Energy and exergy analyses of a novel sulfur–iodine cycle assembled with HI–I2–H2O electrolysis for hydrogen production

A novel sulfur–iodine (SI or IS) cycle integrated with HI–I₂–H₂O electrolysis for hydrogen production was developed and thermodynamically analyzed in this work. HI–I₂–H₂O electrolysis was used to replace the conventional concentration, distillation, and decomposition processes of HI, so as to simplify the flowsheet of SI cycle. And then the new cycle was divided into Bunsen reaction, H₂SO₄ decomposition and HI–I₂–H₂O electrolysis sections. Through incorporating the user-defined module of HI–I₂–H₂O electrolysis with Aspen Plus, the cycle was simulated and 0.448 mol/h (10 L/h) of H₂ was produced. The overall energy and exergy efficiencies of the novel SI system were estimated to be 15.3–31.0% and 32.8%, respectively. Most exergy destruction occurred in the H₂SO₄ decomposer and condenser for H₂SO₄ decomposition and Bunsen reaction sections, which accounted for 93.0% and 63.4%, respectively. A high exergy efficiency of 92.4% for HI–I₂–H₂O electrolysis section with less exergy destruction was determined, mostly due to the transformation of the overall electricity in electrolytic cell to exergy. Appropriate internal heat exchange and waste heat recovery will favor improving the energy and exergy efficiencies.