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Direct methanol fuel cells have emerged as highly promising energy conversion devices in the past few decades. However, some challenges, such as carbon monoxide (CO) poisoning and unsatisfactory long-term stability, remain for platinum (Pt) as a methanol oxidation reaction (MOR) catalyst. This review covers recent advances in Pt alloy MOR catalysts and provides some insights. This review presents MOR catalytic mechanisms based on CO or non-CO pathways. Typical dimension-based designs of MOR catalysts, such as anisotropic nanowires, metallene, nanoframes, and corresponding rationales for performance enhancements, are introduced. More importantly, some key tuning strategies are elaborated, including intermetallic compound synthesis, interface engineering, and surface facet engineering. High-entropy alloys as an intriguing class of MOR catalysts with favorable prospects are also discussed. Finally, future directions and opportunities are outlined. [ABSTRACT FROM AUTHOR]

Utilizing ambient pressure X-ray photoelectron spectroscopy (AP-XPS), the surface segregation and oxidation of Pt3Ni(1 1 1) alloys are investigated as a function of temperature and oxygen pressure. The in situ AP-XPS measurements of oxygen oxidation process show that the Pt "skin" surface is not stable under the exposure of oxygen pressure of 100 mTorr at room temperature. As the temperature and pressure are elevated, the formations of Ni2O3, NiOx, and NiO are observed on surface while Pt atom starts to reduce its adsorbed oxygen, which is a clear sign of surface segregation of Ni to surface. Upon the evacuation of oxygen gas, i.e. ultrahigh vacuum condition, both of NiOx and NiO oxide get reduced and Ni2O3 remains on the surface. The DFT calculation is employed to explain the formation of surface oxides under oxidation condition.

Utilizing ambient pressure X-ray photoelectron spectroscopy (AP-XPS), the surface segregation and oxidation of Pt3Ni(1 1 1) alloys are investigated as a function of temperature and oxygen pressure. The in situ AP-XPS measurements of oxygen oxidation process show that the Pt "skin" surface is not stable under the exposure of oxygen pressure of 100 mTorr at room temperature. As the temperature and pressure are elevated, the formations of Ni2O3, NiOx, and NiO are observed on surface while Pt atom starts to reduce its adsorbed oxygen, which is a clear sign of surface segregation of Ni to surface. Upon the evacuation of oxygen gas, i.e. ultrahigh vacuum condition, both of NiOx and NiO oxide get reduced and Ni2O3 remains on the surface. The DFT calculation is employed to explain the formation of surface oxides under oxidation condition.

In this work, the electrocatalytic oxidation of ethanol was studied in acidic media at the wholly electrosynthesized nanocomposites: platinum and its alloys (copper and nickel) anoparticles/reduced graphene oxide on the carbon-ceramic electrode (Pt/rGO/CCE, Pt-Cu/rGO/CCE, and Pt-Ni/rGO/CCE electrocatalysts). The electrosynthesized nanocomposites were characterized by scanning electron microscopy, X-ray powder diffraction, and energy-dispersive X-ray spectroscopy. Electrocatalytic activities of the Pt/rGO/CCE, Pt-Cu/rGO/CCE and Pt-Ni/rGO/CCE toward ethanol oxidation were investigated via cyclic voltammetric and chronoamperometric techniques in 0.1 M H2SO4 solution containing 0.3 M ethanol. The obtained results show that the Pt-Ni/rGO/CCE was catalytically more active and exhibits better electrocatalytic performance toward ethanol oxidation (ECSA=25.28, Jpf=0.156 mA/cm2, Jpf/Jpb=1.12 and Eonset=0.2 V) than Pt-Cu/rGO/CCE (ECSA=19.09, Jpf=0.108 mA/cm2, Jpf/Jpb=0.99 and Eonset=0.3 V) and Pt/rGO/CCE (ECSA=28.28, Jpf=0.092 mA/cm2, Jpf/Jpb=0.55 and Eonset=0.35 V). The result of some effective and important investigational factors was studied and optimize conditions were suggested. Based on the obtained data one can be expected that the studied systems are promising systems for ethanol fuel cell applications.

