Oxygen Reduction Performance Research Articles

Effects of N-doping Methods on the Microstructure and Oxygen Reduction Performance of Carbon Materials

The ongoing search for new non-precious-metal catalysts with excellent electrocatalytic performance to replace Pt-based catalysts is viewed as an important strategy to promote the development of fuel cells. In here, N-doped carbon materials are fabricated by different methods and used as electrocatalysts for oxygen reduction reaction (ORR). The resulting samples are systemically characterized by XRD, SEM, TEM, Raman, XPS and electrochemical measurements to study the synthesis-structure-performance correlation of the N-doped carbon materials for ORR. The experimental results indicates that the synthesis methods have an significantly impact on the bonding state of nitrogen atom in resulting carbon materials, microstructure and electro-catalytic performance of products, and confirms that the obtained 3D interpenetrating microstructured N-doped graphene has an excellent catalytic activity for ORR due to its well-developed porous nanostructures and interconnected conductive networks could provide more electroactive sites and fast ionic channels for electrochemical reaction.

Preparation of nitrogen-doped graphene by high-gravity technology and its application in oxygen reduction

Electrochemical oxygen reduction is key to many clean and sustainable energy technologies, including proton exchange membrane fuel cells and metal–air batteries. However, the high activation barriers in the oxygen reduction reaction often make it the bottleneck of energy conversion processes; thus, high-performance oxygen reduction electrocatalysts are desired. At present, the best commercially available oxygen reduction catalyst is based on the precious metal Pt. However, it suffers from resource scarcity and unsatisfactory operational stability, hindering its widespread and large-scale application in clean and sustainable technologies. Nitrogen-doped graphene has excellent electrocatalytic properties for oxygen reduction. In this paper, a scalable method to prepare nitrogen-doped graphene with high quality was introduced, in which the graphene oxide prepared by high-gravity technology and urea was reacted under hydrothermal conditions. Accompanying the hydrothermal reaction, graphene oxide reduction and nitrogen doping were accomplished at the same time. The effect of the content of nitrogen on the performance of nitrogen-doped graphene was investigated. When the mass ratio (graphene oxide/urea) was 1:400, the nitrogen-doped graphene had the best oxygen reduction performance. Compared with the undoped samples, the initial reduction voltage of the nitrogen-doped samples distinctly shifted 45mV to the right. When the voltage was −1.0V, the electron transfer number was 4.1, indicating good oxygen reduction activity. The preparation method is feasible, simple, and can be easily scaled up.

Defect locating: One-step to monodispersed CoFe2O4/rGO nanoparticles for oxygen reduction and oxygen evolution

In this work, monodispersed CoFe2O4/reduced graphene oxide (rGO) nanoparticles have been successfully synthetized in one step from Co(Ⅱ) acetylacetonate, Fe(Ⅲ) acetylacetonate, benzylamine and graphene oxide (GO). A facile solvent method was designed to skillfully integrate the crystal growth process of CoFe2O4, the reduction process of GO and their compound process. In synthesis process, large numbers of defects on GO thin layers were smartly used to disperse CoFe2O4 nanoparticles. The micromorphology and the distribution of as-prepared samples were identified via X-ray diffraction (XRD), transmission electron microscope (TEM) and element mapping spectra. Results showed that the monodispersed CoFe2O4 nanoparticles were uniformly coupled with rGO thin layers. Good performance for both oxygen reduction and oxygen evolution of as-prepared CoFe2O4/rGO (0.92 V onset potential for oxygen reduction and 1.59 V overpotential at 10 mA cm−2 for oxygen evolution, vs. RHE) were found during a series of electrochemical tests, which make it a promising bi-functional catalyst in the field of fuel cells and metal-air batteries.

The impact of solvent properties on the performance of oxygen reduction and evolution in mixed tetraglyme-dimethyl sulfoxide electrolytes for Li-O2 batteries: Mechanism and stability

