A tailored double perovskite nanofiber catalyst enables ultrafast oxygen evolution (original) (raw)
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Advanced Functional Materials, 2018
It is shown that producing PrBaCo2O5+δ and Ba0.5Sr0.5Co0.8Fe0.2O2+δ nanoparticle by a scalable synthesis method leads to high mass activities for the oxygen evolution reaction (OER) with outstanding improvements by 10× and 50×, respectively, compared to those prepared via the state-of-the-art synthesis method. Here, detailed comparisons at both laboratory and industrial scales show that Ba0.5Sr0.5Co0.8Fe0.2O2+δ appears to be the most active and stable perovskite catalyst under alkaline conditions, while PrBaCo2O5+δ reveals thermodynamic instability described by the density-functional theory based Pourbaix diagrams highlighting cation dissolution under OER conditions. Operando X-ray absorption spectroscopy is used in parallel to monitor electronic and structural changes of the catalysts during OER. The exceptional BSCF functional stability can be correlated to its thermodynamic meta-stability under OER conditions as highlighted by Pourbaix diagram analysis. BSCF is able to dynamically self-reconstruct its surface, leading to formation of Co-based oxy(hydroxide) layers while retaining its structural stability. Differently, PBCO demonstrates a high initial OER activity while it undergoes a degradation process considering its thermodynamic instability under OER conditions as anticipated by its Pourbaix diagram. Overall, this work demonstrates a synergetic approach of using both experimental and theoretical studies to understand the behavior of perovskite catalysts.
Iron-Based Perovskites for Catalyzing Oxygen Evolution Reaction
The Journal of Physical Chemistry C, 2018
The slow kinetics of the oxygen evolution reaction (OER) is the main cause of energy loss in many low-temperature energy storage techniques, such as metal-air batteries and water splitting. A better understanding of both the OER mechanism and the degradation mechanism on different transition metal oxides is critical for the development of the next generation of oxides as OER catalysts. In this paper, we systematically investigated the catalytic mechanism and lifetime of ABO 3-δ perovskite catalysts for OER, where A = Sr or Ca and B = Fe or Co. During the OER process, the Fe-based AFeO 3-δ oxides with δ ≈ 0.5 demonstrate no activation of lattice oxygen or pH dependence of OER activity, which is different from the SrCoO 2.5 with similar oxygen 2p-band position relative to the Fermi level. The difference was attributed to the larger changes in the electronic structure during the transition from the oxygen-deficient brownmillerite structure to the fully-oxidized perovskite structure and the poor conductivity in Fe-based oxides, which hinders the uptake of oxygen from the electrolyte to the lattice under oxidative potentials. The low stability of Fe-based perovskites under OER conditions in basic electrolyte also contribute to the different OER mechanism compared with the Co-based perovskites. This work reveals the influence of transition metal composition and electronic structure on the catalytic mechanism and operational stability of perovskite OER catalysts.
Chemistry of Materials, 2017
Oxygen electrocatalysis is at the heart of the emerging energy conversion and storage devices including reversible fuel cells and metal-air batteries. However, replacing the noble-metal-based oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts with affordable and robust alternatives remains challenging to date. Herein, we report a cation-ordered double perovskite oxide, i.e., PrBa 0.85-Ca 0.15 MnFeO 5+δ , with excellent stability and activity in both OER and ORR. The layered crystal structure provides ordered oxygen vacancy channels and a vast amount of surface oxygen defects, while the moderate amount of iron dopant keeps the B-site cations at high oxidation state with optimal e g fillings. Importantly, the DFT calculations along with the advanced TEM analysis verify that the incorporation of Ca at the A-site stabilizes the perovskite structure under potential bias. Such a bifunctional catalyst shows comparable, if not better, activity relative to the state-of-the-art perovskite oxides (e.g., Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ) while demonstrating remarkably enhanced robustness. This work presents a rational approach of designing efficient, robust, and cost-effective perovskite oxide for oxygen electrocatalysis and sheds light on the influences of the crystallographic structure on the catalytic property.
Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solution
Nature Communications, 2013
The electronic structure of transition metal oxides governs the catalysis of many central reactions for energy storage applications such as oxygen electrocatalysis. Here we exploit the versatility of the perovskite structure to search for oxide catalysts that are both active and stable. We report double perovskites (Ln 0.5 Ba 0.5)CoO 3 À d (Ln ¼ Pr, Sm, Gd and Ho) as a family of highly active catalysts for the oxygen evolution reaction upon water oxidation in alkaline solution. These double perovskites are stable unlike pseudocubic perovskites with comparable activities such as Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3 À d which readily amorphize during the oxygen evolution reaction. The high activity and stability of these double perovskites can be explained by having the O p-band centre neither too close nor too far from the Fermi level, which is computed from ab initio studies.
