The Reversible Hydrogen Electrode (RHE) is a primary reference electrode widely used in electrocatalysis, water splitting, fuel cell, and photoelectrochemical research. Unlike conventional reference electrodes, the RHE automatically accounts for the pH of the electrolyte, allowing direct comparison of electrochemical measurements across acidic, neutral, and alkaline conditions. Its potential is based on the reversible hydrogen evolution/oxidation reaction, making it the preferred reference for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) studies. The electrode provides highly stable and reproducible potential measurements while eliminating the need for post-experimental pH corrections. RHEs are commonly used in electrolyzers, fuel cells, semiconductor characterization, and catalyst performance evaluation. Their direct relation to the hydrogen redox scale ensures accurate determination of overpotentials, reaction kinetics, and electrocatalytic activity. Compatible with most electrochemical workstations, the RHE is considered the industry-standard reference electrode for advanced energy and electrochemical research.