Mahendra Rao Somalu

Nanostructured and Nonsymmetrical NiO–SDC/SDC Composite Anode Performance via a Microwave-Assisted Route for Intermediate-Temperature Solid Oxide Fuel Cells

This work investigates the electrical properties of NiO–SDC/SDC anode sintered at approximately 1200°C for 1 h via the microwave method. Nanopowders Sm0.2Ce0.8O1.9 (SDC—samaria-doped ceria) and NiO were mixed using a high-energy ball mill and subsequently co-pressed at three different compaction pressures of 200, 300, and 400 MPa. This study determines the effect of compaction pressure on the electrochemical performance of Ni–SDC/SDC anode, with no binder used between layers. The electrical behavior of the prepared anode was studied via electrochemical impedance spectroscopy in controlled atmospheres, operating at high temperatures (600–800°C). The results indicate that decreasing the compaction pressure and increasing the operating temperature lead to a high electrochemical performance of the nonsymmetrical NiO–SDC/SDC anode. The mechanism for manufacturing NiO–SDC/SDC involves ball milling, dry pressing, and microwave furnace sintering processes.

Optical, mechanical and electrical properties of LSCF–SDC composite cathode prepared by sol–gel assisted rotary evaporation technique

AbstractLa0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) is a perovskite-type oxide that exhibits excellent mixed ionic–electronic conducting properties and is a suitable cathode material for intermediate temperature solid oxide fuel cells. This study investigates the microstructural, optical, mechanical, and electrical properties of an LSCF–samarium-doped ceria (SDC) composite cathode. LSCF–SDC composite cathode powders were prepared by mixing 50 wt% SDC electrolyte with LSCF cathode powders obtained by the rotary evaporation technique. The band gap of the prepared powders was determined via diffuse reflectance UV–visible spectroscopy. The chemical composition, mechanical properties, and electrochemical properties of the sintered pellets were characterized using Raman spectroscopy, Vickers hardness, and impedance spectroscopy, respectively. X-ray diffraction and Rietveld analysis showed that phase purity was only 96%. Moreover, a small fraction of tetragonal phase impurity was observed on the LSCF powders. Impurities significantly affected the phase stability and microstructure of the LSCF–SDC composite cathode. The addition of the SDC electrolyte enhanced the densification of the composite cathode, thereby improving mechanical properties. However, the addition of SDC exerted different effects on the DC electrical conductivity and area-specific resistance (ASR) of the composite cathode. At 800 °C, the ASR value of the LSCF was only 2% that of the LSCF–SDC composite cathode. Overall, the electrical properties of the LSCF–SDC composite cathode are closely related to the crystal structure, purity, and microstructure of LSCF cathode powders.

Effect of compaction pressure on the performance of a non-symmetrical NiO–SDC/SDC composite anode fabricated by conventional furnace

Abstract The electrochemical performance of NiO–SDC/SDC anode was studied. The anode was compacted by pressing, after which sintering was conducted in a conventional furnace at 1200 °C. A high-energy ball mill was used to mix the Sm0.2Ce0.8O1.9 (SDC) nanopowder and NiO. A pressing technique was applied to fabricate the NiO–SDC/SDC anode cells. The effect of different compaction pressures (200, 300, and 400 MPa) on the performance of the anodes was investigated via electrochemical impedance spectroscopy at an intermediate temperature range (600–800 °C). The nanoindentation technique and Archimedes method, which were used to measure stiffness and bulk density, respectively, revealed that increases in porosity were correlated with decreases in compaction pressure. High electrochemical performance can be achieved if the compaction pressure is decreased and the operating temperature is increased because of hydrogen spillover during the operation.

