Anchored Pt-Co Nanoparticles on Honeycombed Graphene as Highly Durable Catalysts for the Oxygen Reduction Reaction.
13 Jul 2021-ACS Applied Materials & Interfaces (American Chemical Society (ACS))-Vol. 13, Iss: 29, pp 34397-34409
TL;DR: In this article, the spatial protection of the carrier to nanoparticles was considered to improve the durability of the catalyst, and appropriate oxygen groups were introduced on the 3D reduced hierarchical porous graphene oxide (3D rHPGO) to improve dispersion of Pt-Co NPs on the surface of carrier.
Abstract: Durability is an important factor in evaluating the performance of a catalyst. In this work, the spatial protection of the carrier to nanoparticles was considered to improve the durability of the catalyst. It is found that a honeycombed graphene with a three-dimensional (3D)-hierarchical porous structure (3D HPG) can help to reduce the shedding of Pt-Co nanoparticles (Pt-Co NPs) because 3D HPG can form a protective layer to reduce the direct erosion of Pt-Co NPs on the interface by an electrolyte. Then, appropriate oxygen groups were introduced on the 3D reduced hierarchical porous graphene oxide (3D rHPGO) to improve the dispersion of Pt-Co NPs on the surface of the carrier. It was found that the Pt d-band of the catalyst was anchored by π sites of carbonyl of an oxygen group. After optimization, the catalyst (referred to as Pt-Co/3D rHPGO) achieved a 2-fold enhancement in mass activity than that of a commercial Pt/C catalyst. More importantly, after the accelerated durability test (ADT) of 20 000 cycles, the Pt-Co/3D rHPGO catalyst can almost sustain this level of performance, whereas other catalysts showed a comparatively large loss of activity. According to the results, the high durability of Pt-Co/3D rHPGO was attributed to spatial protection of Pt-Co NPs and the defects on the surface allowed the electrolyte to enter. In addition, oxygen groups provided an anchoring effect on nanoparticles. Thus, the Pt-Co/3D rHPGO electrocatalyst exhibited splendid durability, holding a potential to be applied in PEMFC for long-term work.
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TL;DR: Weber et al. as mentioned in this paper used high-resolution scanning transmission electron microscopy in combination with electron energy loss spectroscopy (STEM-EELS) to explore the detailed structure of the activated PtCoOx catalyst with a Pt-enriched shell.
Abstract: A self-supported Pt-CoO alloy catalyst has recently been reported as a new concept for Pt-based catalysts combining high surface area with high ORR activity. [1] Very recently, the presence of cobalt oxide species within Pt-Co catalyst after electrochemical dealloying in acidic media has also been reported by Weber et al. [2] However, the elemental distribution particularly for light elements like oxygen as well as the influence of the Co oxide on the ORR activity are still unclear to date.
We prepared a disordered PtCoOx alloy catalyst using wet-impregnation - freeze-drying - thermal annealing method. [3] After electrochemical activation by dealloying, the less noble metal is dissolved from the nanoparticle surface and the remaining Pt surface atoms are forming a protective particle shell referred to as core-shell catalyst. [2, 3] Using high resolution scanning transmission electron microscopy in combination with electron energy loss spectroscopy (STEM-EELS) we were able to explore the detailed structure of the activated PtCoOx catalyst with a Pt-enriched shell. Based on the EELS elemental maps of Pt, Co and O, we observed that oxygen is mainly located at the interface between the Pt-enriched shell and the PtCoOx alloy core. Thus, the CoOx species are highly stable during the electrochemical dealloying in acidic media. The ORR mass activity (0.56 ± 0.14 A mgPt
-1 at 0.9 VRHE) of the PtCoOx core-shell catalyst is 2.5-times higher, whereas the ORR specific activity (592 ± 171 µA cmPt
-2 at 0.9 VRHE) is 3-times higher than that for commercial Pt/C (0.24 ± 0.05 A mgPt
-1, 187 ± 29 µA cmPt
-2). The stability of the CoOx species and the electrochemical catalyst durability were tested by using an accelerated stress test (AST, 10,000 cycles from 0.5 to 1.0 VRHE) in acidic media. Here, the PtCoOx core-shell catalyst showed an improved electrochemical durability compared to Pt/C and maintains 85% of the initial ECSA, 54% of the initial ORR mass activity and 68% of the initial ORR specific activity, respectively. From the STEM-EELS and XPS measurements, we revealed an increase of the thickness of the Pt-enriched shell of several monolayers after the AST protocol. Very surprisingly, the cobalt oxide in the sub-surface layers still remains, but it is less narrowly distributed than before the AST experiment.
Thus, we suggest that the Co oxide species in PtCoOx alloy catalyst might have a positive effect on the ORR performance and durability and could even be a yet undiscovered alternative to metallic cobalt.
Reference:
[1] G.W. Sievers et al., Nat. Mater., 2021, 20, 208-213;
[2] D.J. Weber et al., J. Mater. Chem. A, 2021, 9, 15415-15431;
[3] M. Oezaslan et al., J. Electrochem. Soc., 2012, 159, B394-B405.
