Oxygen Reduction Performance Research Articles

Cellulose-derived nitrogen and phosphorus dual-doped carbon as high performance oxygen reduction catalyst in microbial fuel cell

Microbial fuel cells (MFCs) couple functions of waste removal and electricity generation. The future success of MFCs inevitably depends on the increase of performance at decrease of material cost. Therefore, the use of renewable and sustainable materials, e.g. cellulose, to prepare high performance materials for MFCs would be an inevitable trend. In this communication, nitrogen and phosphorus dual-doped carbons were prepared by pyrolysis of cellulose using ammonium phosphate as doping source and employed as oxygen reduction reaction (ORR) catalyst in air-cathode of MFCs. A maximum power density of 2293 ± 50 mW m−2 was generated by the air-cathode using the dual-doped carbon catalyst, which was higher than the air-cathode using Pt/C catalyst with Pt load of 0.5 mg cm−2 (1680 ± 32 mW m−2). This study provided a facile and sustainable way to prepare low-cost and high-efficient ORR catalyst for scaled-up MFC applications.

Unusual high oxygen reduction performance in all-carbon electrocatalysts.

Carbon-based electrocatalysts are more durable and cost-effective than noble materials for the oxygen reduction reaction (ORR), which is an important process in energy conversion technologies. Heteroatoms are considered responsible for the excellent ORR performance in many carbon-based electrocatalysts. But whether an all-carbon electrocatalyst can effectively reduce oxygen is unknown. We subtly engineered the interfaces between planar graphene sheets and curved carbon nanotubes (G-CNT) and gained a remarkable activity/selectivity for ORR (larger current, and n = 3.86, ~93% hydroxide + ~7% peroxide). This performance is close to that of Pt; and the durability is much better than Pt. We further demonstrate the application of this G-CNT hybrid as an all-carbon cathode catalyst for lithium oxygen batteries.We speculate that the high ORR activity of this G-CNT hybrid stems from the localized charge separation at the interface of the graphene and carbon nanotube, which results from the tunneling electron transfer due to the Fermi level mismatch on the planar and curved sp2 surfaces. Our result represents a conceptual breakthrough and pioneers the new avenues towards practical all-carbon electrocatalysis.

Metal-free ionic liquid-derived electrocatalyst for high-performance oxygen reduction in acidic and alkaline electrolytes

We report herein a new simplified approach to metal-free N-doped carbon aerogels made from ionic liquids by a bottom-up “salt templating” strategy, which are known to be promising electrocatalytic materials. An optimized pore transport system as well as a high catalytically active surface allowed the ionic liquid-derived carbons to possess favourably high electrocatalytic performance in oxygen reduction under alkaline and, not found for similar materials made by other pathways, under technically more relevant acidic conditions. Even in acid, the performance favourably compares with a commercial Pt-based catalyst.

Direct synthesis of nitrogen-doped carbon nanosheets with high surface area and excellent oxygen reduction performance.

Graphene-like nitrogen-doped carbon nanosheets (NCN) have become a fascinating carbon-based material for advanced energy storage and conversion devices, but its easy, cheap, and environmentally friendly synthesis is still a grand challenge. Herein we directly synthesized porous NCN material via the facile pyrolysis of chitosan and urea without the requirement of any catalyst or post-treatment. As-prepared material exhibits a very large BET surface area of ~1510 m(2) g(-1) and a high ratio of graphitic/pyridinic nitrogen structure (2.69 at. % graphitic N and 1.20 at. % pyridinic N). Moreover, compared to a commercial Pt/C catalyst, NCN displays excellent electrocatalytic activity, better long-term stability, and methanol tolerance ability toward the oxygen reduction reaction, indicating a promising metal-free alternative to Pt-based cathode catalysts in alkaline fuel cells. This scalable fabrication method supplies a low-cost, high-efficiency metal-free oxygen reduction electrocatalyst and also suggests an economic and sustainable route from biomass-based molecules to value-added nanocarbon materials.

Preparation of Graphene Oxide-Sliver Electrodes By Electrophoretic Deposition and Its Catalytic Performance for Oxygen Reduction

not Available.

