Boosting oxygen reduction activity and enhancing stability through structural transformation of layered lithium manganese oxide

Abstract

Structural degradation in manganese oxides leads to unstable electrocatalytic activity during long-term cycles. Herein, we overcome this obstacle by using proton exchange on well-defined layered Li2MnO3 with an O3-type structure to construct protonated Li2-xHxMnO3-n with a P3-type structure. The protonated catalyst exhibits high oxygen reduction reaction activity and excellent stability compared to previously reported cost-effective Mn-based oxides. Configuration interaction and density functional theory calculations indicate that Li2-xHxMnO3-n has fewer unstable O 2p holes with a Mn3.7+ valence state and a reduced interlayer distance, originating from the replacement of Li by H. The former is responsible for the structural stability, while the latter is responsible for the high transport property favorable for boosting activity. The optimization of both charge states to reduce unstable O 2p holes and crystalline structure to reduce the reaction pathway is an effective strategy for the rational design of electrocatalysts, with a likely extension to a broad variety of layered alkali-containing metal oxides.

Enabling Anionic Redox Stability of P2‐Na5/6Li1/4Mn3/4O2 by Mg Substitution

“…[ 31 ] To obtain the accurate valence of Mn in this stage, we carried out SXAS measurements with total fluorescence yield (TFY) mode with a detection depth of few hundreds of nanometers. As shown in Figure S6 in the Supporting Information, the Mn L 2,3 ‐edge IPFY spectrum of discharged NMLM at 2.6 V is similar to that of Li 2 MnO 3 , [ 32 ] indicating that the valence of Mn in NMLM at 2.6 V is still +4. Figure S7 in the Supporting Information exhibits the Mn L 2,3 ‐edge IPFY spectrum (yellow) of NMLM at 2.0 V and its fitted spectrum (bule) using LaMnO 3 (Mn 3+ ) [ 33 ] and NMLM at 2.6 V (Mn 4+ ) as references.…”

Electronic Properties of Fully Strained La1–xSrxMnO3 Thin Films Grown by Molecular Beam Epitaxy (0.15 ≤ x ≤ 0.45)

“…The Mn 3+ symmetry is considered to be D 4h (due to a Jahn–Teller distortion) and the Mn 2+ and Mn 4+ to be O h . The charge transfer parameters for Mn 2+ , Mn 3+ , and Mn 4+ were selected from previous work on MnO, LaMnO 3 , and MnO 2 , respectively. − The crystal field parameters D s and D t (tetragonal parameters) for the Mn 3+ , generated from the transition O h to D 4h distortion, , were selected with the opposite sign that indicates an axial compression (compression of the octahedral/tensile strain) in LSMO sample growth on STO substrates. The relative concentration of Mn 3+ and Mn 4+ was chosen from the previous Mn quantification performed on the Mn 2p XPS fit.…”

Electronic engineering of amorphous Fe–Co–S sites in hetero-nanoframes for oxygen evolution and flexible Al–air batteries

“…The electron transfer number ( n ) during the ORR was calculated from the Koutecky–Levich (K–L) equations: 20 where j , j L , and j K correspond to the measured, diffusion-limiting, and kinetic current densities, respectively; ω is the rotation rate (rpm), F is the Faraday constant (96 485C mol −1 ), C 0 is the bulk concentration of oxygen (1.26 × 10 −6 mol cm −3 ), D 0 is the diffusion coefficient of oxygen (1.9 × 10 −5 cm 2 s −1 ), and n is the kinetic viscosity (0.01 cm 2 s −1 ).…”