Mukhlis A. Rahman

A review on the fabrication of electrospun polymer electrolyte membrane for direct methanol fuel cell

Proton exchange membrane (PEM) is an electrolyte which behaves as important indicator for fuel cells performance. Research and development (R&;D) on fabrication of desirable PEM have burgeoned year by year, especially for direct methanol fuel cell (DMFC). However, most of the R&;Ds only focus on the parent polymer electrolyte rather than polymer inorganic composites. This might be due to the difficulties faced in producing good dispersion of inorganic filler within the polymer matrix, which would consequently reduce the DMFCs performance. Electrospinning is a promising technique to cater for this arising problem owing to its more widespread dispersion of inorganic filler within the polymer matrix, which can reduce the size of the filler up to nanoscale. There has been a huge development on fabricating electrolyte nanocomposite membrane, regardless of the effect of electrospun nanocomposite membrane on the fuel cells performance. In this present paper, issues regarding the R&;D on electrospun sulfonated poly (ether ether ketone) (SPEEK)/inorganic nanocomposite fiber are addressed.

Role of lithium oxide as a sintering aid for a CGO electrolyte fabricated via a phase inversion technique

The incorporation of lithium oxide (Li2O) as a sintering additive has specific advantages for electrolyte membrane fabrication. However, the viability of the sintering additive to be implemented in a phase inversion technique is still ambiguous. In this first attempt, lithium was doped into a gadolinium-doped ceria (CGO) crystal structure using the metal nitrate doping method and calcined at four different temperatures, i.e. 140, 300, 500 and 700 °C. The prepared Li-doped CGO (Li–CGO) powders were analyzed by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), N2 adsorption/desorption, and Fourier-transform infrared (FTIR). Primary results demonstrate that the calcination temperature of the Li–CGO influences the condition of the electrolyte suspension. Li–CGO calcined at 700 °C (D-700), as compared with other Li–CGO, possessed a strong interaction between the Li and CGO. The D-700 was then incorporated into the electrolyte flat sheet membrane which was prepared by a phase inversion technique. The membrane was then sintered at different sintering temperatures from 1350 °C to 1450 °C. In comparison with the unmodified CGO, the morphological results suggest that the Li2O can remarkably promote the densification of CGO at a lower sintering temperature (1400 °C). These findings help to promote the use of sintering additives in a ceria-based electrolyte suspension specifically for the phase inversion technique.

The influence of PEEK as a pore former on the microstructure of brush-painted LSCF cathodes

At lower operation temperature of intermediate temperature solid oxide fuel cells (IT-SOFC), polarization resistance was recognized as a limiting step because polarization at cathode is dependent on the rate of oxygen reduction reaction. The enhancement of cathode microstructure is one of the effective ways to improve the reaction rate. Pore former addition method is proven to be able to tailor the microstructure of cathode. The addition of polyether ether ketone (PEEK) as pore former was evaluated and compared with common pore formers (corn starch and graphite) for the microstructure cathode layer. Brush painting technique was used to deposit cathode layer on anode/electrolyte dual layer support hollow fiber. X-ray diffraction (XRD) analysis had proven that the resulting layer was free from impurities after the sintering treatment. Corn starch was able to induced cathode layer with coarse and large interconnected pores for efficient gas diffusion, as was proven by the SEM analysis. Additionally, SEM analysis also showed the formation of fine micropores throughout the layer when graphite was used as the pore former that can provide the increase in triple phase boundary region (TPB) in the layer. PEEK was able to generate both high porosity for oxygen diffusion to the reactive sites and increased number of TPB by the formation of fine microstructure pores in the cathode layer.

Efficient reduction of graphene oxide nanosheets using Na2C2O4 as a reducing agent

The efficient synthesis of reduced graphene oxide (RGO) nanosheets via chemical reduction process of exfoliated graphene oxide (GO) nanosheets was performed by introducing sodium oxalate (Na2C2O4) as a reducing agent. To study the effects of the reduction time on the synthesized RGO, the GO was reduced within -1/2, 1 and 2 h for RGO-1, RGO-2 and RGO-3, respectively. The C/O atomic ratio of the synthesized RGO-3 has increased from 2.16 to 6.32 after reduction as determined by X-ray photoelectron spectroscopy (XPS). The morphology analysis of the RGO-3 was determined by high-resolution transmission electron microscopy (HRTEM) almost revealed the formation of single layer. The number of RGO layers decreases as the time of the reduction increases. Based on these analysis results, sodium oxalate plays an important role in the efficient removal of the oxygen containing groups in the GO to produce high quality of RGO.

Structural, optical and electrical evolution of Al and Ga co-doped ZnO/SiO2/glass thin film: Role of laser power density

This study investigates the characteristics of laser annealed thin films of Al–Ga co-doped zinc oxide (ZnO:Al–Ga) nanoparticles on top of SiO2/glass. The samples are synthesized using simple sol–gel, spin coating and radio frequency magnetron sputtering methods. The studies on the structural, optical and electrical properties of the pre-annealed sample and samples annealed at different power densities are conducted using a variety of characterization techniques. The samples exhibit a hexagonal wurtzite structure. Spectroscopic and nano-imaging techniques confirm that by increasing the laser power density, the crystallinity of the samples is improved and the nanoparticle size is enhanced from ∼10 nm to ∼35 nm. Spectroellipsometry is employed to calculate the refractive index, extinction coefficient, and real and imaginary components of the dielectric constant. The resistivity exhibits a minimum value at 440 mJ cm−2. Results demonstrate that the optical band gaps of the samples are between 3.29 and 3.41 eV, which are greater than that of pure bulk ZnO (band-gap of 3.21 eV). Several vibrational modes occur as a result of the dopant combination in the ZnO lattice. A discussion on the origins of modes and their intensity changes is provided. This work suggests that a laser annealing process can be an effective tool to fabricate various thin films with enhanced crystallinity. The optical and electrical properties can also be adjusted by varying the power density.

