Highly dispersed Pt catalyst supported on nanoporous carbon derived from waste PET bottles for reductive alkylation

Nanoporous carbon (NPC) derived from waste polyethyleneterephthalate (PET) bottles was prepared by a MgO-templated method and employed as a support for a highly dispersed platinum catalyst. The NPCs and Pt/NPCs catalysts were characterized by BET, SEM, TEM, XRD and ICP-OES. The catalytic performance of the NPC supported Pt catalysts for reductive alkylation of p-aminodiphenylamine (p-ADPA) with methyl isoamyl ketone (MIAK) was investigated. The textural properties of the NPC prepared could be tailored by changing the size of the MgO-template and the MgO/waste PET powder mass ratio. When the pore size was below 14 nm, the catalytic performance of the Pt/NPCs for the reductive alkylation could be improved with increasing the pore size of the NPCs. Profiting from the higher mechanical strength and the ideal pore structure, Pt/O@NPC50(1/1)–PTA had excellent reusability, which could maintain 98% conversion of p-ADPA after reused 10 times.

Nanoporous carbon (NPC) derived from waste polyethyleneterephthalate (PET) bottles was prepared by a MgO-templated method and employed as a support for a highly dispersed platinum catalyst.     

Highly efficient and self-supported 3D carbon nanotube composite electrode for enhanced oxygen reduction reaction

A binder-free and self-supported 3D carbon nanotube composite electrode with NiFe nanoalloys, N doping and Fe/Ni–N_x–C structures was fabricated by a facile method. The strong synergistic effects of multi-components and the unique structural merits of the optimized sample endowed it outstanding oxygen reduction reaction activity with an onset potential of 1.048 V vs. RHE in 0.1 M KOH solution.

A binder-free and self-supported 3D-CNT composite electrode was prepared, containing multi-components of NiFe nanoalloys, N doping and Fe/Ni–N_x–C structures, synergistically promoting the electrocatalytic activity of oxygen reduction reaction.     

Core@shell structured Co–CoO@NC nanoparticles supported on nitrogen doped carbon with high catalytic activity for oxygen reduction reaction

A composite with a hierarchical structure consisting of nitrogen doped carbon nanosheets with the deposition of nitrogen doped carbon coated Co–CoO nanoparticles (Co–CoO@NC/NC) has been synthesized by a simple procedure involving the drying of the reaction mixture containing Co(NO₃)₂, glucose, and urea and its subsequent calcination. The drying step is found to be necessary to obtain a sample with small and uniformly sized Co–CoO nanoparticles. The calcination temperature has a great effect on the catalytic activity of the final product. Specifically, the sample prepared at the calcination temperature of 800 °C shows better catalytic activity of the oxygen reduction reaction (ORR). Urea in the reaction mixture is crucial to obtain the sample with the uniformly sized Co–CoO nanoparticles and also plays an important role in improving the catalytic activity of the Co–CoO@NC/NC. Additionally, there exists a strong electronic interaction between the Co–CoO nanoparticles and the NC. Most interestingly, the Co–CoO@NC/NC is highly efficient for the ORR and can deliver an ORR onset potential of 0.961 V vs. RHE and a half-wave potential of 0.868 V vs. RHE. Both the onset and half-wave potentials are higher than those of most catalysts reported previously and even close to those of the commercial Pt/C (the ORR onset and half-wave potential of the Pt/C are 0.962 and 0.861 V vs. RHE, respectively). This, together with its high stability, strongly suggests that the Co–CoO@NC/NC could be used as an efficient catalyst for the ORR.

A simple method has been developed for the synthesis of Co–CoO@NC/NC, which exhibits high and stable performance for the ORR.     

