Unveiling the Catalytic Origin of Nanocrystalline Yttrium Ruthenate Pyrochlore as a Bifunctional Electrocatalyst for Zn–Air Batteries

Abstract

Zn-air batteries suffer from the slow kinetics of oxygen reduction reaction (ORR) and/or oxygen evolution reaction (OER). Thus, the bifunctional electrocatalysts are required for the practical application of rechargeable Zn-air batteries. In terms of the catalytic activity and structural stability, pyrochlore oxides (A[BA]O) have emerged as promising candidates. However, a limited use of A-site cations (e.g., lead or bismuth cations) of reported pyrochlore catalysts have hampered broad understanding of their catalytic effect and structure. More seriously, the catalytic origin of the pyrochlore structure was not clearly revealed yet. Here, we report the new nanocrystalline yttrium ruthenate (Y[RuY]O) with pyrochlore structure. The prepared pyrochlore oxide demonstrates comparable catalytic activities in both ORR and OER, compared to that of previously reported metal oxide-based catalysts such as perovskite oxides. Notably, we first find that the catalytic activity of the Y[RuY]O is associated with the oxidations and corresponding changes of geometric local structures of yttrium and ruthenium ions during electrocatalysis, which were investigated by in situ X-ray absorption spectroscopy (XAS) in real-time. Zn-air batteries using the prepared pyrochlore oxide achieve highly enhanced charge and discharge performance with a stable potential retention for 200 cycles.

Ruthenium Oxide Nanosheets for Enhanced Oxygen Evolution Catalysis in Acidic Medium

“…[6,7] In an acidic environment, however, only a limited number of OER catalysts are known to operate in a stable way. This has already led to the development of several single-phase and multiphase oxides such as double perovskites Ba 2 MIrO 6 (M = Y, La, Ce, Pr, Nd, and Tb), [10] pyrochlores Y 2 Ir 2 O 7 , [11] [12] The fabrication of highly active and robust hexagonal ruthenium oxide nanosheets for the electrocatalytic oxygen evolution reaction (OER) in an acidic environment is reported. [8] While iridium oxides are more robust, ruthenium oxides exhibit better performance.…”

Toward Promising Cathode Catalysts for Nonlithium Metal–Oxygen Batteries

“…The resulted YRO particles exhibited a good bifunctional capability, with a high ORR onset potential of ≈0.85 V versus RHE and a low OER onset potential of ≈1.45 V. The high activity of YRO was attributed to the increased oxidation state of the cations during OER/ORR, leading to a better electron transfer to facilitate the catalysis process. By using this YRO catalyst in rechargeable Zn–O 2 batteries, a low polarization of about 0.22 V was achieved, together with a small charge/discharge potential difference of ≈0.84 V after 200 cycles (Figure c), which were comparable to the Pt/C + IrO 2 composite catalyst . To reveal the underlying mechanism for the improved catalytic activity of YRO particles, in situ X‐ray absorption spectroscopy (XAS) technique was used to investigate the changes on electron configurations and geometric local structures of cations over reaction.…”

“…a) Schematics of the synthesis of the YRO NPs; b) the corresponding SEM image (inset: the magnified SEM image); c) cycling performance of the rechargeable Zn–O 2 batteries at 10 mA cm −2 ; d) schematics of the ORR/OER catalysis processes on YRO. Reproduced with permission . Copyright 2017, American Chemical Society…”

Ein aktiver und widerstandsfähiger difunktioneller Sauerstoff‐Elektrokatalysator durch kohlenstofffreie hierarchische Funktionalisierung

“…[1][2][3] Noch wichtiger ist, dass billige Alternativen wie etwa N-dotierter Kohlenstoff sowie unedle Metalle wie Fe,Co, Ni und deren Metalloxide mit Perowskit-, [4,5] Spinell-, [6,7] Brownmillerit- [8,9] und Pyrochlor-Struktur [10,11] auch als Katalysatoren verwendbar sind, was alkalische MABs praktisch attraktiver macht. Aufgrund einer günstigeren Kinetik und geringerer Überspannungen sind ORR und OER in alkalischem Milieu vorteilhafter als in sauren Umgebungen.…”

“…[1][2][3] Noch wichtiger ist, dass billige Alternativen wie etwa N-dotierter Kohlenstoff sowie unedle Metalle wie Fe,Co, Ni und deren Metalloxide mit Perowskit-, [4,5] Spinell-, [6,7] Brownmillerit- [8,9] und Pyrochlor-Struktur [10,11] auch als Katalysatoren verwendbar sind, was alkalische MABs praktisch attraktiver macht. [4][5][6][7][8][9][10][11] Ein Problem kohlenstoffbasierter Katalysatoren ist die Kohlenstoffoxidation (Korrosion) während des OER-Vorgangs,d ie einen allmählichen Leistungsabfall zur Folge hat. [3] Verglichen mit wasserbasierten MABs arbeiten MABs mit organischen Elektrolyten bei hçheren Spannungen, sie haben jedoch schwerwiegende Probleme mit der Lebensdauer aufgrund des ständigen Angriffs von H 2 Ound CO 2 (aus der Luft) auf die organischen Elektrolyte,d urch einen allmählichen Verlust an organischen Elektrolyten sowie infolge der Massetransportbegrenzung durch die Bildung fester Produkte (zum Beispiel Li 2 O 2 )w ährend der elektrochemischen Reduktion von Sauerstoff,w as zu einer sehr schlechten Reversibilitätf ührt.…”