Rotating Disk Electrode Technique Research Articles

Studies of selectivity of oxygen reduction reaction in acidic electrolyte on electrodes modified by products of pyrolysis of polyacrylonitrile and metalloporphyrins

The rotating disk electrode technique was used to study in 0.5 M H2SO4 catalytic properties of products of pyrolysis of the metal-free polyacrylonitrile/carbon black composite, polyacrylonitrile/iron/carbon black composite, and also supported pyropolymers of Co(II) tetramethoxyphenyl porphyrine (CoTMPP) and Fe(III) tetramethoxyphenyl porphyrin chloride (FeTMPPCl). It is shown that the metal-free polyacrylonitrile/carbon black composite catalyzes the oxygen reduction reaction via the parallel path. Addition of up to 2% of Fe into the composite results in abrupt growth of the catalytic activity and share of the four-electron reaction, which provides the parallel–serial reaction path. The parallel reaction with no further catalytic conversion of H2O2 occurs on catalysts of the CoTMPP/Vulcan XC72 and FeTMPPCl/Vulcan XC72 series. The chemical composition is one of the key factors affecting activity and selectivity of CoTMPP/Vulcan XC72 catalysts. An increase in the precursor content from 5 to 30% is accompanied by an increase in selectivity k 1/k 2 from 0.14–0.30 to 0.5–1.7, where k 1 is the rate constant of the reaction of O2 reduction to H2O, k 2 is the rate constant of the reaction of O2 reduction to H2O2.

Study of IrxMny(CO)n(DMF)z as Electrocatalyst for Oxygen Reduction and Hydrogen Oxidation in the Presence of Fuel Cell Contaminants

The oxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR) have been studied on a wide range of elec-trocatalysts, including bimetallic materials which are based solely on platinum group metals and their alloys. This work reports the synthe-sis and characterization of a novel bimetallic electrocatalyst, IrxMny(CO)n(DMF)z, for the ORR and HOR in acid media. The material was synthesized by reacting Ir4(CO)12 and MnCl2·4H2O in DMF. It was characterized structurally by FT-IR and micro-Raman spectroscopy, X-ray diffraction, SEM and energy-dispersive X-ray spectroscopy; the electrochemical characterization was made by the rotating disk elec-trode technique, at room temperature. The electrocatalytic activity of the new material for the ORR and HOR does not show appreciable variations due to the presence of methanol or carbon monoxide, respectively, even at high concentrations of these contaminants (2 mol L-1 methanol and 0.5% CO). This tolerance is a very important property with respect to platinum-based catalysts, which are poisoned by low concentrations of such contaminants. The kinetic parameters of the novel catalyst, such as Tafel slope (b), exchange current density (jo) and charge transfer coefficient (α), are reported as well. The results show that the novel electrocatalyst is attractive for evaluation as cath-ode/anode in PEM fuel cells.

Electrocatalysis of oxygen reduction on CoNi-decorated-Pt nanoparticles: A theoretical and experimental study

A CoNi-decorated-Pt (40:40:20 wt%) electrocatalyst was theoretically studied and experimentally validated for the oxygen reduction reaction (ORR) in acid media. To predict the activity of the electrocatalyst a Co16Ni16-decorated-Pt3 cluster was employed. The O and O2 adsorption energies were used as descriptors of the catalytic activity for the ORR. All calculations were performed using the density functional theory approach as implemented in the deMon2k code. A combined synthesis of high energy milling-galvanic displacement was performed to produce the CoNi-decorated-Pt electrocatalyst. The physical characterization of the electrocatalyst was developed using X-ray diffraction (XRD) for the phases identification, energy disperse X-ray spectroscopy (EDX) for compositional analysis and scanning transmission electron microscopy (STEM) to determine morphology and particle size of the synthesized electrocatalyst. Cyclic voltammetry and rotating disk electrode techniques were used for the electrochemical characterization of the synthesized electrocatalyst. The O and O2 adsorption energies showed that CoNi-decorated-Pt (Co16Ni16–Pt3 cluster) electrocatalyst represents an attractive candidate for the ORR. STEM micrographs showed homogeneous nanocrystalline particles of 5–10 nm size. The CoNi-decorated-Pt nanoparticles presented high specific activity, 40% above of the determined from Pt/C and similar mass activity from the same commercial Pt/C, used as comparison. Electrochemical results confirm the feasibility of a combined synthesis method to produce nanocatalysts which exhibit similar catalytic activity than that of commercially available Pt/C electrocatalyst.

