Electrical conductivity proton-conducting oxides

In the previous section, /1-aluminas were discussed. If one replaces Na+ by H30+ or NH4 in these oxide compounds by, for example, electrolysis, then proton conducting materials can be obtained. Their ionic conductivity, however, is relatively low (10—5 Q-1 cm-1) because of the strong interactions between the small H+ ions and O2- ions in the conduction plane (OH ). The electrical conductivity is markedly higher in crystals of NH4 -/ -Ga203. 

Although the motion of protons does not lead to electrical conduction in the case of benzoic acid, electronic and even ionic conductivity can be found in other molecular crystals. A well-studied example of ionic conduction is a film of polyethylene oxide (PEO) which forms complex structures if one adds alkaline halides (AX). Its ionic conductivity compares with that of normal inorganic ionic conductors (log [cr (Q cm)] -2.5). Other polymers with EO-units show a similar behavior when they are doped with salts. Lithium batteries have been built with this type of... 

PANI is unique in that its most oxidized state, the pernigraniline form (which can be accessed reversibly), is not conducting. In fact, it is the intermediately oxidized emeraldine base that exhibits the highest electrical conductivity. Protonic Acid Doping is the most general means by which to obtain this partially pro-tonated form of PANI [301]. Exposure of the emeraldine salt to alkali solutions reverses this process and brings a return to the insulating state. 

CNTs were also demonstrated to be a perfect support for cheap transition metal oxides of poor electrical conductivity, such as amorphous manganese oxide (a-Mn02 H20) [5,96], The pseudocapacitance properties of hydrous oxides are attributed to the redox exchange of protons and/or cations with the electrolyte as in Equation 8.13 for a-Mn02 H20 [97] ... 

The electrolyte membrane presents critical materials issues such as high protonic conductivity over a wide relative humidity (RH) range, low electrical conductivity, low gas permeability, particularly for H2 and O2, and good mechanical properties under wet-dry and temperature cycles has stable chemical properties under fuel cell oxidation conditions and quick start-up capability even at subfreezing temperatures and is low cost. Polyperfluorosulfonic acid (PFSA) and derivatives are the current first-choice materials. A key challenge is to produce this material in very thin form to reduce ohmic losses and material cost. PFSA ionomer has low dimensional stability and swells in the presence of water. These properties lead to poor mechanical properties and crack growth. 

Shown in Figure 6 is a diagram of a nickel support and a Pt-loaded nanoparticulate oxide acting as a porous cathode. Organic-based fuel cell cathodes often have some Nafion added to improve proton conductivity but at the cost of electrical conductivity. However, we have the reverse problem - we have excellent proton conductivity in the inorganic cathode, but the oxides are electrical insulators. We need to boost the electrical conductivity of the cathode in order to fabricate a total inorganic MEA. This is a major objective of our future work. 

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