Solid State Phenomena Vol. 307

Abstract: Three electrochemical double layer capacitor (EDLC) cells (Cell X, Y and Z) made from an electrode of 90 wt. % of the multiwalled commercial carbon nanotubes, 10 wt. % of poly (vinylidene fluoride-co-hexafluoropropylene) and three different samples of electrolytes polymer electrolyte made up of a compositions of 50:50, 60:40 and 70:30 wt.% of H₃PO₄/PVA (in ratio) soaked in a filter paper was characterized in this study. The aim is to ascertain the disparities in performances of the cells in relation to their respective scan rates. Cyclic voltammetry (CV) measurement of cells shows a high specific capacitance of 313 Fg⁻¹ for the scan rates 10 mV was recorded from the cell with the highest composition H₃PO₄/PVA ratio (i.e. 70:30 wt.%). However, when the CV of the cell was measured with different scan rates, disparities in the performance occurred, as only 94 and 174 Fg⁻¹ was recorded at the scan rates 100 and 50 mV respectively for cell-X. The result was not different when the two other cells (60:40 and 70:30 wt. % of H₃PO₄/PVA) were measured at the same scan rates.

Abstract: Ordered carbon was prepared via nanocasting method with Santa Barbara Amorphous (SBA)-15 as the template and sucrose as the carbon precursor. The ordered carbon surface was then modified with oxygen and nitrogen species to alter its chemical and physical properties. All surface-modified ordered carbon samples were evaluated using nitrogen adsorption-desorption analyser and electrochemical impedance spectroscopy. Post modifications, the KOH electrolyte ion transportation are affected due to significant change in the ordered carbon structural properties.

Abstract: Spinel LiMn₂O₄ is one of the promising cathode materials used in commercial Li-ion batteries. In this study, Ni was partially substituted in order to give the material LiMn_1.8Ni_0.2O₄, which was successfully synthesized using a self-propagating combustion (SPC) method. Results from Simultaneous Thermogravimetric Analysis (STA) show the small mass loss about 4.6%. The precursor then was calcined at temperature of 800 °C for 24 h, 48 h and 72 h. X-Ray Diffraction (XRD) confirms that the final products are pure and single phase with no impurities present. The morphology and crystallite size of pure samples are examined using Field Emission Scanning Electron Microscope (FESEM). The result shows that all the materials consist of crystalline particles with smooth surface and polyhedral shaped materials.

Abstract: In this work, an anode-supported button cell was fabricated with compositionally gradient (CG) NiO-BaCe_0.54Zr_0.36Y_0.1O_2.95 (NiO-BCZY) anode functional layer (AFL). The button cell has a configuration of NiO-BCZY (50:50) | NiO-BCZY (30:70) | NiO-BCZY (10:90) | BCZY | LSCF. All powder materials were synthesized using a sol-gel method. Firstly, NiO-BCZY anode substrate was fabricated using dry-pressing method. Next, NiO-BCZY CG-AFL and BCZY electrolyte thin film were spin-coated on the anode substrate and lastly the La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) cathode was spin-coated on the electrolyte thin film. The microstructure of the fabricated button cell with good adhesion between all the layers, thin and dense electrolyte layer, and gradient increase in density of materials from anode substrate to electrolyte were observed using Scanning Electron Microscopy (SEM). Cell’s performance in terms of resistivity was evaluated using Electrochemical Impedance Spectroscopy (EIS) and conductivity meter using four-point probe method. Values of ohmic (R_o) and polarization resistance (R_p) of the cell are 7.3 and 2.4 Ωcm² at 700 °C, respectively. The lower resistance values obtained compared to our previous work on a conventional 3-layers BCZY-based single button cell (R_o = 9.6 and R_p = 7.8 Ωcm² at 700 °C) confirmed the functionality of GC-AFL in enhancing the cell’s performance. This preliminary result shows that simple deposition technique of CG-AFL plays a significant role in the optimization of PCFC button cell designs and electrochemical performance.

