Oxygen Reduction In Alkaline Solution Research Articles

Characterization of Pulse Plated Ni and NiZn Alloys

Nickel, zinc and nickel-rich NiZn alloys were formed on platinum by galvanostatic pulse plating from aqueous sulfate baths. The alloys were formed in three steps, first in anomalous deposition by a current pulse, secondly by dissolution and oxidation during the open circuit potential in each cycle and finally by anodic stripping of the fully plated sample. The treatment leaves a stable phase with an alloy composition of Ni0.8Zn0.2. The potential-time curves during the plating procedure were used to qualitatively describe the nucleation and growth processes. For Zn a fully covered surface was obtained after one pulse while for Ni and NiZn three-dimensional clusters were obtained in the first pulse. Further growth of these layers involves nucleation on the substrate and deposited clusters. The films were characterized with optical microscopy, SEM/EDX, AFM, XPS, TEM and by electrochemical methods. XPS revealed that the surfaces become gently oxidized by the stripping in the plating solution. For Ni a bi-layer of NiO/Ni(OH)2 was found on the surface while for NiZn mainly the hydroxide was detected. The electrocatalytic properties of the layers toward oxygen reduction in alkaline solution were explored and the NiZn alloy was proven to be an excellent catalyst for hydrogen peroxide production.

Tungsten carbide promoted Au–Pd–Pt as methanol-tolerant electrocatalysts for oxygen reduction reaction

Au–Pd–Pt nanotrimetallic particles supported on nanocrystaline tungsten carbide as a cathodic electrocatalyst for oxygen reduction reaction (ORR) were prepared by an intermittent microwave heating (IMH) method. XRD measurement revealed that Au–Pd–Pt alloy formed during the IMH process. These novel electrocatalysts could offer the activities which surpass that of the state-of-the-art Pt-based electrocatalysts for oxygen reduction reaction. The AuPdPt-WC/C electrocatalyst showed better performance for oxygen reduction in alkaline solution than that of Pt/C catalyst. The results revealed that an over 90 mV shift towards more positive potentials compared to Pt/C electrode for ORR. The methanol tolerance and selectivity of the AuPdPt-WC/C electrocatalyst are favourable for the ORR in the presence of methanol which makes it a promising cathodic electrocatalyst in direct methanol fuel cells (DMFCs). The ORR is hardly affected in the methanol-containing solutions up to 1·0 mol L−1 methanol. The advantage seemed to come from the novel support of tungsten carbide which itself has the catalytic activity to enhance the catalytic activity of the metal electrocatalysts.

Comparative study of CoFeNx/C catalyst obtained by pyrolysis of hemin and cobalt porphyrin for catalytic oxygen reduction in alkaline and acidic electrolytes

Comparative studies of the oxygen reduction kinetics and mechanisms of CoFeNx/C catalysts have been conducted with rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) in aqueous acid and alkaline solutions, as well as acidic and alkaline polymer electrolytes. The CoFeNx/C catalysts in this study were obtained by the pyrolysis of hemin and a cobalt porphyrin. In an alkaline electrolyte, a larger electron transfer coefficient (0.63) was obtained in comparison to that in an acidic electrolyte (0.44), signifying a lower free energy barrier for oxygen reduction. The kinetic rate constant (2.69 × 10−2 cm s−1) for catalytic oxygen reduction in alkaline solution at 0.6 V (versus RHE) is almost 4 times larger than that in acidic solution (7.3 × 10−3 cm s−1). A synergetic catalytic mechanism is proposed. The overall reduction is a 4-electron reduction of oxygen. The obtained CoFeNx/C catalyst was further evaluated as a cathode catalyst in single fuel cells with acidic, neutral and alkaline electrolyte membranes. The order of the single cell performances either for power density or for stability is acidic > neutral > alkaline. The different behaviors of the CoFeNx/C catalyst in half cell and single cell are discussed.

Synthesis and electrocatalytic activity of highly porous hollow palladium nanoshells for oxygen reduction in alkaline solution

A series of hollow Pd nanoshells are prepared by employing Co nanoparticles as sacrificial templates with different concentrations of a Pd precursor (1, 6, 12, 20, and 40 mM K2PdCl4), denoted hPd-X (X: concentration of K2PdCl4 in mM unit). The synthesized hPd series are tested as a cathodic electrocatalyst for oxygen reduction reaction (ORR) in alkaline solution. The morphology and surface area of the hPd catalysts are characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and cyclic voltammetry (CV). Rotating disk electrode (RDE) voltammetric studies show that the hPd-20 (prepared using 20 mM K2PdCl4) has the highest ORR activity among all the hPd series, while being comparable to commercial Pd and Pt catalysts (E-TEK). The more facilitated ORR at hPd-20 is presumably induced by the enhanced Pd surface area and efficiently high porosity of Pd nanoshells.

