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Sponge-like nitrogen-containing carbon (SNC) was synthesized via a template-free approach through pyrolyzing a mixture of bipyridine and iron (III) chloride. Transmission electron microscopy revealed that the prepared SNC comprised an interconnected highly porous three-dimensional framework. Using rotating disk electrode measurements to measure oxygen reduction activity and methanol tolerance, SNC was found to have a 22.2 mV more negative half-wave potential than that of commercial Pt/C and strong methanol tolerance. We conclude that SNC affords a promising 'non-precious' oxygen reduction catalyst in alkaline medium. [ABSTRACT FROM AUTHOR]

A novel electrocatalyst for the oxygen reduction reaction (ORR) is fabricated by directly annealing oxidized carbon nanotubes and tripyrrolyl[1,3,5]triazine in nitrogen. The structural and chemical properties of the resultant N-doped carbon nanotubes (NCNTs) are systematically investigated. The electrocatalytic activity of the NCNTs towards ORR in O 2 -saturated 0.1 M KOH electrolyte is evaluated using rotating disk electrode voltammetry. The results demonstrate that the as-prepared NCNT-900 (annealed at 900 °C) exhibits excellent electrochemical performance towards ORR in alkaline medium with an onset potential of −0.038 V ( vs Ag/AgCl), a high kinetic current density of 31.26 mA cm −2 at −0.25 V, a dominant four-electron transfer mechanism (n = 3.88 at −0.25 V), and excellent methanol tolerance and durability. The results obtained are significant for the development of N-doped carbon-based electrocatalysts for alkaline fuel cells. [ABSTRACT FROM AUTHOR]

Efficient electrocatalyst of oxygen reduction reaction (ORR) is crucial for a variety of renewable energy applications and heteroatom-doped carbon materials have demonstrated promising catalytic performance towards ORR. In this paper we report a bioinspired method to synthesize nitrogen/sulfur (N/S) co-doped graphene as an efficient ORR electrocatalyst via self-polymerization of polydopamine (PDA) thin layer on graphene oxide sheets, followed by reacting with cysteine and finally thermal annealing in Argon (Ar) atmosphere. As-prepared N/S co-doped graphene exhibits significantly enhanced ORR catalytic activity in alkaline solution compared with pristine graphene or N-doped graphene. It also displays long-term operation stability and strong tolerance to methanol poison effect, indicating it a promising ORR electrocatalyst. [ABSTRACT FROM AUTHOR]

In this study, the preparation of a highly efficient metal-free electrocatalyst, boron and nitrogen codoped reduced graphene oxide (BN-rGO), with an excellent durability is reported. The BN-rGO were prepared in one step using boric and nitric acid mixture, exhibiting highly improved oxygen reduction reaction (ORR) activity than those of the pristine GO and single doped rGOs. The electrocatalyst also showed the excellent long-term durability and CO tolerance than those of the commercial Pt/C catalysts. [ABSTRACT FROM AUTHOR]

Two catalysts are synthesized by wet impregnation of multi walled carbon nanotubes (MWCNT) with a complex formed between Co(II) ions and the nitrogen-containing molecule 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ), followed by one or two identical heat treatments in N 2 atmosphere at 800 °C for 3 h. Catalysts are fully characterized by FESEM, EDX, BET, XRD, FTIR, TGA, XPS analyses, and electrochemical techniques. The electrocatalytic activity towards oxygen reduction reaction (ORR) of the catalysts in acid conditions is assessed by means of a rotating disk electrode (RDE) apparatus and a specific type of cell equipped with a gas diffusion working electrode (GDE). In both testing approaches, the catalyst heat-treated twice (Co-N/MWCNT-2) exhibits higher electroactivity than the catalyst heat-treated once (Co-N/MWCNT-1). Chronoamperometries both in RDE and GDE cell are also performed, showing less electroactivity decay and better current performance for the catalyst heat-treated twice. [ABSTRACT FROM AUTHOR]

Developing an effective bifunctional catalyst is a significant issue, as rechargeable metal-air batteries are very attractive for future energy systems. In this study, a facile one-pot process is introduced to prepare an advanced bifunctional catalyst (op-LN) incorporating nitrogen-doped carbon nanotubes (NCNTs) into perovskite La0.5Sr0.5Co0.8Fe0.2O3 nanoparticles (LSCF-NPs). Confirmed by half-cell testing, op-LN exhibits synergistic effects of LSCF-NP and NCNT with excellent bifunctionality for both the oxygen reduction reaction and the oxygen evolution reaction. Furthermore, op-LN exhibits comparable performances in these reactions to Pt/C and Ir/C, respectively, which highlights its potential for use as a commercially viable bifunctional catalyst. Moreover, the results obtained by testing op-LN in a practical Li-air battery demonstrate improved and complementary charge/discharge performance compared to those of LSCF-NP and NCNT, and this confirms that simply prepared op-LN is a promising candidate as a highly effective bifunctional catalyst for rechargeable metal-air batteries. [ABSTRACT FROM AUTHOR]

