Excellent Methanol Tolerance Research Articles

Synthesis of a N-doped mesoporous carbon as an efficient electrocatalyst for oxygen reduction

A facile and effective approach was developed for the preparation of mesoporous Fe-NC by pyrolyzing the mixture of FeCl2, urea, (NH4)2MoO7, phthalic anhydride and SBA-15, during which the in-situ formation of iron phthalocyanine is confirmed. The obtained catalyst exhibits high catalytic activity towards ORR, whose half-wave potential can be 53 mV more positive than that of commercial Pt/C catalyst. Besides, the catalyst also exhibits high selectivity of four electron path, along with excellent stability and methanol tolerance in alkaline media. Based on the characterization results, we suggest, the higher surface areas, highly porous structures induced by SBA-15 addition, as well as high graphitic N content should be the proper origins for its outstanding catalytic performance.

Heterogeneous atoms-doped titanium carbide as a precious metal-free electrocatalyst for oxygen reduction reaction

Developing precious metal-free electrocatalysts with both high and stable oxygen reduction reaction (ORR) electrochemical activity is still the key challenge in the wide application of clean energy, e.g. fuel cells or metal air batteries. Here, TiC based precious metal-free ORR catalyst has been studied by doping heterogeneous atoms. N-doping results in enhanced ORR performance of N/TiC, which was further elevated by introducing metal (e.g. Fe, Co) into TiC powders. Especially, the resultant Fe-N/TiC demonstrates the highest ORR activity among the prepared samples, which exhibits approximate 4e− pathway with a comparable electron-transfer number to the benchmark 20 wt%Pt/C, and much higher methanol tolerance than the latter in alkaline media. The high ORR performance of Fe-N/TiC composite could be ascribed to the cooperative effects of both N and metal doping, in which the N doping would lead to the change of electronic structure near the TiC surface and the formation of C-N active sites, and the metal species addition leads to the formation of a certain amount of Me-Nx active sites resulting in the further ORR activity enhancement. The reasonably high and stable electrochemical catalytic activity and the excellent methanol tolerance make the precious-metal free Fe-N/TiC composite a promising candidate cathode catalyst in ORR.

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.

Self‐Sacrificial Template Synthesis of a Nitrogen‐Doped Microstructured Carbon Tube as Electrocatalyst for Oxygen Reduction

AbstractThe development of low‐cost, efficient and stable electrocatalysts for the oxygen reduction reaction (ORR) is desirable but remains a great challenge. We report a self‐sacrificial template synthesis approach for nitrogen‐doped hollow carbon microtubes as electrocatalyst for ORR. Typically, Fe‐MIL (Materiaux de l'Institute Lavosier) nanocrystals cast as self‐sacrificial template. Polyaniline (PANI) was in situ‐synthesized and deposited on the surface of Fe‐MIL nanocrystals. By a two‐step pyrolysis of the MIL‐101 (Fe)@PANI hybrids, unique microstructured carbon tubes with Fe3O4 nanoparticles encapsulated inside the wall were fabricated after the self‐sacrificial template decomposed. The optimized C‐PANI‐MIL‐2 catalyst exhibits a high onset potential of 1.0 V in alkaline media. Out of the negative effect of the disruption of metal‐organic frameworks (MOF) morphology, the ingenious catalytic activities may be ascribed to the well‐defined microtube architecture with a high accessible surface area, the existence of FeN2+2/FeN4 and rich active nitrogen atoms. Moreover, C‐PANI‐MIL‐2 exhibited excellent methanol tolerance and durability compared to a commercial Pt/C catalyst in both electrolytes. This work may provide a new strategy for the design and preparation of microstructured non‐precious metal based catalysts supported on hollow carbon tubes for fuel cells.

