Electron Oxygen Reduction Research Articles

NiFe layered double hydroxide as an efficient bifunctional catalyst for electrosynthesis of hydrogen peroxide and oxygen

Two electron oxygen reduction reaction to produce hydrogen peroxide (H2O2) is a promising alternative technique to the multistep and high energy consumption anthraquinone process. Herein, Ni–Fe layered double hydroxide (NiFe-LDH) has been firstly demonstrated as an efficient bifunctional catalyst to prepare H2O2 by electrochemical oxygen reduction (2e− ORR) and oxygen evolution reaction (OER). Significantly, the NiFe-LDH catalyst possesses a high faraday efficiency of 88.75% for H2O2 preparation in alkaline media. Moreover, the NiFe-LDH catalyst exhibits excellent OER electrocatalytic property with small overpotential of 210 mV at 10 mA cm−2 and high stability in 1 M KOH solution. On this basis, a new reactor has been designed to electrolyze oxygen and generate hydrogen peroxide. Under the ultra-low cell voltage of 1 V, the H2O2 yield reaches to 47.62 mmol gcat−1 h−1. In order to evaluate the application potential of the bifunctional NiFe-LDH catalyst for H2O2 preparation, a 1.5 V dry battery has been used as the power supply, and the output of H2O2 reaches to 83.90 mmol gcat−1 h−1. The excellent electrocatalytic properties of 2e− ORR and OER make NiFe-LDH a promising bifunctional electrocatalyst for future commercialization. Moreover, the well-designed 2e− ORR-OER reactor provides a new strategy for portable production of H2O2.

Synergetic Dual-Ion Centers Boosting Metal Organic Framework Alloy Catalysts toward Efficient Two Electron Oxygen Reduction.

Herein, a strategy of synergetic dual-metal-ion centers to boost transition-metal-based metal organic framework (MOF) alloy nanomaterials as active oxygen reduction reaction (ORR) electrocatalysts for efficient hydrogen peroxide (H2 O2 ) generation is proposed. Through a facile one-pot wet chemical method, a series of MOF alloys with unique Ni-M (M-Co, Cu, Zn) synergetic centers are synthesized, where the strong metallic ions 3d-3d synergy can effectively inhibit O2 cleavage on Ni sites toward a favorable two-electron ORR pathway. Impressively, the well-designed NiZn MOF alloy catalysts show an excellent H2 O2 selectivity up to 90% during ORR, evidently outperforming that of NiCo MOF (45%), and NiCu MOF (55%). Moreover, it sustains efficient activity and robust stability under a continuous longterm ORR operation. The correlative in situ synchrotron radiation X-ray adsorption fine structure and Fourier transform infrared spectroscopy analyses reveal at the atomic level that, the higher Ni oxidation states species, regulated via adjacent Zn2+ ions, are favorable for optimizing the adsorption energetics of key *OOH intermediates toward fast two electron ORR kinetics.

The enhancing selectivity and activity for 2-electron oxygen reduction reaction by tuned oxygen defect on amorphous hydroxide catalysts

Open AccessCCS Chemistry26 Feb 2021The enhancing selectivity and activity for 2-electron oxygen reduction reaction by tuned oxygen defect on amorphous hydroxide catalysts Junheng Huang, Changle Fu, Junxiang Chen, Nangan Senthilkumar, Xinxin Peng and Zhenhai Wen Junheng Huang Google Scholar More articles by this author , Changle Fu Google Scholar More articles by this author , Junxiang Chen Google Scholar More articles by this author , Nangan Senthilkumar Google Scholar More articles by this author , Xinxin Peng Google Scholar More articles by this author and Zhenhai Wen Google Scholar More articles by this author https://doi.org/10.31635/ccschem.021.202100750 SectionsSupplemental MaterialAboutPDF ToolsAdd to favoritesTrack Citations ShareFacebookTwitterLinked InEmail Amorphous catalysts, thanks to their unique coordinately unsaturated properties and abundant of defect sites, incline to possess higher activity and selectivity than their crystalline counterparts. In this work, we report a facile and general solvent-controlled-precipitation method to prepare hybrids of graphene oxide (GO) supporting amorphous metal hydroxide (A-M(OH)x/GO, M = Cu, Co, Mn), which provides us with tangible materials to study the structure-performance relationship of various amorphous oxides. The systematic investigations on A-Cu(OH)2/GO by coupling ex-situ/in-situ characteristic techniques with electrochemical studies reveal that electrocatalytic activity and selectivity toward 2 electron oxygen reduction reaction (ORR) is highly dependent on the coordinated Cu catalytic sites and the disorder structure of A-Cu(OH)2. In-situ X-ray absorption near edge structure (XANES) and density functional theory (DFT) calculation verify that the degree of OH* poisoning (ΔG0OH*) tuned by 3-OHcoordinated Cu sites in amorphous structures play a crucial role in selective catalysis of ORR for H2O2 production. The optimized A-Cu(OH)2/GO shows superior activity and high selectivity (∼95%) toward H2O2, as demonstrated by a Zinc-air battery that is capable of on-site producing H2O2 with a production rate of as high as 3401.5 mmol h−1 g−1. Download figure Download PowerPoint Previous article FiguresReferencesRelatedDetails Issue AssignmentNot Yet AssignedSupporting Information Copyright & Permissions© 2021 Chinese Chemical Society Downloaded 103 times Loading ...