The instability of the electrolyte and the sluggish kinetics of the reactions hinder the application of Li-O2 batteries. In this study, we aim to better understand the behavior of oxygen reduction (ORR) and evolution (OER) reactions in dimethyl sulfoxide (DMSO), Tetraglyme (G4) and their blend DMSO-G4, with emphasis on the role of solvent nature in the mechanism and reaction route, using rotating ring-disc electrode (RRDE) and differential electrochemical mass spectrometry (DEMS). Interestingly, RRDE results showed that the stability and the ratio of the formed O2−·: Li2O2 increase with addition of DMSO to G4. A proposed mechanism for ORR is discussed. Depending on the solvation ability of the solvent, which primarily determines the lifetime and solubility of the superoxide intermediate in solution, a solution or a surface-based pathway is followed: in highly solvating solvents (e.g. those with high donor or acceptor number) such as DMSO, superoxide is stabilized in solution; while in low solvating solvent, it is further reduced to Li2O2, blocking the surface. The results of the scan rate variation under defined mass transport in DMSO suggest a sequential formation of monolayers of Li2O2 during reduction. In G4-solutions, despite of the reversible formation of Li2O2, deactivation of the electrode takes place, as evidenced by DEMS. This could arise from a reduction products-induced decomposition of the electrolyte, forming a deactivating film on the surface during ORR, which is only partially removed at higher potentials evolving CO2. Also, we found that DMSO is more active towards OER than G4. The electrode material as well influences the kinetics, in particular of OER. These findings could have implications for the development of Li-air battery.

Platinum stabilized by defective activated carbon with excellent oxygen reduction performance in alkaline media

The exploration of highly active and durable cathodic oxygen reduction reaction (ORR) catalysts with economical production cost is still the bottleneck to realize the large-scale commercialization of fuel cells and metal-air batteries. Given that carbon support is crucial to the electrocatalysts, and Pt is the best-known ORR catalyst so far, in this work, we employed a simple impregnation method for synthesizing a kind of defective activated carbon (D-AC) supported low Pt content electrocatalysts for the ORR. The reduction conditions of the Pt-containing precursor were firstly optimized, and the influence of the Pt loading amount on the ORR was investigated as well. The results show that the obtained D-AC@5.0%Pt sample (contains 5 wt% Pt) has surpassed the commercial Pt/C with 20 wt% Pt for the ORR in an alkaline solution. In the meantime, it is more stable than the commercial Pt/C. The outstanding ORR performance of the D-AC@5.0%Pt confirms that both the unique defects in the D-AC and the introduced Pt particles are indispensable to the ORR. Particularly, the ORR activity of the synthesized catalysts is superior to most of the reported counterparts, but with much easier preparation methods and lower production cost, making them more advantageous in practical fuel cell applications.

Space-Confined Pyrolysis for the Fabrication of Fe/N/C Nanoparticles as a High Performance Oxygen Reduction Reaction Electrocatalyst

In this manuscript, we develop a novel method based on the combination of space-confined pyrolysis and second heat-treatment for the synthesis of Fe/N-doped Carbon (Fe/N/C) ORR catalyst, targeting solving the low yield, insufficient nitrogen-doped level, and nanostructure collapse problems. The silica-confined space is constructed by covering an outer inorganic silica layer onto the surface Fe/Phenanthroline/C (Fe/Phen/C) precursor. Within this silica-confined space, the precursor loss, particle coagulation and structure collapse that are commonly encountered during high-temperature pyrolysis in an open system can be eliminated. Moreover, the porosity and nitrogen-doped configuration can further be tuned by a second heat-treatment process. The resultant Fe/N/C catalyst show excellent ORR activity in alkaline media, better durability and stronger methanol tolerance compared to those of state-of-the-art Pt/C catalyst.

(Invited) High-Performance PGM-Free Electrocatalysts for the Polymer Electrolyte Fuel Cell Cathode

The activity of oxygen reduction reaction (ORR) catalysts often determine performance of polymer electrolyte fuel cells (PEFCs) as measured by their power output, open circuit voltage, and fuel conversion efficiency. Currently, Pt-nanoparticle catalysts, either supported on high surface-area carbons or prepared in a form of contiguous thin layer on conductive or non-conductive supports, represent the state of the art in ORR electrocatalysis at the PEFC cathode. However, the high and variable price and scarceness of Pt have limited its widespread implementation in the -temperature fuel cells to date, especially in automotive transportation. Under these circumstances, platinum group metal-free (PGM-free) ORR catalysts have received growing attention in recent years as a possible replacement for Pt-based formulations. The progress achieved since the development of the first nature-inspired electrocatalysts of oxygen reduction in the seminal work by Jasinski in the 1960s (Nature 201, 1212, 1964), which mostly happened through the broad implementation of the high-temperature synthesis approach, makes replacement of Pt in ORR electrocatalysts with earth-abundant elements, such as Fe, Co, N, and C, a realistic possibility. In this this presentation, we will summarize recent progress in research targeting development of high-performance PGM-free catalysts for oxygen reduction reaction (ORR) at Los Alamos National Laboratory. Two approaches will be discussed in a greater detail: (i) the approach involving fine-tuning of the catalyst porosity and surface area using pore-forming compounds and (ii) the method specifically focusing on the development of atomically dispersed transition metal moieties and avoiding the formation of transition metal-rich nanoparticles during the heat treatment of catalyst precursors. We will demonstrate the impact that porosity/surface area optimization, through the use of either pore formers (cyanamide, ZnCl2) precursor templating (metal organic frameworks) or both, can have on the fuel cell performance of PGM-free catalysts. We will also show how modifications to the electrode structure through the change in the ionomer content and ionomer equivalent weight can lead to substantial improvements in the fuel cell performance at both low- and high current densities (aerial power density of more than 0.50 W/cm2 in H2-air testing at 80°C). Finally, we will recapitulate the challenges still facing PGM-free research that, in spite of all the progress achieved in recent years, is yet to produce materials capable of competing with the incumbent Pt-based catalysts in terms of oxygen reduction activity, performance durability, and cost (specifically, when extended to the overall cost of a fuel cell stack). Acknowledgement Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged.

