Pt-based Catalysts For Oxygen Reduction Reaction Research Articles

Facile Preparation of a Surface-Enriched Pt Layer Over Pd/C as an Efficient Oxygen Reduction Catalyst With Enhanced Activity and Stability

Abstract Pt-enriched surface layer formation on Vulcan carbon-supported Pd (Pt@Pd/C) was successfully prepared through a simple and one-pot formic acid reduction approach without any stabilizing agent. The electrocatalytic performance of Pt@Pd/C catalyst toward an oxygen reduction reaction (ORR) in alkaline medium was studied and also compared with standard carbon-supported Pt (Pt/C) and Pd (Pd/C) catalysts. The Pt@Pd/C exhibits higher electrochemical active surface area (74.7 m2/g) and mass activity (1.38 mA/µg) than Pt/C, Pd/C, and contending with standard reported catalysts. In durability tests, Pt@Pd/C showed negligible loss of intrinsic activity (∼10%) after 10,000 cycles which confirmed improved stability than Pt-based catalysts for ORR in KOH medium. This improved electrocatalytic performance could be attributed to their structural characteristics of the Pt-enriched surface layer on Pd/C-core and the compressive lattice strain on Pt. The present investigation demonstrates the simple preparation procedure for surface-enriched Pt on Pd/C and its improved performance for ORR, suggesting that it is a promising contender to benchmark ORR catalysts for alkaline fuel cells.

Role of Protons on Activity and Selectivity of Fe-N-C Electroctatalysts for Oxygen Reduction Reaction

As one of the most promising candidates to replace Pt-based electrocatalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cell (PEMFC), iron-nitrogen-carbon (Fe-N-C) materials have attracted tremendous research interests in recent years. Different from platinum-group-metal (PGM) catalysts, Fe-N-C have several categories of active sites: Fe-Nx has 4-electron pathway; pyrrolic-N and hydrogenated pyridinic-N can partially reduce oxygen into peroxide; pyridinic-N can reduce peroxide into water. Due to this complicated environment and numerous synthesis approaches from various precursors, the electrocatalysis mechanism of Fe-N-C still needs intensive investigation. Here we report the proton independence/dependence of rate-determining step (RDS) for a specific Fe-N-C catalyst via kinetic isotope effect (KIE), in addition to the activity inhibition of proton-involved N active sites via two molecular inhibitors. It is found that Fe-N-C can behave proton independent RDS like conventional Pt electrocatalyst in kinetic-controlled region, but it undergoes proton-coupled electron transfer in mass transport-controlled region, probably attributed to N active sites. It is also discovered that two molecules, tris(hydroxymethyl)aminomethane and etidronic acid, can inhibit and transform two categories of N active sites respectively: tris can effectively poison Fe-Nx active sites and pyridinic-N, resulting in obvious increase of peroxide yielding and drop of half-wave potential; etridonic acid can readily inhibit pyrrolic-N as well as hydrogenated pyridinic-N but no damage to Fe-Nx active sites, leading to decrease of peroxide yielding and no change of half-wave potentials. These results elucidate that Fe-N-C catalysts could, in principle, compete with Pt-based ORR catalysts through careful optimization of structure and morphology. Figure 1

Computational Screening for Developing Optimal Intermetallic Transition Metal Pt-Based ORR Catalysts at the Predictive Volcano Peak

Practical development of cost-effective and environmentally sustainable oxygen reduction reaction (ORR) catalysts has not yet been fully realized despite years of effort. Specifically, state-of-the-art ORR catalysts typically require high Pt-loading while still suffering significant overpotential losses and only providing moderate current density. In this work, we present results from new DFT calculations screening a wide range of Pt3(MN)1 ternary catalysts to see the range of values for oxygen adsorption energy (the known ORR volcano plot descriptor) such systems can achieve. Our results identify many promising materials based purely on performance via this descriptor; unfortunately, many of these promising candidates still require a very high loading of rare precious transition metals in the guest (MN) composition role. We have further used our results to generate a predictive fitted model for the ORR descriptor value itself based on the normalized valence and mass of a given fcc(111) Pt3(MN)1 surface c...

