Abstract: According to one embodiment, an etching solution is provided. The etching solution is used for etching of silicon nitride. The etching solution includes: phosphoric acid; tetrafluoroboric acid; a silicon compound; water; and at least one of sulfuric acid and an ionic liquid.

Abstract: According to one embodiment, an electrode structure is provided. The separator includes an organic fiber layer. The organic fiber layer includes an organic fiber having an aspect ratio (V1/H1) in a cross section which is 0.97 or less. The cross section intersects with a length direction of the organic fiber. The organic fiber having the aspect ratio (V1/H1) is in contact with a surface of the active material-containing layer having a roughness higher than an arithmetic mean surface roughness Ra of the active material-containing layer in the cross section. The V1 denotes a length parallel to a thickness direction of the active material-containing layer. The H1 denotes a length horizontal to an in-plane direction of the active material-containing layer.

Abstract: According to one embodiment, an aging device includes an operation and measurement unit, and a control unit. The operation and measurement unit is configured to perform application of potential between at least any one of a counter electrode and a reference electrode provided in a constant-potential electrolytic gas sensor and a working electrode provided in the constant-potential electrolytic gas sensor and measurement of an electric current flowing between the working electrode and the counter electrode. The control unit is configured to calculate the potential at a start of the flow of the electric current between the working electrode and the counter electrode and control the operation and measurement unit such that potential higher than the potential at the start of the flow of the electric current is applied between at least any one of the counter electrode and the reference electrode and the working electrode.