Abstract Developments of high efficient materials for electrocatalyst are significant topics of numerous researches since a few decades. Recent global interests related with energy conversion and storage lead to the expansion of efforts to find cost-effective catalysts that can substitute conventional catalytic materials. Especially, in the field of fuel cell, novel materials for oxygen reduction reaction (ORR) have been noticed to overcome disadvantages of conventional platinum-based catalysts. Various approaching methods have been attempted to achieve low cost and high electrochemical activity comparable with Pt-based catalysts, including reducing Pt consumption by the formation of hybrid materials, Pt-based alloys, and not-Pt metal or carbon based materials. To enhance catalytic performance and stability, numerous methods such as structural modifications and complex formations with other functional materials are proposed, and they are basically based on well-defined and well-ordered catalytic active sites by exquisite control at nanoscale. In this review, we highlight the development of nano-structured catalytic materials for ORR based on recent findings, and discuss about an outlook for the direction of future researches.

Platinum is a main catalyst for the electroreduction of oxygen, a reaction of primary importance to the technology of low-temperature fuel cells. Due to the high cost of platinum, there is a need to significantly lower its loadings at interfaces. However, then O2-reduction often proceeds at a less positive potential, and produces higher amounts of undesirable H2O2-intermediate. Hybrid supports, which utilize metal oxides (e.g., CeO2, WO3, Ta2O5, Nb2O5, and ZrO2), stabilize Pt and carbon nanostructures and diminish their corrosion while exhibiting high activity toward the four-electron (most efficient) reduction in oxygen. Porosity of carbon supports facilitates dispersion and stability of Pt nanoparticles. Alternatively, the Pt-based bi- and multi-metallic catalysts, including PtM alloys or M-core/Pt-shell nanostructures, where M stands for certain transition metals (e.g., Au, Co, Cu, Ni, and Fe), can be considered. The catalytic efficiency depends on geometric (decrease in Pt–Pt bond distances) and electronic (increase in d-electron vacancy in Pt) factors, in addition to possible metal–support interactions and interfacial structural changes affecting adsorption and activation of O2-molecules. Despite the stabilization of carbons, doping with heteroatoms, such as sulfur, nitrogen, phosphorus, and boron results in the formation of catalytically active centers. Thus, the useful catalysts are likely to be multi-component and multi-functional.

Interatomic potentials for Pt-M (M = Al, Co, Cu, Mo, Ni, Ti, V) binary systems have been developed on the basis of the second nearest-neighbor modified embedded-atom method (2NN MEAM) formalism. The parameters of pure Mo have also been newly developed to solve a problem in the previous 2NN MEAM potential in which the sigma and α-Mn structures become more stable than the bcc structure. The potentials reproduce various materials properties of alloys (structural, thermodynamic and order-disorder transition temperature) in reasonable agreements with relevant experimental data and other calculations. The applicability of the developed potentials to atomistic investigations for the shape and atomic configuration of Pt bimetallic nanoparticles is demonstrated. [ABSTRACT FROM AUTHOR]

Pt 3 Co catalyst nanoparticles of 4.9 nm size present on the cathode side of a PEMFC membrane-electrode assembly (MEA) were analyzed by transmission electron microscopy after 10 K voltage cycles under different operating conditions. The operating conditions include baseline (0.4–0.95 V, 80° C, 100% Relative Humidity (RH)), high potential (0.4–1.05 V, 80° C, 100% RH), high temperature (0.4–0.95 V, 90° C, 100% RH), and low humidity (0.4–0.95 V, 80° C, 30% RH). Particle growth and particle loss to the membrane is more severe in the high potential sample than in the high temperature and baseline MEAs, while no significant particle growth and particle precipitation in the membrane can be observed in the low humidity sample. Particles with different morphologies were seen in the cathode including: 1-Spherical individual particles resulting from modified electro-chemical Ostwald ripening and 2-aggregated and coalesced particles resulting from either necking of two or more particles or preferential deposition of Pt between particles with consequent bridging. The difference in the composition of these morphologies results in composition variations through the cathode from cathode/diffusion media (DM) to the cathode/membrane interface. [ABSTRACT FROM AUTHOR]