Electrochemical stability of silica-templated polyaniline-derived mesoporous N-doped carbons for the design of Pt-based oxygen reduction reaction catalysts

In order to improve the stability of carbon supported Pt-based oxygen reduction reaction catalyst a mesoporous N-doped carbon support (MPNC) was developed which shows both a higher resistance against carbon corrosion and Pt agglomeration compared to a commercial Pt catalysts supported on Vulcan XC72R. The MPNC were synthesized via a hard templating approach based on the oxidative polymerisation of aniline in the presence of SiO2 nanospheres as hard templates. Carbonization of the resulting PANI/SiO2 composite and template removal yielded MPNCs with pores imprinted in terms of size and shape by the SiO2 templates. The first part of the paper describes how the properties of the MPNCs were modified. Differences in shape, porosity, graphitization and N-doping are investigated by elemental analysis, scanning transmission electron microscopy, N2 physisorption analysis and near edge x-ray absorption fine structure spectroscopy. The carbon structure/morphology of the different MPNCs was then correlated with their electrochemical stability during accelerated stress test cycling. The MPNCs stability was thereby addressed and compared to Vulcan XC72R by evaluating changes in the double layer capacity. Finally, the stability of a MPNC supporting Pt NPs is shown and discussed by its comparison to a commercial available Pt catalyst supported on Vulcan XC72R.

Nanoscale Structure Design for High-Performance Pt-Based ORR Catalysts.

Proton-exchange-membrane fuel cells (PEMFCs) are of considerable interest for direct chemical-to-electrical energy conversion and may represent an ultimate solution for mobile power supply. However, PEMFCs today are primarily limited by the sluggish kinetics of the cathodic oxygen reduction reaction (ORR), which requires a significant amount of Pt-based catalyst with a substantial contribution to the overall cost. Hence, promoting the activity and stability of the needed catalyst and minimizing the amount of Pt loaded are central to reducing the cost of PEMFCs for commercial deployment. Considerable efforts have been devoted to improving the catalytic performance of Pt-based ORR catalysts, including the development of various Pt nanostructures with tunable sizes and chemical compositions, controlled shapes with selectively displayed crystallographic surfaces, tailored surface strains, surface doping, geometry engineering, and interface engineering. Herein, a brief introduction of some fundamentals of fuel cells and ORR catalysts with performance metrics is provided, followed by a detailed description of a series of strategies for pushing the limit of high-performance Pt-based catalysts. A brief perspective and new insights on the remaining challenges and future directions of Pt-based ORR catalysts for fuel cells are also presented.

Oxygen Reduction Reaction Properties for Dry-Process Synthesized Pt/TaCx Nanoparticles

Oxygen reduction reaction (ORR) activity and electrochemical structural stability of Pt/Ta-carbide nanoparticles (Pt/TaCx NPs) were investigated. The Pt/TaCx NPs were fabricated via arc plasma deposition (APD) of Ta under CH4 partial pressure (0.05 Pa) onto a highly oriented pyrolytic graphite (HOPG) substrate, followed by electron-beam deposition of Pt in ultra-high vacuum (UHV; ~10-8 Pa). X-ray diffraction patterns of the APD-TaCx samples showed that the diffraction peak due to TaC (rock-salt structure), exhibiting tantalum carbide which can be synthesized through the APD of Ta in CH4 atmosphere. The ORR activity of pristine Pt/TaCx samples is higher than that of the Pt/Ta alloy NPs prepared in UHV. Furthermore, the accelerated durability test results showed that the carbonization of Ta improves the ORR durability. The results clearly reveal that early transition metal carbides, e.g., TaC, are effective as core materials of core-shell-type Pt-based ORR catalysts.