A low cost, superhydrophobic and superoleophilic hybrid kaolin-based hollow fibre membrane (KHFM) for efficient adsorption–separation of oil removal from water

Inspired by the lotus leaf surface structure, which possesses a hydrophobicity behaviour, a low cost, high performance superhydrophobic and superoleophilic kaolin hollow fibre membrane (KHFM) was obtained by a simple sol–gel grafted method using tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) for oil removal from water. The KHFM was grafted at various grafting times ranging from 1 to 5 coating cycles. Prior to the calcination process at 400 °C, the grafted KHFM was dried in an oven at 100 °C for 1 hour for each grafting coating cycle. The grafting process efficiency was measured by the contact angle of water and hexane. Scanning electron microscopy (SEM) and Atomic Force Microscopy (AFM) were used to study the morphology and surface roughness, respectively, of the grafted KHFM. The oil removal was conducted by using the homogeneous mixture of hexane and water. The highest hydrophobicity and oleophilicity was obtained for the KHFM grafted at 2 coating cycles with a contact angle value equal to 157° and 0°, respectively. In fact, the mechanical strength of KHFM was also improved from 16.21 MPa to 72.33 MPa after grafting. In terms of performance, KHFM grafted for 2 coating cycles obtained an almost 99.9% absorption of oil. Thereby, KHFMs were assembled into a module for a filtration study. A high oil flux of 102 L m−2 h−1 was obtained for superhydrophobic and superoleophilic KHFM with 2 grafting coating cycles of 2, and this result is in agreement with the trend of the adsorption result.

Effect of organic ligand-decorated ZnO nanoparticles as a cathode buffer layer on electricity conversion efficiency of an inverted solar cell

Efficiency improvement of the industrial scale solar cells to capture sunlight as an important renewable energy source is attracting significant attention to prevent the consumption of a finite supply of unsustainable fossil fuels. ZnO nanoparticles decorated with an imine-linked receptor have been used in the fabrication of a photocathode based on dye-sensitized solar cells for the purpose of photovoltaic efficiency enhancement. Various characterization techniques have been employed to investigate the structural, morphological, and optical behaviors of the solar cell having ZnO nanoparticles and ZnO nanoparticles decorated with an organic ligand as a photocathode layer. The decorated nanoparticles have a stable wurtzite structure and an average grain size of ∼45 nm, confirmed by the TEM image and XRD through the Scherrer equation. The ZnO sample emits wide peaks in the visible range, and the emission intensity of the ZnO-DOL sample increases along with a red-shift (0.38 eV) in the band gap. This shift can be explained using deep level transition, surface plasmon energy of a surfactant, and coupling of ZnO with local surface plasmon energy. UV-vis absorption spectra together with photoluminescence spectra confirm the higher absorption rate due to organic ligand decoration on ZnO nanoparticles. The greatest solar power-to-electricity conversion efficiency (η) of 3.48% is achieved for the ZnO-DOL sample. It is enhanced by 3.13% as compared to that of the ZnO-based solar cell. The ZnO-DOL device exhibits a higher external quantum efficiency (EQE), responsivity (Rλ), and photocurrent-to-dark current ratio; this confirms the improvement in the solar cell performance.

Effects of SPEEK/Cloisite concentration as electrospinning parameter on proton exchange membrane for direct methanol fuel cell application

In this study, a fine fibers mat were produced from SPEEK/Cloisite solution and the effect of the dope concentration on the fibers morphology was performed.The electrospun fibers were denoted as e-spunCL and fabricated as dense membrane (SP/e-spunCL) by immersing electrospun fibers into half-solidified SPEEK solution The fiber’s mechanical stability study was also conducted. The fibers diameters and morphology were observed by using Scanning Electron Microscopy (SEM).While the mechanical properties of the fibers was observed via tensile strength test. The results showed that as the concentration increased (0.05 wt%, 0.10 wt%, 0.17 wt%, 0.25 wt% and 0.30 wt%), the fibers diameters become larger which varies from 9.257 μm to 495.4 nm. The highest tensile strength among all fibers was recorded from SP/e-SpunCL17 which was found to be 19.96882±1.49458MPa. SP/e-spunCL17 showed the most promising physico chemical properties with the highest water uptake and proton conductivity of 25.87±1.9827 %, 12.12±0.2837 mScm-1 and the lowest methanol permeability with 1.22±0.3748 x10-8 cm2s-1.

Pore size measurements and distribution for ceramic membranes

This chapter discusses various methods in characterizing porous ceramic membranes. The fundamental theory and calculation for every approach are given to relate the basic concept of each technique to the results obtained from experiments. A number of techniques are discussed, including gas adsorption/desorption isotherm, permporometry, mercury porosimetry, thermoporometry, bubble point method, and liquid displacement technique. This chapter includes some step-by-step methodologies in obtaining the results of pore properties for ceramic membranes. The view and comparisons that include the advantages and limitations are given in the end of this chapter.

Fourier transform infrared (FTIR) spectroscopy

The use of Fourier transform infrared (FTIR) spectroscopy has been considered to be one of the most effective techniques to study and understand the chemical and surface chemistry in various types of membrane. In this chapter, the role of FTIR techniques to monitor the change of membrane surface chemistry was discussed. Without knowing the specific functional group, which had altered the membrane surface behavior, the researcher is unable to explain different physicochemical properties that significantly changed the membrane performance. In addition, the FTIR techniques can also be used to monitor the stability and durability of the specific membrane toward their performance. In general, the use of FTIR analysis in the field of membrane application is crucial to support the justification of the changes in their properties and performance in various applications.