Proton exchange membrane electrolysis

Figure 1.7. Schematic layout of proton exchange membrane electrolysis cell.

PEM (proton exchange membrane) electrolysis the electrodes are separated by a proton-conducting polymeric solid electrolyte (membrane)... 

Proton exchange membrane electrolysis cell (PEMEC) the electrolyte is a conductive proton exchange membrane (mainly Nafion ) and the process works around 100°C. 

Proton exchange membrane electrolysis cells (PEMECs)... 

In proton exchange membrane (PEM) or solid polymer electrolyte (SPE) electrolysis, the electrolyte is replaced by an ion-exchange resin. These units are compact, provide high current densities, but are more expensive, and because of the corrosive nature of the electrolyte, require special construction materials. 

Proton exchange membranes, whether operating in electrolysis mode or fuel cell mode, have the property of higher efficiency at lower current density. There is a 1 1 relationship in electrolysis between the rate of hydrogen production and current applied to the system. 

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. 

Linkous, C.A. et al. Development of new proton exchange membrane electrolytes for water electrolysis at higher temperatures, Int J. Hydrogen Energy, 23, 525-529 (1998). 

Morizonoa, T., Watanabe, K., and Ohstsuka, K., Production of hydrogen by electrolysis with proton exchange membrane (PEM) using sea water and fundamental study of hybrid system with PV-ED-EC, Mem. Fac. Eng., 31, 213-218 (2002). 

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. 

Solid Polymer Electrolysis (SPE) and Proton-exchange Membrane Fuel Cell (PEMFC)... 

Different electrolysis technologies could be applied, from the commercially available method based on alkaline cells to the new advanced cells based on proton exchange membrane (PEM) and solid oxide mixtures as electrolytes. The basic schemes of these electrolysers are shown in Eig. 2.4. 

Reduce the cost of proton exchange membrane (PEM) electrolysis to levels of 1250/kW for 10,000 standard cubic feet per day (scfd) at production levels of 10,000 units per year. 

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. 

The Proton or hydrogen ion is encounteed in various electrochemical processes such as electrolysis and PEMFC. It exists in the form of H+ in acid solutions and proton exchange membranes such as Nafion are well known. 

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-... 

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