Oxygen Reduction Reaction In Acidic Electrolyte Research Articles

Surface curvature effect on single-atom sites for the oxygen reduction reaction: A model of mesoporous MOF-derived carbon

Iron-based single-atom catalysts (Fe-SACs) containing Fe–N4 active sites have shown immense potential in the oxygen reduction reaction (ORR). However, the limited ability to adsorb O2 and catalyze subsequent O–O bond breaking on Fe–N4 sites has hindered their full potential, especially in acidic electrolytes. Here, we present an approach by utilizing a tunable curved surface to enhance the activity of Fe–N4 active sites, with theoretical calculations, demonstrating that Fe–N4 sites anchored on low–curvature surfaces (lc-Fe-N4) is favirable for ORR. Experimental results show that the catalyst exhibits excellent catalytic activity and stability for ORR in acidic electrolytes, with a half-wave potential of 0.82 V vs. RHE, approaching that of commercial Pt/C. This work develops an approach for promoting the catalytic activity by anchoring atomically dispersed Fe–N4 sites, unlocking their potential for extended use in electrocatalytic and energy storage applications.

Carboxyl induced ultrahigh defects and boron/nitrogen active centers in cobalt-embedded hierarchically porous carbon nanofibers: The stable oxygen reduction reaction catalysis in acid

Transition metal-nitrogen-carbon (MNC) type catalysts have been considered a promising alternative to noble metals for oxygen reduction reaction (ORR) electrocatalysis. Nevertheless, poor stabilities of MNC catalysts in acidic solutions limit their commercialization. In this study, we design and synthesize novel three-dimensional (3D) cobalt (Co) nanoparticles encapsulated in ultrahigh content of boron (B) and nitrogen (N) -doped hierarchically porous carbon nanofibers (denoted as Co@BN-PCNFs) by carbonizing the 3D acetic acid/cobalt nitrate/4-hydroxybenzeneboronic acid/polyvinylpyrrolidone precursor networks woven using electrospinning method under a nitrogen atmosphere. The optimal Co@BN-PCNFs-900 catalyst has abundant micro/mesopores and numerous topological defects and exhibits the largest surface area. Under the synergistic effect of oxygen-containing acetic acid molecules and the electrospinning technology, 5.87 at.% of B and 5.91 at.% of N atoms were doped into carbon nanofibers. Specifically, B/N electrocatalytic active centers (including BC3, pyridinic-N/CoNC, pyrrolic-N, and graphitic-N) of approximately 8.70 at.% were successfully introduced into the skeletons of Co@BN-PCNFs-900. In 0.1 M KOH, the ORR onset potential (Eonset) and half-wave potential (E1/2) of Co@BN-PCNFs-900 were ∼ 64 and ∼ 63 mV, respectively, more positive than those of 20 wt% Pt/C. Additionally, in 0.5 M H2SO4, the ORR Eonset and E1/2 values of Co@BN-PCNFs-900 were only ∼ 11 and ∼ 7 mV, respectively, more negative than those of 20 wt% Pt/C. As the 3D hierarchically porous architectures, topological carbon edges, BC3, and partial NC/CoNC are relatively stable, the Co@BN-PCNFs-900 exhibits excellent stability toward ORR catalysis in both acidic and basic media. These favorable properties of Co@BN-PCNFs-900 nanofibers make them the best non-noble metal-based carbonaceous electrocatalysts for ORR in acidic electrolytes.

Polyhedral Carbon Anchored on Carbon Nanosheet with Abundant Atomic Fe‐Nx Moieties for Oxygen Reduction

AbstractCarbon‐based single‐atom iron electrocatalysts with nitrogen coordination (CSAIN) have recently shown enormous promise to replace the costly Pt for boosting the cathodic oxygen reduction reaction (ORR) in fuel cells. However, there remains a great challenge to achieve highly efficient CSAIN catalysts for the ORR in acidic electrolytes. Herein, a novel CSAIN catalyst is synthesized by pyrolyzing a precursor mixture consisting of metal–organic framework and conductive polymer hybrid. After pyrolysis at a high temperature, the CSAIN with a structure of carbon nanosheet supported polyhedral carbon is achieved, where the unique structure endows CSAIN with expediting electron transfer and mass transport, as well as largely exposed surface to host atomically dispersed iron active sites. As a result, the optimal CSAIN catalyst shows a high ORR activity with its half‐wave potential of 0.77 V (vs RHE) and a Tafel slope of 74.1 mV dec–1, which are comparable to that of commercial Pt/C catalyst (0.80 V and 81.9 mV dec–1).

