Sodium Borohydride Oxidation on Pt and/or Pd-Based Electrodes in Hydrogen Peroxide Direct Borohydride Fuel Cells (H2O2-DBFCs)

The direct electrooxidation of sodium borohydride (NaBH4) provides a path to release the high energy of the 8-electron, multi-step borohydride oxidation reaction (BOR). In practice, no single electrocatalyst is known to effectively oxidize all steps of the reaction. We investigate whether more complete BOR is achieved using an anode with a mixed electrocatalyst of nanoparticulate Pt and/or Pd supported on carbon (noted Pt/C and Pd/C). Electrocatalysts are compared in a liquid flow-through hydrogen peroxide direct borohydride fuel cell (H2O2-DBFC) having single Pt/C or Pd/C electrocatalyst, a mixture, or a gradient of the two along the anode flow channel. The best performance and lowest impedance over a broad range of potentials comes from a graded catalyst in which the composition varies from Pd/C at the channel inlet to Pt/C at the outlet, suggesting that catalyst gradients might provide a path to more efficient fuel cells for flow-type reactant systems.