Electrolytes are electrically-conductive materials that are used in:
- fuel cells
- biochemical systems
They contain free ions and are generally available in either solid or liquid form. Some gases can serve as electrolytes under low pressure or high temperature conditions. Typically, however, electrolytes exist as ionic solutions, or as molten salts or solids. Electrolytes in solution may have either a high concentration or a low concentration of ions. Using electrolysis, constituent elements and compounds in these solutions can be extracted.
Electrolytes conduct electricity when a voltage is applied to electrodes called an anode and a cathode. Normally, lone electrons cannot pass through the electrolyte. The chemical reaction that occurs at the cathode, however, consumes electrons from the anode. Conversely, the chemical reaction that occurs at the anode produces electrons that are consumed by the cathode. The result is the development of a negative charge around the cathode and a positive charge around the anode. In the electrolyte, ions move to neutralize these charges and the chemical reactions continue.
Dilute sulfuric acid is used in batteries as a liquid electrolyte. A strong acid, this battery electrolyte is highly-ionized and corrosive, even with the addition of water. In the United States, sulfuric acid solution is shipped with a material safety data sheet (MSDS) and permissible exposure limit (PEL) information from the Occupational Health and Safety Administration (OSHA).
Other liquid electrolytes for batteries, fuel cells, and capacitors include:
- aqueous sodium chloride
- hydrochloric acid
- aqueous sodium hydroxide
There are two basic types of solid electrolytes: point defect and solid state. Along with some oxides, alkali and alkaline earth halides conduct electricity through point defects. Such electrolytes have a compact crystalline structure and relatively high levels of intrinsic conduction activation energy. The second type of electrolyte (solid-state) conducts electricity via sub-lattice ionic disorders. Solid state electrolytes are often used in batteries. Electrolyte salts provide strong thermal and hydrolytic stability. They are used in organic electrolyte-based batteries, non-aqueous electrochemical cells, primary and secondary cells that use organic liquid electrolytes, polymer batteries, and lithium ion cells. Some secondary lithium ion salts are used in high-voltage applications. Others feature an electrical conductivity that is well-suited for sustained-rate applications. Lithium salts for organic, electrolyte-based lithium batteries are organic ions that provide strong covalent bonding and help avoid thermal degradation.
Ozguy89 / CC BY-SA 3.0