Chem

NiCad battery reaction

Cd_(s) + NiO(OH)_(s) + 2H_2O_(l) -> 2Ni(OH)_2(s) + Cd(OH)_2(s)

Fuel Cell: Anode (oxidation half-reaction)

H_2 (g) -> 2H^+_(aq) + 2e^-

Overall fuel cell reaction:

H_2(g) + 1/2O_2(g) -> H_2O_(l)

Electrodes

electrical conductors placed in the cell as sites for chemical reactions; the chemical species oxidized in the cell and the species reduced must be connected in a way such that the electrons released during oxidation are transferred to the species being reduced; different processes take place at each electrode

n-type semiconductor

electrons move easily through the lattice, increasing the electrical conductivity of the material over that of pure silicon (Ar)

Cathode

receives the electrons sent from the anode through the external circuit; where reduction takes place

Reduction half-reaction

shows the reactant that GAINS electrons; the electrons appear on the reactant side of the equation

Oxidation half-reaction

shows the reactant that LOSES electrons; the electrons appear on the product side of the equation

lithium battery

take advantage of the low density of lithium metal to make a lightweight battery, but lithium-iodine cells are so reliable and long-lived that they are often the battery of choice for things such as a pacemaker

Lead-Acid Batteries

the best known rechargeable battery. Called storage batteries: because they "store" electrical energy; consists of six cells

Voltage

the difference in the electrochemical potential between the two electrodes; expressed in the unit called volt (V)

Anode

the electrode where oxidation takes place

Current

the rate of electron flow through an external circuit; measured in amperes (amps, A) or milliamps (mA) for small cells

Electricity

the transfer of electrons through an external circuit produces electricity; the flow of electrons from one region to another that is driven by a difference in potential energy

p-type semiconductor

there are freely moving positive charges, or holes (Gallium)

Direct Methanol Fuel Cell (DMFC):

uses a methanol-water solution as the fuel; increased portability and decreased size are two advantages to getting rid of the fuel reformer

Prius Engine

1.5 L gasoline engine sitting side-by-side w/ nickel metal hydride batteries, an Electric motor, and an electric generator;

Fuel Cell: Cathode (reduction half-reaction)

1/2*O_2_(g) + 2H^+_(aq) + 2e^- ->H_2O

Conversion rate

90%

NiCad battery

Nickel-cadmium battery; rechargeable

Lead-Acid Batteries Reaction

Pb(s) + PbO_2(s) + H_2SO_4(aq) -> PbSO_4(s) + 2 H_2O_(l)

Photovoltaic cells

convert radiant energy directly into electrical energy w/o the intermediary of hydrogen or some other fuel

battery

a battery is a devise consisting of one or more cells that can produce a direct current by converting chemical energy to electrical energy.

Galvanic Cell

a device that converts the energy released in a spontaneous chemical reaction into electrical energy, produce useful energy from reactions involving the transfer of electrons from one substance to another; always involves two half-reactions: one oxidation and the other reduction

Fuel cell

a galvanic cell that produces electricity by converting the chemical energy of a fuel directly into electricity without burning the fuel; sometimes called "flow" batteries because both fuel and oxidizer must constantly flow into the cell to continue the chemical reaction

Reforming

a process using heat, pressure, and catalysts to rearrange the atoms within molecules; allow gasoline or even diesel fuel to be used as the source of hydrogen

Half-reaction

a type of chemical equation that shows the electrons either lost or gained

electrolytic cell

cell in which electrical energy is converted to chemical energy

Doping

common method of adjusting the properties of a pure semiconductor material; a process of intentionally adding small amounts of other elements to pure silicon

Alkaline Battery

ex. AAA to D batteries of Duracell/Energizer; the cell voltage depends primarily on the chemicals that participate in the reaction; voltage does not depend on factors such as overall size of cell, amount of material it contains, or size of electrodes ALL ALKALINE CELLS HAVE SAME VOLTAGE: 1.54 V (flashlight, small appliances)

Fuel Cell: Source of Electrons

instead of the anode being the source of electrons, the anode is the electrode at which the oxidation of the fuel takes place; the other electrode behaves as the cathode, where reduction of the oxidant (usually oxygen) takes place

TRANSFER OF ELECTRONS

involves two changes

Microcells

literally very tiny fuel cells; will become reality before larger scale applications such as electrical generation and powering automobiles

PEM (proton exchange membrane)

permeable to H+ ions and is coated on both sides w/ a platinum-based catalyst; PEM fuel cells currently very popular w/ automakers

Distributed Generation

placing many power-generating modules of 30MW or less near the end user, as opposed to giant centralized power plants supplying many thousands of users; interests exist in using fuel cells to generate power at stationary locations that may or may not be connected to a power grid