Reduction catalyst body for carbon dioxide and manufacturing method thereof, reduction electrode, and reduction reaction device

1. A reduction catalyst body for carbon dioxide, comprising:

a metal layer; and

a projection comprising an aggregate of fine metal particles provided on the metal layer, and possessing a polyhedral structure having surfaces of three faces or more of a polygon, wherein

the projection has a site of reducing carbon dioxide, as at least a part of the surfaces,

the metal layer contains at least one metal element selected from the group consisting of gold, silver, palladium, potassium, and calcium,

each of the fine metal particles has a diameter of not less than 5 nm nor more than 500 nm, and contains the at least one metal element which is contained in the metal layer,

the projection has a shape of at least one selected from a pyramid and a truncated pyramid precipitated on a surface of the metal layer, whose longest side is not less than 1 μm nor more than 50 μm, and

the shape of the projection includes a bottom surface as a precipitation surface which is in contact with the surface of the metal layer and surfaces which are protruded and exposed from the metal layer, and contains at least one of a quadrangular pyramid or a quadrangular truncated pyramid having the bottom surface and the exposed surfaces.

2. The reduction catalyst body according to claim 1 , wherein in an X-ray diffraction measurement of the fine metal particle, when a maximum value of a peak intensity of a {111} plane is set to I 111 , a maximum value of a peak intensity of a {100} plane is set to I 100 , and a maximum value of a peak intensity of a {110} plane is set to I 110 , an I 111 /I 100 ratio is 2.0 or more, and an I 111 /I 110 ratio is 1.2 or more.

3. The reduction catalyst body according to claim 1 , wherein

the metal layer is a porous metal layer, and

the projection is a porous projection.

4. A method for manufacturing the reduction catalyst body for carbon dioxide according to claim 1 , comprising:

immersing, into an electrolytic solution containing a compound including a counter anion capable of forming a salt or a complex with a metal forming the metal layer, a metal base material including the metal;

applying a first electric potential at which the metal can be oxidized, to the metal base material immersed into the electrolytic solution; and

applying a second electric potential at which the metal can be reduced, to the metal base material immersed into the electrolytic solution and after being subjected to the application of the first electric potential.

5. A reduction electrode for carbon dioxide, comprising:

the reduction catalyst body according to claim 1 ; and

a conductive member connected to the reduction catalyst body.

6. A reduction reaction device for carbon dioxide, comprising:

a reaction cell including the reduction electrode according to claim 5 and an oxidation electrode; and

a power supply connected to the reduction electrode and the oxidation electrode.