New insights into the electrochemical oxidation of aniline-dimers in non-aqueous solutions, kinetic parameters obtained by Koutecký-Levich method

The electrochemical oxidation of aniline dimers (4-aminodiphenylamine and 2-aminodiphenylamine) was studied at a glassy carbon electrode in hydrophobic and hydrophilic aprotic solvents and also in ethanol as a neutral amphiprotic solvent. In these solvents, both isomers, show the proton coupled electron transfer mechanism. A linear relationship between the redox potential of these molecules and the donor number of the studied solvents has been found. Our data show that both dynamics of solvent reorientation and the structure of aniline dimer, have a role in the heterogeneous electron transfer rate constant of 4-aminodiphenylamine and 2-aminodiphenylamine. A near linear relationship between the heterogeneous standard rate constant (log ks) and the longitudinal relaxation time (log τL) of the solvents has been found. Furthermore, the mechanism of oxidation of aniline dimers has also been investigated using the rotating disk electrode technique, and the parameters such as heterogeneous rate constant and diffusion coefficient have been determined from Koutecky-Levich plot.

Fluorination: A New Way to Enhance the Durability of Carbon Supports for PEMFC Application

Proton exchange membrane fuel cells (PEMFC) are energy converters that can power nomad, automotive or stationary systems without emission of pollutants. This technology is already used for niche markets, but some challenges must be overcome to enable large-scale deployment. In particular, the electrochemical corrosion of the carbon support at the cathode remains a major concern especially under start-stop conditions. This corrosion causes massive detachment of the supported Pt-based nanocrystallites, negatively affects water management and ultimately results into a collapse of the electrode structure. In this study, we bridged the textural and the structural properties of a set of carbons supports to their resistance to corrosion. The stability of carbon nanotubes (CNT, graphitized but with a low specific surface area), carbon blacks (featuring either large specific surface area but poorly-structured, CBe, or low specific surface area and high degree of graphitization, CBs) and carbon aerogel (controlled texture but low degree of organization, CA) was investigated via accelerated stress tests derived from the FCCJ organization. A trade-off was found in terms of properties: graphitic carbons are more resistant to oxidation, whereas carbon supports featuring high specific surface areas are more favorable to the dispersion of a large amount of catalyst nanoparticles per unit volume. Controlled fluorination of these model carbon supports was performed so as to improve their resistance to electrochemical corrosion [1]. The fluorination was carried out by an easily scalable solid gas process using pure molecular fluorine [2]. The parameters were set in order to limit the fluorination below 0.2 fluorine atom per carbon atom and to avoid any carbon decomposition into gaseous fluorinated compounds such as CF4 and C2F6 [3]. Platinum nanoparticles were also deposited (40 wt.%) by a colloid (polyol) method on the bare and fluorinated carbons. The samples were physically and chemically characterized by XRD, TEM (Figure 1), nitrogen sorption, FTIR and TGA. The catalytic activity of these electrocatalysts towards the oxygen reduction reaction was determined by linear sweep voltammetry (rotating disk electrode technique). Accelerated stress tests, load cycle (0.6-1.0 V) and start-up/shutdown (1.0-1.5 V) protocols, conducted at T= 80°C in a four-electrode cell [4], were performed to investigate the robustness of the bare and fluorinated Pt electrocatalysts. The results and the impact of the fluorination are discussed and compared to those of a commercial 40 wt.% electrocatalyst. [1] S. Berthon-Fabry et al. First insight into fluorinated Pt/carbon aerogels as more corrosion-resistant electrocatalysts for Proton Exchange Membrane Fuel Cell cathodes, Electrocatalysis, 6, 6 (2015) 521-533 [2] N. Batisse, P. Bonnet, M. Dubois, K. Guérin, Fluorination of 0D, 1D and 2D nanocarbons” In: Carbon Nanomaterials Sourcebook (Eds. Taylor & Francis Publisher), 2016[3] Y Ahmad et al., The synthesis of multilayer graphene materials by the fluorination of carbon nanodiscs/nanocones. Carbon, 50, 10 (2012) 3897-3908 [4] L. Dubau, F. Maillard, “Unveiling the crucial role of temperature on the stability of oxygen reduction reaction electrocatalysts”, Electrochem. Commun., 63 (2016) 65-69. This work is funded by the French National Research Agency programme, (ANR-14-CE05-0047 project CORECAT and is supported by Capenergies and Tenerrdis Figure 1: TEM images of bare CBe (left), Pt/CBe (middle) and Pt/F-CB (right) samples Figure 1