Rationally-designed sandwiched nanostructures boosting Fe-N based catalysts toward efficient oxygen reduction electrocatalysis in acidic medium

The development of acidic-available noble-metal-free oxygen reduction reaction (ORR) catalysts with high activity and good long-term durability is of significant importance for efficient proton exchange membrane fuel cells, but is still very challenging. Herein, we develop originally a facile wet-chemical-adsorption, pyrolysis and post-etching strategy to effectively intercalate Fe clusters among two nitrogen-doped carbon (NC) layers, forming unique hollow spherical nanostructures with sandwiched NC/Fe/NC shells as an active ORR catalyst. Thanks to the sandwiched nanostructure and the active Fe-N species, this as-prepared hollow sandwiched NC/Fe/NC catalyst could present superior ORR activity in an acidic medium, with a nice onset potential of 0.92 V and decent diffusion-limited current density of ~5.1 mA/cm2. The NC/Fe/NC catalyst manifests strong methanol tolerance and outstanding durability during a long-term acidic ORR operation, being a promising alternative to Pt-based catalysts toward efficient proton exchange membrane fuel cells. Synchrotron radiation characterizations and X-ray photoemission spectroscopy reveal at the atomic-level that the abundant robust Fe–N bonds presented in the sandwiched shells of hollow NC/Fe/NC spherical catalyst contribute substantially to high electrochemical activity and superior corrosion-resistance for efficient 4e¯ ORR in acidic electrolyte.

Hexagonal boron nitride nanosheets as metal-free electrochemical catalysts for oxygen reduction reactions

A high-performance ball milling technique was developed for synthesizing hexagonal boron nitride (h-BN) carbon paper (CP) electrodes as metal-free catalyst for the oxygen reduction reaction (ORR) and hydrogen storage (electrochemically) in acidic media. The h-BN nanosheets were functionalized with glycine to enhance the number of active sites and to boost the catalytic activity. The ball-milled h-BN catalytic electrodes demonstrated ultra-high catalytic activity toward electrochemical hydrogen adsorption/desorption (∼3.5 times higher than pristine electrodes) as well as ORR in acidic electrolytes. Furthermore, in-situ durability analysis of the h-BN electrodes was performed via conducting a long-duration cycling experiment (>200 cycles). A mechanistic reaction pathway (sequential) including chemisorption and charge transfer reactions (four-electron and two-electron pathways) was also proposed for the ORR. Considering superior catalytic activity of as-prepared h-BN/CP electrodes, this class of metal-free nanostructured materials can be employed as inexpensive catalysts for the electrochemical H-storage and ORR within various energy storage/conversion devices (e.g., batteries, electrolyzers, and fuel cells).

Engineering Pt Nanoparticles onto Resin‐Derived Iron and Nitrogen Co‐Doped Porous Carbon Nanostructure Boosts Oxygen Reduction Catalysis

AbstractThe high cost and deficiency of long‐term durability of carbon supported Pt catalysts have been regarded as obstacle that impeding their practical proton exchange membrane fuel cells (PEMFCs) technologies. Furtherly, iron and nitrogen co‐doped carbons (Fe/NC) are emerging as a steady electrocatalyst. Unfortunately, there are less‐active sites in acidic electrolyte. Herein, combining the advantages of Fe/NC and Pt catalysts, we propose an in‐situ surfactant‐free self‐templating solution reduction strategy to construct Pt nanoparticles (NPs) onto well‐devised Fe/NC porous nanostructures in order to manufacture highly performing Pt−Fe/NC catalyst for oxygen reduction reaction (ORR). The obtained Pt−Fe/NC catalyst displays excellent ORR performance, realizing an account of 2.53 improvement in specific activity and an account of 1.20 strengthening in mass activity toward ORR compared to the commercial Pt/C catalysts. Stability tests confirm that the as‐synthesized Pt−Fe/NC catalyst is more electrochemically steady than the commercial Pt/C catalysts on account of the electronic interaction between Pt and N which result from the difference in electronegativity. Our work provides a promising strategy for exploring the accomplishment of better ORR in acid electrolytes.

