Oxygen In Alkaline Media Research Articles

Polygonal mesopores microflower catalysts for the catalytic oxidation of 2-nitro-4-methylsulfonyltoluene to 2-nitro-4-methylsulfonylbenzoic acid in a continuous-flow microreactor

The development of efficient systems for the catalytic oxidation of 2-nitro-4-methylsulfonyltoluene (NMST) to 2-nitro-4-methylsulfonyl benzoic acid (NMSBA) with atmospheric air or molecular oxygen in alkaline medium presents a significant challenge for the chemical industry. Here, we report the synthesis of FeOOH/Fe3O4/MOF polygonal mesopores microflower templated from a MIL-88B(Fe) at room temperature, which exposes polygonal mesopores with atomistic edge steps and lattice defects. The obtained FeOOH/Fe3O4/MOF catalyst was adsorbed onto glass beads and then introduced into the microchannel reactor. In the alkaline environment, oxygen was used as oxidant to catalyze the oxidation of NMST to NMSBA, showing impressive performance. This sustainable system utilizes oxygen as a clean oxidant in an inexpensive and environmentally friendly NaOH/methanol mixture. The position and type of substituent critically affect the products. Additionally, this sustainable protocol enabled gram-scale preparation of carboxylic acid and benzyl alcohol derivatives with high chemoselectivities. Finally, the reactions can be conducted in a pressure reactor, which can conserve oxygen and prevent solvent loss. Moreover, compared with the traditional batch reactor, the self-built microchannel reactor can accelerate the reaction rate, shorten the reaction time and enhance the selectivity of catalytic oxidation reactions. This approach contributes to environmental protection and holds potential for industrial applications.

Mass Transfer in the Processes of Native Lignin Oxidation into Vanillin via Oxygen

The influence of mass transfer intensity on the kinetics of the catalytic oxidation of flax shives with oxygen in alkaline media to aromatic aldehydes and pulp was studied. The process was carried out in two autoclaves, with moderate stirring (stirrer engine of 8 W) and intense stirring (stirrer engine of 200 W). The oxidation of flax shives into vanillin, syringaldehyde, and pulp was shown to proceed as a completely diffusion-controlled process under the studied conditions, both moderate and intense stirring. Depending on the process conditions, it can be limited by stages of oxygen transfer through the diffusion boundary layer near the gas–liquid interface (low intensity of mass transfer) as well as by reagents’ inner diffusion in the porous and solid matter of the flax shive particle (high intensity of mass transfer). The results on the influence of the stirring speed and volume of the reaction mass on the rates of oxygen consumption and vanillin accumulation were obtained. They were described using a known simple model connecting the intensity of mass transfer and the stirring power density in the bulk of the liquid phase in terms of algebra equations.

Enhancing the bifunctional oxygen reduction and evolution activity of CoNC by introducing a trace amount of Fe.

The potential application of zinc air batteries to tackle the energy shortage and environmental crisis has proposed new requirements of bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Utilizing the special spatial structure of zeolitic imidazolate framework-67 (ZIF-67) as an ideal research platform, the effect of a trace amount of Fe on the composition and structure of as-obtained Fe-CoNC catalysts was investigated. It was revealed that, due to the increased exposed pore structure and metal species located at the near surface, the active sites for the ORR/OER on Fe-CoNC are highly exposed, greatly boosting the activity to the reduction and evolution of oxygen in alkaline media. ZABs with Fe-CoNC have the highest maximum power density of 200 mW cm-2 when operated at current densities as high as 328 mA cm-2, better than not only Fe-free CoNC, but also precious metal-based references with the same catalyst loading.

Nanoscale Catalysts Based on Metal Chalcogenide Cobalt Clusters for Reduction of Oxygen in Alkaline Media

Nanoscale Catalysts Based on Metal Chalcogenide Cobalt Clusters for Reduction of Oxygen in Alkaline Media

