Acids, aqueous electrolytes

An early attempt for ordered growth of a chalcogenide simple compound has been the cathodic deposition of thin (3 p,m) CdTe films on n-type (100) GaAs single crystals from an acidic aqueous electrolyte at 95 °C, which contained Cd(II) and Te traces generated electrolytically in situ by using a pure Te anode [4]. The... 

Cyclic voltammetry studies of single-crystal platinum electrodes in acidic aqueous electrolytes showed that the two characteristic peaks of hydrogen adsorption/desorption on platinum (see Fig. 5.40) correspond in fact to reactions at two different crystal faces the peak at lower potential to Pt(100) and the other one to Pt(lll). 

For acidic aqueous electrolytes, the cheapest valve metal, titanium, is chosen as cathode material. The stability of this metal, however, is questionable in the presence of fluoride and complexing organic anions, so that particular care should be taken if choosing titanium for organoelectrosyn-... 

When used in electropolishing and electropickling processes, strongly acidic aqueous electrolytes create large quantities of metal-laden, corrosive effluent solution, whereas in ionic liquid electrolytes the metals will precipitate and be readily separated and recycled. 

Lead-acid accumulator — (- Sinsteden 1854, - Plante 1859-60) A secondary - battery containing a lead dioxide positive electrode, a metallic lead negative electrode and a sulfuric acid aqueous electrolyte solution. The electrode reactions are... 

First electrochemical studies on structuring and modification of different high superconductor surfaces have recently been started [6.190]. One of the main problems is the instability of oxide ceramic material in neutral and acidic aqueous electrolyte solutions at room temperature [6.196-6.198]. HTSC surfaces corrode, and superconductivity was found to decrease within the topmost layers of IfTSC samples after water contact. This aging effect decreases in alkaline media [6.197]. However, sufficient long term stability of HTSC samples was only found in aprotic solvents such as acetonitrile. Therefore, experiments were carried out in acetonitrile-containing... 

It is worth noticing that the electrolyte nature plays a significant role in the pseu-docapacitive properties of carbon-based materials becanse the snrface functionalities can exhibit different behavior depending on the electrolytes. For example, quinone-type functionalities generate pseudocapacitive effects in the presence of acidic aqueous electrolytes such as H2SO4 since they reqnire protons to proceed as shown in Reaction 2.1, while this effect is hardly observed when alkaline electrolytes are used [76,77]. 

For example, let us consider the interface between a very acidic aqueous electrolyte ipH= 1), containing neither dioxygen nor dihydrogen dissolved species, and a platinum electrode which is inert in this electrolyte. The only electroactive species present in the bulk electrolyte are protons and water. The corresponding redox couples are 02/H20,0H" and H H20/H2. The shape of the current-potential curve (represented in figure 2.25 with a dashed and dotted line) is the sum of the contributions of each couple (grey curves). These couples are supposed to be fast, and the values of the apparent standard potentials are ... 

For such reasons, some materials cannot be used over certain pH ranges although this would give a more advantageous potential this is illustrated by y-MnOj Its potential is 1.01 V versus NHE in an acidic medium, and only 0.71 in neutral medium. However, this oxide should dissolve as Mn " in an acidic aqueous electrolyte during cathodic discharge and the electrode material should consequently disappear. 

Most of the earlier studies on proton insertion in ECDs, have been devoted to acidic aqueous electrolytes. However, since most of the electrochromic materials are chemically unstable in acidic medium, commercially viable ECDs must use other electrolytes. Recently, the use of solid anhydrous proton electrolytes seems to be very promising. We present some of the materials which have been used in ECDs. 

At open circuit, electrode reactions that charge the electrodes lead to a slow oxidation of the electrolyte with H2 evolution at the anode and O2 evolution at the cathode. These reactions represent an irreversible self-discharge. Once the electrolyte is introduced, the battery has a poor shelf life. Under development are acidic aqueous electrolytes in which Pb(II) is soluble rather than condensing into the solid PbS04. This development of the lead-acid cell promises a flow battery not requiring a separation membrane. The separation membrane of redox-flow batteries (see last section) remains a challenging problem for the aqueous redox-flow technology. 

Fig. 5.2 Simplified fuel cell scheme with an acidic aqueous electrolyte, e.g., the polymer electrolyte fuel cell (PEFC). Fuel H2, oxidant O2. Only porous gas diffusion electrodes and electrolyte are shown, cell housing is not shown [8]...

The polymer electrolyte fuel cell, PEFC, and the phosphoric acid fuel cell, PAFC, are acidic fuel cells the PEFC operates in the temperature range below and around 100 °C (PEFC), respectively, and the PAFC at around 200 °C. Hydrogen is the preferred fuel for both types. A PEFC can also be fed by liquid or gaseous methanol, called direct methanol fuel cell, DMFC. Other fuels based on alcohols, e.g., the direct ethanol fuel cell, DEFC, are subject to research. Fuel cell types utilizing an acidic aqueous electrolyte will not be considered here. 

Aqueous electrolytes are used frequently due to low cost and availability. Ion sources include potassium hydroxide, potassium chloride, and sulfuric acid. Aqueous electrolytes are most commonly applied in the development stages of new ES materials. This is because of several key factors that include high ionic conductivity, mobility, and low hazard level. Further, aqueous electrolytes can be used in open environments and do not require water-free envi-ronmenfs as organic electrolyfes do. 

What are the commonalities and differences between electrochemical properties in acetonitrile and acidic aqueous electrolyte media for poly(aromatic amines) For other CP systems ... 

For acid aqueous electrolytes that transport positive ions through the electrolyte (e.g. 

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