Hydroxide-conducting polymer electrolytes

Electrodeposition of conducting polymers on copper has been investigated by several groups, and various salts have been tested to achieve the electrochemical polymerization of pyrrole from aqueous solutions in a one-step process. No serious difficulty was found, and electrolytes used previously on iron, such as oxalic acid [115,116], salicylates [117,118], and tartrate [119] were found suitable for PPy electrodeposition on copper and its alloys aqueous phosphate solutions were also found to provide highly adherent and homogenous films [120]. In all cases, PPy electrodeposition occurred after the preliminary passivation of copper through a mixed copper salt, copper oxide, or copper hydroxide layer. A two-step process, where an oxalate-doped PPy underlayer (PPy-Oxalate) is first deposited, followed by a dodecylbenzenesulfonate-doped PPy layer... 

Alkaline-based polymer electrolyte membranes are relative newcomers on the scene. It has been widely believed that the quaternary ammonium hydroxide functional group (RN4 , OH ), which is the one used in most anion exchange membranes, is self-destructive, because the OH- ion is likely to attack the RN4 cation. In addition, the specific conductivity of an OH conducting ionomer was suspected of being at least a factor 3-A lower than that of the H" conducting... 

Since the type of electrolyte material dictates operating principles and characteristics of a fuel cell, a fuel cell is generally named after the type of electrolyte used. For example, an alkaline fuel cell (AFC) uses an alkaline solution such as potassium hydroxide (KOH) in water, an acid fuel cell such as phosphoric acid fuel cell (PAFC) uses phosphoric acid as electrolyte, a solid polymer electrolyte membrane fuel cell (PEMFC) or proton exchange membrane fuel cell uses proton-conducting solid polymer electrolyte membrane, a molten carbonate fuel cell (MCFC) uses molten lithium or potassium carbonate as electrolyte, and a solid oxide ion-conducting fuel cell (SOFC) uses ceramic electrolyte membrane. 

An HEM is a membrane-form polymer electrolyte capable of conducting hydroxide anions (OH ), and an HEI is a binder-form polymer electrolyte capable of not only conducting hydroxide anions but also creating triple-phase boundary in the electrode catalyst layer. HEMs and HEIs are already used in hydroxide exchange membrane fuel cells (HEMFCs) and can also be used in many other electrochemical energy conservation and storage devices. 

As with the conventional proton exchange membranes (PEMs) whose chief application is in proton exchange membrane fuel cells (PEMFCs), HEMs are thin-membrane polymer electrolytes, and thus HEMECs can achieve high energy density and power density. The difference is in the conducting ion HEMs conduct hydroxides PEMs conduct protons. 

Hydroxide-Ion-Conduction Membrane Used for Electrochemical Conversion of Carbon Dioxide in Alkaline Polymer Electrolyte Membrane Cells... 

Numerous electrolytes are used in commercial electrolytic cells. Aqueous solutions of sodium hydroxide, sodium chloride, hydrochloric acid and electrolytes immobilized in polymers are used. The most common electrolyte is a 25-36 wt.Vo potassium hydroxide solution because of its superior conductivity. 

A three compartment electrolytic cell with two fritted disk separators was used. An auxiliary platinum electrode was placed in each of the two end compartments while an aluminium strip, to which a surface treatment based on chromic acid etching had been applied, was placed in the middle compartment. Ihe monomer solution contained methacrylic acid (0.436 M) and -methylenebisacrylamide (0.145 M) in water. The pH of the above solution was adjusted to desired values by adding either sulfuric acid or aqueous sodium hydroxide. The monomer solution (400 mi) was placed in the middle compartment while two end compartments contained water adjusted to the same pH as the monomer solution. While bubbling nitrogen through the monomers solution, the electrolysis was conducted at 10 vdts for 6 hours such that the cathodic reaction would occur in the center compartment. The polymer coating obtained on the aluminium cathode was washed with fresh water, dried in vacuum oven at room temperature, and weighed. The copolymer was then scraped off from aluminium and its composition determined by elemental analysis. 

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