Metal‐Free Electrocatalyst for Oxygen Reduction: Synthesis‐Controlled Density of Catalytic Centers and Impact on ORR

This work demonstrates a rapid and scalable route for the preparation of N‐doped carbon spheres of 80–120 nm via pyrolysis of polypyrrole as the only carbon and nitrogen source. The resulting porous catalyst has a nitrogen doping level of 6–8 at%. Electrochemical studies show that N‐doped C is very active toward oxygen reduction in alkaline electrolyte and the mechanism of ORR process is controlled by the surface concentration of catalytic active sites that promote either a direct four‐electron or two‐electron process. An interesting observation is that we can generate precursors for the N‐doped carbon with desirable particle size, shape and with the preferential structure (linear polypyrrole from the α? α coupling during slow polymerization or cross‐linked polypyrrole from α? β coupling during fast polymerization) that promotes the formation of favorable catalytic sites for O₂ reduction. The XPS analysis in conjunction with RDE voltammetry highlights the effect of polymer precursor synthesis on the chemical structure and a resulting electrochemical activity of the N‐doped carbon materials.     

Enhanced Multiple Anchoring and Catalytic Conversion of Polysulfides by Amorphous MoS3 Nanoboxes for High‐Performance Li‐S Batteries

The practical implementation of lithium–sulfur batteries is obstructed by poor conductivity, sluggish redox kinetics, the shuttle effect, large volume variation, and low areal loading of sulfur electrodes. Now, amorphous N‐doped carbon/MoS₃ (NC/MoS₃) nanoboxes with hollow porous architectures have been meticulously designed as an advanced sulfur host. Benefiting from the enhanced conductivity by the N‐doped carbon, reduced shuttle effect by the strong chemical interaction between unsaturated Mo and lithium polysulfides, improved redox reaction kinetics by the catalytic effect of MoS₃, great tolerance of volume variation and high sulfur loading arising from flexible amorphous materials with hollow‐porous structures, the amorphous NC/MoS₃ nanoboxes enabled sulfur electrodes to deliver a high areal capacity with superior rate capacity and decent cycling stability. The synthetic strategy can be generalized to fabricate other amorphous metal sulfide nanoboxes.     

Nitrogen‐Doped Graphitic Porous Carbon Nanosheets Derived from In Situ Formed g‐C3N4 Templates for the Oxygen Reduction Reaction

Heteroatom‐doped carbon materials have been considered as potential substitutes for Pt‐based electrocatalysts for the oxygen reduction reaction (ORR) in alkaline fuel cells. Here we report the synthesis of oxygen‐containing nitrogen‐doped carbon (ONC) nanosheets through the carbonization of a mixture that contained glucose and dicyandiamide (DCDA). In situ formed graphitic carbon nitride (g‐C₃N₄) derived from DCDA provided a nitrogen‐rich template, thereby facilitating the formation of ONC nanosheets. The resultant ONC materials with high nitrogen content, high specific surface areas, and highly mesoporous total volume displayed excellent electrochemical performance, including a similar ORR onset potential, half‐potential, a higher diffusion‐limited current, and excellent tolerance to methanol than that of the commercial Pt/C catalyst, respectively. Moreover, the ONC‐850 nanosheet displayed high long‐term durability even after 1000 cycles as well as a high electron transfer number of 3.92 (4.0 for Pt/C). Additionally, this work provides deeper insight into these materials and a versatile strategy for the synthesis of cost‐effective 2D N‐doped carbon electrocatalysts.     

Compositing Amorphous TiO2 with N‐Doped Carbon as High‐Rate Anode Materials for Lithium‐Ion Batteries

Compositing amorphous TiO₂ with nitrogen‐doped carbon through Ti? N bonding to form an amorphous TiO₂/N‐doped carbon hybrid (denoted a‐TiO₂/C? N) has been achieved by a two‐step hydrothermal–calcining method with hydrazine hydrate as an inhibitor and nitrogen source. The resultant a‐TiO₂/C? N hybrid has a surface area as high as 108 m² g^?1 and, when used as an anode material, exhibits a capacity as high as 290.0 mA h g^?1 at a current rate of 1 C and a reversible capacity over 156 mA h g^?1 at a current rate of 10 C after 100 cycles; these results are better than those found in most reports on crystalline TiO₂. This superior electrochemical performance could be ascribed to a combined effect of several factors, including the amorphous nature, porous structure, high surface area, and N‐doped carbon.     

