*Formulation of Objective Function*

In this research work, sum of squared error (SSE) is adopted as an optimization function (OF) for the identification of unknown parameters (*ζ*1, *ζ*2, *ζ*3, *ζ*4, *λ*, *Rc*, and *b*) of PEMFC, which is generally used by the authors in the existing literature [45–47]. The objective function is defined as follows:

$$\text{OF} = \text{Minimize}(SSE) = \text{Minimize}\left(\sum\_{i=1}^{N} \left[V\_{\text{measured}}(i) - V\_{\text{estimated}}(i)\right]^2\right) \tag{19}$$

where *N* represents the number of measured values, *i* denotes the number of iterations, *V*measured denotes the measured voltage while *V*estimated denotes the estimated value of voltage for PEMFC.
