Rational design of hierarchically porous Fe-N-doped carbon as efficient electrocatalyst for oxygen reduction reaction and Zn-air batteries

The rational design and construction of hierarchically porous nanostructure for oxygen reduction reaction (ORR) electrocatalysts is crucial to facilitate the exposure of accessible active sites and promote the mass/electron transfer under the gas-solid-liquid triple-phase condition. Herein, an ingenious method through the pyrolysis of creative polyvinylimidazole coordination with Zn/Fe salt precursors is developed to fabricate hierarchically porous Fe-N-doped carbon framework as efficient ORR electrocatalyst. The volatilization of Zn species combined with the nanoscale Kirkendall effect of Fe dopants during the pyrolysis build the hierarchical micro-, meso-, and macroporous nanostructure with a high specific surface area (1,586 m²·g⁻¹), which provide sufficient exposed active sites and multiscale mass/charge transport channels. The optimized electrocatalyst exhibits superior ORR activity and robust stability in both alkaline and acidic electrolytes. The Zn-air battery fabricated by such attractive electrocatalyst as air cathode displays a higher peak power density than that of Pt/C-based Zn-air battery, suggesting the great potential of this electrocatalyst for Zn-air batteries.

     

ZTIFs derived nitrogen-introduced high specific area and hierarchical porous carbon for oxygen reduction reaction

It is of great allure to construct nitrogen-doped hierarchical porous carbon to replace Pt-based catalysts for efficient ORR. Here, nitrogen-doped hierarchical porous carbon (NHPC) was prepared by carbonizing ZTIF-1 and KOH activating. The resultant NHPC4-700 catalyst exhibits a hierarchical porous structure and high specific area (2404 m² g^?1), which promoted the exposure of enough active sites as well as simultaneously enhanced the electron transfer rate, shorten the mass transfer pathway, enhanced ionic conductivity and carbon wetting. The results are capable of remarkably improving the ORR activities of carbon materials. The NHPC4-700 catalyst exhibits a great catalytic performance with onset potential at 0.90 V and limiting current density of ??6.0 mA cm^?2, which is close to commercial Pt/C electrocatalyst. Meanwhile, the NHPC4-700 catalysts had better stability and methanol resistance than that of Pt/C toward ORR. These superior electrochemical properties of the NHPC4-700 catalysts were closely related to their nitrogen-doped hierarchical porous structure and high specific area.

     

Nitrogen-doping hierarchically porous carbon nanosheets for supercapacitor

Two-dimensional (2D) porous carbon nanosheets attract great attention because of their thin sheet-like morphology, abundant pores and high specific surface area, and their potential applicability in many fields including adsorption, oxygen reduction reaction, organic transistor and energy storage. Herein, a feasible method, named self-templating, to prepare 2D nitrogen-doping hierarchically porous carbon nanosheets (N-HPCNs) with prominent performances as supercapacitor electrode is reported. During the process of preparation, the inexpensive and easily available MgO rods are treated in water to form Mg(OH)₂ nanosheets further using as templates and then nitrogen contained resorcinol–formaldehyde resin oligomers as carbon and nitrogen precursor co-condense onto the templates by electrostatic interaction. The obtained N-HPCNs with large specific surface area, hierarchical pores and unique interconnected sheet-like structure are the potential candidates for high energy storage devices. As an active electrode material for electrochemical double-layer capacitors, N-HPCNs exhibit a capacitance of 201 F g^?1 at current density of 1 A g^?1 and high specific capacitance (78.1% retention of initial capacitance even at 10 A g^?1), with excellent cycling life stability (3.5% loss after 5000 cycles).     

Large-scale production of holey carbon nanosheets implanted with atomically dispersed Fe sites for boosting oxygen reduction electrocatalysis

Atomically dispersed metals stabilized by nitrogen elements in carbon skeleton hold great promise as alternatives for Pt-based catalysts towards oxygen reductio...     

Inflating strategy to fabricate highly dispersed Fe,N co-doped hierarchically porous carbon for ORR and supercapacitor

Doped-carbon nanomaterials as effective electrocatalysts have been received widespread attention in oxygen reduction reaction (ORR) and supercapacitors system. Herein, the high-active Fe atoms dispersed on hierarchically porous N-doped carbon (FeNC-X) is synthesized via inflating the Fe-ion-denatured egg-white, followed by activation and pyrolysis. Among them, the as-prepared FeNC-900 for ORR that has an inner-connecting hierarchically porous structure shows a superior performance with a limiting current density of 5.28 mA cm^?2 and half-wave potential (E_1/2) of 0.839 V (vs RHE), and exhibits a 4 e^? ORR pathway in the alkaline medium. FeNC-900 also shows better durability and good methanol tolerance than those of commercial Pt/C. Besides, FeNC-900 exhibits an outstanding specific capacity of 258 F g^?1 at 1 A g^?1 for supercapacitor. The method presented here may provide a cost-efficient approach to fabricate carbon-based materials for ORR and supercapacitors.