First-Principles Evaluation of the Catalytic Activity of Nanostructured Carbon for the Oxygen Reduction Reaction at Fuel Cell Cathodes

Carbon nanomaterials, including fullerenes, carbon nanotubes (CNTs), graphene, and their composites, have been actively studied as a potential candidate to replace platinum(Pt)-based ORR catalysts as fuel cell cathodes. These sp 2-bonded carbon nanostructures are inherently constituted by largely extended p-conjugation systems, making them essentially unreactive toward molecular oxygen (O2) in their pristine forms. However, the conjugated p-systems can be severely disrupted with localized p electrons through dopant incorporation, defect creation, and/or local lattice distortions. Doped, defective and distorted carbon structures are currently thought to be responsible for O2 adsorption/activation and thus ORR, but the active sites and the exact molecular mechanisms are still uncertain. First principles computational methods are well suited to study in detail reactions at the surface of a heterogeneous catalyst and through these methods we explored the mechanisms by which modification can activate graphene for the adsorption and reduction of oxygen, with an aim to define design guidelines for carbon ORR catalysts. Using density functional theory (DFT) calculations, we have identified a novel method for the activation of graphene while establishing a computational scheme for the study of electrocatalysis by carbon. An important component of our methodology is the application explicitly solvated system to model the ORR at the solid-liquid interface with aqueous solvent. Many previous DFT studies were modeled in the gas phase where O2 adsorption is consistently predicted to be endothermic on carbon. Our study clearly demonstrates that a more accurate description of interactions at the graphene-solvent interface is necessary to properly describe O2 adsorption, which appears strongly influenced by solvation. Ab-initio MD simulations were performed with the explicit solvent model to outline a full reaction mechanism including novel elementary reaction steps. Another unique approach taken in our studies is the use of detailed electronic structure analysis to determine the factors influencing overpotentials in the course of the ORR. In this presentation, we will focus on introducing the computational scheme that we have developed for the investigation of molecular mechanisms underlying the ORR on carbon catalysts and the synergetic effects of doping, defect creation, and lattice distortions on their catalytic performance for oxygen reduction. We will also discuss the key guidelines for the rational design and development of high-efficiency, cost-effective carbon-based ORR catalysts for fuel cell applications.

Protein-enriched fish “biowaste” converted to three-dimensional porous carbon nano-network for advanced oxygen reduction electrocatalysis

Recycling and utilizing organic biowastes will effectively help to decrease the damage to the natural environment and synchronously facilitate the development of new carbon materials for energy applications. In this study, we directly convert protein-rich fish-scale biowaste to hierarchically porous three-dimentional (3D)-network nanocarbons via two-step pyrolysis process combined with ZnCl2 activation and acidic-treatment. It is interestingly found that this material exhibits more excellent oxygen reduction electrocatalytic activity and stability compared to the commercial 20wt% Pt/C catalyst in both alkaline and acidic solutions, which can be closely correlated to its chemical state of nitrogen atoms, BET surface area and inner porous structure. The addition of ZnCl2 activator during pyrolysis process can help to produce the 3D network nanostructure and then to enhance the mesopore surface area, making for the improvement of oxygen reduction performance. More remarkably, the ORR onset potential on our material is about 60mV higher than that on the Pt/C catalyst in alkaline electrolyte. In addition, we also propose that pyridinic- and graphitic-nitrogen species may be key factors to be responsible for the electrocatalytic activity. This study can encourage the exploration of high porosity nanocarbons from widely-existed biowastes, functioning as highly active and stable oxygen reduction electrocatalysts.

