Life cycle cost analysis of alternative vehicles and fuels in Thailand

High crude oil prices and pollution problems have drawn attention to alternative vehicle technologies and fuels for the transportation sector. The question is: What are the benefits/costs of these technologies for society? To answer this question in a quantitative way, a web-based model (http://vehiclesandfuels.memebot.com) has been developed to calculate the societal life cycle costs, the consumer life cycle costs and the tax for different vehicle technologies. By comparing these costs it is possible to draw conclusions about the social benefit and the related tax structure. The model should help to guide decisions toward optimality, which refers to maximum social benefit. The model was applied to the case of Thailand. The life cycle cost of 13 different alternative vehicle technologies in Thailand have been calculated and the tax structure analyzed.     

Pt-modified Au/C catalysts for direct glycerol electro-oxidation in an alkaline medium

Au-based catalysts promoted with Pt were prepared by using polyvinyl alcohol protection method. Different amounts of Pt (5, 10 and 15% of total metal) were added in the Au sol formation step to improve the activity of Au/C toward glycerol electro-oxidation in an alkaline medium. The physical and electrochemical properties of the as-prepared catalysts were explored. The average particle sizes of the Au/C and Pt-modified Au/C catalysts measured by transmission electron microscopy (TEM) were the same at around 4 nm. The PtAu/C alloy formation in the PtAu/C catalysts was confirmed by the increase of lattice parameter calculated from the X-ray diffraction (XRD) patterns and by the absence of Pt ring in the electron diffraction pattern. The change of binding energy in X-ray photoelectron spectroscopy (XPS) results indicated the interaction between Pt and Au. For glycerol electro-oxidation in an alkaline medium, the PtAu/C catalysts were more active than the Au/C catalyst as observed from an early onset potential and a shift of potential at maximum current density to a lower potential. Among the Pt-modified Au/C catalysts, the most active catalyst was Pt₁Au₉/C. The synergistic effects between Pt–Au was proven by a better performance of the PtAu/C compared to the physical mixed catalyst of Au/C and Pt/C at the same Pt:Au ratio. The Pt-modified Au/C catalysts were more stable than the Au/C, especially in a high potential region. This enhancement may be caused by the promotion effect of highly active PtO on the surface of the bimetallic catalyst.     

Key parameters of active layers affecting proton exchange membrane (PEM) fuel cell performance

The 2ⁿ full factorial design was applied to identify the key parameters of the active layer affecting the performance of a proton exchange membrane (PEM) fuel cell. Three main selected parameters were considered: carbon-type (Vulcan XC 72R and Black Pearls 2000 conducting furnace blacks, Cabot Corporation Boston, MA), Pt loading (0.1 and 0.5 mg/cm²), and Nafion™ sulfonic acid fluoropolymer (Du Pont de Nemours, Wilmington, DE) ionomer content (10% and 60%) for variables A, B, and C, respectively. The results from full factorial analysis indicated that the key factors affecting the exchange current density or activation loss were Pt loading whereas the key factors controlling the resistance due to ohmic loss were Nafion content and carbon type. In addition, there are the interactions between these parameters controlling the thin-film active layer performance, especially the interaction of carbon type and Nafion content. From cyclic voltammograms and cell performance testing, a Nafion content of 30% in a catalyst layer consisting of 0.5 mg/cm² Pt on Vulcan XC 72R is optimal.     

The role of an anode microporous layer in direct ethanol fuel cells at different ethanol concentrations

Ethanol crossover and ethanol electrooxidation kinetic effects on direct ethanol fuel cell (DEFC) performance were determined at different ethanol feed concentrations for cells fabricated with and without an anode microporous layer (MPL). Several characterization techniques were used, including cell performance curves, anode polarization, electrochemical impedance spectroscopy (EIS) and ethanol crossover by the voltammetric method. It was found that the optimum ethanol feed concentration depended on the anode structure design and the cell current density operation. A microporous layer could reduce ethanol crossover but induced high mass transfer resistance, resulting in a slow ethanol electrooxidation reaction rate. However, ethanol crossover was not the dominant factor affecting DEFC performance for the ethanol feed concentration range (0.5–5.0 M) studied. The MEA without an anode MPL exhibited better performance than the one with an MPL for the entire range of ethanol concentration.     

