Contrary to the current understanding of Pt-Ru electrocatalyzed oxidation of methanol, the bimetallic alloy is not the most desired form of the catalyst. In the nanoscale Pt-Ru blacks used to electrooxidize methanol in direct methanol fuel cells, (PtRu0)-Ru-0 has orders of magnitude less activity for methanol oxidation than does a mixed-phase electrocatalyst containing Pt metal and hydrous ruthenium oxides (RuOxHy). Bulk, rather than near-surface, quantities of electron-proton conducting RuOxHy are required to achieve high activity for methanol oxidation. The active catalyst forms a nanoscopic, phase-separated hydrons oxide-on-metal structure that retains the Pt metal-RuOxHy boundaries required to oxidize methanol fully to carbon dioxide and water.