Non-Pt-group metal (non-PGM) materials based on transition metal-nitrogen-carbon (M-N-C) and derived from iron salt and aminoantipyrine (Fe-AAPyr) of mebendazole (Fe-MBZ) were studied for the first time as cathode catalysts in double-chamber microbial fuel cells (DCMFCs). The pH value of the cathode chamber was varied from 6 to 11 to elucidate the activity of those catalysts in acidic to basic conditions. The Fe-AAPyr- and Fe-MBZ-based cathodes were compared to a Pt-based cathode used as a baseline. Pt cathodes performed better at pH 6-7.5 and had similar performances at pH 9 and a substantially lower performance at pH 11 at which Fe-AAPyr and Fe-MBZ demonstrated their best electrocatalytic activity. The power density achieved with Pt constantly decreased from 94-99 μW cm−2 at pH 6 to 55-57 μW cm−2 at pH 11. In contrast, the power densities of DCMFs using Fe-AAPyr and Fe-MBZ were 61-68 μW cm−2 at pH 6, decreased to 51-58 μW cm−2 at pH 7.5, increased to 65-75 μW cm−2 at pH 9, and the highest power density was achieved at pH 11 (68-80 μW cm−2). Non-PGM cathode catalysts can be manufactured at the fraction of the cost of the Pt-based ones. The higher performance and lower cost indicates that non-PGM catalysts may be a viable materials choice in large-scale microbial fuel cells. [ABSTRACT FROM AUTHOR]

Synthesized by dripping iron acetate into the N-doped carbon film enriched with pyridinic N and followed by annealing at 800 °C, Fe–N-doped amorphous carbon (d Fe–N -C) with an Fe content of 0.2 at.% showed excellent electrocatalytic activity, stability and methanol tolerance via a four-electron pathway for oxygen reduction reaction (ORR), which outperformed commercial Pt/C catalyst. More importantly, by tuning the Fe content and annealing temperature, the trace Fe in d Fe–N -C was supposed to form high active FeN 4 sites with pyridinic N and played an important role in the excellent electrocatalytic performance for ORR. [ABSTRACT FROM AUTHOR]

A ferrocene-based ionic liquid (Fe-IL) is used as a metal-containing feedstock with a nitrogen-enriched ionic liquid (N-IL) as a compatible nitrogen content modulator to prepare a novel type of non-precious-metal-nitrogen-carbon (M-N-C) catalysts, which feature ordered mesoporous structure consisting of uniform iron oxide nanoparticles embedded into N-enriched carbons. The catalyst Fe10@NOMC exhibits comparable catalytic activity but superior long-term stability to 20 wt% Pt/C for ORR with four-electron transfer pathway under alkaline conditions. Such outstanding catalytic performance is ascribed to the populated Fe (Fe3O4) and N (N2) active sites with synergetic chemical coupling as well as the ordered mesoporous structure and high surface area endowed by both the versatile precursors and the synthetic strategy, which also open new avenues for the development of M-N-C catalytic materials. [ABSTRACT FROM AUTHOR]

The synthesis of highly nitrogen-doped mesoporous carbon spheres (NMCS) is reported. The large pores of the NMCS were obtained through self-polymerization of dopamine (DA) and spontaneous co-assembly of diblock copolymer micelles. The resultant narrowly dispersed NMCS possess large mesopores (ca. 16 nm) and small particle sizes (ca. 200 nm). The large pores and small dimensions of the N-heteroatom-doped carbon spheres contribute to the mass transportation by reducing and smoothing the diffusion pathways, leading to high electrocatalytic activity. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon nanofibers (NCNFs) are prepared by the thermal treatment of carbon nanofibers (CNFs) using urea as nitrogen source. Scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy have been employed to characterize the morphology and composition of CNFs and NCNFs. Compared with CNFs, NCNFs display thinner diameter, rougher surface and higher content of pyrrolic-N. As a metal-free catalyst for ORR, NCNFs exhibit comparable catalytic activity, significantly enhanced long-time stability and selectivity in comparison with commercial available Pt/C catalyst. Importantly, the self-supported NCNFs films could be conveniently utilized for electrode modification which is attractive in fuel cells. This work offers a promising metal-free catalyst as an alternative for Pt/C catalyst. [ABSTRACT FROM AUTHOR]

The successful commercialization of fuel cells requires the efficient electrocatalyst to make the oxygen reduction reaction (ORR) fast because of the sluggish nature of ORR and the high cost of the platinum catalysts. In this work, we report the excellent performance of metal-free nitrogen-doped porous carbon nanosheets (NPCN) with hierarchical porous structure and a high surface area of 1436.02 m 2 g −1 for catalyzing ORR. The active NPCN is synthesized via facile high-temperature carbonization of natural ginkgo leaves followed by purification and ammonia post-treatment without using additional supporting templates and activation processes. In O 2 -saturated 0.1 M KOH solution, the resultant NPCN exhibits a high kinetic-limiting current density of 13.57 mA cm −2 at −0.25 V (vs. Ag/AgCl) approaching that of the commercial Pt/C catalyst (14 mA cm −2 ) and long-term electrochemical stability. Notably, the NPCN shows a slightly negative ORR half-wave potential in comparison with Pt/C (Δ E 1/2 = 19 mV). The excellent electrocatalytic properties of NPCN originate from the combined effect of optimal nitrogen doping, high surface area, and porous architecture, which induce the high-density distribution of highly active and stable catalytic sites. [ABSTRACT FROM AUTHOR]

