THEORETICAL SIMULATION OF DIFFUSIVITY OF POROUS ELECTRODES OF FUEL CELL

Abstract

Energy development by using the fuels such as coal, oil and nuclear power are the conventional sources of energy. Non-conventional sources of energy are solar power, biomass, wind energy, tidal energy, geothermal energy and fuel cells. For a developed or a developing country energy is the basic need for the sustainable development. Non-renewable sources of energy are limited and hence causing the energy crisis and non-renewable sources of energy are also responsible for damaging our health and environment. Fuel cells uses the hydrogen as a fuel, a simplest element consists of a single proton and an electron. Large amount of hydrogen is present in our environment but not naturally as a gas, but in combination of other elements such as water and hydrocarbons. Except water, these hydrocarbons such as natural gas, methanol, propane and n-butane are also potential source of hydrogen but they are present in limited quantity in the nature. Fuel cells are a promising technology for their use as a source of heat and electricity for buildings, and as an energy source for electric motor propelling vehicles. Fuel cells are more efficient as compared to the heat engines but at the same time they are not cost effective for per unit of energy they produce, so the focus area is to have the cost effective fuel cells. Assessment of performance and degradation of fuel cells are also a part of the research in this field so it is necessary to determine the mass transfer coefficient and the kinetic parameters of gaseous fuels through the porous electrodes of the fuel cells to access the overall performance of the fuel cells. A experimental setup called temporal analysis of product (TAP) generally used in the field of heterogeneous catalysis to study `gas —solid' interaction is implemented to determine the mass transfer coefficient and the kinetic parameters of gaseous fuels through the porous electrodes of the fuel cells. Experiments are conducted over the porous micro reactor bed filled with catalyst material used in fuel cells as a electrode, to convert hydrogen gas into positive and negative ions by injecting a small pulse of the gaseous fuels through the micro reactor bed, to determine the diffusivity of those gaseous fuels through the porous micro reactor bed, by simulating the experimental results with the mathematical models. In an another set of experiments, small pulses of alkanes one after another (methane, ethane, propane, n-butane, iso-butane) are injected over the porous catalytic micro reactor bed consist of a small catalytic zone sandwich between two inert zones, to determine the kinetic behaviour of those hydrocarbons; by simulating the experimental results with the iii mathematical models. Experimental and simulation results are validated and they are found to be in a good agreement. It is recommended that this work can further be extended to study the overall performance of fuel cells with more profound models suited for the porous electrodes of fuel cells, since in the present work interpellet diffusivity through the micro reactor bed is considered primarily.