Structure–Activity Relationship in Manganese Perovskite Oxide Nanocrystals from Molten Salts for Efficient Oxygen Reduction Reaction Electrocatalysis

Abstract

We report a synthesis pathway in molten salts toward ligand-free nanoparticles of the layered perovskite La 0.5 Sr 1.5 MnO 4 (l-LSMO) and of the pseudo-cubic perovskite La 0.7 Sr 0.3 MnO 3 (pc-LSMO). These particles are readily implemented as oxygen reduction reaction (ORR) electrocatalysts in alkaline conditions. They show high ORR selectivity for the 4-electrons reduction of O2 in water. Among these two materials, pc-LSMO nanocrystals of 20 nm diameter exhibit high mass-normalized ORR activity for a perovskite material (21.4 A g-1 oxide at 0.8 V/RHE) thanks to their relatively large surface area, high crystallinity and electron mobility. These features provide pc-LSMO nanocrystals with remarkable stability compared to state-of-the-art perovskites, for instance only a 5% increase of the overpotential at-0.05 mA cm-2 oxide over 40 hours. pc-LSMO nanocrystals are then the most stable perovskite ORR electrocatalyst reported up to now. These performances, combined with high activity, high selectivity and absence of precious metals, make La 0.7 Sr 0.3 MnO 3 nanocrystals one of the best compromises for alkaline oxygen reduction reaction.

Experimental Descriptors for the Synthesis of Multicationic Nickel Perovskite Nanoparticles for Oxygen Reduction

“…28 NaNO 2 has been efficiently used as synthesis medium for several systems including ZrO 2 , [28][29][30] MgO, 31 La 0.5 Sr 1.5 MnO 4 . 26 Indeed, the reactivity of Ni(II) and La(III) nitrates drastically increases in NaNO 2 (Figure 1a). NaNO 2 yields a mixture of LaNiO 3 and La 2 NiO 4 at 600 °C (Figure 1a (Figure 1a).…”

Rational Design of Superior Electrocatalysts for Water Oxidation: Crystalline or Amorphous Structure?

“…Under the functions of foreign OER potentials, the surface of these crystalline compound structures would collapse and recombine into amorphous structures. For example, Ruddlesden–Popper (RP) oxides with unstable rock‐salt layers show metastable phases and tend to become amorphous under electrochemical potentials (Figure 1e), for example, La 2 Li 0.5 Ni 0.5 O 4 [ 48 ] and La 0.5 Sr 1.5 MnO 4 [ 49 ] oxides. Interestingly, Yang et al [ 48 ] found that the formed amorphous layers on La 2 Li 0.5 Ni 0.5 O 4 crystalline oxide after the same OER cycles in KOH solutions with different pH values are quite different, where the surface degradation depends on the pH and increased thickness of amorphous layers is formed with increasing pH values.…”

High-Efficiency of Bi-Functional-Based Perovskite Nanocomposite for Oxygen Evolution and Oxygen Reduction Reaction: An Overview

“…The new types of ligand-free powdersbased on two different layered (La 0.5 Sr 1.5 MnO 4 , pc-LSMO) and pseudocubic (La 0.7 Sr 0.3 MnO 3 , I-LSMO) perovskites were synthesized by one-pot route ( Figure 3 a). Among these nanocubes ( Figure 3 b) and nanocrystals ( Figure 3 c), pc-LSMO nanocrystals could exhibit better ORR activity (21.4 A g −1 ) with remarkable cyclic stability under alkaline conditions [ 49 ]. Ruthenium-based pyrochlores (A 2 Ru 2 O 7 , A=Y, Nd, Bi) composite has shown the distribution of nanoparticles, which is analyzed by STEM-EDX analysis and the systematic theoretical study of OER activities [ 50 ].…”

“… ( a ) Reaction pathway yielding layered perovskite (l-LSMO) nanoparticles from pc-LSMO into molten NaNO 2 , ( b ) HRTEM images of pc-LSMO nanocubes and ( c ) HRTEM image of an l-LSMO nanoparticle and corresponding fast Fourier transform.Copyright 2020 by the American Chemical Society [ 49 ]. …”