One-step construction of porous mixed spinel-type MnCoxO4/NCNT as an efficient bi-functional oxygen electrocatalyst

Development of highly active and durable non-precious metal bi-functional electrocatalyst for both oxygen reduction and evolution reaction (ORR and OER) remains a significant challenge. Herein, porous mixed spinel MnCoxO4 was loaded on the N-doped multi-walled carbon nanotubes (MnCoxO4/NCNT) through a facile one-pot hydrothermal method to work as a bi-functional oxygen electrocatalyst. Physical characterizations confirm that the MnCoxO4 nanoparticles are composed of mixed spinel-type Co2MnO4 and (Co, Mn)[Mn, Co]2O4 with a diameter of 5–10 nm, which are dispersed on NCNT with secondary aggregation and resultant porous structure. Electrochemical measurements show that the MnCoxO4/NCNT catalyst exhibits high ORR catalytic activity with a dominant four-electron ORR catalytic pathway, remarkable durability, excellent methanol-tolerance, as well as superior OER catalytic activity with significantly decreased overpotential of 0.479 V in alkaline media. The multiple valence states of Co and Mn ions in MnCoxO4 coupled with the enlarged specific surface area with the help of NCNT exert crucial roles for the superior catalytic performance for both ORR and OER. Such a bi-functional oxygen electrocatalyst based on mixed spinel MnCoxO4 provides a new direction for developing low-cost, highly efficient, and robust multiple valence states transition metal-based electrocatalysts for oxygen electrode.

Tea-leaf-residual derived electrocatalyst: Hierarchical pore structure and self nitrogen and fluorine co-doping for efficient oxygen reduction reaction

The heteroatom-doped carbon materials as metal-free catalysts show great potential for oxygen reduction reaction (ORR) due to the high electrocatalytic activity, low cost, long-term stability, and environmental friendliness. Utilizing biomass as precursors has offered facile and extremely low-cost strategy to large-scale fabrication of highly efficient carbon materials with abundant pore structures and elements. In this work, tea residue was used as precursor to synthesize nitrogen (N) and fluorine (F) co-doped porous carbon materials via one-step annealing process without any activation or post-treatment. The morphology, pore structure, elemental composition of our sample as well as its electrocatalytic performance in ORR were studied. This biomass-based carbon materials has high specific surface area (855.6 m2 g−1) and hierarchical pore structure, which can offer abundant active sites and meanwhile is favorable to ion diffusion of liquid electrolyte. Secondly, the heteroatoms (especially F) doping can induce charge redistribution thanks to the electronegativity difference, which can facilitate electron transfer in ORR. When compared to commercial Pt/C, our catalyst shows a higher limited current density and a high electron transfer number of about 3.8. Finally, the catalyst also demonstrates excellent methanol tolerance in the alkaline medium. Our work provides an economical and facile strategy to synthesize efficient electrocatalyst for ORR.

N-, P-, and S-doped graphene-like carbon catalysts derived from onium salts with enhanced oxygen chemisorption for Zn-air battery cathodes

Compared to currently studied metal-based catalysts, metal-free heteroatom-doped carbon catalysts have many advantages including no issues of degradation and contamination from metal dissolution. Relying on single type of doping usually cannot yield optimal electronic and geometric structures favorable for the oxygen reduction reaction (ORR). Herein, heteroatom N, P, and S simultaneously doped graphene-like carbon (NPS-G) was successfully synthesized from onium salts by a facile one-step pyrolysis method. The resulting metal-free NPS-G catalyst with optimized N, P, and S contents exhibits enhanced catalytic activity towards the ORR in alkaline media, relative to any single doping. In particular, this metal-free catalyst shows an encouraging half-wave potential (E1/2 = 0.857 V) comparable to that of metal-based catalysts. It also demonstrates excellent electrochemical stability and methanol tolerance. This catalyst was further studied as a cathode in a primary Zn-air battery, showing exceptional open-circuit voltage (1.372 V) and power density (0.151 W cm−2). The NPS-G cathode delivers a specific capacity of 686 mA h gZn-1 at a current density of 10 mA cm−2 while utilizing 82.2% of the theoretical capacity (835 mA h gZn-1). The origin of high activity associated with various heteroatom dopings is elucidated through X-ray photoelectron spectroscopy analysis and density functional theory studies. The enhanced chemisorption of oxygen species (*OOH, *O and *OH) onto the dopants of the NPS-G catalysts reduces charge transfer resistance and facilitate the ORR. The porous 2D structure also contributes to the increase of active site density and facile mass transport.

