Development of an electrochemical cell for efficient hydrogen production through the IS process

The Bunsen reaction (SO₂ + I₂ + 2H₂O = H₂SO₄ + 2HI) was examined by an electrochemical cell featuring a cation-exchange membrane as the separator, using sulfuric acid dissolving sulfur dioxide as the anolyte and hydriodic acid dissolving iodine as the catholyte. In galvanostatic electrolysis, the molality of H ₂SO₄ in the anolyte and that of HI in the catholyte were increased up to 17.8 and 14.9 mol kg_H2O^-1, respectively. These concentrations were far higher than those that were obtained by the Bunsen reaction carried out in the presence of a large amount of iodine (such as I₂/HI = 4). I₂ concentration after the concentration procedure was at I₂/HI = 0.95, which is lower than the reported value. I₂ is one of the recycling agents in the IS process. HI and H₂SO₄ were successfully concentrated under low I ₂ concentration. The concentration of HI agreed with the calculated value, based on the amount of electricity consumed, indicating high current efficiency. Heat/mass balance using this type of electrochemical cell through the IS process is discussed for evaluation of the reactor. The thermal efficiency to produce hydrogen was calculated at 42.1%, without heat recovery for electricity, by optimizing HI and H₂SO₄ concentrations after application of the electrochemical cell.