High-performance electrocatalyst based on polyazine derived mesoporous nitrogen-doped carbon for oxygen reduction reaction

Nitrogen-doped porous carbon materials have high potential in metal-free electrocatalysts, which is essential for several renewable energy conversion systems. Herein, we report a convenient and environment-friendly method to fabricate a nitrogen doped mesoporous carbon (NMC) using a nonionic surfactant of Pluronic F127 micelles as the template and a Schiff-base polymer (polyazine) as the precursor. The synthesized NMCs were of spheric morphology and mesoporous structures with surface area up to 1174 m² g⁻¹ and high level of nitrogen (2.9–19 at%) and oxygen (4.9–7.4 at%) simultaneously doped. The electrochemical data of NMCs were analyzed in the context of the BET and XPS information. A correlation between ORR activity and the pyridinic-N was found. The NMC-700 demonstrate the highest electrocatalytic activity for ORR among the studied materials, which can be ascribed to the reasonable surface area and mesoporous structure, as well as the most abundant touchable pyridinic-N, thus providing more effective active sites for the oxygen reduction. In comparsion to the control sample, the NMC-700 provides the ORR electrocatalytic activity approximate to that of commercial Pt/C catalyst with a highly long-term stability.

Nitrogen-doped porous carbon materials have high potential in metal-free electrocatalysts, which is essential for several renewable energy conversion systems.     

Uniformly dispersed platinum nanoparticles over nitrogen-doped reduced graphene oxide as an efficient electrocatalyst for the oxygen reduction reaction

Oxygen reduction reaction (ORR) with efficient activity and stability is significant for fuel cells. Herein, platinum (Pt) nanoparticles dispersed on nitrogen-doped reduced graphene oxide (N-rGO) were prepared by a hydrothermal and carbonized approach for the electrocatalysis of ORR. Polyvinylpyrrolidone plays a significant role in the reduction and dispersion of platinum particles (about 2 nm). The obtained Pt–N-rGO hybrids exhibited superior activity with an electron transfer number of ∼4.0, onset potential 0.90 eV of ORR, good stability and methanol tolerance in alkaline media. These results reveal the interactions between Pt–N-rGO and oxygen molecules, which may represent an oxygen modified growth in catalyst preparation. The excellent electrocatalysis may lead to the decreased consumption of expensive Pt and open up new opportunities for applications in lithium air batteries.

We developed a facile, yet general approach to prepare ultrafine Pt nanoparticles loaded on N-doped reduced graphene (Pt–N-rGO) composites, which showed excellent oxygen reduction reaction performance.     

All carbon hybrid N-doped carbon dots/carbon nanotube structures as an efficient catalyst for the oxygen reduction reaction

This paper reports the facile and scalable synthesis of hybrid N-doped carbon quantum dots/multi-walled carbon nanotube (CD/CNT) composites, which are efficient alternative catalysts for the oxygen reduction reaction (ORR) in fuel cells. The N-doped CDs for large-scale production were obtained within 5 minutes via a one-step polyol process using ethylenediamine (ED) in the presence of hydrogen peroxide as an oxidizing agent. For comparison, different CDs were also prepared using ethylene glycol (EG) and ethanolamine (EA) in the same manner. Physicochemical characterization suggested the successful formation of a CD(ED)/CNT hybrid without individual CD(ED)s and CNTs. The N-doped CD(ED)/CNT catalyst exhibited excellent electrocatalytic activity in an alkaline solution compared to other composites (CD(EG)/CNT and CD(EA)/CNT). The Tafel slope (−60.9 mV dec⁻¹) and durability (∼9.1% decay over 10 h) for CD(ED)/CNT were superior to high-performance Pt/C catalysts. The electrochemical double-layer capacitance on the CD(ED)/CNT hybrid showed apparent improvement of the active surface area because of N-doping and highly decorated CDs on the CNT wall. These results provide an innovative approach for the potential application of all carbon hybrid structures in electrocatalysis.

The ORR measurements showed that the CD(ED)/CNT catalyst was superior to CD(EG)/CNT and CD(EA)/CNT. They even surpassed the activity of commercial Pt/C in terms of durability, Tafel slope, and MeOH tolerance.     

