Characteristics of Pt on zeolite electrocatalyst for direct methanol fuel cell

Characteristics of Platinum (Pt) on zeolite electrocatalysts have been experimentally studied to understand its potentials for direct methanol fuel cell (DMFC) applications. The Y zeolite was chosen as a Pt-supported substrate with 1.5 wt% Pt loading on zeolite. The Pt nanoparticle size and local atomic structure in both electrochemical and gas cell treatments were investigated by using X-ray absorption spectroscopy (XAS), in particular the extended X-ray adsorption fine structure (EXAFS) method, and the electrocatalytic activity of Pt nanoparticle on Y zeolite was determined by cyclic voltammetry (CV). Studies were focused primarily on the observation of hydrogen adsorption and desorption in the hydride region, where the presence of H+ ions was critical for such a process occurred. Analyses have shown that the Pt oxides can be electrochemically reduced, due to a hydrogen ‘spillover’ phenomenon throughout zeolite structures. Based on theoretical estimation and EXAFS data fitting, it was found that the Pt nanoparticle size was 1-1.1 nm from gas cell treatment and 0.7 nm from electrochemical cell treatment. For both scenarios, the number of atoms was estimated 147 and 55 respectively, with 13 atoms at the edge of a Pt cluster for an icosahedron structure. This study demonstrated that the Pt catalytic site on zeolite can be electronically accessible; despite that zeolite is a dc insulator. The Pt/Y zeolite as a new type of electrocatalyst has shown some promises for industrial-scale fuel cell applications, such as reducing higher electrode cost and/or overcoming the difficulty of electrolyte separation

Modelling conjugate flow and heat transfer in a ventilated room for indoor thermal comfort assessment

Conjugate natural and forced convection heat transfers in a domestic model room of finite-thickness walls and a heat source have been numerically studied. A 2-D non-ventilated square model room with a heat source is investigated at first for conditions of Prandtl number Pr=0.7 and Grashof number Gr=107. Computational results are compared with already validated numerical predictions and good agreement has been achieved in terms of stream function and temperature distributions. The study continues to consider 3-D ventilated rectangular model room with a finite-thickness wall and a heat source, in order to evaluate flow and heat transfer characteristics. Key physical features such as temperature distributions in both solid wall and indoor air domains, and heat transfer performance have been quantified, analysed and compared. These results provide the correlations among room heating device arrangement, wall thickness effect, indoor thermal comfort level and energy consumption. It was found that the arrangements of heat source and window glazing had significant impact on the temperature field, and further analysis of wall thickness and thermal conductivity variations revealed the level of the comfort temperature within the occupied zone. It was also found that for an average U-value of 0.22 W/m2K, thermal energy loss through a thinner wall of 20 cm thickness is 53% higher and indoor thermal temperature is 4.6 °C lower, compared with those of a thicker wall of 40 cm thickness. The findings would be useful for the built environment thermal engineers in design and optimisation of domestic rooms with a heat source

Numerical simulation of convective airflow in an empty room

Numerical simulation of airflow inside an empty room has been carried out for a forced convection, a natural convection and a mixed convection respectively, by using a computational fluid dynamics approach of solving the Reynolds-averaged Navier-Stokes fluid equations. Two-dimensional model was studied at first; focusing on the grid refinement, the mesh topology effect, and turbulence model influences. It was found that structured mesh results are in better agreement with available experimental measurements for all three scenarios. Further study using a three-dimensional model has shown very good agreements with test data at measuring points. Furthermore, present studies have revealed low-frequency flow unsteadiness by monitoring the time history of flow variables at measuring positions. This phenomenon has not yet reported and discussed in previous studies

Domain/Mesh Decomposition of Unstructured Grids with Pre-Ordering and Smoothing. G.U. Aero Report 9506

Increasingly large scale computations are using unstructured discrete computational grids. A typical example is unstructured grid calculations based on finite volume methods (FVM) in computational fluid dynamics (CFD). One of the efficient ways to deal with such large scale problems is parallelization. The present paper will focus on domain/mesh decomposition. This is the first step for distributing unstructured computational domains on a MIMD-type parallel computer system. A graph theory framework for this problem will be constructed. Based on the framework three domain decomposition algorithms: recursive coordinate bisection (RCB), recursive angular bisection (RAB) and recursive graph bisection (RGB), will be introduced, tested and discussed. A pre-ordering and smoothing technique is proposed. It is necessary in the procedure for obtaining a 'good' domain partitioning result. Another interesting method, called the domain decomposition technique (DDT), is also investigated, which is driven in an inverse way, i.e. domain decomposition followed by mesh construction. Finally a simple and direct strategy called the mesh tailor technique (MTT) is discussed. Numerical comparisons using 2D CFD problems will be given. The further research work required to carry out a parallel implementation of a flow problem will be mentioned

