Electroreduction Of Molecular Oxygen Research Articles

Superior Performance of an Iron-Platinum/Vulcan Carbon Fuel Cell Catalyst

This work reports on the synthesis of iron-platinum on Vulcan carbon (FePt/VC) as an effective catalyst for the electrooxidation of molecular hydrogen at the anode, and electroreduction of molecular oxygen at the cathode of a proton exchange membrane fuel cell. The catalyst was synthesized by using the simple polyol route and characterized by XRD and HRTEM along with EDS. The catalyst demonstrated superior electrocatalytic activity for the oxygen reduction reaction and the oxidation of hydrogen with a 2.4- and 1.2-fold increase compared to platinum on Vulcan carbon (Pt/VC), respectively. Successful application of FePt/VC catalyst in a self-breathing fuel cell also showed a 1.7-fold increase in maximum power density compared to Pt/VC. Further analysis by accelerated stress test demonstrated the superior stability of FePt on the VC substrate with a 4% performance degradation after 60,000 cycles. In comparison, a degradation of 6% after 10,000 cycles has been reported for Pt/Ketjenblack.

Iron and tin phosphide as polymer electrolyte membrane fuel cell cathode catalysts

A new set of catalysts based on metal-phosphorus/nitrogen-carbon, for the electroreduction of molecular oxygen at the polymer electrolyte membrane fuel cell cathode are reported. These catalysts were simply made from folic acid, phosphoric acid, iron or tin oxides. In particular, the tin oxide-based catalyst exhibited superior electrocatalytic activity against state-of-the-art non-platinum-based catalysts with a mass activity of 6 mA mg−1. Successful application of these catalysts at the cathode of a self-breathing fuel cell is also demonstrated, and this validated the suitability of the catalyst to operate under fuel cell conditions. A power density of 12.6 mW cm−2 at ambient condition (25 °C, 20% relative humidity and dry hydrogen) was achieved. This work provides foundation for the emergence of phosphorous based non-platinum catalysts for fuel cell cathodes.

Low‐Pt NiNC‐Supported PtNi Nanoalloy Oxygen Reduction Reaction Electrocatalysts—In Situ Tracking of the Atomic Alloying Process

AbstractWe report and analyze a synthetic strategy toward low‐Pt platinum‐nickel (Pt‐Ni) alloy nanoparticle (NP) cathode catalysts for the catalytic electroreduction of molecular oxygen to water. The synthesis involves the pyrolysis and leaching of Ni‐organic polymers, subsequent Pt NP deposition, followed by thermal alloying, resulting in single Ni atom site (NiNC)‐supported PtNi alloy NPs at low Pt weight loadings of only 3–5 wt %. Despite low Pt weight loading, the catalysts exhibit more favorable Pt‐mass activities compared to conventional 20–30 wt % benchmark PtNi catalysts. Using in situ microscopic techniques, we track and unravel the key stages of the PtNi alloy formation process directly at the atomic scale. Surprisingly, we find that carbon‐encapsulated metallic Ni@C structures, rather than NiNx sites, act as the Ni source during alloy formation. Our materials concepts offer a pathway to further decrease the overall Pt content in hydrogen fuel cell cathodes.

Graphene-Based Aerogels Possessing Superhydrophilic and Superhydrophobic Properties and Their Application for Electroreduction of Molecular Oxygen

Graphene-Based Aerogels Possessing Superhydrophilic and Superhydrophobic Properties and Their Application for Electroreduction of Molecular Oxygen

P-block single-metal-site tin/nitrogen-doped carbon fuel cell cathode catalyst for oxygen reduction reaction.

This contribution reports the discovery and analysis of a p-block Sn-based catalyst for the electroreduction of molecular oxygen in acidic conditions at fuel cell cathodes; the catalyst is free of platinum-group metals and contains single-metal-atom actives sites coordinated by nitrogen. The prepared SnNC catalysts meet and exceed state-of-the-art FeNC catalysts in terms of intrinsic catalytic turn-over frequency and hydrogen-air fuel cell power density. The SnNC-NH3 catalysts displayed a 40-50% higher current density than FeNC-NH3 at cell voltages below 0.7 V. Additional benefits include a highly favourable selectivity for the four-electron reduction pathway and a Fenton-inactive character of Sn. A range of analytical techniques combined with density functional theory calculations indicate that stannic Sn(IV)Nx single-metal sites with moderate oxygen chemisorption properties and low pyridinic N coordination numbers act as catalytically active moieties. The superior proton-exchange membrane fuel cell performance of SnNC cathode catalysts under realistic, hydrogen-air fuel cell conditions, particularly after NH3 activation treatment, makes them a promising alternative to today's state-of-the-art Fe-based catalysts.