Synthesis of Metal-Free Electrocatalyst Obtained from Different Biomass Sources with High Performance for Oxygen Reduction Reaction in Fuel Cells

The development of electrocatalysts with low or zero noble metal content is a key factor in the large-scale commercialization of fuel cells. Platinum and platinum alloys are the most efficient catalysts for the oxygen reduction reaction (ORR), which occurs in the cathode of the fuel cell. Nanocarbon materials doped with nitrogen (ex. carbon nanotubes and graphene) have been recognized as a promising alternative for the development of platinum-free electrocatalysts for the ORR. However, the synthesis of these carbon materials often involves the use of harmful organic reagents, synthesis´s extreme conditions, high costs and often are restricted to small scale production. Recently, the use of biomass as source of carbon and nitrogen has been explored to obtain metal-free electrocatalysts. The results reported in the literature indicate that biomass is a very promising alternative for obtaining of electrocatalysts of low-cost and highly efficient in the ORR. This work describes a two-step method for producing metal-free electrocatalysts from biomass. Two sources of biomass with high nitrogen content in their molecular structure were selected: sargassum and leather. First, each raw material was subjected to pyrolysis treatment at 700 C for 90 minutes under nitrogen, then an activation treatment was given with KOH in nitrogen at 750 C for 90 minutes. The materials were labeled as PAS and PAL for sargassum and leather respectively. The structural properties of the materials were analyzed by Raman spectroscopy and X-ray diffraction. To determine the morphology scanning electron microscope was used. The electrochemical performance was evaluated by rotating disk electrode technique (RDE). Raman spectra showed the D and G bands characteristic of carbon materials. This results indicate that after pyrolysis and activation treatments carbonaceous materials with high disorder in their molecular structure were obtained. BET analysis confirmed high surface areas (up to 2000 m2 g-1) and SEM showed the formation of larger porosity in the surface of the electrocatalysts from biomass. Finally, electrochemical characterization showed high activity for ORR in alkaline media for both electrocatalysts (PAL and PAS). The sample PAL has major current density than platinum electrocatalyst and very close on-set potential (shift 1145 mV). The results obtaining in this work indicate that electrocatalyst from biomass as sargassum and leather are a promising alternative for cathodic reaction in fuel cells.

Investigation of the Performance of PtCo/C Cathode Catalyst Layers for ORR Activity and Rated Power for Automotive Pemfcs

