File Name: batteries and fuel cells .zip
Make sure you thoroughly understand the following essential ideas which have been presented below. One of the oldest and most important applications of electrochemistry is to the storage and conversion of energy. You already know that a galvanic cell converts chemical energy to work; similarly, an electrolytic cell converts electrical work into chemical free energy. Devices that carry out these conversions are called batteries. In ordinary batteries the chemical components are contained within the device itself.
If the reactants are supplied from an external source as they are consumed, the device is called a fuel cell. The term battery derives from the older use of this word to describe physical attack or "beating"; Benjamin Franklin first applied the term to the electrical shocks that could be produced by an array of charged glass plates. In common usage, the term "call" is often used in place of battery.
For portable and transportation applications especially, a battery or fuel cell should store and be able to deliver the maximum amount of energy at the desired rate power level from a device that has the smallest possible weight and volume.
The following parameters are commonly used to express these attributes:. A secondary or storage battery is capable of being recharged; its electrode reactions can proceed in either direction. During charging, electrical work is done on the cell to provide the free energy needed to force the reaction in the non-spontaneous direction. A primary cell , as expemplified by an ordinary flashlight battery, cannot be recharged with any efficiency, so the amount of energy it can deliver is limited to that obtainable from the reactants that were placed in it at the time of manufacture.
The cell is represented by. The reaction proceeds to the right during discharge and to the left during charging. The state of charge can be estimated by measuring the density of the electrolyte; sulfuric acid is about twice as dense as water, so as the cell is discharged, the density of the electrolyte decreases. The technology of lead-acid storage batteries has undergone remarkably little change since the late 19th century. There are also a few other problems:. The most well-known primary battery has long been the common "dry cell" that is widely used to power flashlights and similar devices.
The electrode reactions are. Despite its name, this cell is not really "dry"; the electrolyte is a wet paste containing NH 4 Cl to supply the hydrogen ions. The chemistry of this cell is more complicated than it would appear from these equations, and there are many side reactions and these cells have limited shelf-lifes due to self discharge.
In some of the older ones, attack by the acidic ammonium ion on the zinc would release hydrogen gas, causing the battery to swell and rupture, often ruining an unused flashlight or other device.
A more modern version, introduced in , is the alkaline cell which employs a KOH electrolyte and a zinc-powder anode which permits the cell to deliver higher currents and avoids the corrosive effects of the acidic ammonium ion on the zinc.
Clearly, these are all primarily kinetic and mechanistic factors which require a great deal of experimentation to understand and optimize. Conventional batteries supply electrical energy from the chemical reactants stored within them; when these reactants are consumed, the battery is "dead". An alternative approach would be to feed the reactants into the cell as they are required, so as to permit the cell to operate continuously. In this case the reactants can be thought of as "fuel" to drive the cell, hence the term fuel cell.
Although fuel cells were not employed for practical purposes until space exploration began in the 's, the principle was first demonstrated in by Sir William Grove, a Welsh lawyer and amateur chemist.
At the time, it was already known that water could be decomposed into hydrogen and oxygen by electrolysis; Grove tried recombining the two gases in a simple apparatus, and discovered what he called "reverse electrolysis"— that is, the recombination of H 2 and O 2 into water— causing a potential difference to be generated between the two electrodes:.
It was not until that the first working hydrogen-oxygen fuel cell was developed by Francis Thomas Bacon in England. Modern cells employ an alkaline electrolyte, so the electrode reactions differ from the one shown above by the addition of OH — to both sides of the equations note that the net reaction is the same :.
Although hydrogen has the largest energy-to-mass ratio of any fuel, it cannot be compressed to a liquid at ordinary temperatures. If it is stored as a gas, the very high pressures require heavy storage containers, greatly reducing its effective energy density. Some solid materials capable of absorbing large amount of H 2 can reduce the required pressure. Other fuels such as alcohols, hydrocarbon liquids, and even coal slurries have been used; methanol appears to be an especially promising fuel.
One reason for the interest in fuel cells is that they offer a far more efficient way of utilizing chemical energy than does conventional thermal conversion. The work obtainable in the limit of reversible operation of a fuel cell is kJ per mole of H 2 O formed.
This limit is a consequence of the Second Law of Thermodynamics. The major limitation of present fuel cells is that the rates of the electrode reactions, especially the one in which oxygen is reduced, tend to be very small, and thus so is the output current per unit of electrode surface.
Coating the electrode with a suitable catalytic material is almost always necessary to obtain usable output currents, but good catalysts are mostly very expensive substances such as platinum, so that the resulting cells are too costly for most practical uses. There is no doubt that if an efficient, low-cost catalytic electrode surface is ever developed, the fuel cell would become a mainstay of the energy economy.
Certain types of bacteria are able to oxidize organic compounds to carbon dioxide while directly transferring electrons to electrodes. These so-called electricigen organisms may make it possible to convert renewable biomass and organic waste directly into electricity without the wasted energy and pollution produced by direct combustion. In one experiment, a graphite electrode immersed in ordinary mud containing humic materials was able to produce measurable amounts of electricity.
