Energy-saving seawater electrolysis for hydrogen production

The change in the polarization potentials of anode and cathode due to pH change on electrode surfaces during galvanostatic polarization was examined in 0.5 M NaCl solutions of different pH. On the basis of these results, feeding of the anolyte after oxygen evolution to the cathode compartment for hydrogen production was examined for energy-saving seawater electrolysis. This was assumed to prevent the occurrence of a large pH difference on cathode and anode in electrolysis of neutral solution if sufficient H⁺ is permeated through the membrane. The cell performance was examined using Nafion 115 or Selemion HSF membranes for separation of anode and cathode compartments. The permeation fraction of H⁺ with Nafion 115 was 45–65% in 0.5 M NaCl and was about 90% in 0.25 M Na₂SO₄. These values were smaller than 97% necessary for prevention of the occurrence of pH difference on cathode and anode. The permeation fraction of H⁺ with Selemion HSF became more than 97% during electrolysis of 0.025 M Na₂SO₄, and the cell voltage was kept at low values. These results indicate the effectiveness of our seawater feeding system if the 97% H⁺ permeation fraction through the membrane is attained. Contribution to the Fall Meeting of the European Materials Research Society, Symposium D: 9th International Symposium on Electrochemical/Chemical Reactivity of Metastable, Warsaw, 17th-21st September, 2007.