What are the types of fuel cells?

At present, there are 5 kinds of known fuel battery type. The name associated with the corresponding electrolyte.

(1) The alkaline fuel cell (AFC) - using potassium hydroxide solution as electrolyte.

The electrolytic efficiency is very high (up to 60. 90%), but affect the purity of impurities, such as carbon dioxide is very sensitive. In the operation, it needs to adopt the pure hydrogen and oxygen. This limits the applied to space flight, and international engineering and other fields.

(2) the proton exchange membrane fuel cell (PEMFC) using a very thin plastic film as the electrolyte. This electrolyte with high power weight ratio and low working temperature Is an ideal material suitable for fixed and mobile device.

(3) phosphoric acid fuel cell (PAFC) with 200 ℃ high temperature of phosphoric acid as the electrolyte. It is very suitable for use in a decentralized cogeneration system.

(4) the molten carbonate fuel cell (MCFC) working temperature is 650 ℃.The battery efficiency is very high, but the material demand is high.

(5) solid chi oxygen fuel cell (SOFC) is a solid electrolyte used (drill

Stone oxide), performance is very good. They need to adopt the corresponding material and process

Technology, because the battery working temperature is about 1000 ℃.

Fuel cell is a kind of the chemical energy of fuel is directly converted into electricity chemical plant, also known as electrochemical generators. It is following the hydropower, thermal power andspecial power generation of the fourth kind of power generation technology. Due to the chemical energy of the fuel cell is through electrochemical reaction fuels of gibbs free energy into electricity, is not limited by car not cycle effect, so the high efficiency; In addition, the fuel cell with fuel and oxygen as no mechanical transmission parts at the same time, so there is no noise raw material, the emission of harmful gases, rare. Noise pollution. Thus, from the point of view of saving energy and protect the ecological environment, the fuel cell is the most promising power generation technology.[1]

The chemical energy of fuel and oxidant by electrochemical reaction directly converted into electricity power. Fuel cells can run under the thermal efficiency of close to 100% in theory, has the very high efficiency. The actual operation of the fuel cell, due to various technical factors limit, to consider the whole device of energy dissipation system, the overall conversion efficiency was 45% ~ 60% more range, if consider heat utilization can reach more than 80%.In addition, the fuel cell devices contain little or no moving parts, reliable operation, less need maintenance, compared with the conventional generating set and quiet. Additional electrochemical reaction clean, completely, seldom produces harmful substances. All of this makes the fuel cell is seen as a very promising energy power plant.[2]

Fuel cell is an electrochemical power generation device, according to the electrochemical methods of isothermal and direct convert chemical energy into electrical energy without a heat engine process, not limited by carnot cycle, high energy conversion efficiency, and no noise, no pollution, is an ideal way of energy utilization. At the same time, along with fuel cell technology matures, and provided the sufficient natural gas source for the west to east gas pipeline project, the commercialization of fuel cell application there are broad prospects for development.[3]

Fuel cell is an energy conversion device, it is according to the principle of electrochemistry, the galvanic battery principle, isothermal stored in the chemical energy of the fuel and oxidant directly into electrical energy, thus the actual process is REDOX reaction. Fuel cell is mainly composed of four parts, namely anode, cathode, electrolyte and external circuit. Fuel gas and oxidation air access by fuel cell anode and cathode respectively. Fuel gas at the anode discharge, electronic conduct by the external circuit to the cathode and combine with oxidizing gas generating ions. Ion under the effect of electric field, through the electrolyte to the anode, and fuel gas reaction, constitute a loop, an electrical current. At the same time, because of itself of electrochemical reaction and battery internal resistance, fuel cell will produce certain heat. The extremes of Yin and Yang battery in addition to the conduction electrons have REDOX reaction catalyst. When the fuel is hydrocarbon anode require higher catalytic activity. Yin and Yang poles usually a porous structure, so that the reaction product gas bubbled into and discharge. The electrolyte ion and separation of fuel gas, the action of oxidizing gas. To stop the two gases mixed results in a short circuit in the battery, the electrolyte is usually dense structure.[3]

Fuel cell is an electrochemical device this principle, the composition and general battery is the same. Its monomer battery consists of two electrodes (cathode electrodes and the anode the fuel-oxidizer electrode) and the composition of the electrolyte. Different is generally of the active material inside the battery storage batteries, therefore, limit the battery capacity. And fuel battery positive and negative does not contain active substances, is a catalytic conversion components. So the fuel cell is to convert chemical energy into electricity energy conversion machine. Batteries fuel and oxidant have external supply, reaction. In principle, as long as the constant input of reactants, reaction product out continuously, fuel cells can continuously generate electricity. Here to hydrogen - oxygen fuel cell as an example to illustrate the fuel cell

Hydrogen - oxygen fuel cell reaction principle of this reaction is the inverse process of electrolysis of water. Electrode should be followed: the cathode: H2 + oh - 2-2 h2o + 2 e -

The positive: 1/2 o2 + H2O + e - 2-2 oh -

Cell response: H2 + o2 = = 1/2 H2O

In addition, only the fuel cell body can't work,

A fuel cell

A fuel cell

Have a set of corresponding auxiliary system, including reactant supply system, heat removal system, drainage system, electrical control system and safety device, etc.

Fuel cells are usually formed by ion conductive electrolyte plate and the pole (anode) on both sides of the configuration of fuel and air (cathode), and on both sides of the gas flow, the effect of gas flow is to make the fuel gas and air (oxidant gas) in the flow through.

