PERFORMANCE OPTIMIZATION OF A PROTON EXCHANGE MEMBRANE WATER ELECTROLYZER

Abstract

Green hydrogen can contribute significantly to combating climate change by helping to decarbonize the world's energy sector. Hydrogen can be produced in a carbon-free manner using renewable energy by electrolysis which is environmentally benign and produces hydrogen with high purity. Water is fed to the electrolytic cell as the reactant and it is dissociated into hydrogen and oxygen by the passage of electricity. Water electrolysis is typically accomplished today by one of three methods: (i) alkaline water electrolysis (AWE); (ii) solid oxide water electrolysis (SOWE); and (iii) proton exchange membrane water electrolysis (PEMWE). PEMWE offers certain advantages including high efficiency and high current density. Therefore, we focus on PEMWE in this study. First, we examine the effect of various operating parameters on PEMWE performance such as water flow rate, temperature, membrane thickness, flow field channel configuration, and porous transport layer properties. This work quantitatively compares the relative magnitude of anode water consumption against the concurrent water transport mechanisms of Fickian diffusion and electroosmotic drag as a function of the applied voltage. This study also gives insights on optimizing PEMWE performance by varying the operating parameters and provides a foundation for the design of a full-scale PEMWE system. Second, we evaluate multiple strategies for gas management in the PEMWE anode. In this study, we employ an electrolysis cell featuring a transparent anode to visualize oxygen bubble production and transport under a range of operating conditions. These strategies include changing the cell’s orientation with respect to gravity, increasing the water flowrate, and adding surfactant to the anode water supply. This study shows that optimally orientating the channels with respect to gravity can assist with oxygen bubble evacuation and improve performance. This study also captures the dynamic behavior of the two-phase flow phenomena in PEMWEs over a range of applied voltages. The results provide suggestions to enhance PEMWE performance by optimizing oxygen gas management within the PEMWE’s flooded anode. Third, we focus on the phenomenon of electroosmotic drag in an operating PEMWE with the goal of accurately measuring the electroosmotic drag coefficient. This study elucidates the effect of the cell temperature and membrane thickness on the relevant water transport phenomena. We also investigate the effect of supplying dry nitrogen to the cathode and provide an explanation for the improved current density based on the Nernst equation. Understanding these mechanisms is essential to improving PEMWE performance and efficiency. Finally, we compare the catalytic performance of nickel iron layered double hydroxide (NiFe LDH) against commercial iridium oxide (IrOx) in an anion exchange membrane water electrolyzer. In this study, we present the structural and performance analysis of NiFe LDH which was prepared in the form of nanosheets through a benzyl alcohol-mediated solvothermal process in one step. The NiFe LDH electrode demonstrated good stability over a 24-hour durability test. Although the electrochemical performance of NiFe LDH was somewhat lower compared to IrOx, it shows promise as a AEMWE catalyst due to its significantly lower cost and capacity for further activity enhancement.