ELECTRODE CATALYST INCLUDING IRIDIUM OXIDE NANOSHEET AS PROMOTER

To provide an electrode catalyst exhibiting high performance as a reversal-resistant anode catalyst in fuel cells. The above-described problem is solved by an electrode catalyst constituted by a composite catalyst obtained by mixing an iridium oxide (IrO2) nanosheet with a Pt/C catalyst as a promoter. A weight ratio (percentage) of the IrO2 nanosheet to a sum of the Pt/C and the IrO2 nanosheet is preferably within a range of 1% or more and 26% or less, and a Pt:Ir (atomic ratio) constituting the composite catalyst is preferably within a range of 1.5:1 to 50:1.