Interfacial enhancement of O∗ protonation on Fe2N/Fe3C nanoparticles to boost oxygen reduction reaction and the fuel cell in acidic electrolyte

Understanding the origin of high activity of Fe–N–C electrocatalysts in oxygen reduction reaction (ORR) is critical but still challenging for developing efficient non-precious metal catalysts in fuel cells and metal-air batteries. Herein, we developed Fe-based ORR catalysts containing highly dispersed interfaces of Fe2N/Fe3C and revealed the origin of its activity by intensively investigating the structure of the catalysts and their correlations with the electrochemical performance. It was found that the Fe2N/Fe3C with a well-matched interface displays a half-wave potential of 0.764 V (vs. RHE) and high current density in acidic electrolytes. In addition, the H2–O2 fuel cell assembled using Fe2N/Fe3C as the cathode exhibits excellent performance with a peak power density of 713 mW/cm−1. The experimental and computational results reveal that the interface of the Fe2N/Fe3C heterojunction is essential for the ORR in acidic electrolytes because it provides a remarkable decrease in the maximum free energy change of O∗ protonation to OH∗.

Weakening Intermediate Bindings on CuPd/Pd Core/shell Nanoparticles to Achieve Pt‐Like Bifunctional Activity for Hydrogen Evolution and Oxygen Reduction Reactions

AbstractAlthough Pd is a potential substitution of Pt‐based catalysts for the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), the binding of *H and oxygenated (*O, *OOH, *OH) intermediates on Pd are stronger than on Pt, leading to its inferior activity for HER and ORR. In this work, CuPd/Pd core/shell nanoparticles with an ultrathin Pd shell (0.5 nm) are developed, which demonstrate the Pt‐like bifunctional activity for HER and ORR in acid electrolytes. The overpotential at 350 mA cm−2 for HER and the half‐wave potential for ORR on the optimal CuPd/Pd core/shell NPs are 76 mV and 0.854 V versus reversible hydrogen electrode (RHE), respectively, which are comparable to that of Pt and among the best of the reported Pd‐based catalysts. Density functional theory calculations indicate that the significantly enhanced HER/ORR activity on CuPd/Pd core/shell NPs with 0.5 nm Pd shell stem from the compressive strain induced downshift of d‐band center for Pd (by 2.0%), which weakens the binding strength of *H and oxygenated intermediates and promotes the reaction kinetics.

Revealing the importance of kinetics in N-coordinated dual-metal sites catalyzed oxygen reduction reaction

In this work, the oxygen reduction reaction (ORR) process on dual-metal-nitrogen-carbon (DM-N-C) catalysts by including two important factors (potential of zero charge and potential-dependent kinetics of O-O bond cleavage) from first-principle calculations is systematically investigated. Our results reveal that the origin for the high activity of dual-metal sites can be attributed to the fact that introducing a second metal site can facilitate the O-O bond cleavage in the key OOH* intermediate during ORR and meanwhile mitigate the *OH removal issue. Importantly, we define a descriptor called “antibonding center” that simplifies the evaluation of the kinetics. Based on the advanced approach used in this work, we demonstrate that several DM-N-C electrocatalysts including FeFeN6, FeCoN6, and CoZnN6 have high ORR activity consistent with previous experiments, and also predict MnCoN6 can be more highly stable and active for acidic ORR. This study demonstrates the advantage of the dual metal sites for the ORR in acidic electrolyte and highlights the significance of kinetics in the theoretical study of ORR electrocatalysts.

