The fuel cell is a kind of chemical device that directly converts the chemical energy of fuel into electrical energy, which is also called electrochemical generator. It is the fourth power generation technology after hydropower generation, thermal power generation and atomic power generation. Because the fuel cell converts part of the Gibbs free energy in the chemical energy of the fuel into electrical energy through an electrochemical reaction, it is not limited by the Carnot cycle effect, so it has high efficiency. Besides, fuel cells use fuel and oxygen as raw materials and emit very few harmful gases. Thus it can be seen that fuel cell is the most promising power generation technology for saving energy and protecting the ecological environment. Fuel cell catalyst refers to the catalyst that can be used in a fuel cell.
Figure 1. Alcohol fuel cell electrode catalyst
Based on the existing research, the fuel cell catalysts can be divided into Pt-based materials and non-Pt materials. Compared with the latter, the former has better compatibility with the current technology and, to some extent, is closer to commercialization.
- Platinum-based catalyst: At present, Pt-based catalyst is still the main choice of fuel cell catalyst. Since the successful use of Pt alloy as fuel cell cathode material in 1980, Pt alloy has been regarded as the second generation fuel cell catalyst after pure Pt catalyst. Due to its excellent catalytic activity and durability, Pt alloy catalyst has been successfully used in phosphoric acid fuel cell power generation. In addition, some researchers deposited the monolayer Cu on another metal (such as Pd) whose oxidation potential is higher than the Cu reduction potential, and then replaced the monolayer Cu with Pt to obtain an M@Pt core-shell catalyst. The core-shell structure catalyst has a monolayer Pt atomic shell and a very high electrochemical active area, which can greatly save the amount of Pt.
Figure 2. Illustration of Pt monolayer deposition on a foreign metal core involving the Cu UPD and subsequent Pt displacement.
- Carbon-based catalyst: Among the non-precious metal catalysts, carbon-based materials are one of the most studied fuel cell catalysts because of their low cost, high electrical conductivity and good stability. They mainly include non-metallic heteroatom-doped carbon materials, metal/nitrogen co-doped carbon materials, and carbon catalysts coated with nanoparticles. Some researchers have reported that macrocyclic complex CoPc/C can be used as a cathodic reaction catalyst, which opens up a new field for the study of electrode reaction catalysts. In addition, some 3D transition metals such as Fe, Co, Mn, Ni and Zn have been successfully doped into nitrogen-containing carbon materials. The center of metal element is the active site of catalysis, so even if the content of metal elements is small, it may have an important effect on the activity of cathodic reaction.
- Transition metal chalcogenide compounds: Studies have shown that Mo4Ru2Se8 has cathodic catalytic activity under acidic conditions. However, metal chalcogenide compounds are easy to be oxidized when exposed to air for a long time and exhibit catalytic effect under acidic conditions. There is also a large gap between the activity of metal chalcogenide compounds and the activity of Pt/C catalysts, so it is difficult to replace Pt-based catalysts with metal chalcogenide compounds.
- Zhang J, Vukmirovic M B, Xu Y, et al. (2005) "Controlling the Catalytic Activity of Platinum-Monolayer Electrocatalysts for Oxygen Reduction with Different Substrates". Angewandte Chemie International Edition, 44(14): 2132-2135.
- Zhou W P, Sasaki K, Su D, et al(2010)."Gram-Scale-Synthesized PdzCo-Supported Pt Monolayer Electrocatalysts for Oxygen Reduction Reaction". The Journal of Physical Chemistry C,114(19):8957-8957.