A Brief Review on Key Role of Perovskite Oxides as Catalyst

AbstractThe research work conducted mainly on the reduction reaction of NOx, the oxidation reaction of CO, and hydrocarbons, electro‐catalysis of oxygen in alkaline medium, and photocatalytic water splitting has proved excellent catalytic behavior of perovskite oxides.[16–23] Although only a few reports published usages of the perovskite oxides as catalysts for the organic transformation such as catalytic hydrogenation, Ullmann, Sonogashira reactions, and Suzuki couplings.[24–26] Yoon et al. have prepared K2CO3 based LaMn1‐xCuxO3 perovskite oxide as a potential catalyst and discussed their mechanistic aspects in various reactions occurring at room temperature.[27] Recently, Wu and Ajayan group has demonstrated the relationship between stoichiometry and activity of pure and B‐site substituted layered perovskite oxide in the decomposition reaction of isopropanol by considering Sr2Sn1‐xRuxO4 (0≤x≤1) as catalyst.[28] In this scenario, present work aims to summarize the contribution of perovskite oxides as catalyst in numerous organic syntheses and catalysis, photocatalysis, and electrocatalysis reactions.

Impact of ball-milling of carbide-derived carbons on the generation of hydrogen peroxide via electroreduction of oxygen in alkaline media

Ball-milling is an effective method to decrease the size of carbide-derived carbon (CDC) grains, but milling might also affect other properties of CDC materials including but not limited to specific surface area (SSA), porosity, elemental composition and electrochemical properties. Thus, the goal of this work is to ball-mill various CDCs synthesised from silicon or titanium carbides and explore the effect of milling conditions on their physico-chemical and electrochemical properties. N 2 physisorption studies reveal that small ZrO 2 beads (0.5 mm in diameter) affect the SSA much less than bigger balls (5 mm in diameter) and the total porosity increases in the milled CDCs as compared to the initial microporous CDC materials referring to the formation of mesopores. Scanning electron microscopy (SEM) studies show that the morphology of the ground CDCs resembles that of submicron carbon powder. Slight changes regarding the total content of oxygen-containing groups on CDCs after grinding was confirmed by X-ray photoelectron spectroscopy (XPS). No significant change was observed between the activity of the initial and ball-milled CDCs towards the oxygen reduction reaction (ORR) in alkaline media by rotating ring-disc electrode (RRDE) method. The ORR on CDCs proceed via 2 + 2e − mechanism: O 2 reduction to HO 2 − followed by further electroreduction of HO 2 − to OH − . • Ball-milling with small beads (0.5 mm) have drastic impact on the CDC's morphology. • High specific surface area of CDC materials is maintained if small beads are used. • The electrocatalytic ORR activity slightly improved after ball-milling of CDCs. • Pristine and ball-milled CDCs produce high yield of HO 2 − at low overpotentials.

Carbon Nanotube Modified by (O, N, P) Atoms as Effective Catalysts for Electroreduction of Oxygen in Alkaline Media

The influence of the types and amounts of oxygen (O), nitrogen (N), and/or phosphorus (P) heteroatoms on the surface of carbon nanotubes (CNTs) on stability and catalytic activity in the oxygen reduction reaction (ORR) was investigated in alkaline media. It is shown that functionalization of CNTs leads to growth of the electrochemically active surface and to an increase in activity in the ORR. At the same time, a decrease in stability is observed after functionalization of CNTs under accelerated corrosion testing in alkaline media. These results are most significant on CNTs after functionalization in HNO3, due to the formation of a large number of structural defects. However, subsequent doping with N and/or P atoms provides a further activity increase and enhances the corrosion stability of CNTs. Thus, as shown by the studies of characteristic parameters (electrochemical active surface values (SEAS); E1/2; corrosion stability), CNTs doped with N and NP are promising catalytic systems that can be recommended for use as fuel cell cathodes. An important condition for effective doping is the synthesis of carboxyl and carbonyl oxygen-containing groups on the surface of CNTs.

Carbon-supported cobalt (III) complex for direct reduction of oxygen in alkaline medium

