Efficient Oxygen Reduction Catalyst Research Articles

Novel CdFe Bimetallic Complex-Derived Ultrasmall Fe- and N-Codoped Carbon as a Highly Efficient Oxygen Reduction Catalyst.

During the development of oxygen reduction reaction electrocatalysts, transition-metal nanoparticles embedded in N-doped graphene have attracted increasing attention owing to their low-priced, minimal environmental impact, and satisfying performance. In this study, a new organic-cadmium (Cd) complex formed through Cd2+ coordination with p-phenylenediamine (PPD) was used to synthesize highly active Fe-embedded N-doped carbon catalysts for the first time. It is significant that with the decreasing molar ratio of Cd/Fe, an obvious microstructure evolution was observed in Cd-Fe-PPD from diamond-like blocks to thick flakes, and further bloomed into flowerlike shapes with ultrathin petals and then eventually exhibited large block starfish-like shapes. After carbonization, Cd was removed, slack and porous N-doped carbon was formed, and Fe was assembled in the N-doped carbon. Similar phenomenon was also observed in Co-PPD. The optimized Fe/NPC-2 material featuring uniform and well-dispersed 3-5 nm Fe nanoparticles embedded in two-dimensional ultrathin carbon nanosheets delivered excellent electrocatalytic performance ( Eonset: 0.96 V vs reversible hydrogen electrode (RHE), E1/2: 0.84 V vs RHE), which is very close to those of commercial platinum on carbon (Pt/C) ( Eonset: 0.95 V vs RHE, E1/2: 0.84 V vs RHE), and its methanol tolerance and durability also surpass those of Pt/C.

RuN4 Doped Graphene Oxide, a Highly Efficient Bifunctional Catalyst for Oxygen Reduction and CO2 Reduction from Computational Study

The searching of highly efficient bifunctional catalysts for both oxygen reduction reaction (ORR) and CO2 reduction reaction (CO2RR) for energy conversion and storage has attracted particular atten...

Nitrogen–Fluorine Dual Doped Porous Carbon Derived from Silk Cotton as Efficient Oxygen Reduction Catalyst for Polymer Electrolyte Fuel Cells

Porous carbon derived from silk cotton and heteroatom engineering is explored in this study for developing metal-free electrocatalysts for oxygen reduction (ORR). Individual and dual doping of N and F heteroatoms was conducted to regulate defects and the pore geometry to the porous carbon matrix. Microscopic analysis of N–F co-doped cotton carbon (N–F/CTC) undergoes morphological amendments in its textural properties and defects responsible in creating active sites for ORR. N–F/CTC catalyst exhibits excellent ORR catalytic activity and methanol and CO tolerance in the alkaline medium, which makes it a potential metal-free ORR catalyst for the polymer electrolyte membrane fuel cell. N–F/CTC catalyst is subjected to 10 000 repeated potential cycles with no degradation in its activity. XPS analysis of N–F/CTC catalyst revealed the presence of N in the form of pyridinic-N, pyrrolic-N, graphitic-N, active species, and F in the form of C–F ionic and C–F semi-ionic active forms. The maximum C–C bond polarization...

An architecture of dandelion-type Ni-Co3O4 microspheres on carbon nanotube films toward an efficient catalyst for oxygen reduction in zinc-air batteries

Sluggish kinetics of oxygen reduction reaction (ORR) at an air cathode of a rechargeable zinc-air battery (ZAB) is a serious obstacle hindering the development of the ZAB. In the present work, hierarchical Co3O4 nanowires doped with Ni atoms (Ni-Co3O4) were fabricated and self-assembled into dandelion-type microspheres on CNT films (Ni-Co3O4/CNTs) by a hydrothermal method. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and high resolution transmission electron microscope (HRTEM) results verified the successful incorporation of Ni atoms into the Co3O4 lattice. Electrochemical measurements, such as cyclic voltammetry (CV) and linear sweep voltammetry (LSV) techniques, revealed that the dandelion-type Ni-Co3O4/CNT composite could greatly enhance the catalytic activity and ORR durability of the air cathode in the O2-saturated 0.1 M KOH electrolyte. Here, we report that the synergistic effect between Ni-Co3O4 nanowires and CNTs could greatly improve the stability and electrochemical performance of Co3O4 catalysts. Especially, the Ni-Co3O4/CNTs prepared at 160 °C exhibited the best catalytic capability and long-term durability (93.34% after 8.3 h) in the present work, which are better in comparison with the performance of the 20 wt% commercial Pt/C electrode in ZABs.