Nitrogen-doped graphene as catalysts and catalyst supports for oxygen reduction in both acidic and alkaline solutions

Solving slow kinetics of oxygen reduction reaction is critically important for the development of hydrogen fuel cells and direct methanol/ethanol fuel cells. In this study, graphene and nitrogen (N)-doped graphene were synthesized by a solvothermal method and investigated as catalysts as well as catalyst supports for oxygen reduction reactions. In comparison to graphene, N-doped graphene demonstrated higher electrocatalytic activity in both acidic and alkaline solutions. N-doped graphene can act directly as a catalyst to facilitate four-electron oxygen reductions in alkaline solution and two-electron reductions in acidic solution. On the other hand, when used as catalyst supports for Pt and Pt–Ru nanoparticles, N-doped graphene can contribute to four-electron oxygen reductions in acidic solution, yet demonstrate much slower reaction kinetics in alkaline solution. Our findings conclude that N-doped graphene can be developed as an efficient catalyst for oxygen reductions to replace the use of precious Pt catalysts in alkaline solution but not in acidic solution.

Effect of carbon nanofiber surface functional groups on oxygen reduction in alkaline solution

Carbon nanofibers (CNFs) with different content of surface functional groups which are carboxyl groups (CNF–OX), carbonyl groups (CNF–CO) and hydroxyl groups (CNF–OH) and nitrogen-containing groups (CNF–ON) are synthesized, and their electrocatalytic activities toward oxygen reduction reaction (ORR) in alkaline solution are investigated. The result of X-ray photoelectron spectroscopy (XPS) characterization indicates that a higher concentration of carboxyl groups, carbonyl groups and hydroxyl groups are imported onto the CNF–OX, CNF–CO and CNF–OH, respectively. Cyclic voltammetry shows that both the oxygen- and nitrogen-containing groups can improve the electrocatalytic activity of CNFs for ORR. The CNF–ON/GC electrode, which has nitrogen-containing groups, exhibits the highest current density of ORR. Rotating disk electrode (RDE) characterization shows that the oxygen reduction on CNF–ON/GC electrode proceeds almost entirely through the four-electron reduction pathway, the CNF–OX/GC, CNF–CO/GC and CNF–OH/GC electrodes proceed a two-electron reduction pathway at low potentials (−0.2 V to −0.6 V) followed by a gradual four-electron reduction pathway at more negative potentials, while the untreated carbon nanofiber (CNF–P/GC) electrode proceeds predominantly by a two-electron reduction pathway within the whole range of potential studied.

TiO2@carbon Core-Shell Nanostructure Electrodes for Improved Electrochemical Properties in Alkaline Solution

We report nanostructure electrodes with <TEX>$TiO_2$</TEX> as a core and carbon as a shell (<TEX>$TiO_2$</TEX>@C) for oxygen reduction in alkaline solution. The structure of core-shell electrodes is characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction method, and X-ray photoelectron microscopy. The electrochemical properties of the <TEX>$TiO_2$</TEX>@C electrodes are characterized using a potentiostat and compared with those of carbon supported Pt catalyst. In particular, the core-shell electrode with dominant pyridinic-N component exhibits an imporved electrocatalytic activity for oxygen reduction reaction in alkaline solution.

High Active Hollow Nitrogen‐Doped Carbon Microspheres for Oxygen Reduction in Alkaline Media

AbstractDopamine, a sustainable and cheap raw material, was selected as the carbon and nitrogen sources to synthesize hollow nitrogen‐doped carbon microspheres (HNCMS). The obtained HNCMS were used as a non‐noble‐metal electrocatalyst for oxygen reduction in alkaline solution and show high electrocatalytic activity, excellent long‐term stability, and tolerance to crossover effect of methanol.

Thin-film flooded agglomerate model for silver-based oxygen depolarized cathodes

A mathematical model for a porous, silver-based electrode for the oxygen reduction in alkaline solutions, based on the thin film flooded agglomerate theory, was developed. These electrodes are employed in the energy-efficient chlor-alkali electrolysis with oxygen depolarized cathodes. The model parameters were determined from overpotentials at different oxygen concentrations obtained in half-cell measurements. For the description of the reaction kinetics, it was necessary to introduce two Tafel equations, which might be explained by a change of the adsorption isotherm of the intermediate species during oxygen reduction. The model allows for a successful description of the overpotentials in the region of industrially relevant current densities. The analysis of the oxygen concentration distribution in the liquid electrolyte reveals that massive diffusion limitations occur although the calculated size of the agglomerates is only in the range of a few micrometers.