Currently, the development of nitrogen (N) doped carbon based non-precious metal ORR catalysts has become one of the most attractive topics in low temperature fuel cells. Here, we demonstrate a green synthesis route of N-self-doped carbon materials by using eggs as N sources combining with iron sources and multi-walled carbon nanotubes (CE–Fe–MWNT). After carbonized, such hybrid materials possess an outstanding electrocatalytic activity towards ORR comparable to the commercial Pt/C catalyst in alkaline media, and both superior stability and fuel (methanol and CO) tolerance than the commercial Pt/C catalyst, which provide a promising alternative to noble metal catalysts by using abundant natural biological resources. [ABSTRACT FROM AUTHOR]

Abstract: Hierarchical porous iron and nitrogen co-doped carbons (HP–Fe–N–Cs) as efficient cathode catalysts for oxygen reduction reaction (ORR) in neutral media are reported. The HP–Fe–N–Cs are prepared by using polypyrrole as nitrogen source and poly(vinyl alcohol) (PVA) hydrogel-based composites as in-situ templates. In studying the effect of the iron and the hierarchical porous structure on the nitrogen-doped carbon support for ORR, we find that HP–Fe–N–Cs show more positive onset potential, higher cathodic current density, and higher electron transfer number for the ORR in neutral media than iron-free hierarchical porous nitrogen-doped carbon (HP–N–C) and non-hierarchical porous iron and nitrogen co-doped carbon (Fe–N–C), highlighting the importance of the iron and the hierarchical porous structure for improving the ORR performance. Furthermore, HP–Fe–N–Cs show better durability than the commercial Pt/C catalysts in neutral media, and the microbial fuel cells (MFCs) equipped with HP–Fe–N–Cs catalysts on cathodes exhibit comparable power outputs with those of MFCs with commercial Pt/C cathode catalysts. [Copyright &y& Elsevier]

We demonstrate a general and efficient self-templating strategy towards transition metal-nitrogen containing mesoporous carbon/graphene nanosheets with a unique two-dimensional (2D) morphology and tunable mesoscale porosity. Owing to the well-defined 2D morphology, nanometer-scale thickness, high specific surface area, and the simultaneous doping of the metal-nitrogen compounds, the as-prepared catalysts exhibits excellent electrocatalytic activity and stability towards the oxygen reduction reaction (ORR) in both alkaline and acidic media. More importantly, such a self-templating approach towards two-dimensional porous carbon hybrids with diverse metal-nitrogen doping opens up new avenues to mesoporous heteroatom-doped carbon materials as electrochemical catalysts for oxygen reduction and hydrogen evolution, with promising applications in fuel cell and battery technologies. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ionic liquids are promising precursors for nitrogen-doped carbon catalyst for ORR. [•] Use of transition metal in the pyrolysis of IL is important for high ORR activity. [•] The graphitic-N content in the sp2-carbon network is key factor for high ORR. [•] Co is an effective metal compared to Ni for nitrogen-doped carbon catalyst. [Copyright &y& Elsevier]

Highlights: [•] Few-walled carbon nanotubes (FWCNTs) are synthesized by a CVD method. [•] N-FWCNTs are obtained by treatment with polyaniline and pyrolysis at high temperature. [•] N-FWCNTs with only ∼0.5at.% show high activity for oxygen reduction reaction (ORR). [•] ORR activity comparable to Pt-C is observed both in electrochemical cell and alkaline fuel cell. [Copyright &y& Elsevier]

An ion-exchange resin-based methodology has been used to synthesize the N-doped graphene-like metal-free catalyst (NGMFC). This catalyst is hierarchical porous structured with high surface area. In acidic media, the NGMFC shows a high electrocatalytic performance and good stability towards oxygen reduction reaction (ORR) in rotating ring-disk electrode measurements. The onset potential of the catalyst for ORR is 0.99 V which is very close the onset potential of Pt/C catalyst. This research demonstrates that the ion-exchange resin-based methodology can be a potential alternative to produce efficient metal-free catalyst at extremely low cost for ORR. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) Fe, N-doped carbon foams (3D-CF) as efficient cathode catalysts for the oxygen reduction reaction (ORR) in alkaline solution are reported. The 3D-CF exhibit interconnected hierarchical pore structure. In addition, Fe, N-doped carbon without porous strucuture (Fe-N-C) and 3D N-doped carbon without Fe (3D-CF’) are prepared to verify the electrocatalytic activity of 3D-CF. The electrocatalytic performance of as-prepared 3D-CF for ORR shows that the onset potential on 3D-CF electrode positively shifts about 41 mV than those of 3D-CF’ and Fe-N-C respectively. In addition, the onset potential on 3D-CF electrode for ORR is about 27 mV more negative than that on commercial Pt/C electrode. 3D-CF also show better methanol tolerance and durability than commercial Pt/C catalyst. These results show that to synthesize 3D hierarchical pores with high specific surface area is an efficient way to improve the ORR performance. [ABSTRACT FROM AUTHOR]