Transition metal-nitrogen-carbon catalysts obtained from pyrolysis of simple sources of metal and nitrogen or metal-organic frameworks are envisioned as promising replacement of Pt-based catalysts for oxygen reduction reaction (ORR) in fuel cells and metal-air batteries. However, the lack of clarity on the active site structure is a fundamental problem in developing efficient catalysts for the complete reduction of oxygen with maximum active site density. In this study, we have synthesized a simple metal-organic complex, [Co(bpy)2CO3]NO3 ⋅5H2O, 1 (bpy = 2, 2′-bipyridine) and studied its ORR activity in 0.1 M KOH supporting on Ketjenblack EC-600JD, 1/C. The crystal structure of 1 was unambiguously determined using single-crystal X-ray diffraction. The onset potential of ORR, Tafel slopes, kinetic current density, the fraction of oxygens reduced to peroxyl ion (χHO2−) and the electron transfer number (n) were compared with relevant literature and commercial 20 wt % Pt/C. Primarily, 1/C reduces O2 through the direct 4-electron pathway. ‘n’ and χHO2−on 1/C were found to be 3.87 and 7% at 0.7 ViR-freevs. RHE, respectively. The turn-over frequencies for the 4- and 2-electron process were found to be 0.124 and 0.001 electrons [Co]−1 s−1 at 0.7 ViR-freevs. RHE, respectively. Density-functional theory analysis reveals that the preferential activation of the side-on mode of adsorption on 1 is responsible for high selectivity in the direct 4-electron pathway.

Controlled Electropolymerization of Porphyrin-Based Materials

Porphyrin-based materials have unlocalized p-electrons; additionally, they form complexes through coordinating transition metal ions and can assemble as supramolecular structures. Due to these exceptional properties, they have found widespread applications in optoelectronic devices such as solar energy harvesting systems and photonic materials[1]. Porphyrins have also been used as the building blocks of covalent organic frameworks (COFs). An example of these materials is COF 420. Conjugated Porphyrin polymer and porphyrin-based COF have shown promising performances in electrocatalysis, especially toward oxygen reduction reaction (ORR) and in fuel cells and metal-air batteries [2,3]. In this work, we investigated the parameters, influencing the electropolymerization of tetrakis(4-aminophenyl)porphyrin (TAPP) and cobalt- tetrakis(4-aminophenyl)porphyrin (Co-TAPP) in organic media. The results have shown that the morphology and crystallinity of electrodeposited film are strongly dependent on the experimental conditions such as temperature, electropolymerization rate, electrode surface, and the monomer concentration. Rational adjustment of these parameters enabled us to gain control over the growth of the crystalline domains of pTAPP and p(Co-TAPP) films. Stacking of the porphyrin frameworks via p-p interactions, we explored the possibility of bottom-up synthesis of porphyrin-COF dendrites. We observed a structure-to-function relationship between the ordering of the covalent organic polymers and their electrocatalytic activities in reducing oxygen in alkaline media. Lian, Wenhui, et al. "Synthesis and properties of 5, 10, 15, 20-tetra [4-(3, 5-dioctoxybenzamidephenyl] porphyrin and its metal complexes." Journal of the Serbian Chemical Society3 (2012): 335-348.Day, Nicholas U., and Carl C. Wamser. "Poly-tetrakis-5, 10, 15, 20-(4-aminophenyl) porphyrin Films as Two-Electron Oxygen Reduction Photoelectrocatalysts for the Production of H2O2." The Journal of Physical Chemistry C21 (2017): 11076-11082.Walter, Michael G., and Carl C. Wamser. "Synthesis and characterization of electropolymerized nanostructured aminophenylporphyrin films." The Journal of Physical Chemistry C17 (2010): 7563-7574.

Gold/silver bimetal nanoparticles incorporated graphitic carbon nitride nanohybrid materials for oxygen reduction reaction

