Pt-Rh/TiO₂ /activated carbon as highly active and stable HI decomposition catalyst for hydrogen production in sulfur-iodine (SI) process

Abstract

Pt-TiO 2 loaded on activated carbon was studied as an active and stable catalyst to HI decomposition for H 2 formation in the sulfur-iodine process. Although the activity of TiO 2 -loaded catalyst was slightly lower HI conversion than that of CeO 2 loaded one, the higher stability against HI decomposition reaction was achieved and almost equilibrium conversion was sustained over~65 h examined. Moreover, effects of Rh or Ir addition on HI conversion were studied and it was found that Pt-Rh bimetallic system was highly active and stable to HI decomposition. Scanning transmission electron micrograph observation suggested that the increased HI decomposition activity was assigned to the increased dispersion of Pt particles. High dispersion state of Pt was sustained after HI decomposition at 773 K by addition of Rh. Since the formation of PtI 4 was suggested by X-ray photoelectron spectroscopy measurement during HI decomposition, increased stability by addition of Rh seems to be assigned to the high chemical stability of Rh against iodine. Almost the equilibrium HI conversion on Pt-Rh-TiO 2 /M563 was sustained over 300 hours at 673 K.

Modeling and experimental assessment of the novel HI‐I 2 ‐H 2 O electrolysis for hydrogen generation in the sulfur‐iodine cycle

“…The influence of operating temperature on the electrolytic performance was analyzed in two opposite aspects. First, increase in temperature enhances the activity of species in the solution and increases the reaction kinetic rate because of the endothermic characteristic of HI decomposition . On contrary, the rising temperature reduces the local current density according to Equation .…”

“…And excess H 2 O is also necessary for making the Bunsen reaction more thermodynamically favorable . As a result, the practical excess amounts of I 2 and H 2 O with respect to their stoichiometric value usually reach 4 to 6 and 11 to 13 according to Lee et al The produced light H 2 SO 4 phase (most H 2 SO 4 , H 2 O and less HI, I 2 ) and the heavy HIx phase (most HI, I 2 , H 2 O and less H 2 SO 4 ) require liquid phase separation and purification before the catalytic decomposition of H 2 SO 4 and HI . A large amount of energy is required to remove and recycle the excess iodine and water after liquid phase separation.…”

“…19 As a result, the practical excess amounts of I 2 and H 2 O with respect to their stoichiometric value usually reach 4 to 6 and 11 to 13 according to Lee et al 17 The produced light H 2 SO 4 phase (most H 2 SO 4 , H 2 O and less HI, I 2 ) and the heavy HIx phase (most HI, I 2 , H 2 O and less H 2 SO 4 ) require liquid phase separation 16 and purification [20][21][22] before the catalytic decomposition of H 2 SO 4 and HI. [23][24][25][26] A large amount of energy is required to remove and recycle the excess iodine and water after liquid phase separation. Wang and coworkers 27 has proposed the electrolysis of the HI/H 2 SO 4 /H 2 O/toluene mixture from Bunsen reaction so as to avoid the liquid phase separation.…”

“…[32][33][34] But the complexity of HIx section and high energy consumption are disadvantages. After handling by the above traditional technologies, the high enriched HI gas is catalytically decomposed at low decomposition ratio, 24,25,[35][36][37][38][39] which is a challenge for the high-efficient operation of the SI cycle. Membrane reactors have been applied to improve HI decomposition.…”

Hybrid photoelectrochemical–photocatalytic hydrogen evolution reaction with reduced graphene oxide–binary metal chalcogenide composites

“…In this regard, the most abundant energy resource, the Sun, is a promising way toward the realization of a sustainable carbon‐neutral society 4‐6 . Hydrogen generation via the solar route has drawn attention since hydrogen is a clean, energy‐dense, storable, and transportable fuel 7‐10 . Recent reports carefully lined out the possible routes to the solar–hydrogen technologies 11 .…”