Copper-promoted nitrogen-doped carbon derived from zeolitic imidazole frameworks for oxygen reduction reaction

Rational design of oxygen reduction reaction (ORR) electrocatalysts based on earth-abundant elements is critical important towards sustainable energy applications. Among various reported ORR electrocatalysts, transition metal-nitrogen doped carbon (TM-N/C) materials such as Fe-Nx/C and Co-Nx/C exhibit excellent catalytic activity. Nevertheless, comprehensive understanding of these TM-N/C electrocatalytic systems is still lacking, which demands extension of investigation to other TM-N/C systems (Cu, and Mn, etc.). Herein, we developed a Cu promoted nitrogen-doped carbon (Cu-N/C) via high temperature pyrolysis of Cu-adsorbed zeolite imidazole frameworks (Cu@ZIF-8). The Cu-N/C electrocatalyst exhibited satisfactory ORR activity with half-wave potential of 0.813 V in 0.1 M KOH electrolyte. Moreover, it also showed excellent methanol tolerance and long-term stability. The enhanced ORR electrocatalytic performance is attributed to the strong synergetic effect between Cu(II)-N ligands and Cu0 NPs, sufficient active sites, and fast mass transfer.

Zingiber striolatum diels derived O/N dual-doped porous carbon for high performance oxygen reduction reaction and energy storage

Biomass-derived porous carbon materials have recently attracted intensive attentions because of the inherent sustainability and renewability of biomass precursors. In this work, a novel biomass-derived, O/N dual-doped porous carbon with twisted cabbage-leaf-like structure is synthesized by directly pyrolyzing the inflorescences of zingiber striolatum diels (ZSD). The obtained porous carbon (ZSD-900) has high specific surface area (1064 m2 g−1) as well as effective O/N dual-doping (7.63 at.% O and 2.72 at.% N). The ZSD-900 used as metal-free ORR electrocatalyst exhibits excellent activity (Eo = −3 mV; E1/2 = −155 mV vs. Ag/AgCl), high methanol and CO tolerance, together with good long-term stability. In addition, the assembled ZSD-900//ZSD-900 symmetric supercapacitor in 1 M Na2SO4 aqueous electrolyte displays high power density (17.4 kW kg−1) and excellent cycling stability (97.8% capacitance retention after 20,000 cycles). The outstanding electrochemical performance demonstrates that ZSD-900 is one of the most promising candidates for efficient ORR catalysts and advanced supercapacitors.

N‐doped Hierarchical Porous Carbon Nanomeshes as Oxygen Reduction in pH‐Universal Media and Oxygen Evolution Electrocatalysts

AbstractThe design and synthesis of highly active and long‐term durable carbon‐based electrocatalysts with inexpensive raw materials and an environment‐friendly method for many renewable energy conversion and storage technologies remain a major challenge. Herein, we demonstrate a novel synthesis of nitrogen‐doped hierarchically porous carbon nanomeshes. This is the first report of using a green fermentation method to introduce nitrogen sources with grape skins as a single precursor which are a green and highly economical biomass waste globally generated at over 8 million tons per year. The resultant material has a high BET surface area (1029.41 m2 g−1), abundant hierarchical porosity and shows the impressive electrocatalytic performance, durability and excellent methanol tolerance in pH‐universal media for the oxygen reduction reaction (ORR) and alkaline media for the oxygen evolution reaction (OER). This low‐cost fermentation approach provides a brief pathway to prepare outstanding N‐doped carbon‐based electrocatalysts straightforward from waste biomass.

