Abstract
Four as-received carbon blacks from a Black Pearl family with surface areas between 30 and 1600 m2 g−1 were chosen to be tested as oxygen reduction catalysts in an alkaline environment. As main descriptors of their performance an onset potential, electron tranfer number and kinetic current density have been chosen. Even though the onset potential was smaller than that on Pt/C, the electron transfer number and kinetic current density reached the values measured on Pt/C. To find surface features governing the good performance, porosity and surface chemistry of the samples were evaluated in detail using nitrogen adsorption, thermal analysis, potentiometric titration, and XPS. The results indicated the linear dependence of the onset potential and electron transfer number on the surface area/porosity. The most porous sample exhibited an excellent catalytic behavior due to its developed ultramicropores. They attracted O2 from an electrolyte and, through strong adsorption forces, contributed to the brake of oxygen-oxygen bonds and thus to its further reduction and protonation. The importance of the surface affinity to attract oxygen for ORR was demonstrated by linear dependences of both the electron transfer number and onset potential on the extent of oxygen adsorption from its saturated solution.
Published Version
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