Efficient Photocatalytic Hydrogen Peroxide Production over TiO2 Passivated by SnO2

Photocatalysis provides an attractive strategy for synthesizing H2O2 at ambient condition. However, the photocatalytic synthesis of H2O2 is still limited due to the inefficiency of photocatalysts and decomposition of H2O2 during formation. Here, we report SnO2-TiO2 heterojunction photocatalysts for synthesizing H2O2 directly in aqueous solution. The SnO2 passivation suppresses the complexation and decomposition of H2O2 on TiO2. In addition, loading of Au cocatalyst on SnO2-TiO2 heterojunction further improves the production of H2O2. The in situ electron spin resonance study revealed that the formation of H2O2 is a stepwise single electron oxygen reduction reaction (ORR) for Au and SnO2 modified TiO2 photocatalysts. We demonstrate that it is feasible to enhance H2O2 formation and suppress H2O2 decomposition by surface passivation of the H2O2-decomposition-sensitive photocatalysts.

Selenium-Coupled Reduced Graphene Oxide as Single-Atom Site Catalyst for Direct Four-Electron Oxygen Reduction Reaction

A single-atom site catalyst for direct four electron oxygen reduction reaction (ORR) is identified where selenium (ultrasmall amount of Se, ≲1 at. % ) is the active center that couples reduced graphene oxide (rGO) sheets. This metal-free catalyst is found to be undergoing ORR through the direct four-electron pathway in alkaline medium, similar to platinum, whereas rGO prefers a two-electron path, and the experimental observation is correlated with theoretical study. The role of Se-like elements in graphene, which have similar electronegativity as carbon, is unraveled with a detailed density functional theory-based analyses.

Nanohybrid Catalysts for Efficient Synthesis of Hydrogen Peroxide at Ambient Temperature and Pressure

The catalytic activity of gold nanoparticle-loaded metal oxides (Au/MOs) for the two electron-oxygen reduction reaction (2e–-ORR) by formic acid increases with a rise in Fermi energy of the support...

Graphene-hBN non-van der Waals vertical heterostructures for four- electron oxygen reduction reaction.

A novel vertical non-van der Waals (non-vdW) heterostructure of graphene and hexagonal boron nitride (G/hBN) is realized and its application in direct four-electron oxygen reduction reaction (ORR) in alkaline medium is established. The G/hBN differs from previously demonstrated vdW heterostructures, where it has a chemical bridging between graphene and hBN allowing a direct charge transfer - resulting in high ORR activity. The ORR efficacy of G/hBN is compared with that of graphene-hBN vdW structure and individual layers of graphene and hBN along with that of benchmark platinum/carbon (Pt/C). The ORR activity of G/hBN is found to be on par with Pt/C in terms of current density but with much higher electrochemical stability and methanol tolerance. The onset potential of the G/hBN is found to be improved from 780 mV at a glassy carbon electrode to 930 mV and 940 mV in gold and platinum electrodes, respectively, indicating its substrate-dependent catalytic activity. This opens possibilities of new benchmark catalysts of metals capped with G/hBN atomic layers, where the underneath metal is protected while keeping the activity similar to that of pristine metal. Density functional theory-based calculations are found to be supporting the observed augmented ORR performance of G/hBN.