In the past decade, polymer electrolyte membrane fuels (PEMFCs) have been evaluated for both automotive and stationary applications. One of the main obstacles for large scale commercialization of this technology is related to the sluggish oxygen reduction reaction that takes place on the cathode side of fuel cell. Consequently, ongoing research efforts are focused on the design of cathode materials that could improve the kinetics and durability. Majority of these efforts rely on novel synthetic approaches that provide control over the structure, size, shape and composition of catalytically active materials. This article highlights the most recent advances that have been made to tailor critical parameters of the nanoscale materials in order to achieve more efficient performance of the oxygen reduction reaction (ORR). [ABSTRACT FROM AUTHOR]

This paper reports on oxygen reduction activity and methanol tolerance of PtV/C prepared by a polyol method and the effects of heat treatments in reducing environments at low temperatures (up to 300 °C). The as-prepared catalyst showed a low content of alloyed vanadium, but it was considerably more active for the oxygen reduction reaction than Pt/C and had superior methanol tolerance. Dispersive X-ray absorption spectroscopy measurements around the Pt L edge indicated that the presence of vanadium in the catalyst increased the Pt 5d-band vacancy at the time that it seems to diminish the Pt coverage by adsorbed OH species. Heat treatments at 150, 200, and 300 °C carried out in strongly reducing conditions produced minor changes in the degree of alloying together with a moderate particle growth. The largest incorporation of vanadium in the alloyed phase was observed after heating at 150 °C while a decrease in the alloying and Pt segregation to the surface were observed for higher treatment temperatures. In general, heat treatments were detrimental for oxygen reduction activity, suggesting that the presence of vanadium oxides might play a role. In addition, the decreased in methanol tolerance might be associated to Pt segregation to the surface. [ABSTRACT FROM AUTHOR]

Utilizing ambient pressure X-ray photoelectron spectroscopy (AP-XPS), the surface segregation and oxidation of Pt 3 Ni(1 1 1) alloys are investigated as a function of temperature and oxygen pressure. The in situ AP-XPS measurements of oxygen oxidation process show that the Pt “skin” surface is not stable under the exposure of oxygen pressure of 100 mTorr at room temperature. As the temperature and pressure are elevated, the formations of Ni 2 O 3 , NiO x , and NiO are observed on surface while Pt atom starts to reduce its adsorbed oxygen, which is a clear sign of surface segregation of Ni to surface. Upon the evacuation of oxygen gas, i.e. ultrahigh vacuum condition, both of NiO x and NiO oxide get reduced and Ni 2 O 3 remains on the surface. The DFT calculation is employed to explain the formation of surface oxides under oxidation condition. [ABSTRACT FROM AUTHOR]

A performance test of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at Korean Basic Science Institute (KBSI) in Daejeon, Korea is carried out. The NAP-XPS at KBSI is equipped with SPECS PHOIBOS 150 analyzer and 2-dimensional-delay line detector, which provides improved detection efficiency with 1-dimensional chemical imaging mode. The in-situ gas-pressure cell is designed to operate at pressure up to 25 mbar with differential pumping scheme. A micro-focused Al Kα X-ray source is utilized as photon excitation source. The NAP-XPS is composed of two separate chambers, e.g. a main preparation chamber and a measurement chamber, which hold a low energy electron diffraction, a high pressure cell, an ion sputter gun, a multi-cell E-beam evaporators, and a four-axis manipulator with heating and cooling capability. As a test run of NAP-XPS, a CO oxidation experiment is carried out on Pt 3 Ti polycrystalline surface. During the active phase of CO oxidation, a clear formation of Ti oxide is found on surface, revealing the intriguing role of surface metal oxide in surface chemical reaction. [ABSTRACT FROM AUTHOR]