Reduced Graphene Oxide-Supported Cobalt Phosphide Nanoflowers via in situ Hydrothermal Synthesis as Pt-Free Effective Electrocatalysts for Oxygen Reduction Reaction

Cobalt phosphide (CoP) has aroused extensive research interest in a field of electrochemical application due to its excellent catalytic activities. CoP and its compounds have been widely reported using in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, few reports about CoP as electrocatalysts for oxygen reduction reaction (ORR) were presented. In this work, we prepare reduced graphene-oxide(rGO)-loaded CoP (rGO@CoP) as an electrocatalyst for ORR through in situ hydrothermal treatment. The rGO@CoP as ORR catalyst exhibits excellent activities where its onset potential has a positive increase of 129[Formula: see text]mV, and the ORR potential achieves an increase of 330[Formula: see text]mV at a current density of 1.0[Formula: see text]mA[Formula: see text]cm[Formula: see text] compared with that of pure CoP. The current density is also significantly improved with an increase of 0.51[Formula: see text]mA[Formula: see text]cm[Formula: see text] at [Formula: see text]350[Formula: see text]mV, and the Tafel slope has a decrease of 19[Formula: see text]mV dec[Formula: see text]. Further tests show that the electron transfer number of rGO@CoP is 3.66, which is larger than 2.19 of pure CoP, indicating that it is dominated by a four-electron transfer pathway. Moreover, its stability (remained 98.6% current after working 6000[Formula: see text]s) and methanol tolerance are outstanding. These results show that rGO@CoP may be considered to replace traditional Pt-based ORR catalysts for fuel cells, and rGO loading has been proven to be an effective strategy to enhance the ORR performance of CoP, which may provide a new idea to synthesize transition metal phosphides as ORR catalysts.

Revealing the Role of the Metal in Non-Precious-Metal Catalysts for Oxygen Reduction via Selective Removal of Fe

Non-precious-metal catalysts have been investigated as alternatives to Pt-based oxygen reduction reaction catalysts for more than 50 years. While the incorporation of a metal is known to be necessary to generate a catalyst with high activity, the exact role of the metal is still not well-understood. In this work, we prepare an active oxygen reduction reaction catalyst containing Fe and then selectively remove the Fe from the catalyst while preserving the carbon and nitrogen species. By comparing the oxygen reduction reaction activity of the catalyst before and after treatment, we show that in the absence of Fe the carbon and nitrogen sites in the catalyst exhibit a larger overpotential and lower selectivity for the 4e– reduction of oxygen in both acidic and alkaline conditions. These findings reveal the direct involvement of the metal in the active site of non-precious-metal catalysts and provide important guidance for future catalyst improvements.

Tailoring Carbon Materials Substrate to Modify the Electronic Structure of Platinum for Boosting Its Electrocatalytic Activity

Tailoring chemical architecture of precious-metal based materials provides the opportunity to improve their catalytic activity, which is important for various kinds of fuel cells. Herein, we show that iron/cobalt/nitrogen codoped carbon (FeCo/C/N) substrate can greatly promote electrocatalytic oxygen reduction reaction (ORR) activity of platinum by modifying its’ electronic structure in comparison to those of nitrogen/carbon and carbon supports. FeCo/C/N substrate induces the negative shift of Pt 4f binding energy and increases the electron density of Pt outer orbital, which is used for the optimization of absorption energy between ORR intermediates and Pt surface. The experiments and theoretical simulation confirm the change of Pt electronic structure and enhancement of ORR kinetic, which provide a guiding principle for rational design of Pt-based ORR catalysts.

Nitrogen and Fluorine-Codoped Porous Carbons as Efficient Metal-Free Electrocatalysts for Oxygen Reduction Reaction in Fuel Cells.

The severe dependence of oxygen reduction reaction (ORR) in fuel cells on platinum (Pt)-based catalysts greatly limits the process of their commercialization. Therefore, developing cost-reasonable non-precious-metal catalysts to replace Pt-based catalysts for ORR is an urgent task. Here, we use the composite of inexpensive polyaniline and superfine polytetrafluoroethylene powder as precursor to synthesize a metal-free N,F-codoped porous carbon catalyst (N,F-Carbon). Results indicate that the N,F-Carbon catalyst obtained at the optimized temperature 1000 °C exhibits almost the same onset (0.97 V vs RHE) and half-wave potential (0.84 V vs RHE) and better durability and higher crossover resistance in alkaline medium compared to commercial 20% Pt/C, which is attributed to the good dispersion of fluorine and nitrogen atoms in the carbon matrix, high specific surface area, and the synergistic effects of fluorine and nitrogen on the polarization of adjacent carbon atoms. This work provides a new strategy for in situ synthesis of N,F-codoped porous carbon as highly efficient metal-free electrocatalyst for ORR in fuel cells.