In order to simultaneously meet the automotive PEMFC targets of cost, performance and durability, Pt-alloys electrocatalysts are being intensively investigated.1,2,3 Pt-alloys show promise of higher ORR mass activities that will permit the use of lower Pt loadings (~0.1 mgPt/cm2) in the cathode catalyst layers. In this work we have studied several Pt-Co/C catalysts that exhibit mass activities that exceed the DOE target of 440 mA/mgPt at 0.90V, 80oC, 100% RH for ORR activity. The performance at rated power density of 1W/cm2 at 0.60V is more difficult to achieve at low loadings due to unanticipated transport resistances. In addition to carrying out ORR activity studies both in TF-RDE set-ups4,5 as well as in MEAs of subscale cells, we have also applied complementary diagnostics of wet and dry H2-Air curves, microscopy of catalyst powders and catalyst layer films, EIS and dilute oxygen limiting current studies6 on these materials. Rigorous base-lining was carried out to obtain the ORR activity of a commercial Pt/C catalyst in order to benchmark the Pt-Co/C catalysts under study using identical protocols.7,8 Although we easily achieve the mass activity targets at 0.90V, we only approach the rated power targets indicating that further understanding of the transport resistances at high current densities and low Pt loadings is necessary to identify and mitigate the losses. Acknowledgements: This work was funded through the DOE FC-PAD Consortium. References Mathias MF, Makharia R, Gasteiger HA, Conley JJ, Fuller TJ, Gittleman CJ, Kocha SS, Miller DP, Mittelsteadt CK, Xie T, Van SG. Two fuel cell cars in every garage. Electrochem. Soc. Interface. 2005;14(3):24-35. Gasteiger HA, Kocha SS, Sompalli B, Wagner FT. Activity benchmarks and requirements for Pt, Pt-alloy, and non-Pt oxygen reduction catalysts for PEMFCs. Applied Catalysis B: Environmental. 2005 Mar 10;56(1):9-35.Kongkanand A, Mathias MF. The Priority and Challenge of High-Power Performance of Low-Platinum Proton-Exchange Membrane Fuel Cells. The journal of physical chemistry letters. 2016 Mar 11;7:1127-37.Kocha SS, Zack JW, Alia SM, Neyerlin KC, Pivovar BS. Influence of ink composition on the electrochemical properties of Pt/C electrocatalysts. ECS Transactions. 2013 Mar 15;50(2):1475-85.Shinozaki K, Zack JW, Pylypenko S, Pivovar BS, Kocha SS. Oxygen Reduction Reaction Measurements on Platinum Electrocatalysts Utilizing Rotating Disk Electrode Technique II.Baker DR, Caulk DA, Neyerlin KC, Murphy MW. Measurement of oxygen transport resistance in PEM fuel cells by limiting current methods. Journal of The Electrochemical Society. 2009 Sep 1;156(9):B991-1003.Kocha SS. Principles of MEA Preparation in Handbook of Fuel Cells: Fundamentals, Technology, and Applications; Vol. 3, edited by W. Vielstich, A. Lamm, and HA Gasteiger. Ch.;43:538.Neyerlin KC, Gu W, Jorne J, Clark A, Gasteiger HA. Cathode catalyst utilization for the ORR in a PEMFC analytical model and experimental validation. Journal of The Electrochemical Society. 2007 Feb 1;154(2):B279-87.

Oxygen Reduction Reaction Activity and Durability for Model Pt Shell Layers on Ir(111) Prepared by Molecular Beam Epitaxy

We fabricated well-defined Pt–Ir bimetallic surfaces through monolayer-thick Pt epitaxial growth on Ir(111) substrates (Pt n ML/Ir(111):n = 1–4) using molecular beam epitaxy in ultrahigh vacuum (UHV). The surface structures of Pt n ML/Ir(111) were verified using reflection high-energy electron diffraction in UHV. Electrochemical characterization tests, including evaluations of oxygen reduction reaction (ORR) activity and durability, were performed using cyclic voltammetry and rotating disk electrode techniques in 0.1 M HClO4. Regarding the initial ORR activity for Pt n ML/Ir(111) surfaces, Pt2ML/Ir(111) surfaces exhibited the highest ORR activity (24 times that of the clean Pt(111) surfaces). Initial ORR activities declined when square-wave potential cycles (PCs) were applied between 0.6 and 1.0 V vs. reversible hydrogen electrode. The Pt4ML/Ir(111) surface exhibited the highest ORR activity even after 5000 PC loadings (6 times that of the clean Pt(111) surfaces), suggesting that Pt-shell/Ir-core core–shell nanoparticles have potential for use as practical Pt-based bimetallic ORR catalysts.

