Nitrogen-doped Porous Carbon Materials Research Articles

Enhancing CO2 adsorption performance of porous nitrogen-doped carbon materials derived from ZIFs: Insights into pore structure and surface chemistry

In this work, a novel approach for the synthesis of porous nitrogen-doped carbon materials (PNCs) with a highly microporous structure through low-temperature carbonization of ZIF-8 and ZIF-61 assisted by KCl and NaCl is reported. The introduction of KCl and NaCl during the carbonization process can adjust the surface chemical properties and pore structures of the PNCs derived from ZIF-8 and ZIF-61. The effects of pore structures and surface groups of PNCs on CO2 adsorption capacity are explored. Results show that the cumulative pore volume in the pore size range of 5–7 Å (V5-7 Å), pyrrolic-N content, and COOH content exert favorable influences on CO2 adsorption capacity at 1 bar and 25 °C. Notably, V5-7 Å is the key factor in enhancing the CO2 adsorption capacity of PNCs. Moreover, the degree of contribution of V5-7 Å, V7-9 Å, pyrrolic-N content, pyridinic-N content, and COOH content to the CO2 adsorption capacity is evaluated by establishing a multiple linear regression equation, and the results show that on the basis of PNCs possessing optimum pore structures (V5-7 Å > 0.10 cm3/g), pyrrolic-N content in PNCs becoming the dominant contributor to CO2 adsorption capacity. The as-prepared 2CN8-KCl-600 sample demonstrates high CO2 adsorption capacity, which reaches 4.61 mmol/g at 25 °C and 6.70 mmol/g at 0 °C (1 bar), respectively. Besides, 2CN8-KCl-600 exhibits high CO2/N2 selectivity (39.5) under the typical flue gas scenario and high cycling stability. This work offers a novel perspective on preparing highly efficient carbon-based adsorbents for CO2 and provides the fundamental understanding for enhanced CO2 adsorption performance on PNCs.

Mild and Efficient One-Step Synthesis of Nitrogen-Doped Multistage Porous Carbon for High-Performance Supercapacitors.

Biomass-derived carbon materials have broad application prospects in energy storage, but still face problems such as complex synthesis paths and the massive use of corrosive activators. In this study, we proposed a mild and efficient pathway to prepare nitrogen-doped porous carbon material (N-YAC) using one-step pyrolysis with solid K2CO3, tobacco straw, and melamine. The optimized material (N-YAC0.5) was not only enriched with nitrogen, but also exhibited a high specific surface area (2367 m2/g) and a reasonable pore size distribution (46.49% mesopores). When utilized in electrodes, N-YAC0.5 exhibited an excellent capacitance performance (338 F/g at 1 A/g) in the three-electrode system, and benefitted from a high mesopore distribution that maintained a capacitance of 85.2% (288 F/g) at high current densities (20 A/g). Furthermore, the composed symmetric capacitor achieved an energy density of 14.78 Wh/kg at a power density of 400 W/kg. In summary, our work provides a novel and eco-friendly approach for converting biomass into high-performance energy-storage materials.

Nitrogen-doped coal-based microporous carbon material co-activated by HCOOK and urea for high performance supercapacitors

The doping of heteroatoms can adjust the surface chemical state of porous carbons, which is conducive to improving the surface activity, and enhancing the hydrophicity and conductivity of carbon electrodes. Herein, we developed a facile and green strategy to obtain nitrogen-doped coal-derived porous carbon dominated by micropores for high performance supercapacitor. The hydrothermal treatment of coal and urea can not only achieve the doping of nitrogen atoms, but also conducive to the subsequent activation process. Benefiting from the large micropore volume and specific surface area (0.68 cm3 g−1 and 1563 m2 g−1), suitable micropore size, and high content of surface CO, N-Q and N-5, the optimal sample exhibits a large capacitance of 371 F g−1 (1 A g−1), high capacitance retention of 67% (50 A g−1), and outstanding cyclic durability in a three-electrode system (aqueous electrolyte). Furthermore, the symmetrical supercapacitor in neat EMIM BF4 shows a high energy density of 40 Wh kg−1 (625 W kg−1). This work proposes a facile and potential strategy for preparing nitrogen-doped porous carbon materials with outstanding electrochemical property for supercapacitors and provides a novel insight for the efficient and low carbonization utilization of coal resources.

