Activation Factors of the Oxygen Reduction Reaction on Pt<sub>3</sub>Co Alloy Single Crystal Electrode in Diethylmethylammonium Triflate [dema][TfO]

Increasing the activity of oxygen reduction reaction (ORR) is an important subject for the development of a fuel cell.Operation temperature of a fuel cell of a heavy-duty vehicle (HDV) is more than 100 C, and the combination of ionic liquids and Pt alloy catalysts can contribute to the increase of the ORR activity at more than 100C.We have studied the ORR activity on single crystal electrodes of Pt3Co in diethylmethylammonium triflate ([dema][TfO]).The activity of the ORR at 0.9 V(RHE) at 120 C increases as Pt3Co(111) < Pt3Co(110) < Pt3Co(100).This order of the activity completely differs from that in 0.1 M HClO4: Pt3Co(100) < Pt3Co(110) < Pt3Co(111).The activity of Pt3Co(100) in [dema][TfO] at 120 C was higher than that in 0.1 M HClO4 at 25 C.The ORR current densities at 0.6 V(RHE) in [dema][TfO] at 120 C exceed the limiting current densities in 0.1 M HClO4 at 25 C on all the surfaces.The Arrhenius plots show that the frequency factor depends on the surface structure markedly: PtCo(111) << PtCo(110) << PtCo(100).This result suggests that the difference of the number of active sites contributes to the activity for the ORR on Pt3Co single crystal electrodes.