In essence, fuel cell is a kind of power generation device that can isothermal and directly convert the chemical energy stored in fuel and oxidizer into electricity, which has the advantages of high efficiency and no pollution. Furthermore, fuel cell does not have to go through thermal engine process, and it is not limited by Carnot cycle, so the energy conversion efficiency of the full cell is high. Therefore, fuel cells have attracted worldwide attention once reported. Fuel cells generate electricity in the same way as chemical power sources, with electrodes providing a place for electron transfer. During fuel cell operation, the anode catalyzes fuel and the cathode catalyzes oxidant. Moreover, conducting ions migrate in an electrolyte that separates anode from cathode, and electrons pass through an external circuit to do work and form an electrical circuit. At the anode, hydrogen reacts with OH- in the base to produce water and electrons under the action of an electrocatalyst. The electrons pass through the external circuit to the cathode and participate in the reduction reaction of oxygen under the action of cathode electrocatalyst.
- Proton exchange membrane fuel cells (PEMFC): Proton exchange membrane fuel cells are mainly used in stationary power supply and mobile power supply. Stationary power supply can be divided into large scale central power plant and small decentralized configuration power plant. Mobile power supply includes portable power supply, vehicle power supply and others. Proton exchange membrane is the core component of proton exchange membrane fuel cell. It is not only a membrane material, but also the substrate of electrolyte and electrode active material. In addition, the proton exchange membrane is a selective permeable membrane, mainly plays the role of conducting protons to separate oxidizer and reducing agent.
Figure 1. Schematic representation of proton exchange membrane fuel cell.
- Solid oxide fuel cell (SOFC): Solid oxide fuel cell is one of the most promising power generation technologies because of its outstanding advantages such as high energy conversion efficiency, environmental friendliness, strong fuel applicability and non-corrosion. One of the key technologies of solid oxide fuel cell is its structural design, which requires compact structure and high compactness. The battery pack must have sufficient mechanical strength, and the cost should be moderate. The current structural design of SOFC can be divided into tubular SOFC, flat SOFC, integrated SOFC and segmented SOFC. From the practical point of view, the component form of SOFC unit structure mainly adopts tubular design and flat plate design.
Figure 2. The operation of solid oxide fuel cell.
- Others: Other major types of fuel cells include alkaline fuel cell, phosphoric acid fuel cell, molten carbonic acid fuel cell and direct alcohol fuel cell. Alkaline fuel cell is the first generation of fuel cell, which has been successfully used in the space flight field in the 1960s. Phosphoric acid fuel cell is also the first generation fuel cell, which has entered commercial application and mass production. At present, the United States, Japan and European countries have many generators put into use or in the installation. Moreover, molten carbonic acid fuel cell is the second generation fuel cell. At present, the research countries of molten carbonate fuel cell are the United States, Japan and Western Europe. Direct alcohol fuel cell is a kind of cell that uses alcohol as fuel directly.
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