## 1 Introduction
Their experimental results showed that with relative humidity decreasing from 100 to 25 percent, the voltage reached from 0.675 V to 0.358 V and the performance and production capacity of the fuel cell decreased, since, with decreasing of humidity, the electrode reaction and mass penetration rate were slower and membrane resistance increases. They indicated that by enhancing the relative humidity from 25 to 100 percent, the pressure drop in the anode and the cathode increases, and the partial pressure of oxygen and hydrogen decreases, which are a function of the input relative humidity at temperature of 120 \({}^{\circ}\)C and pressure of 1 atmosphere. [PERSON] et al. [27] experimentally and numerically studied the performance of HT-PEMFCs. Their model is a single cell with a serpentine channel, and their simulation were implemented in steady-state, three-dimensional, and isothermal. [PERSON] et al. [28] addressed the three-dimensional and isothermal simulation of an HT-PEMFC with PTFE membrane. They examined the parameters such as the distribution of saturated water, membrane conductivity, temperature, flow density, etc. on the performance of the fuel cell. [PERSON] et al. [29] investigated the start-up process modeling of an HT-PEMFC using Comsol software. Starting HT-PEM fuel cells from room temperature to a proper operating temperature is a challenge. In this study, the preheated air was used to increase the temperature of the cooling channel or gas channel, and the optimum state was selected by checking the start-up time and temperature behavior of the fuel cell. [PERSON] and [PERSON] [30] experimentally investigated the effects of the micro-porous layer on the performance of an HT-PEMFC based on PBI. Using PBI electrolyte, they expressed the effect of MPLcompounds, including PTFE and carbon and extracted an optimal state. The results showed that the micro-porous layer with a content of 40 wt% of PTFE and loading of 1 mg/cm\({}^{2}\) carbon yielded the optimum performance of the cell. [PERSON] [31] performed a three-dimensional simulation of a single-channel HT-PEMFC in a steady state. In this research, the Comsol software was used for simulation, and the concentration of species, namely, hydrogen and oxygen, and water concentration in the cathode and anode gas channels were investigated. [PERSON] et al. [32] examined the effect of gas flow channel dimensions and operating conditions such as pressure and temperature on the efficiency of HT-PEMFCs. They used a developed mathematical model in their research. They also calculated the concentration of gas species in the electrodes through mass transfer analysis. Since their model required less computer computing, it has been used to analyze many samples with different gas flow channels and different operating conditions, and its optimal mode has been selected. [PERSON] et al. [33] investigated developed a three-dimensional and isothermal modeling for an HT-PEMFC. Triple mixed serpentine flow channel single-cell with PBI membrane was applied for the model. The model was defined in steady-state, isothermal and single-phase, and simulated for different operating temperatures in the range of 100 to 180 \({}^{\circ}\)C. The results show that the increase in temperature has improved the performance of the fuel cell. Also, the distribution of current density at different voltages was investigated, and it was deduced that at higher operating voltages, local flow density is more uniform. Pressure drop contours and distribution of oxygen concentration along the gas flow channel were also evaluated. Moreover, in another study [34], they improved a mathematical non-isothermal and 3D model of HT-PEMFC. The distribution of temperature and pressure along the channels and the membrane current density distribution over the entire membrane electrode active area were shown. Results were obtained for two operating voltages of 0.45, and 0.6 volts and the results of this model were compared with the results of the isothermal model in the previous study.