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Performance Optimization of Direct Methanol Fuel Cell

Abstract

Direct Methanol Fuel Cells (DMFCs) sustain an electrochemical reaction which converts the chemical energy stored in methanol directly into electricity. The main challenge in DMFC technology is that during the reaction, methanol crosses through the nafion membrane, i.e. from the anode to the cathode side, causing losses in electrical potential that leads to lower power output and inefficient fuel consumption. The main goal of the present work is to determine the optimal membrane thickness and operational temperature that will yield the highest current and power densities (CD and PD, respectively). To carry out this experiment, Membrane Electrode Assemblies (MEAs) with similar catalyst loadings and variable nafion membrane thicknesses of N117 (0.177 mm), N115 (0.127 mm) and N212 (0.076 mm) were purchased and utilized. A fuel cell with an active area of 50 cm2 was assembled and connected to an electronic loading device to record output current, voltage and power. A temperature controlled system was used to set the cell temperature in the range from 20 °C to 70 °C, in 10 °C increments. It was found that at a temperature of 50 °C, MEAs containing N212 and N115 experienced a significant power increase; higher temperatures did provide higher power but were not as significant as the increase from 40 °C to 50 °C. It has also been observed that thinner membranes, at 50 °C and above, provided a greater PD and could achieve higher CD; N212 at 70 °C exceeded the PD and CD of all other tested MEAs. This is an indication that methanol crossover was not the main contributing parameter to power output, as originally thought. The benefits of reaction kinematics at elevated temperatures must have overcome the effects of excess crossover. N212 at 70 °C achieved the highest performance.

Introduction

DMFCs and Hydrogen Fuel Cells (HFC) offer a promising solution to the world’s problem of finite energy resources1-2. Today’s major players in the energy field are petroleum, natural gas, coal and nuclear electric power; renewable energy only accounts for about 7% of the United States energy sources. Possible applications for fuel cells can range from automotive to cellular phones. DMFCs are already being developed to replace lithium batteries as a power source for most handheld and small electronics. Unlike lithium batteries, which take extended time to recharge, a DMFC can be refilled with a water methanol mix to recharge in a relatively short time3-4. The design parameters of a fuel cell allow cells to be stacked in series, to achieve the desired current and voltage output. Considering the existing infrastructure for storage and transport of liquid fuel, DMFCs have an advantage over HFCs5.

Fuel cells are constructed as shown in Fig. 1. (http://www.eng.wayne.edu/legacy/images/AEImages/DMFC.gif)

On the anode side, the methanol solution is supplied. Air is supplied on the cathode side. The gas diffusion layers (GDLs) are composed of carbon cloth or paper, the MEA consists of a nafion membrane and catalysts on both sides to allow the reaction to occur6-7.

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Santiago, D., & Tawfik, H., & Ryu, Y., & El-Khatib, K., & Mahajan, D. (2010, June), Performance Optimization Of Direct Methanol Fuel Cell Paper presented at 2010 Annual Conference & Exposition, Louisville, Kentucky. 10.18260/1-2--16512