Enhanced electrocatalytic activity via phase transitions in strongly correlated SrRuO₃thin films

Abstract

2Transition metal oxides have been extensively studied and utilized as efficient catalysts. However, the strongly correlated behavior which often results in intriguing emergent phenomena in these materials has been mostly overlooked in understanding the electrochemical activities. Here, we demonstrate a close correlation between the phase transitions and oxygen evolution reaction (OER) in a strongly correlated SrRuO3. By systematically introducing Ru-O vacancies into the singlecrystalline SrRuO3 epitaxial thin films, we induced phase transition in crystalline symmetry which resulted in corresponding modification in the electronic structure. The modified electronic structure significantly affect the electrochemical activities, so a 30% decrease in the overpotential for the OER activity was achieved. Our study suggests that a substantial enhancement in the OER activity can be realized even within single material systems, by rational design and engineering of their crystal and electronic structures. 3Transition metal oxides show promising chemical activities that can be applied in solid oxide fuel cells (SOFC), rechargeable batteries, catalytic converters, oxygen-separation membranes, and gas sensors. [1][2][3][4][5] Oxygen evolution reaction (OER, 4OH -→ O 2 + 2H 2 O + 4e -) is one of the most important steps in energy conversion and storage mechanisms, and is the efficiency-limiting process in electrolytic water splitting and metal-air batteries. 6,7 The ultimate goal of OER study is to develop low-cost, highly active, and stable catalysts. 8,9 Recently, perovskite oxides (ABO 3 ), such as Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ , Pr 0.5 Ba 0.5 CoO 3-δ , and LaCoO 3 , have attracted much attention owing to their intrinsically high OER activity. [10][11][12] More interestingly, properties such as surface oxygen binding energy, number of outer shell electrons in the transition metal ion, electron occupancy of the e g orbitals, and the proximity of the oxygen p-band to the Fermi level, have been proposed as descriptors for OER activity. 10,11,13,14 Such approaches, however, have been mainly tested by comparing systems containing different transition metal elements.Unintentionally, such variations in the identity of the elements therein involve commensurate changes in the atomic structures, valence states, electric resistivities, crystalline surfaces, and the overall and specific electronic structures of the materials. Therefore, approaches based on simplified electronic structure may not apply to distinctive material systems, and more carefully controlled study, for example, one using a single-material system, is necessary to precisely understand the effect of the catalyst's electronic structure on the OER. 15In order to probe the link between electronic structure and catalytic activity within a singlematerial system, we exploit the strongly correlated behavior in complex oxides. In particular, the strong coupling among the degrees of freedom of the d-electrons, i.e., charge, spin, orbital, and lattice, in transition...

Epitaxial catalysts for oxygen evolution reaction: model systems and beyond

“…In [2], the authors show the formation of a stable surface phase during OER, which is formed and stabilized on epitaxial SrIrO 3 catalyst layers and results in increasing OER activity, rather than degradation over time. In [5], phase-sensitive catalytic activity was reported for SrRuO 3 , while the different phases (tetragonal/orthorhombic) were obtained via defined control of the epitaxial growth process.…”

“…The materials screening approach of the community has identified perovskite oxides as promising candidates, particularly focussing on iridates, ruthenates, cobaltites, and nickelates [2][3][4][5], which (similar to pure metal compounds) group at the top of the volcano plot [6]. The beauty of these materials lies in the much lower volume concentration of metal ions as compared to pure metals, and even more in the wide range of chemical compositions and physical properties available within the family of perovskite oxides, and the extraordinary tunability of physical properties via the coupled ionic and electronic degrees of freedom in these materials.…”

Nanoscale Perovskites as Catalysts and Supports for Direct Methanol Fuel Cells

“…[53] catalystf or OER, Ru is still relatively expensivea sc ompared with other earth-abundant metals.N ot surprisingly,p erovskite oxides, such as but not limited to LaMnO 3 ,S rRuO 3 ,a nd LaCoO 3 ,h ave attracted significant attention and promisea s OER catalysts. [74] In our group, we prepared as eries of lanthanum nickel oxide (LaNiO 3 )n anorods [1] prepared by using a) as imple and novel template-assisted co-precipitation methodo fl anthanum hydroxide-nickel hydroxide precursors followed by b) am ild annealing of as-prepared lanthanum hydroxide-nickel oxyhydroxide composite nanorods, as shown in Figure 7A-D. In the absence of an underlying conductive carbon support, our assynthesized LaNiO 3 rods yieldeda no nset potential of 1.56 V versus RHE and an OER activity of 10.0 mA cm À2 ,m easured at 1.8 Vv ersus RHE with a0 .08 mg loading ( Figure 7E).…”

Structural, magnetic, electrical, and electrochemical properties of Sr–Co–Ru–O: A hybrid‐capacitor application

“…Another study by Miao et al has investigated thermoelectric performance of SrRuO 3 by first principles density functional theory and has reported the Seebeck coefficient as below 35 μV/K at room temperature with p‐type conductivity. In addition, Lee et al have scrutinized the electro‐catalytic activity for solid oxide fuel cell applications and they have found 30% voltage decrease in the over potential by modification of the electronic structure of SrRuO 3 through changing the lattice symmetry.…”