Photo-electrolytic catalyst systems and method for hydrogen production from water

Abstract

A photo-electrolytic catalyst system which comprises two materials: (a) a semiconductor material with a non-zero energy gap Eg which, in response to an incident radiation having an energy greater than Eg, generates electron-hole pairs as charge carriers; and (b) a facilitating material in electronic contact with the semiconductor material to facilitate separation of the radiation-generated electrons from the holes to reduce the probability of charge carrier recombinations The catalyst makes use of both majority and minority charge carriers to promote photo-electrolysis reactions for producing hydrogen directly from water or an aqueous electrolyte at higher rates and improved efficiencies.

1 . A photo-electrolytic catalyst system for hydrogen production from water, said catalyst system comprising: 
 (a) a first semiconductor material with a non-zero energy gap Eg 1  which, in response to an incident radiation having an energy greater than Eg 1 , generates electron-hole pairs as charge carriers; and    (b) at least a first facilitating material in electronic contact with said semiconductor material to facilitate separation of the radiation-generated electrons from the holes to reduce the probability of charge carrier recombination.    
     
     
         2 . The catalyst system as defined in  claim 1 , wherein both said first semiconductor material and said first facilitating material have at least one dimension being nanometer-scaled, smaller than or equal to 100 nm.  
     
     
         3 . The catalyst system as defined in  claim 1 , wherein at least one of said semiconductor material and facilitating material is porous.  
     
     
         4 . The catalyst system as defined in  claim 1 ,  2 , or  3 , wherein said first facilitating material comprises an electron-drawing atom, molecule, or ion.  
     
     
         5 . The catalyst system as defined in  claim 1 ,  2 , or  3 , wherein said first semiconductor material comprises an element or compound selected from the group consisting of group IV semiconductors, III-V compounds, II-VI compounds, mixed crystals of II-VI compounds, mixed crystals of III-V compounds, I-III-V 2  compounds, I-IV-V 2  compounds, ZMO compounds (where Z=an alkaline or alkali metal and M=a transition metal or rare earth metal element), oxides, phosphides, arsenides, sulfides, selenides, tellurides, chalcogenides, chalcopyrites and combinations thereof  
     
     
         6 . The catalyst system as defined in  claim 1 ,  2 , or  3 , wherein said first semiconductor material has an energy band gap greater than 1.6 eV.  
     
     
         7 . The catalyst system as defined in  claim 1 ,  2 , or  3 , wherein said first facilitating material comprises an element selected from Group VI and Group VII of the Periodic Table of Elements.  
     
     
         8 . The catalyst system as defined in  claim 1 ,  2 , or  3 , wherein said first facilitating material comprises a transition metal element or a rare earth metal element.  
     
     
         9 . The catalyst system as defined in  claim 1 ,  2 , or  3 , wherein said facilitating material comprises an element selected from the group consisting of Fe, Mn, Co, Ni, Cr, and Ti.  
     
     
         10 . The catalyst system as defined in  claim 1 , wherein said first semiconductor material and/or said facilitating material has a dimension smaller than 1 μm.  
     
     
         11 . The catalyst system as defined in  claim 1 , wherein said first semiconductor material and/or said facilitating material is a nano-scaled material with a dimension smaller than 100 nanometers.  
     
     
         12 . The catalyst system as defined in  claim 1 ,  2 , or  3 , further comprising a second semiconductor material with an energy gap Eg 2  different from Eg 1 , wherein said second semiconductor material is in electronic contact with said first facilitating material.  
     
     
         13 . The catalyst system as defined in  claim 1 ,  2 , or  3 , wherein said first semiconductor material is of n-type and said catalyst system further comprises a second semiconductor material of p-type in electronic contact with said first facilitating material.  
     
     
         14 . The catalyst system as defined in  claim 1 ,  2 , or  3 , further comprising a second semiconductor material in electronic contact with said first semiconductor material, wherein said second semiconductor material has an energy gap Eg 2  different from Eg 1 .  
     
     
         15 . The catalyst system as defined in  claim 14 , further comprising at least a third semiconductor material, wherein said first, second and third semiconductor materials are connected in series.  
     
     
         16 . The catalyst system as defined in  claim 14 , further comprising a second facilitating material in electronic contact with said second semiconductor material.  
     
     
         17 . The catalyst system as defined in  claim 1 ,  2 , or  3 , further comprising a second facilitating material in electronic contact with said first semiconductor material.  
     