Porous Pt3Ni with enhanced activity and durability towards oxygen reduction reaction

The size of nanocrystals (NCs) is regarded as one of the vital factors determining their electrochemical performance. To achieve high electrochemical activity and durability at the same time still remains a big challenge. This work has demonstrated the successful synthesis of Pt₃Ni nanocrystals of large size with porous characteristics (PNC-Pt₃Ni). The mass and specific activity of the as-prepared catalyst are 6 and 6.6 times more than those of commercial Pt/C at 0.9 volts versus the reversible hydrogen electrode (RHE), respectively. More importantly, PNC-Pt₃Ni prevails against a durability test (23.7% loss of mass activity after 10 000 potential cycling) with little change to the porous morphology under harsh experimental conditions. Density functional theory calculations show a much lower activation energy for PNC-Pt₃Ni during the process of dissociation of the oxygen molecule adsorbed on the surface of the catalyst, which may account for the improvement in the catalytic activity. The lower series resistance for PNC-Pt₃Ni is also verified by electrochemical impedance spectroscopy (EIS) data, resulting from fewer grain boundaries for nanocrystals with large sizes. This exciting work contributes a new strategy for the optimization of electrochemical performance and durability.

Porous Pt₃Ni nanocrystals of large size possess enhanced electrochemical activity and durability towards oxygen reduction reaction is preferred.     

Highly active electrocatalysts of iron phthalocyanine by MOFs for oxygen reduction reaction under alkaline solution

Metal–nitrogen–carbon materials (Fe–N/C) have been extensively studied as one of the most excellent electrocatalysts with good catalytic activities and cheap price towards the oxygen reduction reaction (ORR). The rational design of metal–organic framework (MOF) derived carbon materials with rapid mass transport ability and good stability is a great challenge to achieve. Herein, intensive research of Fe–N/C catalysts prepared from assembling MOFs with cheap iron phthalocyanine (FePc) for the ORR is innovatively carried out. A series of Fe–N/C nano-architectures are simply synthesized by a convenient assembling method under different temperatures (800 to 1000 °C). The assembly method at high temperatures tunes the number of FeN_x active sites and intensifies the exposure of interior active sites. The highly dispersing Fe20–N/C electrocatalyst treated at 900 °C exhibits remarkable stability and excellent ORR activities with a half-wave potential of 0.866 V (vs. RHE) in alkaline solution, which is higher than that of commercial Pt/C (0.838 V vs. RHE) under the same test conditions. X-ray photoelectron spectroscopy results illustrate that incorporated MOFs interact with the active centre of FePc, tend to enhance the electron transition and to promote the kinetics of the ORR. Overall, highly dispersed Fe–N/C MOF-based materials are excellent non-precious metal electrocatalysts for energy and environmental applications.

Rational design of FePc and MOFs can result in good nanoarchitecture Fe–N/C catalysts with improved ORR activity and stability.     

Cu assisted loading of Pt on CeO2 as a carbon-free catalyst for methanol and oxygen reduction reaction

The widely studied Pt/C catalyst for direct methanol fuel cells (DMFCs) suffers severe carbon corrosion under operation, which undermines the catalytic activity and durability. It is of great importance to develop a carbon-free support with co-catalytic functionality for improving both the activity and durability of Pt-based catalysts. The direct loading of Pt on the smooth surface of oxides may be difficult. Herein, the Cu assisted loading of Pt on CeO₂ is developed. Cu pre-coated CeO₂ was facilely synthesized and Pt was electrochemically deposited to fabricate the carbon-free PtCu/CeO₂ catalyst. The PtCu/CeO₂ catalyst has a mass activity up to 1.84 and 1.57 times higher than Pt/C towards methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR), respectively. Better durability is also confirmed by chronoamperometry and accelerated degradation tests. The strategy in this work would be greatly helpful for developing an efficient carbon-free support of Pt-based catalysts for applications in DMFCs.