Pt, PtCo, and PtNi electrocatalysts were prepared by mechanical alloying, and their activity for oxygen reduction reaction in 0.5 M KOH was investigated using cyclic voltammetry (CV) and rotating ring-disk electrode techniques. Electrocatalysts were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Physical characterization showed that all electrocatalysts are alloys in the form of agglomerated particles that consist of nanocrystals. To perform an electrocatalytic evaluation, polarization curves, Koutecky-Levich and Tafel plots were obtained to calculate the kinetic parameters. Additionally, the molar fraction of the generated HO and the number of transferred electrons were determined. PtCo alloy showed a better performance for oxygen reduction reaction with a higher exchange current density, a lower overpotential, as well as higher specific and mass activities due to a synergistic effect between Pt and Co atoms as a result of the alloying process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Direct CO electroreduction to HCHO realized with Pt-metal (Ni, Fe, Cu) alloys. • Record high HCHO formation rate (r HCHO) achieved by Pt-Ni alloy catalyst. • Promote r HCHO by tuning CO chemisorption and hydrogen deposition competition. Direct CO reduction to formaldehyde (CORTF) provides an alternative, energy-efficient route for production of formaldehyde, a critical chemical commodity as well as promising hydrogen carrier. However, the conventional thermal catalysis approach is challenged with slow reaction kinetics, which can be attributed to imbalanced CO and hydrogen competitive chemisorption to catalyst, with stronger CO adsorption significantly inhibiting hydrogen adsorption that suppresses their reaction towards formaldehyde generation. We report a new, innovative CORTF mechanism to promote the reaction by utilizing hydrogen underpotential deposition to balance the species coverage on catalyst surface. Our study shows that, by separately tuning Pt alloy nanoparticle catalyst composition to control CO chemical adsorption favorability and tuning hydrogen underpotential deposition potential to control hydrogen electrochemical adsorption favorability, the formaldehyde production rate with Pt alloys (866 mg/g cat /h) is 300 times higher compared to conventional thermal catalysis method (2.6 mg/g cat /h) and 50 time higher than previously reported molybdenum phosphide (MoP, 16.3 mg/g cat /h) electrocatalyst. DFT simulations show reduced energy barriers for the rate-limiting steps by means of balancing hydrogen and CO adsorption, thus supporting this new mechanism to achieve more dramatically improved CORTF kinetics. This CORTF mechanism provides a new strategy towards efficient formaldehyde production. [ABSTRACT FROM AUTHOR]

The microstructures of Pt/C and PtM/C (M = Ni, Cu, or Ag) electrocatalysts were studied using X-ray diffraction and transmission electron microscopy (TEM). The electrochemically active surface areas of the prepared materials were estimated by cyclic voltammetry in 1 M HSO. The materials, with metal contents ranging from 30 to 35 wt.%, were synthesized by chemically reducing the metal precursors in water-ethylene glycol solutions. The actual composition of the bimetallic nanoparticles corresponds to a theoretical (1:1) composition for the PtAg/C catalysts, whereas in the PtNi/C and PtCu/C materials, a portion of the alloying component exists in an oxide form. Decreasing the average metallic crystallite sizes from 3.5 to 1.6 nm does not increase the electrochemically active surface area. This apparent contradiction is because a majority of the PtNi and PtCu nanoparticles consist of 2-4 disordered crystallites. In addition, a portion of the PtNi or PtCu nanoparticle surface is covered by nickel or copper oxides, respectively. PtAg nanoparticles, which have a smaller size relative to other bimetallic particles according to the TEM data, are characterized by an intense platinum surface segregation. The agglomeration processes are lowest for the PtAg nanoparticles. [ABSTRACT FROM AUTHOR]

We review our recent progress in the development of Pt-Ni bimetallic electrocatalysts with both high sustained activity and sustained stability for oxygen reduction reaction (ORR). This was achieved by an atomic understanding and rational control of the core-shell compositional patterns and size-related nanoporosity within the bimetallic nanoparticles formed during chemical and electrochemical pretreatment and electrocatalysis. In particular, we reveal how the size of the nanoparticle directly influences the nanoporosity formation and thereby the near surface composition, catalytic activity and stability. Our atomic insights provide a clearer picture on how bimetallic nanoparticles should be tailored for optimal ORR performance. [ABSTRACT FROM AUTHOR]