Metal‐Nitrogen‐doped Porous Carbons Derived from Metal‐Containing Ionic Liquids for Oxygen Reduction Reaction

This study describes a self‐doping and additive‐free strategy for the synthesis of metal‐nitrogen‐doped porous carbon materials (CMs) via carbonizing well‐tailored precursors, metal‐containing ionic liquids (M‐ILs). The organic skeleton in M‐ILs serves as both carbon and nitrogen sources, while metal ions acts as porogen and metallic dopants. A high nitrogen content, appropriate content of metallic species and hierarchical porosity synergistically endow the resultant CMs (MIBA‐M‐T) as effective electrocatalysts for the oxygen reduction reaction (ORR). MIBA‐Fe‐900 with a high specific surface area of 1567 m² g^?1 exhibits an activity similar to that of Pt/C catalyst, a higher tolerance to methanol than Pt/C, and long‐term durability. This work supplies a simple and convenient route for the preparation of metal‐containing carbon electrocatalysts.     

Synthesis of High‐Surface‐Area Nitrogen‐Doped Porous Carbon Microflowers and Their Efficient Carbon Dioxide Capture Performance

Sustainable carbon materials have received particular attention in CO₂ capture and storage owing to their abundant pore structures and controllable pore parameters. Here, we report high‐surface‐area hierarchically porous N‐doped carbon microflowers, which were assembled from porous nanosheets by a three‐step route: soft‐template‐assisted self‐assembly, thermal decomposition, and KOH activation. The hydrazine hydrate used in our experiment serves as not only a nitrogen source, but also a structure‐directing agent. The activation process was carried out under low (KOH/carbon=2), mild (KOH/carbon=4) and severe (KOH/carbon=6) activation conditions. The mild activated N‐doped carbon microflowers (A‐NCF‐4) have a hierarchically porous structure, high specific surface area (2309 m² g^?1), desirable micropore size below 1 nm, and importantly large micropore volume (0.95 cm³ g^?1). The remarkably high CO₂ adsorption capacities of 6.52 and 19.32 mmol g^?1 were achieved with this sample at 0 °C (273 K) and two pressures, 1 bar and 20 bar, respectively. Furthermore, this sample also exhibits excellent stability during cyclic operations and good separation selectivity for CO₂ over N₂.     

Single Cobalt Atoms with Precise N‐Coordination as Superior Oxygen Reduction Reaction Catalysts

A new strategy for achieving stable Co single atoms (SAs) on nitrogen‐doped porous carbon with high metal loading over 4 wt % is reported. The strategy is based on a pyrolysis process of predesigned bimetallic Zn/Co metal–organic frameworks, during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800 °C. The spherical aberration correction electron microscopy and extended X‐ray absorption fine structure measurements both confirm the atomic dispersion of Co atoms stabilized by as‐generated N‐doped porous carbon. Surprisingly, the obtained Co‐N_x single sites exhibit superior ORR performance with a half‐wave potential (0.881 V) that is more positive than commercial Pt/C (0.811 V) and most reported non‐precious metal catalysts. Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C. Our findings open up a new routine for general and practical synthesis of a variety of materials bearing single atoms, which could facilitate new discoveries at the atomic scale in condensed materials.     

Fabrication of Porous Nitrogen‐Doped Carbon Materials as Anodes for High‐Performance Lithium Ion Batteries

The hierarchical porous nitrogen‐doped carbon materials (HNCs) were prepared by using nitrogen containing gelatin as the carbon source and nano‐silica obtained by a simple flame synthesis approach as the template. All of the as‐obtained HNCs show much higher Li storage capacity as compared with commercial graphite. Specifically, HNC‐700 with biggest micropore volume and highest nitrogen content exhibited optimal reversible capacities of 1084 mAh·g^??1 at the current density of 37.2 mA·g^?1 (0.1 C) and 309 mAh·g^?1 even at 3.72 A·g^?1 (10 C). This result suggests that HNCs should be a promising candidate for anode materials in high‐rate lithium ion batteries (LIBs).     

Fe2O3‐N‐doped Honeycomb‐like Porous Carbon Derived from Nature Silk Sericin as Electrocatalysts for Oxygen Evolution Reaction

A facile method is reported to form a honeycomb‐like porous nanomaterial by intercalation of iron nitrate using nature silk sericin (SS) as nitrogen and carbon source. A series of Fe₂O₃ nanoparticles anchored on Fe₂O₃‐N‐doped graphite carbon electrocatalysts (SS‐Fe) were synthesized, exhibits well‐defined pore structure and excellent oxygen evolution reaction (OER) catalytic activities. Among these materials, SS‐Fe‐0.5 shows the best performance, the overpotential of SS‐Fe‐0.5 at 10 mA · cm^–2 is 440 mV (vs. RHE) and the Tafel slope is only 68 mV · dec^–1. The results indicate that it is promising to the preparation of carbon catalyst materials using natural, renewable and abundant resources for electrocatalysis.     

