With the aggravation of environmental pollution and the shortage of fossil energy, the development and utilization of alternative energy materials has become a hot topic in the world today. Alternative energy material not only has less pollution emissions, but also alleviates the problem of energy shortage to a certain extent. As a kind of green renewable new energy conversion device, fuel cell has the possibility of large-scale promotion and use in the world, so it is favored by scientists all over the world. Nowadays, great breakthroughs have been made in the research of fuel cells. However, due to the slow redox reaction rate of fuel cells, catalysts have become one of the key factors restricting the commercialization of fuel cells. Therefore, how to prepare more stable catalysts with high activation energy and low cost is particularly important for the development of fuel cell industry.
- Noble metal catalysts: Noble metal catalyst mainly refers to platinum catalyst, which is the most efficient fuel cell electrode catalyst. Platinum catalysts have high catalytic activity, excellent environmental adaptability, minimal manufacturing process and durable stability, which make them the best choice for cathode catalysts for fuel cells. In addition, platinum catalysts have a broad application prospect because of the long life and the nature of regeneration, activation and reuse.
- Non-noble metal and oxide catalysts: On the basis of the research on noble metal catalysts, scientists began to study some non-noble metal compound catalysts, hoping to replace noble metal catalysts with lower preparation cost. Such catalyst materials mainly include cobalt phthalocyanine and transition metal oxides. With the deepening of research, transition metal oxides have become the mainstream materials in this direction due to their advantages of abundant resources, cheap raw materials, easy preparation and environmental friendliness. In addition, the researchers also found that the transition metal oxides have higher catalytic activity and better stability under alkaline conditions. Furthermore, when the transition metal elements are mainly iron, copper, cobalt and nickel, these metal elements have strong adsorption capacity for oxygen, which is an important research direction for researchers.
Figure 1. An example of transition metal oxide catalyst used in fuel cell.
- Others: In addition to the above catalysts, there are many other types of fuel cell catalysts including carbon nanomaterial catalyst, hetero-atom doped carbon nanomaterial catalyst, transition metal nitrogen-doped carbon material catalyst, diatomic doped transition metal carbon material catalyst and others. Currently, carbon nanomaterials studied by researchers mainly include carbon nanotubes, graphene and conductive carbon black, all of which have large specific surface area and good electrochemical and mechanical properties. In addition, along with the research of carbon nanomaterial catalyst, people hope to improve the performance of carbon nanomaterial catalyst by atomic doping, so the doped carbon nanomaterial catalysts appear. For example, due to the high electronegativity of nitrogen atoms, the incorporation of nitrogen atoms into carbon nanomaterials will make some carbon atoms in the original carbon material gain positive charge, making them become active centers, thus improving the catalytic activity of carbon nanomaterials. Furthermore, the process of nitrogen atom doping is relatively simple, and experiments show that nitrogen atom doped carbon material has higher activity and better stability.
Figure 2. An example of doped carbon nanomaterial catalyst used in fuel cell.
- Tran P D, Morozan A, Archambault S, et al. A noble metal-free proton-exchange membrane fuel cell based on bio-inspired molecular catalysts[J]. Chemical Science, 2015, 6(3):2050-2053.
- Shui J, Wang M, Du F, et al. N-doped carbon nanomaterials are durable catalysts for oxygen reduction reaction in acidic fuel cells[J]. Science Advances, 2015, 1(1):e1400129-e1400129.