Ionic liquid fuel cell

Particularly when doped appropriately, the ionic liquid fuel cell (ILFC) gives clearly superior performance [18]. Using an ambient temperature version of the (technologically unacceptable) difluoride IL illustrated in Figure 2.8, equally good performance can be obtained at ambient temperature It is expected that this application of the ionic liquid concept will receive considerable attention in the immediate future. Results using more efficient Teflon sandwich cells and colloidal Pt electrodes will be reported separately [41]. 

Fig. 5.6-4 Schematic illustration of a supported ionic liquid fuel cell containing the Wacker oxidation system (SMSEC supported molten salt electro-catalyst) for co-generatlon of acetaldehyde and electricity from ethanol [55],...

Mysyk, R., V. Ruiz, E. Raymundo-Pinero, R. Santamaria, and F. Beguin. 2010. Capacitance evolution of electrochemical capacitors with tailored nanoporous electrodes in pure and dissolved ionic liquids. Fuel Cells 10 834-839. 

Hagiwara R, Nohira T, Matsumoto K and Tamba Y (2005) A Fluorohydrogenate Ionic Liquid Fuel Cell Operating Without Humidification, Electrochemical and Solid-State Letters, 8, pp. A231-A233. 

It was quite recently reported that La can be electrodeposited from chloroaluminate ionic liquids [25]. Whereas only AlLa alloys can be obtained from the pure liquid, the addition of excess LiCl and small quantities of thionyl chloride (SOCI2) to a LaCl3-sat-urated melt allows the deposition of elemental La, but the electrodissolution seems to be somewhat Idnetically hindered. This result could perhaps be interesting for coating purposes, as elemental La can normally only be deposited in high-temperature molten salts, which require much more difficult experimental or technical conditions. Furthermore, La and Ce electrodeposition would be important, as their oxides have interesting catalytic activity as, for instance, oxidation catalysts. A controlled deposition of thin metal layers followed by selective oxidation could perhaps produce cat-alytically active thin layers interesting for fuel cells or waste gas treatment. 

As for the other electrochemical storage/conversion devices, the fuel cell electrolyte must be a pure ionic conductor to prevent an internal short circuit of the cell. It may have an inert matrix that serves to physically separate the two electrodes. Fuel cells may contain all kinds of electrolytes including liquid, polymer, molten salt, or ceramic. 

It is possible to make nonstoichiometric solids that have ionic conductivities as high as 0.1-1000 S m-1 (essentially the same as for liquid electrolytes) yet negligible electronic conductances. Such solid electrolytes are needed for high energy density electrical cells, fuel cells, and advanced batteries (Chapter 15), in which mass transport of ions between electrodes is necessary but internal leakage of electrons intended for the external circuit... 

As long as fuel cells are using liquid electrolytes like phosphoric acid or concentrated caustic potash, the catalyst utilization is usually not limited by incomplete wetting of the catalyst. Provided the amount of electrolyte is sufficiently high, the hydrophilic porous particles are not only completely flooded but due to their expressed hydrophilicity are wetted externally by an electrolyte film that together with the whole electrolyte-filled hydrophilic pore system establishes the ionic contact of an electrode to the respective counterelectrode. 

Introduction of room-temperature ionic liquids (RTIL) as electrochemical media promises to enhance the utility of fuel-cell-type sensors (Buzzeo et al., 2004). These highly versatile solvents have nearly ideal properties for the realization of fuelcell-type amperometric sensors. Their electrochemical window extends up to 5 V and they have near-zero vapor pressure. There are typically two cations used in RTIL V-dialkyl immidazolium and A-alkyl pyridinium cations. Their properties are controlled mostly by the anion (Table 7.4). The lower diffusion coefficient and lower solubility for some species is offset by the possibility of operation at higher temperatures. 

