# Technology for Green Hydrogen Production: Desk Analysis
## 2 Background of Analysis
### Water Electrolysis Process
For AE, the electrolyte is a solution of  
\begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline  
KOH, the separator is ZrO2 stabilized with a PPS mesh, and the electrodes are nickel-coated stainless steel with a nickel mesh as the porous transport layer. The bipolar plates are made of nickel-coated stainless steel. PEM electrolyzers use PFSA membranes as the electrolyte, a solid electrolyte for the separator, and platinum nanoparticles on carbon black for the hydrogen side electrode. The oxygen side electrode is made of high-surface-area Ni or NiFeCo alloys, and the bipolar plates are nickel-coated steel or stainless steel. AEM electrolyzers employ DVB polymer support with either KOH or NaHCO3 as the electrolyte, a solid electrolyte separator, and perovskite-type catalysts like LSCF or LSM for the oxygen side electrode. The hydrogen side uses high-surface-area nickel, and the bipolar plates are made of nickel-coated stainless steel. SOEs utilize yttria-stabilized zirconia (YSZ) as both the electrolyte and separator. The oxygen side electrode is made of perovskite-type materials, and the hydrogen side uses Ni/YSZ. The bipolar plates are constructed from nickel-coated stainless steel or cobalt-coated stainless steel. The current limitations in electrolyzer technology that are being actively addressed by R&D strategies include many factors, such as efficiency, cost, durability and lifetime, scalability, energy source integration, hydrogen compression and storage, system integration and control [5; 6; 10; 11; 16; 21; 64; 72]. While electrolyzers can convert electricity into hydrogen, the process is not yet as efficient as desired. Energy losses occur due to electrical resistance, heat generation, and inefficiencies in the electrochemical reactions. R&D is focused on improving the efficiency of the electrolysis process, which includes developing better catalysts, optimizing cell design, and improving the electrical conductivity of materials [21; 86; 92; 105; 106; 107]. The cost of electrolyzers and their components, such as membranes, catalysts, and bipolar plates, is currently high [13; 14; 15; 18; 20; 24; 25; 26; 27; 28; 29; 30; 46; 48; 49]. This is partly due to the use of expensive materials like precious metals as catalysts. R&D is working on reducing costs by finding alternatives to these expensive materials, improving manufacturing processes, and scaling up production to benefit from economies of scale. Electrolyzers need to operate for thousands of hours under varying conditions to be economically viable (Table 2) [16]. However, degradation of components over time can lead to reduced efficiency and increased maintenance costs [33; 34; 38; 39; 40; 41; 68; 108; 109]. R&D is focused on enhancing the durability of electrolyzer components, including the development of more robust membranes, catalysts, and other materials that can withstand corrosive environments and maintain performance over extended periods. To meet the growing demand for green hydrogen, electrolyzers need to be scaled up effectively. This involves not only building larger electrolyzers but also ensuring that they can be manufactured and operated at scale without significant increases in cost or decreases in efficiency. R&D is exploring modular designs and standardization to facilitate scalability [72; 110]. Electrolyzers are most environmentally beneficial when powered by RESs like wind and solar. However, the intermittent nature of these sources can pose challenges for continuous hydrogen production. R&D is investigating ways to better integrate electrolyzers with variable RESs, including energy storage solutions and smart grid technologies. After production, hydrogen needs to be compressed and stored for transportation or use. This step can account for a significant portion of the overall cost and energy requirements. R&D is exploring inexpensive and effective methods for hydrogen compression and storage, including new materials for storage tanks and innovative compression technologies.