Durable Electrocatalysts For Oxygen Reduction Reaction Research Articles

Laser-optimized Pt-Y alloy nanoparticles embedded in Pt-Y oxide matrix for high stability and ORR electrocatalytic activity

The development of active yet stable catalysts for oxygen reduction reaction (ORR) is still a major issue for the extensive permeation of fuel cells into everyday technology. While nanostructured Pt catalysts are to date the best available systems in terms of activity, the same is not true for stability, particularly under operating conditions. In this work, PtXY alloy nanoparticles are proposed as active and durable electrocatalysts for ORR. PtXY nanoalloys are synthesized and further optimized by laser ablation in liquid followed by laser fragmentation in liquid. The novel integrated laser-assisted methodology succeeded in producing PtxY nanoparticles with the ideal size (<10 nm) of commercial Pt catalysts, yet resulting remarkably more active with E1/2 = 0.943 V vs. RHE, specific activity = 1095 μA cm−2 and mass activity > 1000 Ag−1. At the same time, the nanoalloys are embedded in a fine Pt oxide matrix, which allows a greater stability of the catalyst than the commercial Pt reference, as directly verified on a gas diffusion electrode.

Conductive tungsten oxynitride supported highly dispersed cobalt nanoclusters for enhanced oxygen reduction

Herein, a high-performance electrocatalyst for oxygen reduction reaction (ORR), which is composed of highly dispersed Co nanoclusters loaded on conductive oxygen-deficient tungsten oxynitride framework structured with three-dimensionally ordered macropores (3DOM Co@WNO) was proposed. The tungsten oxynitride carrier decorated with oxygen vacancies can improve the conductivity and electrochemical stability of the catalyst. At the same time, it offers strong anchoring interaction and ensures good dispersion for the loaded Co metals, thus achieving high catalytic activity and durability. Theoretical calculations show that electron transfer occurs at the interface between WNO and Co4 leading to a higher accumulation of electrons around the Co site, promoting the ORR reaction kinetics. Due to these advantages, 3DOM Co@WNO was found to possess ORR activity comparable to Pt/C and superior primary Zn-air battery performance over Pt/C and excellent stability as well. This study advances the evolvement of high-efficiency and durable ORR electrocatalysts using intrinsically robust and conductive oxynitride support strategy with strong metal-support interactions.

Well entrapped platinum-iron nanoparticles on three-dimensional nitrogen-doped ordered mesoporous carbon as highly efficient and durable catalyst for oxygen reduction and zinc-air battery

The high-performance and durable oxygen reduction reaction (ORR) catalyst on air cathode is a key component in assembly of Zn-air batteries. Herein, three-dimensional N-doped ordered mesoporous carbon (3D N-OMC) was first prepared with silica as a template via pyrolysis with assistance of dicyandiamide as a N-doping agent, combined by full adsorption of platinum (II) acetylacetonate (Pt(acac)2) and iron (II) phthalocyanine (FePc) via π-π interactions. After further pyrolysis of the resulting mixture, many PtFe nanoparticles were efficiently incorporated in 3D N-OMC (termed as PtFe@3D N-OMC for simplicity). Control experiments were certificated the important role of the pyrolysis temperature played in this synthesis. The resultant composite synergistically combines advantages of hierarchically accessible surfaces, highly open structure, and well-dispersed PtFe particles, which endow the PtFe@3D N-OMC with onset and half-wave potentials of 0.98 and 0.86 V in alkaline media, respectively, showing appealing catalytic activity for the ORR. Most significantly, the PtFe@3D N-OMC based Zn-air battery has a high power density of 80.57 mW cm−2 and long-term durability (220 h, 660 cycles). This work opens a new avenue for design of high-efficiency and durable ORR electrocatalysts in energy conversion and storage systems.

Synergistic Binary Fe-Co Nanocluster Supported on Defective Tungsten Oxide as Efficient Oxygen Reduction Electrocatalyst in Zinc-Air Battery.