Room-Temperature Salt Template Synthesis of Nitrogen-Doped 3D Porous Carbon for Fast Metal-Ion Storage.

The water-soluble salt-template technique holds great promise for fabricating 3D porous materials. However, an equipment-free and pore-size controllable synthetic approach employing salt-template precursors at room temperature has remained unexplored. Herein, we introduce a green room-temperature antisolvent precipitation strategy for creating salt-template self-assembly precursors to universally produce 3D porous materials with controllable pore size. Through a combination of theoretical simulations and advanced characterization techniques, we unveil the antisolvent precipitation mechanism and provide guidelines for selecting raw materials and controlling the size of precipitated salt. Following the calcination and washing steps, we achieve large-scale and universal production of 3D porous materials and the recycling of the salt templates and antisolvents. The optimized nitrogen-doped 3D porous carbon (N-3DPC) materials demonstrate distinctive structural benefits, facilitating a high capacity for potassium-ion storage along with exceptional reversibility. This is further supported by in situ electrochemical impedance spectra, in situ Raman spectroscopy, and theoretical calculations. The anode shows a high rate capacity of 181 mAh g-1 at 4 A g-1 in the full cell. This study addresses the knowledge gap concerning the room-temperature synthesis of salt-template self-assembly precursors for the large-scale production of porous materials, thereby expanding their potential applications for electrochemical energy conversion and storage.

A hierarchical porous N-doped carbon material as catalyst derived from the folic acid-Zn/KBr hydrogel: Reaction network and kinetics and mechanism for the oxidation of furfural to maleic acid

A novel hydrogel (named FA-Zn/KBr) was prepared, by taking advantage of the hydrogen-bonding and π-π stacking interactions between the pterin heterocycles of the folic acid (FA) molecules. The hydrogel is composed of highly dispersed KBr, coordinated zinc ions, and stacked arrays of folate tetramers. Due to the presence of KBr, a hierarchical porous nitrogen-doped carbon (PNC-800) material with a specific surface area 2807.9 m2/g can be formed through the calcination of the FA-Zn/KBr xerogel under N2. PNC-800 is used to catalyze the oxidation of furfural to maleic acid in the presence of H2O2. Representative nine reactions constitute the reaction network. The reaction rate constants and apparent activation energy were obtained for each reaction. Based on the kinetics parameters, the simulated results are in good agreement with the experimental data. The mechanism of the reaction catalyzed by PNC-800 is proposed based on ample experimental evidence. The graphitic nitrogen species in PNC-800 are the active sites. PNC-800 catalyzes the decomposition of hydrogen peroxide to generate hydroxyl radical (HȮ), which oxidizes furfural to furfural radical, and the furfural radical is subsequently converted to 5-hydroxy-furan-2(5H)-one (HFONE). The conversion of furfural to maleic acid via the formation of HFONE is the main reaction pathway. In addition, the hierarchical porous structure with a high specific surface area facilitates the interaction of reactant with the active sites. PNC-800 has been shown an excellent catalytic activity for the production of maleic acid from furfural. For the oxidation of 1000 mM furfural using 50 mg PNC-800 at 80 °C within 9 h, the conversion of furfural is 100 % with a maleic acid yield 67.5 %.

