# Portable Prototype of Hydrogen Fuel Cells for Educational Training
## 2 Theoretical Background
### Cell and the Stack
#### 2.3.2 Fuel Cell Stack and Components  
The anode is a negative electrode where the oxidation of fuel occurs. Free electrons produced are transferred from the anode to an external circuit. The anode is provided with fuel channels for the even distribution of fuel on the catalyst surface. The cathode is a positive electrode where reduction takes place. It is supplied with flow channels that help to distribute oxidants over the catalyst surface. At the cathode, electrons are collected from an external circuit that combines oxygen and hydrogen, forming water. The electrolyte helps conduct ions and is also called a proton exchange membrane. It is a permeable membrane that allows ions to pass through it while blocking electrons. Current collectors transfer electrons between two electrodes in the case of one cell, while in the case of a stack, they conduct electrons from one cathode to another cell's cathode. In most designs, structure integrity is provided by the current collector. Coolants are also provided to current collectors for the dissipation of waste heat.  
The one-cell voltage is 0.9 V, which is very small. Various cells are connected in series or parallel to draw a higher power output depending on the application's requirement for a higher voltage or current. For a series connection, the cathode and anode are connected. In contrast, for a parallel connection, the anode of one cell is connected to the anode of  
\begin{table}
\begin{tabular}{l c c c} \hline \hline  & **Alkaline** & **PEM** & **Solid Oxide** \\ \hline Electrolyte & 15-35\% NaOH or KOH & Perfluorosulfonic acid & ZrO\({}_{2}\) doped \\ Cell seperator & Diaphragm & Electrolyte membrane & Electrolyte membrane \\ Anode reaction & 4 OH\({}^{-1}\rightarrow\) O\({}_{2}+2H_{0}+4c^{-}\) & H\({}_{0}\)O \(\rightarrow\) 2H\({}^{+}\) + 0 SO\({}_{2}+2c^{-}\) & H\({}_{0}\)O + 2\(c^{-}\) \(\rightarrow\) H\({}_{2}+\) O\({}^{2-}\) \\ Cathode reaction & 2H\({}_{0}\)O + 2\(c^{-}\) + H\({}_{2}\) + 2 OH\({}^{+}\) & 2H \({}^{+}\) + 2\(c^{-}\) \(\rightarrow\) H\({}_{2}\) & O\({}^{2-}\) \(\rightarrow\) 0S \(\rightarrow\) 2\(c^{+}\) 2\(c^{-}\) \\ Typical Temperature & 50-20 C & 80-100 C & 750-1000 C \\ Durability & 100,000 h & 10,000-50,000 h & - 500 - 2000 h \\ Capacity & 1–700 Nm\({}^{3}\) per hour & 1–100 Nm\({}^{3}\) per hour & 1–10 Nm\({}^{3}\) per hour \\ Cost & 1300S per kWh & 200S per kWh & 2300S per kWh \\ \hline \multirow{4}{*}{Advantages} & \multicolumn{2}{c}{- Commercial technology} & \multicolumn{2}{c}{- Commercial technology} & \multicolumn{2}{c}{- High efficiency} \\  & \multicolumn{2}{c}{- Cost effective} & \multicolumn{2}{c}{- Fast dynamic characteristics} & \multicolumn{2}{c}{- High efficiency} \\  & \multicolumn{2}{c}{- High nominal output power} & \multicolumn{2}{c}{- Fast start operation} & \multicolumn{2}{c}{- Direct synthesis gas generation} \\  & \multicolumn{2}{c}{- Abundance of raw material} & \multicolumn{2}{c}{- Pure hydrogen output} & \multicolumn{2}{c}{- Still in development phase} \\ \hline \multirow{3}{*}{Disadvantages} & \multicolumn{2}{c}{- Slow cold start} & \multicolumn{2}{c}{- Electrodes are made of valuable electrodes} & \multicolumn{2}{c}{- High cost} \\  & \multicolumn{2}{c}{- vulnerability to impurities in} & \multicolumn{2}{c}{- High cost} & \multicolumn{2}{c}{- Slow start} \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison of different types of electrolyzers.  
another adjacent cell, and the same goes for cathodes. A conduction plate called a bipolar plate is used between the anode of one cell and the cathode of the next cell. This bipolar plate is made up of graphite, which offers good electrical conductivity and helps supply gas electrodes. However, it is challenging for bipolar plates to achieve good conductivity and gas supply. Therefore, on bipolar plates, a set of grooves is made. A bipolar plate has two surfaces used for the diagonal flow of hydrogen and oxygen [39]. Figure 2 shows the internal component of FC and the stack.