This study conducts a comprehensive life cycle assessment (LCA) of four electrolyzer technologies: alkaline electrolyzer (AEL), proton-exchange membrane (PEM), anion-exchange membrane (AEM), and solid oxide electrolyzer (SOE). It evaluates their environmental impacts across four main categories: climate change (CC), human health (HH), ecosystem quality (EQ), and abiotic stock resources (ASRs). In order to highlight the critical raw materials (CRMs) used in their manufacturing processes, the research identifies potential material replacements and reveals distinct environmental impacts associated with material choices, such as steel in AEL and AEM, platinum in PEM, and nickel in both SOE and AEL. Additionally, we examine the integration of diverse electrolyzer technologies under various scenarios of renewable electricity sources. Together with a sensitivity analysis of regional electricity mixes and the degradation of stacks across different years, the study provides insights into significant opportunities for performance enhancements in emerging electrolyzer technologies.