TEM images of the PtCu/CeO₂-21 catalyst. The scale bar in image (B) is 5 nm. Image (C) shows the area chosen for elemental mapping; image (D, E, and F) show the mapping of Ce, Cu, and Pt, respectively.     

Nitrogen-doped carbon derived from horse manure biomass as a catalyst for the oxygen reduction reaction

A massive amount of animal biomass is generated daily from livestock farms, agriculture, and food industries, causing environmental and ecological problems. The conversion of animal biomass into value-added products has recently gained considerable interest in materials science research. Herein, horse manure (HM) was utilized as a precursor for synthesizing nitrogen-doped carbons (NCs) via hydrothermal ammonia treatment and the post pyrolysis process. The ammonia concentration varied between 0.5, 1.0, and 1.5 M in the hydrothermal process. From the comprehensive characterization results, horse manure-derived nitrogen-doped carbons (HMNCs) exhibited an amorphous phase and a hierarchical nanoporous structure. The specific surface area decreased from 170.1 to 66.6 m² g⁻¹ as the ammonia concentration increased due to micropore deterioration. The nitrogen content was 0.90 atom% even with no ammonia treatment, indicating self-nitrogen doping. With hydrothermal ammonia treatment, the nitrogen content slightly enhanced up to 1.54 atom%. The electrocatalytic activity for the oxygen reduction reaction (ORR) of HMNCs in an alkaline solution was found to be related to nitrogen doping content and porous structure. The ORR activity of HMNCs mainly proceeded via a combination of two- and four-electron pathways. Although the ORR activity of HMNCs was still not satisfactory and comparable to that of a commercial Pt/carbon catalyst, it showed better long-term durability. The results obtained in this work provide the potential utilization of HM as a precursor for ORR catalysts and other related applications.

This work shows the potential utilization of horse manure as a precursor for synthesizing nitrogen-doped carbons for electrocatalytic oxygen reduction reaction.     

Highly active postspinel-structured catalysts for oxygen evolution reaction

The rational design principle of highly active catalysts for the oxygen evolution reaction (OER) is desired because of its versatility for energy-conversion applications. Postspinel-structured oxides, CaB₂O₄ (B = Cr³⁺, Mn³⁺, and Fe³⁺), have exhibited higher OER activities than nominally isoelectronic conventional counterparts of perovskite oxides LaBO₃ and spinel oxides ZnB₂O₄. Electrochemical impedance spectroscopy reveals that the higher OER activities for CaB₂O₄ series are attributed to the lower charge-transfer resistances. A density-functional-theory calculation proposes a novel mechanism associated with lattice oxygen pairing with adsorbed oxygen, demonstrating the lowest theoretical OER overpotential than other mechanisms examined in this study. This finding proposes a structure-driven design of electrocatalysts associated with a novel OER mechanism.

Postspinel-structured oxides, CaB₂O₄ (B = Cr³⁺, Mn³⁺, and Fe³⁺), have exhibited systematically higher catalytic activities in the oxygen evolution reaction (OER) than nominally conventional counterparts of perovskite LaBO₃ and spinel ZnB₂O₄.     

Coherent nanoscale cobalt/cobalt oxide heterostructures embedded in porous carbon for the oxygen reduction reaction

Cost-effective and efficient electrocatalysts for the oxygen reduction reaction (ORR) are crucial for fuel cells and metal–air batteries. Herein, we report the facile synthesis of a Co/CoO/Co₃O₄ heterostructure embedded in a porous carbon matrix by refluxing and annealing. This composite exhibits several structural merits for catalyzing the ORR: (1) the existence of metallic Co and graphitic carbon enhanced the electrical conduction; (2) the porous, loose carbon network facilitated the electrolyte permeation and mass transport; (3) more importantly, the nanosized coherent CoO/Co₃O₄ heterojunctions with structural defects and oxygen vacancies enhanced the charge transport/separation at the interface and adsorption affinity to O₂, thus promoting the ORR kinetics and lowering the reaction barrier. Consequently, the composite electrode manifests high electrocatalytic activity, attaining a current density of 6.7 mA cm⁻² at −0.8 V (vs. Ag/AgCl), which is superior to pure CoO nanoparticles (4.7 mA cm⁻²), and has good methanol tolerance. The present strategy based on heterostructure and vacancy engineering may pave the way for the exploration of more advanced, low-cost electrocatalysts for electrochemical reduction and evolution processes.