A similar distinction between a system with pre-electrolysis with only one electrode (in this case anodic) process, and a system with simultaneous anodic and cathodic processes (in which anode and cathode are on opposite walls of a microchannel so that each liquid is only in contact with the desired electrode potential, analogous to the fuel cell configurations discussed above) was made by Horii et al. (2008) in their work on the in situ generation of carbocations for nucleophilic reactions. The carbocation is formed at the anode, and the reaction with the nucleophile is either downstream (in the pre-electrolysis case) or after diffusion across the liquid-liquid interface (in the case with both electrodes present at opposite walls). The concept was used for the anodic substitution of cyclic carbamates with allyltrimethylsilane, with moderate to good conversion yields without the need for low-temperature conditions. The advantages of the approach as claimed by the authors are efficient nucleophilic reactions in a single-pass operation, selective oxidation of substrates without oxidation of nucleophile, stabilization of cationic intermediates at ambient temperatures, by the use of ionic liquids as reaction media, and effective trapping of unstable cationic intermediates with a nucleophile. 

Solid Polymer Electrolyte Fuel Cell Here, there is no apparent liquid solution, or high-temperature ionic conductor. The usual ionic solution between the electrodes is replaced by a well-humidified membrane made of a perfluorosulfonic acid polymer that conducts protons. 

A combination of 98% H3P04 and 2% water provides a liquid that can be heated to > 200 °C at atmospheric pressures. A high temperature of 150 °C is required to polymerize phosphoric acid to pyrophosporic acid (H4P207), which has a considerably higher ionic conductivity than the parent acid. It was necessary to raise the operating temperature of the fuel cell to 200 °C in order to tolerate a carbon monoxide level of... 

PROTON TRANSFER IONIC LIQUIDS AS NOVEL FUEL CELL ELECTROLYTES... 

Surprisingly, it is only a very recent recognition that protic ionic liquids can serve as proton transfer electrolytes in hydrogen-oxygen fuel cells. A current report from the laboratory of Watanabe [40] describes the performance of a hydrogen electrode utilizing, as the electrolyte, the salt formed by proton transfer from the acid form of f>/i-trifluoromethanesulfonyl imide (HTFSI) to the base imidazole. 

Especially to be noted is the high potential of the cell relative to the value obtained when the IL is replaced by 98% H3PO4 with, (0.9 vs. 0.75 V), which is maintained under load when using ethylammonium nitrate as electrolyte. It is evident that with the protic ionic liquid, a much higher exchange current density at the oxygen electrode can be obtained than in other fuel cells. 

Room-temperature ionic liquids (denoted RTILs) have been studied as novel electrolytes for a half-century since the discovery of the chloroaluminate systems. Recently another system consisting of fluoroanions such as BF4 and PFg , which have good stability in air, has also been extensively investigated. In both systems the nonvolatile, noncombustible, and heat resistance nature of RTILs, which cannot be obtained with conventional solvents, is observed for possible applications in lithium batteries, capacitors, solar cells, and fuel cells. The nonvolatility should contribute to the long-term durability of these devices. The noncombustibility of a safe electrolyte is especially desired for the lithium battery [1]. RTILs have been also studied as an electrodeposition bath [2]. 

Ionic liquids (ILs) are being considered more and more as alternatives for conventional electrolyte materials [5-7]. ILs offer the unique features of nonvolatility and nonflammability even in a liquid state. Systems that show ionic conductivity of over 10 S cm at room temperature have been reported close to the level required for fuel cell applications [8-10]. However, this value is based on the IL itself, and they do not include target ions such as the proton. This is a critical subject of research on making the present system viable. 

Molten salts at room temperature, so-called ionic liquids [1, 2], attracting the attention of many researchers because of their excellent properties, such as high ion content, liquid-state over a wide temperature range, low viscosity, nonvolatility, nonflammability, and high ionic conductivity. The current literature on these unique salts can be divided into two areas of research neoteric solvents as environmentally benign reaction media [3-7], and electrolyte solutions for electrochemical applications, for example, in the lithium-ion battery [8-12], fuel cell [13-15], solar cell [16-18], and capacitor [19-21],... 

Because ionic liquids (ILs) consist only of ions, they offer two brilliant features very high concentration of ions [1] and high mobiUty of component ions at room temperature. Because many ILs show the ionic conductivity of over 10 S cm at room temperature [2, 3], there are plenty of possible applications as electrolyte materials, among these, for rechargeable lithium-ion batteries [4—8], fuel cells [9-12], solar cells [13-17], and capacitors [18-23],... 

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