Hydrogen Evolution Reaction

The hydrogen evolution reaction is the chemical step that produces hydrogen gas by reducing protons, a reaction that normally needs a catalyst. It is the central reaction of water electrolysis, the process that splits water into hydrogen and oxygen using electricity, and is seen as a cleaner route to hydrogen fuel than steam methane reforming, which releases large amounts of greenhouse gas. In nature, hydrogenase enzymes built around iron and nickel catalyze the reaction; industrial electrolyzers typically use nickel-based catalysts, while proton exchange membrane electrolyzers rely on platinum supported on carbon. In acidic conditions the reaction runs as two protons and two electrons combining into hydrogen gas, and in neutral or alkaline conditions as water and electrons producing hydrogen gas and hydroxide, proceeding at the cathode by one of two known reaction pathways. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/