Oxygen Reduction In Acidic Media Research Articles

Why is Gold such a Good Catalyst for Oxygen Reduction in Alkaline Media?

The two faces of gold: the reduction of oxygen on gold electrodes in alkaline solutions has been investigated theoretically. The most favorable reaction leads directly to adsorbed O(2)(-), but the activation energy for a two-step pathway, in which the first step is an outer-sphere electron transfer to give solvated O(2)(-), is only slightly higher. d-band catalysis, which dominates oxygen reduction in acid media, plays no role. The reason why the reaction is slow in acid media is also explained.

Design of Pt catalyst with high electrocatalytic activity and well tolerance to methanol for oxygen reduction in acidic medium

The low-content deposition of Pt on the working electrode during the electrochemical test showed high activity for oxygen reduction reaction (ORR) and much low activity for methanol oxidation reaction (MOR), indicating that there exists a difference in the ORR and MOR on the surface of few Pt nanoparticles . Based on this difference, we designed and prepared the Pt/carbon nanotube catalyst with ca. 0.86 wt.% Pt, which exhibited high ORR activity and well tolerance to methanol in acidic media, showing a good potential application for a future acidic direct methanol fuel cell device.

Synthesis of Nanosize Tungsten Oxide and Its Evaluation as an Electrocatalyst Support for Oxygen Reduction in Acid Media

WO3 was investigated as a possible support material for monolayer Pt ORR electrocatalysts in acid electrolyte. It was found that as-prepared Pt/WO3 showed enhanced activity for the ORR and superior electron transfer ability compared to conventional Pt/C and bulk polycrystalline Pt. However, similar to other tungsten derived supports, most notably WC, the Pt/WO3 electrocatalyst showed significant performance degradation that was tied directly to the formation of water-soluble hydrogen tungsten bronze (HxWO3) on the support surface that was identified by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). This information, combined with previous work by our group on WC supports, are also combined to propose a series degradation pathway for WC and WO3 supports in acid media, which is relevant for proton exchange membrane (PEM) fuel cells.

Solvothermal Synthesis of Nitrogen-Containing Graphene for Electrochemical Oxygen Reduction in Acid Media

Graphene is ideally suited to electrochemistry by virtue of its high surface area and impressive electronic properties. Nitrogen incorporation can be used to tailor the properties of graphene. Here we present a simple solvothermal technique to produce a nitrogen-containing foam-like macroporous graphene powder doped with up to 15 wt% nitrogen. This is applied as an effective non-precious, metal-free electrochemical catalyst for oxygen reduction in acid media. [DOI: 10.1380/ejssnt.2012.29]

Different length linkages of graphene modified with metal nanoparticles for oxygen reduction in acidic media

This paper reports the chemical synthesis and experimental characterization of various graphene oxide (GO)-supported platinum (Pt) and palladium (Pd) nanoparticle (NP) catalysts. To investigate the relationship between the linker length and the catalytic activities of the metal-decorated GO catalysts, six samples were prepared with three different linker molecules, HS(CH2)2SH, HS(CH2)3SH and HS(CH2)4SH (denoted as GO-l-NPs), and two different metal NPs, Pt and Pd. All GO-l-NP catalysts were tested in oxygen reduction reaction (ORR) using electrochemical techniques such as cyclic voltammetry (CV) and rotating ring disk electrode (RRDE) hydrodynamic voltammetry to quantitatively obtain the ORR kinetic constants and the reaction mechanisms on a glassy carbon electrode (GCE) in 0.5 M H2SO4 solution. All GO-l-NPs/GCE electrodes showed significantly improved ORR activity and mechanisms. GO-l-NPs were characterized by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). The results showed that Pt and Pd were successfully attached onto the GO surface. A more positive potential catalytic ORR was observed in the modified GO-l-NPs with longer chain linker lengths in both cases.

Porous Pd Layer-Coated Au Nanoparticles Supported on Carbon: Synthesis and Electrocatalytic Activity for Oxygen Reduction in Acid Media

This paper reports the simple synthesis and characterization of carbon-supported Pd layer-coated Au nanoparticles (AuPd/C). A series of AuPd/C with various Pd/Au weight percentage ratios were prepared by the spontaneous deposition of a Pd shell on a Au nanoparticle core using different Pd precursor concentrations (0.5, 5, 10, 20 mM PdCl2). Au nanospheres encapsulated by the porous Pd shells are confirmed by transmission electron microscopy (TEM), UV–vis absorption spectroscopy, and scanning TEM. The catalytic activity of the AuPd/C for the oxygen reduction reaction (ORR) was investigated by rotating disk electrode voltammetry in 0.5 M H2SO4. In particular, a AuPd/C with a Pd/Au ratio of 0.61 shows superior ORR activity along with satisfactory stability and methanol tolerance under acidic conditions.