Coral-like cobaltous sulfide/N,S-codoped carbon with hierarchical pores as highly efficient noble metal-free electrocatalyst for oxygen reduction reactions

To develop efficient nonprecious electrocatalysts for the oxygen reduction reaction (ORR) on cathode in fuel cell is urgently required. Herein, a promising coral-like N,S-codoped hierarchical porous carbon with supported cobaltous sulfide nanoparticles (CoxSy/NS-HPC) with different molar ratio of S:Co was successfully fabricated via an economic method. The role of thiourea in the preparation process was found to be triplex. It is not only as a sulfur source, but also as sulfur-nitrogen dopant, and most importantly it participates in the formation of the hierarchical porous carbon which will reduce the diffusion resistance of the reactants and expose more active sites. Benefited from the carbon support, the hybrid architecture CoS1.097/NS-HPC (S:Co = 3:1) possesses high specific surface area (549 m2/g) and more active sites, as result it was developed as decent ORR electrocatalyst for fuel cell. Surprisingly, we found that CoS1.097/NS-HPC provides a more positive onset potential, higher cathodic current density and half-wave potential in alkaline media than CoS1.097 NPs and CoS1.097 supported on conventional mesoporous carbon (CoS1.097/MC). More importantly, compared with commercial Pt/C, CoS1.097/NS-HPC manifests higher current density, better durability, and more excellent methanol tolerance.

Nickel–Cobalt–Phosphide Catalyst Derived from MOF-74 for Oxygen Reduction Reactions

In recent years, energy conversion and storage systems have been playing a crucial role in alleviating the pressure of energy crisis. Oxygen reduction reactions (ORRs) play an important role in energy conversion and storage systems, such as fuel cells and metal air batteries. Herein, it is critical important to develop high efficient and stable electrocatalysts for ORRs to replace platinum-based catalytic materials. In this work, nickel-cobalt bimetallic metal-organic framework (NiCo-MOF-74) and its derivatives (oxide, phosphide and sulfide) were synthesized and their electrochemical performances for ORRs were evaluated. The series of NiCo-MOF-74 products with rod-like structure show excellent electrochemical performance, especially phosphide. The phosphide exhibits higher current density, excellent methanol tolerance and long-term stability compared with the Pt/C catalyst. Therefore, the series of NiCo-MOF-74 derivatives have great potential in ORRs as highly active, stable and low-cost catalysts.

Porous nitrogen-doped graphene prepared through pyrolysis of ammonium acetate as an efficient ORR nanocatalyst

In the work presented here, a facile approach for the preparation of nitrogen-doped porous graphene was applied for the first time using ammonium acetate as a nitrogen rich precursor via pyrolysis at 900 °C for 2 h.The physicochemical properties of the prepared samples were determined using Field Emission Scanning Electron Microscopy (FE-SEM), Energy-dispersive X-ray spectroscopy (EDS) mapping, Raman spectroscopy and X–ray photoelectron spectroscopy (XPS). The prepared samples were further applied for the oxygen reduction reaction (ORR) in alkaline solution, and the electrochemical performance was investigated and compared with porous graphene and Pt/C 20 wt.%. The results revealed that introducing nitrogen to the graphene structure leads to improvement in catalytic activity, enhanced catalytic current as well as more positive potential. Furthermore, N-doped graphene prepared using ammonium acetate exhibited excellent methanol tolerance and long-term stability. Finally, it was shown that the optimal pyrolysis temperature was obtained at 900 °C. Therefore, it is concluded that ammonium acetate could be used as an effective precursor for the ORR.

