Understanding GDL properties and performance in polymer electrolyte fuel cells

The Gas Diffusion Layer (GDL) has the important role of transporting the reactants into, and products out of the cell. This study aims to provide insights for understanding the relationship between GDL properties and the performance of PEFCs. Ex-situ characterisation techniques were employed to study the mechanical, physical and electrical properties of the GDL. The relationship between the various properties of GDL was investigated and discussed in this work. The study shows that characteristics such as GDL thickness, bulk density, PTFE and MPL content, porosity, hydrophobicity, permeability and electrical conductivity are closely connected. The effect of compression on the cathode GDL performance in PEFC membrane electrode assembly (MEA) is discussed using Polarisation (IV) curve and electrochemical Impedance Spectroscopy (EIS). Compression affects the electrical and mass transport properties of the GDL and therefore needs to be optimised. The results show that there is an optimum compression point, at which; a minimum contact resistance and optimum water transport are achieved. The optimum compression level is dependent on the GDL properties. The optimum compression ratio varies for the different GDLs according to the difference in the material properties. At optimum compression, the performance of the different GDL materials was compared to understand the effect of the GDL properties on the performance. GDL characteristics such as structure, thickness, bulk density, PTFE loading, and MPL presence have a direct effect on the MEA performance and need to be optimized for the different PEFC applications

Composite Polymers Development and Application for Polymer Electrolyte MembraneTechnologies—A Review

Nafion membranes are still the dominating material used in the polymer electrolyte membrane (PEM) technologies. They are widely used in several applications thanks to their excellent properties: high proton conductivity and high chemical stability in both oxidation and reduction environment. However, they have several technical challenges: reactants permeability, which results in reduced performance, dependence on water content to perform preventing the operation at higher temperatures or low humidity levels, and chemical degradation. This paper reviews novel composite membranes that have been developed for PEM applications, including direct methanol fuel cells (DMFCs), hydrogen PEM fuel cells (PEMFCs), and water electrolysers (PEMWEs), aiming at overcoming the drawbacks of the commercial Nafion membranes. It provides a broad overview of the Nafion-based membranes, with organic and inorganic fillers, and non-fluorinated membranes available in the literature for which various main properties (proton conductivity, crossover, maximum power density, and thermal stability) are reported. The studies on composite membranes demonstrate that they are suitable for PEM applications and can potentially compete with Nafion membranes in terms of performance and lifetime

An examination of the catalyst layer contribution to the disparity between the Nernst potential and open circuit potential in proton exchange membrane fuel cells

The dependency of the Nernst potential in an operating proton exchange membrane fuel cell (PEMFC) on the temperature, inlet pressure and relative humidity (RH) is examined, highlighting the synergistic dependence of measured open circuit potential (OCP) on all three parameters. An alternative model of the Nernst equation is derived to more appropriately represent the PEMFC system where reactant concentration is instead considered as the activity. Ex situ gas diffusion electrode (GDE) measurements are used to examine the dependency of temperature, electrolyte concentration, catalyst surface area and composition on the measured OCP in the absence of H2 crossover. This is supported by single-cell OCP measurements, wherein RH was also investigated. This contribution provides clarity on the parameters that affect the practically measured OCP as well as highlighting further studies into the effects of catalyst particle surrounding environment on OCP as a promising way of improving PEMFC performance in the low current density regime

Preparation of gadolinium-doped ceria barrier layer for intermediate temperature solid oxide fuel cells by spin coating and evaluation of performance degradation by impedance analysis

Thin gadolinium-doped ceria (GDC) films were deposited via the cost-effective aqueous spin coating technique and with rapid one-step sintering at 1200 °C, to be used as barrier layer between a lanthanum strontium cobalt ferrite (LSCF) cathode and a scandia-ceria-stabilised zirconia (ScCeSZ) electrolyte within a solid oxide fuel cell (SOFC) configuration. A 5.5 μm-thick GDC film was deposited using a 50 wt% GDC slurry in 3 cycles. The single cell comprising this GDC film produced a peak power density of over 1.00 W•cm−2 at 750 °C in hydrogen operation. Electrochemical impedance spectroscopy was carried out to investigate the SOFC performance evolution with potential changes in microstructure over time. An operational stability test was also conducted at a current density of 0.2 A•cm−2 for over 1200 h. The degradation behaviour of each electrochemical process as a function of cell operating time was evaluated by the distribution of relaxation times method based on the obtained electrochemical impedance spectra