Make sure you thoroughly understand the following essential ideas which have been presented above. It is especially imortant that you know the precise meanings of all the highlighted terms in the context of this topic. Chem1 Virtual Textbook. Learning Objectives Make sure you thoroughly understand the following essential ideas which have been presented below. A battery is a galvanic cell in which some of the free energy change associated with a spontaneous electron-transfer reaction is captured in the form of electrical energy.
A secondary or storage battery is one in which the electron-transfer reaction can be reversed by applying a charging current from an external source. A fuel cell is a special type of battery in which the reactants are supplied from an external source as power is produced. The cathodic reduction of O 2 is kinetically limited, necessitating the use of electrode surfaces having high catalytic activity.
The electrodes in batteries must have very high effective surface areas, and thus be highly porous. This requirement may conflict with the other important one of efficient diffusion of reactants and products in the narrow channels within the pores. Batteries and fuel cells designed to power vehicles and portable devices need to have high charge-to-weight and charge-tovolume ratios. Introduction The term battery derives from the older use of this word to describe physical attack or "beating"; Benjamin Franklin first applied the term to the electrical shocks that could be produced by an array of charged glass plates.
Primary and Secondary Batteries A secondary or storage battery is capable of being recharged; its electrode reactions can proceed in either direction. There are also a few other problems: The sulfuric acid electrolyte becomes quite viscous when the temperature is low, inhibiting the flow of ions between the plates and reducing the current that can be delivered.
This effect is well-known to anyone who has had difficulty starting a car in cold weather. These batteries tend to slowly self-discharge, so a car left idle for several weeks might be unable to start.
Over time, PbSO 4 that does not get converted to PbO 2 due to lack of complete discharge gradually changes to an inert form which limits the battery capacity. Also, "fast" charging causes rapid evolution of hydrogen from the water in the electrolyte; the bubbles form on the lead surface and can tear PbO 2 off the positive plate.
Eventually enough solid material accumulates at the bottom of the electrolyte to short-circuit the battery, leading to its permanent demise. The Fuel Cell Conventional batteries supply electrical energy from the chemical reactants stored within them; when these reactants are consumed, the battery is "dead".
Commonly used electrolytes are NaOH solution, phosphoric acid, or solid oxides. A major limitation of any oxygen-consuming fuel cell is the slow rate of the reduction of this element at a cathode. The best cathode surfaces are usually made of platinum, which is a major cost factor in fuel cell design.
Microbobial Fuel Cells Certain types of bacteria are able to oxidize organic compounds to carbon dioxide while directly transferring electrons to electrodes. Summary Make sure you thoroughly understand the following essential ideas which have been presented above.
Many people get confused by the difference between a battery and a fuel cell. Both can be used as sources of power — but in different ways. The electrical energy contained within a battery is either from the factory where it was made, or from charging the battery via an outlet. If your battery dies, you are dependent on either being near a source of electricity to re-charge, or near a store to buy a new one. A fuel cell is different.
PDF | This study provides an analysis of the technological barriers for all-electric vehicles, either based on batteries (BEVs) or on H2-powered proton | Find.
In this section we outline the key principles and processes occurring within a range of different fuel cells. Electricity is perhaps the most versatile and easy to exploit form of energy. Fuel cell technology offers the opportunity of creating environmentally friendly portable power supplies capable of producing enough energy to run devices and motor vehicles. The basic principle is simple: Oxygen from the air is reacted with hydrogen Stored in the device to form water. This is a redox process in which electrons are transferred, the trick of a fuel cell is to use the electrons generated during the reaction to perform work.
Applied Chemistry pp Cite as. Electrochemistry is concerned with the effect of electrical voltages and currents on chemical reactions ionics and chemical changes which produce the voltages and currents electrodics. This is illustrated in Table 9.
A fuel cell, uses an external supply of chemical energy and can run indefinitely, as long as it is supplied with a source of hydrogen and a source of oxygen usually air. The source of hydrogen is generally referred to as the fuel and this gives the fuel cell its name, although there is no combustion involved. Oxidation of the hydrogen instead takes place electrochemically in a very efficient way.
Use the form on the right to subscribe to Connection , our monthly public roundup of fuel cell and hydrogen energy news. The Fuel Cell and Hydrogen Energy Association FCHEA is the trade association for the fuel cell and hydrogen energy industry, and is dedicated to the commercialization of fuel cells and hydrogen energy technologies. Fuel cells and hydrogen energy technologies deliver clean, reliable power to leading edge corporate, academic and public sector users, and FCHEA members are helping to transform our energy future. FCHEA represents the full global supply chain, including universities, government laboratories and agencies, trade associations, fuel cell materials, components and systems manufacturers, hydrogen producers and fuel distributors, utilities and other end users. A fuel cell is a device that generates electricity through an electrochemical reaction, not combustion. In a fuel cell, hydrogen and oxygen are combined to generate electricity, heat, and water. Fuel cells are used today in a range of applications, from providing power to homes and businesses, keeping critical facilities like hospitals, grocery stores, and data centers up and running, and moving a variety of vehicles including cars, buses, trucks, forklifts, trains, and more.
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