Metal-organic framework-derived Fe3C@NC nanohybrids as highly-efficient oxygen reduction electrocatalysts in both acidic and basic media

Developing low-cost and high-performance non-precious metal catalysts (NPMCs) for oxygen reduction reaction (ORR) is of critical importance for commercialization of fuel cells. Herein, we report a NPMC consisting of Fe3C nanoparticles encapsulated in mesoporous N-doped carbon (N-C), which is synthesized by a simple two-step strategy comprising pyrolysis of a mixture of MIL-100(Fe) and dicyandiamide under inert atmosphere, followed by treatment of the product with acidic solution to leach removable Fe3C species from the material. Fe3C@NC-800 (the material prepared at 800 °C) exhibits superior electrocatalytic activity, high durability and excellent methanol tolerance for ORR, with catalytic performance comparable to that of commercial Pt/C in both alkaline and acidic media. Fe3C@NC-800's excellent catalytic activity and stability in ORR are due to its large BET surface area, its large total pore volume, its nitrogen dopants and the cooperative effects between the reactive functionalities in it as well as its excellent conductivity.

Amino acid-derived non-precious catalysts with excellent electrocatalytic performance and methanol tolerance in oxygen reduction reaction

In polymer electrolyte membrane fuel cells (PEMFCs), slow kinetics and high over-potential of oxygen reduction reaction (ORR) can result in a significantly large amount of Pt usage. Thus, non-precious metal (NPM) catalysts, especially, for ORR, that can be utilized instead of Pt-based catalysts, have been intensively studied. Herein, doped carbon nanostructures as NPM catalysts for ORR in an acid medium were synthesized using a template method with nontoxic, eco-friendly cysteine and iron (III) tetramethoxyphenylporphyrin (Fe-TMPP, 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphyrin iron(III) chloride) used as carbon and doping sources, respectively. To obtain the doped mesoporous carbon nanostructure, mixtures of cysteine and Fe-TMPP with intended ratios (CysX/FeZ) were heated under an N2 atmosphere at 900 °C for 3 h. In particular, Cys2/Fe0.3/C synthesized with an appropriate ratio of cysteine and Fe-TMPP showed a relatively high specific surface area and fairly high portion of doped species such as pyridinic and pyrrolic N, thiophenic S, and Fe-Nx. Moreover, Cys2/Fe0.3/C exhibited significantly enhanced ORR activity and stability in 0.5 M H2SO4 and superior tolerance of methanol in 0.5 M H2SO4 in the presence of CH3OH.

Comparative Study of Various Types of Metal-Free N and S Co-Doped Porous Graphene for High Performance Oxygen Reduction Reaction in Alkaline Solution.

Heteroatom doping into carbon structures is an effective approach to enhance the electrochemical performance of carbon materials. In the work presented here, the electrocatalysts including: nitrogen and co-doped nitrogen and sulfur on porous graphene (PG) were synthesized by different precursors. The physico-chemical properties of the prepared samples were determined using X-ray Diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), N2 sorption-desorption, Transmission electron microscopy (TEM), Field Emission Scanning Electron Microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). The prepared samples were further applied for oxygen reduction reaction (ORR) and the effects of pyrolysis temperature, precursor type and dose, on the prepared samples structure and their electrochemical performances were investigated. The results revealed that synergistic effect of nitrogen and sulfur co-doped on the graphene structure leads to improvement in catalytic activity and current. Furthermore, S and N co-doped graphene prepared using sulfur trioxide pyridine complex exhibited excellent methanol tolerance and long-term stability.

Boron and nitrogen co-doped graphene aerogels: Facile preparation, tunable doping contents and bifunctional oxygen electrocatalysis

Rational design of low-cost and highly-efficient bifunctional oxygen electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is currently critical for renewable energy storage and conversion devices. Herein, we represent a series of three-dimensional porous B and N co-doped graphene aerogels (BN-GAs) using NH4B5O8 as precursor for B and N source by hydrothermal method and freeze-drying process. In this facile strategy, we can tune doping contents of B and N configurations in BN-GAs by simply changing the synthesis conditions. Linear sweep voltammetry results confirm that the increasing doping contents of pyridinic N and BC3 phases in BN-GAs can boost ORR activity, which may be because the enhanced synergy that arises from combining pyridinic N and BC3 phases can greatly improve ORR activity. The proposed BN-GAs not only show similar ORR activity to commercial Pt/C, but also more superior stability and excellent methanol tolerance than commercial Pt/C. Remarkably, the resultant BN-GAs also exhibit considerable OER activity and achieve desired performance as an air cathode for a rechargeable zinc-air battery device. Notably, this work may assist in a new insight to feasible preparation and molecular design of more advanced graphene-based catalyst, and can be extended to other catalytic system.