A facile method for the preparation of bimetal AuAg (gold/silver) alloy nanoparticles (NPs) incorporated graphitic carbon nitride (g-C3N4) nanohybrids (NHs) materials embedded in Nafion matrix (Nf/g-C3N4/AuAg NHs) and its application towards electrocatalytic reduction of oxygen in alkaline medium are reported. The prepared Nf/g-C3N4/AuAg NHs were characterized by using X-ray diffraction (XRD), absorption spectroscopy, high resolution transmission electron spectroscopy (HRTEM), scanning electron microscopy-energy dispersive X-ray spectrophotometer (SEM-EDX), SEM-EDX elemental mapping, SEM-EDX lines scan spectra and cyclic voltammetry (CV) techniques. The absorption spectra of Nf/g-C3N4/AuAg NHs showed the characteristic surface plasmon resonance (SPR) absorption band for AuAg alloy NPs and was found in between the wavelength regions of the monometal NPs (Au and Ag NPs). The bimetal alloy formation was confirmed from the observation of single SPR absorption band and further a blue shifting in the SPR band was observed with increasing Ag content in the g-C3N4/AuAg NHs. The HRTEM images explicitly demonstrated the formation of Au, Ag and alloy AuAg NPs on g-C3N4 surface where the size of the bimetal AuAg NPs are found to be smaller than the corresponding monometals (Au and Ag NPs). The electrochemical characteristics of bimetal AuAg NPs at the Nf/g-C3N4/Au, Nf/g-C3N4/Ag and Nf/g-C3N4/AuAg NHs modified electrodes were studied using cyclic voltammetry. The combination of Nf/g-C3N4 and bimetal AuAg alloy NPs enhanced the electrocatalytic oxygen reduction reaction at the modified electrode. The GC/Nf/g-C3N4/Au75Ag25 modified electrode showed the highest catalytic current among the other controlled NHs materials towards the electrocatalytic oxygen reduction in alkaline medium. The Koutecky-Levich (K-L) plots obtained from the modified RDE studies showed four-electron transfer of oxygen reduction reaction (ORR) at the GC/Nf/g-C3N4/Au75Ag25 modified electrode.

Trimetallic Carbon-Supported Catalysts for Borohydride Oxidation and Oxygen Reduction in Alkaline Solutions

Borohydrides present a particularly attractive option for alkaline liquid fuel systems, having high energy densities, a low standard potential for its oxidation, and good stability in alkaline conditions. A key area in the success of a fuel cell utilizing borohydride is the development of an anode, which can make use of the full 8-electron oxidation, directly oxidising the borohydride with as little of the undesired hydrolysis reaction occurring as possible. This is in addition to the common requirements of high activity, high stability, good electronic conductivity and effective transport of reactants and products. Here we present new studies on the oxidation of borohydride and reduction of oxygen in alkaline media under various conditions for a selection of trimetallic carbon-supported catalysts based on Pd, prepared by quick and straightforward synthetic routes. The prepared catalysts were characterised by cyclic voltammetry, chronoamperometry, and RDE based procedures. Notably, PdAuNi/C prepared via a NaBH4-2-propanol complex presents highly dispersed trimetallic alloy particles, as determined by XRD, XPS and TEM. The best performing electrodes under characterisation conditions were tested in a direct borohydride fuel cell under several different conditions. The influence of experimental parameters (temperature, borohydride concentration, as well as NaOH concentration) on the electrical behaviour of the fuel cell were studied and optimized. These results show that Pd-based trimetallic catalysts supported on carbon provide a ready route to successfully operate borohydride based fuel cells. Acknowledgements: A. Elsheikh acknowledges a Newton-Mosharafa Scholarship (Reference no. NMJ8/15) for funding. The Portuguese Foundation for Science and Technology (FCT, Portugal) is acknowledged for PhD grant no. SFRH/BD/137470/2018 (R.C.P. Oliveira), contract no. IST-ID/156/2018 (B. Šljukić) and contract no. IF/01084/2014/CP1214/CT0003 under IF2014 Programme (D.M.F. Santos). Keywords: Palladium, trimetallic catalysts, nanomaterials, borohydride oxidation, oxygen reduction, fuel cell, kinetic parameters.

Electrospun carbon nanofibers loaded with spinel-type cobalt oxide as bifunctional catalysts for enhanced oxygen electrocatalysis

Abstract The electrocatalysis of oxygen in alkaline media is a challenging issue, influencing the performance of many electrochemical devices: fuel cells, unitized regenerative fuel cells, electrolyzers and metal-air batteries. This new manuscript proposes the synthesis of graphitic carbon nanofibers obtained by electrospinning with a cobalt-based spinel oxide, Co3O4/CNF. By means of a simple, reproducible and scalable method, a bifunctional catalyst with a promising performance is obtained, being able of carrying out the electrocatalysis of oxygen (oxidation of water, evolution and reduction of oxygen) in a basic solution. The combination of the active species on cobalt oxide (Co2+, Co3+ and Co-Nx), along with active species in the carbon nanofiber (graphitic and pyridinic N), gives rise to a catalyst with a remarkable reversibility (difference between E10 mA/cm2 (evolution) and Ehalf-wave-potential (reduction)): ΔE =795 mV), a low over-potential for the evolution of oxygen (η =416 mV) and 919 mV of oxygen reduction onset potential, very similar to that of a benchmark catalyst, Pt/C.