Preparation of Nitrogen‐Doped Porous Carbon Nanofibers and the Effect of Porosity, Electrical Conductivity, and Nitrogen Content on Their Oxygen Reduction Performance

AbstractNitrogen‐doped carbon nanostructures are considered as a possible alternative to platinum‐based catalysts for fuel cells. The surface density of catalytic sites, electrical conductivity, and nitrogen content play important roles in designing electrode materials for fuel cells. Herein, N‐doped carbon fibers are prepared by electrospinning the poly(acrylonitrile) (PAN) solution followed by carbonization. Some of the key issues of the oxygen reduction reaction (ORR) are addressed in terms of nitrogen content, porosity, and electrical conductivity in the N‐containing carbon nanofibrous system. Nitrogen content and the amount of the graphitic phase are varied by changing the carbonization temperature. In addition, N‐doped carbon fibers with high porosity are prepared by electrospinning the solution mixture of poly(ethylene oxide) (PEO)/PAN followed by carbonization, and the porosity is tuned by varying the ratio of PEO to PAN. The effect of porosity or the surface density of catalytic sites on the ORR is studied. A medium porous sample prepared from the PEO/PAN mixture in a 1:1 ratio by carbonization at 1000 °C is found to be favorable for improved ORR performance for such a system. The observations made herein are explained in terms of trade‐offs between electrical conductivity, nitrogen content, and surface density of active sites.

The value of mixed conduction for oxygen electroreduction on graphene–chitosan composites

Graphene-based electrocatalysts have been widely investigated for their excellent performance in electrocatalytic oxygen reduction. The surface chemistry of graphene-based electrocatalysts is important for developing more efficient fuel cells and metal-air batteries. In addition, the nanostructured gas-diffusion electrode (GDE) on which the electrocatalysts are loaded needs to be carefully tailored to facilitate mass transport (reactants and products). A polymer binder is often used to fabricate the GDE which means there is a need to optimize the ratio of binder to electrocatalyst. Herein we demonstrate the impacts of graphene-based GDE nanostructures on the efficiency of oxygen electroreduction by comparing a series of graphene/chitosan composites with varying compositions. In these nanostructured GDEs graphene acts as the electrocatalyst and chitosan as the binder. Our results illustrate a critical ratio of graphene to chitosan for enhanced electrocatalytic surface area and facilitated mass transport, while a continuous network for electron conduction is effectively established. We believe this work is an important piece of the puzzle to better understanding the electrode behavior of electrocatalysts consisting of graphene-like two-dimensional materials in oxygen reduction reaction.

Effect of phosphorus and copper additions on the structure of Pt and Pt–Cu nanoparticles in a radiation-induced reduction method

The effects of phosphorus (PH2O2 −) and copper (Cu2+) additions to the aqueous precursor solution on the structure of Pt–Cu nanoparticles were investigated for a radiation-induced reduction method. Addition of PH2O2 − in the precursor solution reduced the diffraction intensity of Pt or Pt–Cu crystallites due to smaller size and/or lower crystallinity. Both the diffraction intensity and the particle size (measured by an electron microscope) were minimized when Cu/Pt ratio was 0.05–0.25, which was attributed to the effects of copper and phosphorus to stabilize crystallites and particles through the negative heat of mixing. The concomitant increase in phosphorus content suggested that PH2O2 − is partly reduced and taken into the Pt lattice. Further increase of copper content caused larger particles and decrease in phosphorus content. These trends were also consistent with electrochemical surface area and oxidation/reduction behavior of Pt surface. The radiation-induced reduction method is suited to produce small Pt–Cu particles uniformly distributed on carbon support, which are potentially served for heat treatment for improved oxygen reduction performance.

Improved Oxygen Reduction Performance of Pt–Ni Nanoparticles by Adhesion on Nitrogen-Doped Graphene

Graphene and its derivatives hold great potential as support for nanocatalyst in various energy applications, such as fuel cells, batteries, and capacitors. In this work, we used density functional ...

The Influence of N‐doped Carbon Materials on Supported Pd: Enhanced Hydrogen Storage and Oxygen Reduction Performance

N-doped graphene has become an important support for Pd in both hydrogen storage and catalytic reactions. The molecular orbitals of carbon materials (including graphene, fullerene, and small carbon clusters) and those of the supported Pd species will hybrid much stronger as N dopants are introduced, owing to the increased electrostatic attraction at the interface. This enhances the carbon substrates' catching force for the supported Pd, preventing its leaching and aggregation in many practical applications. The better dispersion and stabilization of Pd nanoparticles, which are induced by various carbon supports with N-doping, are pleasing to us and could increase their efficiency and facilitate their recycling during various reaction processes in several fields.

