(1)AFC: Compared with other fuel cells, AFC has higher power density and
specific power and reliable performance. However, it uses pure hydrogen as fuel,
pure oxygen as oxidant, and must use precious metals such as PT, Au, and Ag as
catalysts, which are expensive. The corrosion of the electrolyte is serious and
the life is short. These characteristics determine that AFC is limited to
aerospace or special applications and is not suitable for civilian use.
(2) pAFC: Using phosphoric acid as the electrolyte, it can tolerate the
presence of CO2 in fuel gas and air. This makes pAFC the first fuel cell to be
applied on the ground or for civilian use. Compared with AFC, it can operate at
180°C to 210°C. The fuel gas and air processing system is greatly simplified.
When running under pressure, it can form a cogeneration of heat and power.
However, the power generation efficiency of pAFC can currently only reach 40% to
45% (LHV). It requires precious metal platinum as an electrocatalyst; the fuel
must be externally reformed: and the concentration of CO in the fuel gas must be
less than 1% (175℃) - 2% (200℃), otherwise the catalyst will be poisoned; the
corrosive effect of the acidic electrolyte will make it difficult for the pAFC
life to exceed 40,000 hours. pAFC's current technology has matured and its
products have entered commercialization. As a distributed power supply, on-site
portable power supply and backup power supply for special users, pAFC still has
a market, but it is difficult to use it as a large-capacity centralized power
station.
(3) MCFC: operating at 650°C to 700°C, nickel can be used as the
electrocatalyst instead of precious metals: the fuel can be internally reformed,
which improves power generation efficiency and simplifies the system; CO can be
directly used as fuel; waste heat can be used The temperature is higher and a
gas/steam combined cycle can be formed to further increase the power generation
capacity and efficiency. Compared with SOFC, the advantages of MCFC are: lower
operating temperature, lower-priced metal materials can be used, simple
manufacturing process of electrodes, separators, and bipolar plates, relatively
small technical difficulties in sealing and assembly, and easy to increase
capacity , lower cost. The disadvantages are: a CO2 circulation system must be
configured; H2S and CO in the fuel gas are required to be less than 0.5ppM;
molten carbonate is corrosive and volatile; compared with SOFC, the life is
shorter; the efficiency of combined cycle power generation is lower than SOFC .
Compared with low-temperature fuel cells, the disadvantage of MCFC is that it
takes a long time to start up and is not suitable for backup power supply. MCFC
is close to commercialization, and the scale of the demonstration power plant
has reached 2MW. Judging from the technical characteristics and development
trends of MCFC, MCFC is one of the ideal choices for future civil power
generation (distributed power sources and central power stations).
(4) SOFC: The electrolyte is a solid and can be made into a tube shape, a
plate shape or a whole shape. Compared with liquid electrolyte fuel cells (AFC,
pAFC and MCFC), SOFC avoids the problems of electrolyte evaporation and
corrosion of battery materials, and the battery has a longer life (has reached
70,000 hours). CO can be used as fuel, making it possible for fuel cells to use
gas as fuel. The operating temperature of SOFC is around 1000°C, and the fuel
can be reformed within the cell. Due to the high operating temperatures, sealing
between metal and ceramic materials is also difficult. Compared with
low-temperature fuel cells, SOFC has a longer start-up time and is not suitable
for emergency power supply. Compared with MCFC, SOFC's combined cycle has higher
efficiency and longer life (can be greater than 40,000 hours); however, SOFC
faces greater technical difficulties and may be more expensive than MCFC.
Demonstration performance proves that SOFC is one of the ideal choices for
future fossil fuel power generation technology. It can be used as both a small
and medium-capacity distributed power supply (500kw-50MW) and a large-capacity
central power station (>100MW). In particular, the demonstration of combining
pressurized SOFC with micro gas turbine to form a combined cycle power
generation will further demonstrate the advantages of SOFC.
(5) pEFC: pEpC has a low operating temperature (about 80°C), its startup
time is very short, and it can reach full load within a few minutes. Compared
with pAFC, the current density and specific power are higher, the power
generation efficiency is also higher (45% to 50% (LHV)), and the allowable value
of CO is higher (<10ppm). The waste heat temperature of pEFC is low and the
heat utilization rate is low. Compared with liquid electrolyte fuel cells such
as pAFC and MCFC, it has the characteristics of long life and reliable
operation. pEFC is an ideal portable power supply and one of the ideal choices
for power supplies for mobile tools such as electric vehicles, special
applications, and spacecraft. At present, there is a certain market in mobile
power supplies, distributed power supplies for special users and household power
supplies, which are not suitable for large-capacity central power stations.
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