PTFE/rGO Aerogels with Both Superhydrophobic and Superhydrophilic Properties for Electroreduction of Molecular Oxygen

Aerogels based on polytetrafluoroethylene (60 and 50 mass %) and graphene oxide were obtained. After hydrazine reduction and annealing in an inert atmosphere, the aerogels became superhydrophobic w...

Electro-Reduction of Molecular Oxygen Mediated by a Cobalt(II)octaethylporphyrin System onto Oxidized Glassy Carbon/Oxidized Graphene Substrate

The oxygen reduction reaction (ORR) is the most important reaction in life processes and in energy transformation. The following work presents the design of a new electrode which is composed by deposited cobalt octaethylporphyrin onto glassy carbon and graphene, where both carbonaceous materials have been electrochemically oxidized prior to the porphyrin deposition. The novel generated system is stable and has an electrocatalytic effect towards the oxygen reduction reaction, as a result of the significant overpotential shift in comparison to the unmodified electrode and to the electrodes used as target. Kinetic studies corroborate that the system is capable of reducing molecular oxygen via four electrons, with a Tafel slope value of 60 mV per decade. The systems were morphologically characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) Electrochemical impedance spectroscopy studies showed that the electrode previously oxidized and modified with cobalt porphyrin is the system that possesses lower resistance to charge transfer and higher capacitance.

Electrochemical Properties of Tetrasubstituted Cobalt Phthalocyanines with Fragments of Benzoic Acid

The method of cyclic voltammetry is used for the first time to study the electrochemical behavior of cobalt phthalocyanine derivatives with fragments of benzoic acid CoPc(4-O–C6H4COOH)4 and CoPc(4- S–C6H4COOH)4 in an aqueous alkaline solution. Comparative analysis is carried out of the electrochemical behavior and change in the electrocatalytic activity of metal phthalocyanines in the reaction of molecular oxygen electroreduction depending on the functional substitution in the macrocycle molecule. In the case of the CoPc(4-O–C6H4COOH)4 and CoPc(4-S–C6H4COOH)4 compounds, central metal ion oxidation (Co2+ → Co3+) and reduction (Co2+→ Co1+) processes and also two successive one–electron stages of phthalocyanine ligand electroreduction are registered. It is shown that the studied cobalt phthalocyanine derivatives manifest electrocatalytic activity in the process of molecular oxygen electroreduction.

Synthesis and redox characteristics of iron complexes with triphenylsubstituted corrols in the presence of argon and oxygen

para-Substituted iron meso-triphenylcorrole derivatives [Fe(ms-p-R-Ph)3Cor] containing electron- donating (R = OMе) and electron-drawing (R = NO2) groups in phenyl rings are synthesized and characterized by 1H NMR, electronic absorption spectroscopy, and mass spectrometry. The effect of the nature of functional groups within iron complexes on the redox processes involving these complexes in water–alkaline solutions is analyzed. Electronic transitions in the ligand (Ered/ox = 0.820–0.850 V) and the metal (Ered/ox =–0.005 to–0.190 and–0.790 to–0.870 V for the Fe4+ ↔ Fe3+ and Fe3+ ↔ Fe2+ transitions, respectively) were found in the cyclic voltammograms. Iron in the synthesized complexes I–IV under the conditions under study exists in the +4 oxidation state. The activity of iron complexes in electroreduction of molecular oxygen significantly depends on the nature of a substituent, increases in the series: Fe(ms-p-NO2Ph)3Cor (II) < Fe(ms-p-MeOPh)3Cor (I) < Fe(β-Br)8(ms-Ph)3Cor (IV) < Fe(ms-Ph)3Cor (II) and is caused by the fact that low-energy redox electron transitions occur in the molecules. The electrocatalytic activity of iron corroles is much higher than that of metal porphyrins with a similar structure.

Tuning the Electrocatalytic Oxygen Reduction Reaction Activity and Stability of Shape-Controlled Pt-Ni Nanoparticles by Thermal Annealing - Elucidating the Surface Atomic Structural and Compositional Changes.