Rational design of metal oxide supported non‐precious metals is essential for the development of stable and high‐efficiency oxygen reduction reaction (ORR) electrocatalysts. Here, an efficient ORR catalyst consisting of binary Fe/Co nanoclusters supported by defective tungsten oxide and embedded N‐doped carbon layer (NC) with a 3D ordered macroporous architecture (3DOM Fe/Co@NC‐WO2− x ) is developed. The oxygen deficient 3DOM WO2− x not only serves as a porous and stable support, but also enhances the conductivity and ensures good dispersion of the binary Fe/Co nanocluster, benefiting its ORR catalytic activity. Theoretical calculation shows that there exists a synergistic effect of electron transfer from Fe to Co in the supported binary Fe/Co cluster, promoting the ORR reaction energetics. Accordingly, the 3DOM Fe/Co@NC‐WO2− x catalyst exhibits excellent ORR activity in alkaline medium with a half wave potential (E 1/2) of 0.87 V higher than that of Pt/C (0.85 V). The zinc–air batteries assembled by 3DOM Fe/Co@NC‐WO2− x cathode deliver a higher power density and specific capacity than that of Pt/C. A new strategy of combining synergistic binary‐metal nanoclusters and conductive metal oxide support design is provided here to develop efficient and durable ORR electrocatalyst.

Toward High-Performance and Durable Hierarchical “Core-Shell” Carbon Nitride Electrocatalysts for the Oxygen Reduction Reaction

Proton exchange membrane fuel cells (PEMFCs) are one of the cornerstones of the “hydrogen economy” and are expected to play a pivotal role in today’s worldwide efforts to decarbonize the energy sector. The redox processes taking place at the electrodes of a PEMFC require suitable electrocatalysts (ECs) to minimize the associated overpotentials and achieve the exceptional energy conversion efficiency that characterizes these devices. The largest source of overpotential in direct hydrogen PEMFCs is the oxygen reduction reaction (ORR). State-of-the-art ECs for the ORR still require a significant loading of platinum-group metals, PGMs, to achieve a performance and durability level matching the requirements of practical applications. Hence, the development of advanced, highly active and durable ORR ECs with a minimized loading of PGMs is a major objective of the research.Several approaches have been proposed to obtain ORR ECs beyond the state of the art in terms of improved kinetics and longer durability [1]. However, the corresponding synthetic routes are complex, intrinsically difficult to upscale, and thus liable not to be of high relevance for industry in light of the forthcoming large-scale rollout of PEMFCs in both stationary and automotive applications.A promising avenue to prepare easily large amounts of ORR ECs exhibiting a performance and durability beyond the state of the art has been proposed in our laboratory more than 15 years ago [2]. The procedure is extremely flexible, allowing to tailor crucial EC features such as the chemical composition of the active sites and the morphology. The best ORR ECs exhibit a “core-shell” morphology: a hierarchical carbon-based “core” is covered by a carbon nitride “shell” stabilizing the active sites in C- and N-based “coordination nests”.A critical step in the preparation of ECs by means of the proposed route is the last “activation” yielding the final product. This process reconfigures significantly the most relevant features of the material including the bulk composition, the surface chemistry, the morphology and the structure. This “physicochemical metamorphosis” has a crucial effect on the ORR performance and durability, which are raised dramatically and finally exceed significantly the figures exhibited by state-of-the-art ECs [3].This work elucidates the interplay between the various approaches pursued to achieve the last “activation” (e.g., chemical attack and/or application of a time-dependent electrochemical potential) and the corresponding evolution of the physicochemical properties of the ECs. The general fundamental mechanisms underlying the “physicochemical metamorphosis” are discussed. Lastly, their outcome on the electrochemical properties of the final products are discussed to identify the most promising avenues for the design of ORR ECs able to surpass the performance and durability levels of today’s state of the art. Acknowledgements The research leading to the results reported in this work has received funding from: (a) the European Union’s Horizon 2020 research and innoavation programme under grant agreement 881603; (b) the project ‘Advanced Low-Platinum hierarchical Electrocatalysts for low-T fuel cells’ funded by EIT Raw Materials; and (c) the project ‘Hierarchical electrocatalysts with a low platinum loading for low-temperature fuel cells e HELPER’ funded by the University of Padova.

Ga‐Doped Intermetallic Pd3Pb Nanocubes as a Highly Efficient and Durable Oxygen Reduction Reaction Electrocatalyst

AbstractPd‐based nanocrystals are a promising candidate as non‐Pt electrocatalysts for oxygen reduction reaction (ORR), but their performance still has large room to be improved. Here, we have successfully synthesized Ga‐doped Pd3Pb nanocubes with different amounts of Ga by a simple one‐pot approach. When evaluated as electrocatalysts for ORR, the Ga‐doped Pd3Pb nanocubes exhibited substantially enhanced catalytic properties in an alkaline media relative to the Pd3Pb nanocubes and commercial Pt/C. Interestingly, the Ga‐doped Pd3Pb nanocubes showed a volcano‐like relationship in ORR activity as a function of the amount of Ga with the 1.76 % Ga‐doped Pd3Pb nanocubes (Pd3Pb/Ga‐2 NC) being the best ORR electrocatalysts. Specifically, the Pd3Pb/Ga‐2 NC/C exhibited the highest specific (7.57 mA cm−2) and mass activities (0.91 mA μgPd−1), which were 18.0 and 4.3 times higher than those of the commercial Pt/C. In addition, such Pd3Pb/Ga‐2 NC/C displayed the higher durability with an increase of 14.2 % in mass activity after 20000 cycles relative to commercial Pt/C (74.9 % loss). This enhancement in both activity and durability can be attributed to the strong hybridization interactions and the formation of Pd shells on the surface by leaching of Pb.

