oxide fuel cells by microwave-induced monomer gelation and gel combustion synthesis process

A microwave-induced monomer gelation and gel combustion synthesis process was successfully developed to synthesize well-dispersed Pr 0.35Nd 0.35Sr 0.3MnO 3− δ (PNSM)/YSZ composite cathode powders for tubular solid oxide fuel cells (SOFCs). The thermo-gravimetric (TG) analysis of as-prepared ash indicated the decomposition process of most of metal nitrates during gel combustion. The X-ray diffraction (XRD) pattern of the powders calcined at 1000 °C showed only pure PNSM and YSZ phase. Transmission electron microscopy (TEM) revealed that the morphology of powders was characterized with the YSZ particles enwrapped by fine PNSM particles so that PNSM/YSZ composite powders were much better-dispersed compared with the powders made simply by mechanical mixing process. The cell made from PNSM/YSZ composite powder showed lower cathode ohmic resistance and polarization resistance, and produced higher power density subsequently.

La0.6Sr0.4Co0.2Fe0.8O3 - Ce0.8Sm0.2O2−δ Composite Cathode for Operation Below 600°C

Composite cathodes of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 and Ce 0.8 Sm 0.2 O 2-σ were evaluated by impedance analysis for assessing their potential for utilization in intermediate temperature solid oxide fuel cells operating at temperatures below 600°C. The composite cathodes were formed onto Ce 0.8 Sm 0.2 O 2-σ electrolytes by spraying suspensions of submicron-scale composite cathode powders and then firing the coated electrolyte pellets in air. Impedance measurements showed that the electrode resistances of the composite cathodes have a dependence on their firing temperatures. The composite cathodes of 70 wt% La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 and 30 wt% Ce 0.8 Sm 0.2 O 2-σ fired at 750 or 850°C were found to achieve area specific resistances of 0.3 Ωcm 2 at around 590°C, and 0.5 Ωcm 2 at 565°C, respectively, while the composite cathode fired at 950°C showed nearly one order of magnitude higher resistance values.

The source of first-cycle capacity loss in LiFePO 4

The electrochemical extraction of lithium from solid-state synthesised LiFePO 4 has been studied by neutron powder diffraction. A “coffee-bag” type cell of configuration 〈Li-metal |liq. el.| LiFePO 4〉 has been charged to 4.1 V, dismantled in a glovebox, and the composite cathode powder sample scraped from the current collector. Two-phase Rietveld refinement gave a triphylite (LiFePO 4) to heterosite (FePO 4) phase-ratio of 18:82. In the absence of significant absorption effects, this ratio is a true representation of the conversion of LiFePO 4 to FePO 4. Possible mechanisms for lithium extraction/insertion during the first-cycle are discussed.