Investigation of zeolite supported platinum electrocatalyst for electrochemical oxidation of small organic species

© 2016 Hydrogen Energy Publications LLC Zeolite supported Pt electrocatalysts, made by ion exchange method using Pt/Y type zeolite, have been investigated to determine Pt electrochemical activity of HCOOH and CH3OH oxidation using the cyclic voltammetry (CV) and the extended X-ray adsorption fine structure (EXAFS) techniques. The study reveals that the introduction of excess H+ ions during electrocatalyst pre-treatment could enhance electrochemical reaction on Pt surface due to higher Pt dispersion, regardless of zeolite being a direct current electronic conducting insulator. Two possible conduction pathways might contribute to the electrocatalytic reaction on Pt surface with Pt particle size and loading: (1) hydrogen atoms/H+ ions spillover through zeolite framework and at the electrode and solution interface; (2) surface mobility of adsorbed species on electrode surface. The water may act as a carrier in assisting the migration of the H+ ions throughout zeolite channels to facilitate the charger and electron transfer in such an electrical system

Domain/Mesh Decomposition of Unstructured Grids with Pre-Ordering and Smoothing. G.U. Aero Report 9506

Increasingly large scale computations are using unstructured discrete computational grids. A typical example is unstructured grid calculations based on finite volume methods (FVM) in computational fluid dynamics (CFD). One of the efficient ways to deal with such large scale problems is parallelization. The present paper will focus on domain/mesh decomposition. This is the first step for distributing unstructured computational domains on a MIMD-type parallel computer system. A graph theory framework for this problem will be constructed. Based on the framework three domain decomposition algorithms: recursive coordinate bisection (RCB), recursive angular bisection (RAB) and recursive graph bisection (RGB), will be introduced, tested and discussed. A pre-ordering and smoothing technique is proposed. It is necessary in the procedure for obtaining a 'good' domain partitioning result. Another interesting method, called the domain decomposition technique (DDT), is also investigated, which is driven in an inverse way, i.e. domain decomposition followed by mesh construction. Finally a simple and direct strategy called the mesh tailor technique (MTT) is discussed. Numerical comparisons using 2D CFD problems will be given. The further research work required to carry out a parallel implementation of a flow problem will be mentioned

Zeolite supported palladium nanoparticle characterization for fuel cell application

© 2017 Hydrogen Energy Publications LLC Palladium (Pd) has been widely used as a type of hydrogen storage material and has attracted much attention for fuel cell applications, due to its high solubility and mobility of hydrogen in Pd. In this study, Pd nanoparticles made by 1.5 wt% Pd loading on Y-zeolite under pre-treatment was employed to investigate their electrochemical activities using cyclic voltammetry (CV), and detailed local structural characterization of Pd cluster was probed by the extended X-ray absorption fine structure. Pd nanoparticle sizes were predicted at 0.81 nm–1.2 nm and the CV measurement has demonstrated that Pd zeolite catalyst has exhibited a similar tendency to those 40% Pd on XC-72R carbon. The hydrogen spillover process and surface conductance pathways contribute to the electrochemical behavior on Pd surface. In electrochemical environment, hydrogen is able to form hydride phase on Pd surface by either direct hydrogen adsorption or migrating to the centre of Pd

High order resolution and parallel implementation on unstructured grids

The numerical solution of the two-dimensional inviscid Euler flow equations is given. The unstructured mesh is generated by the advancing front technique. A cell-centred upwind finite volume method has been adopted to discretize the Euler equations. Both explicit and point implicit time stepping algorithms are derived. The flux calculation using Roe's and Osher's approximate Riemann solvers are studied. It is shown that both the Roe and Osher's schemes produce an accurate representation of discontinuities (e.g. shock wave). It is also shown that better convergence performance has been achieved by the point implicit scheme than that by the explicit scheme. Validations have been done for subsonic and transonic flow over airfoils, supersonic flow past a compression corner and hypersonic flow past cylinder and blunt body geometries. An adaptive remeshing procedure is also applied to the numerical solution with the objective of getting improved results. The issue of high order reconstruction on unstructured grids has been discussed. The methodology of the Taylor series expansion is adopted. The calculation of the gradient at a reference point is carried out by the use of either the Green-Gauss integral formula or the least-square methods. Some recently developed limiter construction methods have been used and their performance has been demonstrated using the test example of the transonic flow over a RAE 2822 airfoil. It has been shown that similar pressure distributions are obtained by all limiters except for shock wave regions where the limiter is active. The convergence problem is illustrated by the mid-mod type limiter. It seems only the Venkatakrishnan limiter provides improved convergence. Other limiters do not appear to work as well as that shown in their original publications. Also the convergence history given by the least-square method appears better than that by the Green-Gauss method in the test