Two-step oxygen reduction on spinel NiFe2O4 catalyst: Rechargeable, aqueous solution- and gel-based, Zn-air batteries

Electrocatalysts that lead to a four electron oxygen reduction reaction are generally proposed for metal-air batteries. Herein, we show that spinel NiFe2O4 catalyses oxygen reduction reaction by a two step process through stable peroxide species in aqueous medium. Further, it acts as an efficient bifunctional catalyst for oxygen reduction and oxygen evolution reactions with favourable rechargeable-battery characteristics. The kinetic parameters are deduced using electrochemical techniques. Rechargeable zinc-air batteries have been assembled using aqueous solution-as well as gel-based electrolytes and the battery characteristics are studied.

A Cathodic Electro-Fenton Catalyst Derived from Ionic-Liquid: Peroxide Generation and Di-Valent Iron Regeneration

The highly nitrogen-doped porous carbon materials for peroxide generation and di-valent iron regeneration were synthesized by the pyrolysis of ionic-liquid, which are precursor of carbon and nitrogen, using a silica nanoparticle template. In acidic solution, both of two/four electron oxygen reduction reaction (ORR) activities of ionic-liquid derived nitrogen-doped carbon catalyst increased significantly with pyridinic/graphitic N ratio in their structure. From the cyclic voltammogram, we confirmed that di-valent/tri-valent iron redox property enhanced with increasing surface carbonyl functional group, formed during removal of silica template. The degradation experiments of azo-dye and trace pharmaceutical compounds showed that the Fenton reaction (hydroxyl radical formation) drastically increased when double working electrodes (electrode 1: peroxide generation, electrode 2: di-valent iron regeneration) were used at the same time, and as a result, the removal efficiency was drastically increased. Based on the physical/electrochemical analysis, the ionic-liquid is a candidate precursor of highly nitrogen-doped carbon as energy effective electro-Fenton catalyst. Acknowledgements This work was supported by the Korea Ministry of Environment as a “Global Top Project” (Project No. 2016002190003).

Organic Molecular Catalyst for Electrochemical Production of Hydrogen Peroxide

Hydrogen peroxide (H2O2) as a low cost, safe and clean disinfection agent plays an important role in providing clean water for human society. Compared with complicated industrial anthraquinone process or direct catalytic synthesis from H2 and O2, the distributed production of H2O2 in a polymer electrolyte fuel cell system (PEFC) has numerous merits, including lower financial and energy cost, safer process, use of small-scale, easily deployable device.1,2 For these reasons, there is strong interest in developing electrocatalysts with high activity and selectivity for H2O2 production via the electrochemical reduction of molecular oxygen. Up until now, H2O2 electrocatalysts have been based on precious-metal amalgams, which are costly, scarce, and difficult to handle safely due to the use of Hg.2,3 Carbon-based electrocatalysts have been considered for H2O2 production,4-6 as have been metal-free and nitrogen-containing molecular catalysts known to be selective for two-electron reduction of O2 in various media.7-9 In this presentation, we will demonstrate a new catalyst based on a small organic molecule that enables electrochemical production of H2O2 in an aqueous acidic electrolyte (0.5 M H2SO4). When adsorbed onto glassy carbon this molecular catalyst shows a high onset potential of around 0.6 V vs. RHE, and a specific current density > 1.3 mA/cm2 ECA at 0 V vs. RHE in electrochemical cell test. Rotating ring-disk electrode (RRDE) studies indicate high selectivity for H2O2 production, with H2O2 yield over 80%, and current efficiency over 67%. The durability of this molecule has been evaluated in an electrochemical cell, as well as in a PEFC. Based on experimental data and density functional theory (DFT) calculations, a two electron oxygen reduction mechanism on this molecular catalyst will be proposed. References (1) Centi, G.; Perathoner, S.; Abate, S. In Modern Heterogeneous Oxidation Catalysis; Wiley-VCH Verlag GmbH & Co. KGaA: 2009, p 253. (2) Siahrostami, S.; Verdaguer-Casadevall, A.; Karamad, M.; Deiana, D.; Malacrida, P.; Wickman, B.; Escudero-Escribano, M.; Paoli, E. A.; Frydendal, R.; Hansen, T. W.; Chorkendorff, I.; Stephens, I. E. L.; Rossmeisl, J. Nat. Mater. 2013, 12, 1137. (3) Verdaguer-Casadevall, A.; Deiana, D.; Karamad, M.; Siahrostami, S.; Malacrida, P.; Hansen, T. W.; Rossmeisl, J.; Chorkendorff, I.; Stephens, I. E. L. Nano Lett. 2014, 14, 1603. (4) Yamanaka, I.; Onizawa, T.; Takenaka, S.; Otsuka, K. Angew. Chem. Int. Ed. 2003, 42, 3653. (5) Yamanaka, I.; Onisawa, T.; Hashimoto, T.; Murayama, T. ChemSusChem 2011, 4, 494. (6) Fellinger, T.-P.; Hasché, F.; Strasser, P.; Antonietti, M. J. Am. Chem. Soc. 2012, 134, 4072. (7) Hatay, I.; Su, B.; Méndez, M. A.; Corminboeuf, C.; Khoury, T.; Gros, C. P.; Bourdillon, M.; Meyer, M.; Barbe, J.-M.; Ersoz, M.; Záliš, S.; Samec, Z.; Girault, H. H. J. Am. Chem. Soc. 2010, 132, 13733. (8) Wu, S.; Su, B. Chem. Eur. J. 2012, 18, 3169. (9) Savéant, J.-M. Chem. Rev. 2008, 108, 2348.

