The climbing demand for green hydrogen requires scalable and efficient production methods. This hydrogen will be generated from sustainable energy to serve as a replacement for fossil fuels. Consequently, the demand for electrolyzers is increasing, necessitating scalable production processes. Water electrolyzers play a crucial role in this transition, yet their assembly remains predominantly manual, leading to high costs and inefficiencies. This paper presents an optimized hybrid assembly process for water electrolyzers in a human-robot interaction cell. The technical boundary conditions were analyzed, and key target criteria as ergonomics, quality, and process time were defined. A skill-oriented allocation of assembly tasks was developed to leverage the respective strengths of humans and robots. Process times were determined using MTM-UAS for human tasks and a specially developed Robot-PMTS method for robotic operations. Based on these findings, an optimized assembly sequence was derived, reducing physical strain on workers, ensuring high-quality standards, and minimizing throughput time. A standardized work plan was created to facilitate practical implementation. The proposed approach was validated through simulation, confirming its feasibility and effectiveness. The result provides a scalable, ergonomic, and cost-efficient assembly concept for the industrialized production of water electrolyzers.