Carbon-based lanthanum nickelate material La2−x−yNdxPryNiO4+δ (x = 0, 0.3, and 0.5; y = 0 and 0.2) as a bifunctional electrocatalyst for oxygen reduction in alkaline media

The kinetics and mechanism of oxygen reduction reaction (ORR) in alkaline medium are studied on lanthanum nickelate materials La2−x−yNdxPryNiO4±δ (x = 0, 0.3 and 0.5; y = 0 and 0.2) using the electrochemical technique of the rotating disk electrode in a 0.5-M solution of NaOH. The oxide powders are synthesized by the citrate–nitrate method. Structural and surface characterizations are performed by X-ray diffraction (XRD) and X-ray photoelectron spectrometry (XPS), while the morphology is studied by scanning electron microscopy (SEM). Electrochemical studies are carried out by linear voltamperometry, cyclic voltamperometry, and impedance spectroscopy. The doped and undoped electrocatalyst composites (La2−x−yNdxPryNiO4±δ/C), made of the rare earth nickel oxides mixed with carbon black (Vulcan XC-72(C)), are deposited as a thin layer on a glassy carbon substrate. At room temperature, the undoped electrocatalyst La2NiO4±δ material shows single-step kinetics unlike the doped materials. The doping by the rare earths Nd or/and Pr significantly enhances the electrical conductivity of the electrode under air and the diffusion of oxygen. On the other hand, the steric hindrance between the atomic oxygen orbital (π-orbital (O2)–π-orbital (O2)) and the dz2–orbital (Ni)–π-orbital (O2) influences the training model of the liaison (dz2(Ni)–π (O2)). The structure, oxygen adsorption, and oxidation states of the catalyst elements have a large influence on the mechanism and kinetics of the ORR. The LNNO3/C and LNPNO5/C electrocatalysts have better electrocatalytic performances, which allow them to be used as a bifunctional electrocatalyst for the reduction of oxygen in alkaline media.

Structural, magnetic and dielectric properties of pure and Dy-doped Co3O4 nanostructures for the electrochemical evolution of oxygen in alkaline media

In this study, spinel-type cobalt oxide (Co3O4) and Co3-xDyxO4 (x = 0.04 and 0.05 molar ratio) nanoparticles were synthesized via combustion method at 700 °C. Crystallite nature, phase purity and thermal analysis of the prepared compounds were investigated by PXRD, FT-IR and TGA techniques. Structural analyses were performed by the FullProf program employing profile matching with constant scale factors. The results showed that the patterns had a main cubic structure with space group of Fd3m. The cell parameter data calculated by rietveld analysis showed that the cell parameters were nearly constant. The morphological and structural properties of the obtained materials were examined by FESEM and TEM images. Besides, the magnetic measurements of Co3O4 and Co3-xDyxO4 nanoparticles were performed by vibration sampling magnetometer (VSM). Coercivity (Hc) and remanent magnetization (Mr) were found to be reduced in Dy3+ doped Co3O4 while saturation magnetization (Ms) was increased moderately. The effect of dysprosium ion addition was also studied using cyclic voltammetry (CV) for the oxygen evolution reaction in an alkaline environment. The obtained data showed that the presence of Dy3+ exhibited a much higher oxygen evolution activity and lower over potential compared to Co3O4.

Reduced-Graphene-Oxide with Traces of Iridium or Gold as Active Support for Pt Catalyst at Low Loading during Oxygen Electroreduction

