# Technology for Green Hydrogen Production: Desk Analysis
## 4 Results and Discussion
### Current Technologies Used for Green Hydrogen Production
#### 4.2.4 Anion Exchange Membrane Electrolyzers
R&D efforts are focused on improving the membrane, catalysts, durability, and the balance of plant components. The electrode area for a cold start to nominal load should be less than 300 cm\({}^{2}\) for a time under 20 min or less than 1000 cm\({}^{2}\) for under 5 min. The capital costs for a stack with a minimum size of 1 MW are currently unknown but are expected to be less than USD 100/kW, while the system costs for a minimum of 10 MW are also unknown but targeted to be less than USD 200/kW. The need for substantial advancements in AEM technology to achieve the desired cost reductions and efficiency improvements for green hydrogen production, which is crucial for meeting the stringent climate goals set for 2050 is emphasized [16]. AEM electrolyzers are of interest due to their potential to use less expensive materials compared to PEM electrolyzers, as they can operate with non-noble metal catalysts and may allow for the use of a wider range of membrane materials. However, they face challenges such as the stability of the membrane and electrolyte in the highly alkaline environment \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Parameter** & **2020** & **Target 2050** & **R\&D Focus** \\ \hline Nominal current density & 0.2–2 A cm\({}^{-2}\) & \textgreater{}2 A cm\({}^{-2}\) & Membrane, reconversion \\ \hline Voltage range (limits) & 1.4–2.0 V & \textless{}2 V & Catalyst \\ \hline Operating temperature & 40–60 \({}^{\circ}\)C & 80 \({}^{\circ}\)C & Effect on durability \\ \hline Cell pressure & \textless{}35 bar & \textgreater{}70 bar & Membrane \\ \hline Load range & 5–100\% & 5–200\% & Membrane \\ \hline Hydrogen purity & 99.9–99.999\% & \textgreater{}99.9999\% & Membrane \\ \hline Voltage efficiency (LHV) & 52–67\% & \textgreater{}75\% & Catalysts \\ \hline Electrical efficiency (stack) & 51.5–66 kWh kg\({}^{-1}\) H\({}_{2}\) & \textless{}42 kWh kg\({}^{-1}\) H\({}_{2}\) & Catalysts/membrane \\ \hline Electrical efficiency (system) & 57–69 kWh kg\({}^{-1}\) H\({}_{2}\) & \textless{}45 kWh kg\({}^{-1}\) H\({}_{2}\) & Balance of plant \\ \hline Lifetime (stack) & \textgreater{}5000 h & 100,000 h & Membrane, electrodes \\ \hline Stack unit size & 2.5 kW & 2 MW & MEA \\ \hline Electrode area & \textless{}300 cm\({}^{2}\) & 1000 cm\({}^{2}\) & MEA \\ \hline Cold start (to nominal load) & \textless{}20 min & \textless{}5 min & Insulation (design) \\ \hline Capital costs (stack) minimum 1 MW & Unknown & \textless{}USD 100/kW & MEA \\ \hline Capital costs (system) minimum 10 MW & Unknown & \textless{}USD 200/kW & Rectifier \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Operating parameters of AEMs, where MEA—membrane electrode assembly [16]. and the management of the gas and water interfaces within the cell. R&D efforts in this area are ongoing to improve the performance and durability of AEM electrolyzers [174; 175; 176; 177; 178; 179; 180; 181; 182; 183]. AEMs represent a nascent technology in the realm of electrolyzers, with only a handful of companies currently commercializing the product [173]. AEMs offer a promising synthesis of the milder conditions found in alkaline electrolyzers and the efficiency of PEM electrolyzers. This technology allows for the use of non-precious catalysts and titanium-free components, and like PEM, can operate under differential pressure. However, AEMs currently face challenges with chemical and mechanical stability, which results in inconsistent lifespan and performance that falls short of expectations. These issues are primarily due to low membrane conductivity, suboptimal electrode design, and sluggish catalyst kinetics. Efforts to enhance performance, such as adjusting membrane conductivity or introducing supporting electrolytes, may inadvertently compromise durability. The intrinsic lower conductivity of hydroxide ions compared to protons in PEM necessitates either thinner membranes or those with higher charge density for AEMs. Despite these challenges, AEM electrolyzers share many design principles with PEM electrolyzers.