Multi-electron Transfer Process Research Articles

Redox reactions of selenium as catalyzed by magnetite: Lessons learned from using electrochemistry and spectroscopic methods

Although previous studies have demonstrated redox transformations of selenium (Se) in the presence of Fe-bearing minerals, the specific mechanism of magnetite-mediated Se electron transfer reactions are poorly understood. In this study, the redox chemistry of Se on magnetite is investigated over an environmentally relevant range of Eh and pH conditions (+0.85 to −1.0V vs. Ag/AgCl; pH 4.0–9.5). Se redox peaks are found via cyclic voltammetry (CV) experiments at pH conditions of 4.0–8.0. A broad reduction peak centered at −0.5V represents a multi-electron transfer process involving the transformation of selenite to Se(0) and Se(−II) and the comproportionation reaction between Se(−II) and Se(IV). Upon anodic scans, the oxidation peak centered at −0.25V is observed and is attributed to the oxidation of Se(−II) to higher oxidation states. Deposited Se(0) may be oxidized at +0.2V when pH is below 7.0. Over a pH range of 4.0–8.0, the pH dependence of peak potentials is less pronounced than predicted from equilibrium redox potentials. This is attributed to pH gradients in the microporous media of the cavity where the rate of proton consumption by the selenite reduction is faster relative to mass transfer from the solution.In chronoamperometry measurements at potentials ⩾−0.6V, the current–time transients show good linearity between the current and time in a log–log scale. In contrast, deviation from the linear trend is observed at more negative potentials. Such a trend is indicative of Se(0) nucleation and growth on the magnetite surface, which can be theoretically explained by the progressive nucleation model. XPS analysis reveals the dominance of elemental selenium at potentials ⩽−0.5V, in good agreement with the peak assignment on the cyclic voltammograms and the nucleation kinetic results.

(Invited) Understanding the Chemistry of Photocatalytic Processes

Any enhancement of the efficiency of the utilization of photogenerated charge carriers on the surface of photocatalysts requires an enhanced understanding of the entire photocatalytic process. The reduction potentials of most substrates, as well as those of the intermediates formed during the photocatalytic reaction(s), are well known; nevertheless, it is essential to realize that thermodynamic properties may change upon the adsorption of these molecules at the photocatalyst surface. Therefore, a detailed understanding of the processes occurring on the photocatalyst surface before, during, and after light absorption is of utmost importance. On the other hand, the charge carriers generated upon light absorption that survive recombination and reach the semiconductor surface may suffer surface recombination processes or recombination via an electron shuttle mechanism (Z scheme deactivation mechanism), thus reducing the total efficiency of the photocatalytic system. Moreover, since the overall efficiency of a photocatalytic process will be determined by the efficiency of the slowest reaction step it is crucial to know whether this is the reductive or oxidative half-reactions. Besides the obvious one-electron transfer steps these reactions entail in particular multi-electron transfer processes, e.g. , the four-electron oxidation of water or the eight-electron reduction of CO2. Hence, this lecture provides some necessary tools for the understanding and the development of the photocatalytic reaction mechanism.

Unraveling a Single-Step Simultaneous Two-Electron Transfer Process from Semiconductor to Molecular Catalyst in a CoPy/CdS Hybrid System for Photocatalytic H2 Evolution under Strong Alkaline Conditions.

Electron transfer processes from semiconductor to molecular catalysts was studied in a model hybrid photocatalytic hydrogen evolution system composed of [Co((III))(dmgH)2PyCl] (CoPy) and CdS under different pH conditions. Thermodynamic and kinetic studies revealed that photocatalytic H2 evolution under high pH conditions (pH 13.5) can only account for the thermodynamically more favorable single-step simultaneous two-electron transfer from photoirradiated CdS to Co(III)Py to produce unavoidable intermediate Co(I)Py, rather than a two-step successive one-electron transfer process. This finding not only provides new insight into the charge transfer processes between semiconductors and molecular catalysts but also opens up a new avenue for the assembly and optimization of semiconductor-molecular catalyst hybrid systems processed through multielectron transfer processes.

