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 Hp 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 Hwith Nafion 115 was 45-65% in 0.5 M NaCl and was about 90% in 0.25 M Na(2)SO(4). These values were smaller than 97% necessary for prevention of the occurrence of pH difference on cathode and anode. The permeation fraction of Hstop with Selemion HSF became more than 97% during electrolysis of 0.025 M Na(2)SO(4), 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.