## 4 Experimental Procedure and Results
### Continuous Hydrogen Production Testing  
After the individual module tests mentioned above, a 24 h continuous closed-loop iodine-sulfur cycle hydrogen production experiment was conducted in January 2025. The integrated test bench was equipped with a spray cleaning system and a smoke alarm system to address acid corrosion risks and gas leakage hazards, respectively. This setup ensures safe operation by neutralizing residual corrosive substances and providing early warnings for potential gas-related emergencies. Following the experimental conditions used in 2021, the molar ratio of H\({}_{2}\)SO\({}_{4}\):H:I\({}_{2}\):H\({}_{2}\)O was set to 1:2:2:12. Two identical batches of materials were prepared containing 10.765 kg of H\({}_{2}\)SO\({}_{4}\) (98 wt%), 50 kg of HI (57 wt%), 54.5 kg of I\({}_{2}\), and 0.5 kg of H\({}_{2}\)O. These batches were added to the Bunsen reactor. While the first batch underwent static separation in the liquid-liquid separation tank, the second batch was introduced into the Bunsen reactor for the reaction, thereby ensuring continuous operation. After phase separation, the upper sulfuric acid phase and lower iodide acid phase solutions were first sent to the purification tower and then to the distillation column to obtain high-concentration H\({}_{2}\)SO\({}_{4}\) and HI solutions. The temperatures of various components in the HI decomposition module during the entire pilot test are shown in Figure 13, where T1 represents the evaporator outlet temperature, T2 represents the heat exchanger outlet temperature, T3 represents the super-heater outlet temperature, and T4 represents the reactor outlet temperature. The hydrogen production rate, purity, and HI decomposition rate are shown in Figure 14. In this pilot test, the HI solution first entered the evaporator at a rate of 200 L/h. The HI vapor was then superheated and decomposed in the catalytic decomposition reactor, ultimately reaching a peak hydrogen production rate of approximately 1536 L/h. To match the hydrogen production rate, the H\({}_{2}\)SO\({}_{4}\) solution was fed at a rate of 6.68 L/h and subsequently decomposed  
Figure 12: Key component temperature and O\({}_{2}\) production rate of three-stage H\({}_{2}\)SO\({}_{4}\) decomposition reactor. in the catalytic decomposition reactor. Later, due to the relatively low power of the HI condenser and superheater, the inlet temperature of the catalytic decomposition reactor gradually decreased. Consequently, the HI solution feed rate was reduced to 27 L/h to the evaporator. The system ran continuously for 24 h, with a stable hydrogen production rate of approximately 300 L/h. Figure 14: The hydrogen production, purity, and decomposition rates during continuous operation of the system. Figure 13: The temperatures of various components in the HI decomposition module during continuous operation of the system. Following a reduction in feed rate, a significant increase in the superheater outlet temperature was observed. At the same time, the HI decomposition rate increased due to the higher inlet temperature. Initially, because the system had not yet stabilized, the HI that had previously remained in the reactor continued to decompose. This led to an initially high decomposition rate, which then gradually decreased to a stable value. As shown in Figure 14, after 18 h of continuous operation, as the concentration of HI solution entering the evaporator decreased, the water content increased. When the water content and 1\({}_{2}\) content in the solution increase, according to the Le Chatelier principle, it will hinder the forward progress of the reaction, resulting in a decrease in decomposition rate. However, throughout the operation, the hydrogen purity gradually increased and eventually reached 98.75%. Subsequently, a gas analyzer was used to analyze the gas composition, revealing small amounts of CO and CH\({}_{4}\).