Bifunctional Perovskite Oxide Catalysts for Oxygen Reduction and Evolution in Alkaline Media
Chemistry, an Asian journal, 2015
Oxygen electrocatalysis, namely of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), governs the performance of numerous electrochemical energy systems such as reversible fuel cells, metal-air batteries, and water electrolyzers. However, the sluggish kinetics of these two reactions and their dependency on expensive noble metal catalysts (e.g,, Pt or Ir) prohibit the sustainable commercialization of these highly innovative and in-demand technologies. Bi-functional perovskite oxides have emerged as a new class of highly efficient non-precious metal catalysts (NPMC) for oxygen electrocatalysis in alkaline media. In this review, we discuss the state-of-the-art understanding of bifunctional properties of perovskites with regards to their OER/ORR activity in alkaline media, review the associated reaction mechanisms on the oxides surface and the related activity descriptors developed in recent literature. We also summarize the present strategies to modify their elect...
Science advances, 2018
Highly active and durable bifunctional oxygen electrocatalysts have been of pivotal importance for renewable energy conversion and storage devices, such as unitized regenerative fuel cells and metal-air batteries. Perovskite-based oxygen electrocatalysts have emerged as promising nonprecious metal bifunctional electrocatalysts, yet their catalytic activity and stability still remain to be improved. We report a high-performance oxygen electrocatalyst based on a triple perovskite, NdBaCoFeMnO (NBCFM), which shows superior activity and durability for oxygen electrode reactions to single and double perovskites. When hybridized with nitrogen-doped reduced graphene oxide (N-rGO), the resulting NBCFM/N-rGO catalyst shows further boosted bifunctional oxygen electrode activity (0.698 V), which surpasses that of Pt/C (0.801 V) and Ir/C (0.769 V) catalysts and which, among the perovskite-based electrocatalysts, is the best activity reported to date. The superior catalytic performances of NBCFM...
Oxygen-deficient BaTiO3− perovskite as an efficient bifunctional oxygen electrocatalyst
Nano Energy, 2015
Perovskite oxide catalysts have emerged as the most promising bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts for electrochemical energy conversion and storage. In this work, a new type of oxygen-deficient BaTiO 3À x has been synthesized using a solgel method followed by a reductive heat treatment at 1300 1C in vacuum. The prepared perovskite nanoparticles have an average particle size on the order of 100 nm with uniform size distribution. X-ray diffraction shows that this perovskite catalyst consists of a significant amount of hexagonal BaTiO 3À x. State-of-the-art IrO 2 nanoparticles were also prepared in this work, which were used for reference and has excellent OER activity. Importantly, the oxygen-deficient perovskite catalysts exhibited high catalytic activity simultaneously for the ORR and the OER in alkaline electrolyte. The more challenged OER activity measured with the perovskite exceeds the IrO 2 catalyst at relatively low potentials (o1.6 V) evidenced by a much reduced onset potential (1.32 V) and increased current density. In order to clearly elucidate the structure of the oxygen-deficient BaTiO 3À x catalysts, X-ray and neutron diffraction experiments were further carried out, indicating that the hexagonal phase in the best performing BaTiO 3À x catalyst is oxygen-deficient with a stoichiometry of BaTiO 2.76. The oxygen vacancies in the perovskite crystal structure may lead to vastly enhanced electrocatalytic activity toward the ORR and OER. This work demonstrates a new type of highly efficient perovskite bifunctional catalyst for electrochemical energy technologies relying on oxygen electrocatalysis.
Nature materials, 2017
The growing need to store increasing amounts of renewable energy has recently triggered substantial R&D efforts towards efficient and stable water electrolysis technologies. The oxygen evolution reaction (OER) occurring at the electrolyser anode is central to the development of a clean, reliable and emission-free hydrogen economy. The development of robust and highly active anode materials for OER is therefore a great challenge and has been the main focus of research. Among potential candidates, perovskites have emerged as promising OER electrocatalysts. In this study, by combining a scalable cutting-edge synthesis method with time-resolved X-ray absorption spectroscopy measurements, we were able to capture the dynamic local electronic and geometric structure during realistic operando conditions for highly active OER perovskite nanocatalysts. Ba0.5Sr0.5Co0.8Fe0.2O3-δ as nano-powder displays unique features that allow a dynamic self-reconstruction of the material's surface during...
High activity and durability of novel perovskite electrocatalysts for water oxidation
Development of highly active and cost-effective electrocatalysts is central to the large-scale electrolysis of water for renewable energy generation. Perovskite oxides are a group of promising candidates to lower the oxygen evolution reaction (OER) barriers in water splitting and further improvement of their activity and durability is an important objective. Here we report scandium and niobium cation (Sc3+ and Nb5+) doped strontium cobaltite perovskites (SrScxNbyCo1-x-yO3-δ) as a family of highly active and durable electrocatalysts for the OER in alkaline solution. These perovskites not only manifest up to a factor of 50 increase of the intrinsic activity compared to the gold-standard OER electrocatalysts (such as IrO2 and RuO2) and a factor of 5.8 enhancement to the perovskite-Ba0.5Sr0.5Co0.8Fe0.2O3-δ at overpotential of 0.35 V, but also, more importantly, show excellent durability in alkaline solutions under operation.