One-Step Synthesis of Nitrogen-Doped Porous Carbon Derived from Biomass for Lithium-Ion Battery

Bamboo shoot is renewable biomass rich in carbon and nitrogen. To take advantage of its sources of carbon and nitrogen, hierarchical porous nitrogen-doped carbon materials derived from bamboo shoot were acquired via a one-step method in this study. The obtained carbons were characterized by using XRD, Raman, N2 sorption, SEM, TEM, XPS, etc. The carbon calcinated at 700 °C with KHCO3 treatment (BSC) displays a large surface area (1475.5 m2 g−1) and typically porous structure from micro- to macropores, a self-nitrogen content, and many defects, which could offer transport channels and active sites for lithium ions while used as carbon anode. Based on the above features and the synergistic effects among them, BSC exhibits the typical electrochemical performance of a carbon-based anode material, with a specific capacity as high as 611.3 mA h g−1 (a Coulombic efficiency of 98.7%) after 100 cycles at a current density of 0.1 A g−1. Meanwhile, it also has a good rate performance and excellent cycling properties (436.1 mA h g−1 after 300 cycles at 0.1 A g−1) compared with NBSC (carbon directly carbonized at 700 °C). Thus, it is promising for further improvements made to porous carbon derived from biomass and used as anode in the application of energy storage, and could be a guideline for the preparation of high-value-added carbon materials derived from biomass.

Nitrogen-doped porous carbon transformed from polymer carbon nitride for persulfate activation towards efficient degradation of tetracycline via the electron transfer-dominated non-radical pathway

BackgroundMetal-free carbon materials have been extensively researched for the removal of aqueous pollutants by persulfate activation. However, it was still worth exploring the contribution of adsorption of carbon materials to the catalytic efficiency as well as the ROS degradation pathway. MethodsA series of g-C3N4 and nitrogen-doped porous carbon materials were prepared by combining l-ascorbic acid with melamine-cyanuric acid (MCA) for the removal of tetracycline from wastewater. The carbon materials were analyzed by using XRD, XPS, Raman and other characterization methods. Furthermore, the effect of different reaction parameters on TC degradation was investigated, and the active species were identified by scavenging experiments and EPR. Significant findingsThe prepared porous carbon sample LAA-NC0.6 has a high nitrogen content of 31.93 at%. LAA-NC0.6 could completely remove TC within 40 min with first-order kinetic constant as high as 0.14995 min−1, which was 167-fold higher than that of pristine g-C3N4. Catalytic studies showed that the degradation of TC was a non-radical pathway dominated by electron transfer and that adsorption had a marked influence on the catalytic performance of the LAA-NC0.6/PS system.

MOF-derived N-doped porous carbons activate peroxomonosulfate to efficiently degrade organic pollutants via non-radical pathways

Carbon-based heterogeneous catalysts have attracted extensive attention due to their environmentally friendly nature and the absence of metal leaching concerns. Nonetheless, enhancements in catalyst preparation and their efficacy in activating Peroxymonosulfate (PMS) to degrade organic pollutants remain areas of research. This work synthesized a novel nitrogen-doped porous carbon material (NPCs) at different temperatures using MET-6 [Zn(C2N3H2)2] Metal-organic frameworks (MOFs) precursor through a one-step pyrolysis process. The optimized NPC-900 demonstrated an elevated specific surface area and richer pore structure, validated through diverse characterization techniques. The NPC-900 was employed to activate (PMS) to degrade organic pollutants. Key catalytic active sites contributing to rhodamine B (RhB) degradation by NPC-900 were identified as graphite N and sp2 hybrid carbons, achieving 99.75 % RhB degradation. Through radical scavenging tests and electron paramagnetic resonance (EPR) spectroscopy, both free radicals (SO4−, ·OH and O2−) and non-free radicals (1O2 and electron transfer) were detected during the RhB degradation process. As the reaction progressed, non-free radicals increasingly asserted their dominant role. Employing electrospray ionization-mass spectrometry (EIS-MS) further elucidated RhB degradation intermediates, facilitating the postulation of a probable mechanism for NPC-900 activation of PMS and the subsequent RhB degradation pathway. In summary, this study introduced a metal-free catalyst capable of activating PMS through an accessible synthetic approach, offering valuable insights for the proficient degradation of organic pollutants in wastewater.