Design of high efficient oxygen reduction catalyst from the transition metal dimer phthalocyanine monolayer

Due to the large surface area, unique atomic configurations and dispersed metal sites, metal-organic porous monolayers provide a promising strategy for catalysis. Among them, the transition metal dimer phthalocyanine (TM2Pc) monolayer is one of the interesting members. Herein, we studied the oxygen reduction reaction (ORR) of TM2Pc with a series of transition metal dimers (M = Mn-Cu and Ru-Pd) by using the density functional theory. Volcano plot suggests that Fe2Pc has the best ORR activity. This is also confirmed by thermodynamic and kinetic study. Among the studied TM2Pc, Fe2Pc has the highest working potential of 0.98 V (smallest overpotential of 0.25 V), larger than 0.78 V for pure Pt. The energy barrier calculations show that for Fe2Pc, the rate-determining step is the *OOH hydrogenation to form *OH + *OH with an energy barrier of 0.25 eV, much smaller than 0.80 eV for pure Pt. Therefore, Fe2Pc has good ORR activity compared with pure Pt. These results also indicate that the introduction of transition metal dimer on phthalocyanine monolayer would provide a novel strategy for the design of high efficient ORR catalysts.

Freestanding 1D Hierarchical Porous Fe‐N‐Doped Carbon Nanofibers as Efficient Oxygen Reduction Catalysts for Zn–Air Batteries

High‐performance nonprecious metal‐doped 1D carbon catalysts for oxygen reduction reactions (ORR) are viable candidates in lieu of platinum‐based catalysts. Hierarchical porous Fe‐N‐doped carbon nanofibers (Fe‐NHCFs) are fabricated via carbonization of MOF nanofibers with a specific surface area of 294 m2 g−1 and inherent hierarchical porosity. Benefiting from the Fe‐N doping‐induced active sites, unique hierarchical porosity, and 1D honeycomb conductive networks to facilitate electron transfer, the freestanding Fe‐NHCFs confer a current density (5.2 mA cm−2) at 0.70 V (vs reversible hydrogen electrode), comparable with the commercial 20 wt% Pt/C (5 mA cm−2) in alkaline medium. Especially, the parallel characteristics with Pt/C is acquired in an assembled Zn–air battery, which deliver a discharge current density of 90 mA cm−2 and an output peak power density of 61 mW cm−2. This simple synthesis strategy would leverage a new geometry for tailored utility of active sites for ORR in a 1D carbon framework.

Cobalt-nitrogen-doped graphdiyne as an efficient bifunctional catalyst for oxygen reduction and hydrogen evolution reactions

For replacing the use of rare precious metals, finding an electrocatalyst with low-cost, stable and excellent activity for both the oxygen reduction reactions (ORR) and hydrogen evolution reactions (HER) is desirable and challenging. Herein, a novel electrocatalyst of cobalt (Co) and nitrogen (N) doped graphdiyne (Co-N-GDY) was designed and synthesized using a facile method with just a small amount of Co precursor to reach up to 1.3 wt % based on XPS data. Among them, the 1% Co-N-GDY, synthesized with 1 wt % of Co in the preparation stage, was demonstrated as the most effective ORR and HER catalyst. Due to the synergistic effect of Co, N, GDY and strong interaction between Co and GDY, the Co-N-GDY exhibited excellent ORR and HER catalytic performance. As for ORR, the activity of 1% Co-N-GDY is comparable to that of commercial Pt/C. Especially the half-wave potential of 1% Co-N-GDY is superior to most previously reported Co-based carbon materials. In HER, the 1% Co-N-GDY shows a low onset overpotential of 97 mV and a small Tafel slope of 132 mV per decade, which exhibits comparable or even better performance than many reported non-precious metals catalysts.

