Anodic treatment of direct methanol fuel cell single cells was carried out at anode potentials of 0.1, 0.4, 0.7, and 1.0 V. An increase in maximum power density by 48% was achieved after anodic treatment at 0.7 V. Electrochemical impedance spectroscopy showed that the methanol electro-oxidation activity of the PtRu catalyst was promoted by the anodic treatment. Oxidation states of Ru changed from Ru metal (43%) and RuO2 (57%) to RuO2 (33%) and RuOxHy (67%), which were studied by X-ray photoelectron spectroscopy. The results showed that the formation of RuOxHy occurred at a potential range of 0.4-0.7 V. (c) 2006 The Electrochemical Society.