Nitrogen-Doped Porous Carbon Derived from Coal for High-Performance Dual-Carbon Lithium-Ion Capacitors.

Lithium-ion capacitors (LICs) are emerging as one of the most advanced hybrid energy storage devices, however, their development is limited by the imbalance of the dynamics and capacity between the anode and cathode electrodes. Herein, anthracite was proposed as the raw material to prepare coal-based, nitrogen-doped porous carbon materials (CNPCs), together with being employed as a cathode and anode used for dual-carbon lithium-ion capacitors (DC-LICs). The prepared CNPCs exhibited a folded carbon nanosheet structure and the pores could be well regulated by changing the additional amount of g-C3N4, showing a high conductivity, abundant heteroatoms, and a large specific surface area. As expected, the optimized CNPCs (CTK-1.0) delivered a superior lithium storage capacity, which exhibited a high specific capacity of 750 mAh g-1 and maintained an excellent capacity retention rate of 97% after 800 cycles. Furthermore, DC-LICs (CTK-1.0//CTK-1.0) were assembled using the CTK-1.0 as both cathode and anode electrodes to match well in terms of internal kinetics and capacity simultaneously, which displayed a maximum energy density of 137.6 Wh kg-1 and a protracted lifetime of 3000 cycles. This work demonstrates the great potential of coal-based carbon materials for electrochemical energy storage devices and also provides a new way for the high value-added utilization of coal materials.

One-step preparation of magnetic N-doped sodium alginate-based porous carbon and efficient adsorption of bisphenol A.

To resourcefully utilize algal biomass and effectively remove bisphenol A (BPA) from water, sodium alginate (SA) was prepared as the nitrogen-doped magnetic porous carbon material (SAC/N/Fe) with well-developed pore structure according to a one-step method using K2CO3, melamine, Fe(NO3)3·9H2O as the activator, nitrogen dopant, and magnetic precursor, respectively, in this study. The best product, SAC/N/Fe-0.2, was obtained by adjusting the mass ratio of raw materials, and its specific surface area and pore volume were 2240.65 m2g-1 and 1.44 cm3g-1, respectively, with a maximum adsorption capacity of 1248.23mgg-1 for BPA at 308K. SEM, XRD, XPS, VSM, and FT-IR characterization confirmed that the iron was successfully doped, giving the porous carbon a magnetic separation function. The adsorption process of BPA was more consistent with the Langmuir model and the proposed secondary kinetics, and the adsorption effect was stable and efficient in a wide pH range and under the interference of different metal ions. At the same time, the porous carbon was easy to separate and recover with good regeneration performance.

An unconventional direct path for the chemoselective hydrogenation of nitroarenes over a metal-free catalyst

In recent years, significant efforts have been devoted to the fabrication of heteroatom-doped carbon materials as ecofriendly catalysts to replace metal-based catalysts employed in the hydrogenation of nitroarenes. However, the reaction pathway of metal-free catalysts has not been thoroughly studied. In this study, nitrogen-doped hollow hierarchical porous carbon materials have been successfully prepared. The porous nitrogen-doped carbon was prepared by carbonizing at 900°C (PNC-900) and exhibited an exceptional catalytic performance in the chemoselective hydrogenation of nitroarenes with high tolerance to various substrates under mild reaction conditions. The analysis of the experimental results and characterizations, revealed that graphitic N species were the primary catalytic active sites and played a crucial role in efficient hydrogenation. The reaction followed a special direct path in the hydrogenation of nitrobenzene (NB) owing to the absence of nitrosobenzene (NSB) as an intermediate, which was markedly different from the other metal-free catalysts. Moreover, the PNC-900 catalyst exhibited excellent reactivity and selectivity even after six cycling tests, thus demonstrating unconventional high performance in terms of both recyclability and stability.