Surface segregation and stability of core–shell alloy catalysts for oxygen reduction in acid medium

Density functional theory is used for the evaluation of surface segregation, trends for dissolution of Pt surface atoms in acid medium, and oxygen reduction reaction activity of core-shell materials, containing a monolayer of platinum over a monometallic or bimetallic core. Two groups of cores are investigated: Pt/X with X = Ir, Au; Pd, Rh, Ag; Co, Ni, Cu; and Pt/Pd(3)X, with X = Co, Fe, Cr, V, Ti, Ir, Re. It is found that all the 4d and 5d pure cores may serve as stable cores, and their beneficial effect on the Pt monolayer may be further tuned by alloying the core to another element, here chosen from 3d or 5d groups. The Pd(3)X cores enhance the stability of the surface Pt atoms both in vacuum and under adsorbed oxygen; however the high oxygen philicity of some of the X elements induces their surface segregation that may cause surface poisoning with oxygenated species and their dissolution in acid medium.

Carbon‐Supported, Selenium‐Modified Ruthenium–Molybdenum Catalysts for Oxygen Reduction in Acidic Media

The stability and oxygen reduction activity of two carbon-supported catalyst materials are reported. The catalysts, Se/Ru and Se/(Ru-Mo), were prepared by using a chemical reduction method. The catalyst nanoparticles were evenly dispersed onto globular amorphous carbon supports, and their average size was ca. 2.4 nm. Thermal treatment at 500 °C for 2 h in an inert argon atmosphere resulted in coarsening of the nanoparticles, and also in some decrease of their activity. A gradual reduction of activity was also observed for Se/Ru during potential-cycle experiments. However, the incorporation of small amounts of Mo into the Se/Ru catalysts considerably improved the stability of the catalyst against dissolution. The Mo-containing samples showed excellent oxygen reduction activities even after cycling the potential 1000 times between 0.7 and 0.9 V. Furthermore, they showed excellent fuel-cell behavior. The performance of the Se/Ru catalysts is greatly improved by the addition of small amounts of elemental Mo. Possible mechanisms responsible for the improvement of the activity are discussed.

Electrocatalytic Performances of Carbon Supported Metallophthalocyanine and Pt/Metallophthalocyanine Catalysts Towards Dioxygen Reduction in Acidic Medium

Electrocatalytic performances of phthalocyanines (Pcs) involving N-benzyl-4-phenyloxyacetamide moieties, dispersed on a high-surface area carbon substrate, Vulcan XC-72 (VC) and Nafion (Nf), towards oxygen reduction in acidic medium were determined and compared. The VC/Nf/CoPc(5) catalyst showed much higher catalytic activity than those of the other Pc(1–4)-based catalysts (H2Pc 1, ZnPc 2, NiPc 3 and CuPc 4) and that of unsubstituted CoPc-based one. The comparison of the performance of VC/Nf/Pt-5 dual catalyst with that of VC/Nf/Pt one indicated that the former can be a good alternative to the latter as a cathode catalyst both in direct methanol and H2/O2 fuel cell applications.

Cobalt Porphyrin Functionalized Carbon Nanotubes for Oxygen Reduction

Carbon nanotube (CNT) compositions were prepared by covalently grafting a Co(II) porphyrin to functionalized multiwalled carbon nanotubes (MWCNTs) via zwitterionic functionalization of the CNT sidewalls followed by a SN2 substitution reaction. The MWCNT−Co−porphyrin compositions, mixed with Nafion, displayed excellent catalytic performance for oxygen reduction in acidic media (pH range, 0.0−5.0) at room temperature. With low catalyst loading, the oxygen reduction rates achieved are more than 1 order of magnitude higher than previously reported values for similar Co−porphyrin catalysts. These results demonstrate the advantages of systems of MWCNTs covalently linked to electrocatalytic molecules. The electrodes are easily fabricated by a drop-casting vacuum drying procedure. Rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) measurements revealed the mechanism to be a direct four-proton and four-electron reduction of oxygen to water. These results demonstrate that new MWCNT electrocatalyt...

In situ PEI and formic acid directed formation of Pt NPs/MWNTs hybrid material with excellent electrocatalytic activity

A hybrid material based on Pt nanoparticles (Pt NPs) and multi-walled carbon nanotubes (MWNTs) was fabricated with the assistance of PEI and formic acid. The cationic polyelectrolyte PEI not only favored the homogenous dispersion of carbon nanotubes (CNTs) in water, but also provided sites for the adsorption of anionic ions PtCl42− on the MWNTs’ sidewalls. Deposition of Pt NPs on the MWNTs’ sidewalls was realized by in situ chemical reduction of anionic ions PtCl42− with formic acid. The hybrid material was characterized with TEM, XRD and XPS. Its excellent electrocatalytic activity towards both oxygen reduction in acid media and dopamine redox was also discussed.