In proton exchange membrane fuel cells (PEMFCs), it is very important to develop a cathode catalyst with high oxygen reduction reaction activity and high chemical stability while reducing the Pt content. Alloying Pt with transition metals is one of options to achieve this goal, but it generally suffers from stability issues caused by transition metals. We demonstrate a mass-producible carbon layer-protected and chemically ordered PtFe alloy cathode nanocatalyst of about 4 nm size with high activity, stability, and Pt utilization efficiency. The catalyst is prepared via a facile and easily scaled synthesis route where the formation of PtFe nanoparticles, phase transition from chemically disordered to chemically ordered PtFe phase, and carbon layer-covering occurs simultaneously. The synthesized catalyst with the highest degree of phase transition to chemically ordered PtFe achieves a mass activity of 848 A g Pt −1 at 0.9 V on rotating disk electrode, and maintains its performance over 30,000 stability test cycles. The PEMFC with this catalyst also stably performs 0.8 A cm−2 at 0.66 V (1.1 A cm−2 at 0.6 V) over 30,000 stability test cycles at an ultra-low total Pt loading of 0.100 mg Pt cm−2, far exceeding the 2025 US Department of Energy (DOE) stability target. [Display omitted] • A carbon-layer-protected fct -PtFe nanocatalyst for ORR is synthesized. • The catalyst maintains high fuel cell performance over 30,000 cycles. • The performance of the fuel cell surpasses the 2025 DOE target. • The facile synthesis route enables the mass production of the catalysts. [ABSTRACT FROM AUTHOR]

Abstract: Carbon supported platinum and platinum alloys (PtCo, PtNi and PtCu) for PEMFC cathodes were prepared and studied for their oxygen reduction reaction activity and durability under potential cycling at 80°C in 0.5M HClO4. Catalysts with different metal alloy composition and particle size were synthesized by annealing at different temperatures to discriminate between the effects of alloying and particle size on the electrocatalytic activity and durability. XRD was used for the structural characterization of pristine catalysts, while the bulk compositions were analyzed by EDS before and after durability tests. XPS was employed to determine the surface composition of selected alloys after durability tests. The particle size of the fresh and aged catalysts was determined by TEM. Rapid dealloying, particularly from non-noble metal rich alloys, was already witnessed for the alloys potentially cycled at room temperature. Significant particle growth depending on the initial particle size was observed for both Pt and Pt alloys after the durability tests. For the alloys with similar initial particle size, the initial electrocatalytic activity depends on the initial alloy composition. Although a 3-fold enhancement in the ORR activity was observed for the non-noble metal rich alloys after initial dealloying, the specific activity of Pt and Pt alloys becomes quite similar at the end of the durability tests. Annealing of Pt/C and Pt alloys at 950°C results in catalysts with the highest specific and mass activity and with the highest stability. [Copyright &y& Elsevier]

Abstract: The kinetics of the oxygen reduction reaction (ORR) were examined on a series of Pt100−x−y Ni x Pd y ternary alloys. Films were produced by electrodeposition that involved a combination of underpotential and overpotential reactions. For Pt-rich Pt100−x−y Ni x Pd y alloy films (x <0.65) Ni co-deposition occurred at underpotentials while for Ni-rich films (x >0.65) deposition proceeded at overpotentials. Rotating disk electrode (RDE) measurements of the ORR kinetics on Ni-rich Pt100−x−y Ni x Pd y thin films revealed up to ∼6.5-fold enhancement of the catalytic activity relative to Pt films with the same Pt mass loading. More than half of the electrocatalytic gain may be attributed to surface area expansion due to Ni dealloying. Surface area normalization based on the H upd charge reduced the enhancement factor to a value less than 2. The most active ternary alloy film for ORR was Pt25Ni73Pd2. Comparison of the ORR on Pt, Pt20Ni80, Pt25Ni73Pd2 thin films indicate that the binary alloy is the most active with a H upd normalized ORR enhancement factor of up to 3.0 compared to 1.6 for the ternary alloy. [ABSTRACT FROM AUTHOR]

While it is fairly straightforward to predict the relative chemical reactivity of pure metals, obtaining similar structure-performance relationships for alloys is more challenging. In this contribution we present experimental analysis supported with quantum chemical DFT calculations which allowed us to propose a simple, physically transparent model to predict the impact of alloying on the local electronic structure of different sites in alloys and on the local chemical reactivity. The model was developed through studies of a number of Pt alloys. The central feature of the model is that hybridization of d-orbitals in alloys does not lead to significant charge transfer between the constituent elements in the alloy, and therefore the width of the local density of d-states projected on a site, which is easily calculated from tabulated parameters, is an excellent descriptor of the chemical reactivity of the site. [ABSTRACT FROM AUTHOR]