     

Structural revolution of atomically dispersed Mn sites dictates oxygen reduction performance

An efficient preparation and local coordination environment regulation of isolated single-atom sites catalysts (ISASC) for improved activity is still challenging. Herein, we develop a solid phase thermal diffusion strategy to synthesize Mn ISASC on highly uniform nitrogen-doped carbon nanotubes by employing MnO₂ nanowires@ZIF-8 core-shell structure. Under high-temperature, the Mn species break free from core-MnO₂ lattice, which will be trapped by carbon defects derived from shell-ZIF-8 carbonization, and immobilized within carbon substrate. Furthermore, the poly-dispersed Mn sites with two nitrogen-coordinated centers can be controllably renovated into four-nitrogen-coordinated Mn sites using NH₃ treatment technology. Both experimental and computational investigations indicate that the symmetric coordinated Mn sites manifest outstanding oxygen reduction activity and superior stability in alkaline and acidic solutions. This work not only provides efficient way to regulate the coordination structure of ISASC to improve catalytic performance but also paves the way to reveal its significant promise for commercial application.

     

Natural tea-leaf-derived,ternary-doped 3D porous carbon as a high-performance electrocatalyst for the oxygen reduction reaction

To commercialize fuel cells and metal-air batteries, cost-effective, highly active catalysts for the oxygen reduction reaction (ORR) must be developed. Herein, we describe the development of low-cost, heteroatom (N, P, Fe) ternary-doped, porous carbons (HDPC). These materials are prepared by one-step pyrolysis of natural tea leaves treated with an iron salt, without any chemical and physical activation. The natural structure of the tea leaves provide a 3D hierarchical porous structure after carbonization. Moreover, heteroatom containing organic compounds in tea leaves act as precursors to functionalize the resultant carbon frameworks. In addition, we found that the polyphenols present in tea leaves act as ligands, reacting with Fe ions to form coordination compounds; these complexes acted as the precursors for Fe and N active sites. After pyrolysis, the as-prepared HDPC electrocatalysts, especially HDPC-800 (pyrolyzed at 800 °C), had more positive onsets, half-wave potentials, and higher catalytic activities for the ORR, which proceeds via a direct four-electron reaction pathway in alkaline media, similar to commercial Pt/C catalysts. Furthermore, HDPC-X also showed enhanced durability and better tolerance to methanol crossover and CO poisoning effects in comparison to commercial Pt/C, making them promising alternatives for state-of-the-art ORR electrocatalysts for electrochemical energy conversion. The method used here provides valuable guidelines for the design of high-performance ORR electrocatalysts from natural sources at the industrial scale.

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Porphyrin-like Fe-N<Subscript>4</Subscript> sites with sulfur adjustment on hierarchical porous carbon for different rate-determining steps in oxygen reduction reaction

We developed a strategy based on coordination polymer to synthesize singleatom site Fe/N and S-codoped hierarchical porous carbon (Fe₁/N,S-PC). The as-obtained Fe₁/N,S-PC exhibited superior oxygen reduction reaction (ORR) performance with a half-wave potential (E_1/2, 0.904 V vs. RHE) that was better than that of commercial Pt/C (E_1/2, 0.86 V vs. RHE), single-atom site Fe/N-doped hierarchical porous carbon (Fe₁/N-PC) without S-doped (E_1/2, 0.85 V vs. RHE), and many other nonprecious metal catalysts in alkaline medium. Moreover, the Fe₁/N,S-PC revealed high methanol tolerance and firm stability. The excellent electrocatalytic activity of Fe₁/N,S-PC is attributed to the synergistic effects from the atomically dispersed porphyrin-like Fe-N₄ active sites, the heteroatom codoping (N and S), and the hierarchical porous structure in the carbon materials. The calculation based on density functional theory further indicates that the catalytic performance of Fe₁/N,S-PC is better than that of Fe₁/N-PC owing to the sulfur doping that yielded different rate-determining steps.

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过渡金属和磷共掺杂多孔碳作为氧气还原电催化剂

碳基材料作为非贵金属催化剂具有导电性能高、稳定性能好、价格低廉、环境友好等优点,在燃料电池阴极催化剂领域中引起了广泛的关注,尤其是过渡金属和异原子共掺杂能够显著提高碳材料的氧气还原催化活性。本文采用聚醚(F127)作为软模版,苯酚、甲醛作为碳源,四苯基溴化膦作为磷源,硝酸盐作为过渡金属来源,通过挥发溶剂自组装及高温煅烧过程制备了过渡金属(Co、Fe、Ni、Mn)和磷(P)共掺杂多孔碳材料(TM-P-C)。通过旋转环盘电极研究了TM-P-C在0.1 mol/L KOH电解液中的氧气还原电催化性能。研究结果表明：TM-P-C催化剂具有较高的氧化还原反应(ORR)电催化性能,其ORR活性为P-Co-C>P-NiC>P-Fe-C>P-Mn-C,其中P-Co-C的ORR电催化性能可与商业20wt%Pt/C催化剂相媲美,其电流密度与20wt%Pt/C催化剂的电流密度相当,与20wt%Pt/C仅存在66 mV的半波电位差,表现为ORR的4e–转移途径。制备的TM-P-C催化剂所具有的较高氧气还原电催化活性主要来自于过渡金属和P原子之间的协同作用。此外,TM-P-C催化剂表现出优异的...     