Influence of Copper on Trivalent Chromium Conversion Coating Formation on Aluminum

In the present work, modified copper-containing trivalent chromium conversion (TCC) coating processes for aluminum were investigated. The copper addition to the TCC bath was made for the purposes of reducing the generation of hydrogen peroxide and chromium (VI) species during the coating growth. The morphologies and compositions of the coatings were examined using high-resolution electron microscopy, energy-dispersive X-ray spectroscopy and Raman spectroscopy. UV photometric measurements were employed to determine the amount of hydrogen peroxide in the TCC solution. The resultant coatings contained zirconium oxides, chromium hydroxide and fluorides and sulfate constituents, as well as copper oxides and copper-rich deposits that were preferred cathodic sites for oxygen reduction. Of most significance, no chromium (VI) species were detected in the coatings by Raman spectra. It is suggested that this results from reduced generation of hydrogen peroxide, as disclosed by photometric measurements, at the cathodic copper-rich particles, due to favoring of the four electron oxygen reduction reaction.

Electrode Reactions Coupled with Chemical Reactions of Oxygen, Water and Acetaldehyde in an Ionic Liquid: New Approaches for Sensing Volatile Organic Compounds

Water and oxygen are ubiquitous present in ambient conditions. This work studies the unique oxygen, trace water and a volatile organic compound (VOC) acetaldehyde redox chemistry in a hydrophobic and aprotic ionic liquid (IL), 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([Bmpy][NTf2]) by cyclic voltammetry and potential step methods. One electron oxygen reduction leads to superoxide radical formation in the IL. Trace water in the IL acts as a protic species that reacts with the superoxide radical. Acetaldehyde is a stronger protic species than water for reacting with the superoxide radical. The presence of trace water in the IL was also demonstrated to facilitate the electro-oxidation of acetaldehyde, with similar mechanism to that in the aqueous solutions. A multiple-step coupling reaction mechanism between water, superoxide radical and acetaldehyde has been described. The unique characteristics of redox chemistry of acetaldehyde in [Bmpy][NTf2] in the presence of oxygen and trace water can be controlled by electrochemical potentials. By controlling the electrode potential windows, several methods including cyclic voltammetry, potential step methods (single-potential, double-potential and triple-potential step methods) were established for the quantification of acetaldehyde. Instead of treating water and oxygen as frustrating interferents to ILs, we found that oxygen and trace water chemistry in [Bmpy][NTf2] can be utilized to develop innovative electrochemical methods for electroanalysis of acetaldehyde.

Nitrogen and sulfur co-doping of 3D hollow-structured carbon spheres as an efficient and stable metal free catalyst for the oxygen reduction reaction.

