Cross-Linked Polyphosphazene Hollow Nanosphere-Derived N/P-Doped Porous Carbon with Single Nonprecious Metal Atoms for the Oxygen Reduction Reaction

Heteroatom-doped polymers or carbon nanospheres have attracted broad research interest. However, rational synthesis of these nanospheres with controllable properties is still a great challenge. Herein, we develop a template-free approach to construct cross-linked polyphosphazene nanospheres with tunable hollow structures. As comonomers, hexachlorocyclotriphosphazene provides N and P atoms, tannic acid can coordinate with metal ions, and the replaceable third comonomer can endow the materials with various properties. After carbonization, N/P-doped mesoporous carbon nanospheres were obtained with small particle size (≈50 nm) and high surface area (411.60 m² g⁻¹). Structural characterization confirmed uniform dispersion of the single atom transition metal sites (i.e., Co-N₂P₂) with N and P dual coordination. Electrochemical measurements and theoretical simulations revealed the oxygen reduction reaction performance. This work provides a solution for fabricating diverse heteroatom-containing polymer nanospheres and their derived single metal atom doped carbon catalysts.     

Atomically Dispersed Nickel(I) on an Alloy‐Encapsulated Nitrogen‐Doped Carbon Nanotube Array for High‐Performance Electrochemical CO2 Reduction Reaction

Single‐atom catalysts (SACs) show great promise for electrochemical CO₂ reduction reaction (CRR), but the low density of active sites and the poor electrical conduction and mass transport of the single‐atom electrode greatly limit their performance. Herein, we prepared a nickel single‐atom electrode consisting of isolated, high‐density and low‐valent nickel(I) sites anchored on a self‐standing N‐doped carbon nanotube array with nickel–copper alloy encapsulation on a carbon‐fiber paper. The combination of single‐atom nickel(I) sites and self‐standing array structure gives rise to an excellent electrocatalytic CO₂ reduction performance. The introduction of copper tunes the d‐band electron configuration and enhances the adsorption of hydrogen, which impedes the hydrogen evolution reaction. The single‐nickel‐atom electrode exhibits a specific current density of ?32.87 mA cm^?2 and turnover frequency of 1962 h^?1 at a mild overpotential of 620 mV for CO formation with 97 % Faradic efficiency.     

Kinetically Controlled Assembly of Nitrogen‐Doped Invaginated Carbon Nanospheres with Tunable Mesopores

Mesoporous hollow carbon nanospheres (MHCS) have been extensively studied owning to their unique structural features and diverse potential applications. A surfactant‐free self‐assembly approach between resorcinol/formaldehyde and silicon alkoxide has emerged as an important strategy to prepare MHCS. Extending such a strategy to other substituted phenols to produce heterogeneous‐atom‐doped MHCS remains a challenge due to the very different polymerization kinetics of various resins. Herein, we report an ethylenediamine‐assisted strategy to control the cooperative self‐assembly between a 3‐aminophenol/formaldehyde resin and silica templates. Nitrogen‐doped mesoporous invaginated carbon nanospheres (N‐MICS) with an N content of 6.18 at %, high specific surface areas (up to 1118 m² g^?1), large pore volumes (2.47 cm³ g^?1), and tunable mesopores (3.7–11.1 nm) have been prepared. When used as electrical double‐layer supercapacitors, N‐MICS show a high capacitance of 261 F g^?1, an outstanding cycling stability (≈94 % capacitance retention after 10 000 cycles), and a good rate performance.     

Hollow Nanotubes of N‐Doped Carbon on CoS

Low‐cost, single‐step synthesis of hollow nanotubes of N‐doped carbon deposited on CoS is enabled by the simultaneous use of three functionalities of polyacrylonitrite (PAN) nanofibers: 1) a substrate for loading active materials, 2) a sacrificial template for creating hollow tubular structures, and 3) a precursor for in situ nitrogen doping. The N‐doped carbon in hollow tubes of CoS provides a high‐capacity anode of long cycle life for a rechargeable Li‐ion or Na‐ion battery cell that undergoes the conversion reaction 2 A⁺+2 e^?+CoS →Co+A₂S with A=Li or Na.     

