Lab-scale water-splitting hydrogen production test of modified hybrid sulfur process working at around 550 °C

Detailed kinetic modeling of homogeneous H2SO4 decomposition in the sulfur–iodine cycle for hydrogen production

“…However, the O 2 production rate of reaction (12) was significantly higher than that of reactions (3), (8), and (13), especially above 10 À5 s at 1000-1200 K, due to low collision probability of HO 2 and O and high activation energy of reaction (13). Therefore, reaction (3) had the most important influence on O 2 production rate in the initial stage, and reaction (12) had the highest rate on O 2 production above 10 À5 s.…”

“…7. Reaction (3) was the most important one for O 2 production rate in the initial stage, and reaction (12) had a dominant role in O 2 production rate, followed by reactions (13) and (8) in the second stage. As shown in Fig.…”

“…The three chemical reactions in the SI cycle are described as follows: Reaction (b) principally consists of a dehydration process at approximately 727 K and a catalytic decomposition process of SO 3 at approximately > 973 K. The former process produces gaseous SO 3 and H 2 O, whereas the latter process produces SO 2 In the SI cycle and hybrid sulfur cycle, the sulfuric acid decomposition section demanding the highest temperature and sulfuric acid concentration leads to the largest energy consumption. Previous studies [6,7] revealed that H 2 SO 4 is rapidly converted into SO 3 and H 2 O at 773 K [8]; however, the temperature needed for SO 3 to be converted into SO 2 focused on reaction (e). Sulfur trioxide electrolysis is conducted to reduce the maximum operating temperature to 773-823 K [8,9].…”

“…Previous studies [6,7] revealed that H 2 SO 4 is rapidly converted into SO 3 and H 2 O at 773 K [8]; however, the temperature needed for SO 3 to be converted into SO 2 focused on reaction (e). Sulfur trioxide electrolysis is conducted to reduce the maximum operating temperature to 773-823 K [8,9]. The catalytic decomposition of SO 3 using nuclear energy [10][11][12] is one of the most promising methods.…”

Hydrogen production via thermochemical water splitting

“…The HHLT process is made up of the same reactions as the hybrid sulfur process. However, whereas the hybrid sulfur process needs a maximum temperature of 1173e1273 K for reaction (11.16), the HHLT process only needs 773e823 K. To achieve this, it employs two electrolyzers, one of which is an innovative gaseous sulfur trioxide electrolyzer for the sulfuric acid decomposition reaction (Takai, Kubo, Nakagiri, & Inagaki, 2011): The process was demonstrated in a small laboratory-scale apparatus achieving hydrogen production rates up to 5 cm 3 /h for 60 h (Takai, Kubo, et al, 2011). The experimentally achieved thermal efficiency was only 0.5%, but calculations suggested that the potential is much higher and can exceed 28% by optimizing operating conditions and improving equipment performance, optimizing the flow rate of sulfuric acid vaporization, concentrating sulfuric acid with a multiple-effect evaporator, and reducing overpotential and thereby the cell voltages required for the electrolyzers.…”