Multi-walled carbon nanotube-supported tungsten oxide-containing multifunctional hybrid electrocatalytic system for oxygen reduction in acid medium

Combination of multi-walled carbon nanotubes, cobalt porphyrin and tungsten oxide in the film (deposited onto glassy carbon electrode substrate) produces an electrocatalytic system capable of effective reduction of oxygen in such acid medium as 0.5 mol dm −3 H 2SO 4. Co-existence of cobalt porphyrin and tungsten oxide, together with dispersed carbon nanotubes, leads to the enhancement effect evident from some positive shift in the oxygen reduction voltammetric potential and the significant increase of voltammetric currents (relative to those characteristic of the system free of carbon nanotubes and WO 3). The multi-component electrocatalytic film has also exhibited relatively higher activity towards reduction of hydrogen peroxide. It is reasonable to expect that the reduction of oxygen is initiated at the cobalt porphyrin redox centers, and the undesirable hydrogen peroxide intermediate is further reduced at the tungsten oxide support. An important function of carbon nanotubes is to improve transport of electrons within the electrocatalytic multi-component film.

Electrocatalytic activity, methanol tolerance and stability of perfluoroalkyl-substituted mononuclear, and ball-type dinuclear cobalt phthalocyanines for oxygen reduction in acidic medium

Electrocatalytic activity, methanol tolerance and stability of three phthalocyanine (Pc) complexes (a heptadecafluorononyl-substituted mononuclear CoPc 1, a pentaerythritol-bridged ball-type dinuclear Co2Pc2 2 and a heptadecafluorodecyl-substituted, pentaerythritol-bridged ball-type dinuclear Co2Pc2 3) and the performance of dual catalysts of 2/Pt and 3/Pt, dispersed on a high surface area carbon substrate, Vulcan XC-72 (VC) and Nafion (Nf), towards oxygen reduction (OR) were investigated and compared by surface cyclic voltammetry, rotating disk electrode, rotating ring-disk electrode and chronoamperometry experiments in acidic medium. The VC/Nf/3 modified glassy carbon electrode showed much higher catalytic performance, compared to VC/Nf/2 and VC/Nf/1 modified ones. The long term stability of the VC/Nf/3 catalyst in acidic medium was better than that of VC/Nf/2. It was found that the VC/Nf/1, VC/Nf/2 and VC/Nf/3 catalysts are nearly insensitive to the presence of methanol. In the presence of 1 M methanol in the electrolyte, the catalytic performances of 2- and 3-based catalysts were much better than that of the Pt-based one. Thus, it was shown that the VC/Nf/2-Pt and VC/Nf/3-Pt dual catalysts can be good alternatives to VC/Nf/Pt as cathode catalysts in direct methanol fuel cells. Moreover, in the absence of methanol, the mixing of 3 with Pt resulted in the enhancement of catalytic activity for OR, when compared to 3 and even Pt in the high overpotentials region.

Templated Ru/Se/C electrocatalysts for oxygen reduction

Highly porous Ru/Se/C electrocatalysts have been successfully synthesized via a template-based method, which was carried out by the impregnation of a hard template (silica gel) with a mixture of RuCl 3· xH 2O, SeO 2 and sucrose dissolved in water. The resulting Ru/Se/C catalysts show good catalytic activity for oxygen reduction in acidic media. The electrocatalysts are believed to consist of selenium-modified ruthenium nanoparticles, which are embedded in a high surface area carbon matrix. The structural properties of the prepared Ru/Se/C electrocatalysts were investigated using nitrogen physisorption measurements, X-ray diffraction and transmission electron microscopy. The elemental composition of prepared Ru/Se/C electrocatalysts was determined using electron microprobe. The catalytic activity was tested using the rotating-ring-disk-electrode technique in 0.1 M HClO 4 solution at room temperature.

PdNi electrocatalyst for oxygen reduction in acid media

The PdNi nanoparticles dispersed on Nafion solution was used as an ink-type electrode for oxygen reduction reaction (ORR), in acid media. This bimetallic catalyst was synthesized via the metallic reductive precipitations of the chloride precursors with NaBH 4 in tetrahydrofuran (THF) at 25 ∘ C . The characterization of the electrocatalyst using X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed bimetallic nanoparticles having a narrow size ranged 8 – 10 nm with face-centered cubic (fcc) hexagonal structure. Cyclic voltammograms and polarization curves from rotating-disk electrode measurements showed significantly higher activity on PdNi than observed on Pd catalyst, with a mechanism involving four electrons transfer to water formation. The incorporation of Ni, a less electronegative metal to Pd shifts the onset potential for the ORR approximately 110 mV more positive, and at 0.5 mA cm - 2 the cathode overpotential is reduced by 260 mV in relation to that obtained on Pd, in a 0.5 M H 2 SO 4 solution at 25 ∘ C .