Shape-controlled octahedral Pt-Ni alloy nanoparticles exhibit remarkably high activities for the electroreduction of molecular oxygen (oxygen reduction reaction, ORR), which makes them fuel-cell cathode catalysts with exceptional potential. To unfold their full and optimized catalytic activity and stability, however, the nano-octahedra require post-synthesis thermal treatments, which alter the surface atomic structure and composition of the crystal facets. Here, we address and strive to elucidate the underlying surface chemical processes using a combination of ex situ analytical techniques with in situ transmission electron microscopy (TEM), in situ X-ray diffraction (XRD), and in situ electrochemical Fourier transformed infrared (FTIR) experiments. We present a robust fundamental correlation between annealing temperature and catalytic activity, where a ∼25 times higher ORR activity than for commercial Pt/C (2.7 A mgPt-1 at 0.9 VRHE) was reproducibly observed upon annealing at 300 °C. The electrochemical stability, however, peaked out at the most severe heat treatments at 500 °C. Aberration-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy (EDX) in combination with in situ electrochemical CO stripping/FTIR data revealed subtle, but important, differences in the formation and chemical nature of Pt-rich and Ni-rich surface domains in the octahedral (111) facets. Estimating trends in surface chemisorption energies from in situ electrochemical CO/FTIR investigations suggested that balanced annealing generates an optimal degree of Pt surface enrichment, while the others exhibited mostly Ni-rich facets. The insights from our study are quite generally valid and aid in developing suitable post-synthesis thermal treatments for other alloy nanocatalysts as well.

ELECTROCHEMICAL PROPERTIES OF VARIOUS CARBON MATERIALS. CALCULATION OF OXYGEN ADSORPTION

New carbon materials such as oxidized (OG) and thermally expanded (TEG) graphite modified with salts of transition metals have been applied in chemical power sources (CPS) as a catalyst. An optimal combination of properties of the porous structure and chemical composition of the surface allows creating high power adsorption system. Particular attention is paid to the system of oxygen storage, widely used in various fields of human activity. The electrocatalytic activity and electrochemical properties of various carbon materials modified with salts of cobalt and iron were studied by cyclic voltammetry in alkaline solution. Working electrode polarization modes are set using the potentiostat and the PC with the interface unit. The current-voltage graphs were obtained on a personal computer with advanced signal processing on the interface device. The relative error does not exceed 3% at the determination of the redox potential values. The potentials were recorded for the observed processes with an accuracy of ± 0.01. The Randles – Shevchik equation was used to calculate the number of electrons in order to clarify the mechanism of electroreduction process in a flow of molecular oxygen (2 or 4). To assess the effect of electrocatalisis not only high current density can be used, but also the half-wave potential of the reduction of molecular oxygen. On the cathode side of the graph with the introduction of oxygen into the electrolyte there is a significant increase in current at the potential range from -0.2 to -0.6 V and from -0.7 to -0.9 V the increase in current occurs due to a process of electroreduction of molecular oxygen. Quantified characteristics of adsorption of molecular oxygen, such as the maximum amount of adsorption and Langmuir adsorption coefficient were determined based on the electrochemical properties. Langmuir adsorption coefficient characterizes the interaction energy of the adsorbate with the adsorbent. The data obtained can be used for further research cathodes with air (oxygen) depolarization.For citation:Filimonov D.A., Yudina T.F., Bazanov M.I., Bratkov I.V., Leontiev N.A. Electrochemical properties of various carbon materials. Calculation of oxygen adsorption. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 2. P. 20-25.

