What is the performance of electrolyte-based fuel cells?

What is the performance of electrolyte-based fuel cells?

Practical fuel cells designed and developed during the 1960s and 1970s focused on the design configurations of three types of fuel cells using different electrolytes, the performance, reliability, and lifetime of which are described below with emphasis. Three different fuel cell designs are available depending on the type of electrolyte used in the cell. The potential advantages and disadvantages of each type are briefly described, with emphasis on efficiency, safety, and reliability. The three different fuel cell types are as follows:

● Use semi-solid molten electrolyte;
●Use of solid electrolyte;
● Use an aqueous electrolyte.

Based on the published literature, 10 aqueous electrolyte battery systems, 6 molten electrolyte battery systems, and 3 solid electrolyte battery systems were initially designed, developed, and tested by different scientists. As mentioned earlier, a fuel cell is an energy conversion device in which chemical energy is isothermally converted into direct current (DC). Furthermore, it can convert chemical energy into electrical energy without involving the thermodynamic relationships that limit the efficiency of heat engines as demonstrated by the Carnot cycle.

High-temperature fuel cells with semi-solid molten electrolytes. High temperature fuel cells contain a molten salt electrolyte, usually a mixture of salts such as sodium, potassium, and lithium carbonate. The electrolyte acts as an electrochemical liquid melt consisting of a porous mixture of MgO and Na, K, and lithium carbonate LiCO3. The magnesia disc is filled with molten salt. The electrode surfaces consist of metal powders such as silver for air or oxygen cathodes and iron, nickel and zinc oxide/silver mixtures for fuel anodes. The porous sheets firmly compress the powder to hold the metal powder against the electrolyte while conducting electricity, but they do not act as electrodes, as shown in Figure 1. At high operating temperature (500 ~ 750 ℃), the material is usually difficult to carry out electrochemical reaction to obtain a high current density of about 100 mA/cm² and a polarization voltage of 0.7 V, and the use of Ag electrode only has obvious effects on the carbon monoxide (CO) side. polarization but not on the air or oxygen side. As previously mentioned, hydrogen produces electricity in these fuel cells, but this may be due to rapid thermal decomposition or the formation of CO in the presence of steam. The efficiency of these cells is 30% to 35%, which is about 1/2 of the possible efficiency of cells that mainly use fuels such as coal, natural gas, and oil [2]. According to technical literature in the 1970s, because high temperature fuel cell technology exists There are many technical difficulties, and scientists are hesitant to study them more broadly. Instead, fuel cell designers have focused on low temperature cell research. When operating under moderate temperature and pressure conditions, the electrodes of double-framework catalysts require less weight and size without compromising the electrical performance and reliability of the battery.

What is the performance of electrolyte-based fuel cells?
Figure 1. High temperature fuel cell using semi-solid electrolyte and its key components

Typical electrical performances of semi-solid electrolyte fuel cells using tubular structures, sheet-like nickel anodes, silver cathodes, and double-framework catalyst electrodes are summarized in Table 1.

Current density/(mA/cm²)40°80°
500.040.02
1000.080.04
1500.140.08
2000.170.10
2500.220.14
3000.300.18
Table 1 Polarization voltage (V) of semi-solid electrolyte fuel cells with temperature and current density

The data presented in Table 1 shows 100% Faradaic efficiency, i.e. full utilization can be achieved with little polarization loss, and current density is limited by optimizing the microporous coating. Microscopic pores in the electrolyte must prevent gas leakage. For scientists and engineers in the field of electrochemistry, Faradaic efficiency refers to the efficiency of gas consumption.