Hydrogen PEFC components

Direct hydrogen PEFC systems require extensive thermal and water management to ensure that the PEFC stack operates under the desired design conditions (Figure 3-10). Key components are... 

When hydrogen is produced by steam reforming of methanol or hydrocarbons, CO is the second-largest byproduct component (about 1 vol %) after CO2- In application to PEFC, to remove CO to a concentration of 100 ppm, CO should be reduced to methane or oxidized to CO2. Oxidation is advantageous because it potentially consumes less hydrogen. 

The membrane in the polymer electrolyte fuel cell (PEFC) is a key component. Not by chance does the type of membrane brand the cell name - it is the most important component determining cell architecture and operation regime. Polymer electrolyte membranes are almost impermeable to gases, which is crucial for gas-feed cells, where hydrogen (or methanol) oxidation and oxygen reduction must take place at two separated electrodes. However, water can diffuse through the membrane and so can methanol. Parasitic transport of methanol (methanol crossover) severely impedes the performance of the direct methanol fuel cell (DMFC). 

The Membrane Electrode Assembly (MEA) is the core component of a PEFC, in which electric current is generated by anodic oxidation of the fuel which typically is hydrogen or methanol and cathodic reduction of the oxidant which typically is oxygen from the air. The MEA contains all electrochemically relevant interfaces at the anode and the cathode side. The central part of the MEA is formed by the... 

The CLs are the most important components in a PEFC in which the hydrogen oxidation reaction (HOR) and Oxygen reduction reaction (ORR) take place in the anode and cathode, respectively. CLs are usually thin with a thickness of about 10 gm. Several materials contained in a CL are critical to the electrochemical... 

In a fuel cell, feed gas consmnption can affect the hydrodjmamics of channel flow. For example, in PEFCs hydrogen atoms are consmned in the anode channel and appear in the cathode channel as a component of the water molecules. The electro-osmotic effect causes the transfer of water from the anode chaimel to the cathode channel. Due to these fluxes the mass of the flow changes, which may affect flow density and velocity. 

Presently, the major focus of R D on PEFC technology is to develop a fuel cell for terrestrial transportation, which requires the development of low-cost cell components. Hydrogen is considered the primary fuel for transportation applications, while reformed natural gas is the prime candidate for stationary applications. For automotive applications, the focus has shifted to... 

The first primitive cells of Schoenbein and Grove utilized platinum wire electrodes. Today, high-performance PEFC stacks are approaching commercial readiness in transportation applications, yet Pt remains as their critical materials component. Pt exhibits a benign combination of an exceptional activity for hydrogen oxidation and oxygen reduction reactions, and an unusual corrosion resistance under strongly acidic conditions in the fuel cell (Debe, 2012). 

Water is the active medium of PEFCs. From a chemical point of view, water is the main product of the fuel cell reaction. It is the only product in hydrogen fuel cells. Cells supplied with direct methanol or ethanol as the fuel produce water and carbon dioxide in stoichiometric amounts. The low operating temperature implies that water is present in liquid form. It mediates direct electrostatic as well as colloidal interactions in solutions or ink mixtures containing ionomeric, electronic, and electrocatalytic materials. These interactions control phase separation and structural relaxation phenomena that lead to the formation of PEMs and CLs. Variations in water content and distribution, thus, lead to transformations in stable structures of these media, which incur modifications in their physicochemical properties. It is evident that many of the issues of understanding the structure and function of fuel cell components under operation are intimately linked to water fluxes and distribution. 

The history of research on polymer electrolyte fuel cells spans about 50 years. PEFCs appeared in the focus of scientific interest toward the end of the 1980s. Generally, PEFC design is simple and all the needed components are available on the market. Take two gas-diffusion electrodes separated by a polymer electrolyte membrane and clamp this membrane-electrode assembly between two graphite plates with channels for hydrogen and air supply—the cell is ready. 

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