A Template‐Free Method for Preparation of Cobalt Nanoparticles Embedded in N‐Doped Carbon Nanofibers with a Hierarchical Pore Structure for Oxygen Reduction

Designing and preparing porous materials without using any templates is a challenge. Herein, single‐nozzle electrospinning technology coupled with post pyrolysis is applied to prepare cobalt nanoparticles embedded in N‐doped carbon nanofibers with a hierarchical pore structure (HP‐Co‐NCNFs). The resultant HP‐Co‐NCNFs have lengths up to several millimeters with an average diameter of 200 nm and possess abundant micro/meso/macropores on both the surface and within the fibers. Such a microstructure endows the surface area as high as 115 m² g^?1. When used as an electrocatalyst for the oxygen reduction reaction (ORR), the HP‐Co‐NCNFs exhibit outstanding electrochemical performance in terms of activity, methanol tolerance, and durability. The hierarchically porous structure and high surface area can effectively decrease the mass transport resistance and increase the exposed ORR active sites. The sufficient amount of exposed ORR active sites along with accessible transport channel and enhanced electrical conductivity may be responsible for the good electrocatalytic performance.     

A Carbon‐Sulfur Hybrid with Pomegranate‐like Structure for Lithium‐Sulfur Batteries

A carbon‐sulfur hybrid with pomegranate‐like core–shell structure, which demonstrates a high rate performance and relatively high cyclic stability, is obtained through carbonization of a carbon precursor in the presence of a sulfur precursor (FeS₂) and a following oxidation of FeS₂ to sulfur by HNO₃. Such a structure effectively protects the sulfur and leaves enough buffer space after Fe³⁺ removal and, at the same time, has an interconnected conductive network. The capacity of the obtained hybrid is 450 mA h g^?1 under the current density of 5 C. This work provides a simple strategy to design and prepare various high‐performance carbon‐sulfur hybrids for lithium‐sulfur batteries.     

Boosting ORR Catalytic Activity by Integrating Pyridine‐N Dopants,a High Degree of Graphitization,and Hierarchical Pores into a MOF‐Derived N‐Doped Carbon in a Tandem Synthesis

N‐doped carbon materials represent promising metal‐free electrocatalysts for the oxygen reduction reaction (ORR), the cathode reaction in fuel cells, metal–air batteries, and so on. A challenge for optimizing the ORR catalytic activities of these electrocatalysts is to tune their local structures and chemical compositions in a rational and controlled way that can achieve the synergistic function of each factor. Herein, we report a tandem synthetic strategy that integrates multiple contributing factors into an N‐doped carbon. With an N‐containing MOF (ZIF‐8) as the precursor, carbonization at higher temperatures leads to a higher degree of graphitization. Subsequent NH₃ etching of this highly graphitic carbon enabled the introduction of a higher content of pyridine‐N sites and higher porosity. By optimizing these three factors, the resultant carbon materials displayed ORR activity that was far superior to that of carbon derived from a one‐step pyrolysis. The onset potential of 0.955 V versus a reversible hydrogen electrode (RHE) and the half‐wave potential of 0.835 V versus RHE are among the top ranks of metal‐free ORR catalysts and are comparable to commercial Pt/C (20 wt %) catalysts. Kinetic studies revealed lower H₂O₂ yields, higher electron‐transfer numbers, and lower Tafel slopes for these carbon materials compared with that derived from a one‐step carbonization. These findings verify the effectiveness of this tandem synthetic strategy to enhance the ORR activity of N‐doped carbon materials.     

