The HI section of the iodine-sulfur (I-S) thermochemical cycle for hydrogen production is one of the most energy-intensive sections and with significant material handling challenges, primarily due to the azeotrope formation and the corrosive nature of the hydroiodic acid-iodine-water mixture (HI). As an alternative, the single-step direct electrochemical decomposition of the hydroiodic acid (HI) to generate hydrogen can circumvent the challenges associated with the conventional multistep HI section in the I-S cycle. In this work, we present new insights into the electrochemical HI decomposition process by deconvoluting the contributions from the anodic and the cathodic sections in the electrochemical cell system, specifically, the redox reactions involved and the overpotential contribution of the individual sections (anolyte and catholyte) in the overall performance. The studies on the redox reactions indicate that the HI solution output from the Bunsen reaction section should be used as the anolyte. In contrast, aqueous HI without any iodine (I) should be used as the catholyte. In the anodic section, the oxidation proceeds with I as the final oxidized species at low bias potentials. Higher positive potentials result in iodate formation along with oxygen evolution. For the catholyte section, I and tri-iodide ion reduction precede the hydrogen evolution reaction when I is present along with HI. Furthermore, the potential required for hydrogen production becomes more negative with an increasing I/HI ratio in the catholyte. Polarization studies were conducted with simultaneous deconvolution of the anodic and cathodic behavior in a two-compartment cell. Model fitting of the polarization data revealed that the anolyte section's activation overpotential is negligibly low. In contrast, the activation overpotential requirement of the catholyte section is higher and dictates the onset of hydrogen production in the cell. Furthermore, the catholyte section dominates the total overpotential losses in the cell system. Operation in the ohmic resistance-dominated zone resulted in close to 90% current efficiency for the electrochemical HI decomposition. The results highlight that the potential for process improvement lies in reducing the ohmic resistance of the anolyte section and in lowering the activation overpotential of hydrogen evolution in the catholyte section.
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http://dx.doi.org/10.1007/s11356-023-30154-y | DOI Listing |
Environ Sci Pollut Res Int
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CPRAC Research Center, Centre de Recherche Scientifique et Technique en Analyses Physico-Chimiques, Bou-Ismail CP, Tipaza, 42004, Algeria.
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Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul, 03722, Republic of Korea.
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School of Biological and Chemical Engineering, NingboTech University, Ningbo 315100, China. Electronic address:
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College of Food Science and Technology, Guangdong Ocean University, Zhanjiang 524088, China; Shenzhen Institute of Guangdong Ocean University, Shenzhen 518108, China; National Research and Development Branch Center for Shellfish Processing (Zhanjiang), Zhanjiang 524088, China; Guangdong Provincial Key Laboratory of Aquatic Products Processing and Safety, Guangdong Provincial Engineering Technology Research Center of Seafood, Zhanjiang 524088, China. Electronic address:
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School of Physics and Electronic Sciences, Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering, Changsha University of Science and Technology, Changsha 410114, PR China. Electronic address:
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