Electrolysis stacks are devices used to split water molecules into hydrogen and oxygen through the process of electrolysis. They consist of an anode and cathode, a membrane, a power supply, and a method of collecting the hydrogen and oxygen gases that are produced. The anode and cathode create an electric field between them, while the membrane separates the water into its two components. The power supply provides the electricity to the stack, which ionizes the water molecules, allowing the hydrogen and oxygen atoms to separate. The gases are then collected and stored for later use.