Synthesis and Electrocatalytic Oxygen Reduction Performance of the Sulfur-Doped Carbon Nanocages

The sluggish oxygen reduction reaction (ORR) is the bottleneck in the development of fuel cells, and replacing precious and nondurable Pt catalysts by the material with low cost, high activity and good stability is a main challenge. Car- bon-based metal-free ORR electrocatalysts have become a promising alternative of commercial Pt/C catalyst due to their superior catalytic activity, high stability and low cost. Recent studies revealed that the doping of N, B, P or S atoms could boost the ORR electrocatalytic performance of carbon nanomaterials, and the catalytic activities were highly dependent on the doping elements, amounts and microstructures. In this study, sulfur-doped carbon nanocages (SCNCs) were synthesized by chemical vapor deposition method using in situ generated MgO as template and thiophene/benzene as precursors. The resultant SCNCs possessed high specific surface area of ca. 1000 m 2 •g -1 , abundant pore structure and superior graphitization degree. The X-ray photoelectron spectroscopy result showed sulfur atoms were doped into the carbon framework as the C― S―C moieties. The content of sulfur in the SCNCs was adjusted in the range of 0~3.45 at% by changing the amount of thiophene in the precursor. All the SCNCs samples had comparable specific surface area and similar pore structure. As an electrocatalyst for oxygen reduction reaction (ORR) in alkaline medium, the SCNCs exhibited a sulfur-content-dependent performance. The SCNCs with sulfur content of 0.84 at% demonstrated the optimal ORR performance. With further increas- ing the sulfur content, the ORR performance of the SCNCs gradually degraded and even inferior to that of the pure CNCs when the sulfur content was higher than 1.61 at%. In addition, the SCNCs showed better stability and immunity to methanol crossover than the Pt/C catalyst. This result is suggestive for designing advanced metal-free ORR electrocatalysts by regulat- ing the species and content of dopants and doping microstructures. Keywords carbon nanocages; sulfur doping; oxygen reduction; metal-free; fuel cells

Nanoparticle catalysts for proton exchange membrane fuel cells: can surfactant effects be beneficial for electrocatalysis?

Platinum (Pt) nanoparticles were prepared in aqueous dispersion using the non-ionic surfactant nonylphenolethoxylate (NP9) and the cationic surfactant tetradecyltrimethylammonium bromide (TTAB). The surfactants were added to give colloidal stability. Such species are generally considered to block electrochemical active sites and to be undesirable for the oxygen reduction reaction (ORR). However, the procedures used to remove them are likely to cause particle aggregation. The purpose of this work was to investigate the effect of surfactants on Pt ORR performance. The nanoparticles prepared using NP9 showed good oxygen reduction performance when compared with the commercial Pt/C catalyst TKK, without removing the surfactant. In contrast, Pt nanoparticles prepared using the cationic surfactant TTAB showed very poor ORR performance, exemplifying the importance of careful surfactant selection in catalyst synthesis.

Long-term, stable, and improved oxygen-reduction performance of titania-supported PtPb nanoparticles

Anatase-type titania-supported intermetallic PtPb nanoparticles synthesized through a wet-chemical route showed a long-term, stable, and improved oxygen reduction reaction performance.

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.

Carbon-supported Fe/Co-N electrocatalysts synthesized through heat treatment of Fe/Co-doped polypyrrole-polyaniline composites for oxygen reduction reaction