Metal‐Organic Framework Derived N/C Supported Austenite Nanoparticles as Efficient Oxygen Reduction Catalysts

AbstractAustenite (γ‐Fe) is thermodynamically unstable at room temperature. Relatively little attention has been directed in the past for the synthesis and properties of γ‐Fe nanoparticles. Herein, we demonstrate a NaOH‐assisted and metal‐organic framework (MOF)‐derived method to prepare a novel catalyst featured by γ‐Fe nanoparticles encapsulated into the porous N‐doped carbon matrix. The Fe atoms doped in the MOF structure play an important role in the formation of stable γ‐Fe. The catalysts exhibit superior catalytic activity with the four‐electron transfer pathway for oxygen reduction reaction (ORR) in alkaline solution. Besides the Fe−Nx sites, γ‐Fe nanoparticles are believed to play an important role in the superior ORR activity. However, it is suggested that the metal nanoparticles are not ORR active species, whereas they may activate the surrounding N/C layers, thus making the N/C layers more active toward ORR. In addition, the oxidized surface of the metal nanoparticles may also act as active species contributing to the ORR activity.

Electrospun MOF-Based FeCo Nanoparticles Embedded in Nitrogen-Doped Mesoporous Carbon Nanofibers as an Efficient Bifunctional Catalyst for Oxygen Reduction and Oxygen Evolution Reactions in Zinc-Air Batteries

Low-price, high-performance and strong-stability electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are highly significant in the application of clean energy d...

Low‐Work‐Function Silver Activating N‐doped Graphene as Efficient Oxygen Reduction Catalysts in Acidic Medium

AbstractNon‐platinum graphene‐based electrocatalysts are vital for low‐cost energy conversion by hydrogen fuel cell. However, high oxygen reduction reaction (ORR) overpotentials limit their efficiency and stability. Here, we propose a strategy to increase graphene Fermi level by graphene encapsulating a metal with lower work function than graphene, aiming to enhance the ORR activity of graphene‐based materials. As an example, Ag nanoparticles (function work, 4.2 eV) are embedded into N‐doped graphene (function work, 4.5 eV) (Ag@NG). The Ag@NG exhibits the ORR onset potential of 0.804 V and excellent stability over 10000 electrochemical cycles in acidic electrolyte. Spectroscopic analysis confirms Ag−N coordination bond as an efficient electron transfer route significantly benefiting upshift of graphene Fermi level that enhances the ORR activity and stability.

Fluorine-enriched mesoporous carbon as efficient oxygen reduction catalyst: understanding the defects in porous matrix and fuel cell applications.

Herein, fluorine enrichment in mesoporous carbon (F-MC) was explored to introduce maximum charge polarization in the porous matrix, which is beneficial for the preferential orientation of O2 molecules and their subsequent reduction. Ex situ doping of F to porous carbon derived from phloroglucinol–formaldehyde resin using Pluronic F-127 as a structure-directing agent is standardized. The optimized F-MC catalyst exhibited excellent electrocatalytic activity towards the oxygen reduction reaction (ORR) in alkaline media (0.1 M KOH) with an onset potential of −0.10 V vs. SCE and diffusion-limiting current of 4.87 mA cm−2, while displaying only about 50 mV overpotential in the half-wave region compared to Pt–C (40 wt%). In the stability test, the catalyst showed only 10 mV negative shift in its half-wave potential after 10 000 potential cycles. The rotating ring disk electrode (RRDE) experiments revealed that F-MC follows the most preferable 4e− pathway (n = 3.61) with a moderate peroxide (HO2−) yield. This was further supported by density functional theory calculations and also deeply explains the existence of defects being beneficial for the ORR. The F-MC catalyst owing to its promising ORR activity and long-term electrochemical stability can be viewed as a potential alternative ORR catalyst for anion exchange membrane fuel cell applications.

Air cathode of zinc-air batteries: a highly efficient and durable aerogel catalyst for oxygen reduction.