Cost-effective and efficient electrocatalysts for the oxygen reduction reaction (ORR) are crucial for fuel cells and metal–air batteries.     

Iron phosphide anchored nanoporous carbon as an efficient electrode for supercapacitors and the oxygen reduction reaction

Inspired by their distinctive properties, transition metal phosphides have gained immense attention as promising electrode materials for energy storage and conversion applications. The introduction of a safe and large-scale method of synthesizing a composite of these materials with carbon is of great significance in the fields of electrochemical and materials sciences. In the current effort, we successfully synthesize an iron phosphide/carbon (FeP/C) with a high specific surface area by the pyrolysis of the gel resulting from the hydrothermal treatment of an iron nitrate–phytic acid mixed solution. In comparison with the blank (P/C), the as-synthesized FeP/C appears to be an efficient electrode material for supercapacitor as well as oxygen reduction reaction (ORR) applications in an alkaline medium in a three-electrode system. In the study of supercapacitors, FeP/C shows areal capacitance of 313 mF cm⁻² at 1.2 mA cm⁻² while retaining 95% of its initial capacitance value after 10 000 cycles, while in the ORR, the synthesized material exhibits high electrocatalytic activity with an onset potential of ca. 0.86 V vs. RHE through the preferred four-electron pathway and less than 6% H₂O₂ production calculated in the potential range of 0.0–0.7 V vs. RHE. The stability is found to be better than those of the benchmark Pt/C (20 wt%) catalyst.

Synthesis of a nanoporous FeP/C material through a two-step method involving hydrothermal and carbonization processes for supercapacitors and the oxygen reduction reaction.     

Enhanced electrocatalytic performance of N-doped carbon xerogels obtained through dual nitrogen doping for the oxygen reduction reaction

The development of high efficiency and low-cost electrocatalysts for the oxygen reduction reaction (ORR) is urgently desired for many energy storage and conversion systems. Nitrogen-doped carbon xerogels (NCXs) which have been successfully applied as effective electrocatalysts for the ORR have continued to attract attention due to their competitive price and tunable surface chemistry. A new dual N-doped NCX (NCoNC) electrocatalyst is fabricated as a carbon based catalyst though a facile impregnation of peptone in a precursor and ammonia etching pyrolysis method. XPS analysis demonstrates that the NCoNC electrocatalyst not only has a high N doping amount, but also has an optimized chemical state composition of N doping, which play an important role in improving the microstructure and catalytic performance of the catalysts. XRD and HRTEM results show that the doped metal nano-particles are coated with a double carbon layer of graphene carbon (inner layer) and amorphous carbon (outer layer) forming serrated edges that facilitate the ORR process. The as-obtained NCoNC catalyst exhibits good electrocatalytic performance and excellent stability for the ORR in both acidic and alkaline environments. In particular, in alkaline electrolyte, the decrements of both the limiting current density and the half-wave potential of the NCoNC catalyst were significantly lower than those of a commercial Pt/C catalyst during accelerated aging tests. When serving as an air electrode in Zn–air batteries, the catalyst also exhibits superior catalytic performance with a peak power density of 78.2 mW cm⁻² and a stable open-circuit voltage of 1.37–1.43 V. This work presents a novel tactic to regulate the microstructure and composition of carbon-based electrocatalysts by the facile and scalable dual-effect nitrogen doping method which may be conducive to promoting and developing highly efficient and promising electrocatalysts for the ORR.

This work presents a novel tactic to regulate the microstructure and composition of carbon-based catalysts by the facile and scalable dual-effect nitrogen doping method which may be conducive to promoting highly efficient electrocatalysts for ORR.     

