New Oxygen Reduction Electrocatalysts Based on Oxide Nanosheet Materials

摘要

Three types of titania nanosheet-based materials, a H_3O~+-exchanged rolled nanosheet (nanotube) (H_3O~+-NT(Ti)), layered titanate (H_3O~+-RG(Ti)), and restacked titania nanosheets (H_3O~+-RE(Ti)) 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℃ in 0.05 M H2SO4. All the samples showed similar onset potentials (E_(on)) of the ORR current, ～ 0.50 vs. reversible hydrogen electrode, while the efficiencies (Eff_4) of the 4-electron reduction of oxygen depended on their nanostructures, i.e. the stacking morphology of nanosheets, specific surface area and kinds of inserted cation between the nanosheets. Both H_3O~+-RG(Ti) and H_3O~+-RE(Ti) samples showed higher Eff_4 values as compared with Cs~+-form layered titanate (Cs~+-RG(Ti)) and the H~+-form restacked titania nanosheets (H~+-RE(Ti)). This reveals that the H_3O~+ ions and the number of the active sites for ORR are related to the ORR activity. The H_3O~+-RE(Ti) exhibited the best Eff_4 value (> 90%), which is comparable to that of a conventional 20 mass% Pt/C catalyst. The effects on the ORR activity are also observed in alkaline (0.1 M KOH) aqueous solution, i.e. the H_3O~+-RE(Ti) exhibited the best E_(on)(～ 0.8 V) and Eff_4 values (> 90%).