Alkaline electrolyte membrane

Li YS, Zhao TS, Liang ZX (2009) Performance of alkaline electrolyte-membrane-based direct ethanol fuel cells. J Power Sources 187 387-392... 

Sun, H. Zhang, G. Liu, Z. Zhang, N. Zhang, L. Ma, W. Zhao, C. Qi, D. Li, G. Na, H., Self-crosslinked alkaline electrolyte membranes based on quaternary ammonium poly(ether sulfone) for high-performance alkaline fuel cells. International Journal of Hydrogen Energy 2012,37(12), 9873-9881. 

Alkaline solutions are generally known to lead to better catal5Tic activities than acidic solutions for many relevant electrode reactions. However, owing to the paucity in the development of suitable electrolyte materials, such as alkaline membranes, there has been much less fundamental work in the area of fuel cell catalysis in alkaline media. Nevertheless, there are a few hopeful developments in new alkaline polymer membranes [Varcoe and Slade, 2005] that are currently stirring up interest in smdying fuel cell catalytic reactions in alkalme solution. 

Aqueous, alkaline fuel cells, as used by NASA for supplemental power in spacecraft, are intolerant to C02 in the oxidant. The strongly alkaline electrolyte acts as an efficient scrubber for any C02, even down to the ppm level, but the resultant carbonate alters the performance unacceptably. This behavior was recognized as early as the mid 1960 s as a way to control space cabin C02 levels and recover and recycle the chemically bound oxygen. While these devices had been built and operated at bench scale before 1970, the first comprehensive analysis of their electrochemistry was put forth in a series of papers in 1974 [27]. The system comprises a bipolar array of fuel cells through whose cathode chamber COz-containing air is passed. The electrolyte, aqueous Cs2C03, is immobilized in a thin (0.25 0.75 mm) membrane. The electrodes are nickel-based fuel cell electrodes, designed to be hydrophobic with PTFE. 

Vandenborre Hv Leysen R., Baetsle L.H., Alkaline inorganic-membrane-electrolyte (IME) water electrolysis, bit.. Hydrogen Energ., 5(2), 165-171,1980. 

At least two factors should be considered in this context. First, the current should not include significant contributions from electrochemical reactions other than the oxidation of hydrogen. If the membrane is made of steel, this can be achieved by the choice of an alkaline electrolyte in the anode chamber and application of a potential that passivates the steel. 

The cells shown in Figs. 28 and 29 all operate according to the same principles, which have been developed by Arup. The interior of the cell acts as the anode chamber, and a metal oxide cathode placed inside the cell in an alkaline electrolyte acts as the counter electrode. The hydrogen flux across the integrated membrane (coated with palladium on the internal surface) can be measured as the potential drop across a resistor placed between the membrane and the counter electrode. 

Unlike alkaline, phosphoric acid, and polymer electrolyte membrane fuel cells, MCFCs don t reguire an external reformerto convert more energy-dense fuels to hydrogen. Due to the high temperatures at which they operate, these fuels are converted to hydrogen within the fuel cell itself by a process called internal reforming, which also reduces cost. 

The chloralkali electrolysis process is by far the most important source of electrolytically generated hydrogen because hydrogen from alkaline or membrane water electrolysis usually cannot compete with hydrogen from steam reforming followed by shift reaction and PSA purification and therefore is not performed on a large scale (62, 40). 

A schematic diagram of the microbial sensor is illustrated in Figure 1. The sensor consisted of double membranes of which one layer was the bacteria-collagen membrane (thickness 40jam), the other an oxygen permeable Teflon membrane (thickness 27jam), an alkaline electrolyte, a platinum cathode, and a lead anode. 

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

Note PAFC phosphoric acid fuel cell PEMFC proton exchange membrane fuel cell/polymer electrolyte membrane fuel cell MBFC microbiological fuel cell DMFC direct methanol conversion fuel cell AFC alkaline fuel cell MCFC molten carbonate fuel cell SOFC solid oxide fuel cell ZAFC zinc air fuel cell. 

