Editing Regenerative fuel cell (section)

==Process description==
A hydrogen fueled [[proton-exchange membrane fuel cell]], for example, uses [[hydrogen gas]] (H<sub>2</sub>) and oxygen (O<sub>2</sub>) to produce electricity and water (H<sub>2</sub>O); a regenerative hydrogen fuel cell uses electricity and water to produce hydrogen and oxygen.<ref>{{cite web |url=http://www.nfcrc.uci.edu/2/ACTIVITIES/PROJECTS/hydrogen/ElectrolyzerandReversibleFuelCell.aspx |title=Electrolyzer and Reversible Fuel Cell |publisher=Nfcrc.uci.edu |accessdate=2009-09-24 |url-status=dead |archiveurl=https://web.archive.org/web/20090618111819/http://www.nfcrc.uci.edu/2/ACTIVITIES/PROJECTS/hydrogen/ElectrolyzerandReversibleFuelCell.aspx |archivedate=2009-06-18 }}</ref><ref>{{cite web|url=https://cordis.europa.eu/project/id/19802 |title=Proton Exchange Membrane- based Electrochemical Hygrogen Generator |publisher=European Commission |date=2005-10-01 |accessdate=2021-10-18}}</ref><ref>{{cite web |url=http://gltrs.grc.nasa.gov/reports/2005/TM-2005-214032.pdf |title=Hydrogen-oxygen PEM regenerative fuel cell |accessdate=2009-09-24 |url-status=dead |archiveurl=https://web.archive.org/web/20110303170325/http://gltrs.grc.nasa.gov/reports/2005/TM-2005-214032.pdf |archivedate=2011-03-03 }}</ref>

When the fuel cell is operated in regenerative mode, the anode for the electricity production mode (fuel cell mode) becomes the cathode in the hydrogen generation mode (reverse fuel cell mode), and vice versa. When an external voltage is applied, water at the anode side will undergo electrolysis to form oxygen and protons; protons will be transported through the solid electrolyte to the cathode where they can be reduced to form hydrogen. In this reverse mode, the polarity of the cell is opposite to that for the fuel cell mode.  
The following reactions describe the chemical process in the hydrogen generation mode:

At the anode (where water is oxidized): H<sub>2</sub>O→1/2O<sub>2</sub> + 2H<sup>+</sup> + 2e<sup>−</sup>

At the cathode (where hydrogen is produced): 2H<sup>+</sup> + 2e<sup>−</sup>→ H<sub>2</sub>

Overall, the reaction can be summarized as: H<sub>2</sub>O→ 1/2O<sub>2</sub> + H<sub>2</sub>