Three-dimensional, hollow-structured carbon sphere nanocomposites (N,S-hcs) doped with nitrogen and sulfur were prepared using a soft template approach followed by a high-temperature treatment. The synthesized N,S-hcs nanomaterials exhibited favourable catalytic activity for the oxygen reduction reaction (ORR) compared to carbon spheres doped solely with nitrogen (N-hcs), polypyrrole (PPY) solid nanoparticles and irregular fragments of polyaniline (PAN). These results demonstrated the co-doping of N/S and the relatively large surface area of the mesoporous carbon structure that enhanced the catalytic activity of the resulting material. Notably, the prepared N,S-hcs electrocatalysts provided four electron oxygen reduction selectivity, long-term durability and high resistance to methanol poisoning, all of which represented improvements over the conventional Pt/C electrocatalyst. The progress represented by this reported work is of great importance in the development of outstanding non-metal based electrocatalysts for the fuel cell industry.

Modification of Electrodeposited Co-Pd Alloy Catalysts By Superimposed High Magnetic Field

Palladium and its alloys have been a subject of interest in many research centers all over the world. Due to the price and accessibility of Pd, intensive tests are conducted aiming to invent alloys with catalytic properties similar to those of platinum, but much cheaper than palladium itself. Alloys of Co-Pd, Pd-Fe, Pd-Ni and Pd-Cr exhibit high catalytic activity for the four electron oxygen reduction reaction.The properties of Co-Pd alloys for the hydrogen evolution reaction are close to the properties of pure platinum. This makes it possible to use them, for example, in fuel cells. Tests performed so far have demonstrated that the Pd-Co alloys are characterized by much better electrocatalytic properties for HER than pure palladium. Application of an external magnetic field during the deposition of an alloy causes an additional convection at the electrode surface through the magnetohydrodynamic effect (MHD), paramagnetic force and magnetic field gradient force. This additional convection results in changes of the alloy composition, structure and morphology, and these, in turn, affect the further properties as magnetic as catalytical of the produced alloys. Magnetic field applied parallel to the surface of the electrode generates convection (magnetohydrodynamic effect MHD) of the electrolyte; it results in a laminar flow on the surface of the electrode which reduces the diffusion layer and increases the concentrations gradients. This results in change of the size of the grains and thus can also influence the texture and formation of various phases of the deposits. These various effects can be caused at the same time by the above mentioned convection but also by the magnetic properties, when the field is superimposed the growth in the direction of easier magnetization appears. Optimal conditions of electrolytic deposition of cobalt matrix nanoalloys will be sought through selection of proper composition of electrolyte, changes of electrolysis parameters and by application of external electromagnetic field with intensity up to 12 Tesla. Initial experiments, when the magnetic field was limited up to 1 T, show the improvement of catalytical properties together with increase of magnetic field orientated parallel to the surface of electrode. The influence of magnetic field with higher strength on electrodeposition of alloys with catalytical properties is needed to be clarified. Acknowledgement This work was supported by Polish National Science Center under grants 011/01/N/ST5/05509 and 2013/09/B/ST8/00211. This work was also supported by Polish Ministry of Science and Higher Education under grant IP2012/001072.

Ceria and Doped Ceria Nanoparticle Additives for Polymer Fuel Cell Lifetime Improvement

