RedoxFlow

RedoxFlow, in the context of energy storage, refers to redox flow batteries, electrochemical devices in which energy is stored in liquid electrolytes held in external tanks. The electrolytes circulate through a reactor where redox reactions at the electrodes convert chemical energy to electrical energy and back.

A redox flow battery comprises two liquid electrolytes, a pumping system, a cell stack, and a membrane separator. Electrolytes flow past the electrodes; electrons travel through an external circuit while ions move through the membrane to balance charge. Energy capacity scales with electrolyte volume; power scales with cell stack size.

Chemistries vary. The vanadium redox flow battery (VRFB) is the most established; other types include iron/chromium, zinc–bromine, and all-vanadium systems. VRFBs use different oxidation states of vanadium in each tank, enabling reduced crossover; membranes and ion exchangers influence efficiency and cycle life.

Advantages include decoupled energy and power, long cycle life, and safety advantages for large-scale storage. Disadvantages are relatively low energy density, higher capital cost, membrane and electrolyte management issues, and the need for auxiliary equipment such as pumps and tanks.

Since the 1980s, redox flow technology has been explored for grid storage and renewable integration. It sees ongoing research to lower costs, raise energy density, and improve materials for membranes, catalysts, and electrolytes, with commercial deployments in some utilities and industrial facilities.