Chemically-reduced graphene-oxide-supported gold nanoparticles and traces of iridium are considered here together with loadings of platinum as catalytic materials for reduction of oxygen in alkaline and acid media, respectively. Comparison is made to the analogous systems based on conventional Vulcan carbon carriers. Gold nanoparticles are prepared by the chemical reduction method, in which the NaBH4-prereduced Keggin-type phosphomolybdate heteropolyblue acts as the reducing agent for the precursor (HAuCl4). Polyoxmetallate (PMo12O40 3-) capping ligands stabilize gold nanoparticle deposits, facilitate their dispersion and attachment to carbon supports. Indeed, it is apparent from the independent diagnostic voltammetric experiments (in 0.5 mol dm-3 H2SO4) that heteropolymolybdates form readily stable adsorbates on nanostructures of both gold and carbon (reduced graphene oxide and Vulcan). It is reasonable to expect that the polyoxometallate-assisted nucleation of gold has occurred in the proximity of oxygenated defects existing on carbon substrates. Under conditions of electrochemical diagnostic experiments (performed in 0.1 mol dm-3 KOH) the phosphomolybdate adsorbates are removed from the interface as they undergo dissolution in alkaline medium; and the Au nanoparticles (Au loading, 30 µg cm-2) remain well-dispersed on the carbon as evident from transmission electron microscopy. High electrocatalytic activity of the reduced-graphene oxide-supported Au nanoparticles toward reduction of oxygen in alkaline medium is demonstrated using cyclic and rotating ring-disk electrode (RDE) voltammetric experiments. Among important issues are possible activating interactions between gold and the support, as well as presence of structural defects existing on poorly organized graphitic structure of reduced graphene oxide (as evident from Raman spectroscopy). When using the silica or titania functionalized reduced graphene oxide as carriers for Au (or Ir) and Pt nanoparticles, the resulting systems have exhibited typically higher (certainly not lower) O2-reduction currents (relative to those recorded at conventional Vulcan-supported Pt at the same loading) in acid medium (0.5 M H2SO4). The RDE data are consistent with even lower formation of hydrogen peroxide. Furthermore, the durability of this family of catalysts was outstanding. Finally, by doping the reduced graphene oxide supported Pt with traces of Ir (<1 µg cm-2), decreases amounts of produced H2O2 (<1%) at potentials 0.6 V (vs RHE) or lower.

Poly-porphyrin electrocatalytic films obtained via new superoxide-assisted electrochemical deposition method

We present electrocatalytic films of ClFe(III)5,10,15,20-tetrakis(p-aminophenyl) porphyrin (FeClT(p-NH2Ph)P) formed by new electrochemical deposition method using oxygen saturated dimethyl sulfoxide solutions (DMSO) as a medium. Superoxide promotes the poly-porphyrin film formation on the working electrode surface due to it high affinity both to hydrogen atom and to proton. The most favorable pathway of the superoxide-assisted electrochemical polymerization is proposed. The resulting poly-FeClT(p-NH2Ph)P films are smooth, golden colored, well adhesed with substrate and quite insoluble in water, ethanol and dichloromethane. The film formation accompanied with broadening and red-shifting of the Soret band. Atomic force microscopy (AFM) investigation shows homogeneity, low roughness and nanoscale globular structure of the poly-FeClT(p-NH2Ph)P films. Electrocatalytic activity of obtained films was tested for electroreduction of oxygen in alkaline media. The current of oxygen electroreduction is increased and oxygen electroreduction onset is shifted to the positive about 0.14V in the presence of poly-FeClT(p-NH2Ph)P film. The stability of the poly-FeClT(p-NH2Ph)P film was tested under oxygen electroreduction conditions. It was found that for >20cycles the oxygen electroreduction parameters were unchanged. The modified electrodes removed from the electrochemical cell had the same view as before testing.

Co3O4 nanoparticles assembled on polypyrrole/graphene oxide for electrochemical reduction of oxygen in alkaline media

The development of highly efficient catalysts for cathodes remains an important objective of fuel cell research. Here, we report Co3O4 nanoparticles assembled on a polypyrrole/graphene oxide electrocatalyst (Co3O4/Ppy/GO) as an efficient catalyst for the oxygen reduction reaction (ORR) in alkaline media. The catalyst was prepared via the hydrothermal reaction of Co2+ ions with Ppy-modified GO. The GO, Ppy/GO, and Co3O4/Ppy/GO were characterized using scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The incorporation of Ppy into GO nanosheets resulted in the formation of a nitrogen-modified GO porous structure, which acted as an efficient electron-transport network for the ORR. With further anchoring of Co3O4 on Ppy/GO, the as-prepared Co3O4/Ppy/GO exhibited excellent ORR activity and followed a four-electron route mechanism for the ORR in alkaline solution. An onset potential of −0.10 V vs. a saturated calomel electrode and a diffusion limiting current density of 2.30 mA/cm2 were achieved for the Co3O4/Ppy/GO catalyst heated at 800 °C; these values are comparable to those for noble-metal-based Pt/C catalysts. Our work demonstrates that Co3O4/Ppy/GO is highly active for the ORR. Notably, the Ppy coupling effects between Co3O4 and GO provide a new route for the preparation of efficient non-precious electrocatalysts with hierarchical porous structures for fuel cell applications.

