Fuel cell

catalyst (catalyst) is one of the key materials of fuel cell, its role is to reduce the activation energy of the reaction, promote the REDOX process of hydrogen and oxygen on the electrode, and improve the reaction rate. Due to the low exchange current density of oxygen reduction reaction (ORR), it is the control step of the total reaction of fuel cell. At present, the commonly used commercial catalyst in fuel cells is Pt/C, a supported catalyst consisting of Pt nanoparticles dispersed onto a carbon powder (such as XC-72) carrier.

Proton exchange membrane is a polymer electrolyte membrane, which plays an important role in conducting protons, isolating cathode and anode reactants in fuel cells, and is also used as a catalyst support in the preparation of CCM membrane electrodes, which is the core device of fuel cells and a key component that determines the performance, life and cost of fuel cells. In practical applications, the proton exchange membrane is required to have high proton conductivity and good chemical and mechanical stability.

membrane electrode assembly MEA (membrane electrode assembly MEA) is a combination of membrane, catalytic layer and diffusion layer, and is also one of the core components of fuel cells. At present, 3 generations of MEA technology routes have been developed internationally (Figure 4). Among them, the first and second generation technology has been basically mature, and domestic new source power, Wuhan New Energy and other companies can provide membrane electrode products. The third generation of ordered membrane electrode technology is still in the research stage at home and abroad.

The function of bipolar plates in fuel cells is to conduct electrons, distribute reactive gas and assist in discharging generated water, which requires that the bipolar plate material is a good conductor of electricity and heat, has a certain strength and gas density. In terms of performance stability, the bipolar plate is required to have corrosion resistance in the fuel cell acidic (pH=2 ~ 3), potential (~ 1.1V), wet and hot (gas-water two-phase flow, ~ 80℃) environment, and is compatible with other fuel cell components and materials without pollution, and has a certain hydrophobicity to assist the discharge of water generated by the battery. From the aspect of productization, the bipolar plate material is required to be easy to process and low cost. The bipolar plate materials commonly used in fuel cells include hard carbon plate, composite bipolar plate and metal bipolar plate.

The Fuel Cell Stack is the core of the fuel cell power generation system. Usually in order to meet certain power and voltage requirements, the stack is usually formed by hundreds of single batteries in series, and the reaction gas, water, refrigerant and other fluids are usually in parallel or in a specially designed way (such as series parallel) through each single battery. The uniformity of fuel cell stack is an important factor restricting the performance of fuel cell stack.

3. Main types of fuel cells

Normally, fuel cells can be divided into phosphate fuel cells, solid oxide fuel cells, alkaline fuel cells, proton exchange membrane fuel cells, lysocarbonate fuel cells, etc., as shown in Table 1. In recent years, with the deepening of the research on fuel cells, direct carbon fuel cells, microbial fuel cells, direct methanol fuel cells, glucose /O2 enzyme fuel cells and so on have been gradually born. Among the above categories, the earliest fuel cells to be developed are phosphoric acid fuel cells and alkaline fuel cells, also known as the first generation of fuel cells, which have developed more mature technologies. The second generation fuel cell is a molten carbonate fuel cell, and the third generation fuel cell is a solid oxide fuel cell.

4. Current status and future R&D direction

China has a layout in the vehicle, system and stack, but there are still fewer relevant enterprises in the parts and components, especially the most basic key materials and components, such as proton exchange membrane, carbon paper, catalyst, air compressor, hydrogen circulation pump, etc. Although relevant domestic enterprises have begun to intervene, there is still a large gap in reliability and durability compared with international advanced products, and most of the key components and key materials are still dependent on imports.

Although fuel cell vehicles are developing rapidly, from the perspective of commercialization requirements, there is still a certain gap in China's automotive fuel cell technology, and the future needs to strengthen the layout of the following aspects:

1) Improve fuel cell stack performance and specific power. At present, the power level of domestic fuel cell vehicle stack is still generally low. Domestic automotive fuel cell piles are mainly 30 ~ 50 kW, which is far from the fuel cell power level of about 100 kW for international premium vehicles.

2) Improve the durability of the fuel cell. Improving the durability of fuel cell stacks and systems is a prerequisite for fuel cell commercialization. At present, improving the system control strategy is one of the effective ways to improve the durability of fuel cell vehicles.