In this communication, N-doped carbon shell encapsulated Co3O4@Co nanoparticles (NPs) were assembled on N-doped reduced graphene oxide to form non-precious metal aerogels (Co3O4@Co/N-r-GO) for oxygen reduction. In an alkaline medium, the aerogels exhibit comparable oxygen reduction reaction (ORR) performances to the commercial Pt/C with respect to half-wave potential, current density and durability. Zn-air batteries (ZABs) assembled with Co3O4@Co/N-r-GO as the air cathode display high average voltages of ∼1.38 and ∼1.3 V at a current density of 1 and 5 mA cm-2, respectively, and show a specific capacity of ∼800 mA h g-1. These results demonstrate that Co3O4@Co/N-r-GO materials are highly active and durable ORR catalysts for ZABs. The unique structure of the composite aerogel, i.e. the carbon shell encapsulated Co3O4@Co NPs and the 3D interconnected macroporous N-r-GO matrix, is responsible for its high ORR activity and stability.

Locally-ordered PtNiPb ternary nano-pompons as efficient bifunctional oxygen reduction and methanol oxidation catalysts.

To accurately control the composition and structure of Pt-based alloys is essential for engineering highly active and stable catalysts, yet challenging. Here, ternary PtNiPb nano pompons (NPs) combining the features of a highly open structure, local-ordering and the introduction of Pb have been synthesized via a seed-mediated growth method. Taking advantage of the reduction potential differences, gradient distribution of Pb and Ni throughout the NPs is realized, and both the elemental composition and distribution can be facilely regulated by reaction time. The PtNiPb NPs exhibit much enhanced catalytic performance for both the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR), of which the ORR specific activity is 7.4- and 2.3-fold larger than those of the commercial Pt/C catalyst and binary PtNi NPs. Density functional theory (DFT) calculations reveal that the weak coupling between Pb-p and Pt-d orbitals together with the regulation of the over-compressed Pt surface by the local-ordering structure and embedded Pb atoms optimize the surface oxygen adsorption character and eventually boost the ORR.

Cu single atoms on Ti2CO2 as a highly efficient oxygen reduction catalyst in a proton exchange membrane fuel cell

MXene supported single-atom catalysts catalyze the oxygen reduction reaction in a proton exchange membrane fuel cell.

Pyrolysis of iron phthalocyanine on activated carbon as highly efficient non-noble metal oxygen reduction catalyst in microbial fuel cells

To improve the power generation of microbial fuel cells (MFCs), iron–nitrogen/activated carbon (Fe–N/AC), an excellent oxygen reduction reaction (ORR) electrocatalyst, was prepared by pyrolyzing iron(II) phthalocyanine (FePc)-coated AC, which was formed via an evaporation-induced self-assembly method. Given the high content of nitrogen and iron elements, crystalline structure, high surface area, and appropriate composition of micropores and mesopores, Fe–N/AC synthesized with 50.0 wt% of FePc loading on AC exhibits enhanced ORR electrocatalytic activity. The Fe–N/AC can catalyze ORR via an indirect four-electron pathway in neutral medium with onset potential of 0.883 V versus reversible hydrogen electrode and electron transfer number of 3.91. In comparison with AC, the charge transfer resistance and exchange current density of Fe–N/AC decreases by 62% and increases by a factor of three, respectively. The maximum power density of MFC using Fe–N/AC reaches 1092 mW m−2, which is 63.23% higher than that of AC and equal to that of Pt/C. This study proposes a new approach for the design of alternative non-precious metal ORR electrocatalysts in neutral pH medium, which may have potential application in practical MFCs as cathode catalysts in the future.

Controlled synthesis of graphene via electrochemical route and its use as efficient metal-free catalyst for oxygen reduction

The oxygen reduction reaction (ORR) is a critical step in the operation of fuel cells. The exploration of efficient, low cost and durable non-precious ORR catalysts, to replace the rare and expensive Pt-based catalysts, is promising towards the large-scale commercialization of fuel cells. Here, we report the fabrication of high-quality graphene (GP) with controllable layers, using a simple, versatile and cost-effective electrochemical exfoliation method. Our systematic studies revealed that the graphite precursor, electrolyte temperature, and pyrolysis conditions largely affect the number of layers and quality of the graphene, which consequently has a significant effect on its ORR performance. The optimized graphene sample was subsequently heat-treated in the NH3 atmosphere to obtain the nitrogen-doped graphene (N-GP). As a metal-free electrocatalyst, N-GP exhibit much enhanced ORR activity than GP, and comparable ORR activity to the state-of-the-art Pt/C catalyst. Moreover, it also shows better stability than Pt/C catalyst in alkaline solution.

