Engineering Chemistry Copyright  2011 Wiley India Pvt. Ltd. All rights reserved.

The galvanic cells used to form batteries can be classified as: A battery is a combination of cells either in series or parallel or both, in order to get the required amount of electrical energy. It is a portable source of electrical energy. The galvanic cells used to form batteries can be classified as: Primary cells: In these cells, the chemical energy is converted into electrical energy as long as the chemical components are active. Secondary cells: In these cells, the redox reaction that converts chemical energy into electrical energy can be reversed by passage of current. Engineering Chemistry Copyright  2011 Wiley India Pvt. Ltd. All rights reserved.

Components of a Battery Anode It contains active materials which spontaneously take part in the oxidation reactions. Cathode It contains active materials which spontaneously take part in the reduction reactions. Electrolyte It helps in the migration of the ions leading to the generation of electrical energy. Separator It is a thin polymeric membrane which prevents the mixing of products formed at the electrodes. Engineering Chemistry Copyright  2011 Wiley India Pvt. Ltd. All rights reserved.

(a) Discharging and (b) charging processes in a battery Discharging and Charging of a Battery The process in which spontaneous redox reaction occurs is called discharging. This process of conversion of an inactive material back into active materials in a cell is called charging. (a) Discharging and (b) charging processes in a battery Engineering Chemistry Copyright  2011 Wiley India Pvt. Ltd. All rights reserved.

Lithium Batteries Lithium is a light metal with low electrode potential and good conductivity. It is, therefore, a good material for batteries, and can be expected to have high potential and high energy density. The group of batteries where lithium is used as an anode are known as lithium batteries and they were commercialized in 1990. Anode—Li Cathode-MnO2, Electrolyte ia a mixture of LiCl, LiBr, Li AlO4 and LiClO4 dissolved in organic solvents like propylene carbonate and 2-dimethoxyethane. EMF=3.0V Used in memory backups, automatic cameras and calculators. These batteries have the following characteristics: The batteries are light in weight and compact. They are known for low maintenance and have high energy density.

Lithium Ion Cells

Fuel Cells Comparison with Conventional Galvanic Cells The conversion into electrical energy involves a number of steps and there is loss of energy at every step. The efficiency of the process is around 40%. There is also a viable way of converting the chemical energy of fuel directly into electrical energy through catalytically activated redox reactions. Such devices are called fuel cells. Fuel cells are galvanic cells in which electrical energy is directly derived from redox reactions of the fuel. Comparison with Conventional Galvanic Cells They consist of two catalytic electrodes. The reagents used are fuel and oxidant. The fuel and oxidant are not stored in the cell. No pollutants and hence fuel cells are environmentally friendly. No toxic species are formed in a fuel cell. They do not need charging.

Fuel Cells Advantages Limitations They offer high energy conversions (almost 75%). These cells have high energy density. These cells use inexpensive fuels. Limitations The electrodes used are either Pt, Ag or the alloys of noble metal which are prohibitively costly. The power generated is moderate.

Cell Representation Frequently used fuels are hydrogen, methanol, ethanol, hydrazine, formaldehyde, CO And alkane. Oxidants could be more oxygen or air.

Hydrogen–Oxygen Fuel Cell Setup consists of chambers. First chamber Serves as inlet for hydrogen, second for oxygen. There are two electrodes Hydrogen passes over anode and oxygen passes Over cathode. In middle, is a proton exchange membrane Separating two electrodes from one another, Where these two gases can interact with each other. Electrolyte separating two electrodes is an ion-conducting material When electricity is applied following reactions takes place

Water is released in the fourth chamber Water is released in the fourth chamber. Anodic reaction gives protons and electrons. These are separated and hydrogen ions are allowed to pass through the electrolyte to the cathode while Electrons travel via an external circuit as DC to power electrical devices. In the cathode, hydrogen ions combine with oxygen to form water along with the heat , Completing the circuit,

Advantages of Hydrogen–Oxygen Fuel Cell It just emits water vapor and no other harmful chemicals to the environment. High Efficiency Hydrogen is the lightest element and provides a lot of energy, and also it can be transported easily to places where required. Hydrogen fuel can replace the use of batteries and causes less noise pollution.

Limitations of Hydrogen–Oxygen Fuel Cell Hydrogen is explosive. For very good efficiency, it turns out to be very expensive, and even the initial research which is to be carried out costs a lot of money. Hydrogen is actually gas, so a large investment of cost and energy is required to compress it into liquefied form. While using these fuel cells in an automobile, a high pressure is created inside the engine, which is quite risky. Another great disadvantage would be that since hydrogen is never present as it is, but always in combined form with either oxygen or some other element, it needs to be separated first.