Abstract: Abstract. Solid oxide fuel cell (SOFC) is an electrochemical conversion device that undergoes a thermal cycling at various operating temperature where lead to the degradation of its mechanical properties. Electrolyte among the main component in SOFC plays a crucial part in defined the overall performance which facing a lattice expansion event when exposed to heating. Thus, in this paper BaCe0.54Zr0.36Y0.1O3-δ (BCZY) was selected as potential electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) to investigate its lattice expansion as a function of temperature. The sample was prepared via a sol gel method and calcined at 1100°C for 10 hours to form a powder and then pressed to become a pellet. To ensure a good densification in such pellet, two-steps sintering processes was indicated at 1500°C and ground to a powder form prior to the lattice expansion measurements. High temperature X-ray diffraction (HT-XRD) was used to study the lattice expansion of sample in the temperature range of 25°C to 700°C with interval 100°C under air atmosphere. HT-XRD analysis was done using X’pert Highscore Plus software and Visual for Electronic and Structural Analysis (VESTA) software was used to observe the crystal structure. Phase and structural analysis of BCZY electrolyte materials were discussed. Apparently, the BCZY shows an average of 97% phase purity from room temperature to 700°C. Rietveld refinement analysis revealed that the BaCe0.54Zr0.36Y0.1O3-δ exhibits cubic symmetrical structure with unit cell, a=b=c that varied from 4.3440Å - 4.3731Å for all the temperature studied. Thus, the expansion percentage for the lattice expansion from room temperature to 700°C was about 12.6 %.

Abstract: Cathode is one of the important parts in performing the high efficiency of proton conducting fuel cell (PCFC). Selection of appropriate cathode material may resolve the major drawbacks at the cathode part associated with the high R_p. Accordingly, tremendous effort have been done to reduce the R_p and one of the alternatives is the modification of cathode microstructure that can be achieved by introducing dispersing agent in the synthesis route. Thus, in this present work, a functionalized carbon nanotubes (f-CNTs) obtained from acidification process was used as a dispersing agent in the synthesis of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) cathode material. The amount of 4 mg, 8 mg and 12 mg of f-CNTs were respectively added to LSCF cathode during the synthesizing process by a sol-gel method. Semi-solid gel obtained was calcined at 900 °C to form high purity of LSCF powder and respectively denoted as LSCF4, LSCF8 and LSCF12. The powder was characterized by Fourier Transform Infrared (FTIR) Spectroscopy, Pycnometer, Particle Size Analyzer and Scanning Electron Microscopy with Energy Dispersive X-ray (SEM/EDX). The FTIR analysis depicted the peak of respective metal complexes, metal oxide, symmetrical and asymmetrical stretching of carboxylate. The pycnometer showed the lowest density of LSCF4 was 2.8777 g/cm³. The Particles Size Analyzer confirmed the particle size of 38 nm ultrafine powder for LSCF4. The SEM image depicted the highly disperse spherical particles found in LSCF4 with particle size about 30 nm. The elemental composition of the samples is comparable with the nominal stoichiometric of LSCF4 as corroborated by the EDX analysis. Therefore, the LSCF with optimum 4 mg f-CNTs as dispersing agent has potential as nanoporous cathode material for proton conductivity fuel cell.

Abstract: Y-doped barium cerate-zirconate ceramic oxide is proven to be a competent material as an electrolyte with high proton conductivity as well as chemical and mechanical stabilities in carbon dioxide and water vapour atmospheres. This ceramic oxide requires high processing temperature which will results in the increase of particle/grain size. Hence, modification on the synthesis route has been studied in reducing the particle/grain size of the ceramic by lowering the calcination temperature. In this work, BaCe_0.54Zr_0.36Y_0.1O_2.95 (BCZY) powder was synthesized with addition of surfactant (Brij-97) through an established modified sol-gel route. Single BCZY perovskite phase was successfully obtained at calcination temperature of 950°C which was lower than our previous study (T=1100°C). The prepared sample was made into pellet by a dry pressing technique with diameter, d=13 mm and thickness, t~2 mm and then subjected to a two-step sintering method prior to morphological and electrical measurements. Impedance measurement was carried out at intermediate temperatures (500-800°C) using an Electrochemical Impedance Spectroscopy (EIS) in wet nitrogen atmosphere. Impedance spectrum was analysed to obtain the behaviour of grain core and grain boundary responses by a fitting procedure using a brick-layer model. Scanning electron microscope (SEM) analysis of fractured pellet revealed that BCZY prepared with the assisted of Brij-97 exhibited dense, homogenous and less agglomerate grain with grain size around 88 nm, which may explain the enhancement in the total conductivity of the BCZY electrolyte.