In Situ 3D Imaging of Catalysis Induced Strain in Gold Nanoparticles

Multielectron transfer processes are crucially important in energy and biological science but require favorable catalysts to achieve fast kinetics. Nanostructuring catalysts can dramatically improve their properties, which can be difficult to understand due to strain- and size-dependent thermodynamics, the influence of defects, and substrate-dependent activities. Here, we report three-dimensional (3D) imaging of single gold nanoparticles during catalysis of ascorbic acid decomposition using Bragg coherent diffractive imaging (BCDI). Local strains were measured in single nanoparticles and modeled using reactive molecular dynamics (RMD) simulations and finite element analysis (FEA) simulations. RMD reveals the pathway for local strain generation in the gold lattice: chemisorption of hydroxyl ions. FEA reveals that the RMD results are transferable to the nanocrystal sizes studied in the experiment. Our study probes the strain-activity connection and opens a powerful avenue for theoretical and experimental studies of nanocrystal catalysis.

Study of distinctions in the synergistic effects between carbon nanotubes and different metal oxide nanoparticles on enhancing thermal oxidative stability of silicone rubber

In this work, the distinctions in the synergistic effects between carbon nanotubes (CNTs) and different metal oxide (MeO) nanoparticles on enhancing the thermal oxidative stability of silicone rubber (SR) were studied in depth. Specifically, three kinds of MeO nanoparticles were attached onto the surface of CNTs, obtaining Fe2O3–CNTs, TiO2–CNTs, and SnO2–CNTs, respectively. These MeO nanoparticles-attached CNTs were then separately embedded into SR matrix to investigate their effect on the thermal oxidative stability of SR. The results indicated that different synergies between CNTs and different metal oxides existed: both Fe2O3 and SnO2 had positive synergistic effects with CNTs, while a negative synergic effect existed between TiO2 and CNTs. This phenomenon may be attributed to the fact that the existence of CNTs could promote the radical-capture reactions to some extent for Fe and Sn element, while a reverse trend was found in TiO2–CNTs/SR. Meanwhile, all the performances of SnO2–CNTs/SR exhibited a much higher positive synergy than those of Fe2O3–CNTs/SR: the synergy percentages of the tear strength and elongation at break for SnO2–CNTs/SR were even above 100 %. This result may be ascribed to the combined effect of the multi-electron transfer process in SnO2–CNTs/SR and the restriction of crystalline form of Fe2O3 in Fe2O3–CNTs/SR during thermal aging.

Atomic Force Microscopy for Solar Fuels Research: An Introductory Review

Although research on solar fuel production via water oxidation, hydrogen evolution, and carbon dioxide reduction (i.e., artificial photosynthesis) has grown tremendously in recent years, practical solar fuel devices remain elusive. For these multi-electron transfer processes to take place efficiently, integrated systems constructed from materials with very different chemical, mechanical, and electrical properties are required. This complicated integration presents numerous challenges, including the need for increased characterization of material surfaces and interfaces for both fundamental studies and device optimization. Atomic force microscopy (AFM) is a powerful tool for surface and interface analysis. Although solar fuel research has frequently utilized the basic AFM function of topographic mapping for routine surface analysis, some researchers have avoided more advanced AFM methodologies due to the complexity of these integrated solar fuel generating systems. This article provides researchers in this area with an introduction to various advanced AFM techniques for mechanical, electrical, and chemical analysis on the nanoscale. It also discusses the possibility of in situ study while providing an outline of the working principles of different AFM application modes.

ChemInform Abstract: Metal—Metal Multiple Bonding in C3‐Symmetric Bimetallic Complexes of the First Row Transition Metals

AbstractReview: 101 refs.

Enhanced Visible-Light Photoactivity of CuWO4 through a Surface-Deposited CuO

Several papers have shown that CuWO4 is active under visible light for water oxidation at an applied potential bias and for organic degradation in an aerated aqueous suspension. In this work, we report that the observed reduction of O2 on the irradiated CuWO4 is a multielectron transfer process with the formation of H2O2. More importantly, the surface modification of CuWO4 with 1.8 wt % of CuO can increase the activity by approximately 9 times under UV light and by 5 times under visible light, for phenol degradation in aerated aqueous suspension. The catalyst was prepared by a hydrothermal reaction between Cu(NO3)2 and Na2WO4, followed by thermal treatment at 773 K. High-resolution transmission electron microscopy revealed that triclinic CuWO4 (40 nm) was covered by monoclinic CuO (4 nm). Through a combination of photo- and electrochemical measurement, a plausible mechanism responsible for the activity enhancement is proposed, involving an interfacial electron transfer from CuO to CuWO4 and an interfacial...