Performance and Durability of Pt-Ti Catalyst for Oxygen Electroreduction

Fuel cells are expected to be a key next-generation energy source used for vehicles and homes, offering high energy conversion efficiency and minimal pollutant emissions. The high efficiency arises from the fact that fuel cells convert chemical energy directly into electrical energy without the Carnot limitation of thermal engines. However, due to the extreme operating environment, Pt was almost exclusively the only practical catalyst for molecular oxygen electroreduction in PEM fuel cells. Recently, considerable efforts have been made to investigate synergy effects of platinum alloyed with base metals to improve the sluggish kinetics of oxygen reduction reaction of Pt catalyst. The more active Pt-alloy catalysts, in return, may arise the durability issue under the extreme environment of PEM fuel cell operation. In this presentation, results of a more active yet durable PtTi alloy catalyst will be discussed for oxygen reduction reaction in acidic media, including (i) combinatorial high-throughput discovery of PtTi alloy composition; (ii) synthesis and characterization of nano-scale PtTi particles with controllable size, phase, and individual particle composition; and (iii) electrochemical STM and ICP characterization of coarsening and corrosion of PtTi alloy catalyst in comparison with Pt and PtCo catalysts. A novel combinatorial high-throughput electrocatalyst discovery workflow and associated tools were developed [1-4], where thin films of alloys can be made through a Multi-sources Physical Vapor Deposition system [5], and the resulted materials can be electrochemically screened by a Multi-channel Rotating Disk Electrode system [6]. PtTi binary system has been screened using this methodology for activity-stability-composition relationship and the best alloy composition was identified. In addition to the discovery of alloy compositions, engineering the PtTi alloy particles in nanoscale has been a challenge. Several synthesis technologies were studied and developed to achieve capabilities of controlling particle size and particle microcomposition [7]. The results show that by careful engineering the particle size and microcomposition in nanoscale, it is able to achieve the superior electrocatalytic activity predicted by the combinatorial high-throughput discovery. Electrochemical STM technique, in combination with electrochemical potentiostating, potential cycling, and ICP analysis, was used to monitor the coarsening and base metal corrosion under dynamic fuel cell operation conditions and compared with phenomena observed from Pt and PtCo catalysts [8-10]. The results show that PtTi not only is more active than Pt and much stable than PtCo, but also can mitigate the catalyst coarsening. Reference [1] T. He and E. Kreidler, Phys. Chem. Chem. Phys. 10, 3731 (2008). “Combinatorial screening of PtTiMe ternary alloys for oxygen electroreduction”. [2] E. Kreidler and T. He, in Catalysts for Oxygen Electroreduction – Recent Developments and New Directions (Ed. T. He, Transworld Research Network) Chapter 4, p.63 (2009). “Oxygen reduction on Pt alloys: high throughput combinatorial screening of Pt binary alloys”. [3] T. He, E. Kreidler, L. Xiong and E. Ding, J. Power Sources 165, 87 (2007). “Combinatorial screening and nano-synthesis of platinum binary alloys for oxygen electroreduction”. [4] T. He, E. Kreidler, L. Xiong, J. Luo and C.J. Zhong, J. Electrochem. Soc. 153, A1637 (2006). “Alloy electrocatalysts: combinatorial discovery and nano-synthesis”. [5] T. He, E.R. Kreidler and T. Nomura, US 8,944,002 (2015). “High throughput physical vapor deposition system for material combinatorial studies”. [6] T. He, US 7,077,946 (2006). “High throughput multi-channel rotating disk or ring-disk electrode assembly and method”. [7] E. Ding, K.L. More and T. He, J. Power Sources 175, 794 (2008). "Preparation and characterization of carbon-supported PtTi alloy electrocatalysts". [8] L. Tang, B. Han, K. Persson, C. Friesen, T. He, K. Sieradzki and G. Ceder, J. Am. Chem. Soc. 132, 596 (2010). “Electrochemical stability of nanometer-scale Pt particles in acidic environments”. [9] Q. Xu, E. Kreidler, D.O. Wipf and T. He, J. Electrochem. Soc. 155, B228 (2008). "An in-situ electrochemical STM study of potential-induced coarsening and corrosion of platinum nano crystals". [10] Q. Xu, T. He and D. Wipf, Langmuir 32, 9098 (2007). "An in-situ electrochemical STM study of the coarsening of platinum islands at double-layer potentials".

Oxygen Electrocatalysis on Dealloyed Pt Nanocatalysts

We review the fundamental principles, the preparation and catalytic performance of dealloyed Pt core–shell electrocatalysts for the electroreduction of molecular oxygen. This reaction is key to the efficiency of all fuel cell cathodes, as the oxygen electrocatalysis exhibits much larger kinetic overpotentials compared to typical fuel cell anode reactions. We discuss structural surface lattice strain in metal overlayers and show that they serve as models for nanostructured core–shell catalysts. We address preparation pathways with particular emphasis on the dealloying routes. Trends in reactivity of different dealloyed Pt core–shell catalysts are compared with a focus on the dealloyed Pt–Ni alloy system. Size effects are discussed. Practical catalytic performance data in automotive fuel cells and under automotive fuel cell conditions is provided and contrasted to other state-of-art catalyst concepts. This review concludes that dealloyed Pt core–shell cathode catalysts are currently the most attractive commercialization candidate for automotive applications.

New functional materials based on conductive polymer—metal complexes modified with metallic nanoelectrodes

The results of the synthesis and investigation of new composite functional materials are presented. The new materials are conductive polymer layers of the cobalt, nickel, and palladium complexes with the Schiff bases (poly[MSchiff)]) with gold and platinum nanoelectrodes inserted into the layers using the electrochemical deposition method. The materials were studied by cyclic voltammetry, impedance spectroscopy, scanning electron microscopy with X-ray microanalysis, and a quartz crystal microbalance. The composite materials poly[Ni(Schiff)]/Pt and poly[Co(Schiff)]/Au exhibit catalytic activity in the reactions of hydrogen evolution and electroreduction of molecular oxygen, respectively.

