A 'stack', the black core component of the electrolyser that filters water before it is electrolysed. It is at the heart of a Proton Exchange Membrane (PEM) electrolyser at a hydrogen energy pilot project inside Gasunie's Hystock site. An electrolyser is a system that uses electricity to break water into hydrogen and oxygen in a process called electrolysis. 

This electrolyser system, made by UK firm ITM Power, creates hydrogen gas, an energy carrier that can be used to power any hydrogen fuel cell electric application. The entire system also contains pumps, vents, storage tanks, a power supply, separator and other components.