How is deuterium concentrated by electrolysis of water?

Deuterium is concentrated through the electrolysis of water—typically a solution containing an electrolyte such as sodium hydroxide—by exploiting the different reaction rates of hydrogen isotopes.12

During the process, the hydrogen gas evolved at the cathode contains a smaller fraction of deuterium than the remaining liquid water. Because ordinary hydrogen is released more readily than deuterium, the latter becomes progressively concentrated in the residual water. By continuing this process until the volume of the original water is reduced to a tiny fraction—approximately one hundred-thousandth of its starting volume—practically pure deuterium oxide (heavy water) can be obtained.123