MOF-derived dual metal (Fe, Ni) –nitrogen–doped carbon for synergistically enhanced oxygen reduction reaction

Fe-N-C materials have been shown as promising non-precious electrocatalysts for oxygen reduction reaction (ORR), yet the activity as well as the durability in acidic electrolytes is still far from satisfactory. Herein, a dual metal (Fe, Ni)-nitrogen-doped carbon (FeNi-NC) was prepared by pyrolysis of Fe, Ni co-doped ZIF-8. The FeNi0.25-NC catalyst exhibits a comparable activity for the ORR to the commercial Pt/C catalyst, with the half-wave potential at 0.79 VRHE in HClO4 and 0.86 VRHE in NaOH electrolyte. Especially, FeNi0.25-NC shows excellent ORR activity in phosphorous acid electrolyte superior to the commercial Pt/C catalyst, owing to the excellent tolerance of the Fe, Ni active sites to phosphate anions. The systematic investigation manifests that Ni plays a double role in improving the ORR activity and stability of Fe-N-C. One side, Ni-N and Fe-N moieties synergistically boost the ORR especially in the high ORR overpotential region, and another side, Ni acts as a catalyst during the high temperature carbonization process to promote graphitization and increase the stability of the FeNi-N-C catalyst. It is demonstrated that the MOF-derived dual metal (Fe, Ni) -nitrogen-doped carbon catalyst (FeNi-NC) has a great potential application in both fuel cells and metal-air batteries. This work provides an effective dual-metal strategy in modulating both the activity and stability of the M-N-C catalysts for the ORR in acidic electrolytes.

Engineering Pt Nanoparticles with Fe and N Codoped Carbon to Boost Oxygen Reduction Catalytic Performance in Acidic Electrolyte

While high cost and lack of long‐term stability of Pt‐based catalysts have been impeding their practical application in oxygen reduction reaction (ORR) in fuel cell technologies, iron and nitrogen codoped carbons (Fe–N–C) are appearing to be stable but unfortunately less‐active catalysts in acidic electrolyte. Herein, an in situ surfactant‐free Pt deposition approach to fabricate Pt nanoparticles (NPs) onto well‐designed Fe–N–C nanostructures for producing highly performing Pt/Fe–N–C catalyst for ORR in acidic electrolyte is reported. Physical and electrochemical characterizations uncovered that electron transfer from Fe–N–C to their supported Pt NPs would weaken the adsorption of O2 on the Pt surface, therefore improving the intrinsic activity of Pt for ORR. On optimizing the Pt loading, the intrinsic and mass‐specific activity data of Pt in Pt/Fe–N–C are maximized at ≈0.93 mA cm−2 and 0.46 A mg−1‐Pt, respectively, much higher than those for commercial Pt/C (0.21 mA cm−2, 0.19 A mg−1‐Pt). The Pt/Fe–N–C catalyst also shows an intriguing long‐term stability during the accelerated durability test. A new avenue for taking the advantages of Pt and non‐noble metal ORR catalysts is pointed for achieving much better ones to accomplish ORR in acidic electrolyte.

Promoting H2O2 production via 2-electron oxygen reduction by coordinating partially oxidized Pd with defect carbon

Electrochemical synthesis of H2O2 through a selective two-electron (2e−) oxygen reduction reaction (ORR) is an attractive alternative to the industrial anthraquinone oxidation method, as it allows decentralized H2O2 production. Herein, we report that the synergistic interaction between partially oxidized palladium (Pdδ+) and oxygen-functionalized carbon can promote 2e− ORR in acidic electrolytes. An electrocatalyst synthesized by solution deposition of amorphous Pdδ+ clusters (Pd3δ+ and Pd4δ+) onto mildly oxidized carbon nanotubes (Pdδ+-OCNT) shows nearly 100% selectivity toward H2O2 and a positive shift of ORR onset potential by ~320 mV compared with the OCNT substrate. A high mass activity (1.946 A mg−1 at 0.45 V) of Pdδ+-OCNT is achieved. Extended X-ray absorption fine structure characterization and density functional theory calculations suggest that the interaction between Pd clusters and the nearby oxygen-containing functional groups is key for the high selectivity and activity for 2e− ORR.