Some of the common electrolysers are Alkaline Electrolysers, Polymer Electrolyte Membrane (PEM) Electrolysers (also known as Proton Exchange Membrane electrolysers), and Steam Electrolysers. In alkaline electrolysers a liquid electrolyte, such as a 25% potassium hydroxide solution, is used. At... 

Figure 3.5. Process diagram of alkaline electrolysis for the production of H2 Polymer Electrolyte Membrane (PEM) Electrolysis...

A second class of fuel cells employs hydroxide-conducting (alkaline) electrolytes, again either in form of a solid membrane (alkaline membrane fuel cells) or a liquid electrolyte (alkaline fuel cells). While the modem era of fuel cells began with the latter type, the former type is under intense research today because a stable, highly conducting alkaline membrane with good C02 tolerance has remained elusive to date. 

Alkaline fuel cells (AFC) — The first practical -+fuel cell (FC) was introduced by -> Bacon [i]. This was an alkaline fuel cell using a nickel anode, a nickel oxide cathode, and an alkaline aqueous electrolyte solution. The alkaline fuel cell (AFC) is classified among the low-temperature FCs. As such, it is advantageous over the protonic fuel cells, namely the -> polymer-electrolyte-membrane fuel cells (PEM) and the - phosphoric acid fuel cells, which require a large amount of platinum, making them too expensive. The fast oxygen reduction kinetics and the non-platinum cathode catalyst make the alkaline cell attractive. 

In this book the focus is on PEMFCs therefore, in the following sections we will only discuss several major types of PEMFCs, such as H2/air (02) fuel cells, direct liquid fuel cells, PAFCs, and alkaline fuel cells. PEMFCs, also called solid polymer electrolyte fuel cells, use a polymer electrolyte membrane as the electrolyte. They are low-temperature fuel cells, generally operating below 300°C. 

Fuel cells are classified primarily according to the nature of the electrolyte. Moreover, the nature of the electrolyte governs the choices of the electrodes and the operation temperatures. Shown in table 10.1 are the fuel cell technologies currently under development. "" Technologies attracting attention toward development and commercialization include direct methanol (DMFC), polymer electrolyte membrane (PEMFC), solid-acid (SAFC), phosphoric acid (PAFC), alkaline (AFC), molten carbonate (MCFC), and solid-oxide (SOFC) fuel cells. This chapter is aimed at the solid-oxide fuel cells (SOFCs) and related electrolytes used for the fabrication of cells. 

B. Xing and O. Savadogo. Hydrogen/oxygen polymer electrolyte membrane fuel cells (PEMECs) based on alkaline-doped polybenzimidazole (PBI). Electrochemistry Communications 2, 697-702 2000. 

In the past two decades, fuel cells and in particular imi-exchange membranes have become a top priority topic in material research. Fuel cells are seen as promising alternative energy conversion systems replacing the combustion-based techniques. Among the various types of fuel cells, the low-temperature fuel cells like the polymer electrolyte membrane fuel cell (PEMFQ, DMFC, or alkaline fuel cell (AFC) are the most flexible ones concerning range of appUcations e.g. portable, automotive, and stationary. 

Most studies of membrane conductivity in alkaline electrolytes have been carried out in concentrated solutions. The conductivity of Nafion in concentrated alkaline solutions is generally one order of magnitude smaller than that in pure water or in acid electrolytes, because the membranes absorb far less electrolyte when in neutralized form, as shown by Eq. (6). 

It has been recently reported " that Nafion membranes show an ohmic behavior in 5 M NaOH, while in 10 M NaOH solution the specific conductance of the membranes increases with increasing current density. It is suggested that the passage of high currents at a severely dehydrated membrane may produce morphological changes that alter the character of the ionic conduction paths in the polymer. Hsu et have observed that the membrane conductivity of Nafion in alkaline electrolyte exhibits ion percolation behavior and can be described by... 

Yeo et al have reported an analysis of the conductivity of Nafion in different alkaline electrolytes, based on the correlation of membrane conductivity with water content. The analysis reveals that larger conductivities arise when the membranes are equilibrated with NaOH solutions than with KOH solutions of equal molarity. Also, it is shown that better conductivity can be realized with thinner and lower-EW membranes. These effects have been proven in an alkaline-water electrolyzer and in relation to the conductivity... 

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