Fuel cell

Complete analysis of fuel cell - comparison and prospect

Fuel cell is the fourth-generation power generation technology after hydropower, thermal power, and nuclear power generation, and have broad application prospects in both military and civilian applications.
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Fuel cell operates continuously with little pollution. The electric energy output per unit weight of the fuel cell is large, and the output power per unit weight is large. This article will introduce the working principle and classification of fuel cell, as well as analyze the characteristics and comparison of fuel cell and lithium ion battery.

How does fuel cell works

The fuel cell contains two electrodes, positive and negative, which are filled with electrolyte respectively, and the gap between the two electrodes is composed of a permeable membrane. Hydrogen enters the fuel from the anode, and oxygen (or air) enters the cell from the cathode. Through the action of the catalyst, the hydrogen atoms in the anode are decomposed into hydrogen protons and electrons.

Among them, protons enter the electrolyte, are “attracted” by oxygen to the other side of the film, electrons form a current through an external circuit, and then reach the cathode. Under the action of the cathode catalyst, hydrogen protons, oxygen and electrons react to form water molecules. This is exactly the inverse of the electrolysis of water, so water is the only emission from the fuel cell. Using this principle, the fuel cell can continuously transmit electricity to the outside when it is working, and it is a kind of “generator”.

Types of fuel cells
Hydorgen fuel cell

Types of fuel cells

According to the fuel cell electrolyte

1.Alkaline fuel cell (AFC): Alkaline fuel cell has high efficiency and its development is very mature, but its working conditions require the isolation of CO2, and its application fields are mainly concentrated in aerospace.

2.Phosphoric acid fuel cell (PAFC): Phosphoric acid fuel cell technology is called the first-generation fuel cell, which is the closest to commercial fuel cell, but phosphoric acid fuel cell needs to use precious metal platinum catalyst, the cost is high, and its work The temperature is not high enough, and the waste heat utilization value is low.

3.Molten carbonate fuel cell (MCFC): Molten carbonate fuel cell is called the second generation fuel cell. Due to its high operating temperature, the requirements for battery materials are also high.

4. Solid oxide fuel cell (SOFC): Solid oxide fuel cell is called the third generation fuel cell. It has high working efficiency and is considered to be the most suitable for cogeneration with good performance. Due to its high operating temperature, the requirements for battery materials are also high. Compared with the proton exchange membrane fuel cell (PEMFC), its unique advantages are more obvious, such as not using noble metal catalysts, more fuel selectivity, high waste heat temperature, and high power generation efficiency.

5. Proton exchange membrane fuel cell (PEMFC): Proton exchange membrane fuel cell technology has developed rapidly in the near future. It uses a thinner polymer membrane as the electrolyte, which has high specific power and low operating temperature. It is especially suitable as a portable power supply and a vehicle power supply for new energy vehicles. However, the main problem at present is the cost is too high.

Direct methanol fuel cell (DMFC) is a kind of proton exchange membrane fuel cell. DMFC, which is still in the development stage, uses perfluorosulfonic acid membrane as electrolyte, and its working temperature is from room temperature to 200°C. It is used for micro mobile power supply.

Fuel cell type AFC PAFC PEMFC MCFC SOFC
Electrolyte Potassium hydroxide solution Phosphoric acid Proton permeable membrane Potassium carbonate Solid oxide
Fuel Pure hydrogen Natural gas, Hydrogen Hydrogen, methanol, Natural gas Natural gas, Coal gas, Biogas Natural gas, Coal gas, Biogas
Oxidizer Pure hydrogen Air Air Air Air
Efficiency 60%~90% 37%~42% 43%~58% 50%~60% 50%~65%
Working temperature 60~120 160~220 60~120 600~1000 600~1000

According to the operation mechanism of fuel cell

Acid fuel cell
Alkaline fuel cell

According to fuel type

Hydrogen fuel cell
Methane fuel cell
Methanol fuel cell
Ethanol fuel cell

Regarding fuel cells, we have also sorted out the top 10 fuel cell manufacturers in China for your reference.

What fuels can be used in fuel cell

Fuel cells can flexibly use various types of fuels. While hydrogen is the most common fuel source (hence the colloquial name hydrogen fuel cell), hydrogen-rich fuels such as natural gas and ammonia are also feasible.