Penyediaan serbuk lantanum strontium kobalt oksida melalui kaedah sol-gel terubahsuai

A simple low temperature synthesis route has been presented for the preparation of single perovskite phase of La0.6Sr0.4CoO3-δ (LSCO) for cathode application in intermediate temperature proton conducting solid oxide fuel cell (SOFC). A wet chemical method namely a modified sol-gel method has been applied in this work. In this method, a combined citric acid and ethylenediaminetetraacetic acid (EDTA) has been used as a chelating agent. Ethylene glycol (EG) and activated carbon (AC) have been used as surfactants in this process. The synthesized powders were characterized by X-ray diffractometer (XRD), scanning electron microscope (FESEM) equipped with energy dispersive X-ray (EDX) spectrometer and particle size analyzer (PSA) for phase formation, morphology and particle size analysis, respectively. XRD result revealed that a single LSCO perovskite phase for both surfactants formed at calcination temperature of 900 °C. The produced single phase powders consist of homogeneous and almost identical shape of particles as shown in SEM images. However, the powder prepared using EG has a smaller average particle size diameter as compared with the powder prepared using AC which is 149 nm and 190 nm, respectively.

Electrical properties of extruded milled carbon fibre and polypropylene

A milled carbon fibre and polypropylene polymer composite at high filler loading was developed to produce conductive polymer composites for high conductive applications. Current research of conductive polymer composite material has reported about in-plane conductivity that was often higher than through-plane conductivity, which contradicted with the target of applications that required higher electrical conductivity in the through-plane direction. Therefore, electrical conductivity in parallel and transverse to extrusion directions were investigated. The general-effective media and modified fibre contact model were adapted to predict the electrical conductivity of the composite material. The experimental conductivity data of polypropylene/milled carbon fibre composites for transverse and parallel directions were not correlated with the general-effective media model with 2.009 and 0.663 S/cm, respectively, at the highest filler loading of 80 wt.%. This disagreement was due to various critical exponential, t values (2–3.25) that were obtained in this study. However, the modified fibre contact model seemed to have good agreement with the experimental data in the parallel to extrusion direction. This model was unable to predict electrical conductivity in the transverse direction due to lack of orientation occurring in that direction. The electrical conductivity increased as the filler loading increased as explained in percolation theory. Predicting the electrical conductivity of conductive polymer composites material is still in the preliminary stages where the researcher often obtains fluctuating agreement with the experimental values. Thus, contact between filler and orientation is considered as the main factor that influences the electrical conductivity and mechanical strength of the conductive polymer composites material.

Preparation of nickel oxide-samarium-doped ceria carbonate composite anode powders by using high-energy ball milling for low-temperature solid oxide fuel cells

The characteristics of the starting powder in powder preparation method are important for enhancement of cell performance. In this study, the composite anode powders of NiO–samarium-doped ceria carbonates (SDCC) were prepared by using different NiO loadings (50–70 wt.%) via high-energy ball milling. The composite anode powders were ball-milled in ethanol at a milling speed of 550 rpm. The obtained NiO–SDCC composite anode powders were characterized by XRD, FTIR, FESEM, and EDS. Results indicate that the composite anode powders demonstrated good chemical compatibility between NiO and SDCC, given that no new phases were detected in the XRD analysis. FTIR spectra confirmed that the composite anode powders contain carbonates in amorphous state after high-energy ball milling. FESEM investigation revealed well-distributed fine particles and significant reduction of particle size at nanoscale compared with the powder prepared using NiO particles as the starting material. EDS mapping verified the homogeneity of the composite powder with good elemental distribution. Thus, high-energy ball milling is an effective method to prepare NiO–SDCC composite anode powders within a relatively short processing time.

Effects of Die Configuration on the Electrical Conductivity of Polypropylene Reinforced Milled Carbon Fibers: An Application on a Bipolar Plate

Die configurations, filler orientations, electrical conductivity, and mechanical properties of polypropylene reinforced milled carbon fibers were studied as functions of their manufacturing processes. Series of manufacturing processes often deteriorate the material properties, hence, finding a suitable process aid is key to improving the electrical and mechanical properties of composite materials. Compared with the conventional manufacturing process, extrusion is a key process in the production of a highly conductive composite. A twin-screw extruder was used at a temperature of 230 °C and a rotational speed of 50 rpm before the compression molding process was carried out at 200 °C and 13 kPa. This research examined different die configurations, namely rod and sheet dies. The results indicated that the rod dies showed better mechanical properties and electrical conductivity with 25 MPa and 5 S/cm compared to the sheet dies. Moreover, rod dies are able to orientate to 86° and obtain longest filler length with 55 μm compared to the sheet dies. The alteration of the filler orientation in the produced material at a high shear rate further enhanced the electrical conductivity of the material.

