@phdthesis{Ojong2018, author = {Ojong, Emile Tabu}, title = {Characterization of the performance of PEM water electrolysis cells operating with and without flow channels, based on experimentally validated semi-empirical coupled-physics models}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-46504}, school = {BTU Cottbus - Senftenberg}, year = {2018}, abstract = {PEM water electrolysis is a clean technology for hydrogen production. In spite of its many advantages, the costs of the conventional PEM electrolysis cell makes it commercially less competitive vis-{\`a}-vis its peers. An alternative cell design has been proposed which has up to a 25 \% costs advantage over the conventional cell. In this alternative cell design, the flow channel plate which bears the most costs in the conventional cell design has been replaced with a 3-D Porous Transport Layer (PTL) structure. It has however, been observed that the conventional cell by far out performs the low cost cell at high current density operations, due to increased mass transport limitation in the later. Industrial and commercial hydrogen production efforts are focused towards high current density operation (> 3 A/cm²), so the alternative cell design must be optimized for mass transport limitation. PEM water electrolysis is a clean technology for hydrogen production. In spite of its many advantages, the costs of the conventional PEM electrolysis cell makes it commercially less competitive vis-{\`a}-vis its peers. An alternative cell design has been proposed which has up to a 25 \% costs advantage over the conventional cell. In this alternative cell design, the flow channel plate which bears the most costs in the conventional cell design has been replaced with a 3-D Porous Transport Layer (PTL) structure. It has however, been observed that the conventional cell by far out performs the low cost cell at high current density operations, due to increased mass transport limitation in the later. Industrial and commercial hydrogen production efforts are focused towards high current density operation (> 3 A/cm²), so the alternative cell design must be optimized for mass transport limitation. This work seeks to understand the source of, and to eliminate the mass transport losses in the alternative cell design to get it performing at least as good as the conventional cell at current densities up to 5 A/cm². A 2-D non-isothermal semi-empirical fully-coupled models of both cell designs have been developed and experimentally validated. The developed validated models were then used as tools to simulate and predict the best operating conditions, design parameters and micro-structural properties of the PTL at which the mass transport issues in the alternate cell will be at its minimum, at high current densities. The models are based on a multi-physics approach in which thermodynamic, electrochemical, thermal and mass transport sub-models are coupled and solved numerically, to predict the cell polarization and individual overpotentials, as well as address heat and water management issues. The most unique aspect of this work however, is the development of own semi-empirical equations for predicting the mass transport overpotential imposed by the gas phase (bubbles) at high current densities. For the very first time, calculated polarization curves up to 5 A/cm² have been validated by own experimental data. The results show that, the temperature and pressure, water flowrate and thickness of the PTL are the critical parameters for mitigating mass transport limitation. It was found that, for the size of the cells studied (25 cm² active area each), when both cells are operating at the same temperature of 60 °C, alternative design will have a comparable performance to the conventional designed cell even at 5 A/cm² current density when; the operating pressure is ≥ 5 bar, the feed water flowrate is ≥ 0.024l/min∙cm², PTL porosity is 50 \%, PTL pore size is ≥ 11 µm and PTL thickness is 0.5 mm. At these operating, design and micro-structural conditions, the predicted difference between the polarizations of both cells will be only ~10 mV at 5 A/cm² operating current density.}, subject = {PEM Electrolysis; Porous Transport Layer; Mass Transport; Modelling; Experimental Validation; PEM-Elektrolyse; Por{\"o}se Transportschicht; Massentransport; Modellierung; Experimentelle Validierung; Polymer-Elektrolytmembran-Brennstoffzelle; Str{\"o}mungsmechanik; Stoff{\"u}bertragung; Kanalstr{\"o}mung}, language = {en} }