Membrane proton exchange

A second commercially available electrolyzer technology is the solid polymer electrolyte membrane (PEM). PEM electrolysis (PEME) is also referred to as solid polymer electrolyte (SPE) or polymer electrolyte membrane (also, PEM), but all represent a system that incorporates a solid proton-conducting membrane which is not electrically conductive. The membrane serves a dual purpose, as the gas separation device and ion (proton) conductor. High-purity deionized (DI) water is required in PEM-based electrolysis, and PEM electrolyzer manufacturer regularly recommend a minimum of 1 MQ-cm resistive water to extend stack life. 

Ideal Stack Potential Actual Stack Potential 

The HHV of hydrogen is 39 kWh kg-1 and the ideal stack potential is a function of temperature and pressure. All efficiencies are referenced to the HHV of hydrogen. The minimum amount of energy that must be consumed to split water into hydrogen 

Hydrogen as an energy carrier and potentially widely used fuel is attractive because it can be produced easily without emissions by splitting water. In addition, the readily available electrolyzer can be used in a home or business where off peak or surplus electricity could be used to make the environmentally preferred gas. Electrolysis was first demonstrated in 1800 by William Nicholson and Sir Anthony Carlisle and has found a variety of niche markets ever since. Two electrolyzer technologies, alkaline and proton exchange membrane (PEM), exist at the commercial level with solid oxide electrolysis in the research phase. 

When comparing literature from fuel cell (FC) models with water electrolysis work it is important to remember the differences between the system anode and cathode. This basic understanding may be trivial to most but is many times confused when switching between the two processes. The anode is always the electrode at which oxidation occurs, where electrons are lost. The cathode is defined as the electrode at which electrons enter, where reduction takes place. In electrolysis the cathode is the electrode where H2 gas is created, in FC systems the anode is the electrode where H2 is introduced. 

The alkaline electrolyzer is a well-established technology that typically employs an aqueous solution of water and 25-30 wt.% potassium hydroxide (KOH). However, sodium hydroxide (NaOH), sodium chloride (NaCl) and other electrolytes have also been used. The liquid electrolyte enables the conduction of ions between the elec 

PEM technology was originally developed as part of the Gemini space program.16 In a PEM electrolyzer, the electrolyte is contained in a thin, solid ion-conducting membrane rather than the aqueous solution in the alkaline electrolyzers. This allows the H+ ion (proton) or hydrated water molecule (HsO+) to transfer from the anode side of the membrane to the cathode side, and separates the hydrogen and oxygen 

PEM fuel cell schematic. (From http //www.ballard.com) 

3 Fuel Cell Components 1.2.3.1 Proton Exchange Membrane 

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GE develops Proton Exchange Membrane (PEM) y Fuel Gell for NASA s Gemini Program (1966)... 

Proton Exchange Membrane 0-85 Can operate at ambient temperature High power density Sensitive to CO-poisoning Need for humidification Transportation Distributed Power... 

The most promising fuel cell for transportation purposes was initially developed in the 1960s and is called the proton-exchange membrane fuel cell (PEMFC). Compared with the PAFC, it has much greater power density state-of-the-art PEMFC stacks can produce in excess of 1 kWA. It is also potentially less expensive and, because it uses a thin solid polymer electrolyte sheet, it has relatively few sealing and corrosion issues and no problems associated tvith electrolyte dilution by the product water. 

As with batteries, differences in electrolytes create several types of fuel cells. The automobile s demanding requirements for compactness and fast start-up have led to the Proton Exchange Membrane (PEM) fuel cell being the preferred type. This fuel cell has an electrolyte made of a solid polymer. 

Ford Motor Company. (1997). Direct Ilydrogcn-Fuclcd Proton Exchange Membrane Fuel Cell System for Transportation Applications Hydrogen Vehicle... 

Proton Exchange Membrane Fuel Cells (PEMFCs)... 

Propylene glycol, glycolysis of polyurethanes with, 572 Propylene oxide (PO), glycolysis of polyurethanes with, 572-573 Propylene oxide (PO) polyols, 211, 223 Proton exchange membrane fuel cells (PEMFCs), 272-273 Proton NMR integrations, 386. See also H NMR spectroscopy Protonic acids, reactions catalyzed by, 67-68... 