Surface structure effects of platinum-based catalysts for oxygen reduction reaction

Summary The structural sensitivity is one of the major themes in electrocatalysis, and it is now well established that the reaction rate of oxygen reduction reaction (ORR) on Pt-based catalysts depends strongly on the surface structure. This paper presents a brief overview of insights of surface structure effects of Pt-based catalysts for ORR. We first introduce some typical extended Pt-based surface and then focus on Pt-based nanoparticles in both ORR activity and stability.

Recent development of efficient electrocatalysts derived from porous organic polymers for oxygen reduction reaction

Porous organic polymers (POPs) have recently emerged as promising candidates for catalyzing oxygen reduction reaction (ORR). Compared to conventional Pt-based ORR catalysts, these newly developed porous materials, including both non-precious metal based catalysts and metal-free catalysts, are more sustainable and cost-effective. Their porous structures and large surface areas facilitate mass and electron transport and boost the ORR kinetics. This mini-review will give a brief summary of recent development of POPs as electrocatalysts for the ORR. Some design principles, different POP structures, key factors for their ORR catalytic performance, and outlook of POP materials will be discussed.

Identification of Highly Active Catalytic Sites for Oxygen Reduction Reaction in Carbon Nanostructures from First-Principles Investigation

Proton-exchange membrane (PEM) fuel cells are considered to be a promising technology for use as alternative energy sources for transport, stationary and portable applications. They use hydrogen and oxygen to generate electricity through an electrochemical process which includes the oxygen reduction reaction (ORR) at the cathode. Currently, platinum (Pt)-based catalysts are commonly used to speed up the sluggish ORR that limits the efficiency of low temperature PEM fuel cells. However, Pt is expensive and scarce, drawing much interest in developing non-Pt catalysts. Carbon nanomaterials, including fullerenes, carbon nanotubes (CNTs), graphene, and their composites, have been actively studied as a potential candidate to replace Pt-based ORR catalysts. These sp 2-bonded carbon nanostructures are inherently constituted by largely extended p-conjugation systems, making them essentially unreactive toward molecular oxygen (O2) in their pristine forms. However, the conjugated p-systems can be severely disrupted with localized p electrons through dopant incorporation, defect creation, and/or local lattice distortions. The doped, defective and distorted carbon structures are currently thought to be responsible for O2 adsorption/activation and thus ORR, but the active sites and the exact molecular mechanisms are still uncertain. We have theoretically explored the mechanisms by which modification can activate graphene for the adsorption and reduction of oxygen, with an aim to define design guidelines for carbon ORR catalysts. Our effort has been focused on identification of active sites that allow favorable O2 adsorption and subsequent reduction based on extensive first-principles quantum-mechanical calculations. In this talk, we will present some of our recent findings. Using density functional theory (DFT) calculations, we have identified a novel method for the activation of graphene. This modification creates quasi-localized electron states in the graphene π-bonding system which are vulnerable to form bonds with O2. The result is favorable O2 adsorption, which despite being necessary for ORR activity is not predicted for previously proposed active sites. In this work, we applied an explicitly solvated system to model the ORR at the solid-liquid interface with aqueous solvent. Many previous DFT studies were modeled in the gas phase where O2 adsorption is consistently predicted to be endothermic on carbon. Our study clearly demonstrates that a more accurate description of interactions at the graphene-solvent interface is necessary to properly describe O2 adsorption, which appears strongly influenced by solvation. Ab-initio MD simulations were performed with the explicit solvent model to outline a full reaction mechanism including novel elementary reaction steps. The rate limiting step of the ORR in this system is predicted to be desorption of final reduction products. DFT allows us to study this desorption separately from the accompanying electron injection. We predict that there is a small but surmountable activation barrier that must be overcome for the reduction product to be removed. Excitingly, the predicted maximum overpotential for any elementary reaction step of the modified carbon structures that we have found is approximately 0.6 eV, which can be competitive when compared to standard carbon supported Pt (Pt/C) catalysts. Our study provides insight into molecular mechanisms underlying the superior ORR activity of nanostructured carbon materials and also guidelines for the rational design and development of high-efficiency, cost-effective carbon-based ORR catalysts for fuel cell applications.