Molecular oxygen chemisorption on the edge sites of nitrogen, boron, or oxygen doped and non-doped carbon has been studied by means of density functional theory in order to obtain a better insight into the first step of the oxygen reduction reaction (ORR) in fuel cells. The calculated chemisorption energies enabled us to evaluate thermodynamic favorability of the chemisorption products, and the activation energies revealed the most probable pathways of molecular oxygen chemisorption. It has been found that oxygen doped carbon edge sites can oxidize easily with disruption of the heterocyclic ring. Boron doped carbon edge sites can form stable B-O-C species and thus cause changes in the chemical structure of a boron doped carbon based catalyst. Molecular oxygen binding on carbon edge sites doped with graphitic nitrogen has been found to be improved compared to non-doped, boron and pyridinic nitrogen doped carbon edge sites. Carbon edges doped with pyridinic nitrogen can serve as the sites for molecular oxygen chemisorption only in the presence of valence unsaturated carbon atoms. In general, the ORR both on non-doped and heteroatom doped carbon edges initiates on the adjacent edge carbon atoms and is enhanced by the presence of graphitic nitrogen. [ABSTRACT FROM AUTHOR]

[Display omitted] • Highly dispersed Co atoms anchored in porous N-doped carbon is synthesized. • The p –Co–N–C exhibits excellent activity and selectivity for H 2 O 2 electrosynthesis. • The p –Co–N–C shows promising application for the degradation of organic pollutants. Cobalt–nitrogen–carbon (Co–N–C) materials exhibit great potential for H 2 O 2 electrosynthesis through the oxygen reduction reaction (ORR). However, the encapsulated Co nanoparticles reduce the Faradic efficiency of H 2 O 2 production. Herein, highly dispersed cobalt atoms anchored in porous N-doped carbon (p –Co–N–C) via a carbonization-alkalization-acidification strategy are prepared and prove to be efficient for H 2 O 2 electrosynthesis in acidic media. The H 2 O 2 selectivity on the p –Co–N–C is over 90%, which is three times higher than that of Co nanoparticles encapsulated in N-doped carbon. Notably, the p –Co–N–C displays a H 2 O 2 production rate of 2,460.8 mg L−1h−1 and a malachite green degradation rate of 90% within 8 min when employed in a flow cell. The enhanced performance of p –Co–N–C for H 2 O 2 electrosynthesis originates from the highly dispersed Co–N x species and hierarchical porous architecture. The Co–N x species can provide active sites for O 2 and reaction intermediate adsorption and the hierarchical porous architecture can promote the diffusion of H 2 O 2 into the bulk solution. This work provides a facile synthesis strategy for non-precious metal materials in various energy-related applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Single-Cu-atoms and Cu clusters anchored nitrogen-doped porous carbon is developed. • As-prepared porous carbon shows ultra-high specific surface area of 3264 m2 g−1. • The catalysts exhibit the pH-universal electrocatalytic activity for oxygen reduction reaction. • The catalytic activity in acidic medium outperforms all of reported Cu-based catalysts. • The enhanced activity can be attributed to the synergistic effects of single-Cu-atom and Cu cluster. Oxygen reduction reaction (ORR) plays a significant role in many renewable energy storage and conversion devices. Various kinds of transition metal-based electrocatalysts were developed to promote the ORR. Among them, Cu-based catalysts were rarely studied due to their intrinsic de-active feature in bulk state, especially in acidic medium. In this work, single Cu atoms and Cu clusters-anchored nitrogen-doped porous carbons are rationally developed. As electrocatalysts for ORR, half-wave potential (E 1/2) of 0.88 V and diffusion limiting current density (J L) of 5.88 mA cm−2 can be achieved in 0.1 M KOH, exceeding the most of reported non-precious catalysts and commercial Pt/C. Significantly, as-prepared catalysts exhibit the state-of-the-art performance in acidic medium among all of reported Cu-based catalysts with the E 1/2 of 0.80 V and J L of 5.86 mA cm−2. Theoretical calculations indicate that the nitrogen-coordinated Cu atoms are the dominating active sites, and the neighboring Cu cluster increases the electron density of d orbitals of single-Cu-atom, which weakened the O-O interaction, thus further boost ORR performance. This work not only presents a facile strategy to fabricate efficient catalysts but also identifies the great potential of Cu based materials for ORR in both alkaline and acidic media. [ABSTRACT FROM AUTHOR]

[Display omitted] • Influence of Fe bonded with different type N on the stability of ORR was analyzed. • Fe-N-C catalyst with high pyridinic N content was successfully prepared. • Fe-N-C with high pyridinic N content presents much enhanced ORR stability. • The practical value of catalyst was tested in PEMFC and Zn-air cell. Developing advanced non-precious metal catalysts towards acidic oxygen reduction reaction (ORR) is critical for electrochemical energy conversion devices. Fe-N-C catalysts are demonstrated to be the most promising alternatives to platinum-based catalysts for ORR. Herein, Fe single atoms (SAs) coordinated by pyridinic nitrogen catalysts (denoted as Fe-pyridinic N-C) are synthesized through pyrolysis of ZIF-8 encapsulating ferrocene. Owing to the synergistic effects between Fe SAs and pyridinic N, Fe-pyridinic N-C exhibits remarkable ORR activity and outstanding stability in acid media, evidenced by golden kinetic current density of 9.71 mA cm−2 at 0.8 V, along with only 21 mV decrease in half-wave potential after 20,000 cycles. Theoretical calculations demonstrate that pyridine-type N possesses stronger binding energy with Fe SAs compared with pyrrole-type N, in other words, high pyridinic N content will help stabilize the catalyst. This study will be of great significance for the development of non-noble metal catalysts towards ORR with enhanced stability in acidic media. [ABSTRACT FROM AUTHOR]