15 citations
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Abstract: The greatest challenge of our times is to identify low cost and environmentally friendly alternative energy sources to fossil fuels. From this point of view, the decarbonization of industrial chemical processes is fundamental and the use of hydrogen as an energy vector, usable by fuel cells, is strategic. It is possible to tackle the decarbonization of industrial chemical processes with the electrification of systems. The purpose of this review is to provide an overview of the latest research on the electrification of endothermic industrial chemical processes aimed at the production of H2 from methane and its use for energy production through proton exchange membrane fuel cells (PEMFC). In particular, two main electrification methods are examined, microwave heating (MW) and resistive heating (Joule), aimed at transferring heat directly on the surface of the catalyst. For cases, the catalyst formulation and reactor configuration were analyzed and compared. The key aspects of the use of H2 through PEM were also analyzed, highlighting the most used catalysts and their performance. With the information contained in this review, we want to give scientists and researchers the opportunity to compare, both in terms of reactor and energy efficiency, the different solutions proposed for the electrification of chemical processes available in the recent literature. In particular, through this review it is possible to identify the solutions that allow a possible scale-up of the electrified chemical process, imagining a distributed production of hydrogen and its consequent use with PEMs. As for PEMs, in the review it is possible to find interesting alternative solutions to platinum with the PGM (Platinum Group Metal) free-based catalysts, proposing the use of Fe or Co for PEM application.
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Abstract: Fuel cells powered by hydrogen from secure and renewable sources are the ideal solution for non-polluting vehicles, and extensive research and development on all aspects of this technology over the past fifteen years has delivered prototype cars with impressive performances. But taking the step towards successful commercialization requires oxygen reduction electrocatalysts--crucial components at the heart of fuel cells--that meet exacting performance targets. In addition, these catalyst systems will need to be highly durable, fault-tolerant and amenable to high-volume production with high yields and exceptional quality. Not all the catalyst approaches currently being pursued will meet those demands.
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TL;DR: A new class of Pt-Co nanocatalysts composed of ordered Pt(3)Co intermetallic cores with a 2-3 atomic-layer-thick platinum shell with high activity and stability are described, providing a new direction for catalyst performance optimization for next-generation fuel cells.
Abstract: To enhance and optimize nanocatalyst performance and durability for the oxygen reduction reaction in fuel-cell applications, we look beyond Pt-metal disordered alloys and describe a new class of Pt-Co nanocatalysts composed of ordered Pt(3)Co intermetallic cores with a 2-3 atomic-layer-thick platinum shell. These nanocatalysts exhibited over 200% increase in mass activity and over 300% increase in specific activity when compared with the disordered Pt(3)Co alloy nanoparticles as well as Pt/C. So far, this mass activity for the oxygen reduction reaction is the highest among the Pt-Co systems reported in the literature under similar testing conditions. Stability tests showed a minimal loss of activity after 5,000 potential cycles and the ordered core-shell structure was maintained virtually intact, as established by atomic-scale elemental mapping. The high activity and stability are attributed to the Pt-rich shell and the stable intermetallic Pt(3)Co core arrangement. These ordered nanoparticles provide a new direction for catalyst performance optimization for next-generation fuel cells.
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TL;DR: A new one-step ion-exchange/activation combination method using a metal-ion exchanged resin as a carbon precursor is used to prepare a ultrahigh surface area and three-dimensional hierarchical porous graphene-like networks for fast and highly stable supercapacitors.
Abstract: A new one-step ion-exchange/activation combination method using a metal-ion exchanged resin as a carbon precursor is used to prepare a ultrahigh surface area and three-dimensional hierarchical porous graphene-like networks for fast and highly stable supercapacitors.
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TL;DR: In this paper, the authors highlight breakthroughs, challenges and future directions for both platinum group metal (PGM) and PGM-free ORR cathode catalysts, and highlight the important role of carbon supports in enhancing overall performance.
Abstract: Proton exchange membrane fuel cells can use hydrogen and air to power clean electric vehicles. However, technical barriers including high cost, limited lifetime and insufficient power density limit their broad applications. Advanced cathode catalysts for the kinetically-sluggish oxygen reduction reaction (ORR) in acidic media are essential for overcoming these barriers. Here, we highlight breakthroughs, challenges and future directions for both platinum group metal (PGM) and PGM-free ORR cathode catalysts. Among PGM catalysts, highly-ordered PtM intermetallic nanostructures exhibit enhanced activity and stability relative to PtM random alloys. Carbon supports, with optimal balance between graphitization degree and porosity, play an important role in enhancing overall performance. Among PGM-free catalysts, transition metal and nitrogen co-doped carbons (M-N-C) perform best. However, degradation at practical voltages (>0.6 V) still prevents their practical application. For all catalysts, translating intrinsic activity and stability into device performance requires electrodes with robust three-phase interfaces for effective charge and mass transfer. Proton exchange membrane fuel cells can efficiently provide clean power for electric vehicles, although more efficient and economic cathode catalysts are still required. This Review highlights recent breakthroughs, challenges and future research directions for Pt group metal (PGM) and PGM-free oxygen reduction catalysts.
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371 citations