Mathematical modeling of processes in flow-through 3D electrode with account for reactions preceding to reduction of metal ions to metallic phase

A mathematical model is presented that allows studying multistage processes of electrooxidation and electroreduction of metal ions with account for reduction of hydrogen ions and molecular oxygen in a flow-through 3D electrode. The mathematical model takes into account the possibility of redistribution of the flow rate of electrolyte, porosity, specific surface area, specific electrode conductivity, and other characteristics in the local electrode bulk in the course of electrolysis. Model equations and results of numeric studies are presented for the electrochemical process in a flow-through 3D electrode of a carbon fiber material for the Fe(III)/Fe(II)/Fe system with account for the reaction of electroreduction of hydrogen ions and molecular oxygen.

Electroreduction of molecular oxygen on the silver/perfluorinated ion-exchange membrane MF-4SK/dispersed carbon nanocomposite

By chemical deposition of silver in an ion-exchange matrix, the Ag0/MF-4SK/C nanocomposite has been fabricated, which is capable of changing the amount of deposited silver by varying the concentration of ionic groups in the MF-4SK membrane. Transmission electron microscopy has revealed the presence of silver particles of a 3 nm size. On an electrode coated with the MF-4SK membrane, electroreduction of oxygen occurs on the carbon substrate and the membrane is a diffusion barrier. Since the polymer matrix contains counterions H+ localized near fixed −SO3 groups, the hydrogen ion takes part in the stage of charge transfer to the oxygen molecule. An increase in the dioxygen electroreduction current on the Ag0/MF-4SK/C nanocomposite relative to the MF-4SK/C composite is due to the presence of silver particles, which result in acceleration of the reaction by the catalytic action, and to an increased contribution of the four-electron process as compared with the two-electron process characteristic of carbon materials.

Effect of size in oxygen electroreduction on gold over a wide range of pH

The electroreduction of molecular oxygen on polycrystalline gold and 20Au/C nanoparticles synthesized on XC72R soot is studied over a wide range of pH. Changes in the character of the polarization curves and a considerable increase in half-wave potential (∼100 mV) upon transitioning from a compact to a nanodisperse metal were established. A triple increase in the exchange currents is observed for nanoparticles relative to polycrystalline gold. It is suggested that the enhancement of the catalytic activity of a nanodisperse metal is a result of changes in the electronic structure of the d-sublevel of surface atoms.

A rotating ring disk electrode study of the oxygen reduction reaction in lithium containing non aqueous electrolyte

We show the effect of a very small addition of LiClO4 to tetraethyl ammonium perchlorate (TEAP) in acetonitrile on the electro-reduction of molecular oxygen (ORR) at a rotating ring (Pt) glassy carbon (GC) disk electrode. While TEA+ cations stabilize the first electron reduction product in acetonitrile, superoxide O2−, in the absence of Li+ the ORR proceeds by two one-electron sequential steps to the stabilized peroxide. Addition of 10μM LiClO4 (<1:800 Li+ to TEA+ ratio) strongly affects the ORR mechanism: Both disk (ID) and ring (IR) currents strongly decrease, with less than 0.5% O2− produced at the GC disk reaching the ring electrode, but still IR follows the same potential dependence as ID. On the other hand, addition of DMSO to acetonitrile 0.1M LiClO4 stabilizes soluble O2− detected at the ring since DMSO preferentially solvates Li+ preventing disproportionation of LiO2 into O2 and passivating Li2O2.

Electroreduction of molecular oxygen on carbon electrode modified by dispersed silver

Silver particles are formed by electrochemical deposition on the carbon electrode surface. It is found that the deposition process occurs according to the progressive nucleation mechanism, which results in formation of silver particles with the size of 95 to 190 nm as dependent on the electrodeposition time. The values of silver particle size and support surface coverage by metal obtained on the basis of microphotographs indicate that cathodic polarization in the presence of dissolved oxygen results in particle size redistribution due to the reaction of silver particle dissolution with further deposition simultaneously with oxygen electroreduction. The reaction of molecular oxygen electroreduction on a carbon electrode with deposited dispersed silver occurs via a mixed two- and four-electron mechanism. The observed limiting reaction current is of diffusion nature.

Electrochemical and electrocatalytic properties of meso-triphenylcorrole and its complexes with Mn(III), Co(III), Cu(III), and Zn(II)

The method of cyclic voltammetry (CV) was used to compare electrochemical and electrocatalytic properties of meso-triphenylcorrole [H3(ms-Ph)3Cor] and also its complexes with Mn(III), Co(III), Cu(III), and Zn(II) in 0.1M KOH. Metal-localized redox transitions are detected in the complexes of Mn (III → IV) and (III → II), Co (III → II), Cu (III → II). It is shown that the manganese complex features most effective catalytic properties in the reaction of molecular oxygen electroreduction.