Simultaneous accomplishment of high hydrogen oxidation reaction (HOR) activity and suppressed hydrogen peroxide (H₂O₂) generation is desired for anode catalysts of polymer electrolyte fuel cells. 0.3 monolayer-thick-Pt-deposited Ir(111) showed three-fold higher HOR activity than Pt(111) and suppressed H₂O₂ generation under the detection limit, providing insights for effective catalyst development.