Hydrogen: When hydrogen is produced using renewable electricity such as solar, wind and hydroelectric power, the production process can be completely carbon-neutral. Hydrogen fuel cell that use hydrogen as fuel, generate electricity, heat and water without releasing carbon dioxide or other pollutants into the air.

Natural gas: Since green hydrogen has not yet been mass-produced, natural gas is still the main source of hydrogen production. In this case, the fuel cell is not completely emission-free, but it does emit much lower emissions than other fuels such as oil and coal.

Ammonia: Ammonia is mainly used as a fertilizer in agriculture. In recent years, some companies have devoted themselves to the development of green ammonia, which can be driven by water electrolysis to produce hydrogen through alternative energy sources, which makes it an alternative low-carbon fuel.

What fuels can fuel cell use

Features and performance of fuel cell

1.High power generation efficiency

Fuel cell power generation is not limited by the Carnot cycle. In theory, its power generation efficiency can reach 85% to 90%. However, due to the limitations of various polarizations during work, the current energy conversion efficiency of fuel cell is about 40% to 60%. If cogeneration of heat and power is realized, the total utilization rate of fuel can be as high as 80%.

2.Less environmental pollution

When the fuel cell uses hydrogen-rich gas such as natural gas as fuel, the emission of carbon dioxide is reduced by more than 40% compared with the heat engine process, which is very important for alleviating the global warming effect.

In addition, because the fuel gas of the fuel cell must be desulfurized before the reaction, and the electricity is generated according to the electrochemical principle, there is no high-temperature combustion process, so almost no nitrogen and sulfur oxides are emitted, which reduces the pollution to the atmosphere.

3. High specific energy

The specific energy of the liquid hydrogen fuel cell is 800 times that of the nickel-cadmium battery, and the specific energy of the direct methanol fuel cell is more than 10 times higher than that of the lithium-ion battery (the rechargeable battery with the highest energy density). At present, although the actual specific energy of the fuel cell is only 10% of the theoretical value, it is still much higher than the actual specific energy of the general battery.

4.Low noise

The fuel cell has a simple structure, few moving parts, and low noise during operation. Even in the vicinity of an 11MW class fuel cell power plant, the measured noise is less than 55dB.

For fuel cell, as long as substances containing hydrogen atoms can be used as fuels, such as natural gas, petroleum, coal and other fossil products, or biogas, alcohol, methanol, etc., therefore, fuel cell is very suitable for the needs of energy diversification and can slow down the exhaustion of mainstream energy sources.

Comparison of lithium-ion battery vs fuel cell

Comparison of lithium-ion battery vs fuel cell

The working principle of the fuel cell: its battery directly turns into electrical energy through the chemical action of hydrogen and oxygen without burning, so no pollutants are produced, and the fuel utilization rate is very high. The working principle of the lithium battery is also the working principle of the hybrid. Most of the hybrid models now (in the initial stage) use lithium batteries.

Fuel cell cannot store electricity, that is, they are used immediately, and there is no electricity without refueling. In other words, lithium batteries convert energy from electrical energy to chemical energy to electrical energy, while fuel cell directly convert chemical energy into electrical energy.

Lithium batteries can store electricity, are easy to carry, and can be used as batteries for mobile power. Lithium batteries are widely used in household energy storage, golf carts, power wheels, and other equipment. The common specification of lithium battery is 12v lithium ion battery. Fuel cell was born for electric/hybrid vehicles. Both batteries are the most popular source of power for cars.

In terms of cruising range, fuel cell has more advantages, almost twice that of lithium-ion batteries

Both fuel cell and lithium-ion battery have low impact on the environment. The combustion product of the former is water, and does not produce the greenhouse gas generated after gasoline/diesel combustion. The discharge products of lithium-ion batteries may be lithium oxide, lithium hydroxide, etc., and will not affect the environment. In addition, lithium-ion batteries are reusable.

Fuel cell will charge faster than Li-ion battery.

However, because lithium batteries are more mature, the cost of charging stations and batteries is much lower than that of fuel cell.

Both types of batteries are promising, but their future directions may differ. Lithium batteries are more suitable for passenger cars, while hydrogen fuel cell is more suitable for commercial vehicles. Lithium-ion battery systems are more suitable for replacing gasoline engines, and hydrogen fuel cell systems are more suitable for replacing diesel engines. This is the reason why current technical research focuses on fuel cell commercial vehicles. For the comparison of fuel cells and other batteries, you can also refer to flow battery vs fuel cell.

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