Oxygen Reduction Electrode Properties of Oxide Nanosheet-Based Materials

Two types of oxide nanosheet-based materials, a H3O+-exchanged layered titanate and restacked titania nanosheets (H3O+-RE) were synthesized by soft chemical methods, and their oxygen reduction reaction (ORR) activities were examined by semi-steady-state voltammetry with a rotating ring-disc electrode at 70°C in 0.05 M H2SO4. Both samples showed similar onset potentials of the ORR, ~ 0.50 vs. reversible hydrogen electrode, while the efficiencies (Eff4) of the 4-electron reduction of oxygen depended on their nanostructures, i.e. the stacking morphology of nanosheets, specific surface area and kinds of cation between the nanosheets. Both H3O+-form samples showed high Eff4 values are compared with Cs+-form layered titanate.and the H+-form restacked titania nanosheets. This reveals that the H3O+ions and the number of the active sites for ORR are related to the ORR activity. The H3O+-RE exhibited the best Eff4 value (> 90%), which is comparable to that of a conventional 20 mass% Pt/C catalyst.