# Technology for Green Hydrogen Production: Desk Analysis
## 4 Results and Discussion
### Current Technologies Used for Green Hydrogen Production
#### 4.2.2 Proton Exchange Membrane Electrolyzers
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Parameter** & **2020** & **Target 2050** & **R\&D Focus** \\ \hline Nominal current density & 0.3–1 A cm\({}^{-2}\) & \textgreater{}2 cm\({}^{-2}\) & Electrolyte, electrodes \\ \hline Voltage range (limits) & 1.0–1.5 V & \textless{}1.48 V & Catalysts \\ \hline Operating temperature & 700–850 \({}^{\circ}\)C & \textless{}600 \({}^{\circ}\)C & Electrolyte \\ \hline Cell pressure & 1 bar & \textgreater{}20 bar & Electrolyte, electrodes \\ \hline Load range & 30–125\% & 0–200\% & Electrolyte, electrodes \\ \hline Hydrogen purity & 99.9\% & \textgreater{}99.9999\% & Electrolyte, electrodes \\ \hline Voltage efficiency (LHV) & 75–85\% & \textgreater{}85\% & Catalysts \\ \hline Electrical efficiency (stack) & 35–50 kWh kg\({}^{-1}\) H\({}_{2}\) & \textless{}35 kWh kg\({}^{-1}\) H\({}_{2}\) & Electrolyte, electrodes \\ \hline Electrical efficiency (system) & 40–50 kWh kg\({}^{-1}\) H\({}_{2}\) & \textless{}40 kWh kg\({}^{-1}\) H\({}_{2}\) & Balance of plant \\ \hline Lifetime (stack) & \textless{}20,000 h & 80,000 h & All \\ \hline Stack unit size & 5 kW & 200 kW & All \\ \hline Electrode area & 200 cm\({}^{2}\) & 500 cm\({}^{2}\) & All \\ \hline Cold start (to nominal load) & \textgreater{}600 min & \textless{}300 min & Insulation (design) \\ \hline Capital costs (stack) minimum 1 MW & \textgreater{}USD 200/kW & \textless{}USD 200/kW & Electrolyte, electrodes \\ \hline Capital costs (system) minimum 10 MW & Unknown & \textless{}USD 300/kW & All \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Operating parameters of SOEs [16]. surface modification, grain boundary engineering, and the use of composite materials. Doping the A-site with acceptor dopants like alkaline earth metals can create oxygen vacancies, facilitating proton transport via the Grothuss mechanism [161]. Codoping the A and B sites can further improve proton conductivity and stability by balancing oxygen vacancies and excess ions. Hydrogenation treatment introduces hydroxyl groups into the perovskite structure, acting as proton donors and enhancing conductivity. Surface modification with catalytic materials like Pt or Pd can improve proton exchange kinetics, while grain boundary engineering through sintering and additives can reduce resistance and enhance conductivity. Microstructural engineering, such as creating composite materials with other proton conductors, can provide additional proton transport pathways. To enhance the chemical stability of the perovskite oxides, the choice of dopants and the doping level are critical. Dopants that do not significantly disrupt the perovskite structure and maintain a high tolerance factor are preferred. Additionally, doping strategies that minimize the formation of secondary phases and maintain structural integrity under operating conditions are essential for achieving high chemical stability. Perovskite oxides, such as those based on barium zirconate (BaZrO3) and barium cerate (BaCeO3), exhibit high proton conductivity at intermediate temperatures, which is crucial for efficient electrolysis [152; 153; 154; 155; 156; 157; 158; 159; 160]. The electrolyte must be stable under the reducing conditions at the cathode and the oxidizing conditions at the anode. Perovskite oxides are generally stable in a wide range of oxygen partial pressures. For efficient electrolysis, the electrolyte should have low electronic conductivity to minimize ohmic losses and ensure that the current is carried predominantly by protons. The properties of perovskite oxides can be tailored by doping the A or B sites with different elements. The electrolyte material must be easily sintered to form a dense layer that prevents gas leakage and has sufficient mechanical strength to withstand thermal cycling and operating conditions. The cost and availability of the materials used in the perovskite structure are important considerations for commercial viability. Researchers are exploring alternative cations that are less expensive and more abundant.