Effects of porous transport layers on the performance ofpem water electrolyzers

Abstract

The escalating global energy demand, combined with the dwindling reserves of fossil fuels and their detrimental environmental effects, drives the urgent need for a transition to renewable and sustainable energy sources. Hydrogen, possessing an elevated energy density, versatility and clean combustion properties, is an ideal candidate for a zero-emission energy carrier. Among various hydrogen production methods, water electrolysis powered by renewable energy stands out as the most sustainable option. Proton Exchange Membrane Water Electrolyzers (PEMWEs), known for their compact design, rapid response time and high efficiency, are key technologies in the transition to a green hydrogen economy. They offer unique advantages, such as operating at low temperatures, producing high-purity hydrogen directly at pressure and being scalable to meet diverse energy demands. PEMWEs have the potential to significantly contribute to decreasing reliance on fossil fuels, improving energy security, and facilitating the widespread use of clean hydrogen in various sectors such as industry, transportation, and power generation. Despite their advantages, the widespread adoption of PEMWEs faces challenges related to cost and durability. Among the critical components of PEMWEs, the Porous Transport Layer (PTL) plays a crucial role in ensuring efficient water and gas transport, maintaining low resistance, and providing uniform current distribution. PTLs also serve as the boundary between catalyst layer and bipolar plate or mesh, directly influencing contact resistance and reactant accessibility. The structural features of PTLs (sintered or fibrous structure), including their thickness, pore structure and size distribution, have a significant effect on PEM water electrolyzer performance. This thesis investigates the performance impact of titanium-based Porous Transport Layers (PTLs) with varying thicknesses, porosities, and structural properties in PEMWEs. A series of experiments were conducted using PTLs of different configurations under controlled operating conditions. The study systematically examined the influence of PTL structural features, including thickness and porosity, on parameters derived from polarization curves and Nyquist plots obtained through electrochemical impedance spectroscopy. Findings indicated that thinner PTLs demonstrated better performance especially at high current densities, achieving higher overall efficiency. Additionally, higher porosity was found to enhance gas removal and reactant transport, contributing to improved PEM water electrolyzer performance under various operating conditions. Moreover, PTLs that underwent a rolling process to mechanically reduce thickness and, consequently, porosity, are also investigated in this research. The impact of the mechanical thinning process on performance is examined, and the effects of these types of PTLs on efficiency are evaluated. These additions provide insights into how different manufacturing methods and techniques interact in optimizing PTL design. The findings contribute to a deeper understanding of PTL design optimization, aiming to improve PEMWE performance and reduce hydrogen production costs. These advancements align with global sustainability goals, promoting green hydrogen as a cornerstone of the transition to renewable energy systems. Ultimately, this work enhances the understanding of PEMWE components, bridging the gap between research and practical application, and supporting the development of a cleaner, more sustainable energy future.