Redox Flow Batteries, Alkali Membrane Fuel Cells, AMFCs

What are Redox Flow Batteries, Alkali Membrane Fuel Cells, AMFCs

Flow Batteries are energy storing devices which can be understood as being technology-wise between fuel cells and rechargeable batteries. Flow or Redox Flow batteries comprise of two, typically rather large liquid compartments separated by a membrane. In the two compartments liquid electrolyte, catholyte and anolyte, are pumped against each other and convert chemical to electrical energy. They usually suffer from lower energy density and need higher current density compared to lithium batteries and have lower charge and discharge rates, while they need to be larger to compensate this. The material demands are however less critical, and the design can be very flexible. They are usually long-lasting and use less harmful and cheaper chemicals, which makes them attractive for larger energy stationary storage alternatives. Due to the use of alkaline electrolyte Redox Flow Batteries are related to but not the same as Alkaline fuel cells (AFCs), alkaline membrane (AMFC) or alkaline anion exchange membrane fuel cell (AAEMFC). They are based on the transport of alkaline anions, usually hydroxide OH−, between the electrodes. Original AFCs used aqueous potassium hydroxide (KOH) as an electrolyte. NASA has used alkaline fuel cells in the 1960s for Apollo and Space Shuttle projects. Many recent developments focused on the Anion Exchange Membrane (AEM), which is the critical aspect of AFCs, since it is responsible for the transport of OH- ions. This is in contrast to PEM, which is a H+ conductive membrane, which is the main reason for a reduced interest in this kind of Fuel Cells. Both technologies, Redox Flow or AMFCs are collected in this field due to the close relation.