Improvement in the efficiency of carbon dioxide reduction reaction is achieved. A gas supply unit having a plurality of pores is established in a lower portion of a reduction chamber, and carbon dioxide is supplied as bubbles into an aqueous solution. This can elevate a concentration of carbon dioxide dissolved in the aqueous solution without stirring the aqueous solution using a stirring bar, and render the concentration uniform in the aqueous solution. Therefore, the efficiency of reduction reaction of carbon dioxide in a reduction electrode can be improved.

An electrochemical cell has a first reaction chamber having a first electrode, a second reaction chamber having a second electrode, a membrane-electrode assembly having an ion-exchange membrane, and a photovoltaic system for absorbing solar energy and producing an output voltage between a first output terminal selectively couplable to the first electrode and a second output terminal selectively couplable to the second electrode. The ratio between a photosensitive area of the photovoltaic system and an active area of the first and second electrodes is less than or equal to fifty. A plurality of photovoltaic cells is selectively couplable between the first and second output terminals. An electronic control unit couples the photovoltaic cells as a function of at least one among one or more user-settable parameters, one or more signals received from an external control unit, one or more signals received from one or more sensors included in the electrochemical cell.

An electrochemical cell has a first reaction chamber having a first electrode, a second reaction chamber having a second electrode, a membrane-electrode assembly having an ion-exchange membrane, and a photovoltaic system for absorbing solar energy and producing an output voltage between a first output terminal selectively couplable to the first electrode and a second output terminal selectively couplable to the second electrode. The ratio between a photosensitive area of the photovoltaic system and an active area of the first and second electrodes is less than or equal to fifty. A plurality of photovoltaic cells is selectively couplable between the first and second output terminals. An electronic control unit couples the photovoltaic cells as a function of at least one among one or more user-settable parameters, one or more signals received from an external control unit, one or more signals received from one or more sensors included in the electrochemical cell.

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.

A carbon dioxide reduction device includes: an oxidation electrode that receives light from the outside; an oxidation bath that holds an electrolytic solution in which the oxidation electrode is immersed; an electrolyte membrane that constitutes a part of one surface of the oxidation bath excluding a surface on which the light is incident; a reduction electrode that is connected to the electrolyte membrane; a reduction unit in which the reduction electrode is disposed and to which a gas containing carbon dioxide is supplied from the outside; and a blower that generates an airflow toward the reduction electrode inside the reduction unit. The reduction electrode has a plate shape, and one surface of the reduction electrode is in contact with the electrolyte membrane.

A carbon dioxide reduction device includes: an oxidation electrode that receives light from the outside; an oxidation bath that holds an electrolytic solution in which the oxidation electrode is immersed; an electrolyte membrane that constitutes a part of one surface of the oxidation bath excluding a surface on which the light is incident; a reduction electrode that is connected to the electrolyte membrane; a reduction unit in which the reduction electrode is disposed and to which a gas containing carbon dioxide is supplied from the outside; and a blower that generates an airflow toward the reduction electrode inside the reduction unit. The reduction electrode has a plate shape, and one surface of the reduction electrode is in contact with the electrolyte membrane.

Provided is a photocatalyst with significantly enhanced water splitting performance in YTOS or in a composition in which the yttrium element of YTOS has been replaced with another element. Also provided is a method for producing a photocatalyst that has a composition represented by the following general formula (I), the method including mixing, with a raw material of the photocatalyst, a flux component at a mass ratio of 0.01 times to 50 times, the flux component being composed of one or more chlorides and/or iodides of at least one selected from Li, Na, K, Rb, Mg, Ca, Sr, and Ba, and calcining a resultant product at 450? C. to 1050? C.:

M.sub.aTi.sub.bO.sub.cS.sub.d(I)

(where M is a combination of one or more selected from Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Y, a is a number of 1.7 to 2.3, b is a number of 2, c is a number of 4.7 to 5.3, and d is a number of 1.7 to 2.3).

Provided is a photocatalyst with significantly enhanced water splitting performance in YTOS or in a composition in which the yttrium element of YTOS has been replaced with another element. Also provided is a method for producing a photocatalyst that has a composition represented by the following general formula (I), the method including mixing, with a raw material of the photocatalyst, a flux component at a mass ratio of 0.01 times to 50 times, the flux component being composed of one or more chlorides and/or iodides of at least one selected from Li, Na, K, Rb, Mg, Ca, Sr, and Ba, and calcining a resultant product at 450? C. to 1050? C.:

M.sub.aTi.sub.bO.sub.cS.sub.d(I)

(where M is a combination of one or more selected from Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Y, a is a number of 1.7 to 2.3, b is a number of 2, c is a number of 4.7 to 5.3, and d is a number of 1.7 to 2.3).

A device for catalytic conversion of carbon dioxide (CO.sub.2) includes a substrate having a surface, an array of conductive projections supported by the substrate and extending outward from the surface of the substrate, each conductive projection of the array of conductive projections having a semiconductor composition, and a plurality of nanoparticles disposed over the array of conductive projections, each nanoparticle of the plurality of nanoparticles being configured for the catalytic conversion of carbon dioxide (CO.sub.2). Each nanoparticle of the plurality of nanoparticles includes a Group VA element, the Group VA element being a metal or a metalloid.

A device for catalytic conversion of carbon dioxide (CO.sub.2) includes a substrate having a surface, an array of conductive projections supported by the substrate and extending outward from the surface of the substrate, each conductive projection of the array of conductive projections having a semiconductor composition, and a plurality of nanoparticles disposed over the array of conductive projections, each nanoparticle of the plurality of nanoparticles being configured for the catalytic conversion of carbon dioxide (CO.sub.2). Each nanoparticle of the plurality of nanoparticles includes a Group VA element, the Group VA element being a metal or a metalloid.