Characterization of PEM Electrolyzer and PEM Fuel Cell Stacks Using Electrochemical Impedance Spectroscopy

In order to compete with currently available hydrogen production technologies, proton exchange membrane (PEM) water electrolysis must be cost effective and efficient. Characterization of the PEM electrolyzer stack can provide better understanding of the processes at the electrode level and losses during the operation to help improve its energy efficiency, important understanding to shape future research and the optimization of stack designs. PEM fuel cells have seen significant developments in recent years due to their capability as an efficient and environment friendly solution for energy conversion. Understanding the behavior of the PEM fuel cell stack at varying loads is vital for optimizing hybrid systems efficiency. Therefore, it is important to characterize all aspects of a fuel cell when it is running under realistic operating conditions. Electrochemical impedance spectroscopy (EIS) is the sophisticated method to study the PEM cell behavior due to its electrochemical nature. Characterizing PEM cell stacks using EIS technique has a major advantage of differentiating between contributions of each process towards the overall performance of PEM cell stacks. The contributions of ohmic, kinetic and mass transport losses can be differentiated using EIS studies. A 1.2 kW PEM fuel cell and 6 kW PEM electrolyzer were characterized using this technique. Fuel cell EIS testing was accomplished using a frequency response analyzer (FRA) and programmable electronic DC load over a frequency range from 20 kHz to 50 mHz. EIS studies of 6 kW PEM electrolyzer were carried using the FRA, modified linear DC power supply and custom build current transformer core. The experimental impedance data were analyzed using Nyquist and Bode plots for different types of losses. Electrolyzer modeling was also done based on thermodynamic principles. Stack parameters such as membrane conductivity, anode and cathode exchange current densities were extracted using Mathematica from experimental data obtained at various temperatures. Some aspects of hydrogen conditioning and compression are also addressed as a part of this study. A novel technique of hydrogen drying using thermoelectric coolers was developed and tested. Hydrogen compression using electrochemical cell was studied, mathematically modeled and compared with its counterpart mechanical compressor