Carbonaceous direct fuel cells are hampered by sluggish anode kinetics associated with CO poisoning and therefore typically require a high load of costly Pt-based electrocatalysts. Direct borohydride fuel cells (DBFCs) have an inherent advantage due to the absence of CO and are characterized by high thermodynamic specific energy (9.3 Wh g(NaBH4)(-1)). Here we show for the first time, using fundamental electrochemical methods combined with fuel cell experiments, that osmium nanoparticles are kinetically superior and stable catalysts for borohydride electro-oxidation compared to Pt and PtRu. Osmium favors the direct oxidation of BH4- by a total of seven electrons as opposed to in situ hydrogen generation. The complex network of reactions involved in the oxidation of BH4- to BO2- is analyzed in the context of the experimental data. The current densities obtained with DBFC at 0.6 V with 1 mg cm(-2) 20% Os/C anode were 30 mA cm(-2) at 298 K and 100 mA cm(-2) at 333 K. (c) 2008 The Electrochemical Society.