Oxygen reduction at Fe–N-modified multi-walled carbon nanotubes in acidic electrolyte

Multi-walled carbon nanotubes (MWCNTs) modified with iron tetramethoyxphenyl-porphyrin chloride (FeTMPP-Cl) and heat treated are active towards electrocatalytic oxygen reduction in acidic media. The activity slightly depends on the heat treatment temperature (850 < 550 °C) and the amount of porphyrin deposited onto the nanotubes before the heat treatment step. In comparison with as-received MWCNTs no increase in activity has been found with iron phenanthroline or iron acetate impregnated and heat treated MWCNTs. When MWCNTs are pretreated in an oxidation step using HNO 3, there is only a slight increase in activity after FeTMPP-Cl modification and heat treatment compared to the not pretreated MWCNTs. The HNO 3 treatment itself, however, leads to an increase in activity of the unmodified MWCNTs. TEM-measurements revealed an amorphous layer surrounding the MWCNTs after HNO 3 treatment, while XPS showed an increased amount of oxygen functional groups. It is suggested that there are different kinds of active sites at the catalyst surface, the first ones consisting of oxygen functionalities or other entities introduced by the HNO 3 treatment, and the second ones containing nitrogen (and probably iron) introduced via the porphyrin. Pyridine-type nitrogen has been found by XPS after heat treatment at both temperatures, indicating that the active sites are already formed at 550 °C.

Mechanically milled RuxFey Electrocatalyst for Oxygen Reduction in acid media

Mechanically milled RuxFey Electrocatalyst for Oxygen Reduction in acid media

Electrocatalysis of oxygen reduction and hydrogen oxidation in platinum dispersed on tungsten carbide in acid medium

Tungsten carbide dispersed on a high surface area carbon (W2C/C) prepared by a sonochemical method was used as the support of a Pt-based electrocatalyst (Pt-W2C/C). The resulting materials were tested for two important reactions with practical interest in fuel cells, that is, the oxygen reduction and hydrogen oxidation reactions, in acid medium. The electrochemical techniques considered were cyclic voltammetry, linear sweep voltammetry, and steady-state polarization curves, obtained utilizing an ultrathin catalyst layer in a rotating ring–disk electrode. The results showed that the Pt-W2C/C catalyst led to a remarkable enhancement of the oxygen reduction in acid medium, when compared to the standard Pt/C, both following a four-electron mechanism. The hydrogen oxidation reaction showed similar kinetics on Pt-W2C/C and Pt/C following the direct discharge mechanism on both catalysts. The W2C/C support presented remarkable activity for the hydrogen oxidation reaction, most probably after the Heyrovsky–Volmer mechanism at low overpotential and the direct discharge irreversible mechanism at high overpotentials.

A study of oxygen reduction on improved Pt-WC/C electrocatalysts

Pt on a tungsten carbide nanocrystalline support (Pt-WC/C) has been prepared by the direct reduction of a platinum salt precursor combined with intermittent microwave heating (IMH). The Pt-WC/C electrocatalyst shows better performance for oxygen reduction in acidic media than that of pure Pt/C or Pt-WC/C prepared by a mechanical mixing method. The results reveal that the Pt-WC/C electrocatalyst prepared by present method is very active for oxygen reduction reaction (ORR) with an onset potential of 1.05 V versus standard hydrogen electrode (SHE) at ambient temperature, which is over 150 mV more positive compared to that of commercial Pt/C electrocatalysts.

Rapid Screening of Bimetallic Electrocatalysts for Oxygen Reduction in Acidic Media by Scanning Electrochemical Microscopy

Additional bimetallic electrocatalysts for the oxygen reduction reaction (ORR) in acidic media were designed using a previously reported thermodynamic selection guide. The electrocatalyst mixtures were prepared in large arrays on glassy carbon substrates and the electrocatalytic activity was screened using scanning electrochemical microscopy (SECM). Activities were measured for a range of bimetallic combinations that showed a synergetic electrocatalytic effect during screening, including Au–V, Ag–V, Pd–Mn, and Pd–V. Upon initial screening, a highly active electrocatalytic combination consisting of 60:40 Pd–V was identified. Using rotating disk electrode (RDE) experiments, the high activity of this combination for the ORR in acidic media was confirmed when the electrocatalysts were supported on Vulcan carbon. The electrocatalytic activity of Pd–V was close to that exhibited by Pt, the electrocatalyst of choice for the ORR in acidic media, and thus is another example of a nonplatinum catalyst with high activity that follows the previous strategy for catalyst design.