Fuel cell is an electrochemical reaction device that converts the chemical energy of fuel and oxidizer directly into electrical energy. In order to improve the redox reaction rate of fuel cells, catalysts are usually used. However, using catalyst alone has the problem of large amount of consumption and high price. To solve this problem, catalyst supports are developed. The catalyst support is a special component of solid catalyst, which is dispersant, binder and carrier of active component. In most cases, the catalyst support itself is inert solid material with no activity, and it is present in high concentrations in the catalyst. As one of the key materials of fuel cell, catalyst support distributes the catalytic active group on the surface of the support. The catalyst support not only directly affects the particle size, dispersion and activity of the catalyst, but also affects the conductivity, mass transfer and electrochemical specific surface area of the catalyst layer.
- Carbon nanotube support: In 1911, Japanese scientists discovered carbon molecules made of tube-like coaxial nanotubes, known as carbon nanotubes. Since the discovery of carbon nanotubes, they have triggered a hot wave of research because of the unique structure, good electrical conductivity and mechanical properties. Carbon nanotubes can be divided into single-walled carbon nanotubes and multi-walled carbon nanotubes according to the number of layers of the graphene sheet. A large number of studies have found that the catalyst of fuel cell can be loaded on carbon nanotubes, which can improve the utilization rate of catalyst. Meanwhile, due to the graphitized structure of carbon nanotubes, the stability of carbon nanotubes is relatively high. In addition, carbon nanotubes have good mechanical properties and electrical conductivity. These characteristics make carbon nanotubes an excellent catalytic support for fuel cells.
Figure 1. An example of carbon nanotube used as a catalyst support.
- Mesoporous carbon support: Mesoporous carbon is a kind of new non-silicon-based mesoporous materials discovered recently, which has the advantages of high specific surface area, high pore volume, high porosity and controllable pore size. Because of these advantages, mesoporous carbon can be used in fuel cell as catalyst support. The most commonly used method to prepare mesoporous carbon is hard template method. Mesoporous molecular sieve is usually used as template to select appropriate precursors, which are carbonized under acid catalysis and deposited in the channels of mesoporous materials. Finally, mesoporous carbon can be obtained after the Si group is dissolved with NaOH or HF.
- Others: In addition to the materials described above, catalyst supports also include carbon aerogel carriers, conductive ceramic carriers, tungsten carbide and others. Carbon aerogel is the product of carbonized organic aerogel at high temperature. It has a very small density and is a kind of nanoporous network amorphous carbon material with light weight, well-developed mesopore, large specific surface area, stable electrochemical performance and good electrical conductivity. Conductive ceramics generally have good corrosion resistance, so if used as fuel cell catalyst support, it can have good corrosion resistance in fuel cell working environment. Tungsten carbide powder is black hexagonal crystal, which is a good conductor of electricity and heat. Because of these properties, tungsten carbide can be used as catalyst support for fuel cells.
Figure 2. Crystal structure of TiN ceramic and the atomic structure model of Pt embedded on an N-vacancy sit.
- Tavakkoli M, Holmberg N, Kronberg R, et al. Electrochemical Activation of Single-Walled Carbon Nanotubes with Pseudo-Atomic-Scale Platinum for the Hydrogen Evolution Reaction[J]. Acs Catalysis, 2017:3121-3130.
- Oran Lori and Lior Elbaz. Advances in Ceramic Supports for Polymer Electrolyte Fuel Cells[J]. Catalysts, 2015, 5(3), 1445-1464.