Waste Cigarette Butts-Derived Nitrogen-Doped Carbon Fibers Loaded with Ru Nanoparticles as an Efficient Cathode Catalyst for Lithium-Oxygen Batteries

Low catalytic activity and high cost of cathode catalysts hinder the large-scale commercial application of lithium-oxygen (Li-O2) batteries. In this work, waste cigarette butts, which inherently have a porous fiber structure, were selected as the precursor of the carbon material for the cathode catalyst of Li-O2 batteries. The porous nitrogen-doped carbon material was prepared by simple heat treatment of waste cigarette butts. The rich porous structure of the obtained carbon fiber material effectively enhances the diffusion of oxygen molecules and provides ample space for the discharge products. N doping in carbon fibers enhances the bifunctional catalytic activity toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which was corroborated by density functional theory (DFT) calculation. The assembled Li-O2 battery with C–N fibers-loaded Ru nanoparticles catalyst delivers an initial discharge capacity of up to 12 036.3 mA h g–1 and can be cycled stably for more than 800 cycles (4000 h) at a current density of 200 mA g–1 and a cutoff capacity of 500 mA h g–1. Even at a high current density of 500 mA g–1, the cells still show a high average discharge voltage of 2.28 V with excellent cycle stability and rate capability. XPS analysis proves that the cathode material can effectively inhibit the formation of Li2CO3 and Li2O byproducts. This work provides a cost-effective solution to solve the cathode catalyst problem of Li-O2 batteries and improve their cycling stability as well as environment protection.

Review on Nitrogen-Doped Porous Carbon Materials for CO2 Adsorption and Separation: Recent Advances and Outlook

One of the most serious environmental problems is the global warming brought by CO2 and other greenhouse gases. Thus, the development of Carbon Capture, Utilization, and Storage Technology (CCUS) is urgent. Thereinto, the merits of porous carbon adsorption materials are their substantial specific surface area, stable physical and chemical properties, adjustable pore structure, etc., and they are considered to be good adsorbents for CO2. The adsorption properties of porous carbon material are capable of being directionally controlled by regulating the collocation of carbonization and activation methods and setting the technological parameters used in the preparation process. In addition, nitrogen doping can enhance the effect between adsorbent and adsorbate, leading to higher CO2 adsorption capacity. After in-depth studies, although there is still no clear explanation on the mechanism of nitrogen-doped enhancement of the adsorption properties of the adsorbent, it can be confirmed that the main reason is not the traditional acid–base theory, but a large number of micropores, specific surface area, and induction forces are more likely to be the root cause. The porous carbon materials preparation methods, pore structure adjustment strategies, and the types of functionalization and mechanism between nitrogen-doped sites and adsorbents are highlighted in this Review. Finally, the future development direction and existing challenges of this emerging field are also discussed.

Single atom iron implanted polydopamine-modified hollow leaf-like N-doped carbon catalyst for improving oxygen reduction reaction and zinc-air batteries

Metal-nitrogen-carbon (MNC) catalysts, especially FeNC catalysts, are considered promising candidates to replace Pt-based catalysts, but FeNC catalysts still present certain challenges in controlled-synthesis and energy device applications. In this paper, through the modification strategy of poly-dopamine (PDA) to maintain 2D leaf morphology to obtain more active sites and further adjust the N content, N-doped porous carbon monatomic iron catalyst (FeSA/NPCs) with rich-nitrogen content was prepared. XPS analysis showed that compared with C-ZIF-Fe, the contents of graphite nitrogen and pyridine nitrogen increased in FeSA/NPCs. The hollow structure with defects and Fe-N4 configuration of Fe single atom show more active sites for the catalyst, and positively promote the diffusion of reactants, oxygen exchange and electron transport, thus changing the reaction kinetics and promoting the improvement of ORR activity. FeSA/NPCs electrocatalyst exhibits good half-wave potential and onset potential at low loading (E1/2 = 0.93 V, Eonset = 1.0 V). In addition, the methanol tolerance, stability and Tafel slope are better than those of commercial Pt/C. Excitingly, the zinc-air cell with FeSA/NPCs as cathode material achieves a power density of 223 mW cm−2 and exhibits a long-term stability higher than 200 h. This work shows that nitrogen-doped porous carbon materials as well as iron monoatoms play important roles in improving electrocatalytic performance.