Combined platinum/perovskite catalyst for an efficient nanostructured air electrode

This work shows the stepwise improvement of air electrodes by the right combination of catalysts. In all electrodes carbon nanotubes serve as carbon support. The electrodes are produced by ultrasonic mixing of the carbon nanotubes and the catalysts. Their catalytic activity towards oxygen reduction in alkaline solution is evaluated by polarisation curves and electrochemical impedance spectroscopy. In a first step La 1− x Sr x MnO 3 perovskites are investigated, as well as La 0.65Sr 0.35MnO 3 and La 0.6Sr 0.4CoO 3 are compared. It is found that La 0.65Sr 0.35MnO 3 and La 0.6Sr 0.4CoO 3 have a positive impact on different parts of the current–potential curve. In a second step the influence of small amounts of platinum as an additional catalyst besides the perovskite is analyzed with the result that platinum lowers significantly the activation polarisation. Finally, the optimum composition of the electrode is found by using the synergetic effect of platinum, La 0.65Sr 0.35MnO 3 and La 0.6Sr 0.4CoO 3.

Electrochemical reduction of oxygen on double-walled carbon nanotube modified glassy carbon electrodes in acid and alkaline solutions

The oxygen reduction reaction has been investigated on double-walled carbon nanotube (DWCNT) modified glassy carbon (GC) electrodes in acid and alkaline media using the rotating disk electrode (RDE) method. The surface morphology and composition of DWCNT samples was examined by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Aqueous suspensions of DWCNTs were prepared using Nafion and non-ionic surfactant Triton X-100 as dispersing agents. The RDE results indicated that the DWCNT modified GC electrodes are active catalysts for oxygen reduction in alkaline solution. In acid media DWCNT/GC electrodes possess poor electrocatalytic properties for O 2 reduction which indicates lack of metal catalyst impurities in the DWCNT material studied. The oxygen reduction behaviour of DWCNTs was similar to that of multi-walled carbon nanotubes (MWCNTs) observed in our previous studies.

Study of LaCoO 3 as a cathode catalyst for a membraneless direct borohydride fuel cell

In this paper, the perovskite-type oxide LaCoO 3 was studied as a cathode catalyst for use in a direct borohydride fuel cell (DBFC). The experimental results demonstrated that the LaCoO 3-catalysed cathode not only shows good electrocatalytic activity for oxygen reduction in alkaline solutions, but also shows good resistance to poisoning from BH 4 − ions originating from the fuel during discharge performance. Based on this new type of catalyst, a membraneless fuel cell was designed with a hydrogen storage alloy used as the anode catalyst. The maximal current density of 220 mA cm −2 and power density of 65 mW cm −2 were obtained at ambient conditions.

Electrochemical characterisation of air electrodes based on La 0.6Sr 0.4CoO 3 and carbon nanotubes

The efficiency of fuel cells suffers from the high activation polarisation at the cathode, where the oxygen reduction reaction takes place. In order to improve the performance, air electrodes composed of carbon nanotubes (CNTs) and the perovskite La 0.6Sr 0.4CoO 3 are produced by two different methods and investigated. In the first method CNTs are directly grown on the perovskite and in the second method CNTs and perovskite are combined by ultrasonic mixing. Their catalytic activity towards oxygen reduction in alkaline solution is evaluated by polarisation curves and electrochemical impedance spectroscopy. Best performance shows the electrode composed of 25 wt% CNTs, 55 wt% La 0.6Sr 0.4CoO 3 and 20 wt% PTFE as binder, produced by ultrasonic mixing. The Nyquist plot of this electrode displays two potential-dependent semi-circles, accounting for processes on the catalyst surface and for processes depending on the morphology of the electrode.

Peroxide Elimination Activity of Heat-Treated Transition Metal Hexacyanoferrate Catalysts for Oxygen Reduction in Alkaline Solution

Nonprecious metal catalysts for oxygen reduction were prepared by heat-treating transition metal (Mn, Fe, Co, Ni, Cu, and Zn) hexacyanoferrate precursors (Prussian blue analogs) dispersed on carbon black under a nitrogen atmosphere. Polarization measurements for oxygen reduction on the prepared catalysts were carried out with a gas-diffusion electrode floating on the surface of alkaline solution under a stream of oxygen. The catalytic activity toward decomposition of peroxide generated during oxygen reduction at the gas-diffusion electrode was examined in situ by monitoring the open-circuit potential recovery after interruption of steady-state cathodic current. The catalytic activity for oxygen reduction on the carbon-based electrode was well correlated with the activity toward peroxide decomposition. A linear relation between the electrode potential at constant current and the logarithm of the peroxide decomposition rate constant was observed. Among the catalysts consisting of several combinations of 3d transition elements, the catalysts containing cobalt or copper with iron exhibited high operation potential of the electrode, and the catalysts containing copper or zinc with iron exhibited high activity toward peroxide decomposition. When the normalized rate constants toward peroxide decomposition were compared with those reported for the conventional catalyst such as transition metal oxides, the catalytic activity of the present catalysts was comparable to or higher than the conventional catalysts. From these results, the possibility of cost-effective catalysts for air cathodes in alkaline solution is discussed.

