Electrochemical and photoelectrochemical cells for the oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid and/or 2,5-diformylfuran are provided. Also provided are methods of using the cells to carry out the electrochemical and photoelectrochemical oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid and/or 2,5-diformylfuran.

Electrochemical and photoelectrochemical cells for the oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid and/or 2,5-diformylfuran are provided. Also provided are methods of using the cells to carry out the electrochemical and photoelectrochemical oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid and/or 2,5-diformylfuran.

A method for coating a substrate with a CoPi modified BiVO.sub.4/WO.sub.3 heterostructure film includes direct current reactive sputtering tungsten (W) onto a substrate in a gaseous mixture containing oxygen to form a tungsten trioxide (WO.sub.3) film, direct current reactive sputtering bismuth (Bi) onto the tungsten trioxide (WO.sub.3) film in a gaseous mixture containing oxygen to form a dibismuth trioxide (Bi.sub.2O.sub.3) film, drop-casting a vanadyl acetylacetonate solution onto the Bi.sub.2O.sub.3 film and heating at a temperature of at least 450 C. in ambient air to convert the Bi.sub.2O.sub.3 film to a BiVO.sub.4 film, and photoelectrochemically coating the BiVO.sub.4 film with a cobalt-phosphate (CoPi) to form a modified film on the surface of the substrate. A photoanode containing the CoPi modified BiVO.sub.4/WO.sub.3 heterostructure film prepared by the method, and its application in water splitting.

A radiation-assisted (typically solar-assisted)electrolyzer cell and panel for high-efficiency hydrogen production comprises a photoelectrode and electrode pair, with said photoelectrode comprising either a photoanode electrically coupled to a cathode shared with an anode, or a photocathode electrically coupled to an anode shared with a cathode; electrolyte; gas separators; all within a container divided into two chambers by said shared cathode or shared anode, and at least a portion of which is transparent to the electromagnetic radiation required by said photoanode (or photocathode) to apply photovoltage to a shared cathode (or anode) that increases the electrolysis current and hydrogen production.

A radiation-assisted (typically solar-assisted)electrolyzer cell and panel for high-efficiency hydrogen production comprises a photoelectrode and electrode pair, with said photoelectrode comprising either a photoanode electrically coupled to a cathode shared with an anode, or a photocathode electrically coupled to an anode shared with a cathode; electrolyte; gas separators; all within a container divided into two chambers by said shared cathode or shared anode, and at least a portion of which is transparent to the electromagnetic radiation required by said photoanode (or photocathode) to apply photovoltage to a shared cathode (or anode) that increases the electrolysis current and hydrogen production.

Large scale harvesting of renewable energy is proposed by using floating devices which use solar, wind, ocean current, and wave energy to produce compressed hydrogen by electrolysis of deep sea water. Natural ocean currents and winds are used to allow the devices to gather energy from over a large area with minimum transportation cost. The present approach uses a combination of well understood technologies in an optimized manner and at scale. Hydrogen produced in this manner would pave the way for carbon free energy economy.

Large scale harvesting of renewable energy is proposed by using floating devices which use solar, wind, ocean current, and wave energy to produce compressed hydrogen by electrolysis of deep sea water. Natural ocean currents and winds are used to allow the devices to gather energy from over a large area with minimum transportation cost. The present approach uses a combination of well understood technologies in an optimized manner and at scale. Hydrogen produced in this manner would pave the way for carbon free energy economy.

A method for coating a substrate with a Co-Pi modified BiVO.sub.4/WO.sub.3 heterostructure film includes direct current reactive sputtering tungsten (W) onto a substrate in a gaseous mixture containing oxygen to form a tungsten trioxide (WO.sub.3) film, direct current reactive sputtering bismuth (Bi) onto the tungsten trioxide (WO.sub.3) film in a gaseous mixture containing oxygen to form a dibismuth trioxide (Bi.sub.2O.sub.3) film, drop-casting a vanadyl acetylacetonate solution onto the Bi.sub.2O.sub.3 film and heating at a temperature of at least 450 C. in ambient air to convert the Bi.sub.2O.sub.3 film to a BiVO.sub.4 film, and photoelectrochemically coating the BiVO.sub.4 film with a cobalt-phosphate (Co-Pi) to form a modified film on the surface of the substrate. A photoanode containing the Co-Pi modified BiVO.sub.4/WO.sub.3 heterostructure film prepared by the method, and its application in water splitting.

Provided is a method for producing a nitride semiconductor photoelectrode capable of improving the light energy conversion efficiency. The method for producing a nitride semiconductor photoelectrode includes a first step of forming an n-type gallium nitride layer on an insulating or conductive substrate, a second step of forming an indium gallium nitride layer on the n-type gallium nitride layer, a third step of forming a nickel layer n the indium gallium nitride layer, and a fourth step of heat-treating the nickel layer in an oxygen atmosphere.

Provided is a method for producing a nitride semiconductor photoelectrode capable of improving the light energy conversion efficiency. The method for producing a nitride semiconductor photoelectrode includes a first step of forming an n-type gallium nitride layer on an insulating or conductive substrate, a second step of forming an indium gallium nitride layer on the n-type gallium nitride layer, a third step of forming a nickel layer n the indium gallium nitride layer, and a fourth step of heat-treating the nickel layer in an oxygen atmosphere.