Via a simple microwave-assistance without template and metal ligand, nitrogen doped porous carbon polyhedrals supported Fe and Ni dual single-atomic catalysts (FeNi-DACs-PNCH) were sucessfully prepared, and exhibited superb ORR performances with positive E 1/2 (0.89 V vs RHE), excellent durability and strong tolerance to methanol and SCN- in alkaline media. Moreover, with FeNi-DSAs-PNCH as the air cathode and zinc foil as the anode, an assembled Zn-air battery exhibits a higher open-circuit voltage of 1.48 V and a larger specific capacity of 802.18 mAh g−1 than that of the Pt/C-based Zn-air battery (1.37 V and 664.78 mAh g−1, respectively). [Display omitted] • Dual single-atomic catalysts prepared via microwave-aid with no template and metal ligand. • The catalysts have porous structure, large surface area and abundant active sites. • The catalysts showed high ORR activity superior to the commercial Pt/C. • The proposed Zn-air battery exhibits a promising practical application prospect. • DFT calculation verified the d-band center modulating for boosted ORR catalysis. Constructing dual-metal single-atom catalysts (DSAs) now stands for a unique and worthwhile strategy for developing high-efficiency electrocatalysts for oxygen reduction reaction (ORR). However, the facile synthesis of DSAs uniformly located on nitrogen porous carbon materials is still challenging. Herein, Fe and Ni dual-metal single-atomic active sites uniformly located on nitrogen doped porous carbon polyhedrals (FeNi-DSAs-PNCH) are successfully prepared by a facile and rapid microwave-assisted adsorption and subsequent pyrolysis process with free template and free metal ligand. The FeNi-DSAs-PNCH catalyst exhibits boosted ORR activity and long time stability. Experimental investigations and density functional theory calculation results verify that, besides the hierarchical porous structure, large specific surface area and abundant catalytic active sites, the adjacent Ni-Nx atomic sites can modulate the d-band center of Fe-Nx single atomic active centers and balance the adsorption–desorption affinities to O 2 molecules and oxygen-containing intermediates on Fe-Nx, thus leading to an superior ORR activity with a more positive half-wave potential (0.89 V vs. RHE) than the single Fe or Ni atomic catalyst and the commercial Pt/C catalyst. Moreover, with FeNi-DSAs-PNCH as the air cathode and zinc foil as the anode, an assembled Zn-air battery exhibits a higher open-circuit voltage of 1.48 V and a larger specific capacity of 802.18 mAh g−1 than that of the Pt/C-based Zn-air battery (1.37 V and 664.78 mAh g−1, respectively). This work develops a convenient strategy for preparing dual-metal single-atomic cataysts as promising substitutes for the commercial Pt/C catalysts in the practical energy conversion applications, and also offers experimental and theoretical guidance for rational designing and improvement of ORR and other catalysts by tailoring the d-band center of the active sites. [ABSTRACT FROM AUTHOR]

Boron-doped graphene and nitrogen-doped graphene have been respectively synthesized by a facile thermal solid-state reaction of graphene oxide with boric acid and urea. The morphology and structure of the doped graphene have been characterized by the scanning electron microscopy, infrared spectroscopy, ultraviolet visible spectroscopy and X-ray photoelectron spectroscopy, while the electrocatalytic activity toward oxygen reduction reaction has been evaluated by the cyclic voltammetry. It has been shown that the morphology, structure, doping level and fashions of graphene could be finely tuned by the thermal treatment conditions, and which have substantial effects on the activity of oxygen reduction reaction. The boron-doped graphene and nitrogen-doped graphene calcined at 700 °C demonstrate excellent electrocatalytic oxygen reduction activities as the appropriate introduction of boron and nitrogen functional groups in graphene, which might be promising for low temperature fuel cell applications. [ABSTRACT FROM AUTHOR]

In this work, a nitrogen-doped graphene (NG) catalyst was prepared using a hydrothermal method with ammonia as the nitrogen precursor, which was followed by a freeze-dry process. The catalyst was characterized using X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscope, and X-ray photoelectron spectroscopy. The bifunctional catalytic activities for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) were investigated using cyclic voltammetry in an alkaline electrolyte. The results indicate that nitrogen is successfully doped in the NG catalyst, and the catalyst has a loose structure that was produced during the freeze-dry process. The catalyst exhibits an excellent ORR activity with an onset potential of −0.08 V and a high OER activity with an obvious OER current at 0.7 V. The rotating-disk-electrode test results indicate that the ORR process catalyzed by the NG catalyst involves a mix of the two-electron and four-electron transfer pathways. This work preliminarily explores the bifunctional catalytic properties for the ORR and the OER of nitrogen-doped graphene materials in alkaline electrolyte. [ABSTRACT FROM AUTHOR]

