Three-dimensional Os anodes for direct borohydride fuel cells (DBFC) were developed by surfactant assisted electrodeposition of Os on two fibrous graphite substrates, AvCarb (TM) P75 and GF-S3, respectively. Structural characterization of the electrodes using SEM, TEM, and XPS revealed cluster-like Os deposits composed of nano-sized particles of less than 5 nm in diameter with partially oxidized surfaces. The structural and compositional features of the graphite fiber matrixes had a profound influence on the crystallography of the electrodeposited Os. The polycrystalline Os/AvCarb (TM) P75 exhibited superior electrocatalytic activity in cyclic voltammetry compared to Os/GF-S3 with respect to oxidation of adsorbed intermediates. To explain the different activity XRD was used to investigate the crystallographic differences between the two electrodes. A DBFC with Nafion (R) 117 membrane and operated at 333 K, with Os/AvCarb (TM) P75 anode (1.7 mg cm(-2) Os) and 4 mg cm-2 Pt black oxygen cathode catalyst, generated a peak power density of 109 mW cm(-2) with a standard error of the mean of +/- 12 mW cm(-2) at 90% confidence level. The longer-term durability of the newly developed anodes was investigated. (C) 2012 Elsevier B.V. All rights reserved.