Regenerative Fuel Cell

A regenerative fuel cell, also called a reverse fuel cell, is a fuel cell built to run in reverse, consuming electricity and one chemical to produce another rather than consuming fuel to produce electricity, and while almost any fuel cell reaction could in principle be reversed, only purpose built designs such as high pressure electrolyzers, solid oxide electrolyzer cells and unitized regenerative fuel cells achieve useful efficiency running backward. In a hydrogen based version the electrode roles simply swap between the two modes: in reverse operation an applied voltage splits water at the anode into oxygen and protons, and the protons cross the electrolyte to the cathode, where they combine into hydrogen gas, so the overall reaction turns water into hydrogen and oxygen instead of the other way around. A solid oxide regenerative fuel cell runs this reaction at high temperature, which lowers the electricity it needs for electrolysis, and demonstrations of this variant have reached current densities of 0.3 amps per square centimeter at essentially full efficiency and only 1.07 volts, a result researchers see as promising for hydrogen production in the 500 to 750 degree Celsius range.