# A Multiscale Approach to the Numerical Simulation of the Solid Oxide Fuel Cell
## 2 Experimental Examination of the SOFC Stack
### Experimental Set-Up  
The test module for the SOFC stacks used in this study is the modular stack test bench (MSTB), designed and manufactured by the SOLIDPower S.p.a. The set-up was located in Department of Fundamental Research in Energy Engineering, AGH University of Science and Technology, Krakow, Poland. The scheme of the MSTB is shown on Figure 2. Inside the MSTB furnace, the short stack of the nine solid oxide fuel cells, provided by the SOLIDPower S.p.a., was enclosed. Every one of the cells is a planar SOFC, with the solid electrolyte fabricated from yttria-stabilized zirconia (YSZ), the anode made from Ni/YSZ cermet. The layered cathode is fabricated from the gadolinium-doped ceria (GDC) (buffer layer), the LSCF/GDC composite (functional layer) and the pure LSCF perovskite (current collector layer). The thicknesses of the components of every one of the cells are shown in Table 1. Table 2 presents the layered composition of the cathode. The cells have the active area \(6\times 8\) cm\({}^{2}\). The electric load device allows for controlling the current withdrawn from the stack. The air and fuel are supplied through the electromagnetic valves, the mass flow controllers and the inlet heaters to the stack. The products of the electrochemical reactions, unused fuel and air are mixed together and burned in the afterburner. The leftovers are cooled down and the condensate and exhaust are released. The temperature inside the MSTB is controlled by six thermocouples, marked in Figure 2 with 1, and the driver software, MSTestBench (version 15, SOLIDPower S.p.a., Mezzolombardo, Italy), is used to operate the testing system. The operating conditions of the MSTB are shown in Table 3. The temperatures of the inlet electric heaters and of the afterburner are constant during the operation. The total flow rate should also be constant, however, the amount of the hydrogen and nitrogen in the fuel mixture may vary. To avoid fuel starvation, the amount of hydrogen in the fuel should always be less than 70 %. Due to safety reasons, the potential of the stack should not fall below 5.4 V, to avoid operation in the concentration overpotential region. Only the total potential or voltage of the stack is measured. The cell power density \(p_{\text{out}}\) (W cm\({}^{-2}\)) may be calculated using the following formula:  
\[p_{\text{out}}=\frac{IE}{A_{\text{cell}}}, \tag{1}\]  
where \(I\) (A) is the current withdraw from the cell, \(E\) (V) is the average cell potential and \(A_{\text{cell}}\) stands for the cell active area (cm\({}^{2}\)). If not indicated otherwise, the molar fraction of nitrogen is given as \(\chi_{\text{N}_{2}}=1.0-\chi_{\text{H}_{2}}\).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Element** & **Anode** & **Electrolyte** & **Cathode** & **Anode Channel** & **Cathode Channel** \\ \hline
**Thickness [\(\mu\)m]** & 240 & 10 & 50 & 700 & 1400 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Thicknesses of the cell components.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Layer** & **Buffer Layer** & **Active Layer** & **Current Collector Layer** & **Total** \\ \hline
**Thickness [\(\mu\)m]** & 0.5 & 9.5 & 40 & 50 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Layers of the cathode.