Nitrogen-doped graphene is studied as a kind of non-noble metal catalyst for the oxygen reduction reaction in the cathode of fuel cells. Graphene is synthesized by pyrolyzing ion exchange resin and nitrogen doping is realized by a second pyrolysis step with nitrogen precursor. High resolution transmission electron microscopy proves the graphene is composed by 8–10 graphitic layers. The defect of graphene caused by nitrogen doping is detected by Raman spectra. The nitrogen group of the doped graphene is studied in detail with X-ray photoelectron spectroscopy spectra and a special type of nitrogen: valley-N is distinguished. The valley-N is proved to play an important role in the oxygen reduction reaction. Nitrogen content is found not directly related with the activity of the oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

The combination of surface science and electrochemistry is an effective method to approach a fundamental understanding of electrocatalytic systems, especially of the catalyst/support assemblies. Extrinsic chemical defects in the support can affect the performances and this topic is much investigated in recent electrocatalyst research. In this work, nitrogen functional groups are introduced into the outermost layers of highly oriented pyrolytic graphite (HOPG) by ion implantation with a beam energy of 100 eV. Palladium nanoparticles (Pd NPs) are then electrochemically deposited onto both pure and nitrogen doped HOPG (N-HOPG). Pd 2+ species located at the interface between the NPs and the nitrogen-rich surface were observed in the latter case. The supported Pd NPs on N-HOPG show the same electrocatalytic activity for oxygen reduction reaction (ORR) as compared with those supported on pure HOPG. However, the stability of Pd NPs on N-HOPG towards potential cycling decreases strongly due to the existence of Pd 2+ at the interface, which can accelerate the dissolution of Pd atoms. This result is contradictory to results on supported Pt NPs from the literature where the merit of the N-doping was outlined. [ABSTRACT FROM AUTHOR]

The most promising non-precious metal oxygen reduction catalysts are M-Nx/C (M = Fe and/or Co) materials. Moreover, N-containing precursor is one of the important factors that affect oxygen reduction reaction (ORR) activity of M-Nx/C materials. In this paper, we want to study nitrogen precursor effects on ORR activity of Co-Nx/C catalysts by varying N content and N/C ratio of the nitrogen precursor. In this regard, three Co-Nx/C catalysts were synthesized using a solvent-milling method followed by high temperature treatment. The results showed that the increase in N content and N/C ratio did not necessarily cause the improvement of ORR activity of the Co-Nx/C catalyst. The most active catalyst, Co-HQ/C-800 (heat treatment of carbon supported Co-HQ complex at 800 °C for 2 h), was obtained using 8-hydroxyquinoline (8-HQ) as the nitrogen precursor. XPS analysis demonstrated that more graphitic N and Co-Nx active sites were responsible for better ORR activity of the Co-HQ/C-800 catalyst. The electrochemical property of the three Co-Nx/C catalysts was evaluated by linear sweep voltammetry (LSV), chronoamperometric measurements, accelerated durability tests (ADT) and H 2 /O 2 alkaline fuel cell (AFC) tests. [ABSTRACT FROM AUTHOR]

Abstract: Melamine-derived N-doped mesoporous carbon (MNMC) is synthesized by the pyrolysis of lysine and melamineunder at nitrogen atmosphere using ferric chloride as a dopant and SiO2 nanoparticles as hard templates to form mesoporous architecture. The N content in the bulk of carbon materials is as high as 11.3% and ca. 40.6% of N is in the form of pyridinic-N. The surface area of MNMC is ca. 650 m2 g−1 with a pore size distribution in the range of 2.2–34.5 nm. Compared to commercial Pt/C (20 wt%), MNMC exhibits much better electrocatalytic activity, better durability, and higher methanol tolerance for oxygen reduction reaction (ORR) in alkaline medium. Particularly, the onset ORR potential and half-wave ORR potential of MNMC are 1.059 and 0.871 V vs. RHE respectively, which are higher than those of commercial Pt/C. [Copyright &y& Elsevier]

A cost-effective chemical, N,N′-bis(salicylidene)ethylenediamine (salen), is used as a ligand to form a carbon-supported Co-salen complex (Co-salen/C) by a simple solid-sate reaction. The Co-salen/C is then pyrolyzed at 600, 700, 800, 900, and 1000 °C to form carbon-supported Co–N–S/C catalysts for the oxygen reduction reaction (ORR). XRD, EDX, TEM, and XPS are used to characterize the catalysts' composition, crystalline nature, morphology, and possible surface groups induced by heat-treatment. Investigation of the catalytic activity and the ORR mechanisms using rotating disk electrode and rotating ring-disk electrode techniques demonstrates that all of these Co–N–S/C catalysts are highly active for the ORR in an O2-saturated 0.1 M KOH solution, but the catalyst heat treated at 700 °C gives the best ORR activity. The overall electron transfer number for the catalyzed ORR was determined to be 3.6–3.9, with 3.7–19.9% H2O2 production over the potential range of −0.05 to −0.60 V, suggesting that the ORR catalyzed by Co–N–S/C catalysts is dominated by a 4-electron transfer pathway from O2 to H2O. In addition, these catalysts exhibit superior methanol tolerance to commercial 40% Pt/C catalyst, thus the Co–N–S/C catalysts are promising for use as electrocatalysts in alkaline polymer electrolyte membrane fuel cells. [ABSTRACT FROM AUTHOR]

