DMFC

Objective

This article reviews on direct methanol fuel cell system design for active and passive system.

Introduction

The direct methanol fuel cell (DMFC) presents several interesting scientific and engineering problems. There are many engineering issues that arise from the cell materials, feed and product management, mass and heat transport. Among the various fuel cell technologies, the DMFC, which uses methanol directly to the system, has high-energy efficiency and a wide application prospect .A good design of the flow field can easily facilitate uniform distribution of reactants and by-product in electrodes to improve the performance of micro-DMFCs. Thus, design fuel and heat management are related with the flow-field design.

Chemistry diagnosis of direct methanol fuel cell

2.1.-Backing layer

MEA consists of three important components which are backing layer, catalyst layer and membrane.

The main function of the GDL is to diffuse the methanol to the catalyst layer. The GDL is usually made of a carbon-based porous substrate, such as carbon paper or carbon cloth, with a thickness of about 0.2e0.5 mm and a dual-layer structure. The great majority of engineering has come to include graphitic microstructures or disordered graphitic microstructures.

Ideal backing layer is required to effectively deliver reactive gas to the catalyst layers. The diffusion layer comprises carbon micro material inactive or nanomaterial.

2.2. Catalyst layer

The most important catalyst layers objective is to obtain the highest reactivity or transfer current density with a minimum amount of catalyst. In DMFC, bimetallic Pt-Ru is the most widely used catalytic material due to its high catalytic activity towards the electro oxidation reaction of methanol (MOR) in the anode.

2.3. Membrane layer

The main function of the membrane in a fuel cell system is to transport protons from the anode to the cathode. Membrane polymers facilitate the transport of protons ( via its sulfonic acid groups ) , to keep the fuel and oxidant separately to avoid the mixing of the two gases , to withstand harsh conditions, including active catalysts , high temperatures or temperature fluctuations, strong oxidants, and reactive radicals .

Therefore, the ideal polymer must have excellent proton conductivity , chemical and thermal stability , strength, flexibility , low permeability to water and methanol , low cost and good availability.

Currently, the Nafion membranes are commonly used for DMFC . Methanol crossover through such membrane is therefore significantly large. The common strategy to mitigate methanol crossover is the use of a membrane 115 or 117 , which exhibits the best performance.

3. Microsystems Engineering in methanol fuel cell

3.1. Flow field design

The main tasks of these field flow plates are necessary for the distribution of fuel or air to the reaction surface and remove products from the cell. Currently, the mainly symmetrical network, serpentine parallel flow fields are used in the active system for both the anode and cathode to facilitate mass transport

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