Name: 燃料電池 (Fuel cell)
Uploaded: 2021-01-14T06:25:54.000Z
Duration: 57 min 26 s
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關係子句

A fuel cell is a device that converts the chemical energy from a fuel into electricity

through a chemical reaction with oxygen or another oxidizing agent.

Hydrogen produced from the steam methane reforming of natural gas is the most common fuel, but

for greater efficiency hydrocarbons can be used directly such as natural gas and alcohols

like methanol. Fuel cells are different from batteries in that they require a continuous

source of fuel and oxygen/air to sustain the chemical reaction whereas in a battery the

chemicals present in the battery react with each other to generate an electromotive force.

Fuel cells can produce electricity continuously for as long as these inputs are supplied.

The first fuel cells were invented in 1838. The first commercial use of fuel cells came

more than a century later in NASA space programs to generate power for probes, satellites and

space capsules. Since then, fuel cells have been used in many other applications. Fuel

cells are used for primary and backup power for commercial, industrial and residential

buildings and in remote or inaccessible areas. They are also used to power fuel-cell vehicles,

including forklifts, automobiles, buses, boats, motorcycles and submarines.

There are many types of fuel cells, but they all consist of an anode, a cathode and an

electrolyte that allows charges to move between the two sides of the fuel cell. Electrons

are drawn from the anode to the cathode through an external circuit, producing direct current

electricity. As the main difference among fuel cell types is the electrolyte, fuel cells

are classified by the type of electrolyte they use followed by the difference in startup

time ranging from 1 sec for PEMFC to 10 min for SOFC. Fuel cells come in a variety of

sizes. Individual fuel cells produce relatively small electrical potentials, about 0.7 volts,

so cells are "stacked", or placed in series, to increase the voltage and meet an application's

requirements. In addition to electricity, fuel cells produce water, heat and, depending

on the fuel source, very small amounts of nitrogen dioxide and other emissions. The

energy efficiency of a fuel cell is generally between 40–60%, or up to 85% efficient in

cogeneration if waste heat is captured for use.

The fuel cell market is growing, and Pike Research has estimated that the stationary

fuel cell market will reach 50 GW by 2020.

The first references to hydrogen fuel cells appeared in 1838. In a letter dated October

1838 but published in the December 1838 edition of The London and Edinburgh Philosophical

Magazine and Journal of Science, Welsh physicist and barrister William Grove wrote about the

development of his first crude fuel cells. He used a combination of sheet iron, copper

and porcelain plates, and a solution of sulphate of copper and dilute acid. In a letter to

the same publication written in December 1838 but published in June 1839, German physicist

Christian Friedrich Schönbein discussed the first crude fuel cell that he had invented.

His letter discussed current generated from hydrogen and oxygen dissolved in water. Grove

later sketched his design, in 1842, in the same journal. The fuel cell he made used similar

materials to today's phosphoric-acid fuel cell.

In 1939, British engineer Francis Thomas Bacon successfully developed a 5 kW stationary

fuel cell. In 1955, W. Thomas Grubb, a chemist working for the General Electric Company,

further modified the original fuel cell design by using a sulphonated polystyrene ion-exchange

membrane as the electrolyte. Three years later another GE chemist, Leonard Niedrach, devised

a way of depositing platinum onto the membrane, which served as catalyst for the necessary

hydrogen oxidation and oxygen reduction reactions. This became known as the "Grubb-Niedrach fuel

cell". GE went on to develop this technology with NASA and McDonnell Aircraft, leading

to its use during Project Gemini. This was the first commercial use of a fuel cell. In

1959, a team led by Harry Ihrig built a 15 kW fuel cell tractor for Allis-Chalmers, which

was demonstrated across the U.S. at state fairs. This system used potassium hydroxide

as the electrolyte and compressed hydrogen and oxygen as the reactants. Later in 1959,

Bacon and his colleagues demonstrated a practical five-kilowatt unit capable of powering a welding

machine. In the 1960s, Pratt and Whitney licensed Bacon's U.S. patents for use in the U.S. space

program to supply electricity and drinking water. In 1991, the first hydrogen fuel cell

automobile was developed by Roger Billings. UTC Power was the first company to manufacture

and commercialize a large, stationary fuel cell system for use as a co-generation power

plant in hospitals, universities and large office buildings. UTC Power continues to be

the sole supplier of fuel cells to NASA for use in space vehicles, having supplied fuel

cells for the Apollo missions, and the Space Shuttle program, and is developing fuel cells

for cell phone towers and other applications. Types of fuel cells; design

Fuel cells come in many varieties; however, they all work in the same general manner.

They are made up of three adjacent segments: the anode, the electrolyte, and the cathode.

Two chemical reactions occur at the interfaces of the three different segments. The net result

of the two reactions is that fuel is consumed, water or carbon dioxide is created, and an

electric current is created, which can be used to power electrical devices, normally

referred to as the load. At the anode a catalyst oxidizes the fuel,

usually hydrogen, turning the fuel into a positively charged ion and a negatively charged

electron. The electrolyte is a substance specifically designed so ions can pass through it, but

the electrons cannot. The freed electrons travel through a wire creating the electric

current. The ions travel through the electrolyte to the cathode. Once reaching the cathode,

the ions are reunited with the electrons and the two react with a third chemical, usually

oxygen, to create water or carbon dioxide.

The most important design features in a fuel cell are:

The electrolyte substance. The electrolyte substance usually defines the type of fuel

cell. The fuel that is used. The most common fuel

is hydrogen. The anode catalyst breaks down the fuel into

electrons and ions. The anode catalyst is usually made up of very fine platinum powder.

The cathode catalyst turns the ions into the waste chemicals like water or carbon dioxide.

The cathode catalyst is often made up of nickel but it can also be a nanomaterial-based catalyst.

A typical fuel cell produces a voltage from 0.6 V to 0.7 V at full rated load. Voltage

decreases as current increases, due to several factors:

Mass transport loss. To deliver the desired amount of energy, the

fuel cells can be combined in series to yield higher voltage, and in parallel to allow a

higher current to be supplied. Such a design is called a fuel cell stack. The cell surface

area can also be increased, to allow higher current from each cell. Within the stack,

reactant gases must be distributed uniformly over each of the cells to maximize the power

output. Proton exchange membrane fuel cells

In the archetypical hydrogen–oxide proton exchange membrane fuel cell design, a proton-conducting

polymer membrane separates the anode and cathode sides. This was called a "solid polymer electrolyte

fuel cell" in the early 1970s, before the proton exchange mechanism was well-understood.

On the anode side, hydrogen diffuses to the anode catalyst where it later dissociates

into protons and electrons. These protons often react with oxidants causing them to

become what are commonly referred to as multi-facilitated proton membranes. The protons are conducted

through the membrane to the cathode, but the electrons are forced to travel in an external

circuit because the membrane is electrically insulating. On the cathode catalyst, oxygen

molecules react with the electrons and protons to form water.

In addition to this pure hydrogen type, there are hydrocarbon fuels for fuel cells, including

diesel, methanol and chemical hydrides. The waste products with these types of fuel are

carbon dioxide and water, when hydrogen is used the CO2 is released when methane from

natural gas is combined with steam in a process called steam methane reforming to produce