Abstract: The role of catalyst stability on the adverse effects of hydrogen peroxide (H2O2) formation rates in a proton exchange membrane fuel cell (PEMFC) is investigated for Pt, Pt binary (PtX, X=Co, Ru, Rh, V, Ni) and ternary (PtCoX, X=Ir, Rh) catalysts supported on ketjen black (KB) carbon. The selectivity of these catalysts towards H2O2 formation in the oxygen reduction reaction (ORR) was measured on a rotating ring disc electrode. These measured values were used in conjunction with local oxygen and proton concentrations to estimate local H2O2 formation rates in a PEMFC anode and cathode. The effect of H2O2 formation rates on the most active and durable of these catalysts (PtCo and PtIrCo) on Nafion membrane durability was studied using a single-sided membrane electrode assembly (MEA) with a built-in reference electrode. Fluoride ion concentration in the effluent water was used as an indicator of the membrane degradation rate. PtIrCo had the least fluorine emission rate (FER) followed by PtCo/KB and Pt/KB. Though PtCo and PtIrCo show higher selectivity for H2O2 formation than unalloyed Pt, they did not contribute to membrane degradation. This result is explained in terms of catalyst stability as measured in potential cycling tests in liquid electrolyte as well as in a functional PEM fuel cell. [Copyright &y& Elsevier]

Abstract: An investigation of carbon-supported Pt/C and PtCo/C catalysts was carried out with the aim to evaluate their stability under high temperature polymer electrolyte membrane fuel cell (PEMFC) operation. Carbon-supported nanosized Pt and PtCo particles with a mean particle size between 1.5nm and 3nm were prepared by using a colloidal route. A suitable degree of alloying was obtained for the PtCo catalyst by using a carbothermal reduction. The catalyst stability was investigated to understand the influence of carbon black corrosion, platinum dissolution and sintering in gas-fed sulphuric acid electrolyte half-cell at 75°C and in PEMFC at 130°C. Electrochemical active surface area and catalyst performance were determined in PEMFC at 80°C and 130°C. A maximum power density of about 700mWcm−2 at 130°C and 3bar abs. O2 pressure with 0.3mgPtcm−2 loading was achieved. The PtCo alloy showed a better stability than Pt in sulphuric acid after cycling; yet, the PtCo/C catalyst showed a degradation after the carbon corrosion test. The PtCo/C catalyst showed smaller sintering effects than Pt/C after accelerated degradation tests in PEMFC at 130°C. [Copyright &y& Elsevier]

Abstract: Phase relationships were studied in Pt-rich, near-equiatomic Zr–Pt alloys. The composition range of the previously unreported rhombohedral compound Zr3Pt4, isomorphous with Zr3Pd4 above room temperature, extends to the Zr-rich composition Zr9Pt11 by the formation of lattice vacancies on certain Pt sites. A metastable tetragonal Zr9Pt11 compound is formed, however, when vacancy formation is inhibited. The rhombohedral structure undergoes a displacement transformation on cooling between 90 and 140°C to a low-temperature structure that is presumably triclinic. The orthorhombic compound ZrPt is stable from room temperature to 1590°C where it transforms to a cubic B2-type structure. Structural data are given for the compounds ZrPt, Zr9Pt11, Zr3Pt4 and Zr7Pt10, and a complete Zr–Pt phase diagram is presented. [Copyright &y& Elsevier]

Abstract: The electrocatalytic oxidation of methanol at a (Pb) lead electrode modified by Pt, Pt–Ru and Pt–Sn microparticles dispersed into poly(o-phenylenediamine) (PoPD) film has been investigated using cyclic voltammetry as analytical technique and 0.5M sulfuric acid as supporting electrolyte. It has been shown that the presence of PoPD film increases considerably the efficiency of deposited Pt and Pt alloys microparticles toward the electrocatalytic oxidation of methanol. The catalytic activity of Pt particles is further enhanced when Ru and especially Sn, is co-deposited in the polymer film. The effects of various parameters such as concentration of methanol, medium temperature as well as the long term stability of modified electrodes have also been investigated. [Copyright &y& Elsevier]