Phthalocyanine tethered iron phthalocyanine on graphitized carbon black as superior electrocatalyst for oxygen reduction reaction

Despite the superior electrocatalytic activity of iron (II) phthalocyanine (FePc) for oxygen reduction reaction (ORR) in alkaline media, the large-scale applications of these FePc-based materials are still greatly hindered by their rapidly declined activity. To overcome this obstacle, it is essential to enhance the catalytic durability of FePc-based electrocatalysts. Herein, we demonstrate a superior FePc-based catalyst by employing low-cost graphitized carbon black as carbon supports, and tuning the Fe coordination environment in FePc, via the delocalized π coordination. Owing to the excellent ORR catalytic activity (the specific activity of 2.26mAcm−2, 3.6-fold enhancements compared with the commercial Pt/C catalyst), the remarkable durability (after 3000 potential cycles, 3-mV shifts for the half-wave potential, only 4.2% decreases from the initial specific activity) and the outstanding selectivity (good methanol tolerance, and free from interfering species effects, including NO3-, SO42-, PO43-, Br-, Cl- and SCN-), the novel FePc-based electrocatalyst is promising substitutes for Pt-based catalysts for ORR. Furthermore, to better elucidate the origin of the ORR performance, the density functional theory (DFT) calculation indicates that the unique structure of phthalocyanine tethered iron phthalocyanine (Pc-FePc) plays a key role in improving of both the catalytic activity and durability.

Active Pt3Ni (111) Surface of Pt3Ni Icosahedron for Oxygen Reduction

Highly active, durable oxygen reduction reaction (ORR) electrocatalysts are extremely important for fuel cell applications. Herein, we provide an efficient way to synthesis of activity Pt3M icosahedra by the one-pot hydrothermal method in the presence of glucosamine which can well adjust the reduction rate of Pt4+ and efficiently control the morphology of final catalysts. Compared to Pt/C, the Pt3Ni icosahedra show 32-fold and 12-fold enhancement in specific and mass activity, respectively. Furthermore, robust durability was also observed in the accelerated durability test. Thus, this Pt3Ni icosahedron is found among the best Pt-based ORR catalysts, moreover, the findings also demonstrate how to mimic active extended surfaces in nanoscale.

Magnetic Purification of PGM-Free Catalysts

To date, Pt-based catalysts have remained the sole, though expensive, solution in electrocatalysis of the sluggish oxygen reduction reaction (ORR) at the hydrogen fuel cell cathode.1 Recently, platinum group metal-free (PGM-free) materials have drawn attention as promising low cost replacement for Pt-based ORR catalysts.2 A prevailing approach in the synthesis of highly active PGM-free catalysts is based on a two-stage heat treatment of precursors containing C, N and transition metals.2,3,4 Studies suggest that Fe-N moieties formed during the heat treatment may play critical role as active sites.5 However, this state-of-the-art synthesis approach involves the acid-leaching of excess non-active iron-rich phases, which inevitably damages some of the active sites. A prolonged second heat treatment at high temperature (700°C-1000°C) is essential to recover the lost active sites. This procedure not only increases the chemical demands and cost to produce ORR PGM-free catalysts, but, more importantly, may not lead to full recovery of all the active sites initially formed. More economical and efficient methods are in demand to purify the PGM-free catalysts. In this presentation, we demonstrate an approach to magnetically purify active PGM-free catalysts while preserving the initial density of active sites. During the process of magnetic purification, the pyrolysis products are subjected to shear mixing in inert solvent to break down the agglomerations. The aggregates containing ferromagnetic phases, such as iron and iron carbides, are extracted efficiently in the magnetic field of a permanent magnet. The recovered active carbon-rich phase is collected and further characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and scanning transmission electron microscopy to understand the chemical and physical properties of the active phase. Our results show that the ferromagnetic metal-rich phases are efficiently removed, leaving behind carbon-based phases. Electrochemical characterization and fuel cell testing show that the magnetically purified catalyst outperforms catalysts prepared with the conventional two-stage heat treatment. The nature of active sites in the purified carbon phases are also studied with X-ray photoelectron spectroscopy and discussed. This innovative approach enables the green and economical purification of active non-precious metal ORR catalysts, without compromising their catalytic performance. Acknowledgement Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged. References Spendelow, J.; Marcinkoski, J., DOE Fuel Cell Technologies Office, Fuel Cell System Cost-2014, (2014).Wu, G.; Zelenay, P., Nanostructured Nonprecious Metal Catalysts for Oxygen Reduction Reaction. Acc. Chem. Res. 46, 1878-1889 (2013).Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P., High-Performance Electrocatalysts for Oxygen Reduction Derived from Polyaniline, Iron, and Cobalt. Science 332, 443-447 (2011).Zhao, D.; Shui, J.-L.; Grabstanowicz, L. R.; Chen, C.; Commet, S. M.; Xu, T.; Lu, J.; Liu, D.-J., Highly Efficient Non-Precious Metal Electrocatalysts Prepared from One-Pot Synthesized Zeolitic Imidazolate Frameworks. Adv. Mater. 26, 1093-1097 (2014).Holby, E. F.; Wu, G.; Zelenay, P.; Taylor, C. D., Structure of Fe–Nx–C Defects in Oxygen Reduction Reaction Catalysts from First-Principles Modeling. J. Phys. Chem. C 118, 14388-14393 (2014).

