Current Density Improvement Evaluation of Polymer Electrolyte Electrochemical Cells (PEEC) for Hydrogen Generation Using Electrochemical Impedance Spectroscopy

One of the hydrogen formations from renewable energy is expected to use water electrolysis. Especially, polymer electrolyte electrochemical cell (PEEC) is known as a suitable energy conversion device from renewable electricity to hydrogen because the PEEC is relatively strong for the input energy fluctuation from a reliability point of view.<br/>The energy conversion efficiency improvement of PEEC is an important issue to establish the hydrogen production from renewable energies. The major improvement research for water electrolysis is reducing the operating voltage at the same current density. Therefore, the improvement of the water oxidation catalyst has been discussed because the over voltage of oxygen evolution reaction (OER) is higher than that of hydrogen evolution reaction (HER). However, the device conversion efficiency of PEEC is not defined only by these reaction overpotentials. The series resistance of the PEEC, which is mainly due to the resistance of polymer electrolyte, and ion concentration difference between anode and cathode also affect the device performance.<br/>Electrochemical impedance spectroscopy is a powerful tool for the evaluation of these resistances. The spectroscopy can be separated the series resistance, and the resistance due to overpotential at the interface between polymer electrolyte and electrode catalyst interface clearly. Although the reduction of polymer electrolyte resistance has been discussed with the polymer electrolyte thickness, it was found that the reduction with polymer electrolyte treatment also improves the PEEC performance. The overpotential at the interface between polymer electrolyte and electrode catalyst interface was also improved with this treatment. These evaluations clarified that not only the catalytic performance but also the other material properties need to control for the improvement of the PEEC performance.<br/>[1] V. Liso, et al., Energies 11 (2018) 3273.<br/>[2] S. Siracusano, et al., Materials 11 (2018) 1368.