**3. Types and Properties of Fuel Cell Systems**

Most fuel cells generate electricity and heat via the chemical reaction between hydrogen and oxygen, and water is created as the product. Various types of fuel cells are being studied, and each of these fuel cells is classified according to the characteristics of its electrolyte. The properties of these cells are described in Figure 1 and Table 3 [19,24].

**Figure 1.** Comparison of efficiency versus power generation in each type of fuel cell.


**Table 3.** Fuel cell types (catalyst, durability, and hydrogen storage).

Although there are various types of fuel cells, such as in Table 3, in this paper, MCFCs are considered to be the main power source for the base load of the ship and were applied on the test bed. Because MCFCs operate at a high temperature, they can achieve a fast reaction rate even with a comparatively low-cost catalyst, a simple system design of a fuel cell, and low initial investment cost. In addition, even when the ship is sailing for a long time, natural gas or coal gas can be directly used as a fuel without installing an external reformer separately [16,22,23].

## **4. Comparative Analysis of Fuel Consumption and CO2 Emission Reductions in Hybrid Power Sources vs. Conventional Commercial Diesel Generators**
