Ca₂Mn₂O₅ as Oxygen-Deficient Perovskite Electrocatalyst for Oxygen Evolution Reaction

Abstract

This paper presents the use of Ca2Mn2O5 as an oxygen-deficient perovskite electrocatalyst for oxygen evolution reaction (OER) in alkaline media. Phase-pure Ca2Mn2O5 was made under mild reaction temperatures through a reductive annealing method. This oxygen deficient perovskite can catalyze the generation of oxygen at ~1.50 V versus (vs) reversible hydrogen electrode (RHE) electrochemically, and reach an OER mass activity of 30.1 A/g at 1.70 V (vs RHE). In comparison to the perovskite CaMnO3, Ca2Mn2O5 shows higher OER activities. The molecular level oxygen vacancies and high spin electron configuration on manganese in the crystal structures are likely the contributing factors for the enhanced performance. This work demonstrates that oxygen-deficient perovskite, A2B2O5, is a new class of high performance electrocatalyst for those reactions that involve active oxygen intermediates, such as reduction of oxygen and OER in water splitting.

Mechanistic Parameters of Electrocatalytic Water Oxidation on LiMn2O4 in Comparison to Natural Photosynthesis

“…The LiMn 2 O 4 –carbon composite electrode reached 10 A g −1 at 1.705(3) V versus RHE (0.476(3) V overpotential) at pH 13.4 and 14.0, which is similar to Ca 2 Mn 2 O 5 (1.70 V versus RHE; 5th cycle; “sub‐micron”)65 and β‐MnO 2 (1.71 V versus RHE; 5 m 2  g −1 ) 66. Yet, the overpotential is higher than that of Mn oxides with higher surface area, for example, solvent‐free α‐MnO 2 ‐SF (1.64 V versus RHE; 112 m 2  g −1 )66 and oxides with similar surface area that exhibit higher activity per oxide surface, for example, ball‐milled Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3‐ δ (1.53 V versus RHE; 3.9 m 2  g −1 ) 7…”

Elucidating dz2 orbital selective catalytic activity in brownmillerite Ca2Mn2O5

“…6 In this work, we combined experimental and theoretical methods to comprehensively investigate the electronic structures of this specific oxide. For pure phase of Ca 2 Mn 2 O 5, it exhibits a paramagnetic insulating behavior at room temperature with a direct band gap of ∼1.35 eV.…”

“…6 X-ray diffraction (Rigaku Corporation, D/max-2500, 40KV,100mA) equipped with Cu K α radiation (λ = 1.5406 Å). It was utilized to collect the data over a 2θ range from 10 • to 80 • with step size of 0.02 • and a scan speed of 0.15 • /min.…”

“…6 Different from the active sites in metallic catalysts, the OH-adsorption position is related to the symmetry of the crystal field in the perovskite oxides. For Ca 2 Mn 2 O 5 , the adsorbed OH-has stronger bonding with the d z 2 orbital of Mn atom than the other 3d-orbitals ( Figure S3, supplementary material).…”

“…The discovery of perovskite catalysts has stimulated extensive interests on searching for lowcost and highly active oxides to replace precious metals for catalysis. 1,2 To date, various perovskite oxides such as La(Co, Ni, Mn)O 3 , 1,3-5 Ca 2 Mn 2 O 5 , 6 etc., have been utilized in oxygen evolution (reduction) reaction (OE(R)R). J. Suntivich et.…”