What is meant by the fuel cell
The fuel cell is that one kind changes into a device of the electric energy chemical energy into directly, do not need to charge, so long as supplement the fuel and oxidant in succession, can operate and generate electricity in succession. The fuel and oxidant can't be mixed, but enter in the fuel cell separately, produce and react specifically in the positive pole of the battery and negative pole.
The fuel produced electrons after electric chemical reaction, the electron flows into another electrode and oxidant and reacts via the electrode and outside line way, after the oxidant accepts electrons, produce the ion, and is conducted the ion by the electrolyte in the battery, form the return circuit that the battery operated.
Enter fuel of the fuel cell Such as the hydrogen And oxidant ( Such as the oxygen) Must all pass the catalysis of the catalyst, in order to raise the speed of reacting, this text focuses on the catalyst that is used in the low temperature type fuel cell of the introduction.
Electric catalysis catalyst of the low-temperature fuel cell
The electric catalysis is the associations of electrochemistry and catalyst, we usable catalyst electrode, make electric chemical reaction can in close to theory voltage and high electric current go on under the density
And the fuel cell utilizes the electric catalysis catalyst to change chemical energy into a power generator of the electric energy directly.
This kind of fuel cell operated under lower temperature, usually mean that uses the whole Fluorine of E.I . Du Pont de Nemours & Company to lead the high polymer electrolyte membrane fuel cell of the proton membrane, comparatively a ripe one is the system taking hydrogen and oxygen as charge-in for engineering at present.
Use the system of direct charge-in of methyl alcohol to call the fuel cell of direct methyl alcohol ( DMFC) Besides acid system, the soda fuel cell that still navigates and uses too systematically ( AFC) .
Accelerate the positive pole catalyst that hydrogen atoms oxidize
Hydrogen molecule and metal mutual interaction different looks phenomenon catalysis promoter know very well.
With the platinum ( Pt) It is the example, when a piece of hydrogen molecule is absorbed by the platinum, will solve from two hydrogen atoms, and two these absorb hydrogen atoms at platinum might is it produce hydrogen molecule and is it enclose into the gaseous state hydrogen to take off to recombine too, this kind of change course is angry - Firm looks surface science desire most ardently research theme one of that find out about fully.
In order to make the area of function reacting increase, is it use valuable metal quantity to reduce, make platinum into about 10 size endure rice (1 endure the rice usually =10-9 metres) Platinum particle,it is in this the dark in platinum of gradeses in fuel cell, because particle little to endure rice magnitudes of yardstick, platinum lose original metallic luster and appear black, so it is black to call the platinum. Adopt the carbon carrier with bigger dispersiveness in order to increase the area of reacting further, called the carbon and supported the platinum catalyst.
The centimeter of every square of platinum consumption only takes about 0.5 milligrams in such a catalyst ( mg) ,Can cable, catalysis of hydrogen oxidize. Molecule absorbs the hydrogen on the surface in the platinum particle, resolve it into specific hydrogen atoms and absorb on a platinum atom, affected by electrochemical electric potential, hydrogen atoms may be oxidized into the proton (the hydrogen and ion) And the electron, the proton conducts the membrane to move to the negative pole from the proton, and the electron is via the neighbouring metal conductor of platinum, conducting it to the carbon structure of supporting, pass to the other circuit, this is a generator system of the fuel cell.
The platinum catalyst of the carbon carrier, its carbon material supported is usually Vulcan XC-72R, it is a conductive material of a kind of high surface area.
Certainly, still have other carbon material of model, BP2000 for instance endure rice carbon in charge of etc.,
In order to make the hydrogen keep in touch with the catalyst surface, the positive pole of the fuel cell is the penetrating electrode of a kind of gas, whom gas enter to spread layer, that electrolyte combine layer catalyst layer inside membrane have with the whole Fluorine.
So electrode catalyst dragon material getting firm by iron, form swimming skill of dredging and kiss hole area of swimming skill, this design can offer the passway where the hydrogen entered, and can prevent the aqueous vapor from condensing but flooded the passway.
The whole Fluorine membrane electrolyte and then because of the electrode, the design is it sell proton and passway that gas pass to construct altogether too, offer hydrogen result and channel that reactant passed in and out, molecule of oxidizing process.
The proton is transmitted, the electron is conducted and the gas should have the rightest arrangement that melts penetratingly, make it become the angry, firm, most effective electrode system of three-phase interface of liquid.
Summarize but the speech, in the penetrating electrode structure of gas, the platinum particle is each independent electrodes, and concentrate on conducting out the electric current with the carbon carrier, so gas penetrating catalyst layer of electrode can regard as one group electrode of person who disperse contact system.
The ones that considered to hydrogen oxidized reacting, besides platinum, such valuable metal as the Pd, gold,etc.
Negative pole catalyst reducing oxygen
The negative pole catalyst reducing oxygen, still take platinum particle catalyst that the carbon supports as the core mainly, but in the soda fuel cell system, can use the non- valuable metal shutting things of the Large Loop by mistake.