High-sulfur coal-derived nitrogen,sulfur dual-doped carbon as an economical metal-free electrocatalyst for oxygen reduction reaction

The search for an economical electrocatalyst for oxygen reduction reaction (ORR) is a worldwide issue for fuel cells and metal–air batteries. Herein, we used cheap and available high-sulfur inferior coal as the single precursor to synthesize an N, S dual-doped carbon (NSC) metal-free electrocatalyst for the ORR. The N, S dual-doped carbon (NSC), prepared at 800 °C (NSC800), possessed a large specific surface area of 942 m² g⁻¹, with an amorphous carbon structure and more defects than the others. Furthermore, it contains 1.06 at% N and 2.24 at% S, where N is resolved into pyridinic-N, pyrrolic-N, and graphitic-N. For the electrochemical behavior, NSC800 displayed a good ORR electrocatalytic activity, with the ORR peak potential at −0.245 V (vs. SCE) and half-wave potential (E_1/2) at −0.28 V (vs. SCE) in an alkaline solution. This study not only gives an original and facile method to prepare an economical ORR electrocatalyst but also provides a novel clean-use of high-sulfur inferior coal.

The search for an economical electrocatalyst for oxygen reduction reaction (ORR) is a worldwide issue for fuel cells and metal–air batteries.     

Electrocatalytic oxygen reduction reaction activity of KOH etched carbon films as metal-free cathodic catalysts for fuel cells

In this article, surface-modified graphite materials as cathodic catalysts are prepared by hot filament chemical vapor deposition and then chemically etched by KOH solution. Surface morphology, elemental composition, microstructure and surface chemical state of the modified graphite films are characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy techniques. Results indicate that the surface of the pristine graphite can be refined to effectively improve the surface area by etching using the KOH solution with a moderate concentration. The graphite catalyst etched with 4.8 mg mL⁻¹ KOH solution shows a higher catalytic activity for the oxygen reduction reaction and a superior methanol tolerance than that of the un-etched and the other etched graphite catalysts. The stability of the etched graphite materials needs to be improved.

The etched graphite catalyst has a higher oxygen reduction activity in KOH solution than the un-etched catalyst.     

Oxidatively induced exposure of active surface area during microwave assisted formation of Pt3Co nanoparticles for oxygen reduction reaction

The oxygen reduction reaction (ORR), the rate-limiting reaction in proton exchange membrane fuel cells, can efficiently be facilitated by properly manufactured platinum catalysts alloyed with late 3d transition metals. Herein we synthesize a platinum : cobalt nanoparticulate catalyst with a 3 : 1 atomic ratio by reduction of a dry metalorganic precursor blend within a commercial household microwave oven. The formed nanoparticles are simultaneously anchored to a carbon black support that enables large Pt surface area. Two separate microwave treatment steps were employed, where step one constitutes a fast oxidative treatment for revealing active surface area while a reductive secondary annealing treatment promotes a Pt rich surface. The resulting Pt₃Co/C catalyst (∼3.4 nm) demonstrates an enhanced ORR activity directly attributed to incorporated Co with a specific and mass activity of 704 μA cm_Pt⁻² and 352 A g_Pt⁻¹ corresponding to an increase by 279% and 66% respectively compared to a commercial Pt/C (∼1.8 nm) catalyst measured under identical conditions. The method''s simplicity, scalability and novelty is expected to further assist in Pt–Co development and bring the catalyst one step closer toward commercialization and utility in fuel cells.

The oxygen reduction reaction (ORR) is efficiently facilitated platinum catalysts alloyed with Co and reveal high electrochemically active surface area via rapid microwave synthesis.     

