HI Decomposition over Carbon-Based and Ni-Impregnated Catalysts of the Sulfur-Iodine Cycle for Hydrogen Production

To find highly active and relatively low-cost catalysts for HI catalytic decomposition in the sulfuriodine thermochemical cycle particularly for hydrogen production, four carbon-based catalysts, namely, activated carbon (AC), multiwalled carbon nanotubes (MWCNT), carbon molecular sieve (CMS), and graphite nanosheets (GNS), were investigated before and after modification treatment with Ni impregnation. Their catalytic activities in HI decomposition were tested from 573 to 773 K. AC showed the highest activity, followed by CMS, MWCNT, and GNS. Evidently, the catalytic activities of all these catalysts were significantly improved with Ni support. The Ni-impregnated AC (Ni/AC) showed the highest catalytic activity. The HI conversion over Ni/AC at 773 K was 22.3%, even equivalent to the thermodynamic yield. Characterization results indicated that carbon supports played a significant role in Ni dispersion on the catalyst surface. A hypothetical mechanism of the HI decomposition aided by the Ni-impregnated catalysts was also established. Metal Ni, structural defects, and edge sites of carbon influenced catalytic activity. The high activity of Ni/AC can be explained by its catalytic property.