Highly efficient electrocatalyst of N-doped graphene-encapsulated cobalt-iron carbides towards oxygen reduction reaction

Development of highly functional and durable catalysts in a cost-effective way is a promising approach for practical energy conversion applications. In this study, a novel catalyst, cobalt iron carbide nanoparticles encapsulated by nitrogen doped graphene nanosheets, is successfully synthesized through a simple refluxing strategy followed by a post annealing process. It is found that the catalyst exhibits excellent catalytic activity for oxygen reduction reaction in alkaline medium. The oxygen reduction reaction kinetics of the catalyst mainly follow a 4-electron transferred pathway along with good diffusion limit current density, highly positive onset potential (−0.04 V) and half-wave potential (−0.11 V). In addition to catalytic activity, the catalyst demonstrates advanced superior stability, and excellent methanol tolerance in comparison with commercial platinum catalyst. The impressive catalytic performance of the catalyst is attributed to the unique mesoporous metal-core/graphene-shell architecture in which high interactions between two transition metals and transition metal-carbon synergistically provide enhanced catalytically active sites, accelerate interfacial charge transfer, and optimize oxygen adsorption energy. The results demonstrate that such catalyst can be an alternative low-cost and efficient catalyst for oxygen reduction reaction in energy conversion applications.

Transition metal-doped carbon sphere as enhanced catalysts for oxygen reduction

Herein, carbon sphere (CS-T) were successfully prepared by pyrolyzation melamine formaldehyde resin. And then different transition metals (Fe, Co, Ni) were doped on carbon sphere (CS-M-900). The scanning electron microscopes and elemental mappings prove that the transition metal particles are uniformly doped on the carbon sphere. Meanwhile, the X-ray photoelectron spectrum prove that the transition metals are zero-valence. Furthermore, the electrochemical testings showed the CS-Co-900 had more positive onset potential (0.93 V), half-wave potential (0.84 V), and peak potential (0.81 V). Furthermore, the CS-Co-900 had lower charge transfer resistance (44 Ω) and smaller Tafel slope (65 mV/dec). Most importantly, the oxygen reduction reaction on the CS-Co-900 turned out to be a four electron procedure with excellent methanol tolerance. The improved electrochemical properties towards oxygen reduction reactions of carbon sphere via cobalt doping suggested a design strategy towards future high-performance electrochemical devices.

One-step electrochemical strategy for in-situ synthesis of S,N-codoped graphene as metal-free catalyst for oxygen reduction reaction

A simple and economic method was developed for synthesizing efficient S,N-codoped graphene based catalyst for oxygen reduction reaction via a one-step electrochemical exfoliation of graphite rod in melamine and (NH4)2SO4 mixture solution. On one hand, melamine and (NH4)2SO4 co-worked as electrolyte to enhance the exfoliation efficiency of graphite into graphene nanosheets. On the other hand, they also provided nitrogen and sulphur sources for in-situ codoping of the as-prepared graphene. As evidenced, the N and S elements are distributed uniformly throughout the graphene nanosheets which possessed larger interlayer spacing, more lattice disorder and higher defect density. Accordingly, the obtained SNG shows efficient ORR catalytic activity with an onset potential of 0.88 V and a dominant four-electron transfer mechanism (n = 3.98 at 0.5 V), long-time durability and excellent methanol tolerance, which are comparable or superior to those of commercial Pt/C catalysts.