Synthesis and Characterization of Sm1-xZrxFe1-yMgyO3 (x, y = 0.5, 0.7, 0.9) as Possible Electrolytes for SOFCs

The novel perovskite oxide series of Sm1-xZrxFe1-yMgyO3 (x,y = 0.5, 0.7, 0.9) were synthesized by solid state reaction method. X-ray diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and conductivity analysis were carried out. XRD patterns of sintered materials revealed the shifted Bragg reflection to higher angle for the higher content of Zr and Mg. This is related to the ionic size of the dopant elements. Rietveld refinement showed that all compounds crystallized in cubic space group of Fm-3m. SEM images showed that the grains were well defined with highly dense surfaces makes it potential as an electrolyte material in solid oxide fuel cells (SOFCs) or gases sensors. Impedance spectroscopy at 550-800 °C shows that conductivity is higher at higher temperature. Sm0.5Zr0.5Fe0.5Mg0.5O3 shows the highest conductivity of 5.451 × 10-3 S cm-1 at 800 °C. It was observed that 50% molar ratio of Mg and Zr doping performed highest conductivity.

Electrical and electrochemical characteristics of La0.6Sr0.4CoO3-δ cathode materials synthesized by a modified citrate-EDTA sol-gel method assisted with activated carbon for proton-conducting solid oxide fuel cell application

AbstractThe electrical conductivity and electrochemical performance of a La0.6Sr0.4CoO3-δ (LSC) cathode produced by a modified citrate-EDTA sol-gel method assisted with activated carbon are characterized for a proton-conducting solid oxide fuel cell (H+ −SOFC) application at intermediate temperature. Thermogravimetric analysis revealed that the decomposition of the unrequired intermediate compounds in the precalcined powder was completed at 800 °C. A single LSC perovskite phase was formed at a calcination temperature of 900 °C, as confirmed by X-ray diffraction analysis. The particle size, crystallite size, and BET-specific surface area of the powder are 219–221 nm, 18 nm, and 9.87 m2 g−1, respectively. The high index value of the extent of agglomeration (5.53) showed that the powder was barely agglomerated. Bulk LSC sintered at 1200 °C for 2 h showed the highest direct-current electrical conductivity (σd.c) compared to that of bulk LSC sintered at 1000 °C and 1100 °C. The value of σd.c was affected by the density and porosity of the sintered samples. The area specific resistance (ASR) of screen-printed LSC working on a proton conductor of BaCe0.54Zr0.36Y0.1O2.95 (BCZY) decreased from 5.0 Ω cm2–0.06 Ω cm2 as the temperature increased from 500 °C to 800 °C with an activation energy of 1.079 eV. Overall, in this work, the LSC material produced with the aid of activated carbon meet the requirements for the application as a cathode in an intermediate temperature H+-SOFC.

Influence of Silver Addition on the Morphological and Thermal Characteristics of Nickel Oxide-Samarium Doped Ceria Carbonate (NiO-SDCC) Composite Anode

Addition of silver (Ag) as an electro-catalyst has been widely investigated to enhance the cathode performance for intermediate-to-low temperature SOFCs. Nevertheless, Ag is seldom incorporated into composite anode materials, especially for low temperature application. Therefore, this study aims to investigate the effects of small amount of Ag on the microstructure and thermal behaviour of NiO-SDC carbonate (NiO-SDCC) composite pellets. NiO-SDCC composite anode powder was prepared through fast milling method. Subsequently, small amount of Ag (1, 3, and 5 wt.%) was added into NiO-SDCC composite powder via ball milling. The pellets were manually pressed and sintered at 600 °C. Characterisation of the composite anodes include X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), dilatometry and porosity measurement. NiO-SDCC had maintained good chemical compatibility regardless of Ag loading. FTIR analysis also confirmed the existence of carbonates, suggesting Ag did not influence the carbonate bonding in all NiO-SDCC. Nonetheless, the porosity of all composite anodes was found within the acceptable range for good anodic performance (20-40%). The thermal expansion of the composite samples matched well with the SDCC electrolyte. This indicates the that addition of small Ag loading into NiO-SDCC is within the acceptable range that had demonstrated promising potential as LTSOFC composite anode.