Oxygen reduction reaction on platinum single-crystal electrodes modified with protonic ionic liquid

[Display omitted] •ORR activity on Pt(111) increases 3.1 times after modification with [MTBD][beti].•Increase in ORR activity by the IL needs more than 10 atomic rows of (111) terrace.•MTBD is the main contributor to the enhancement of ORR activity.•The effects of beti on ORR activity are much smaller than those of MTBD.•A concentration of MTBD 2.0–3.5 × 10–5 M results in the highest ORR activity. The oxygen reduction reaction (ORR) on the low- and high-index planes of Pt modified with a protonic ionic liquid ([7-methyl-1,5,7-triazabicyclo(4.4.0)dec-5-ene][bis(pentafluoroethylsulfonyl)imide], referred to here as [MTBD][beti]) was studied in 0.1 M perchloric acid solution. The specific activity of the ORR on Pt(111) modified with [MTBD][beti] was 3.1 times higher than that on unmodified Pt(111), while the ORR was deactivated on modified Pt(100). [MTBD][beti] slightly enhanced the ORR activity of the Pt n(111)–(111) planes (where n = 2–9). These results show that a larger (111) terrace is essential for a marked increase in the ORR activity on Pt electrodes modified with [MTBD][beti]. Although the ratio of the increase in the activity of n(111)–(111) was lower than that of Pt(111), Pt(331) = 3(111)–(111) showed the highest ORR activity after [MTBD][beti] modification. The effects of MTBD and beti were also studied separately. MTBD provided the main contribution to the increase in ORR activity, giving the highest activity at a concentration of 2.0–3.5 × 10–5 M, whereas beti affected the ORR activity only slightly.