Because of work in practical fuel cell electrolyte is different, after the electrolyte ion species associated with reaction is different also. PAFC and reaction of PEMFC related to hydrogen ions (H +), the reaction is:

Fuel is: H2 = = 2 h + + e - 2 (1)

Air is extremely: 2 1/2 o2 + 2 h + + e - = = H2O (2)

All: H2 + o2 = = 1/2 H2O (3)

In fuel is, the supply of fuel gas H2 into H + and - e, H + mobile to the electrolyte and air supply side reaction of O2.E - via external load circuit, and then reverse back to the air side, participate in air side reaction. A series of reactions contributed to the e - continuously through the external circuit, thus make up power generation. And can be seen from the equation (3) of the type, H2O, generated by the H2 and O2 in addition no other response, H2 has chemical energy into electrical energy. But in fact, with the electrode reaction has certain resistance, can lead to some of the heat energy produced, thus reduced the proportion of converted into electricity. Cause the reaction of a group of cells known as components, the resulting voltage is usually lower than a volt. Therefore, in order to make greater efforts to adopt component multilayer superposition method for high voltage reactor. Electrical connection between components and between the fuel gas and air separation, adopted called clapboard, equipped with gas in the upper and lower sides flow components, PAFC and the partition of PEMFC are composed of carbon materials. Heap of output is determined by the product of the voltage and current, current and battery in reaction area ratio.

PAFC electrolyte concentrated phosphoric acid aqueous solution and proton conductivity polymer electrolytes for PEMFC membrane. Adopt the porous carbon electrodes, in order to promote the reaction, with Pt as the catalyst, CO of the fuel gas will cause poisoning, reduce the electrode performance. For PAFC and the application of PEMFC must limit amount of CO is contained in fuel gas, especially for the low temperature work should strictly restrict PEMFC.

Fuel cell is the basic composition and reaction principle of phosphate: fuel gas or city gas after adding water vapor to the modification, the fuel is converted into a mixture of H2, CO and water vapor, CO and water further hitches in shift reactor catalyst agent into H2 and CO2.After dealing with the so of fuel gas into the heap of the cathode (fuel), at the same time carry oxygen to the positive (air) of the fuel assembly for chemical reaction, with the effect of catalyzer quickly generate electricity and heat.

Type relative PAFC and PEMFC, the high temperature fuel cell MCFC and SOFC don't catalyst, the CO as the main ingredient of coal gasification gas can be applied directly as a fuel, but also is easy to use the high quality exhaust constitute a combined cycle power generation, etc.

MCFC main components. Contains electrode reaction related electrolytes (usually for Li mixed with K carbonate) and up and down with the following 2 pieces of plate electrode (fuel with air pole), and two electrodes respectively the lateral flow of fuel gas and oxidant gas chamber, electrode holder, etc., about 600 ~ 700 ℃ in MCFC electrolyte working temperature of molten liquid, the formation of ion conductive body. Nickel was porous plasmids, the formation of the air chamber with resistance to corrosion of metal.

The working principle is the MCFC. Air of O2 (air) combined with electricity, and CO2 generated CO32 - (carbonate ion), electrolyte CO32 - will be moved to the fuel side, combined with as a fuel supply of H +, release e -, H2O and CO2 generated at the same time. Chemical reaction is as follows:

Fuel is: H2 + CO32 - = = H2O + CO2 + 2 e - (4)

Air, CO2 + o2 + 2 e - 1/2 = = CO32 - (5)

All: H2 + o2 = = 1/2 H2O (6)

In the reaction, e - presence of PAFC, it from the fuel is let out, through the external circuit reverse back to the air, in the external loop by e - uninterrupted flow of fuel cell power generation is realized. In addition, the biggest characteristic of MCFC, must want to have help to response the CO32 - ions, therefore, the supply of oxidant gases must contain carbonic acid gas. And, inside the battery pack catalyst, which will serve as the principal component of natural gas CH4 modification inside the battery, the battery internal directly generate H2 method has been developed. And under the condition of the fuel is gas, its main ingredients CO and H2O reaction generated H2, therefore, can be equivalent to CO to use as a fuel. In order to obtain larger output, usually adopt Ni clapboard and stainless steel to make.

SOFC is composed of ceramic materials, electrolyte usually adopt ZrO2 (ZrO2), it constitutes the O2 - conductive Y2O3 (yttrium oxide) as a stabilization of YSZ (stabilized zirconia) and use. Fuel is used in electrode Ni and YSZ composite porous metal ceramic, air pole adopts LaMnO3 (lanthanum oxide manganese).Partition using LaCrO3 (lanthanum oxide and chrome).In order to avoid because of the shape of the battery, the electrolyte, etc., caused by thermal expansion difference between crack developed work under low temperature SOFC. Battery shapes in addition to the flat as well as other fuel cells, and developed in order to avoid stress concentration of cylinder. SOFC equation is as follows:

Fuel is: H2 + O2 - = = H2O + 2 e - (7)

Air is extremely: 1/2 O2 + 2 e - = = O2 - (8)

All: H2 + o2 = = 1/2 H2O (9)

Fuel, H2 by the electrolyte and mobile, react with O2 - generated H2O and e -.Air generated by O2 and e - O2 -.All the same as other fuel cells generated by H2 and O2 H2O.In the SOFC, because of its type belongs to hot work, therefore, in the case of no other catalysis can directly internally tries to use the principal component reformed into H2 CH4 gas, and gas ingredient CO can directly use as a fuel.

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