Abstract: The behaviour of carbon supported Pt75M25 (M=Co, Ni) electrocatalysts, both as anode and cathode materials, was investigated in direct methanol fuel cells (DMFCs) and compared to that of a pure Pt electrocatalyst on the same carbon support. The physical and morphological characteristics of these electrocatalysts were examined by XRD, XAS and TEM techniques. The performances of Pt75Ni25/C and Pt75Co25/C as cathode materials in DMFC were better than those of the same electrocatalysts as anode materials. When used as cathode materials the cell with Pt75Ni25/C showed a better performance than those with Pt/C or Pt75Co25/C both in terms of mass activity and specific activity. The performances of these electrocatalysts as anode materials in DMFC were similar to that of Pt. The enhanced performance of Pt75Ni25/C as cathode electrocatalyst was ascribed both to the improved activity for oxygen reduction and to the higher methanol tolerance of the alloy. [Copyright &y& Elsevier]

Platinum is a main catalyst for the electroreduction of oxygen, a reaction of primary importance to the technology of low-temperature fuel cells. Due to the high cost of platinum, there is a need to significantly lower its loadings at interfaces. However, then O2-reduction often proceeds at a less positive potential, and produces higher amounts of undesirable H2O2-intermediate. Hybrid supports, which utilize metal oxides (e.g., CeO2, WO3, Ta2O5, Nb2O5, and ZrO2), stabilize Pt and carbon nanostructures and diminish their corrosion while exhibiting high activity toward the four-electron (most efficient) reduction in oxygen. Porosity of carbon supports facilitates dispersion and stability of Pt nanoparticles. Alternatively, the Pt-based bi- and multi-metallic catalysts, including PtM alloys or M-core/Pt-shell nanostructures, where M stands for certain transition metals (e.g., Au, Co, Cu, Ni, and Fe), can be considered. The catalytic efficiency depends on geometric (decrease in Pt–Pt bond distances) and electronic (increase in d-electron vacancy in Pt) factors, in addition to possible metal–support interactions and interfacial structural changes affecting adsorption and activation of O2-molecules. Despite the stabilization of carbons, doping with heteroatoms, such as sulfur, nitrogen, phosphorus, and boron results in the formation of catalytically active centers. Thus, the useful catalysts are likely to be multi-component and multi-functional. [ABSTRACT FROM AUTHOR]

Alloys of platinum and lanthanides present a remarkable activity for the oxygen reduction reaction—both in the form of extended surfaces and nanoparticulate catalysts. Co-sputter-deposited thin film catalysts based on platinum and gadolinium show great oxygen reduction activity improvement over pure Pt. The sputter-deposition technique represents a viable and versatile approach for investigating model catalyst systems with different compositions. In this work, co-sputtered Pt5Gd and Pt7.5Gd thin films were investigated using X-ray absorption spectroscopy as well as standardized electrochemical techniques. These investigations revealed the importance of forming alloys with specific stoichiometry, supporting the need of forming compressively strained Pt overlayers in order to achieve optimum catalytic performances. [ABSTRACT FROM AUTHOR]

Developments of high efficient materials for electrocatalyst are significant topics of numerous researches since a few decades. Recent global interests related with energy conversion and storage lead to the expansion of efforts to find cost-effective catalysts that can substitute conventional catalytic materials. Especially, in the field of fuel cell, novel materials for oxygen reduction reaction (ORR) have been noticed to overcome disadvantages of conventional platinum-based catalysts. Various approaching methods have been attempted to achieve low cost and high electrochemical activity comparable with Pt-based catalysts, including reducing Pt consumption by the formation of hybrid materials, Pt-based alloys, and not-Pt metal or carbon based materials. To enhance catalytic performance and stability, numerous methods such as structural modifications and complex formations with other functional materials are proposed, and they are basically based on well-defined and well-ordered catalytic active sites by exquisite control at nanoscale. In this review, we highlight the development of nano-structured catalytic materials for ORR based on recent findings, and discuss about an outlook for the direction of future researches. [ABSTRACT FROM AUTHOR]

