Oxygen Reduction Electrode Properties of Pyrochlores Ln{sub}2Ru{sub}2O{sub}(7-δ)(Ln=Pr,Nd,Sm) in Aqueous Solutions

摘要

The activity of electrochemical oxygen reduction (EOR) for the pyrochlores Ln{sub}2Ru{sub}(2-X)O{sub}(7-δ)(Ln=Pr,Nd,Sm) [LnR] were examined in 0.1 M KOH aqueous solution at 70°C. The onset voltage (V{sub}0) of the oxygen reduction current and the efficiency (E{sub}4) of 4-electron reduction of oxygen were evaluated by semi-steady state voltammetry with rotating ring-disk electrodes. PrR with the highest EOR activity showed V{sub}0 = ～ 0.85 V vs. reversible hydrogen electrode and E{sub}4 values above 80%. Their V{sub}0 and E{sub}4 values show that LnR containing Ln with a smaller atomic number has a higher EOR activity, i.e. the order of the activity is PrR > NdR > SmR. This was in good agreement with that of the lattice parameters of LnR. These results indicate that the EOR activity of LnR depends on the kind and/or the size of the lanthanide metal ion on the A-site. PrR and NdR exhibited higher E{sub}4 values than known excellent Pb{sub}2Ru{sub}2O{sub}(7-δ) electrocatalyst containing toxic Pb.