Polymer electrolyte fuel cell (PEFC) membrane durability is limited by free radical attack generated from oxygen reduction processes.1,2 The creation of peroxide via two electron oxygen reduction and subsequent decomposition into hydroxyl free radicals may be the major source of nonmetallic fuel cell component chemical degradation. The addition of Ce3+ by ion exchange has greatly improved the durability of PEFCs3. The cerium cations decompose the free radical species at high rates, thus limiting membrane damage and carbon support oxidation. An alternative approach is the addition of cerium oxide nanoparticles as free radical scavengers. The surfaces of CeO2 nanoparticles contain appreciable concentrations of Ce3+that may act as catalytic sites for free radical decomposition. However little is known about the effects of particle size and doping on the free radical scavenging rates, and the selectivity towards peroxide decomposition versus secondary free radical generation has not been previously studied.Ceria and doped ceria (Gd, Pr, Zr) nanoparticles of ~ 5-40 nm crystallite sizes were synthesized and evaluated for their activity and selectivity towards hydrogen peroxide decomposition, Figure 1, and were incorporated into the cathode catalyst layer to evaluate the effect of radical decomposition during fuel cell operation. Accelerated stress tests with fuel cells operating at 80°C and 30% relative humidity of the inlet gases were used to increase degradation of the fuel cell membrane to simulate long-term operation by accelerating free radical generation. Open circuit voltage (OCV), hydrogen crossover, and the fluorine emission rate (FER) from both the anode and cathode exhaust gases were used to quantify the rate of degradation of the fuel cell membrane electrode assembly (MEA) among the different types of fuel cells: those with cerium cations, those with cerium oxide, and those without cerium or ceria stabilizers. Scanning electron microscopy images of the tested membranes were used to determine the extent of thinning of the anode side of the MEA relative to the cathode side of the MEA to independently verify degradation by free radical degradation. The nanoparticle additives were shown to decompose peroxide and in some cases, improve ionomer durability. The catalytic activity and reaction pathway of cerium oxide towards hydrogen peroxide decomposition were influenced by particle size, dopant and the ratio of the Ce+3/Ce+4 sites on the surface. The size and doping of ceria nanoparticles are shown to play an important role on their ability to improve membrane durability. Additionally, the dissolution of ceria nanoparticles and the migration of cerium ions within the membrane electrode assemblies (MEAs) after accelerated stress testing were studied using spatially resolved X-Ray Fluorescence. The Ce cations were very mobile within fuel cells and migration across the MEAs was observed in the test cells in very short time periods4. Figure 1 Inverse selectivity for free radical generation versus peroxide decomposition rate measured using 6-Carboxyfluorescein and O2 generation for various ceria nanoparticles. References E. Endoh, S. Terazono, H. Widjaja and Y. Takimoto, Electrochemical and Solid– State Letters, 7 (7) A209, (2004)F. D. Coms, in Proton Exchange Membrane Fuel Cells 8, Pts 1 and 2, T. Fuller, K. Shinohara, V. Ramani, P. Shirvanian, H. Uchida, S. Cleghorn, M. Inaba, S. Mitsushima, P. Strasser, H. Nakagawa, H. A. Gasteiger, T. Zawodzinski and C. Lamy Editors, p. 235 (2008).E. Endoh, ECS Trans. 2008 volume 16, issue 2, 1229-1240S. M. Stewart, D. Spernjak, R. Borup, A. Datye, and F. Garzon, ECS Electrochem. Lett. 2014 3(4): F19-F22 Acknowledgements The authors wish to acknowledge the financial support of the U.S. DOE, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, as well as Dr. Barry Lai and Dr. Zhonghou Cai of Argonne National Laboratory Advanced Photon Source for their assistance at the APS X-ray Fluorescence Beam line.

One electron oxygen reduction in room temperature ionic liquids: A comparative study of Butler–Volmer and Symmetric Marcus–Hush theories using microdisc electrodes

The voltammetry for the reduction of oxygen at a microdisc electrode is reported in two room temperature ionic liquids: 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide ([Bmpyrr][NTf2]) and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl) imide ([P14,6,6,6][NTf2]) at 298K. Simulated voltammograms using Butler–Volmer theory and Symmetric Marcus–Hush (SMH) theory were compared with experimental data. Butler–Volmer theory consistently provided experimental parameters with a higher level of certainty than SMH theory. A value of solvent reorganisation energy for oxygen reduction in ionic liquids was inferred for the first time as 0.4–0.5eV, which is attributable to inner-sphere reorganisation with a negligible contribution from solvent reorganisation. The developed Butler–Volmer and Symmetric Marcus–Hush programs are also used to theoretically study the possibility of kinetically limited steady state currents, and to establish an approximate equivalence relationship between microdisc electrodes and spherical electrodes resting on a surface for steady state voltammetry for both Butler–Volmer and Symmetric Marcus–Hush theory.

