Photocatalytic electrode for water splitting and water splitting device

Abstract

An object of the present invention is to provide a photocatalytic electrode for water splitting and a water splitting device excellent in the onset potential. The water splitting device of the present invention is a water splitting device which generates gases from a photocatalytic electrode for hydrogen generation and a photocatalytic electrode for oxygen generation by irradiating the photocatalytic electrode for hydrogen generation and the photocatalytic electrode for oxygen generation with light, and includes a bath to be filled with an electrolytic aqueous solution and the photocatalytic electrode for hydrogen generation and the photocatalytic electrode for oxygen generation each disposed in the bath. The photocatalytic electrode for hydrogen generation has a p-type semiconductor layer, an n-type semiconductor layer provided on the p-type semiconductor layer, and a co-catalyst provided on the n-type semiconductor layer. The p-type semiconductor layer is a semiconductor layer containing a CIGS compound semiconductor containing Cu, In, Ga, and Se, and a molar ratio of Ga to a total molar amount of Ga and In in the CIGS compound semiconductor is 0.4 to 0.8.

What is claimed is: 
     
         1 . A water splitting device which generates gases from a photocatalytic electrode for hydrogen generation and a photocatalytic electrode for oxygen generation by irradiating the photocatalytic electrode for hydrogen generation and the photocatalytic electrode for oxygen generation with light, the water splitting device comprising:
 a bath to be filled with an electrolytic aqueous solution; and   the photocatalytic electrode for hydrogen generation and the photocatalytic electrode for oxygen generation each disposed in the bath,   wherein the photocatalytic electrode for hydrogen generation has a p-type semiconductor layer, an n-type semiconductor layer provided on the p-type semiconductor layer, and a co-catalyst provided on the n-type semiconductor layer,   the p-type semiconductor layer is a semiconductor layer containing a CIGS compound semiconductor containing Cu, In, Ga, and Se, and   a molar ratio of Ga to a total molar amount of Ga and In in the CIGS compound semiconductor is 0.4 to 0.8.   
     
     
         2 . The water splitting device according to  claim 1 ,
 wherein the n-type semiconductor layer contains CdS.   
     
     
         3 . The water splitting device according to  claim 1 , further comprising:
 a metal layer provided between the n-type semiconductor layer and the co-catalyst.   
     
     
         4 . The water splitting device according to  claim 1 ,
 wherein the molar ratio of Ga to the total molar amount of Ga and In in the CIGS compound semiconductor is 0.5 to 0.7.   
     
     
         5 . A water splitting device which generates gases from a photocatalytic electrode for hydrogen generation and a photocatalytic electrode for oxygen generation by irradiating the photocatalytic electrode for hydrogen generation and the photocatalytic electrode for oxygen generation with light, the water splitting device comprising:
 a bath to be filled with an electrolytic aqueous solution; and   the photocatalytic electrode for hydrogen generation and the photocatalytic electrode for oxygen generation each disposed in the bath,   wherein the photocatalytic electrode for hydrogen generation has a p-type semiconductor layer, an n-type semiconductor layer provided on the p-type semiconductor layer, and a co-catalyst provided on the n-type semiconductor layer, and   a band offset ΔE which is a difference between a potential p-CBM at a lower end of a conduction band of the p-type semiconductor layer and a potential n-CBM at a lower end of a conduction band of the n-type semiconductor layer satisfies the following relationship,
   Δ E =( n - CBM )−( p - CBM )≤0.1 [eV].
 
   
     
     
         6 . A photocatalytic electrode for water splitting, the electrode comprising:
 a semiconductor layer containing a CIGS compound semiconductor containing Cu, In, Ga, and Se,   wherein a molar ratio of Ga to a total molar amount of Ga and In in the CIGS compound semiconductor is 0.4 to 0.8.   
     
     
         7 . The water splitting device according to  claim 2 , further comprising:
 a metal layer provided between the n-type semiconductor layer and the co-catalyst.   
     
     
         8 . The water splitting device according to  claim 2 ,
 wherein the molar ratio of Ga to the total molar amount of Ga and In in the CIGS compound semiconductor is 0.5 to 0.7.   
     
     
         9 . The water splitting device according to  claim 3 ,
 wherein the molar ratio of Ga to the total molar amount of Ga and In in the CIGS compound semiconductor is 0.5 to 0.7.