Abstract: The present invention concerns an oxygen reduction catalyst comprising composite particles in which primary particles of a titanium compound is dispersed into a carbon structure, wherein the composite particles have titanium, carbon, nitrogen and oxygen as constituent elements, and with regard to a ratio of number of atoms of each of the elements when titanium is taken as 1, a ratio of carbon is larger than 2 and 5 or less, a ratio of nitrogen is larger than 0 and 1 or less, and a ratio of oxygen is 1 or more and 3 or less, and an intensity ratio (D/G ratio) of D band peak intensity to G band peak intensity in a Raman spectrum is in the range of 0.4 to 1.0. The oxygen reduction catalyst according to the present invention has satisfactory initial performance and excellent start-stop durability.

Abstract: An oxygen reduction catalyst, an ink including the catalyst, a catalyst layer including the catalyst, an electrode having the catalyst layer, a membrane electrode assembly having the catalyst layer, and a fuel cell having the membrane electrode assembly. The oxygen reduction catalyst includes titanium dioxide particles, a carbon material and a catalyst component, wherein a surface of the titanium dioxide particles is covered with zinc oxide, and the titanium dioxide particles and the carbon material each support the catalyst component.

Abstract: Provided is a method for operating a fuel cell involving supplying an electrode with a low or non-humidified gas that achieves no significant decrease of voltage as compared with when a high-humidified feed gas is used. The method for operating a fuel cell having a membrane electrode assembly includes a cathode, an anode and an electrolyte membrane interposed between both the electrodes, wherein the cathode has a layer including an oxygen reducing catalyst including composite particles which include atoms of a metal element M1, carbon, nitrogen and oxygen and in which primary particles of a compound of the metal element M1 are dispersed in a carbon structure, which method includes supplying the cathode with an oxidizing agent gas which includes an oxygen gas and which has a relative humidity at a temperature of the membrane electrode assembly of 60% or less, and supplying the anode with a fuel gas.

Abstract: The present invention concerns an oxygen reduction catalyst comprising composite particles in which primary particles of a titanium compound is dispersed into a carbon structure, wherein the composite particles have titanium, carbon, nitrogen and oxygen as constituent elements, and with regard to a ratio of number of atoms of each of the elements when titanium is taken as 1, a ratio of carbon is larger than 2 and 5 or less, a ratio of nitrogen is larger than 0 and 1 or less, and a ratio of oxygen is 1 or more and 3 or less, and an intensity ratio (D/G ratio) of D band peak intensity to G band peak intensity in a Raman spectrum is in the range of 0.4 to 1.0. The oxygen reduction catalyst according to the present invention has satisfactory initial performance and excellent start-stop durability.