Oxygen Electroreduction on Pt Nanoparticles Deposited on Reduced Graphene Oxide and N‐doped Reduced Graphene Oxide Prepared by Plasma‐assisted Synthesis in Aqueous Solution

AbstractPlatinum nanoparticles were deposited on reduced graphene oxide (rGO) and nitrogen‐doped rGO (rGO−N) by He/H2 plasma jet treatment of H2PtCl6 aqueous solution for electroreduction of oxygen. Physical characterization of the prepared catalysts was performed by scanning electron microscopy, transmission electron microscopy and X‐ray photoelectron spectroscopy. Electrochemical characterization was carried out by cyclic voltammetry and CO‐stripping techniques. The oxygen reduction reaction (ORR) activity of the prepared Pt/rGO and Pt/rGO−N catalyst materials was investigated using the rotating disk electrode method in 0.1 M KOH and 0.05 M H2SO4. In both acidic and alkaline electrolytes, the catalyst materials prepared by the plasma jet method demonstrated superior electrocatalytic properties compared to that of commercial 20 wt% Pt/C catalyst. Specific activity values for the ORR in acid electrolyte were 2‐fold and in alkaline media more than 3‐fold higher than that obtained for commercial Pt/C catalyst.

Cobalt nitride nanoparticle-modified nitrogen-doped graphene aerogel used as an efficient catalyst for oxygen reduction reaction in acidic medium

A promising cobalt nitride nanoparticle-modified nitrogen-doped graphene aerogel (CoN–NGA) has been prepared by chemical reduction and thermal treatment for oxygen reduction reaction (ORR). X-ray diffractometry result reveals the presence of cobalt nitride (CoN) nanoparticles on aerogel. X-ray photoelectron spectroscopy analyses reveal that nitrogen atoms have been doped into framework of graphene sheet and nitrogen-doped graphene sheets have been modified with cobalt nitride nanoparticles through CoN–C moieties. Analyses of scanning electron microscopy and Brunauer–Emmett–Teller show that CoN–NGA catalyst displays a various and interconnected pore structure. Because of a huge synergistic effect of the nitrogen-doped graphene, the three-dimensional porous structure and cobalt nitride nanoparticles, the prepared CoN–NGA catalyst displays comparable electrocatalytic activity and the similar onset potential as commercial Pt/C (20% loading). CoN–NGA catalyst exhibits superior stability and excellent methanol tolerance in acidic solution. Nitrogen-doped graphene has been provided positive potential and excellent methanol tolerance through functionalizing with cobalt nitride nanoparticles, because there are strong interactions between N-doped graphene and CoN nanoparticles through CoN–C moieties. It is found that CoN–C moieties are actual ORR active sites rather than CoN nanoparticles themselves. The possible mechanism of ORR on CoN–C moieties has been involved. This study demonstrates a feasible strategy to design non-precious metal nitride-modified heteroatom-doped graphene electrocatalyst for ORR in acidic electrolyte.

Probing the Active Site Structures of Iron-Based ORR Catalysts

Highly active and durable electrocatalysts for the oxygen reduction reaction (ORR) are undoubtedly essential for the commercialization of polymer exchange membrane fuel cells. Recently, two types of iron-based catalysts have been extensively studied and reported to be active and stable towards ORR in acidic electrolyte. One is the well-recognized FeNx/C catalyst, and the other is the catalyst with structures of graphitic layer encapsulated metal particles. Generally, catalysts synthesized by pyrolysis of different iron- and nitrogen-containing precursors always contain both structures, making it impossible to distinguish the role of each structure during the ORR. Using a high temperature autoclave approach, we synthesized two model catalysts with almost exclusively one desired structure in each catalyst. Based on detailed characterizations in terms of catalyst structure and composition as well as electrochemical tests, the active site structures of these two catalysts and their correlation with the ORR performance are explored. Figure 1. Schematic illustration of the two possible active sites. Figure 1

Platinum Alloy Nanocatalyst with Manipulated Particle Composition and Morphology for Improved ORR Property

