Electrically conductive diamond electrode, and sulfuric acid electrolysis method and sulfuric acid electrolysis apparatus each utilizing same

Abstract

The present invention provides an electrically conductive diamond electrode comprising an electrically conductive substrate and an electrically conductive diamond layer coated on the surface of the electrically conductive substrate, featuring that: 1) the thickness of the electrically conductive diamond layer is 1˜25 μm, 2) the potential window fulfills Equation (1) and 3) the ratio (A/B) of the diamond component A and the non-diamond component B by the Raman spectroscopic analysis fulfills Equation (2). 2.1V≦potential window≦3.5V  (1) 1.5< A/B ≦6.5  (2) A: Intensity at the wave number 1300 cm −1 by the Raman spectroscopic analysis B: Intensity at the wave number 1500 cm −1 by the Raman spectroscopic analysis. The present invention intends to provide an electrically conductive diamond electrode with a high durability as electrode, which achieves a high current efficiency of oxidizing agent at a low cell voltage by controlling the thickness of the electrically conductive diamond layer and crystallinity of the electrically conductive diamond, a sulfuric acid electrolysis method and an electrolysis apparatus of sulfuric acid applying the electrically conductive diamond electrode.

1 . Electrically conductive diamond electrode comprising an electrically conductive substrate and an electrically conductive diamond layer coated on the surface of the electrically conductive substrate characterized in that:
 1) the thickness of the electrically conductive diamond layer is in the range of 1˜25 μm,   2) the potential window fulfills Equation (1) and   3) the ratio (A/B) of the diamond component A and the non-diamond component B by the Raman spectroscopic analysis fulfills Equation (2):
   2.1V≦potential window≦3.5V  (1)
 
   1.5 <A/B≦ 6.5  (2),
 
   
       wherein:
 A: Intensity at the wave number 1300 cm −1  by the Raman spectroscopic analysis 
 B: Intensity at the wave number 1500 cm −1  by the Raman spectroscopic 
 
     
     
         2 . The electrically conductive diamond electrode as defined in  claim 1 , wherein the electrically conductive diamond layer contains boron in the range of 100˜6000 ppm. 
     
     
         3 . The electrically conductive diamond electrode as defined in  claim 1 , characterized in that the electrically conductive substrate is silicon substrate. 
     
     
         4 . A sulfuric acid electrolysis method, wherein an anode compartment is separated from a cathode compartment by a diaphragm, an electrically conductive diamond anode is installed in the anode compartment, a cathode is installed in the cathode compartment, electrolyte containing sulfate ion is supplied to the anode compartment and the cathode compartment, respectively, from the outside, oxidizing agent is formed in the anode electrolyte in the anode compartment by electrolysis, characterized in that the electrically conductive diamond electrode as defined in  claim 1  is applied and the concentration of sulfate ion in the electrolyte is in the range of 2˜14 mol/l. 
     
     
         5 . The sulfuric acid electrolysis method as defined in  claim 4 , characterized in that the acid concentration of the electrolyte containing sulfate ion is in the range of 4˜28 mol/l. 
     
     
         6 . A sulfuric acid electrolysis apparatus, wherein an anode compartment is separated from a cathode compartment by a diaphragm, an electrically conductive diamond anode is installed in the anode compartment, a cathode is installed in the cathode compartment, electrolyte containing sulfate ion is supplied to the anode compartment and the cathode compartment, respectively, from the outside, oxidizing agent is formed in the anode electrolyte in the anode compartment by electrolysis, characterized in that the electrically conductive diamond electrode as defined in  claim 1  is applied and a fluororesin type cation exchange membrane or a hydrophilically treated porous fluororesin membrane is applied as diaphragm. 
     
     
         7 . The sulfuric acid electrolysis method, wherein an anode compartment is separated from a cathode compartment by a diaphragm, an electrically conductive diamond anode is installed in the anode compartment, a cathode is installed in the cathode compartment, electrolyte containing sulfate ion is supplied to the anode compartment and the cathode compartment, respectively, from the outside, oxidizing agent is formed in the anode electrolyte in the anode compartment by electrolysis, characterized in that the electrically conductive diamond electrode as defined in  claim 1  is applied and the electrolyte containing sulfate ion is electrolyzed on a condition to satisfy Equation (3) and Equation (4):
   100 ≦X≦ 10000  (3)
 
   25 <Y< 250  (4),
 
 wherein: 
 X=current/anolyte volume (A/l) 
 Y=current density (A/dm 2 ) 
 
     
     
         8 . The sulfuric acid electrolysis method as defined in  claim 7 , wherein a solution containing sulfate ion is electrolyzed on a condition to satisfy Equation (5):
   18000 ≦Z≦ 1080000  (5),
   wherein:
     Z =electric charge per unit volume (C/l)=current value×electrolysis time/anolyte volume (A·s/l)