Synergistic Bimetallic Metallic Organic Framework-Derived Pt-Co Oxygen Reduction Electrocatalysts.

The rational design of Pt-based electrocatalysts is of paramount importance for the commercialization of proton exchange membrane fuel cells (PEMFCs). Pt-Co alloys and nitrogen-doped carbons have been shown to be effective in enhancing the kinetics of the oxygen reduction reaction (ORR). Herein, we reported on two kinds of Pt-Co electrocatalysts, PtCo ordered intermetallic and PtCo2 disordered alloys, supported on bimetallic MOF-derived N-doped carbon. The synergistic interaction between Pt-Co nanoparticles and Co-N-C enhanced the overall ORR activity and maintained the integrity of both structures and their electrochemical properties during long-term stability testing. The optimal activity for both PtCo and PtCo2 occurred after 20 000 potential cycles. The enhanced performance of PtCo was ascribed to the formation of a two-atomic-layer Pt-rich shell and the lattice strain caused by the core-shell PtCo@Pt structure. The increased activity of PtCo2 was ascribed to the formation of large, spongy, and small solid nanoparticles during electrochemical dealloying and thus the exposure of more Pt sites on the surface. The strategy described herein advances our understanding of the structure-activity relationship in electrocatalysis and sheds light on the future development of more active and durable ORR electrocatalysts.

Structurally Ordered Low‐Pt Intermetallic Electrocatalysts toward Durably High Oxygen Reduction Reaction Activity

AbstractCarbon‐supported low‐Pt ordered intermetallic nanoparticulate catalysts (PtM3, M = Fe, Co, and Ni) are explored in order to enhance the oxygen reduction reaction (ORR) activity while achieving a high stability compared to previously reported Pt‐richer ordered intermetallics (Pt3M and PtM) and low‐Pt disordered alloy catalysts. Upon high‐temperature thermal annealing, ordered PtCo3 intermetallic nanoparticles are successfully prepared with minimum particle sintering. In contrast, the PtFe3 catalyst, despite the formation of ordered structure, suffers from obvious particle sintering and detrimental metal–support interaction, while the PtNi3 catalyst shows no structural ordering transition at all but significant particle sintering. The ordered PtCo3 catalyst exhibits durably thin Pt shells with a uniform thickness below 0.6 nm (corresponding to 2–3 Pt atomic layers) and a high Co content inside the nanoparticles after 10 000 potential cycling, leading to a durably compressive Pt surface and thereby both high activity (fivefold vs a commercial Pt catalyst and 1.7‐fold vs an ordered PtCo intermetallic catalyst) and high durability (5 mV loss in half‐wave potential and 9% drop in mass activity). These results provide a new strategy toward highly active and durable ORR electrocatalysts by rational development of low‐Pt ordered intermetallics.

Hollow PdCu2@Pt core@shell nanoparticles with ordered intermetallic cores as efficient and durable oxygen reduction reaction electrocatalysts

Carbon-supported hollow PdCu2@Pt core@shell nanoparticles with ordered intermetallic cores were prepared as an efficient and durable oxygen reduction reaction (ORR) electrocatalyst for polymer electrolyte membrane fuel cells (PEMFCs). PdCu2 cores prepared using a chemical reduction method were thermally treated to produce ordered intermetallic structures. A Pt shell was then deposited via a galvanic displacement process. The effect of the galvanic displacement conditions on the properties and structure of the obtained core–shell nanoparticles was investigated by varying the solution pH and anion concentration. Acidic conditions and low Cl− concentrations were found to provide a uniform Pt layer with a hollow core, while maintaining the ordered intermetallic core structure. These hollow PdCu2@Pt core@shell nanoparticles showed high activity and stability for ORR electrocatalysis in PEMFCs.

