The activity of electrochemical oxygen reduction (EOR) for the pyrochlores Ln2Ru2-XO7-δ (Ln=Pr,Nd,Sm) [LnR] were examined in 0.1 M KOH aqueous solution at 70oC. The onset voltage (Vo) of the oxygen reduction current and the efficiency (E4) 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 Vo = ~ 0.85 V vs. reversible hydrogen electrode and E4 values above 80 %. Their Vo and E4 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 E4 values than known excellent Pb2Ru2O7-δ electrocatalyst containing toxic Pb.
The activities of the pyrochlores Pb2Ru2-xMxO7-δ (M=Mn,Fe,Co,Ni)[PRM(0x)] toward
electrochemical oxygen reduction (EOR) were examined in 0.1 M KOH and 0.05 M H2SO4 aqueous
solutions. The onset voltage (Vo) and the efficiency (E4) of 4-electron reduction of oxygen for
PRM(0x) were evaluated by semi-steady state voltammetry with rotating ring-disk electrodes. In
PRM01, the order of the EOR activities was PRMn01 > PRCo01 > PRNi01 > PRFe01 in both
solutions. This was consistent with the variation of the lattice parameters, i.e. PRM01 with a smaller
lattice parameter showed higher EOR activity. In addition, PRMn05 showed higher EOR activity
than PRMn01. The onset voltages Vo were 0.95 and 0.50 V vs. reversible hydrogen electrode in 0.1
M KOH and 0.05 M H2SO4, respectively, while E4 was almost 100 % in both solutions. These
results indicate that the EOR activity of PRM(0x) depends on the incorporated metal ions on the
B-sites and their contents.
To explore new electrocatalysts for alkaline direct alcohol fuel cells (ADAFCs), oxygen reduction reaction (ORR) activity of the pyrochlores Ln 2 Ru 2 O 7-(LnR, Ln=Pr,Nd,Sm,Gd,Dy,Yb) and Ln 2 Ru 2-x Mn x O 7-(LnRMn x , Ln=Pr,Nd) were examined in 0.1 M KOH solution at 70 o C. The onset potential (E on ) of the oxygen reduction current and the efficiency (Eff 4 ) of 4-electron reduction of oxygen were evaluated by semi-steady state voltammetry with rotating ring-disk electrodes. In the LnR series, PrR with the highest ORR activity showed E on = ~ 0.85 V vs. reversible hydrogen electrode and a Eff 4 value above 90 %. Their E on and Eff 4 values revealed that LnR with a smaller atomic number had a higher ORR activity. This trend was in good agreement with that of electrical conductivities of the LnR. In addition, effects of Mn substitution for the Ru-site were confirmed in both PrRMn x and NdRMn x series. Their ORR activities increased with an increase in the amount of Mn incorporation. The NdRMn 0.25 exhibited the highest ORR activity (E on = 0.95 V and Eff 4 > 90%) in the formation range of the pyrochlore single phase. Moreover, the ORR selectivity was much higher than that of a conventional 20 mass% Pt/C catalyst: the E on value was 0.95 V even in 0.1 KOH containing 1 M methanol, ethanol, ethylene glycol and 2-propernol, whereas the E on the value was 0.7 V for the Pt/C catalyst.
Photocatalytic proton reduction and water oxidation have been studied in a
tris(2,2’-bipyridyl)ruthenium complex-catalyst system. Pyrochlore-type oxides have been used as
proton reduction catalysts with a sacrificial electron donor (Na2EDTA) at pH 7 and as water
oxidation catalysts with a sacrificial electron acceptor (K2S2O8) at pH 3. Rate constants for the
proton reduction were estimated on the basis of photochemical processes. Yb2Ru2O7-δ was found to
be the most active catalyst for proton reduction and water oxidation catalyst in this system.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.