Non-PGM ORR Catalysts Prepared from Polyaniline-Type Polymers with Strong Affinity to Iron

Platinum-based catalysts play an important role in electrocatalysis of the generally sluggish oxygen reduction reaction (ORR) at the polymer electrolyte fuel cell (PEFC) cathode. However, the expensive Pt-based catalysts contribute to more than 40% of the cost of the PEFC stack for automotive applications, constraining the commercialization of fuel cell power systems.1 To lower the fuel cell catalyst cost, non-platinum group (non-PGM) catalysts have drawn attention as a promising low-cost replacement for Pt-based ORR catalysts.2The development of non-PGM catalysts have been the focus of significant research effort for years, aimed at obtaining active and durable materials, typically via the heat treatment of N-containing organic compounds and transition metal salts in inert atmosphere. One of the keys to the ultimate success of those efforts is the selection of suitable nitrogen precursors for the synthesis. In this presentation, we will demonstrate a rational design of polyaniline-type (PANI-type) polymers, as the precursors for active and durable non-PGM catalysts for oxygen reduction. Recently, we have developed well-performing non-PGM catalysts by heat-treating PANI, Fe salts, and carbon in N2 atmosphere.3 The studies of this and similar non-PGM catalysts suggest that Fe-N defects in a carbon matrix may be vital for the ORR activity of such catalysts.4 If so, it is essential to promote the formation of Fe-N bonds during the catalyst synthesis. However, current approaches are still quite rudimentary, largely limited to screening of N-rich precursors and optimizing the Fe salt loading. The rationale behind selecting N-rich precursors is still lacking. In many cases, the N-containing groups in polymers, such as PANI, have poor affinity to Fe salts limiting Fe-N bond formation in the polymer precursor before the heat treatment. An approach to increasing the population of such bonds will be given in this presentation. The subject of this study are PANI-type polymers with N-containing side groups having high affinity to Fe. By this approach, we allow Fe-N bonds to form evenly in the precursor polymers before the subsequent heat treatment. A higher Fe-N bond content is observed compared to previously used PANI-Fe precursors. Following the precursor synthesis, the polymers are converted into a carbon-based non-PGM catalyst via a heat treatment under N2. The catalyst undergoes further characterization by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and scanning transmission electron microscopy, followed by electrochemical characterization and fuel cell testing. The efficiency of the Fe uptake is also determined. This new approach paves the way to rational synthesis of non-PGM ORR catalysts via a rational design of polymer precursors with strong Fe-N interaction, ultimately resulting in a higher ORR active sites. Acknowledgement Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged. References Spendelow, J.; Marcinkoski, J., DOE Fuel Cell Technologies Office, Fuel Cell System Cost-2014, (2014).Wu, G.; Zelenay, P., Nanostructured Nonprecious Metal Catalysts for Oxygen Reduction Reaction. Acc. Chem. Res. 46, 1878-1889 (2013).Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P., High-Performance Electrocatalysts for Oxygen Reduction Derived from Polyaniline, Iron, and Cobalt. Science 332, 443-447 (2011).Holby, E. F.; Wu, G.; Zelenay, P.; Taylor, C. D., Structure of Fe–Nx–C Defects in Oxygen Reduction Reaction Catalysts from First-Principles Modeling. J. Phys. Chem. C 118, 14388-14393 (2014).