SAD–GLAD Pt–Ni@Ni Nanorods as Highly Active Oxygen Reduction Reaction Electrocatalysts

Vertically aligned catalysts comprised of platinum–nickel thin films on nickel nanorods (designated as Pt–Ni@Ni-NR) with varying ratios of Pt to Ni in the thin film were prepared by magnetron sputtering and evaluated for their oxygen reduction reaction (ORR) activity. A glancing angle deposition (GLAD) technique was used to fabricate the Ni nanorods (NRs) and a small angle deposition technique for growth of a thin conformal coating of Pt–Ni on the Ni-NRs. The Pt–Ni@Ni-NR structures were deposited on glassy carbon for evaluation of their ORR activity in an aqueous acidic electrolyte using the rotating disk electrode technique. The Pt–Ni@Ni-NR catalysts showed superior area-specific and mass activities for ORR compared to those of Pt–Ni alloy nanorod catalysts prepared using the GLAD technique and compared to those of conventional large-surface area Pt and Pt–Ni alloy nanoparticle catalysts.

Heterogeneous Electrocatalyst of Palladium-Cobalt-Phosphorus on Carbon Support for Oxygen Reduction Reaction in High Temperature Proton Exchange Membrane Fuel Cells.

Palladium-cobalt-phosphorus (PdCoP) catalysts supported on carbon (Ketjen Black) were investigated as a cathode catalyst for oxygen reduction reaction (ORR) in high temperature proton exchange membrane fuel cells (HT-PEMFCs). The PdCoP catalyst was synthesized via a modified polyol process in teflon-sealed reactor by microwave-heating. From X-ray diffraction and transmission electron microscopic analysis, the PdCoP catalyst exhibits a face-centered cubic structure, similar to palladium (Pd), which is attributed to form a good solid solution of Co atoms and P atoms in the Pd lattice. The PdCoP nanoparticles with average diameter of 2.3 nm were uniformly distributed on the carbon support. The electrochemical surface area (ECSA) and ORR activity of PdP, PdCo and PdCoP catalysts were measured using a rotating disk electrode technique with cyclic voltammetry and the linear sweep method. The PdCoP catalysts showed the highest performances for ECSA and ORR, which might be attributed both to formation of small nanoparticle by phosphorus atom and to change in lattice constant of Pd by cobalt atom. Furthermore, The HT-PEMFCs single cell performance employing PdCoP catalyst exhibited an enhanced cell performance compared to a single cell using the PdP and PdCo catalysts. This result indicates the importance of electric and geometric control of Pd alloy nanoparticles that can improve the catalytic activity. This synergistic combination of Co and P with Pd could provide the direction of development of non-Pt catalyst for fuel cell system.

Porous LaCo1-xNixO3-δ Nanostructures as an Efficient Electrocatalyst for Water Oxidation and for a Zinc-Air Battery.

Perovskites have emerged as promising earth-abundant alternatives to precious metals for catalyzing the oxygen evolution reaction (OER). Herein, we report the synthesis of a series of porous perovskite nanostructures, LaCo0.97O3-δ, with systematic Ni substitution in Co octahedral sites. Their electrocatalytic activity during the water oxidation reaction was studied in alkaline electrolytes. The electrocatalytic OER activity and stability of the perovskite nanostructure was evaluated using the rotating disk electrode technique. We show that the progressive replacement of Co by Ni in the LaCo0.97O3-δ perovskite structure greatly altered the electrocatalytic activity and that the La(Co0.71Ni0.25)0.96O3-δ composition exhibited the lowest OER overpotential of 324 and 265 mV at 10 mA cm(-2) in 0.1 M KOH and 1 M KOH, respectively. This value was much lower than that of the noble metal catalysts, IrO2, Ru/C, and Pt/C. Furthermore, the La(Co0.71Ni0.25)0.96O3-δ nanostructure showed outstanding electrode stability, with no observable decrease in performance up to 114th cycle in the auxiliary linear sweep voltammetry that lasted for 10 h in chronoamperometry studies. The excellent oxygen evolution activity of the La(Co0.71Ni0.25)0.96O3-δ perovskite nanostructure can be attributed to its intrinsic structure, interconnected particle arrangement, and unique redox characteristics. The enhanced intrinsic electrocatalytic activity of the La(Co0.71Ni0.25)0.96O3-δ catalyst was correlated with several parameters, such as the electrochemical surface area, the roughness factor, and the turnover frequency, with respect to variation in the transition metals of the perovskite structure. Subsequently, La(Co0.71Ni0.25)0.96O3-δ was utilized as the air cathode in a zinc-air battery application.