Atomically Dispersed Fe/N-Doped Hierarchical Carbon Architectures Derived from a Metal–Organic Framework Composite for Extremely Efficient Electrocatalysis

Hierarchical graphitic porous carbon architectures with atomically dispersed Fe and N doping have been fabricated from a metal–organic framework (MOF) composite by using a facile strategy, which show high specific surface areas, hierarchical pore structures with macro/meso/micro multimodal pore size distributions, abundant surface functionality with single-atom dispersed N and Fe doping, and improved hydrophilicity. Detailed analyses unambiguously disclosed the main active sites of doped N atoms and FeNx species in the catalyst. The resultant catalyst affords high catalytic performance for oxygen reduction, outperforming the benchmark Pt catalyst and many state-of-the-art noble-metal-free catalysts in alkaline media, particularly in terms of the onset and half-wave potentials and durability. Such catalytic performance demonstrates the significant advantages of the unique hierarchical porous structure with efficient atomic doping, which provides a high density of accessible active sites for much improved m...

3D hierarchical nitrogen-doped carbon nanoflower derived from chitosan for efficient electrocatalytic oxygen reduction and high performance lithium–sulfur batteries

A highly uniform N-doped carbon nanoflower was demonstrated as a bifunctional material for efficient electrocatalytic oxygen reduction and high performance lithium–sulfur batteries.

Bridged-multi-octahedral cobalt oxide nanocrystals with a Co-terminated surface as an oxygen evolution and reduction electrocatalyst

Cobalt oxide nanocrystals with bridged-multi-octahedral structures and Co-terminated surfaces were prepared to exhibit good oxygen evolution and oxygen reduction performances.

Nitrified coke wastewater sludge flocs: an attractive precursor for N,S dual-doped graphene-like carbon with ultrahigh capacitance and oxygen reduction performance

N,S dual-doped graphene-like carbons synthesized from coke wastewater sludge flocs exhibit ultrahigh capacitance and outstanding oxygen reduction performance.

Bimetallic Cu–Pd alloy multipods and their highly electrocatalytic performance for formic acid oxidation and oxygen reduction

Nanoscale Cu–Pd alloy multipods were synthesizedviathe galvanic replacement reaction for catalyzing formic acid oxidation and oxygen reduction.

Fe–Nxmoiety-modified hierarchically porous carbons derived from porphyra for highly effective oxygen reduction reaction

Fe–Nxmoiety-modified nitrogen-doped hierarchically porous carbon, which is derived from porphyra, exhibits an excellent catalytic performance for oxygen reduction.

Out-of-plane FeII–N4 moiety modified Fe–N co-doped porous carbons as high-performance electrocatalysts for the oxygen reduction reaction

A Fe–N–C electrocatalyst with active FeII–N4 sites was synthesized exhibiting superior oxygen reduction performance in both alkaline and acidic electrolytes.

Nitrogen and phosphorus co-doped hierarchically porous carbons derived from cattle bones as efficient metal-free electrocatalysts for the oxygen reduction reaction

Nitrogen and phosphorus co-doped cattle-bone-derived hierarchically porous carbon metal-free electrocatalysts were synthesized exhibiting superior oxygen reduction performance than Pt/C.

Fe–N-Doped carbon foam nanosheets with embedded Fe2O3 nanoparticles for highly efficient oxygen reduction in both alkaline and acidic media

We report a high performance oxygen reduction reaction (ORR) electrocatalyst Fe2O3@Fe–N–C, which is composed of Fe–N-doped carbon foam nanosheets with embedded carbon coated Fe2O3 nanoparticles to enhance the ORR performance in both alkaline and acidic media.

2D quasi-ordered nitrogen and sulfur co-doped carbon materials from ionic liquid as metal-free electrocatalysts for ORR

This study explores the novel 2D heteroatom-doped carbon materials for high performance oxygen reduction reaction (ORR).

Bottom-up fabrication of nitrogen-doped mesoporous carbon nanosheets as high performance oxygen reduction catalysts

Nitrogen-doped mesoporous carbon nanosheets (NMCNs) with uniform hexagonal structures are fabricated via the thermal treatment of polyaniline enwrapped cobalt hydroxide (Co(OH)2) nanosheets and the subsequent acid etching of the resulting composites. It is found that the morphologies, poroisties and compositions of the NMCNs are greatly dependent on the ratio of the added aniline and Co(OH)2 nanosheets, which can in turn affect the electrochemical behavior of the NMCNs. As the electrocatalyst for oxygen reduction reaction in alkaline media, the NMCNs obtained with the aniline/Co(OH)2 ratio of ∼1.2 manifest excellent perfromance with the onset potential of −0.119V, the half-wave potential of −0.182V and the limiting current density of 5.06mAcm−2, which are superior to most of the previously reported N-doped porous carbon nanosheets.