| CPC B01J 37/0244 (2013.01) [B01J 23/14 (2013.01); B01J 23/626 (2013.01); B01J 37/0228 (2013.01); C23C 18/1651 (2013.01); C23C 18/1882 (2013.01); C23C 18/42 (2013.01)] | 10 Claims |

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1. A method for forming a tin oxide multilayer film with a catalyst layer, the method comprising:
dissolving a fluoride in water to form a first liquid having a concentration of 0.3 M or more;
preparing a concentrated liquid by mixing the first liquid with a tin compound, the concentrated liquid being prepared such that a fluorine ion concentration derived from the fluoride is 0.8 times or more, and 3 times or less, than a divalent tin ion concentration derived from the tin compound;
diluting the concentrated liquid with water to prepare a reaction liquid that is a stable divalent tin solution having the fluorine ion concentration of 0.01M to 2.5M;
immersing a substance to be treated in the reaction liquid to form a tin oxide layer having a thickness of 2 nm or more and 60 nm or less on a surface of the substance to be treated; and
immersing the substance to be treated having the tin oxide layer formed on the surface in a catalyst solution containing catalyst metal ions to form a catalyst layer including the catalyst metal on the tin oxide layer; wherein
the catalyst metal is a noble metal.
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