Composite photoanodes

Abstract

The provided method includes photoelectrodeposition of an electrocatalyst onto a semiconductor to form a photoanode. The method yields composite photoanodes showing enhancement of photocurrent (water splitting rate) when incorporated into a photoelectrochemical cell for water electrolysis.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
         1 . A method of forming a composite photoanode, comprising photoelectrodepositing a solid conformal layer of an electrocatalyst from an electrolyte solution on a surface of a semiconductor submerged in the electrolyte solution by simultaneously:
 (1) impinging the surface of the semiconductor with electromagnetic radiation having a first wavelength and a first irradiance, to provide a first photoenergy that is sufficient to excite an electronic transition of the semiconductor; and   (2) applying a first electric bias to the semiconductor, wherein the first electric bias is less than an electrochemical deposition bias, said electrochemical deposition bias being the minimum voltage required to electrodeposit the electrocatalyst onto the surface of the semiconductor without impinging the surface of the semiconductor with electromagnetic radiation having the first photoenergy;   wherein the combination of the first photoenergy and the first electric bias are sufficient to deposit catalyst components from the electrolyte to form the solid conformal layer of the electrocatalyst.   
     
     
         2 . The method of  claim 1 , wherein the electronic transition is a bandgap transition. 
     
     
         3 . The method of  claim 1 , wherein the semiconductor has a physical shape selected from the group consisting of dendrites, wires, belts, rods, mesostructures, nanotubes, and thin films. 
     
     
         4 . The method of  claim 3 , wherein said physical shape has nanoscopic dimensions. 
     
     
         5 . The method of  claim 1 , wherein the semiconductor comprises hematite iron oxide dendrites. 
     
     
         6 . The method of  claim 1 , wherein the electrocatalyst is selected from the group consisting of a cobalt-containing catalyst, an iridium-containing catalyst, a manganese-containing catalyst, a ruthenium-containing catalyst, a nickel-containing catalyst, a cobalt-containing oxygen evolving catalyst, a cobalt oxide/hydroxide catalyst, and a cobalt oxide catalyst. 
     
     
         7 . The method of  claim 1 , wherein the electrocatalyst is cobalt phosphate. 
     
     
         8 . The method of  claim 1 , wherein the layer of the electrocatalyst has a thickness of from 0.5 nm to 30 nm. 
     
     
         9 . The method of  claim 1 , wherein the semiconductor is an n-type semiconductor. 
     
     
         10 . The method of  claim 1 , wherein the formed photoanode, when incorporated into a photoelectrochemical cell for electrolysis of water into oxygen, reduces a water electrolysis onset voltage compared to a second photoanode comprising the semiconductor without the electrocatalyst. 
     
     
         11 . The method of  claim 10 , wherein the water electrolysis onset voltage is reduced by 50 mV to 400 mV. 
     
     
         12 . The method of  claim 1 , wherein the first wavelength of the electromagnetic radiation is from 300 nm to 800 nm. 
     
     
         13 . The method of  claim 1 , wherein the first irradiance of the electromagnetic radiation is from 0.1 W/m 2  to 1100 W/m 2 , or the equivalent in pulsed irradiation. 
     
     
         14 . The method of  claim 1 , wherein the electromagnetic radiation is selected from the group consisting of continuous radiation and pulsed radiation. 
     
     
         15 . The method of  claim 1 , wherein the first electric bias is applied to the semiconductor as part of an electrochemical deposition system comprising a power source in electrical communication with the semiconductor and a counter electrode. 
     
     
         16 . The method of  claim 1 , wherein the electrolyte solution comprises cations selected from the group consisting of cobalt, iridium, manganese, nickel, and ruthenium. 
     
     
         17 . The method of  claim 1 , wherein the electrolyte solution comprises anions selected from the group consisting of phosphate, methyl phosphonate, borate, acetate, sulfate and hydroxide. 
     
     
         18 . The method of  claim 1 , wherein the semiconductor comprises a sensitizer having a sensitizer absorbance wavelength, said sensitizer absorbance being different from a semiconductor absorbance wavelength. 
     
     
         19 . The method of  claim 1 , wherein the semiconductor comprises a group IV semiconductor having a formula selected from the group consisting of binary, ternary, and quaternary. 
     
     
         20 . The method of  claim 19 , wherein the group IV semiconductor further comprises ions selected from the group consisting of cations and anions. 
     
     
         21 . The method of  claim 1 , wherein the semiconductor comprises a material selected from the group consisting of an iron oxide, a zinc oxide, a titanium oxide, a tungsten-bismuth-vanadium oxide, a tungsten oxide, a gallium-zinc-oxide-nitride, or these materials also containing additional cations or anions. 
     
     
         22 . The method of  claim 1 , the wherein the combination of the first photoenergy and the first electric bias are sufficient to oxidize cations to deposit catalyst components from the electrolyte to form the solid conformal layer of the electrocatalyst.