(Invited) Engineering the Microstructure and Atomic Arrangement of Pt-Based ORR Catalyst for High Activity and Durability

Polymer Electrolyte Membrane Fuel Cells (PEMFC) have been developed for passenger vehicle applications for several decades. The durability and activity of the Oxygen Reduction Reaction (ORR) catalysts is one of the main obstacles to be overcome to make PEMFC vehicle commercially viable. Efforts have been focused on: 1) Developing non-precious metal catalysts. 2) Reducing the Pt loading and modifying the d-band structure of Pt by forming nano-sized core-shell structures on various cores including metallic materials, oxides, carbides and borides, and/or alloying Pt with transition metals (Cr, Ni, Co, Mn, etc.). 3) Stabilizing the Pt nano-particles by growing them larger and making the particle size more uniform. 4) Atomically engineering the Pt environment by using hybrid support of conductive metal oxide and carbon. Worldwide efforts have greatly improved the durability of the ORR catalysts, extending the life time of PEM fuel cell vehicles to about 2000 hours, which is still less than half of the required commercialization target of more than 5000 hours. Pt-based ORR catalysts still dominate in PEMFC. The main requirements for an effective ORR catalyst are low Pt loading, high activity and durability. We used a PVD based method to engineer the microstructure and atomic arrangement of Pt into a 2-D connected network on worm-shaped islands of conductive metal oxides, which are deposited on graphitic carbon. A model catalyst was first developed on flat surface graphene, and it showed much improved activity and durability. Later, this desired Pt 2-D structure and morphology was replicated onto graphitic carbon powders. In this talk, we will discuss the catalyst, its development, and structural and electrochemical characterization using RDE and in-situ single cell experiments. A mechanistic understanding for the improvement in both activity and durability will be discussed.

Rational Design of Nanocatalysts for Fuel Cell Reactions

Engineering nanocrystals with size, shape, composition and structure control for enhancing oxygen reduction reaction (ORR) and small molecule oxidation reactions is highly desirable for promoting the development of fuel cell devices. In this presentation, I will focus on my recent advances in rational design and controlled synthesis of high-quality multicomponent nanocrystals for enhancing ORR and small molecules oxidation reactions. I will start with three examples on how to engineer FePt NWs, FePtPd/FePt core/shell nanowires (NWs) and graphene-FePt nanoparticles (NPs) composite for getting advanced Pt-based catalysts for ORR with extremely high activity and stability. After that, I will move to non-Pt catalysts such as graphene-Co/CoO NPs and M/CuPd NPs (M=Ag, Au), which exhibit comparable and even higher ORR activity and stability than commercial Pt catalyst. Finally, I will show two interesting examples on how to engineering trimetallic NPs and NWs for enhancing methanol and formic acid oxidation reactions.

Recent Progress in New Nanocatalysts for Oxygen Reduction Reaction

The design of new functional nanomaterials for enhancing oxygen reduction reaction (ORR) is highly desirable for promoting the development of fuel cell and lithium air battery devices. In this seminar, I will focus on my recent advances in rational design and controlled synthesis of high-quality multicomponent nanocrystals for enhancing ORR. I will start with three examples on how to engineer FePt NWs, FePtPd/FePt core/shell NWs and graphene-FePt NPs composite for getting advanced Pt-based catalysts for ORR with extremely high activity and stability. After that, I will move to non-Pt catalysts such as graphene-Co/CoO NPs and M/CuPd NPs (M=Ag, Au), which exhibit comparable and even higher ORR activity and stability than commercial Pt catalyst.