Abstract: A Ti–Co–Phen/C catalyst was prepared for polymer electrolyte membrane fuel cells (PEMFCs) without precious metals using a modified polymer complex (PC) method with 1,10-phenanthroline (Phen) as the nitrogen precursor. The oxygen reduction reaction (ORR) activity of the Ti–Co–Phen/C catalyst was significantly higher than the ORR activity of the Ti–Co/C catalyst prepared with the PC method because the former had a larger N surface content due to its highly dispersed Co species. The catalyst also exhibited excellent chemical stability in acidic media due to the probable strong interactions between the highly dispersed Ti and Co species. A H2/O2 PEMFC using the Ti–Co–Phen/C catalyst as the cathode demonstrated excellent cell performance. A 0.68 W cm−2 maximum power density was obtained. The cell performance stability did not drop perceptibly during its 550-h lifetime at 0.5 V and its 300-h lifetime at 0.7 V. The prepared Ti–Co–Phen/C catalyst exhibited both high ORR activity and excellent performance stability, making it a promising alternative for the cathode catalysts in PEMFCs. [Copyright &y& Elsevier]

Highlights: [•] Nitrogen doping of ash-free coal and raw coal as a cathode catalyst for a fuel cell. [•] The presence of ash in coal, especially Fe and Al, promotes oxygen reduction. [•] Changed from onion-like fullerene structures to a nanocarbon structure. [•] Increased the pyridinic nitrogen, disordered defect carbons and oxygen reduction. [•] Formed Nitrogen-doped, combined Fe and Al with nanocarbons in the catalyst. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen-doped carbon nanomaterials have been attracted increasing research interests in lithium-O2 and Zinc-O2 batteries, ultracapacitors and fuel cells. Herein, nitrogen-doped graphitic carboncages (N-GCs) have been prepared by mesoporous Fe2O3 as a catalyst and lysine as a nitrogen doped carbon source. Due to the catalysis of Fe2O3, the N-GCs have a high graphitization degree at a low temperature, which is detected by X-ray diffraction and Raman spectrometer. Simultaneously, the heteroatom nitrogen is in-situ doped into carbon network. Therefore, the excellent electrocatalysis performance for oxygen reduction reaction is expected. The electrochemical measurement indicates that The N-GCs for oxygen reduction reaction in O2-saturated 0.1molL−1 KOH show a four-electron transfer process and exhibit excellent electrocatalytic activity (E ORR =-0.05V vs. Ag/AgCl) and good stability (i/i 0 =90% at -0.35V after 4000 s with a rotation rate of 1600rpm). [Copyright &y& Elsevier]

Highlights: [•] NCNT loading effect on ORR in alkaline medium. [•] Temperature effect on ORR at NCNT. [•] non-linear correlation between temperature and kinetic rate. [Copyright &y& Elsevier]

Highlights: [•] There was a linear relation between the binding energy of OOH* and OH* for the N-GNRs. [•] The most OER and ORR active sites were identified near the edge but not exactly on the edge of the armchair nanoribbons. [•] The minimum theoretic OER and ORR overpotential was calculated. [•] The calculations suggested that N-GNRs were a highly promising OER/ORR catalyst. [ABSTRACT FROM AUTHOR]

Nitrogen-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. [ABSTRACT FROM AUTHOR]

Highlights: [•] We propose an alternative method for doping nitrogen in carbon materials. [•] Nitrogen is successfully doped in carbon black and ketjen black confirmed with Raman and XPS. [•] Nitrogen doped carbons exhibit better electrocatalytic activity with high mass activity. [•] Nitrogen doped KB shows better physical and electrocatalytic characteristics of all samples. [Copyright &y& Elsevier]

Abstract: Nitrogen doped holey graphene (NHG), with in-plane holes in its sheet plate, has been synthesized in this work through the potassium hydroxide (KOH) etching and ball milling of nitrogen doped graphene (NG). It shows that the KOH etching and ball milling does not distinctly alter the elemental composition and the relative percentages of functional groups in NG, but produce holes in its in-plane sheet plate. The obtained NHG can then be used as an active electrode material for supercapacitors and as an active electrocatalyst for oxygen reduction reaction, and exhibits significantly higher electrochemical performance than the corresponding NG. Its improved electrochemical performance could be attributed to its specific holey structure in the sheet plate and porous structure in its randomly stacked solid, which provide it with more active edge atoms, better accessibility to electrolyte, larger accommodation space for ions, faster electrolyte diffusion and movement and so on. [Copyright &y& Elsevier]