Nitrogen‐Doped Porous Graphitic Carbon as an Excellent Electrode Material for Advanced Supercapacitors

An advanced supercapacitor material based on nitrogen‐doped porous graphitic carbon (NPGC) with high a surface area was synthesized by means of a simple coordination–pyrolysis combination process, in which tetraethyl orthosilicate (TEOS), nickel nitrate, and glucose were adopted as porogent, graphitic catalyst precursor, and carbon source, respectively. In addition, melamine was selected as a nitrogen source owing to its nitrogen‐enriched structure and the strong interaction between the amine groups and the glucose unit. A low‐temperature treatment resulted in the formation of a NPGC precursor by combination of the catalytic precursor, hydrolyzed TEOS, and the melamine–glucose unit. Following pyrolysis and removal of the catalyst and porogent, the NPGC material showed excellent electrical conductivity owing to its high crystallinity, a large Brunauer–Emmett–Teller surface area (S_BET=1027 m² g^?1), and a high nitrogen level (7.72 wt %). The unusual microstructure of NPGC materials could provide electrochemical energy storage. The NPGC material, without the need for any conductive additives, showed excellent capacitive behavior (293 F g^?1 at 1 A g^?1), long‐term cycling stability, and high coulombic efficiency (>99.9 % over 5000 cycles) in KOH when used as an electrode. Notably, in a two‐electrode symmetric supercapacitor, NPGC energy densities as high as 8.1 and 47.5 Wh kg^?1, at a high power density (10.5 kW kg^?1), were achieved in 6 M KOH and 1 M Et₄NBF₄‐PC electrolytes, respectively. Thus, the synthesized NPGC material could be a highly promising electrode material for advanced supercapacitors and other conversion devices.     

Novel synthesis of nano‐calcium carbonate (CaCO3)/polystyrene (PS) core–shell nanoparticles by atomized microemulsion technique and its effect on properties of polypropylene (PP) composites

Calcium carbonate (CaCO₃)/polystyrene (PS) nanoparticles (<100 nm) with core–shell structure were synthesized by atomized microemulsion technique. The polymer chains were anchored onto the surface of nano‐CaCO₃ through triethoxyvinyl silane (TEVS) as a coupling agent. Ammonium persulfate (APS), sodium dodecyl sulfate (SDS) and n‐pentanol were used as initiator, surfactant, and cosurfactant, respectively. Polymerization mechanism of core–shell latex particles was discussed. Encapsulation of nano‐CaCO₃ by PS was confirmed by using transmission electron microscope (TEM). Grafting percentage of core–shell particles was investigated by Thermogravimetric Analyzer (TGA). Nano‐CaCO₃/PS core–shell particles were characterized by Fourier transform infrared (FTIR) spectrophotometer and differential scanning calorimeter (DSC). The results of FTIR revealed existence of a strong interaction at the interface of nano‐CaCO₃ particle and PS, which implies that the polymer chains were successfully grafted onto the surface of nano‐CaCO₃ particle through the link of the coupling agent. In addition, TGA and DSC results indicated an enhancement of thermal stability of core–shell materials compared with the pure nano‐PS. Nano‐CaCO₃/PS particles were blended with polypropylene (PP) matrix on Brabender Plastograph by melt process with different wt% of loading (i.e. 0.1–1 wt%). The interfacial adhesion between nano‐CaCO₃ particles and PP matrix was significantly improved when the nano‐CaCO3 particles were grafted with PS, which led to increased thermal, rheological, and mechanical properties of (nano‐CaCO₃/PS)/PP composites. Scanning electron microscope (SEM) and atomic force microscope (AFM) images showed a perfect dispersion of the nano‐CaCO₃ particles in PP matrix. Copyright © 2011 John Wiley & Sons, Ltd.     

Radially Inwardly Aligned Hierarchical Porous Carbon for Ultra‐Long‐Life Lithium–Sulfur Batteries

Rational design of hollow micro‐ and/or nano‐structured cathodes as sulfur hosts has potential for high‐performance lithium‐sulfur batteries. However, their further commercial application is hindered because infusing sulfur into hollow hosts is hard to control and the interactions between high loading sulfur and electrolyte are poor. Herein, we designed hierarchical porous hollow carbon nanospheres with radially inwardly aligned supporting ribs to mitigate these problems. Such a structure could aid the sulfur infusion and maximize sulfur utilization owing to the well‐ordered pore channels. This highly organized internal carbon skeleton can also enhance the electronic conductivity. The hollow carbon nanospheres with further nitrogen‐doping as the sulfur host material exhibit good capacity and excellent cycling performance (0.044 % capacity degradation per each cycle for 1000 cycles).     