Electrochemical catalytic activity for oxygen reduction reaction of nitrogen-doped carbon nanofibers

The electrocatalytic activity of nitrogen-doped carbon nanofibers (N-CNFs), which are synthesized directly from vaporized acetonitrile over nickel-iron based catalysts, for oxygen reduction reaction (ORR), was investigated. The nitrogen content and specific surface area of N-CNFs can be controlled through the synthesis temperature (300-680 degrees C). The graphitization degree of N-CNFs also are significantly affected by the temperature, whereas the chemical compositions of nitrogen species are similar irrespective of the synthesis conditions. From measurement of the electrochemical double layer capacitance, the surface of N-CNFs is found to have stronger interaction with ions than undoped-carbon surfaces. Although N-CNFs show higher over-potential than Pt catalysts do, N-CNFs were observed to have a noticeable ORR activity, as opposed to the carbon samples without nitrogen doping. The activity dependency of N-CNFs on the content of the nitrogen with which they were doped is discussed, based on the experiment results. The single cell of the direct methanol fuel cell (DMFC) was tested to investigate the performance of a membrane-electrode assembly that includes N-CNFs as the cathode catalyst layer.     

Shape-controlled synthesis of porous AuPt nanoparticles and their superior electrocatalytic activity for oxygen reduction reaction

Control of structure and morphology of Pt-based nanomaterials is of great importance for electrochemical energy conversions. In this work, we report an efficient one-step synthesis of bimetallic porous AuPt nanoparticles (PAuPt NPs) in an aqueous solution. The proposed synthesis is performed by a simple stirring treatment of an aqueous reactive mixture including K₂PtCl₄, HAuCl₄, Pluronic F127 and ascorbic acid at a pH value of 1 without organic solvent or high temperature. Due to their porous structure and bimetallic composition, as-made PAuPt NPs exhibit excellent electrocatalytic activity for oxygen reduction reaction.     

Ultrafine Sn nanocrystals in a hierarchically porous N-doped carbon for lithium ion batteries

We report a simple method of preparing a high performance,Sn-based anode material for lithium ion batteries (LIBs).Adding H2O2 to an aqueous solution containing Sn2+ and aniline results in simultaneous polymerization of aniline and oxidation of Sn2+ to SnO2,leading to a homogeneous composite of polyaniline and SnO2.Hydrogen thermal reduction of the above composite yields N-doped carbon with hierarchical porosity and homogeneously distributed,ultrafine Sn particles.The nanocomposite exhibits excellent performance as an anode material for lithium ion batteries,showing a high reversible specific capacity of 788 mAh·g-1 at a current density of 100 mA·g-1 after 300 cycles and very good stability up to 5,000 mA·g-1.The simple preparation method combined with the good electrochemical performance is highly promising to promote the application of Sn based anode materials.     

Designing three-dimensional hierarchical porous chrysanthemum flower-like CoNiFe2O4/carbon spheres as high-performance electrode for supercapacitors and oxygen reduction reaction

Journal of Materials Science: Materials in Electronics - Novel three-dimensional electrode materials with high capacitance, long cycle stability and electrocatalytic activity are designed through...     

Trimetallic Au@PdPb nanowires for oxygen reduction reaction

Nano Research - The development of highly efficient and stable Pd-based catalysts is crucial to improve their sluggish oxygen reduction reaction (ORR) kinetics in acid media. To improve ORR...     

A channel-confined strategy for synthesizing CoN-CoOx/C as efficient oxygen reduction electrocatalyst for advanced zinc-air batteries

Designing hybrid transition metal compounds with optimized electronic structure and firmly dispersing them on a matrix to avoid aggregation and shedding is of g...     

氮掺杂碳纳米片负载Fe-Co-Pt复合材料的制备及其氧还原电活性

制备高活性和高稳定性的电催化剂复合材料一直是燃料电池与金属-空气电池的重要研究内容.以双氰胺作为碳氮源,通过酞菁钴和二茂铁提供金属纳米颗粒,对其混合物进行简单的高温热解得到负载铁钴合金的氮掺杂碳纳米片(Fe1-Co1-N/C);最后利用沉积法将少量铂引入到Fe1-Co1-N/C上,得到负载铂铁钴三金属合金的氮掺杂碳纳米...