Nanostructured carbons containing FeNi/NiFe2O4 supported over N-doped carbon nanofibers for oxygen reduction and evolution reactions

Non-precious metal-based electrocatalysts on carbon materials with high durability and low cost have been developed to ameliorate the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER) for electrochemical energy applications such as in fuel cells and water electrolysis. Herein, two different morphologies of FeNi/NiFe₂O₄ supported over hierarchical N-doped carbons were achieved via carbonization of the polymer nanofibers by controlling the ratio of metal salts to melamine: a mixture of carbon nanotubes (CNTs) and graphene nanotubes (GNTs) supported over carbon nanofibers (CNFs) with spherical FeNi encapsulated at the tips (G/CNT@NCNF, 1 : 3), and graphene sheets wrapped CNFs with embedded needle-like FeNi (GS@NCNF, 2 : 3). G/CNT@NCNF shows excellent ORR activity (on-set potential: 0.948 V vs. RHE) and methanol tolerance, whilst GS@NCNF exhibited significantly lower over-potential of only 230 mV at 10 mA cm⁻² for OER. Such high activities are due to the synergistic effects of bimetallic NPs encapsulated at CNT tips and N-doped carbons with unique hierarchical structures and the desired defects.

Non-precious metal-based electrocatalysts on carbon materials with high durability and low cost have been developed to ameliorate the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER).     

High dispersion and oxygen reduction reaction activity of Co3O4 nanoparticles on platelet-type carbon nanofibers

In this study, platelet-type carbon nanofibers prepared by the liquid phase carbonization of polymers in the pores of a porous anodic alumina template were used to prepare the Co₃O₄/carbon electrocatalysts. For comparison, Co₃O₄ nanoparticles were also deposited on multiwall carbon nanotubes (MWCNTs). Both the nitrogen-free platelet-type carbon nanofibers (pCNFs) and the nitrogen-containing analogue (N-pCNFs) exhibited better dispersion and higher amount of deposited Co₃O₄ nanoparticles compared to the MWCNTs. In addition, many individual Co₃O₄ nanoparticles were deposited separately on pCNF and N-pCNF, whereas aggregated deposition was commonplace on MWCNTs. The results indicated that the side wall of the pCNFs, which consisted of carbon edge planes, was the preferential nucleation site of Co₃O₄ nanoparticles rather than the basal planes of carbon that predominated the surface of the MWCNTs. The oxygen reduction reaction (ORR) activity of the Co₃O₄/pCNF composite in 0.1 mol dm⁻³ KOH solution was better than that of Co₃O₄/MWCNTs. The N-pCNF further enhanced the ORR activity of the Co₃O₄/pCNFs even though the dispersion and supported amount of Co₃O₄ nanoparticles were negligibly affected by the presence of the nitrogen species. Synergistic interactions of the Co₃O₄ nanoparticles with N-doped CNFs contributed to the increased ORR activity.

In this study, platelet-type carbon nanofibers prepared by the liquid phase carbonization of polymers in the pores of a porous anodic alumina template were used to prepare the Co₃O₄/carbon electrocatalysts.     

Effect of nitrogen-doping configuration in graphene on the oxygen reduction reaction

In this study, we investigate the oxygen reduction reaction (ORR) reactivity of nitrogen-doped graphene by using density functional theory (DFT), a computational quantum mechanical technique. Four doping configurations and five models were comprehensively studied: quaternary nitrogen (NQ), pyrrolic nitrogen (N5), two forms of pyridinic nitrogen (N6, N6nH) and three-pyridinic nitrogen (3N6). Models for possible sites during each step of ORR were set up and visualized to provide a platform to calculate the free energy of the reaction pathway to determine the suitability of each doping scenario. Associative mechanisms were displayed by all models except N5, which showed dissociative mechanism. The calculated free energy pathways demonstrate that the ranking of the reactivity for ORR by different nitrogen configurations from most reactive to least reactive is N6, NQ, N6nH, 3N6, and N5. Spin density and charge density aid in describing levels of reactivity.

The oxygen reduction reaction (ORR) reactivity of various nitrogen-doped graphene configurations are probed in detail using density functional theory (DFT) calculations.