The proton exchange membrane water electrolyzer (PEMWE) represents a pioneering technology in the field of green hydrogen production. In light of the environmental issues associated with climate change, the reduction of CO₂ emissions has become a matter of increasing relevance, with investments in technology growing on a daily basis. The case study presented in the report is a stack water electrolyzer belonging to the company 1S1 Energy and appears to be highly promising as a high-performance technology. All analyses of the stack were conducted at CO2 circle lab, located at the Environment park in Turin, using a homemade test bench, and they will be presented following a general description of PEMWE.