Increasing energy need and running out of fossil-based fuels direct us to renewable energy resources. Although hydrogen is not an energy source by itself, it is an energy carrier with a high specific heat capacity. As it is used as fuel in unitized regenerative PEM fuel cells, water is separated in electrolyzer mode and stored by producing hydrogen when there is no need for energy. In this study, performance tests on the unitized regenerative PEM electrolyzer/fuel cell were carried out and numerical modelling has been performed. The validity of the developed model was confirmed by the results of the experimental study. Before starting the performance tests, the cell's leakproofness tests were carried out, and the appropriate torque force was optimized, reducing the contact resistance that causes performance loss. The material selection of the cell components and corrosion-resistant materials that can operate in both electrolyzer and fuel cell modes were preferred. In this study, 0.019 slpm of hydrogen and 0.0095 slpm of oxygen gas is produced in the electrolyzer mode, while a power density of 0.353 W/cm2 is obtained in the fuel cell mode at 80 °C, from a unitized regenerative PEM fuel cell with a 5 cm2 active area, whose cell elements are combined with a 3 Nm clamping torque by using 12 bolts. •Three dimensional two phase flow modelling of regenerative PEM FC was performed.•Working parameters of unitized regenerative PEM fuel cell were optimized.•The developed model was verified by comparing the experimental and numerical results.•An increase in cell performance was achieved for both modes.