Mass transport studies during dissolved oxygen reduction to hydrogen peroxide in a filter-press electrolyzer using graphite felt, reticulated vitreous carbon and boron-doped diamond as cathodes

This paper describes the mass transport characterization of oxygen reduction reaction (ORR) to yield hydrogen peroxide at porous electrodes like graphite felt (GF) and reticulated vitreous carbon (RVC, 45 pores per inch) and at a boron-doped diamond (BDD) plate in the presence of a plastic net. A filter-press electrolyzer was used for the reduction of 0.24 mM of O-2 in the presence of 0.5 M of either Na2SO4 or 0.5 M NaClO4 as supporting electrolytes in water at pH 2.8. Linear differential pulse voltammetry (LDPV) was performed at different volumetric flow rates in the range 253-50.6 cm(3) s(-1). Cathodic polarization curves using GF, RVC and BDD revealed that ORR is limited by mass transport at -0.4<E<-0.1 V vs SHE in sulfate medium. However, in perchlorate medium, such limitation appeared at -0.8<E<-0.5V, -0.5<E<-025 V, and -03<E<-0.25 V using GF, RVC and BOO, respectively. From these analyses, limiting current intensities were measured and used to obtain the mass transport correlation, k(m)a = bu(c). The values of constant b, which is related to mass transport properties, shape and cell dimensions, were between 0.0012-0.0028,0.011-0.170 and 0.0007-0.0006 for GF. RVC and BDD, respectively. The constant c exhibited values of 1.47-1.56 and 0.80-0.93 for GF and RVC, as a result of chaotic flow pattern inside the porous structures, and 0.84-1.00 for BDD plate employing the turbulence promoter. Mass transport of 02 depends on the electrode geometry, thus highlighting that the flow pattern is a complex function of the specific surface area and the electrode porosity. (C) 2015 Elsevier B.V. All rights reserved.