Electroreduction of oxygen on multi-walled carbon nanotubes modified highly oriented pyrolytic graphite electrodes in alkaline solution

Abstract The electrochemical reduction of oxygen has been studied on multi-walled carbon nanotubes (MWCNTs) modified highly oriented pyrolytic graphite (HOPG) electrodes in 0.1 M KOH solution using the rotating disk electrode (RDE) technique. The oxygen reduction behaviour of MWCNTs/HOPG electrodes of various modifications was compared. Electrochemical studies indicate that the MWCNTs/HOPG electrodes show a remarkable electrocatalytic activity towards O 2 reduction in alkaline media. The number of electrons transferred per O 2 molecule was a function of potential and it increased up to four at high negative potentials. The O 2 reduction behaviour of MWCNTs/HOPG electrodes using oxidatively treated MWCNTs was also studied. The oxidative pre-treatment of MWCNTs did not change their electrocatalytic properties for oxygen reduction in alkaline solution to a noticeable degree.

Electrocatalysis by UPD of Metal Ad-layers on Single Crystal Au(111) and Polycrystalline Gold Electrodes of Oxygen Reduction in Alkaline Solution

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Enhanced Catalytic Activity of Non-platinum Catalyst for Oxygen Reduction in Alkaline Solution

Abstract Remarkable enhancement in catalytic activity of a non-platinum catalyst for oxygen reduction in alkaline solutions has been achieved by an oxidative pretreatment of a high-area carbon support before dispersion of catalyst precursor (cobalt hexacyanoferrate), followed by pyrolyzing the precursor under an inert atmosphere. The polarization potential for oxygen reduction at substantial current densities at room temperature under air was higher than a potential corresponding to a limit of relative predominance for O2/HO2− couple.

Electrochemical behavior of Au nanoparticle deposited on as-grown and O-terminated diamond electrodes for oxygen reduction in alkaline solution

Au nanoparticle was electrochemically deposited on both as grown and oxygen-terminated (O-terminated) boron-doped diamond (BDD) films. The surface coverages of Au nanoparticle were 0.07 and 0.18 corresponding to the areas of Au 0.012 and 0.029 cm 2, respectively, as noted from linear sweep voltammetry. The SEM studies indicated different morphologies of Au deposition such as random distribution of small spherical particles at both the grain boundaries and the facets on the as grown diamond film and clusters principally on the cross edges of two facets on the O-terminated diamond. The electrochemical behavior for oxygen reduction was examined using differential pulse voltammetry (DPV), which confirmed the higher catalytic efficiencies of Au deposited as grown and O-terminated BDD electrodes when compared to a polycrystalline Au electrode. Moreover, the mechanism of Au nanoparticle deposited BDD films for the oxygen reduction was investigated by ac impedance and hydrodynamic voltammetric methods.

Electrocatalytic activities of REMn2O5 (RE = Dy, Ho, Er, Tm, Yb, and Lu) and Er0.76Zr 0.11Ca0.13Mn2O5 for oxygen reduction in alkaline solution

A series of complex oxides REMn2O5 (RE=Dy, Ho, Er, Tm, Yb, and Lu) and Er0.76Zr0.11Ca0.13Mn2O5 with large specific areas and nanoscale grain sizes were prepared by an improved amorphous citric precursor method (IACP). Their electrocatalytic performances were characterized by the polarization curves of gas diffusion electrodes employing the oxides. The measurement of polarization curves indicated that the REMn2O5 containing different rare earth showed a obviously different electrocatalytic performances for oxygen reduction reaction, being the order Tm>Er>Ho>Dy>Lu>Yb. Temperature-programmed reduction (TPR) analysis revealed that the REMn2O5 containing different rare earth showed a significantly different oxygen contents and TPR peak temperatures. Their catalytic activities depended on both the oxygen contents and TPR peak temperatures. These two factors play a plus and a minus role respectively.

Adsorption of oxygen containing species and their effect on oxygen reduction on Pt 3Co electrode

A rotating Pt 3Co, thermally prepared alloy disc is used to study electrochemical oxygen reduction in alkaline solutions of different pH. In all solutions two Tafel regions are found: at low current densities ∂ E/∂log j=−2.3 RT/ F and at high current densities ∂ E/∂log j=−2.3×2 RT/ F. The reaction order with respect to OH − is confirmed to be −1/2 and 0 for low and high current density regions, respectively. The coverage, θ, with oxygen intermediates, determined by a programmed potentiodynamic method, is found to be a function of potential and pH. In all solutions, substantial coverages are observed only at potentials in the low current density region. It is found that the fractional reaction order at low current densities is related through the adsorption of oxygen species under Temkin conditions and the dependence of activation energy on θ and pH.