     
         18 . The catalyst system as defined in  claim 17 , wherein said first facilitating material comprises a reduction catalyst and said second facilitating material comprises an oxidation catalyst.  
     
     
         19 . A method for converting optical energy into chemical energy to drive a chemical reaction for producing hydrogen gas from an aqueous electrolyte, said method comprising: 
 (A) suspending discrete photo-electrolytic catalysts in said electrolyte; and    (B) illuminating said catalysts with optical energy to produce hydrogen gas; wherein said catalysts comprises (a) a first semiconductor material with a non-zero energy gap Eg 1  which, in response to optical energy, generates electron-hole pairs as charge carriers; and (b) at least a first facilitating material in electronic contact with said semiconductor material to facilitate separation of the optical energy-generated electrons from the holes to reduce the probability of charge carrier recombination.    
     
     
         20 . The method as defined in  claim 19 , further comprising operating means to collect said hydrogen gas produced.  
     
     
         21 . The method as defined in  claim 19 , wherein both said first semiconductor material and said first facilitating material have at least one dimension being nanometer-scaled, smaller than or equal to 100 nm.  
     
     
         22 . The method as defined in  claim 19 , wherein at least one of said semiconductor material and facilitating material is porous.  
     
     
         23 . The method as defined in  claim 19 , wherein said optical energy is provided by solar radiation.  
     
     
         24 . The method as defined in  claim 19 ,  20 ,  21 ,  22  or  23 , wherein said catalysts further comprise a second semiconductor material with an energy gap Eg 2  different from Eg 1 , wherein said second semiconductor material is in electronic contact with said first facilitating material.  
     
     
         25 . The method as defined in  claim 19 ,  20 ,  21 ,  22  or  23 , wherein said first semiconductor material is of n-type and said catalysts further comprises a second semiconductor material of p-type in electronic contact with said first facilitating material.  
     
     
         26 . The method as defined in  claim 19 ,  20 ,  21 ,  22  or  23 , wherein said catalysts further comprise a second semiconductor material in electronic contact with said first semiconductor material, wherein said second semiconductor material has an energy gap Eg 2  different from Eg 1 .  
     
     
         27 . The method as defined in  claim 24 , wherein said catalysts further comprise at least a third semiconductor material and said first, second and third semiconductor materials are connected in series.  
     
     
         28 . The method as defined in  claim 24 , wherein said catalysts further comprise a second facilitating material in electronic contact with said second semiconductor material.  
     
     
         29 . The method as defined in  claim 19 ,  20 ,  21 ,  22  or  23 , wherein said catalysts further comprise a second facilitating material in electronic contact with said first semiconductor material.  
     
     
         30 . The method as defined in  claim 29 , wherein said first facilitating material comprises a reduction catalyst and said second facilitating material comprises an oxidation catalyst.  
     
     
         31 . The method as defined in  claim 19 ,  20 ,  21 ,  22  or  23 , wherein said first facilitating material comprises an electron-drawing atom, molecule, or ion.  
     
     
         32 . The method as defined in  claim 19 ,  20 ,  21 ,  22  or  23 , wherein said first semiconductor material comprises an element or compound selected from the group consisting of group IV semiconductors, II-V compounds, II-VI compounds, mixed crystals of II-VI compounds, mixed crystals of III-V compounds, I-III-V 2  compounds, II-IV-V 2  compounds, ZMO compounds (where Z=an alkaline or alkali metal and M=a transition metal or rare earth metal element), oxides, phosphides, arsenides, sulfides, selenides, tellurides, chalcogenides, chalcopyrites and combinations thereof.  
     
     
         33 . The method as defined in  claim 19 ,  20 ,  21 ,  22  or  23 , wherein said first semiconductor material has an energy band gap greater than 1.6 eV.  
     
     
         34 . The method as defined in  claim 19 ,  20 ,  21 ,  22  or  23 , wherein said first facilitating material comprises an element selected from Group VI and Group VII of the Periodic Table of Elements.  
     
     
         35 . The method as defined in  claim 19 ,  20 ,  21 ,  22  or  23 , wherein said first facilitating material comprises a transition metal element or a rare earth metal element.  
     
     
         36 . The method as defined in  claim 19 ,  20 ,  21 ,  22  or  23 , wherein said facilitating material comprises an element selected from the group consisting of Fe, Mn, Co, Ni, Cr, and Ti.