Analysis of structure and working principle of alkaline fuel cell and phosphoric acid fuel cell

  1. alkaline fuel cell

Alkaline fuel cell uses strong alkali (such as potassium hydroxide and sodium hydroxide) as electrolyte, hydrogen as fuel, pure oxygen or air removing trace carbon dioxide as oxidant, Pt / C, Ag, Ag Au and Ni with good catalytic activity for oxygen electrochemical reduction as electrocatalyst, and porous gas diffusion electrode as oxidation electrode; Pt Pd / C, Pt / C, Ni or nickel boride are used as electrocatalysts, and porous gas electrode is used as hydrogen electrode. With non porous carbon plate, nickel plate or various gold bipolar plate materials of nickel plating or even silver plating and gold plating, various shapes of gas flow channels can be processed on the plate surface to form bipolar plate metal (such as aluminum, magnesium and iron).

1.1. Structure and working principle of alkaline fuel cell

Taking the working principle of single cell in alkaline asbestos film hydrogen oxygen fuel cell as an example, at the anode, hydrogen and oh – in alkali undergo oxidation reaction under the action of electrocatalyst to generate water and electrons. The electrons reach the cathode through the external circuit. Under the action of cathode electrocatalyst, they participate in the reduction reaction of oxygen, and the generated Oh – moves to the hydrogen electrode through porous asbestos saturated with alkali solution.

structure and working principle of alkaline fuel cell
structure and working principle of alkaline fuel cell

1.2. Characteristics of alkaline fuel cell

Compared with other types of fuel cells, alkaline fuel cells have the following characteristics:

(1) Alkaline fuel cell has high efficiency (50% ~ 55%)

(2) The operating temperature is about 80 ℃, so they start quickly, but their power density is more than ten times lower than that of proton exchange membrane fuel cells.

(3) The performance is reliable, and non noble metals can be used as catalysts.

(4) Alkaline fuel cell is one of the fuel cells with the lowest production cost.

(5) Alkaline fuel cell is one of the fastest developing batteries in technology. It mainly provides power and drinking water for space missions, including the space shuttle, and then for transportation. It has a certain development and application prospect.

(6) The use of corrosive liquid electrolyte is dangerous and easy to cause environmental pollution. In addition, some methods used to solve CO2 Poisoning, such as using circulating electrolyte to absorb CO2, increase the complexity of the system.

  1. Phosphoric acid fuel cell

Phosphoric acid fuel cell is an acidic fuel cell with acid as electrolyte. It is the only commercially operated fuel cell in fuel cells at present.

2.1. Structure of phosphoric acid fuel cell

The cell sheet of phosphoric acid fuel cell is composed of fuel electrode composed of substrate and rib plate catalyst layer, electrolyte layer for maintaining phosphoric acid, porous support layer, porous catalyst layer, etc. At the fuel pole, the hydrogen atoms in the fuel release electrons to become atmosphere ions. Hydrogen ions pass through the electrolyte layer and react with oxygen ions at the air electrode to produce water. Several single cells are superimposed, and each cell is superimposed into a cooling plate to reduce the internal heat during power generation, so as to form a basic battery stack with stable output power. In addition, the components for upper and lower fixation and the manifold for gas supply constitute the battery stack of phosphoric acid fuel cell.

2.2. Working principle of phosphoric acid fuel cell

Phosphoric acid fuel cells use liquid phosphoric acid as electrolyte, which is usually located in silicon carbide matrix.

Phosphoric acid fuel cell uses hydrogen as fuel. When hydrogen fuel is injected into the anode, it is oxidized into protons under the action of catalyst. Hydrogen protons combine with water to form hydrated protons, and release two free electrons at the same time. The electrons move to the cathode, while hydrated protons move to the cathode through phosphoric acid electrolyte. Therefore, on the cathode, electrons, hydrated protons and oxygen generate water molecules under the action of catalyst. The electrode reaction equation is as follows.

Working principle of phosphoric acid fuel cell
Working principle of phosphoric acid fuel cell

2.3. Characteristics of phosphoric acid fuel cell

(1) The working temperature of phosphoric acid fuel cell is slightly higher than that of proton exchange membrane fuel cell and alkaline fuel cell, which is at 150 ~ 200 ℃, but the catalyst on the electrode is still needed to accelerate the reaction. The higher operating temperature also makes it more resistant to impurities. When the reactant contains 1% ~ 2% carbon monoxide and a small amount of sulfur, the phosphoric acid fuel cell can still work

(2) The efficiency of phosphoric acid fuel cell is about 40% lower than that of other fuel cells, and its heating time is also longer than that of proton exchange membrane fuel cell.

(3) Phosphoric acid fuel cell has the advantages of simple structure, stability and low electrolyte volatility. Phosphoric acid fuel cells can be used to power buses, and many such systems are running, but they are difficult to use in cars.

At present, phosphoric acid fuel cells can supply power to hospitals, schools and remote areas.

Read more: what is a proton membrane fuel cell。