Oxygen Reduction Reaction Studies of Phosphorus and Nitrogen Co‐Doped Mesoporous Carbon Synthesized via Microwave Technique

AbstractMetal‐free mesoporous P and N co‐doped carbon (PNDC) composites are evaluated for their electrocatalytic activity towards the oxygen reduction reaction (ORR). Carbonization of melamine and hexamine‐modified tannin in the presence of polyphosophoric acid produces PNDCs with prominent oxygen reduction properties in alkaline media. The effect of the P and N content in the carbon material is evaluated in terms of the ORR activity. The compound containing a high amount of N (8.3 atom %) and P (6.8 atom %), denoted PNDC‐1, shows high electrocatalytic activity, stability, durability, and selectivity towards the ORR. PNDC‐1 has an onset potential of 0.10 V versus a reversible hydrogen reference electrode and shows a significantly improved performance in comparison to the carbon materials containing less P and N dopant atoms. PNDCs exhibit superior ORR current densities to that of the 20 % Pt/C catalyst because of the synergetic effect of P and N co‐doping. X‐ray photoelectron spectroscopy studies indicate the presence of pyridinic and graphitic N species, which are responsible for oxygen reduction that results in higher current densities. Rotating disk electrode and rotating ring‐disk electrode studies support a four electron oxygen reduction to water, with negligible generation of hydrogen peroxide.

Amperometric Oxygen Sensor Based on a Platinum Nanoparticle-Modified Polycrystalline Boron Doped Diamond Disk Electrode

Pt nanoparticle (NP)-modified polycrystalline boron-doped diamond (pBDD) disk electrodes have been fabricated and employed as amperometric sensors for the determination of dissolved oxygen concentration in aqueous solution. pBDD columns were cut using laser micromachining techniques and sealed in glass, in order to make disk electrodes which were then characterized electrochemically. Electrodeposition of Pt onto the diamond electrodes was optimized so as to give the maximum oxygen reduction peak current with the lowest background signal. Pt NPs, >0-10 nm diameter, were found to deposit randomly across the pBDD electrode, with no preference for grain boundaries. The more conductive grains were found to promote the formation of smaller nanoparticles at higher density. With the use of potential step chronoamperometry, in which the potential was stepped to a diffusion-limited value, a four electron oxygen reduction process was found to occur at the Pt NP-modified pBDD electrode. Furthermore the chronoamperometric response scaled linearly with dissolved oxygen concentration, varied by changing the oxygen/nitrogen ratio of gas flowed into solution. The sensor was used to detect dissolved oxygen concentrations with high precision over the pH range 4-10.

Oxygen Electro-Reduction on C22 and C276 Nickel Metal Alloy

The C22 and C276 alloy metal surfaces were characterized for eletrochemical activity in alkaline aqueous media in the presence and absence of oxygen and at 30{degree sign}C. The metal was studied by electrochemical impedance spectroscopy (EIS), voltammetry with still electrode and a specialized rotating ring-disk electrode (RRDE) technique, the cyclic potential ring measurement (CPRM) method. The application of the CPRM method to the study of oxygen reduction on C22 and C276 showed strong evidence for a predominantly series 2 step, 2 electron oxygen reduction pathway, where kinetic rate constants k2 (evaluated at -0.7V versus the saturated calomel electrode) and k3 (evaluated at -1.2V) were estimated at 30 {degree sign}C to be 0.001 cm/s and 0.193 cm/s respectively for C22 and 0.013 cm/s and 0.232 cm/s respectively for C276.

Electrochemistry of Shape-Controlled Catalysts: Oxygen Reduction Reaction on Cubic Gold Nanoparticles

This paper describes the electrochemical behavior of shape controlled, deliberately large Au nanoparticles that have been synthesized using a seed-mediated growth method in the presence of cetyl trimethyl ammonium bromide. Transmission electron microscopy micrographs and selected area electron diffraction patterns revealed 40 nm Au nanoparticles with a preferentially cubic shape suggesting a high amount of (100) surface sites. In situ electrochemical structure-sensitive reactions such as lead underpotential deposition confirm that the surface of the nanoparticles contains a large quantity of wide (100) domains. As a consequence, the nanoparticles showed a very high catalytic activity for the four electron oxygen reduction paths in alkaline media. Thus, water was obtained as the final product of the reaction in the whole potential range, while hydrogen peroxide was obtained only in the lower potential region, in a similar way as reported for Au (100) electrodes.