Electrocatalytic Activity of the Pyrochlores Ln2M2O7−δ (Ln = Lanthanoids) for Oxygen Reduction Reaction

Abstract

Electrocatalytic oxygen reduction reaction (ORR) activities of the pyrochlore oxides Ln 2 Zr 2 O 7-d (LnZ) and Ln 2 Sn 2 O 7-d (LnS) (Ln = La, Pr, Nd, Sm) were examined in 0.1 M KOH solution at 70°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 a rotating ring-disk electrode. In both LnZ and LnS series, the E on values were *0.85 V versus reversible hydrogen electrode. A relation was found between the E on values and the lattice parameters; i.e. on the whole, the ORR activity became high with an increase in the lattice parameters. When the Ln ion was the same, the LnZ series exhibited higher ORR activities than the LnS series. The pyrochlore LaZ with the highest ORR activity showed a Eff 4 value higher than 85%. Moreover, Mn-incorporation to LaZ led to a mixed-oxide (1-xLaZ-xLaM) of LaZ and the perovskite LaMnO 3 (LaM). However, the E on value apparently sifted to a more positive potential probably due to LaMnO 3 , and the magnitude of the cathodic ORR current increased with an increase in the mixing content up to x = 0.3. The mixed-oxide 0.7LaZ-0.3LaM exhibited the highest ORR activity (E on = *0.90 V and Eff 4 [ 95%), which was comparable to that of a conventional 20 mass% Pt/C catalyst.

Nonstoichiometric Oxides as Low-Cost and Highly-Efficient Oxygen Reduction/Evolution Catalysts for Low-Temperature Electrochemical Devices

“…Therefore, replacing them with less toxic and less expensive elements, e.g., rare-earth metal or Sn, is a promising route to commercialization. The Ln 2 Sn 2 O 7−δ (Ln = La, Pr, Nd, and Sm) series is identified as a promising candidate for ORR with an onset potential of ∼0.85 V vs RHE . Generally, pyrochlore-type oxygen catalysts require significant enhancement of their electrocatalytic activities to compete with other precious metals and metal oxides.…”

AMnO3 (A = Sr, La, Ca, Y) Perovskite Oxides as Oxygen Reduction Electrocatalysts

“…The generation of OH − from H 2 O 2 can be achieved by either a further reduction reaction (pathway 3), or the decomposition step Platinum-based catalysts remain the benchmark materials for the ORR, in acidic and alkaline environments, but significant efforts have more recently been focused on earth-abundant and lower-cost materials; such as perovskite oxides of the general structure ABO 3 [7][8][9]. Significant efforts have been devoted to establishing electronic descriptors for rationalising and predicting the activity of this class of materials [10][11][12][13].…”

Carbonate Selective Ca2Ru2O7-yPyrochlore Enabling Room Temperature Carbonate Fuel Cells

“…[23][24][25][26][27][28][29] Thus, Method 1 initiated investigations on the synthesis of Ca 2 Ru 2 O 7-y . [23][24][25][26][27][28][29] Thus, Method 1 initiated investigations on the synthesis of Ca 2 Ru 2 O 7-y .…”

“…25,35,39 The external surface area, determined from the linear region of t-plot using Harkins and Jura parameters 40 was 162 m 2 /g. Using Eq.…”