Highly Stable and Efficient Catalyst with In Situ Exsolved Fe–Ni Alloy Nanospheres Socketed on an Oxygen Deficient Perovskite for Direct CO2 Electrolysis (original) (raw)
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Catalysis Today, 2012
Perovskite oxides are promising materials for the ORR in alkaline media. However, catalytic layers prepared from perovskite powders suffer from high Ohmic losses and low catalyst utilization. An addition of carbon to the catalytic layers greatly improves the performance of the electrodes in the ORR. In this work composite thin film electrodes comprised of a perovskite oxide (either LaCoO 3 or La 0.8 Sr 0.2 MnO 3 ) and pyrolytic carbon of the Sibunit family were investigated in aqueous 1 M NaOH electrolyte using cyclic voltammetry and rotating disc electrode (RDE) method with the objective to unveil the influence of carbon on the catalyst utilization and on the ORR electrocatalysis. By systematically varying the oxide to carbon ratio we arrive to the conclusion on the dual role of carbon in composite electrodes. On the one hand, it is required to improve the electrical contact between perovskite particles and the current collector, and to ensure maximum utilization of the perovskite surface. On the other hand, carbon plays an active role in the ORR by catalyzing the O 2 reduction to H 2 O 2 . Composite electrodes catalyze the 4e − ORR in contrast to carbon which is only capable of catalyzing the 2e − reduction. For LaCoO 3 composite electrodes, carbon is responsible for the catalysis of the first steps of the ORR, the role of LaCoO 3 being largely limited to the hydrogen peroxide decomposition and/or reduction. For La 0.8 Sr 0.2 MnO 3 composite electrodes, along with the catalysis of the chemical decomposition and/or reduction of H 2 O 2 produced on carbon, the perovskite also significantly contributes to the first steps of the ORR. The results of this work suggest that the ORR on the carbon and the oxide components of composite cathodes must be considered as coupled reactions whose contributions cannot be always separated, and that neglecting the contribution of carbon to the ORR electrocatalysis may lead to erroneous values of the catalytic activity of perovskite materials.
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.
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...
Reversible perovskite electrocatalysts for oxygen reduction/oxygen evolution
Chemical Science, 2019
The identification of electrocatalysts mediating both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are prerequisite for the development of reversible fuel cells and rechargeable metal-air batteries. The question remains as to whether a bifunctional catalyst, or a single catalyst site, will exhibit potentials converging to +1.23 V RHE. Transition metal-based perovskites provide tunable catalysts where site substitution can influence both ORR and OER, however substitution in the pseudobinary phases results in an anti-correlation in ORR and OER activities. We reveal that La x Mn y Ni 1Ày O 3Àd , compositions with lanthanum A-site sub-stoichiometry exhibit reversible activity correlating with the appearance of the Mn 3+ /Mn 4+ redox couple. The Mn 3+ /Mn 4+ couple is associated with Mn 4+ co-existing with Mn 3+ in the bulk, as La 3+ is substituted by Ni 2+ at the A-site to create a mixed valent system. We also show that a direct A-site substitution by the Ca 2+ cation in La x Ca 1Àx Mn y O 3Àd perovskites also results in the creation of Mn 4+ , the appearance of the Mn 3+ /Mn 4+ redox couple, and a concomitant reversible activity. These results highlight a general strategy of optimizing oxide electrocatalysts with reversible activity.
Nano-Sized Double Perovskite Oxide as Bifunctional Oxygen Electrocatalysts
Annals of Materials Science & Engineering, 2021
Double perovskite oxide La2Co0.5Fe0.5MnO6-d is synthesized by the moltensalt- assisted method with Nano-sized particles (≈55 nm). The as-obtained La2Co0.5Fe0.5MnO6-d exhibits obviously enhanced electro catalytic activities towards oxygen evolution reaction and oxygen reduction reaction compared to the counterpart La2CoMnO6-d. This work provides a simple method to synthesize Nano-sized double perovskite oxide as superior electro catalysts for energy conversion.
New Opportunity for in Situ Exsolution of Metallic Nanoparticles on Perovskite Parent
One of the main challenges for advanced metallic nanoparticles (NPs) supported functional perovskite catalysts is the simultaneous achievement of a high population of NPs with uniform distribution as well as long-lasting high performance. These are also the essential requirements for optimal electrode catalysts used in solid oxide fuel cells and electrolysis cells (SOFCs and SOECs). Herein, we report a facile operando manufacture way that the crystal reconstruction of double perovskite under reducing atmosphere can spontaneously lead to the formation of ordered layered oxygen deficiency and yield segregation of massively and finely dispersed NPs. The real-time observation of this emergent process was performed via an environmental transmission electron microscope. Density functional theory calculations prove that the crystal reconstruction induces the loss of coordinated oxygen surrounding B-site cations, serving as the driving force for steering fast NP growth. The prepared material shows promising capability as an active and stable electrode for SOFCs in various fuels and SOECs for CO 2 reduction. The conception exemplified here could conceivably be extended to fabricate a series of supported NPs perovskite catalysts with diverse functionalities.
Journal of Materials Chemistry, 2012
Sr 0.95 Ce 0.05 CoO 3Àd (SCCO) particles loaded with copper nanoparticles on their surface are shown to be excellent, low-cost, and stable bifunctional catalysts for the oxygen-reduction and oxygen-evolution reactions (ORR and OER) in aqueous solution. Evidence for the presence of Ce 3+ and Co 2+ as well as Co 4+ and Co 3+ ions revealed by XPS measurements as well as XRD analysis indicates that a CeCoO 2.5 brownmillerite phase may be extruded to the surface. A surface Co 4+ /Co 3+ couple is known to be a good OER catalyst. The performance of the SCCO-based catalysts is better at higher current rates (>0.1 mA cm À2 ) than that of Vulcan XC-72 and even close to that of the 50% Pt/carbon-black catalyst. This catalyst could be used in a metal/air battery or a PEM fuel cell as an efficient and stable bifunctional catalyst.
Perovskites in catalysis and electrocatalysis
Science (New York, N.Y.), 2017
Catalysts for chemical and electrochemical reactions underpin many aspects of modern technology and industry, from energy storage and conversion to toxic emissions abatement to chemical and materials synthesis. This role necessitates the design of highly active, stable, yet earth-abundant heterogeneous catalysts. In this Review, we present the perovskite oxide family as a basis for developing such catalysts for (electro)chemical conversions spanning carbon, nitrogen, and oxygen chemistries. A framework for rationalizing activity trends and guiding perovskite oxide catalyst design is described, followed by illustrations of how a robust understanding of perovskite electronic structure provides fundamental insights into activity, stability, and mechanism in oxygen electrocatalysis. We conclude by outlining how these insights open experimental and computational opportunities to expand the compositional and chemical reaction space for next-generation perovskite catalysts.