Hydrogen production from bioethanol reforming in supercritical water

Hydrogen production by reforming and oxidative reforming of ethanol in supercritical water (SCW) at the intermediate temperature range of 500-600 °C and pressure of 25 MPa were investigated at different ethanol concentrations or water to ethanol ratios (3, 20 and 30), with the absence and the presence of oxygen (oxygen to ethanol ratio between 0 and 0.156). Hydrogen was the main product accompanied with relatively low amounts of carbon dioxide, methane and carbon monoxide. Some liquid products, such as acetaldehyde and, occasionally, methanol were present. The ethanol conversion and hydrogen yield and selectivity increased substantially as the water to ethanol ratio and the reaction temperature increased. Ethanol was almost completely reformed and mainly converted to hydrogen giving a H₂/CO ratio of 2.6 at 550 °C and water to ethanol ratio of 30 without carbon formation. Coke deposition was favored at low water to ethanol ratio, especially at high temperatures (≥550 °C). The hydrogen yield improved as the ethanol was partially oxidized by the oxygen added into the feed at oxygen to ethanol ratios <0.071. It was evidenced that the metal components in Inconel 625 reactor wall reduced by a hydrogen stream acted as a catalyst promoting hydrocarbon reforming as well as water-gas-shift reactions while dehydrogenation of ethanol forming acetaldehyde can proceed homogeneously under the SCW condition. However, at high oxygen to ethanol ratio, the reactor wall was gradually deactivated after being exposed to the oxidant in the feed. The loss of the catalytic activity of the reactor surface was mainly due to the metal oxide formation resulting in reduction of catalytic activity of the reactor wall and reforming of carbon species was no longer promoted.     

Dynamic modeling of direct ethanol fuel cells upon electrical load change

A transient, two‐dimensional, and two‐phase model was developed for predicting cell potential decay behavior of direct ethanol fuel cells operated galvanostatically after applying a step change in cell current density. To predict dynamic changes in anode overpotential and product distributions, a multi‐step reaction mechanism based on literatures involving many adsorbed intermediates (CH₃CH₂OH, CH₃CHO, CH₃CO, OH) was incorporated into this model. The kinetic rates of reactions involving electron transfers are described by the Butler‐Volmer equation. The surface coverage balance was used to determine the fractional coverage for each adsorbed species. The model also accounts for ethanol crossover through the membrane to cause cathode mixed potential. From the simulation results, a gradual increase of anode overpotential was caused by the acetyl bottleneck effect, leading to a slow decay of cell potential with time. Based on one set of model parameters, the model could accurately predict the dynamic response of cell voltage behavior after the cell current densities were stepped up as well as product selectivity.     

Au/C catalyst prepared by polyvinyl alcohol protection method for direct alcohol alkaline exchange membrane fuel cell application

An Au/C catalyst was prepared by means of the polyvinyl alcohol-protected Au sol method. Highly dispersed Au nanoparticles with an average particle size of around 3.7 nm were obtained as confirmed by transmission electron microscopy. The cyclic voltammogram of Au/C was similar to that of a bulk Au electrode, but a small shift of Au oxide reduction and oxidation potential peaks were observed. The electrooxidation of methanol, ethanol, ethylene glycol, and glycerol on the Au/C catalyst in an alkaline solution was analyzed. Using a cyclic voltammogram, the maximum current density toward alcohol electrooxidation was found to decrease in the order of glycerol > ethylene glycol > ethanol, while methanol was not oxidized. Compared with PtRu/C, the maximum current densities obtained from the Au/C catalyst for ethylene glycol and glycerol electrooxidation were increased by 1.6 and 3.3 times, respectively. The reaction heavily progressed through a C–C bond dissociation path. It was found that main product of glycerol electrooxidation was formic acid, which accounted for more than 60 % of the total product. Using chronoamperometry, the Au/C catalyst showed much better stability than that of PtRu/C for the reaction without C–C bond dissociation and better stability for the reaction with C–C bond dissociation.