Electrodeposited osmium three-dimensional anodes for direct borohydride fuel cells

Three-dimensional Os anodes for direct borohydride fuel cells (DBFC) were developed by surfactant assisted electrodeposition of Os on two fibrous graphite substrates, AvCarb™ 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™ 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® 117 membrane and operated at 333 K, with Os/AvCarb™ 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.

► Electrodeposition of osmium on graphite fibrous substrates is reported for the first time.
► First report on the use of Os/graphite fiber substrate 3D anode in direct borohydride fuel cells.
► With Os 3D anode the peak power density was 109 mW cm−2 coupled with good durability.