Oxygen Reduction at Carbon Nanotubes (CNTs)/Cobaltous Phthalocyanine (CoPc) and MFC Electricity Generation Affected by Air-Cathode Catalyst Layer Structure

Efficient oxygen reduction reaction (ORR) catalysts - cobaltous phthalocyanine (CoPc) composited with carbon nanotubes (CNTs) were prepared for stable and high power generation in microbial fuel cells (MFCs) treating wastewater. The ORR activities of CoPc composited with CNTs [Long Single-Walled (LSW), Short single-walled (SSW), long multi-walled (LMW) and short multi-walled (SMW)] were investigated and compared. The ORR on SMW-CNTs/CoPc proceeded in a combined 2e− and 4e− pathway, while the others followed a dominant 4e− pathway, supported by the rotating disk electrode techniques and X-ray photoelectron spectroscopy. Cathodes modified with MW-CNTs/CoPc exhibited higher catalytic activity, power output and more stable internal resistance than SW-CNTs/CoPc from CV and power generation results. The Nafion layer either sank into the catalyst composite (SMW-CNTs/CoPc) or spread over it (SSW-CNTs/CoPc), affects internal resistance and MFC performance. The study demonstrated the importance of cathodic catalyst and its surface morphology for higher power generation.

Micro Emulsion Synthesis of LaCoO3Nanoparticles and their Electrochemical Catalytic Activity

The micro emulsion method has been successfully used for preparing perovskite LaCoO3 with uniform, fine-shaped nanoparticles showing high activity as electro catalysts in oxygen reduction reactions (ORRs). They are, therefore, promising candidates for the air-cathode in metal-air rechargeable batteries. Since the activity of a catalyst is highly dependent on its specific surface area, nanoparticles of the perovskite catalyst are desirable for catalyzing both oxygen reduction and evolution reactions. Herein, LaCoO3 powder was also prepared by sol-gel method for comparison, with a broad particle distribution and high agglomeration. The electro catalytic properties of LaCoO3 and LaCoO3-carbon Super P mixture layers toward the ORR were studied comparatively using the rotating disk electrode technique in 0.1 M KOH electrolyte to elucidate the effect of carbon Super P. Koutecky-Levich theory was applied to acquire the overall electron transfer number (n) during the ORR, calculated to be ~3.74 for the LaCoO3-Super P mixture, quite close to the theoretical value (4.0), and ~2.7 for carbon-free LaCoO3. A synergistic effect toward the ORR is observed when carbon is present in the LaCoO3 layer. Carbon is assumed to be more than an additive, enhancing the electronic conductivity of the oxide catalyst. It is suggested that ORRs, catalyzed by the LaCoO3-Super P mixture, are dominated by a 2+2-electron transfer pathway to form the final, hydroxyl ion product.