These chemical compounds have N-4 chelas to shut the structure of things, such as iron tetramethoxyphenylporphrin ( FeTMPP) , cobalt tetramethoxyphenylporphrin ( CoTMPP) , iron octaethylporphrin ( FeOEP) . tetramethoxyphenylporphrin(FeTMPP), tetramethoxyphenylporphrin(CoTMPP) , octaethylporphrin(FeOEP) . The catalysis of these catalysts, is similar to the Large Loop structure of the ferroheme basically, transition metal iron absorb principle of oxygen molecule, oxygen molecule absorbed to make go on electrochemistry is it react to reduce.
To absorb behavior is it is it to react to oxygen, is it is it go on important factor very to react to determine to reduce oxygen. be simple, after the oxygen dissolves and becomes and dissolves oxygen in the electrolyte first, spread to the surface near the electrode, and then but affix to metal surface electric chemical reaction via absorbing. No matter acid or soda system, oxygen is reduced and reacted two all right ways go on, one is the transformation route of four electrons, another route for forming the hydrogen of oxidizing.
Roughly come up and distinguish, the responses of four electrons mostly go on on such valuable metal catalysts as the platinum,etc.; And cross and oxidize the hydrogen ( The thing) In the route, the transformation of two electrons take place in the carbon more ( C) , gold ( Au) And N-4 chela is shut on the metal chemical compound of thing.
It was great that the corrosion ability of the acid solution came than the soda, so oxygen reduces catalysts, regard material that can be anticorrosive as the primary condition selected for use.
With the black electrode that prepared of platinum, platinum alloy or the carbon support the platinum catalyst (Pt/C) System, mainstream of now, future organic Large Loop shut thing may become oxygen reduce catalysts also by mistake.
Oxygen in the soda system reduces catalysts and can be divided into: Valuable metal ( Such as the platinum, lawrencium, iridium) ,Metal oxide ( If the iron or the cobalt is calcium titanium ore of the main fact and spinelle structure) ,Shut things by mistake in organic Large Loop.
One middle period such as times, general with dark to use soda fuel cell for of the electrode platinum have, lose original efficiency because the platinum is black in using the particle will be crescent, so the soda fuel cell system used in industry very much in the boat, use the platinum alloy or the carbon instead and support the platinum catalyst (Pt/C) .
. Shut things through being hot by mistake treatedly in organic Large Loop, in stability and efficiency, also have good behavior, have an opportunity to become the catalyst that oxygen reduced the negative pole in future.
Systematic catalyst of fuel cell oxidizing the methyl alcohol directly
Use the hydrocarbon to be the charge-in directly, can simplify the fuel system of the fuel cell, but with electric catalysis progress of technology at present, petroleum, or methane still very much difficult to go on the electric catalysis promoter in the normal atmospheric temperature, the high polymer membrane fuel cell of direct methyl alcohol charge-in is a system relatively hopeful to be commercialized at present. Methyl alcohol member form the derivative of the carbon monoxide often on the surface in catalyst, produce linear or bridge type chemical bond form, it absorbs to be difficult to take off enclosing at single platinum atom or two platinum atom, and make the platinum atom lose catalyst activation.
Solve the phenomenon of poisonning of this kind of carbon monoxide metal to the platinum, become and design the basic demand that the methyl alcohol oxidized the positive pole catalyst.
Pairs of function catalyst apply electric catalysis catalyst, can is it is it poison phenomenon better to absorb the effort to result in to reduce.
Use the platinum alloy like the platinum ruthenium (Pt-Ru) Or other metal can change the interdynamic that the metal can be taken with the carbon monoxide and molecule, and then reduce the carbon monoxide and molecule and metal key and form the intensity, this kind reduces function that catalysts are poisonned, called the essential mechanism.
If with the platinum and metal oxide ( Such as oxidizing the ruthenium) It is a catalyst, enable absorbing the carbon monoxide on the platinum, have moisture oxygen son offer that absorb neighbouring metal oxide, oxidize but form the course of the carbon dioxide, is called and promoted the mechanism.
As for the ruthenium catalyst of platinum taking carbon as carrier, have this two kinds of mechanisms at the same time, can reduce effectively because the carbon monoxide absorbs phenomena of poisonning produced strongly.
Go through ten research for one year develop, use platinum ruthenium, carbon of carrier catalyst still better choice nowadays.
Besides positive pole catalyst, the negative pole oxygen of the fuel cell of direct methyl alcohol reduces catalysts, use the above-mentioned negative pole catalyst system that reduced oxygen too.
Because the methyl alcohol will pass through the whole Fluorine membrane and reach the negative pole, it is by improving the catalyst activation or controlling the speed of charge-in and trying to reduce piercing through the speed of methyl alcohol, there is a great deal of methyl alcohol that will reach negative pole that oxygen reduces.