Nitrogen-doped porous carbon derived from graphite of solid waste for activating peroxymonosulfate to degradation tetracycline

Nitrogen-doped porous carbon material based on graphite of solid waste and urea was prepared by mixing and pyrolysis method, the performance and mechanism of the prepared materials as catalysts to activate peroxymonosulfate (PMS) for ctetracycline (TC) degradation were investigated. Results indicated that addition of urea and sodium bicarbonate (NaHCO3) effectively enhanced the degradation of TC. When the mass ratio of graphite/urea/NaHCO3 and pyrolysis temperature was 1: 2: 2 and 800 °C, respectively, the obtained catalyst had optimal performance for activating PMS to TC degradation. The degradation efficiency of TC reached 99.8% within 30 min under the conditions of 0.10 g/L catalyst, 0.20 g/L PMS and 20 mg/L TC solution. Results suggested that the catalyst had well catalytic repeatability, versatility and adaptability under different conditions. The radical quenching test, electrochemistry experiment and electron paramagnetic resonance (EPR) measurements suggested that superoxide radical (O2•-) and singlet oxygen (1O2) plays dominant roles in TC degradation. XPS indicated that pyridine N, graphite N and functional groups of CO and –COOH were the potential active sites for PMS activation. This provides new insights for the recycling of solid waste and preparation of high-performance carbon based catalysts for wastewater treatment via Fenton-like process.

ZIF-8-templated synthesis of core-shell structured IPOP@MOF hybrid-derived nitrogen-doped porous carbon for efficient oxygen reduction electrocatalysis and supercapacitor

Nitrogen-doped porous carbon materials based on porous organic polymers and metal-organic framework derivatives are prepared for efficient ORR electrocatalysts and supercapacitor. The classic MOFs material ZIF-8 is selected as the core material. After ZIF-8 is pyrolyzed in an inert atmosphere at 900℃, the low-boiling Zn volatilizes, resulting in a hierarchical open-structured carbon-nitrogen material, which is beneficial to the transport of electrolytes in the electrocatalytic process. To further increase the nitrogen content, the designed nitrogen-rich IPOP-coated ZIF-8 composites were immersed in an aqueous solution of sodium dicyandiamide. The catalyst obtained by replacing Cl−and Br−in the porous organic polymer with nitrogen-containing ions and calcined at high temperature is a porous structure material containing a high concentration of active pyridine nitrogen. In addition to exhibiting superior oxygen reduction reaction (ORR) electrocatalytic activity, NC-900 shows superior stability and good methanol tolerance in comparison to commercial Pt/C catalysts in alkaline media as well as acidic media. Furthermore, in 6 M KOH electrolyte, NPCs-based supercapacitor exhibits a high capacitance of 225 F g − 1 with a current density of 1 A g − 1 and possesses good cycling stability (95.75% capacitor retention after 10,000 cycles).

Preparation of mesoporous chitosan iron supported nano-catalyst for the catalyzed oxidation of primary amine to imine.

Supported nano-catalysts with environmental sustainability and high catalytic performance are of great research interest for sustainable catalysis. In this article, a supported nano-catalyst, FeA-NC, with high catalytic performance was prepared by anchoring the transition metal iron onto nitrogen-doped porous carbon materials using chitosan as a raw material. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) measurement results demonstrated that the obtained catalyst has an excellent mesoporous structure, and that the element Fe is evenly distributed. The support contains abundant N atoms, which can provide sufficient anchoring points for Fe and form Fe-Nx groups with Fe, improving the catalytic activity of the catalyst. Additionally, the FeA-NC with a porous structure can also enhance the mass transfer of reactants to improve the reaction efficiency. In addition, the prepared catalyst was used to catalyze the conversion of primary amines to the corresponding imines. The results showed that the direct oxidation of primary amines to the corresponding imines can be catalyzed by using air as an oxygen source and distilled H2O as a solvent under atmospheric pressure at 90 °C. Finally, the selectivity and stability of the as-prepared catalyst were also verified.