Lithium manganese phosphate-carbon composite as a highly active and durable electrocatalyst for oxygen reduction reaction

Development of Pt-free electrocatalysts for oxygen reduction reaction (ORR) is one of the most important tasks for fuel cell commercialization. Various Mn compounds have been proposed as catalysts for ORR, but poor activity and stability necessitate further advances for their practical utilization. In this study, we demonstrate a lithium manganese phosphate-carbon composite (LMP-C) as a highly active and durable electrocatalyst for ORR in alkaline medium. LMP-C, synthesized by the solid-state method, exhibited significantly enhanced electrical conductivity and electrochemical properties, which led to a substantial increase in ORR performance. Comparison between LMP-C and the manganese phosphate-carbon composite, based on various physicochemical characterizations, revealed a high preference for the formation of the Mn3+ state on the surface of LMP-C that resulted in effective charge transfer during oxygen reduction. Moreover, the excellent stability of LMP-C was confirmed by carrying out 3000 cycles of the accelerated durability test, in which no drop in ORR performance was observed.

Carbon-Supported Ordered Pt-Ti Alloy Nanoparticles as Durable Oxygen Reduction Reaction Electrocatalyst for Polymer Electrolyte Membrane Fuel Cells

Carbon-Supported Ordered Pt-Ti Alloy Nanoparticles as Durable Oxygen Reduction Reaction Electrocatalyst for Polymer Electrolyte Membrane Fuel Cells

Carbon-Supported Ordered Pt-Ti Alloy Nanoparticles as Durable Oxygen Reduction Reaction Electrocatalyst for Polymer Electrolyte Membrane Fuel Cells

Carbon-Supported Ordered Pt-Ti Alloy Nanoparticles as Durable Oxygen Reduction Reaction Electrocatalyst for Polymer Electrolyte Membrane Fuel Cells

Core–shell Pt modified Pd/C as an active and durable electrocatalyst for the oxygen reduction reaction in PEMFCs

A series of Pt modified Pd/C catalysts (Pt/Pd/C) with different Pt/Pd molar ratio (Pt:Pd=1:4, 1:2 and 1:1) are synthesized by a chemical reduction method for oxygen reduction reaction (ORR). X-ray diffraction (XRD), transmission electron microscope (TEM) and cyclic voltammetry (CV) measurements confirm that Pt is deposited on the Pd nanoparticles and the Pt/Pd/C catalysts have a Pdcore@Ptshell structure. In the half cell testing, the catalytic ORR activity of Pt1/Pd2/C and Pt1/Pd4/C are superior to commercial Pt/C. Moreover, the electrochemical durability to potential cycling of Pt1/Pd2/C and Pt1/Pd1/C catalysts is better than Pt/C catalysts. The improved durability is believed to be associated with the dissolution of Pd and the corresponding structure transformation from core–shell structure to Pt-Pd alloy with Pt rich surface. The structure change is confirmed by TEM, CV, XRD and X-ray photoelectron spectroscopy (XPS). In addition, the electrochemical active surface area (ECSA) loss and polarization behavior in the single cell testing also suggest that the Pt/Pd/C show a much better durability than Pt/C catalysts. Similarly, the dissolution of Pd is observed by CV and scanning electron microscope-energy dispersive X-ray spectra (SEM-EDX). The Pt/Pd/C electrocatalysts have high ORR activity and this high activity can be further improved during potential cycling, that is, the activity and durability can be obtained simultaneously. This Pdcore@Ptshell structure allows for the development of highly active and durable ORR electrocatalysts, with potential for the application in proton exchange membrane fuel cells (PEMFCs).

Nanoporous surface alloys as highly active and durable oxygen reduction reaction electrocatalysts

It is of critical importance to design and fabricate highly active and durable oxygen reduction reaction (ORR) catalysts for the application of proton exchange membrane fuel cells (PEMFCs). By a simple two-step dealloying process, the active components in a Pt/Ni/Al ternary alloy were sequentially leached out in a highly controllable manner, generating a novel nanoporous surface alloy structure. Characterized by an open bicontinuous spongy morphology, the resulting nanostructure is interconnected by ∼3 nm diameter ligaments which are comprised of a Pt/Ni alloy core and a nearly pure Pt surface. In the absence of any catalyst support, these nanoporous surface alloys show much enhanced durability and electrocatalytic activity for ORR as compared to the commercial Pt/C catalyst. At a high potential, such as 0.9 V versusRHE, nanoporous Pt/Ni surface alloys show a remarkable specific activity of 1.23 mA cm−2. These nanomaterials thus hold great potential as cathode catalysts in PEMFCs in terms of facile preparation, clean catalyst surface, and enhanced ORR activity and durability.