Effects of Chloride on the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) represents perhaps the best studied redox process in electrocatalysis because of its key role in fuel cells1 and, more recently, metal-air batteries2. As is well known, the problems associated with improving the performance of low and intermediate temperature fuel cells are associated with the lack of suitable catalysts that can reduce the overpotential for the ORR. This multi-electron transfer process has been found to be highly sensitive not only to the detailed electrocatalyst microstructure, but also to the presence of adsorbed species on the surface. Particularly significant are the deleterious effects derived from the adsorption of trace amounts of ionic3,4 and molecular species5. In particular, trace amounts of halides can poison the four-electron reduction of dioxygen, promoting instead, the two-electron reduction to peroxide. This work describes a new approach toward investigating the effect of adsorbed chloride on the ORR on polycrystalline Pt in 0.1 M HClO4 using a rotating ring-disk electrode coupled with transient techniques. EXPERIMENTALMeasurements were performed in a conventional all-glass, three-compartment electrochemical cell with a rotating Pt ring- Pt disk electrode, Pt|Pt RRDE, (Pine Instruments, (A = 0.164 cm2) using a bipotentiostat (Pine Instruments). A Pt foil and a reversible hydrogen electrode in the same solution (RHE) were used as counter and reference electrodes, respectively. Oxygen reduction polarization curves were recorded in oxygen saturated 0.1 M HClO4.RESULTS AND DISCUSSIONShown in the top panel, Fig.1 are polarization curves recorded at a scan rate, ν = 20 mV/s for a Pt disk electrode in oxygen saturated 0.1 M HClO4in the absence (black curve) and in the presence of 20 μM (red curve) and 100 μM NaCl (blue curve). The corresponding currents, measured with the ring polarized at a potential positive enough to detect hydrogen peroxide oxidation under diffusion limited conditions (ca. 1.2 V) are shown in the bottom panel in this figure. As evident from these results, the presence of chloride in the electrolyte leads not only to a significant shift in the onset of oxygen reduction, but also to the generation of hydrogen peroxide. Particularly interesting is the peak-like feature observed in the ring current as a function of the disk potential. Correlations between the chloride coverage and the ORR rate were sought by implementing a method in which the potential was stepped from 0.05 V, a value at which there is no chloride adsorption, to various more positive potentials where chloride adsorption is known to ensue in solutions devoid of oxygen. The results of these experiments, shown in Panel A, Fig. 2, indicate that for certain potentials, the current attains a limiting value associated with the diffusion controlled adsorption of chloride and later decays down to zero signaling that the equilibrium coverage at that potential was reached. Additional insight into this phenomenon was obtained from theoretical simulations performed within the COMSOL platform by coupling the convective diffusion equation with the surface dynamics for the adsorption|desorption process. This strategy yielded transient curves (see Panel B, Fig. 2) which strongly resemble those found experimentally. Efforts are now underway to explore whether a more detailed analysis of the curves will afford reliable values of the kinetic parameters involved.ACKNOWLEDGEMENTSThis work was supported by a grant from NSF.REFERENCES1. J. Zhang, Frontiers in Energy, 5, 137, 2011.2. Wang, Z.-L.; Xu, D.; Xu, J.-J.; Zhang, X.-B., Chem. Soc. Rev. 2014. 3. N. M. Markovic, H. A. Gasteiger, B. N. Grgur, and P. N. Ross, J. Electroanal.Chem., 467, 157, 1999.4. T. J. Schmidt, U. A. Paulus, H. A. Gasteiger, and R. J. Behm, J. Electroanal. Chem., 508, 41, 2001.5. N. M. Markovic, R. R. Adzic, B. D. Cahan, and E. B. Yeager, J. Electroanal.Chem., 377, 249, 1994. Figure Captions: Fig. 1. Polarization curves recorded at a scan rate, ν = 20 mV/s for a Pt disk electrode in oxygen saturated 0.1 M HClO4 in the absence (black) and in the presence of 20 μM (red) or 100 μM (blue) NaCl. The corresponding ring currents recorded when the ring was polarized at Ering= 1.2 V are shown in the lower panel. Fig. 2. Panel A: Chronoamperometric curves recorded in 0.1 M HClO4 with 20μM NaCl at a rotation rate of ɷ= 400 rpm starting from Eini=0.05 V to the various final potentials as indicated in the legend. Panel B : Simulated currents for kads/kdes =106/M, 900 rpm, C0=.1mM, Γmax=2x10-9mol/cm2 and for various values for the adsorption rate (legend). Limiting current is consistent with Levich equation.

