JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech I Year ENGINEERING CHEMISTRY Previous Question Paper (September/October - 2021 - R15)

A Direct Methanol Fuel Cell (DMFC) is an electrochemical device that converts the chemical energy of methanol directly into electrical energy. It consists of an anode, a cathode, and a proton exchange membrane (PEM) electrolyte.

Construction: The cell features two electrodes separated by a polymer electrolyte membrane, typically Nafion. The anode is coated with a catalyst (usually Pt-Ru) to facilitate methanol oxidation, while the cathode is coated with a catalyst (usually Pt) for oxygen reduction.

Working Principle: Aqueous methanol is supplied to the anode, where it undergoes oxidation. Protons pass through the membrane to the cathode, while electrons travel through an external circuit to generate current. At the cathode, oxygen reacts with the protons and electrons to form water.

The rate of corrosion is influenced by both the nature of the metal and the environmental conditions. Key factors include:

• Nature of the Metal: Metals with higher positions in the electrochemical series (more negative reduction potential) corrode faster. Additionally, the formation of a protective, non-porous oxide film can passivate the metal and inhibit further corrosion.
• Nature of the Environment: Humidity, temperature, and the presence of electrolytes (like salts) accelerate corrosion. Higher temperatures generally increase the reaction rate.
• pH of the Medium: Acidic environments significantly increase the rate of corrosion by promoting hydrogen evolution, whereas alkaline environments may promote the formation of protective hydroxide layers.
• Presence of Impurities: The presence of impurities creates local galvanic cells where the less noble metal acts as an anode and undergoes rapid corrosion.
• Conductivity of the Electrolyte: Higher conductivity of the surrounding medium facilitates the flow of ions between anodic and cathodic sites, thereby increasing the corrosion rate.
• Differential Aeration: Differences in oxygen concentration on the metal surface lead to differential aeration corrosion, where the oxygen-poor region acts as an anode.