Nanocarbon-Induced Etching Property of Semiconductor Surfaces: Testing Nanocarbon’s Catalytic Activity for Oxygen Reduction Reaction at a Single-Sheet Level

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In the field of fuel cells, the microscopic understanding of the catalytic activity of nanocarbons or graphene-based materials for oxygen reduction reaction (ORR) is highly demanded. In the current study, a novel concept is presented to achieve it, which is a different approach from familiar electrochemical measurements. To prove this concept, we prepared two nanocarbon materials, whose ORR activities were tested and compared via macroscale cyclic and linear sweep voltammetry. Next, considering the electrochemical potential of ORR and the band-edge position of semiconductors, we chose single-crystalline Ge as the substrate on which the single-sheet nanocarbons were dispersed. We found that etched hollows formed under the loaded nanocarbons after immersing the nanocarbon/Ge sample into O2-containing water. The histogram analysis of the hollows represented the difference in catalytic activities to promote Ge etching between the used nanocarbons, and the corresponding trends agreed qualitatively with the electrochemical measurements.