Abstract
The volumetric mass-transport coefficients (kmAe) for borohydride ion oxidation at various titanium 3D electrode structures in a rectangular flow channel were calculated by chronoamperometry in a three-electrode electrochemical flow cell. The 3D electrodes used for the oxidation of borohydride in alkaline media included flat, mesh, micromesh, fine mesh and felt coated with a Pt-Ir alloy catalysts. Felt, fine mesh and micromesh electrodes showed high electrochemical activity with current enhancement factors (δ) of 100, 64, 22, respectively at a mean linear flow velocity of 6 cm s−1 through the electrodes. In the presence of a turbulence promoter (TP), the currents from the flat and mesh electrodes improved twice compared with no TP. The 3D electrodes were tested in a complete cell with an anolyte consisting of 2.5 mol dm−3 NaBH4 in 2 mol dm−3 and a catholyte of 0.75 mol dm−3 H2O2 in 2 mol dm−3 NaOH. The power density increased in the following order: plate < micromesh < mesh < felt < mesh + 1 TP < fine mesh. The maximum power density at the fine mesh was 44.5 mW cm−2 at a cell potential of 0.44 V and a current density of 100 mA cm−2 at 296 K.