Proton-exchange membrane electrolyzer

Proton decay, delayed, 27 303-304 Proton-exchange membranes, 23 720 electrolyzer, 73 843 Proton exchange membrane process, 73 783... 

The current state-of-the-art proton exchange membrane is Nafion, a DuPont product that was developed in the late 1960s primarily as a permselective separator in chlor-alkali electrolyzers. Nation s poly(perfluorosulfonic acid) structure imparts exceptional oxidative and chemical stability, which is also important in fuel cell applications. 

Currently there are two primary distributed electrolyzer technologies in development and use (1) Alkaline electrolyte electrolyzers and (2) Proton-exchange membrane electrolyzers. 

The nitrate would be electrolyzed in a 24-hr cycle in parallel-plate cells with proton-exchange membranes. The optimal overall NO reduction reactions are... 

Figure 5.28. Production of hydrogen in a Proton Exchange Membrane (PEM) water electrolyzer 18S.

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. 

Baldwin, R. et al.. Hydrogen-oxygen proton-exchange membrane fnel cells and electrolyzers, J. Power Sources, 29, 399, 1990. 

Electrolytes are a critical material in the performance of electrolyzers. Low-temperature electrolysis of water relies on proton exchange membrane (PEM) cells using sulfonated polymers for the electrolytes. Key issues for all electrolyzers are the kinetics of the system that is controlled by reaction and diffusion rates. Catalysts such as platinum, Ir02, and RUO2 are used to improve the reaction kinetics, but they also contribute to the cost of the system, which is also an issue. Steam electrolysis is also a possibility at a temperature of about 1,000°C using ceramic membranes. 

The PEM cell design chosen for tlie current work employs a significantly different geometry than the Westinghouse cell. The PEM electrolyzer consists of a membrane electrode assembly (MEA) inserted between two flow fields. Behind each flow field is a back plate, copper current collector and stainless steel end plates. The MEA consists of a Nafion proton-exchange-membrane with catalyst-coated gas diffusion electrodes bonded on either side. 

The photovoltaic power source can be any commercial BSPM (Battery Specific Photovoltaic Module), or can be an ESPM (Electrolyzer Specific Photovoltaic Module). The electrolyzer can either be a PEM (Proton Exchange Membrane) or an alkaline type. 

Solid electrolyte PEM (proton exchange membrane) electrolyzers can be used in systems to avoid use of caustics as an added safety factor and where no one is available to frequently monitor a fluid electrolyte system. PEM electrolyzers are much more expensive, and do not have the track record that alkaline electrolyzers have in use. Although they are reportedly almost trouble free during use, they do pose problems in terms of cost of replacement parts when they become inoperable. Failures in PEM electrolyzers are usually membrane blow-outs or catalyst degeneration. Both problems are costly to service with replacement parts. 

The metals present can be recovered in a batch process using packed-bed deposition, dissolution, and potentiostatic deposition of individual ions described earlier (cf. [30]). The nitrates can be electrolyzed in a 24 h cycle in parallel plate cells with proton exchange membranes. Thus,... 

Bulk production of hydrogen via electrolysis appears improbable until renewable or nuclear electricity becomes widely available and considerably cheaper than at present. The principal attribute of electrolytic hydrogen is its ultra-purity, which is an important requirement for proton-exchange membrane fuel cells. Nevertheless, the use of valuable electricity to electrolyze water and then feeding the resultant hydrogen to a fuel cell is intrinsically wasteful by virtue of the combined inefficiencies of the two devices involved. This really only makes sense in situations where there is more electricity than can be consumed as such, or where there are reasons for wanting hydrogen that transcend considerations of efficiency and cost. 

Exchange ideas for the development and design of solid oxide fuel cells (SOFC) and proton exchange membrane (PEM) fuel cells for electricity and heat generation, vehicles, reversible fuel cell electrolyzes, and fuel cell microturbine hybrids, for example. 

Bipolar electrolysis systems are characterized by the type of electrolyte. The proton exchange membrane (PEM) system, developed by the General Electric Compare (GE), uses as the electrolyte a thin membrane of sulfonated fiuorocaibon (Nation ) that conducts electricity when saturated with water. Electrodes are formed by depositing a thin platinum film on opposite sides of the merrtbrane to form a bipolar cell. An electrolyzer is made by stacking 50-200 cells in series, with srritably formed separators to direct the exhaust gases into charmels at the sides. Since the membrane is the electrolyte, only pine water needs to be supphed to the cell. When the cell oper-... 

Most of the more recent literature on Ru and Ir and their oxides is related to the areas of proton exchange membrane (PEM) electrolyzers and reversible FC. Due to its instability in the operatitMial voltage range of these devices, metallic Ru has not attracted much interest. Song et al. have shown that in a PEM environment, metallic Ru particles (BET smface area 20.9 m /g) are more active than RUO2, lr02, and metallic Ir [37]. At 1.45 V, the mass activity of their Ru is approximately 110 A/g, or PA orders of magnitude lower than ours. 

SO2/H2SO4 couple has a standard potential of 0.17 V which is much smaller than that of 1.23 V for water (H2O/H2). Although this is an advantage for this process, some technical cmistraints should be overcome for the design. Thus, the use of an electrolyzer with proton exchange membrane, in which the transport rate of reactants to the electrode surface is expected to enhance, was proposed. This method differs from the Westinghouse Process from the aspect of performing the anode reactions in the gas phase [17]. 

For practical appUcatirms, a major goal of research is to minimize the overpotenlials for HOR and HER at current density up to 2 A cm in proton exchange membrane (PEM) fuel cells and water electrolyzer. An effective way to do it is to increase the ratio of Pt surface area to electrode area, Spi-Assuming full utihzatitm of Pt nanocatalysts, the current density is proportional to Spi and thus, the... 

R. Baldwin, M. Pham, A. Leonida, J. McElroy, and T. Nalette, Hydrogen-Oxygen Proton Exchange Membrane Fuel Cells and Electrolyzers, Proceedings of the Space Electrochemical Research and Technology (SERT), NASA LEWIS Research Center, Cleveland, Ohio, April, 1989. 

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