This proton exchange membrane is used in both hydrogen and methanol fuel cells, in which a catalyst at the anode produces hydrogen from the methanol. Because the membrane allows the protons, but not the electrons, to travel through it, the protons flow through the porous membrane to the cathode, where they combine with oxygen to form water, while the electrons flow through an external circuit. 

This automobile is powered by a hydrogen fuel cell with a proton exchange membrane. Its operation is pollution free, because the onl product of the combustion is water. 

PEMFC proton exchange membrane fuel cell... 

The authors developed a multi-layered microreactor system with a methanol reforma- to supply hydrogen for a small proton exchange membrane fiiel cell (PEMFC) to be used as a power source for portable electronic devices [6]. The microreactor consists of four units (a methanol reformer with catalytic combustor, a carbon monoxide remover, and two vaporizers), and was designed using thermal simulations to establish the rppropriate temperature distribution for each reaction, as shown in Fig. 3. 

The catalysts at the anode can be made less sensitive to CO poisoning by alloying platinum with other metals such as ruthenium, antimony or tin[N.M. Markovic and P.N. Ross, New Flectro catalysts for fuel cells CATTECH 4 (2001) 110]. There is a clear demand for better and cheaper catalysts. Another way to circumvent the CO problem is to use proton-exchange membranes that operate at higher temperatures, where CO desorbs. Such membranes have been developed, but are not at present commercially available. 

The electrocatalytic oxidation of methanol has been widely investigated for exploitation in the so-called direct methanol fuel cell (DMFC). The most likely type of DMFC to be commercialized in the near future seems to be the polymer electrolyte membrane DMFC using proton exchange membrane, a special form of low-temperature fuel cell based on PEM technology. In this cell, methanol (a liquid fuel available at low cost, easily handled, stored, and transported) is dissolved in an acid electrolyte and burned directly by air to carbon dioxide. The prominence of the DMFCs with respect to safety, simple device fabrication, and low cost has rendered them promising candidates for applications ranging from portable power sources to secondary cells for prospective electric vehicles. Notwithstanding, DMFCs were... 

Reforming 573 K Shift-Conversion Phosphoric Acid, 473 K or Proton Exchange Membrane Fuel Cells, 363 K... 

PAFC, phosphoric acid fuei ceii MCFC, moiten carbonate fuei ceii SOFC, soiid oxide fuei ceii PEMFC, proton exchange membrane fuei ceii DMFC, direct methanoi fuei ceii AFC, alkaiine fuel cell. 

Figure 4. Schematic design of a proton exchange membrane fuel.

These main objectives can be reached only by modifying the structures and compositions of primarily the anode (methanol electrode) and secondarily the cathode (oxygen electrode) as discussed in Sections 111 and IV, respectively. In addition. Section IV discusses the conception of new proton exchange membranes with lower methanol permeability in order to improve the cathode characteristics. Section V deals with the progress in the development of DMFCs, while in Section VI the authors attempt to make a prognosis on the status of DMFC R D and its potential applications. 

Finally, a simple method for a rapid evaluation of the activity of high surface area electrocatalysts is to observe the electrocatalytic response of a dispersion of carbon-supported catalyst in a thin layer of a recast proton exchange membrane.This type of electrode can be easily obtained from a solution of Nafion. As an example. Fig. 11 gives the comparative... 

In this section, we summarize the kinetic behavior of the oxygen reduction reaction (ORR), mainly on platinum electrodes since this metal is the most active electrocatalyst for this reaction in an acidic medium. The discussion will, however, be restricted to the characteristics of this reaction in DMFCs because of the possible presence in the cathode compartment of methanol, which can cross over the proton exchange membrane. 

Therefore, one main drawback of the PEMFC configuration with a standard proton exchange membrane (such as Nafion) and a standard platinum gas diffusion cathode is the cathode depolarization caused by a mixed potential resulting from the methanol crossover through the mem-... 

The second example describes distributed, mobile and portable power-generation systems for proton-exchange membrane (PEM) fuel cells [106]. A main application is fuel processing units for fuel cell-powered automobiles it is hoped that such processing units may be achieved with a volume of less than 8 1. 

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