# Technology for Green Hydrogen Production: Desk Analysis
## 5 Conclusions  
Water electrolysis is a key process for producing green hydrogen. A comparative analysis of alkaline electrolyzers, PEM electrolyzers, solid oxide electrolyzers, and AEM electrolyzers evaluated based on several criteria, including the electrolyte used, electrode materials, efficiency, capital and operating costs, durability, flexibility, temperature range, scalability, environmental impact, and advantages and challenges revealed that each type of electrolyzer has its unique features, making them suitable for different applications (Table 7). AEs use a liquid alkaline solution as the electrolyte and Ni-based electrodes. They are characterized by moderate efficiency, low capital and operating costs, high durability, and low environmental impact. However, they have lower efficiency compared to some other methods, require robust materials due to the corrosive electrolyte, and have limited dynamic operation [12; 16; 19; 20; 21; 22; 23; 132; 133; 134; 135]. PEM electrolyzers employ a solid polymer electrolyte membrane and use expensive materials like Pt and Ir for the electrodes. They offer high efficiency, fast response times, and high current densities but are challenged by the high cost of materials, limited durability, and the requirement for pure water to prevent membrane degradation [13; 16; 24; 25; 26; 27; 28; 29; 30; 111; 134; 137; 138; 139; 140; 141]. SOEs operate at high temperatures, using a solid ceramic material as the electrolyte and specialized electrode materials. They boast high efficiency due to high operating temperatures, the ability to utilize waste heat, and the potential for integration with high-temperature processes. However, they require specialized materials, have slow startup and shutdown processes, and limited dynamic operation due to thermal stresses [14; 16; 31; 32; 33; 34; 35; 36; 70; 71; 108; 109; 134; 143; 144; 145; 146; 147; 148; 149; 150; 151; 152; 153; 154; 155; 156; 157; 158; 159; 160; 161; 162; 163; 164; 165; 166; 167]. AEM electrolyzers, similar to PEMs, use a solid polymer membrane but conduct hydroxide ions. They offer a lower cost due to less expensive materials, the potential for higher efficiency, and compatibility with less corrosive alkaline electrolytes. However, they suffer from limited durability and stability of membranes and electrodes, lower current densities, and require high-purity water to prevent membrane degradation [168; 169; 176; 177; 178; 179; 180; 173; 176; 177; 175; 176; 177; 178; 179; 180; 174; 175; 176; 177; 178; 179; 181; 177; 173; 176; 177; 178; 179; 182; 183]. The choice of technology for green hydrogen production is influenced by several key factors that vary based on the application and scale of green hydrogen production. The primary considerations concern the scale of production [16; 72; 91]. PEM electrolyzers are often preferred for small-scale applications due to their fast response times and high current densities, making them suitable for variable renewable energy sources. The ability to add or remove modules easily is crucial for scaling up or down based on demand or available renewable energy. AEs are commonly used due to their lower capital costs and proven technology. However, PEM electrolyzers are gaining popularity for their higher efficiency and energy density. The choice between wind, solar, hydro, or a combination thereof depends on the local availability and cost of these resources. SOEs or AEs are often considered for large-scale applications due to their potential for high efficiency and lower operational costs. The ability to integrate with large-scale renewable energy projects, such as wind farms or solar parks, is crucial for maximizing the use of renewable electricity [74; 75; 76]. The decreasing cost and increasing efficiency of renewable energy technologies are key drivers for the reduction in the cost of green hydrogen production [16; 91; 174].