In this paper, we synthesized cathode catalysts (PANI-PPYR, Fe/PANI-PPYR, Co/PANI-PPYR and Fe-Co/PANI-PPYR) with high performance oxygen reduction by using a simple heat treatment process. These catalysts were fabricated by directly calcining the Fe and/or Co doped polyaniline (PANI)-polypyrrole (PPYR) composites. Their electrocatalytic activity for ORR both in acidic and in alkaline media was investigated by voltammetric techniques. Among the prepared catalysts, Co/PANI-PPYR presents the most positive ORR onset potential of 0.62 V (vs. SCE) in 0.5 mol/L H2SO4 solution or −0.09 V (vs. SCE) in 1 mol/L NaOH solution. In addition, the Co/PANI-PPYR catalyst shows the largest limiting-diffusion current density for ORR, which is 4.3 mA/cm2@0.2 V (vs. SCE) in acidic and 2.3 mA/cm2@−0.3 V (vs. SCE) in alkaline media. In acidic media, a four-electron reaction of ORR on the Co/PANI-PPYR and Fe/PANI-PPYR catalysts is more dominant than a two-electron reaction. In alkaline media, however, a four-electron and a two-electron mechanisms are co-present for the ORR on all the prepared catalysts. Co/PANI-PPYR catalyst also presents good electrocatalytic activity stability for ORR both in acidic and in alkaline media.

Graphene: N‐Doped Graphene Natively Grown on Hierarchical Ordered Porous Carbon for Enhanced Oxygen Reduction (Adv. Mater. 43/2013)

Carbon-based materials with high surface area, accessible porosity, and good conductivity are extremely desirable for energy-conversion applications. On page 6226, Shi Zhang Qiao and co-workers report a hybrid material composed of hierarchical ordered porous carbon and in situgrown graphene, which successfully combines the above merits and results in a synergistically enhanced electrochemical catalysis performance for oxygen reduction.

Enhanced Catalytic Oxygen Reduction Performance from Titania Supported PtPb Nanoparticles

not Available.

Manageable N-doped Graphene for High Performance Oxygen Reduction Reaction

Catalysts for oxygen reduction reaction (ORR) are at the heart of key green-energy fuel cell technology. N-doped graphene is a potential metal-free electrode with much better electrocatalytic activity, long-term stability, and tolerance to crossover effect than expensive platinum-based electrocatalysts. Here, we report a feasible direct-synthesis method in preparing N-graphene with manageable N contents in a large scale. The resultant N-graphene used as electrocatalysts exhibits similar catalytic activity but superior stability compared to commercial Pt/C for ORR in an alkaline solution. It was found that their electrocatalytic activities were demonstrated to depend largely on N-doping content. When nitrogen content reaches a high value at about 24–25%, ORR reaction exhibits a favorable formation of water via a four-electron pathway. Furthermore, the effect of pyrolysis temperature and precursor on the activity of N-graphene is systematically analyzed, and may shed some light on the principle of choosing appropriate way for preparing N-graphene.

Investigation of typical properties of nanocrystalline iron powders prepared by ball milling techniques

Metallic powder has applications in many fields. In applications for preservation and anti-oxidation, iron powder has been used as an air oxygen reducer which is capable of decreasing microclimatic oxygen concentrations in a hermetic mini-environment. In this role, if we increase the specific surface area by reducing the particle size of the iron powder, the rate and performance of oxygen reduction will be improved significantly. In addition, the porosity of iron powder also contributes considerably. The iron powder can be fabricated using many methods: chemical deposition, powder metallurgy and mechanical milling. The technique of milling has certain advantages, especially for the formation of technical iron powder. The experimental equipment used was a Fritsch P-6 planetary ball mill. The iron powder was prepared with different milling times, from 1 up to 30 h in acetone as a protective environment. The powder products obtained were analyzed using field emission scanning electron microscope (FE-SEM), energy dispersive x-ray (EDX), x-ray diffraction (XRD), dynamic laser scattering (DLS), Brunauer–Emmett–Teller (BET) techniques and also magnetic characterization by vibrating sample magnetometer (VSM). The results show a correlation between the milling time and the crystallite and particle size, specific surface area, magnetic properties and nanoscale porosity of the iron powder. The iron powders obtained were a kind of mesoporous materials. The properties of the iron powder were examined with respect to their oxygen reducing kinetics.

Synthesis of the nitrogen-doped carbon nanotube (NCNT) bouquets and their electrochemical properties

The nitrogen-doped carbon nanotube (NCNT) bouquets have been synthesized by the pyrolysis of nitrogen-containing ion-exchange resin. The material shows excellent oxygen reduction performance after being supported by the Pt nanoparticles (Pt/NCNTs) compared with commercial Pt/C (46.7wt.% Pt, TKK, Japan) in terms of the onset potential, half-wave potential, mass activity and durability. The better ORR performance of the Pt/NCNTs indicates potential applications in PEMCs.