Investigation of PtNi/C as methanol tolerant electrocatalyst for the oxygen reduction reaction

Platinum–nickel electrocatalysts prepared by a simple and cost-effective procedure have been investigated for the oxygen reduction reaction (ORR) in direct methanol fuel cells (DMFCs). The formic acid method was used to deposit well-dispersed PtxNiy nanoparticles (x:y=3:2) on the surface of a carbon black support (Ketjenblack). Carbothermal reduction of the as-prepared catalyst in an inert gas (Ar) at 900°C produced an alloy and a partial modification of the crystalline structure from the face centered cubic, typical of Pt, to a tetragonal structure of PtNi alloy. An acid leaching treatment was carried out to partially remove unalloyed surface nickel atoms in the outermost layers, leading to an enrichment of Pt concentration (x:y=2:1). Cyclic voltammetry analysis in acidic medium indicated a relatively high electrochemical active surface area (>70m2g−1) for both untreated and thermally treated PtxNiy catalysts. The activity towards the ORR was evaluated in half-cell configuration (0.5M H2SO4) using the rotating disk electrode technique. Similar behavior towards the ORR was found for the untreated and thermally treated PtNi/C catalysts, with an increase in activity compared to a commercial Pt/C catalyst. A remarkably better tolerance to methanol was observed for both PtNi/C cathode catalysts compared to the commercial Pt/C catalyst.

Preparation of Pt/C cathode catalyst supported on chestnut-like mesoporous carbon for fuel cell applications

Fuel cells have received worldwide attention as a next-generation renewable energy technology. However, catalyst cost and durability are the main issue hampering the commercialization of fuel cells. Many studies have focused on the physicochemical properties of the carbon support to improve the catalyst’s properties. Mesoporous carbons are suitable candidates because of their appropriate structural characteristics, including high surface area, large pore size, and regularly interconnected mesopores that permit efficient diffusion of the reactants and by-products. In this study, supports made from chestnut-like carbon consisting of platelet carbon nanofibers were fabricated by selective catalytic gasification of activated carbon. Pt/C catalysts were synthesized from these support structures using the impregnation method. Catalyst performance and characteristics were investigated by N2 adsorption/desorption isotherms, X-ray diffractions, and the rotating disk electrode technique for the oxygen reduction reaction.

Voltammetric monitoring of prostasome aggregation and self-fusion

We have demonstrated the applicability of cyclic voltammetry and rotating disk electrode techniques to study adsorption, aggregation, and self-fusion of prostasomes, nanoparticles present in human semen. Prior to the electrochemical experiments, we have characterized prostasomes through nanoparticle tracking analysis, dynamic light scattering, and zeta potential measurements at various pH. One of our main findings in this work has been the prostasome concentration in human semen, determined to be 4.8×1011cm−3, which is 20000 times higher than the sperm cell concentration. We have found the hydrodynamic diameter of the prostasome to range from 35 to 475nm, with the mean value of 151nm, in agreement with the literature. Then, we have adsorbed a monolayer of prostasomes at the surface of gold rotating disk electrode and studied its effect on the limiting diffusion current at the electrode. We have conducted our measurements in a standard three-electrode cell. We have described the monolayer effect in terms of the equivalent layer thickness of stagnant solution layer. Next, we have added a small amount of prostasomes to the three-electrode cell and decreased pH to 4.0 to allow their aggregation at the surface of rotating disk electrode. We have used the chronoamperometry method to monitor multilayer adsorption of the prostasome for 180min. Then, we have again characterized the adsorbed layer of prostasomes in terms of the equivalent layer thickness. Through a comparison of the equivalent layer thickness determined for the mono- and multilayer, we have found the amount of prostasomes adsorbed during chronoamperometry. We have also compared the number of prostasomes adsorbed at pH 4.0 with the number of prostasomes transported to the rotating disk electrode during this experiment. From that comparison, we have estimated the two-prostasome aggregation probability and the surface area fractions corresponding to the positive and negative surface charges of the prostasome. We believe that our results can be useful for better understanding of prostasome surface properties and, consequently, processes such as prostasome-sperm cell fusion or prostasome-bacterium interactions.