From waste plastics to layered porous nitrogen-doped carbon materials with excellent HER performance.

Herein, layered porous nitrogen-doped carbon sheets (LPNCS) prepared from waste plastics are employed as an electrocatalytic carrier for the HER under alkaline conditions. The N-doped coral-like nanostructure with abundant meso- and macropores would shorten the proton diffusion pathway, reduce the mass transfer resistance and promote Ru dispersion. The prepared Ru/LPNCS shows an excellent performance with an overpotential of 15 mV at 10 mA cm-2, even lower than that of most reported Ru-based catalysts and the commercial Pt/C catalyst (17 mV), which provides a potential application for converting waste plastics into highly efficient HER catalysts.

Metal-Free Triazine-Based Porous Organic Polymer-Derived N-Doped Porous Carbons as Effective Electrocatalysts for Oxygen Reduction Reaction

In recent years, porous heteroatom-doped carbon materials have been very promising for energy conversion. A newly designed porous organic polymer (POPQ) has been synthesized using two organic monomers, i.e., 2,6-diaminoanthraquinone and cyanuric chloride, under reflux conditions for 72 h in an inert atmosphere. The triazine-containing porous organic polymers undergo pyrolysis, which produces two nitrogen-doped porous carbon materials, N/POPQ600 and N/POPQ800, at 600 and 800 °C temperatures, respectively. Since the resultant N-doped porous materials have a higher surface area than the parent porous organic polymer and the materials have a synergistic effect due to the enriched nitrogen content throughout the matrix, the metal-free N/POPQ600 and N/POPQ800 materials exhibit good electrocatalytic activity toward oxygen reduction reaction (ORR). Among these, the N/POPQ800 material shows excellent ORR activity with a nearly four-electron oxygen reduction pathway where the half-wave potential is estimated to be 0.728 V vs reversible hydrogen electrode (RHE), comparable with the commercially available Pt/C catalyst. Most interestingly, the N/POPQ800 catalyst displays outstanding long-lasting stability. It shows a better methanol tolerance capability than Pt/C, which can be attributed to the high specific surface area and N-doped well-defined crystalline porous structure. Also, the homogeneously distributed active sites throughout the carbon framework are the most precious for the electrochemical oxygen reduction reaction.

Immobilization of cobalt oxide nanoparticles on porous nitrogen-doped carbon as electrocatalyst for oxygen evolution

Highly efficient and robust electrocatalysts have been in urgent demand for oxygen evolution reaction (OER). For this purpose, high-cost carbon materials, such as graphene and carbon nanotubes, have been used as supports to metal oxides to enhance their catalytic activity. We report here a new Co 3 O 4 -based catalyst with nitrogen-doped porous carbon material as the support, prepared by pyrolysis of porous polyurea (PU) with Co(NO 3 ) 2 immobilized on its surface. To this end, PU was first synthesized, without any additive, through a very simple one-step precipitation polymerization of toluene diisocyanate in a binary mixture of H 2 O-acetone at room temperature. By immersing PU in an aqueous solution of Co(NO 3 ) 2 at room temperature, a cobalt coordinated polymer composite, Co(NO 3 ) 2 /PU, was obtained, which was heated at 500 °C in air for 2 h to get a hybrid, Co 3 O 4 /NC, consisting of Co 3 O 4 nanocrystals and sp 2 -hybridized N-doped carbon. Using this Co 3 O 4 /NC as a catalyst in OER, a current density of 10 mA·cm −2 was readily achieved with a low overpotential of 293 mV with a Tafel slope of 87 mV·dec −1 , a high catalytic activity. This high performance was well retained after 1000 recycled uses, demonstrating its good durability. This work provides therefore a facile yet simple pathway to fabrication of a new transition metal oxides-based N-doped carbon catalyst for OER with high performance.