Electrocatalyst for oxygen reduction reaction (ORR) has been an area of intensive research for decades because of both its fundamental complexity and practical importance for many applications, including polymer electrolyte membrane fuel cells (PEMFCs) and metal-air batteries. The ORR activity and electrocatalyst durability are two confronted difficulties in the research. Pt remains the most effective element for ORR in acidic electrolyte for both reaction kinetics and durability considerations. Because of a high Pt price and its insufficient activity, extensive studies have been devoted to decreasing the Pt usage by searching new Pt nanostructures with improved ORR property. The discovery that single crystalline Pt3Ni (111) can exhibit exceptionally high ORR activity (18 mA/cm2 Pt at 0.9 V), which is about 90 times the activity of commercial Pt/C, points to an ideal strategy for solving the problem by using octahedral Pt alloy nanoparticles, which are enclosed by the (111) planes and have large specific active area. Several research groups have made good progresses by synthesizing these shaped particles and reporting high ORR activity. However there are two challenges remained with the octahedral Pt alloy nanocatalyst strategy: (1) The developed wet synthetic methods have low scaling-up capacity and surface contamination issue and are thus not suitable for mass production of the shaped Pt alloy nanoparticles, and (2) Currently researched octahedral Pt alloy nanoparticles have insufficient durability. We realize scalable and surfactant-free production of octahedral Pt alloy nanoparticle catalysts by developing a facile solid-state chemistry method. The prepared octahedral Pt1.5Ni/C exhibited high ORR activities of 3.99 mA/cm2 Pt and 1.96 A/mg Pt at 0.90 V vs. RHE, which are about 20 and 10 times the values for commercial Pt/C specifically.[1] The prepared octahedral Pt2CuNi/C uniform alloy nanoparticle catalyst exhibited both excellent ORR mass activity of 2.35 A/mg Pt at 0.90 V vs. RHE and promising stability, with 81.3% and 68.1% retained activity after 4,000 and 10,000 cycles of durability test.[2] The values make the octahedral Pt2CuNi/C a significantly more stable catalyst than the octahedral Pt-Ni/C, which retained only 52.9% and 35.0% of the initial mass activity after the two tests. The much improved durability was attributed to a uniform alloy composition of the ternary nanoparticles, which slowed down the leaching process of Ni and Cu and helped to preserve the octahedral morphology. The finding provides insights on factors determining the particle stability and offers guidance on development of highly active and durable ORR catalyst for real applications.

Co-N Decorated Hierarchically Porous Graphene Aerogel for Efficient Oxygen Reduction Reaction in Acid.

Nitrogen-functionalized graphene materials have been demonstrated as promising electrocatalyst for the oxygen reduction reaction (ORR), owning to their respectable activity and excellent stability in alkaline electrolyte. However, they exhibit unacceptable catalytic activity in acid medium. Here, a hierarchically porous Co-N functionalized graphene aerogel is prepared as an efficient catalyst for the ORR in acid electrolyte. In the preparation process, polyaniline (PANI) is introduced as a pore-forming agent to aid in the self-assembly of graphene species into a porous aerogel networks, and a nitrogen precursor to induce in situ nitrogen doping. Therefore, a Co-N decorated graphene aerogel framework with a large surface area (485 m(2) g(-1)) and an abundance of meso/macropores is effectively formed after heat treatment. Such highly desired structures can not only expose sufficient active sites for the ORR but also guarantee the fast mass transfer in the catalytic process, which provides significant catalytic activity with positive onset and half wave potentials, low hydrogen peroxide yield, high resistance to methanol crossover, and remarkable stability that is comparable to commercial Pt/C in acid medium.

Combined Nitrogen Precursor Approach to Develop Cobalt-Based Non-Precious Catalysts for Polymer Electrolyte Fuel Cell Cathodes