Electrocatalytic Activity and Stability of Ordered Intermetallic Palladium-Iron Nanoparticles toward Oxygen Reduction Reaction

The structurally ordered intermetallic Pd3Fe alloy nanoparticles supported on carbon (O-Pd3Fe/C) are prepared by the impregnation method and employed as the electrocatalyst for the oxygen reduction reaction (ORR). The physical properties of the Pd3Fe nanoparticles are characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. It is revealed that the O-Pd3Fe/C catalyst shows the super lattice characteristics of the long range ordering of Pd and Fe atoms, confirming the formation of ordered intermetallic phase with face centered cubic structure. The electrochemical properties are evaluated by cyclic voltammetry and rotating disc electrode techniques. The O-Pd3Fe/C catalyst exhibits the significantly improved durability, as well as the specific activity of 2.4 and 2.6 times that of the disordered Pd3Fe/C catalyst and Pd/C catalyst, respectively, at 0.8 V. The performance enhancement is attributed to the formation of ordered intermetallic phase, resulting in the optimal compressive lattice strain and the higher degree of alloying.

Nitrogen self-doped electrocatalysts synthesized by pyrolysis of commercial polymer fibers for oxygen reduction reaction

In this study, metal-free electrocatalysts were obtained from the pyrolysis of commercial Kevlar™ and Twaron™ carbon fibers (pKf and pTf, respectively). An easy and low cost synthesis method was developed. The obtained electrocatalysts have a significantly lower cost than conventional platinum based electrocatalysts. Synthesis of the electrocatalyst was made by pyrolysis treatment of the carbon fibers, under nitrogen atmosphere, followed by an activation treatment under carbon dioxide atmosphere. Properties and electrochemical performance of pyrolyzed (pKf, pTf) and activated (aKf and aTf) samples were compared. The electrocatalysts obtained have surface areas of up to 1000 m2/g after the activation treatment. Morphology and structural characteristics were studied by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Raman Spectroscopy and X-ray photoelectron spectroscopy (XPS). The electroactivity of these electrocatalysts was evaluated by the oxygen reduction reaction (ORR) in acid media by rotating disk electrode technique. Carbon fibers showed an improvement in the ORR after receiving the activation treatment.

Coordination compounds as the precursors for preparation of nanosized platinum or platinum-containing mixed-metal catalysts of oxygen reduction reaction

Nanosized mixed-metal platinum-iron, platinum-anganese and platinum-nickel catalysts supported on highly dispersed carbon black are synthesized by using the corresponding metal complexes with the atomic metal ratio of 1:1. The obtained catalysts are characterized by X-ray phase diffraction and scattering analysis, electron dispersion analysis, scanning and transmission electron microscopy. Thin film rotating disk electrode technique was used to study kinetic parameters of the oxygen reduction reaction at these catalysts. It has been demonstrated that electrochemical activity of the prepared catalysts is comparable to that of a commercial E-Tek platinum catalyst. The membrane electrode assembly (MEA) with the synthesized platinum-iron catalyst was tested in a laboratory hydrogen-air fuel cell setup at room temperature. It was shown that the power performance of this MEA was twice better than that of a MEA on the base of a commercial Pt/C E-Tek catalyst.

Different Carbide Derived Nanoporous Carbon Supports and Electroreduction of Oxygen

Using rotating disc electrode technique, the oxygen reduction reaction in 0.1M KOH was studied at various micromesoporous carbide derived carbon powders, synthesized from various binary metal carbides. The catalytic activity and mechanism noticeable depends on the hierarchical structure of the nanoporous carbon electrode. The activation with CO2 increases the differential volume of pores and proportion of mesopores in carbon matrix. It was shown that the partially graphitized carbon C(Mo2C) with a large number of edge plane sites has higher electrocatalytic activity toward oxygen reduction in alkaline media compared with other amorphous or partly graphitized carbons studied. The corresponding relative catalytic activity of catalysts increases in the following order: C(WTiC2) < Vulcan < C(TiC) < C(TiC)-A1 ≤ C(TiC)-A2 < C(Mo2C)-A < C(Mo2C).