Abstract: The activated carbon produced from oil palm empty fruit bunches (ACEFB) shows good properties to act as a dispersing agent in the synthesis of BCZY ceramic material. However, the untreated ACEFB (u-ACEFB) shows some impurities still present after calcination. Thus, it has to be functionalized (f-ACEFB) by using chemical treatment. In this work, three samples of bare BCZY, BCZY u-ACEFB and BCZY f-ACEFB were prepared, respectively. The sol-gel method was used to synthesize the BCZY ceramic powder by using metal nitrate salt as a starting material. The ACEFB was added to the metal precursor accordingly and was dried (T=325°C) followed by calcined (T=1100°C). For the fabrication of pellet, the sample was sintered by two-step sintering (TSS) method. The relative density of pellet was measured and calculated. The Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) were conducted to characterize the synthesized BCZY ceramic material. Based on the characterization, BCZY u-ACEFB have the highest relative density among the others, whereas BCZY f-ACEFB have the lowest relative density. The FTIR results further confirmed the presence of the functional groups corresponded to the BCZY. The SEM micrograph shows a spherical structure of BCZY f-ACEFB with grain size around 134 nm. EDX data further confirm the elemental composition of the pellet. It was observed that the f-ACEFB have an outstanding performance as a dispersing agent in BCZY synthesizing route.

Abstract: OAbstract. One of the approaches that has been done to produce a better performance of an intermediate temperature solid oxide fuel cell (IT-SOFC) is by varying the synthesis methods. This paper focused on the proton conducting electrolyte in particularly barium cerate and barium zirconate system namely BaCe_0.9Y_0.1O_3-δ (BCY) and BaZr_0.9Y_0.1O_3-δ (BZY). Supercritical ethanol processing technique is one of the alternative synthesis routes that able to produce ceramics powder at lower calcination temperature. The samples were synthesized in High-Pressure-High-Temperature (HP-HT) Batch Wise reactor system using ethanol as reaction medium. XRD was used to study the structure of both samples and all the data were refined using Rietveld refinement method by X’pert Highscore software. VESTA software is used to observe the crystal structure for both BCY and BZY samples. Both BCY and BZY have 98.16% and 96.55% purity after being calcined at 700°C and 1100°C, respectively. This study showed that BCY has orthorhombic structure with lattice parameter a=8.76Å, b=6.24Å and c=6.21Å and BZY exhibited cubic structure with a=b=c, and a=4.194Å. It was observed that BCY synthesized by supercritical fluid (SCF) method at reduced calcination temperature exhibited an acceptable value of lattice paramter as compared to other method that used higher processing temperature.

Abstract: Following successful growth of zinc oxide (ZnO) nanorods, a layer of zinc selenide (ZnSe) was electrodeposited onto the nanorods to further enhance its conversion efficiency in the photoelectrochemical (PEC) cell. The electrodeposited ZnSe layer onto the ZnO nanorods was subjected to heat treatment at 200, 250 and 300°C. The prepared films were characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and ultraviolet-visible spectroscopy (UV-Vis) to investigate the structural, morphological and compositional characteristics. Additionally, PEC conversion generated by the prepared thin films were tested with photocurrent measurements under calibrated visible illumination from a halogen lamp. Based on FESEM analysis, the thickness of ZnO thin film increased with temperature. However, the diameters of the ZnO nanorods were found to be in a decreasing trend upon heat treatment at higher temperature. The electrodeposited ZnSe layer at the potential of -0.7 V for 60 seconds (calcined at 200°C) possessed crystallite size of 20.1 nm. According to UV-Vis analysis, band gap energy measured was 2.8 eV, which is very close to standard ZnSe band gap value (2.7 eV). Additional layer of ZnSe electrodeposited enhanced thin film performance in terms of current density as much as 37.4% while having high photocurrent density of 0.2671 mAcm^-2.