A’–B Intersite Cooperation-Enhanced Water Splitting in Quadruple Perovskite Oxide CaCu₃Ir₄O₁₂

Abstract

Developing highly efficient electrochemical catalysts and exploring the basic mechanisms for the oxygen evolution reaction (OER) are key issues for the large-scale commercialization of environmentally friendly electrolytic hydrogen energy. Compared with a simple ABO3 perovskite, the A-site-ordered quadruple structure AA’3 B 4O12 shows enhanced OER activity, but the underlying mechanisms remain unknown. Herein, we find that the quadruple perovskite oxide CaCu3Ir4O12 has stable and superior electrochemical activity with a very low overpotential of 252 mV to achieve the current density of 10 mA·cm–2 in alkaline solution. Operando X-ray absorption spectroscopy reveals that the B-site Ir is an OER active site with a variable valence state from the initial Ir4+ approach to Ir5+, while the A’-site Cu is inactive with a constant valence state during the OER process. Density functional theory calculations demonstrate that the A’–B intersite cooperation synergistically enhances OER activity via the corner-sharing Cu–O–Ir framework owing to the strong 3d–2p–5d orbital hybridizations, regardless of the inactive Cu site. In the structural constitution of CaCu3Ir4O12, a small Cu–O–Ir bond angle (110.7°) forms. The special orbital symmetry as well as the delicate 3d–5d levels enhance the orbital overlap and therefore promote the charge transfer, favoring the superior OER activity of CaCu3Ir4O12.

Effects of A‐site Cations in Quadruple Perovskite Ruthenates on Oxygen Evolution Catalysis in Acidic Aqueous Solutions

“…[ 33 ] The participation of cations at A′ site (Cu in this work) in OER catalysis is also expected from the short A′–O–B bond angle, making the OER processing preferential through the dual sites, which was also observed in other quadruple perovskite systems including CaMn 7 O 12 and CaCu 3 Ir 4 O 12 . [ 34–36 ] CaCu 3 Ru 4 O 12 was found near the top of the volcano, indicating that it had the most appropriate Cu–O bond strength. OER stabilities, that is, the current density ratio of the 100th cycle to the 1st cycle, for all samples are plotted versus the Ru–O bond length in Figure 6b (values of Ru–O bond length obtained from Rietveld refinement of the SXRD patterns were used here).…”

Turning Electrocatalytic Activity Sites for the Oxygen Evolution Reaction on Brownmillerite to Oxyhydroxide

“…We found that CCO-1h exhibited the best OER activity, and the thickness of CoOOH on CCO-1h is neither too thick nor too thin, indicating a synergistic interplay between the surface CoOOH and the substrate. Soft X-ray absorption spectroscopy (XAS) spectra at the Co-L 2,3 -edges were recorded in the surface-sensitive total electron yield (TEY) mode, which is an effective technique to collect information about electronic structures and local coordination environments. ,− The Co L 2,3 -edge XAS spectra in Figure a consist of the following features: the L 3 - and L 2 -edges at about 780 and 795 eV, respectively, which are contributed from the spin–orbital splitting of Co 2p core hole. All the spectra of the treated samples share similar peak positions and shapes with the reference of CoOOH, indicating that the surface of the Co element electronic structure did not change significantly after the surface treatment.…”

High-Pressure Synthesis of Quadruple Perovskite Oxide CaCu3Cr2Re2O12 with a High Ferrimagnetic Curie Temperature

“…Sr 2 FeMoO 6 is a representative DP material with intriguing half-metallic property . On the other hand, three-quarter A-site cations can be substituted by small-size Jahn–Teller active ions such as Mn 3+ (t 2g 3 e g 1 ) and Cu 2+ (t 2g 6 e g 3 ), which tends to form a square-coordinated unit. , As a result, A-site ordered quadruple perovskites (QPs) with the chemical formula AA’ 3 B 4 O 12 with heavily tilted BO 6 octahedra can be formed, and intriguing physical properties can therefore be expected. For example, typical QPs such as CaCu 3 Ti 4 O 12 with a large dielectric constant, LaCu 3 Fe 4 O 12 exhibiting intermetallic charge transfer and unusual negative thermal expansion properties, and multiferroic in RMn 3 Cr 4 O 12 (R = rare earth element and Bi) − have been extensively studied.…”