Abstract: A catalytic solution for a halide ion battery, which is an aqueous solution containing a quaternary ammonium halide salt or a hydrate thereof at 9.0 mol/kg to 11.0 mol/kg, is an electrolyte for a halide ion battery that has excellent safety and a wide potential window.

Abstract: The present invention makes it possible to efficiently utilize catalyst metal particles of a catalyst by fuel cell reaction. In a PFF structure in which a hydrophilic region is formed between the surface of a catalyst and an electrolyte, water is confined within the layer of the electrolyte, therefore by modifying the surface of a carrier by an acidic functional group, particularly by a sulfonic acid group, this acidic functional group is always in contact with the water, and thus protons are supplied therefrom into the water. Consequently, even in an environment, for example, in a micropore of the catalyst, into which the electrolyte cannot get, the protons from the acidic functional group are supplied to catalyst metal particles present at the peripheral surface of the micropore, and the catalyst metal particles contribute to fuel cell reaction.

Abstract: A CO gas sensor is equipped with a detecting unit in which a solid electrolyte membrane is held between a detection electrode and a counter electrode, and a voltage applying unit which applies voltage between the detection electrode and the counter electrode and changes the voltage. The detection electrode includes an electrochemically active first catalyst in an electrically conductive porous body, a reaction layer having a density of 1 ng/cm2-100 &mgr;g/cm2 and having a thickness of 0.3 nm-15 &mgr;m, and the counter electrode includes an electrochemically active second catalyst carried on an electrically conductive porous body.