Trapped in Imidazole: How to Accumulate Multiple Photoelectrons on a Black‐Absorbing Ruthenium Complex

Ruthenium dyes incorporating a 4H-imidazole chromophore as a ligand exhibit a spectrally broad absorption in the UV/Vis region. Furthermore, they show the ability to store two electrons within the 4H-imidazole ligand. These features render them promising molecular systems, for example, as inter- or intramolecular electron relays. To optimize the structures with respect to their electron-storage capability, it is crucial to understand the impact of structural changes accompanying photoinduced charge transfer in the electronic intermediates of multistep electron-transfer processes. The photophysical properties of these (reactive) intermediates might impact the function of the molecular systems quite substantially. However, the spectroscopic study of short-lived intermediates in stepwise multielectron-transfer processes is experimentally challenging. To this end, this contribution reports on the electrochemical generation of anions identical to intermediate structures and their spectroscopic characterization by in situ resonance Raman and UV/Vis spectroelectrochemistry and computational methods. Thereby, an efficient two-electron pathway to the 4H-imidazole electron-accepting ligand is identified.

Metal–metal multiple bonding in C3-symmetric bimetallic complexes of the first row transition metals

Metal-metal multiple bonds have been an intense area of focus in inorganic chemistry for many decades as a result of their fundamentally interesting bonding properties, as well as their potential applications in multielectron transfer and small molecule activation processes. Much of what is known in this field revolves around 2nd and 3rd row transition metals, with fundamental knowledge lacking in the area of bonds between elements of the first transition series. The smaller size and tendency of first row ions to adopt high-spin electron configurations weaken metal-metal interactions and serve to complicate the interpretation of the electronic structure and bonding in bimetallic species containing first row transition metals. Furthermore, traditional tetragonal "paddlewheel" complexes dominate the metal-metal multiple bond literature, and only recently have researchers begun to take advantage of the weaker ligand field in three-fold symmetric bimetallic complexes to encourage more favourable metal-metal bonding interactions. In the past 5 years, several research groups have exploited three-fold symmetric frameworks to investigate new trends in metal-metal bonding involving the first row transition metals. This feature article serves to highlight recent achievements in this area and to use C3-symmetric systems as a model to better understand the fundamental aspects of multiple bonds featuring first row transition metals.

A water-soluble tin(iv) porphyrin as a bioinspired photosensitiser for light-driven proton-reduction

The water-soluble tin(IV) porphyrin dichlorido-5,10,15,20-tetrakis(p-carboxyphenyl)-porphyrinato-tin(IV) (SnTPPC, 1) was synthesised as a mimic of biological chlorophyll photosensitisers. In natural photosynthesis, chlorophyll pigments start the multi-electron transfer processes resulting in water-oxidation and NADP(+)-reduction. The photochemical properties of compound 1 were characterised by measuring absorption and fluorescence spectra. Electrochemical measurements in water revealed well-suited redox potentials of 1 for both proton-reduction to H2 as well as water-oxidation to O2. The tin(IV) porphyrin was then used as a photosensitiser in model systems for light-induced proton-reduction in aqueous solution, where an optimization of the experimental conditions was carried out to achieve reaction rates comparable to those found for [Ru(bipy)3](2+), a standard dye in artificial photosynthesis. By employing UV/Vis-spectroelectrochemistry, we found that the porphyrin ligand of 1 is redox non-innocent in water. A complex set of reduction reactions of the porphyrin macrocycle occurs during photocatalytic experiments involving the ligand's chlorin form as a key intermediate. On the basis of these results, a potential reaction sequence for light-driven H2-formation is formulated, where the reductive quenching of 1 forms the initial reaction step and reduced forms of 1 serve as hydride transfer agents to the H2 evolution catalyst. The spectroscopic, electrochemical and catalytic properties of SnTPPC make this compound class an attractive, affordable and easily accessible choice for photosensitisers in artificial photosynthetic systems. Finally, the detected complicated redox reactions of the porphyrin ring in water offer a possible explanation of why the chlorophylls of P680 or P700 are carefully wrapped in a water-free part of the PSII and PSI proteins.