Abstract: A highly active electrocatalyst for oxygen reduction reaction, manganese modified glycine derivative-carbon (Mn-CN x ), is synthesized by a two-step carbonizing process. X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy are used to characterize structure and morphology of the catalysts. Electrochemical tests show that Mn-CN x has higher catalytic activity for oxygen reduction reaction than CN x derived glycine and Mn modified Vulcan carbon. Moreover, the half-wave potential of Mn-CN x is only 12 mV lower than that of commercial Pt/C. Mn-CN x also has excellent durability to methanol crossover in alkaline solution, and thus provides a promising low cost, non-precious metal cathode catalyst for fuel cells. [Copyright &y& Elsevier]

A class of 2D covalent organic polymers (COPs) incorporating a metal (such as Fe, Co, Mn) with precisely controlled locations of nitrogen heteroatoms and holes were synthesized from various N-containing metal-organic complexes (for example, metal-porphyrin complexes) by a nickel-catalyzed Yamamoto reaction. Subsequent carbonization of the metal-incorporated COPs led to the formation of COP-derived graphene analogues, which acted as efficient electrocatalysts for oxygen reduction in both alkaline and acid media with a good stability and free from any methanol-crossover/CO-poisoning effects. [ABSTRACT FROM AUTHOR]

Abstract: Transition metal is usually required for obtaining N-doped carbon (dN-C) catalysts toward oxygen reduction reaction, leading to an intense debate on whether the active sites in dN-C correlate to transition metal. Here, we report that metal-free amorphous dN-C was synthesized using simple one-step magnetron sputtering at relatively low temperature. The chemical bonding states of N atoms, which play a key role in optimizing the electrocatalytic activity, can be tuned by adjusting deposition temperature. The metal-free dN-C with high pyridinic N content exhibits high electrocatalytic activity, and its stability and methanol tolerance are much better than commercial Pt/C catalyst. [Copyright &y& Elsevier]

Abstract: Porous nitrogen-doped carbon nanosheet on graphene (PNCN) was used as an alternative cathode catalyst for oxygen reduction reaction (ORR) in air-cathode microbial fuel cells (MFCs). Here we report a novel, low-cost, scalable, synthetic method for preparation of PNCN via the carbonization of graphite oxide–polyaniline hybrid (GO–PANI), subsequently followed by KOH activation treatment. Due to its high concentration of nitrogen and high specific surface area, PNCN exhibited an excellent catalytic activity for ORR. As a result, the maximum power density of 1159.34mWm−2 obtained with PNCN catalyst was higher than that of Pt/C catalyst (858.49mWm−2) in a MFC. Therefore, porous nitrogen-doped carbon nanosheet could be a good alternative to Pt catalyst in MFCs. [Copyright &y& Elsevier]

Considerable efforts have been exerted in the development of non-noble metal catalysts (NNMCs) for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs). The effects of the preparation strategy, including carbon support, metal and nitrogen precursors, as well as heat-treatment conditions, on the ORR activity for such NNMCs have also been extensively explored. In this review, we mainly focused on the recent advances in carbon-incorporated NNMCs, specifically carbon-incorporated iron nitride (FeCN)-based catalysts. Influences of pyrolysis temperature on the crystalline and local structures, chemical environment, morphology, and ORR activity of FeCN-based catalysts were discussed, and the ORR mechanism was also proposed. [ABSTRACT FROM AUTHOR]

Abstract: Well defined nitrogen-doped graphene (NG) is prepared by a transfer doping approach, in which the graphene oxide (GO) is deoxidized and nitrogen doped by the vaporized polyaniline, and the GO is prepared by a thermal expansion method from graphite oxide. The content of doped nitrogen in the doped graphene is high up to 6.25 at% by the results of elements analysis, and oxygen content is lowered to 5.17 at%. As a non-precious metal cathode electrocatalyst, the NG catalyst exhibits excellent activity toward the oxygen reduction reaction, as well as excellent tolerance toward methanol. In 0.1 M KOH solution, its onset potential, half-wave potential and limiting current density for the oxygen reduction reaction reach 0.98 V (vs. RHE), 0.87 V (vs. RHE) and 5.38 mA cm−2, respectively, which are comparable to those of commercial 20 wt% Pt/C catalyst. The well defined graphene structure of the catalyst is revealed clearly by HRTEM and Raman spectra. It is suggested that the nitrogen-doping and large surface area of the NG sheets give the main contribution to the high ORR catalytic activity. [Copyright &y& Elsevier]

Abstract: Nitrogen-doped hollow mesoporous carbon spheres has been synthesized from mesoporous silica spheres using glycine as carbon and nitrogen precursor. The wall of the spheres is composed by broken graphene. The metal free nitrogen-doped hollow mesoporous carbon spheres are proven to be active electrocatalyst for the oxygen reduction reaction in alkaline solution. A unique advantage of the nitrogen-doped hollow mesoporous carbon sphere is its methanol-tolerant property because of the absence of active metal. The catalytic activity is ascribed to the pyridinic-nitrogen formed during pyrolysis and the graphene-like structure. To the best of our knowledge this is the first report on the nitrogen-doped hollow mesoporous carbon sphere as a metal-free electrocatalyst for the oxygen reduction reaction which is an important reaction in fuel cell. The prepared mesoporous carbon material can also be used as catalyst support and find application both in the anode and cathode of fuel cell. [Copyright &y& Elsevier]