The evolution of Pt-Ni nanoparticles supported on amorphous carbon is investigated before and after electrochemical potential cycling (0.6-1.1 V), using aberration-corrected scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS). During voltage cycling and due to the dissolution of  nanoparticles, single ions/atoms and ionic/atomic clusters emerge and diffuse across the carbon support toward larger nanoparticles, where they redeposit. We observe that the preferred locations for the dissolution are the steps and corners of the nanoparticles. On the other hand, the redeposition process happens often on {111} type planes. In addition, contrary to the conventional view, where larger particles grow isotropically from smaller ones, this research work shows that anisotropic growth of smaller particles occurs during potential cycling. The reason for this behavior seems to be related to the fact that smaller particles with thicker Pt-rich shells trigger the nucleation and deposition of Pt.

PtCo alloy catalysts for high temperature PEMFCs (protonic exchange membrane fuel cells) were synthesized on a novel noncarbonaceous support (SiCTiC) using the impregnation method with NaBH 4 as the reducing agent at different synthesis temperatures to evaluate the effect of this variable on their physicochemical and electrochemical properties. The catalysts were characterized by inductively coupled plasma optical emission spectrometry, scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscope-energy dispersive X-ray,and temperature-programmed reduction. In addition, the electrochemical characterization (i.e., cyclic voltammetry, oxygen reduction reaction, and chronoamperometry) was carried out with a rotating disk electrode. For the cyclic voltammetry investigation, 400 cycles were performed in hot phosphoric acid and a half-cell to evaluate the stability of the synthesized catalysts. The catalyst synthesized on SiCTiC exhibited excellent durability compared to the catalyst synthesized on a Vulcan support. In addition, all synthesized catalysts exhibited better catalytic activity than that of the PtCo/C catalysts. The best results were observed for the catalyst synthesized at 80 °C due to its shorter Pt-Pt nearest-neighbor and higher alloy degree. Finally, a preliminary stability test was conducted in an HT-PEMFC, and promising results in terms of stability and performance were observed.

Rational design and construction of Pt-based porous nanostructures with large mesopores have triggered significant considerations because of their high surface area and more efficient mass transport. Hydrochloric acid-induced kinetically controlled reduction of metal precursors in the presence of soft template F-127 and hard template tellurium nanowires has been successfully demonstrated to construct one-dimensional hierarchical porous PtCu alloy nanostructures with large mesopores. Moreover, the electrochemical experiments demonstrated that the PtCu hierarchically porous nanostructures synthesized under optimized conditions exhibit enhanced electrocatalytic performance for oxygen reduction reaction in acid media.

Dealloyed Pt bimetallic core-shell catalysts derived from low-Pt bimetallic alloy nanoparticles (e.g, PtNi3 ) have recently shown unprecedented activity and stability on the cathodic oxygen reduction reaction (ORR) under realistic fuel cell conditions and become today's catalyst of choice for commercialization of automobile fuel cells. A critical step toward this breakthrough is to control their particle size below a critical value (≈10 nm) to suppress nanoporosity formation and hence reduce significant base metal (e.g., Ni) leaching under the corrosive ORR condition. Fine size control of the sub-10 nm PtNi3 nanoparticles and understanding their size dependent ORR electrocatalysis are crucial to further improve their ORR activity and stability yet still remain unexplored. A robust synthetic approach is presented here for size-controlled PtNi3 nanoparticles between 3 and 10 nm while keeping a constant particle composition and their size-selected growth mechanism is studied comprehensively. This enables us to address their size-dependent ORR activities and stabilities for the first time. Contrary to the previously established monotonic increase of ORR specific activity and stability with increasing particle size on Pt and Pt-rich bimetallic nanoparticles, the Pt-poor PtNi3 nanoparticles exhibit an unusual "volcano-shaped" size dependence, showing the highest ORR activity and stability at the particle sizes between 6 and 8 nm due to their highest Ni retention during long-term catalyst aging. The results of this study provide important practical guidelines for the size selection of the low Pt bimetallic ORR electrocatalysts with further improved durably high activity., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)