Facile solvothermal synthesis of Pt71Co29 lamellar nanoflowers as an efficient catalyst for oxygen reduction and methanol oxidation reactions

The research for highly efficient and stable electrocatalysts in fuel cells has attracted substantial interest. Herein, bimetallic alloyed Pt71Co29 lamellar nanoflowers (LNFs) with abundant active sites were obtained by a one-pot solvothermal method, where cetyltrimethylammonium chloride (CTAC) and 1-nitroso-2-naphthol (1-N-2-N) served as co-structure-directors, while oleylamine (OAm) as the solvent and reducing agent. The fabricated Pt71Co29 LNFs exhibited the higher mass activity (MA, 128.29 mA mg−1) for oxygen reduction reaction (ORR) than those of home-made Pt48Co52 nanodendrites (NDs), Pt79Co21 NDs and commercial Pt black with the values of 39.46, 49.42 and 22.91 mA mg−1, respectively. Meanwhile, the MA (666.23 mA mg−1) and specific activity (SA, 2.51 mA cm−2) of the constructed Pt71Co29 LNFs for methanol oxidation reaction (MOR) are superior than those of Pt48Co52 NDs (213.91 mA mg−1, 1.99 mA cm−2), Pt79Co21 NDs (210.09 mA mg−1, 1.12 mA cm−2) and Pt black (57.03 mA mg−1, 0.25 mA cm−2). Also, the Pt71Co29 LNFs catalyst exhibited the best durable ability relative to the references. This work demonstrates that the developed strategy provides a facile platform for synthesis of high-performance, low-cost and robust catalysts in practical catalysis, energy storage and conversion.

NiCoO2@CMK-3 composite with nanosheets-mesoporous structure as an efficient oxygen reduction catalyst

Exploiting high efficient non-noble metal catalysts with low-cost and good stability for oxygen reduction reaction (ORR) is vital for fuel cells and metal-air batteries. In this work, we successfully constructed a novel nanosheets-shaped NiCoO2 hierarchical structure supported on CMK-3 support (i.e., NiCoO2@CMK-3 composite) via a facile hydrothermal method. Electrochemical characterization results reveal that the as-prepared NiCoO2@CMK-3 composite exhibits remarkable ORR electrocatalytic activity with a positive peak potential of 0.81 V (vs. RHE), an onset potential of 0.90 V (vs. RHE), a high current density of 4.10 mA cm−2 at 0.4 V, and a nearly four-electron reduction pathway, which are comparable to the state-of-the-art Pt/C catalyst with the same mass. In addition, the NiCoO2@CMK-3 composite possesses excellent methanol-tolerance and electrochemical stability, which are better than Pt/C. The outstanding performance confirms the NiCoO2@CMK-3 composite as a promising efficient ORR catalyst in fuel cells and metal-air batteries.

Promoted activity of nitrogen-doped activated carbon as a highly efficient oxygen reduction catalyst in microbial fuel cells

Despite the wide application of activated carbon (AC) as cathode electrocatalyst in microbial fuel cell (MFC), the enhancement of its catalytic activity is crucial to reduce its high loading on air-cathode. Herein, we synthesize nitrogen-doped activated carbon (NAC) by pyrolyzing phthalocyanine (Pc) adsorbed on AC to develop an efficient oxygen reduction reaction (ORR) electrocatalyst. The optimized mass ratio of AC to Pc improves the crystalline structure and porous structure of the NAC. Elemental analysis indicates that this material contains appropriate content of pyrrolic and pyridinic types of nitrogen and oxygen species. The NAC shows an ORR onset potential of 0.468 V (vs. Standard hydrogen electrode), an electron transfer number of 3.90, and high electrochemically accessible surface area, thereby illustrating enhanced electrocatalytic activity in the neutral medium relative to alkali-treated activated carbon (b-AC) and commercial platinum catalyst. Owing to the high activity, a small amount of NAC with a loading of 15 mg cm− 2 on the air-cathode of MFC is sufficient to achieve the maximum power density of 1026.07 ± 10.83 mW m− 2, which is higher than that of b-AC and comparable to platinum catalyst. The reduced loading of NAC indicates that the material can be used as cathode electrocatalyst for the ongoing effort to scale up MFC in the future.

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.