The cost of the platinum-based catalysts used in polymer electrolyte membrane fuel cells (PEFCs) is estimated to be almost half of the overall fuel cell stack cost under projected conditions of fuel cell vehicle mass production [1]. To reduce this economic constraint, the development of non-platinum group metal (non-PGM) cathode catalysts with high oxygen reduction reaction (ORR) activity is highly desirable. Our group and others have demonstrated immense progress in non-PGM catalyst development, with the specific class of pyrolyzed transition metal-nitrogen-carbon (M-N-C) catalysts achieving high activity [2,3]. In order to realize the successful implementation of these non-PGM catalysts into PEFC systems, the significant issue of operational durability must be addressed. The two most promising M-N-C catalyst technologies are based on either iron or cobalt, with the former conventionally providing enhanced ORR performance, approaching that of commercial platinum catalysts. From a system perspective, however, the presence of iron species in the catalyst layer is highly undesirable. This is owing to the well-known Fenton chemistry, resulting in the formation of highly reactive free-radical species that in turn leads to membrane and/or ionomer decomposition. To address this challenge, we prepared cobalt-based catalysts using the combined-precursor approach recently developed at Los Alamos National Laboratory [4]. This approach utilizes both polyacrylonitrile (PANI) and cyanamide (CM) as nitrogen/carbon precursors that are combined and pyrolyzed with a carbon support and cobalt salt. Individually, both PANI and CM precursors have been previously demonstrated capable of forming highly ORR-active catalysts. Through this approach, we found that the relatively low decomposition temperature (ca. 260°C) of CM allows it to synergistically act as a pore-forming agent and yield high surface-area catalysts. This in turn leads to excellent H2-air fuel cell performance due to the reduced mass transport limitations in the cathode. In this work, Co-CM-PANI-C was formed and found to provide promising activity towards the ORR in acidic electrolyte. Particularly, it was determined that 8.0 wt.% cobalt in the precursor mixture provided optimal ORR activity through half-cell investigation (Figure 1). A half-wave potential of ca. 0.74 V vs.RHE was achieved, with current investigations underway to understand and optimize the structure-performance-durability relationships. These results, along with performance and durability data from both half-cell and MEA evaluation, will be presented at the meeting. Acknowledgements Financial support for this was has been provided by the DOE-EERE through the Fuel Cells Technologies Office and by the Natural Sciences and Engineering Research Council of Canada (NSERC).

DFT Study of Oxygen Reduction Reaction on Os/Pt Core–Shell Catalysts Validated by Electrochemical Experiment

Proton exchange membrane fuel cells (PEMFCs) have attracted much attention as an alternative source of energy with a number of advantages, including high efficiency, sustainability, and environmentally friendly operation. However, the low kinetics of the oxygen reduction reaction (ORR) restricts the performance of PEMFCs. Various types of catalysts have been developed to improve the ORR efficiency, but this problem still needs further investigations and improvements. In this paper, we propose advanced Os/Pt core–shell catalysts based on our previous study on segregation of both bare surfaces and surfaces exposed to ORR adsorbates, and we evaluate the catalytic activity of the proposed materials by density functional theory (DFT). Quantum mechanics was applied to calculate binding energies of ORR species and reaction energy barriers on Os/Pt core–shell catalysts. Our calculations predict a much better catalytic activity of the Os/Pt system than that of pure Pt. We find that the ligand effect of the Os substrate is more important than the lattice compression strain effect. To validate our DFT prediction, we demonstrate the fabrication of Os/Pt core–shell nanoparticles using the underpotential deposition (UPD) technique and succeeding galvanic displacement reaction between the Pt ions and Cu-coated Os nanoparticles. The Os/Pt/C samples were evaluated for electrocatalytic activities toward the ORR in acidic electrolytes. The samples with two consecutive UPD-displacement reaction cycles show 3.5 to 5 times better ORR activities as compared to those of commercially available Pt/C. Our results show good agreement between the computational predictions and electrochemical experimental data for the Os/Pt core–shell ORR catalysts.

Mechanistic studies of oxygen reduction on Fe-PEI derived non-PGM electrocatalysts

Mechanistic studies of oxygen reduction reaction (ORR) on electrocatalysts derived from the pyrolysis of iron salts and polyethyleneimine (PEI) were performed in acidic and alkaline media. The prepared materials have been characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area analysis, and rotating ring-disk electrode (RRDE) methods. Systematic studies of catalyst loading on working electrode allowed establishing a working range suitable for mechanistic studies. It was found that the overall mechanism of ORR in acid electrolyte is not identical with that in alkaline media indicating complex interplay. The dependence of electron transfer numbers on catalyst loading indicates 2×2e− mechanism. The analysis of the Tafel plots corresponding to electrode polarizations have demonstrated difference of the reaction rate limiting steps in alkaline and acid media.