Catalytic Oxidation of Methanol by Aqueous POM on Al2O3 Supported Catalysts and Electrochemical Performance of POM

AbstractPhosphomolybdic acid (H3PMo12O40, POM) was attempted to be used as the energy‐storage agent in this paper to avoid some problems of the direct methanol fuel cell (DMFC), such as catalyst poisoning and methanol permeation. Catalytic oxidation of methanol by aqueous POM on Al2O3 supported catalysts with Pt and Ru active metal was evaluated in the presence of liquid water. The process takes advantage of the high catalytic activities of platinum for methanol oxidation. The effects of temperature, reaction time, and methanol concentration on activity were observed. The catalytic activity of Pt/Al2O3 is better than that of Ru/Al2O3 for the oxidation of methanol by POM. The methanol conversion rate reached 93.55% on the Pt/Al2O3 at 80 °C after reaction for 1 h. The electrochemical experiments indicate that POM shows a larger current density in redox processes on an Au electrode than methanol. The redox process of reduced POM is a reversible multi‐electron transfer process.

확산모델을 이용한 다중전자 전극반응에 대한 순환전위법의 전산모델링

본 연구에서는 전기화학계에서 중요한 다중전자의 이동이 수반되는 전극 반응에 대하여 순환전위법의 특성곡선을 모델링하여, MATLAB 프로그램으로 구현하였다. 전극주변의 전기화학 물질전달계에 대하여 반무한 확산모델의 경계조건을 설정하였고, Fick의 농도방정식은 유한차분법으로 전개하여 수치해를 구하였고, Butler-Volmer 식으로부터 계산된 농도값을 전류의 값으로 전환하였다. 본 연구에서 구현된 수치해는 기존의 실험치들과 합리적으로 설명하고 있었으며, 이를 근거로 다중전자 전기화학 반응계에서 반응메카니즘에 대한 전극반응속도 상수와 CV 주사속도 영향을 효과적으로 해석할 수 있었다. Here is implemented MATLAB program to analyze the characteristic curves of cyclic voltammetry which involves the multi-electron electrode reaction considered as key processes in electrochemical systems. For the electrochemical mass-transfer system, Fick's concentration equation subject to semi-infinite diffusion model for the boundary condition was discretized and solved by the explicit finite difference method. The resulting concentration values were converted into currents at each node by using Butler-Volmer equation. Based on the good agreement between the present numerical solution and the existing experimental results, effects of kinetic constants and CV scan rates on the reaction mechanism in multi-electron transfer processes were investigated effectively.

Analytical Solutions for the Study of Multielectron Transfer Processes by Staircase, Cyclic, and Differential Voltammetries at Disc Microelectrodes

Key processes in (bio)electrochemistry involve multiple electron transfers. The study of the stability of the different oxidation states and the interaction between redox centers is fundamental to understand these processes. In this paper, simple analytical equations are presented for multielectron transfer processes in cyclic voltammetry (CV) and staircase cyclic voltammetry (SCV) at disc electrodes of any size. This provides a simple simulation method for the electrochemical response without demanding computing. The use of CV and SCV, and the corresponding differential techniques, for the characterization of these redox systems is analyzed. Procedures and criteria are given for transient and stationary conditions. The theoretical results are applied to the experimental study of the reduction of anthraquinone-2-sulfonate in water on gold macro- and microdisc electrodes.

Voltammetry of multi-electron electrode processes of organic species

Classically the analysis of the voltammetric response of multi-electron transfer processes is achieved through the use of the Randles–Ševčík equations based on analytical theory. In such it is assumed that the after the ‘rate determining step’ all electron transfers are highly driven. Conversely, it is commonly found experimentally that the formal potentials for different electrochemical steps (1,2,3… ) are found to be at comparable potentials (i.e. Ef,1θ∼Ef,2θ∼Ef,3θ); this leads to significant deviations from the Randles–Ševčík analysis. This article highlights various ‘simple’ electrochemical mechanisms (EE, EC, EEC) and discusses how the voltammetric peak height resulting from linear sweep voltammetry is expected to vary with scan rate and other parameters, with the aim of providing a general theoretical basis upon which analysis of complex voltammetric systems may be approached and understood.

An X-ray Absorption Spectroscopy Study of the Cathodic Discharge of Ag2VO2PO4: Geometric and Electronic Structure Characterization of Intermediate phases and Mechanistic Insights

Bimetallic phosphorus oxides have emerged as attractive candidates for use as cathode materials in the next generation of lithium-based batteries owing to the operation of multielectron transfer processes and thermochemical stabilities conferred by the incorporation of phosphate groups. In particular silver vanadium phosphorus oxide, Ag2VO2PO4, shows a much desired in situ conductivity enhancement upon discharge resulting in inherently high power capability with minimal conductive additives needed. However, the amorphization of Ag2VO2PO4 during electrochemical discharge precludes the use of standard diffraction tools to monitor changes in the local electronic and geometric structure. Here, we have utilized a combination of V K-, V L-, Ag K-, and O K-edge X-ray absorption fine structure spectroscopy to determine the local vanadium and silver oxidation states, local coordination geometry, and stoichiometry for Ag2VO2PO4 samples with varying extents of electrochemical lithiation. Soft X-ray V L- and O K-edge measurements provide a detailed orbital-specific picture of changes in vanadium electronic structure upon discharge.

