Performance of Activated‐Carbon‐Supported Ni, Co, and Ni–Co Catalysts for Hydrogen Iodide Decomposition in a Thermochemical Water‐Splitting Sulfur–Iodine Cycle

Bimetallic Ni–Co/activated carbon (Ni–Co/AC) and monometallic Ni/AC and Co/AC catalysts were prepared to investigate their catalytic activity for hydrogen‐iodide decomposition in the sulfur–iodine (SI) cycle. Transmission electron microscopy (TEM) revealed an average size of approximately 3 nm particles for Ni–Co/AC. Ni–Co/AC possesses a higher I D / I G intensity ratio in Raman spectroscopy than the monometallic catalysts and support, which is an indication of high degree of defects. Hydrogen‐iodide decomposition was performed on a fixed vertical bed quartz reactor at a weight hourly space velocity (WHSV) of 12.9 h −1 and different temperatures (400–550 °C). Bimetallic catalysts exhibited better activity and stability than the monometallic catalysts. The composition of Ni/Co in the bimetallic Ni–Co catalyst played the key role in dictating the activity of catalyst. It was observed that the loading ratio of 3:1 for Ni/Co achieved the maximal hydrogen‐iodide conversion value. Bimetallic Ni(3 %)–Co(1 %)/AC showed excellent time‐on‐stream stability of 70 h for the hydrogen‐iodide decomposition reaction. The post‐reaction characterization studies (X‐ray diffraction and Brunauer–Emmett–Teller surface area measurements) confirmed that the bimetallic Ni–Co/AC catalyst has a stable structure and shows high corrosion resistance against the corrosive hydrogen iodide environment. Also, it was observed that the apparent activation energy of the bimetallic Ni–Co/AC catalyst was smaller than the monometallic Ni and Co catalysts. The effect of iodine on hydrogen‐iodide conversion was also studied.