Bullet‐like Cu9S5 Hollow Particles Coated with Nitrogen‐Doped Carbon for Sodium‐Ion Batteries

Metal sulfides with excellent redox reversibility and high capacity are very promising electrode materials for sodium‐ion batteries. However, their practical application is still hindered by the poor rate capability and limited cycle life. Herein, a template‐based strategy is developed to synthesize nitrogen‐doped carbon‐coated Cu₉S₅ bullet‐like hollow particles starting from bullet‐like ZnO particles. With the structural and compositional advantages, these unique nitrogen‐doped carbon‐coated Cu₉S₅ bullet‐like hollow particles manifest excellent sodium storage properties with superior rate capability and ultra‐stable cycling performance.     

An Efficient Synthesis of 1,3‐Diphenyl‐3‐phenylamino‐propan‐1‐one and its Derivatives by Mannich Reaction in the Presence of Doped Porous Carbon by Nitrogen and Sulfur (NS‐PCS) as Catalyst

Synthesis of β‐amino carbonyl compounds by Mannich reaction involves the creation of various bonds in a single action and is attracting great attention as one of the most powerful synthetic tools for the expansion of molecular convolution and versatility. Carbon spheres (CSs) combine the advantages of carbon materials with spherical colloids, which gives them several inimitable features as catalysts. In this work, the reaction between acetophenone, aromatic aldehydes, and aromatic amines has been efficiently catalyzed by porous carbon spheres which were doped by nitrogen and sulfur (NS‐PCS) at ambient temperature to give diverse β‐amino carbonyl compounds in nearly high yields.     

Intrinsically Sulfur‐ and Nitrogen‐Co‐doped Carbons from Thiazolium Salts

Carbon materials that are intrinsically co‐doped with nitrogen and sulfur heteroatoms are synthesised by facile annealing of nitrile‐functionalised thiazolium salts. Extremely high degrees of doping are achieved, especially for sulfur. The method further allows for direct tuning of the amounts of both N and S, establishing a new synthetic pathway in the emerging field of S‐doped carbon materials.     

Bottom‐Up Fabrication of a Sandwich‐Like Carbon/Graphene Heterostructure with Built‐In FeNC Dopants as Non‐Noble Electrocatalyst for Oxygen Reduction Reaction

High‐performance non‐noble electrocatalysts for oxygen reduction reaction (ORR) are the prerequisite for large‐scale utilization of fuel cells. Herein, a type of sandwiched‐like non‐noble electrocatalyst with highly dispersed FeN_x active sites embedded in a hierarchically porous carbon/graphene heterostructure was fabricated using a bottom‐up strategy. The in situ ion substitution of Fe³⁺ in a nitrogen‐containing MOF (ZIF‐8) allows the Fe‐heteroatoms to be uniformly distributed in the MOF precursor, and the assembly of Fe‐doped ZIF‐8 nano‐crystals with graphene‐oxide and in situ reduction of graphene‐oxide afford a sandwiched‐like Fe‐doped ZIF‐8/graphene heterostructure. This type of heterostructure enables simultaneous optimization of FeN_x active sites, architecture and interface properties for obtaining an electron‐catalyst after a one‐step carbonization. The synergistic effect of these factors render the resulting catalysts with excellent ORR activities. The half‐wave potential of 0.88 V vs. RHE outperforms most of the none‐noble metal catalyst and is comparable with the commercial Pt/C (20 wt %) catalyst. Apart from the high activity, this catalyst exhibits excellent durability and good methanol‐tolerance. Detailed investigations demonstrate that a moderate content of Fe dopants can effectively increase the intrinsic activities, and the hybridization of graphene can enhance the reaction kinetics of ORR. The strategy proposed in this work gives an inspiration towards developing efficient noble‐metal‐free electrocatalysts for ORR.     

Heteroatom‐Doped Porous Carbon Materials with Unprecedented High Volumetric Capacitive Performance

The design of carbon‐based materials with a high mass density and large porosity has always been a challenging goal, since they fulfill the demands of next‐generation supercapacitors and other electrochemical devices. We report a new class of high‐density heteroatom‐doped porous carbon that can be used as an aqueous‐based supercapacitor material. The material was synthesized by an in situ dehalogenation reaction between a halogenated conjugated diene and nitrogen‐containing nucleophiles. Under the given conditions, pyridinium salts can only continue to perform the dehalogenation if there is residue water remaining from the starting materials. The obtained carbon materials are highly doped by various heteroatoms, leading to high densities, abundant multimodal pores, and an excellent volumetric capacitive performance. Porous carbon tri‐doped with nitrogen, phosphorous, and oxygen exhibits a high packing density (2.13 g cm^?3) and an exceptional volumetric energy density (36.8 Wh L^?1) in alkaline electrolytes, making it competitive to even some Ni‐MH cells.