Kinetic and Mechanistic Investigations of Multielectron Transfer Reactions Induced by Stored Electrons in TiO2 Nanoparticles: A Stopped Flow Study

The kinetics and the mechanism of various multielectron transfer reactions initiated by stored electrons in TiO(2) nanoparticles have been investigated employing the stopped flow technique. Moreover, the optical properties of the stored electrons in the TiO(2) nanoparticles have been studied in detail following the UV (A) photolysis of deaerated aqueous suspensions of TiO(2) nanoparticles in the presence of methanol. The reduction of common electron acceptors that are often present in photocatalytic systems such as O(2), H(2)O(2), and NO(3)(-) has been investigated. The experimental results clearly show that the stored electrons reduce O(2) and H(2)O(2) to water by multielectron transfer processes. Moreover, NO(3)(-) is reduced via the transfer of eight electrons evincing the formation of ammonia. On the other hand, the reduction of toxic metal ions, such as Cu(II), has been studied mixing their respective anoxic aqueous solutions with those containing the electrons stored in the TiO(2) particles. A two-electron transfer is found to occur, indicating the reduction of the copper metal ion into its non toxic metallic form. Other metal ions, such as Zn(II) and Mn(II), could not be reduced by TiO(2) electrons, which is readily explained on the bases of their respective redox potentials. The underlying reaction mechanisms are discussed in detail.

Evaluation of RuxWySez Catalyst as a Cathode Electrode in a Polymer Electrolyte Membrane Fuel Cell

AbstractThe oxygen reduction reaction (ORR) on RuxWySez is of great importance in the development of a novel cathode electrode in a polymer electrolyte membrane fuel cell (PEMFC) technology. The RuxWySez electrocatalyst was synthesised in an organic solvent for 3 h. The powder was characterised by transmission electron microscopy (TEM), and powder X‐ray diffraction (XRD). The electrocatalyst consisted of agglomerates of nanometric size (∼50–150 nm) particles. In the electrochemical studies, rotating disc electrode (RDE) and rotating ring‐disc electrode (RRDE) techniques were used to determine the oxygen reduction kinetics in 0.5 M H2SO4. The kinetic studies include the determination of Tafel slope (112 mV dec–1), exchange current density at 25 °C (1.48 × 10–4 mA cm–2) and the apparent activation energy of the oxygen reaction (52.1 � 0.4 kJ mol–1). Analysis of the data shows a multi‐electron charge transfer process to water formation, with 2% H2O2 production. A single PEMFC with the RuxWySez cathode catalysts generated a power density of 180 mW cm–2. Performance achieved with a loading of 1.4 mg cm–2 of a 40 wt% RuxWySez and 60 wt% carbon Vulcan (i.e. 0.56 mg cm–2 of pure RuxWySez). Single PEMFC working was obtained with hydrogen and oxygen at 80 °C with 30 psi.

Synthesis and characterization of Pd 0.5Ni xSe (0.5− x) electrocatalysts for oxygen reduction reaction in acid media

Pd 0.5Ni x Se (0.5− x) electrocatalysts with different chemical composition, X = 0.25, 0.35, 0.45, were synthesized by a NaBH 4 reduction of PdCl 2, NiCl 2 and SeO in a THF solution and evaluated for the oxygen reduction reaction (ORR) in acid media by electrochemical techniques of rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE). The electrocatalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and CO adsorption/stripping. The relation of Se to Ni in the samples has a profound effect on the nature of the cathode catalytic activity toward the oxygen reduction process, enhanced as the Se content in the electrocatalysts was reduced. Electrochemical results show that the ORR takes place by a multi-electron charge transfer process (n = 4e −) with the formation of less than 1% of hydrogen peroxide. The enhanced activity was attributed to the high active surface area deduced from CO adsorption/stripping analysis. The research activities are reported within the focus on the activity-stability of the bimetallic chalcogenides electrocatalysts.