The Bunsen reaction (SO2 + I-2 + 2H(2)O= H2SO4 + 2HI) in the thermochemical IS process to produce hydrogen was successfully employed using an electrochemical membrane reactor. H2SO4 and HI were concentrated in the anode side and the cathode side of the reactor, respectively. 1, is the dominant bulk of the recycling chemicals in this process, and 12 concentration at the outlet of the reactor was reduced ca. 93% by using this technique. The electric energy consumption for the reaction was about 50% smaller by reducing the concentration of I-2 indicating that the IS process can be operate efficiently at low 12 concentration. The reaction was carried out for 4 h, and the HI concentration was increased by 26%. This amount was the same within 10% as the values calculated from the total loaded electricity. In order to decrease the overpotential at the anode side, small amount of HI was added to the anode side solution. The total voltage was reduced by 0.03 V by the addition of III. 9 (C) 2004 Elsevier B.V. All rights reserved.