The working principle of the fuel cell

The working principle of the fuel cell

A fuel cell is a power generation device that directly converts the chemical energy of fuel and oxidant into electrical energy. In 1839, British scientist W.R.Grove discovered and verified the phenomenon of fuel cells in the laboratory. However, due to the failure of the research on the dynamics of generators and electrode processes to keep up, the research on fuel cells did not make substantial progress until the 1950s. In the 1960s, fuel cells were successfully applied to the Apoiio spacecraft. Since then, hydrogen-oxygen fuel cells have been widely used in the aerospace field, and at the same time, megawatt-level phosphoric acid fuel cells have also been successfully developed. Since the 1980s, various low-power fuel cells have also begun to be used in various fields such as aerospace, transportation, and military. In February 2014, according to the Physicists Organization Network, American scientists developed a low-temperature fuel cell that can directly use biomass as a raw material. This fuel cell can convert rice straw, sawdust, algae and even organic fertilizers into electricity with the help of solar energy or waste heat. The energy density is nearly 100 times higher than that of cellulose-based microbial fuel cells. According to forecasts by the international energy community, fuel cells will be one of the most attractive power generation methods in the 21st century.

A fuel cell is essentially an electrochemical device, which can generate electrical energy by feeding fuel and air into the fuel cell separately. Its composition is similar to that of a general battery, mainly composed of anode, cathode and electrolyte. The anode is equivalent to the negative electrode, that is, the fuel electrode; the cathode is equivalent to the positive electrode, that is, the oxidizer electrode. The difference is that the general battery stores the active material inside the battery, so the battery capacity is limited; while the anode and cathode of the fuel cell itself do not contain any active material, it is just a catalytic converter, and its fuel and oxidant are supplied externally. Therefore, the fuel cell cannot “storage electricity”, but is a “power plant” that converts chemical energy into electrical energy.

The process of decomposing water into hydrogen and oxygen using electricity is usually the electrolysis of water. Fuel cells use the reverse reaction of water electrolysis, that is, hydrogen and oxygen synthesize water and output electrical energy. Since there are many types of electrolytes that can be used in fuel cells, different types of fuel cells have different electrochemical reactions. The following uses an acid fuel cell as an example to illustrate the working principle of the fuel cell.

Figure 1 shows the working principle diagram of the fuel cell. During operation, fuel (H2 or other fuel) is supplied to the anode of the fuel cell, and oxidant (air or O2) is supplied to the cathode. H2 decomposes at the anode, releasing electrons and producing hydrogen ions (also called protons). Hydrogen ions enter the electrolyte, while electrons move to the cathode along the external circuit. On the cathode, oxygen combines with the hydrogen ions in the electrolyte and the electrons on the electrode to form water. The electrons move from the anode to the cathode through the external circuit to form a current, and the electrical load connected to the external circuit can obtain electrical energy.

The working principle of the fuel cell
Figure 1 – Working principle diagram of fuel cell

Its chemical reaction formula is

Anode: H2=2H++2e

Cathode: 2H++1/2O2+2e=H2O

The total reaction formula: H2+1/2O2=H2O

Generally, in order to accelerate the electrochemical reaction on the electrode, a catalyst is added to the electrode of the fuel cell, which is generally made into a porous shape to increase the contact surface between the fuel, the electrolyte and the electrode. This kind of porous electrode containing catalyst is also called gas diffusion electrode, which is a key component of fuel cell.

In addition to the above components, the fuel cell also needs a set of corresponding auxiliary systems, including a reactant supply system, a heat rejection system, a drainage system, a control system, and a safety system. Since hydrogen is the most important fuel for fuel cells, fuel cells are usually associated with the use of hydrogen energy.

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