**3. Application**

Two modes of operation are available for using this model, as displayed in Figure 3. First, the cell performance can be calculated solely based on physical parameters. Second, the cell performance can be estimated based on the voltage deviation from a supplied polarization table. In the latter case, a distinction can be made between using a single or multiple polarization curves as reference.

For this purpose, the inputs of the MATLAB-function are divided into two categories: one for the state variables mandatory to estimate the cell performance and another for the polarization table references. When running in mode *1*, the inputs from the second category are ignored. In mode *2a*, the model expects reference values for the experimental conditions of the polarization curve recording. Lastly, in the case of *2b*, internal calculations for voltage deviation can be disabled by supplying state

variables as table references. e.g., when using polarization curves for different temperatures, supplying the current cell temperature will lead to no additional adjustments for this factor, since current and reference values are identical. The operation mode has no impact on the calculations for concentration overpotential and water transport, however, since these heavily depend on stack composition and media supply.

**Figure 3.** Modes of operation. 1: cell mode; 2a: table mode, single curve polarization table; 2b: table mode, multi curve polarization table; S: state variable; T: polarization table; R: polarization table reference values.

It is also possible to use this model outside of the MATLAB environment via Co-Simulation. As an example, the program code can be run inside of a MATLAB-Function-block within a Simulink model, which can be compiled as C/C++ code. Depending on the target software, the exact Simulink model composition—regarding inputs, outputs and parameters—and compilation procedure may be wary and has to be looked up in the corresponding documentation. Following this practice allows the fuel cell model to be used in any simulation platform with support for Simulink coupling.