Inorganic frameworks based on bimetallic nanoparticles encapsulated in hollow MnO2 structures

A novel microwave-assisted hydrothermal route has been demonstrated to allow the synthesis of hollow MnO2 particles with dandelion-like structure. The as-prepared particles show the ability to enclose PtAu bimetallic nanoparticles which good electrocatalytic activity toward the oxidation of glycerol and the reduction of oxygen in alkaline media, in addition to high stability, what we attribute to the MnO2 cage, which is responsible for the confinement of reaction intermediates impeding their diffusion to the bulk electrolyte. Considering the inherent properties of MnO2, such as low acute toxicity to living organisms, biocompatibility, stability in neutral and alkaline media and the ability to enclose other possible different materials, including functionalized nanoparticles, we suggest a broad field of potential application for these structures, such as drug delivery and bioimaging, catalysis, (bio)sensing, etc.

Evaluation of reduced-graphene-oxide-supported gold nanoparticles as catalytic system for electroreduction of oxygen in alkaline electrolyte

Chemically-reduced graphene-oxide-supported gold nanoparticles with a diameter, of 40–60nm are considered here as catalytic materials for the reduction of oxygen in alkaline medium in comparison to analogous systems based on conventional Vulcan carbon carriers. Gold nanoparticles are prepared by the chemical reduction method, in which the NaBH4-prereduced Keggin-type phosphomolybdate heteropolyblue acts as the reducing agent for the precursor (HAuCl4). Polyoxometallate (PMo12O403−) capping ligands stabilize gold nanoparticle deposits, facilitate their dispersion and attachment to carbon supports. Indeed, it is apparent from the independent diagnostic voltammetric experiments (in 0.5moldm−3 H2SO4) that heteropolymolybdates form readily stable adsorbates on nanostructures of both gold and carbon (reduced graphene oxide and Vulcan). It is reasonable to expect that the polyoxometallate-assisted nucleation of gold has occurred in the proximity of oxygenated defects existing on carbon substrates. Under conditions of electrochemical diagnostic experiments (performed in 0.1moldm−3 KOH): (i) the phosphomolybdate adsorbates are removed from the interface as they undergo dissolution in alkaline medium; and (ii) the Au nanoparticles (Au loading, 30μgcm−2) remain well-dispersed on the carbon as evident from transmission electron microscopy. High electrocatalytic activity of the reduced-graphene oxide-supported Au nanoparticles toward reduction of oxygen in alkaline medium is demonstrated using cyclic and rotating ring-disk voltammetric experiments. The latter system could also act as the active support for Pt nanoparticles during the reduction of oxygen. Among important issues are possible activating interactions between gold and the support, as well as presence of structural defects existing on poorly organized graphitic structure of reduced graphene oxide (as evident from Raman spectroscopy).

Porous N,P-doped carbon from coconut shells with high electrocatalytic activity for oxygen reduction: Alternative to Pt-C for alkaline fuel cells

This study introduces a new, environmentally-friendly method to synthesize N,P-doped porous carbon by high conversion (46% yield) of coconut shell residues for the reduction of oxygen in alkaline media. The obtained materials display an excellent electrocatalytic activity, making them suitable as cathode catalyst for alkaline fuel cells. The synthesis procedure included an efficient single-step activation with phosphoric acid to achieve high surface area (1216m2g−1) and pore volume (1.15cm3g−1 with 72% mesopores). Urea was used as a low-cost and ecologically-sound source for nitrogen doping of the as-synthesized porous carbon. Remarkably, the biomass-derived electroactive carbon demonstrates a superior performance compared to a reference material, the state-of-the-art commercial Pt-C catalyst: (a) comparable electrocatalytic activity; (b) better tolerance to methanol crossover effects and, (c) improved long-term durability towards oxygen reduction reaction in alkaline media.