Biomass‐derived Nitrogen and Phosphorus Co‐doped Hierarchical Micro/mesoporous Carbon Materials for High‐performance Non‐enzymatic H2O2 Sensing

Nitrogen and phosphorus co‐doped hierarchical micro/mesoporous carbon (N,P‐MMC) was prepared by simple thermal treatment of freeze‐dried okra in the absence of any other additives. The 0.96 wt % of N and 1.47 wt % of P were simultaneously introduced into the graphitic framework of N,P‐MMC, which also possesses hierarchical porous structure with mesopores centered at 3.6 nm and micropores centered at 0.79 nm. Most importantly, N,P‐MMC carbon exhibits excellent catalytic activity for electrocatalytic reduction of H₂O₂, resulting in a new strategy to construct non‐enzymatic H₂O₂ sensor. The N,P‐MMC‐based H₂O₂ sensor displays two linear detection range about 0.1 mM–10 mM (R²=0.9993) and 20 mM–200 mM (R²=0.9989), respectively. The detection limit is estimated to be 6.8 μM at a signal‐to‐noise ratio of 3. These findings provide insights into synthesizing functional heteroatoms doped porous carbon materials for biosensing applications.     

Nitrogen,Phosphorus, and Sulfur Co‐Doped Hollow Carbon Shell as Superior Metal‐Free Catalyst for Selective Oxidation of Aromatic Alkanes

Metal‐free heteroatom‐doped carbocatalysts with a high surface area are desirable for catalytic reactions. In this study, we found an efficient strategy to prepare nitrogen, phosphorus, and sulfur co‐doped hollow carbon shells (denote as NPS‐HCS) with a surface area of 1020 m² g⁻¹. Using a poly(cyclotriphosphazene‐co‐4,4′‐sulfonyldiphenol) (PZS) shell as carbon source and N, P, S‐doping source, and the ZIF‐67 core as structural template as well as extra N‐doping source, NPS‐HCS were obtained with a high surface area and superhydrophilicity. All these features render the prepared NPS‐HCS a superior metal‐free carbocatalyst for the selective oxidation of aromatic alkanes in aqueous solution. This study provides a reliable and facile route to prepare doped carbocatalysts with enhanced catalytic properties.     

Uniform silver nanoparticles on tunable porous N‐doped carbon nanospheres for aerobic oxidative synthesis of aryl nitriles from benzylic alcohols

Tunable N‐doped carbon nanospheres from sucrose as carbon source and Tris(2‐aminoethyl)amine (TAEA) as nitrogen source by a simple and easily reproducible method were prepared. It was demonstrated that the tunable N‐doping of carbon spheres could be realized by altering the ratio of TAEA in the raw materials. The content of doped nitrogen, surface area, pore volume and pore size of carbon nanospheres were increased with the increasing of TAEA amount in the hydrothermal process. Prepared N‐doped carbon nanospheres act as solid ligand for anchoring of Ag NPs which generated via chemical reduction of Ag ions. Benzylic alcohols and aldehydes were converted into the aryl nitriles by using Ag/N‐CS‐1 nanospheres as the catalyst and O₂ as the oxidant, efficiently. This catalyst was stable and could use for 6 successful runs.     

Nitrogen,Phosphorus, and Sulfur Co‐Doped Hollow Carbon Shell as Superior Metal‐Free Catalyst for Selective Oxidation of Aromatic Alkanes

Metal‐free heteroatom‐doped carbocatalysts with a high surface area are desirable for catalytic reactions. In this study, we found an efficient strategy to prepare nitrogen, phosphorus, and sulfur co‐doped hollow carbon shells (denote as NPS‐HCS) with a surface area of 1020 m² g^?1. Using a poly(cyclotriphosphazene‐co‐4,4′‐sulfonyldiphenol) (PZS) shell as carbon source and N, P, S‐doping source, and the ZIF‐67 core as structural template as well as extra N‐doping source, NPS‐HCS were obtained with a high surface area and superhydrophilicity. All these features render the prepared NPS‐HCS a superior metal‐free carbocatalyst for the selective oxidation of aromatic alkanes in aqueous solution. This study provides a reliable and facile route to prepare doped carbocatalysts with enhanced catalytic properties.     

From Metal–Organic Frameworks to Single‐Atom Fe Implanted N‐doped Porous Carbons: Efficient Oxygen Reduction in Both Alkaline and Acidic Media

It remains highly desired but a great challenge to achieve atomically dispersed metals in high loadings for efficient catalysis. Now porphyrinic metal–organic frameworks (MOFs) have been synthesized based on a novel mixed‐ligand strategy to afford high‐content (1.76 wt %) single‐atom (SA) iron‐implanted N‐doped porous carbon (Fe_SA‐N‐C) via pyrolysis. Thanks to the single‐atom Fe sites, hierarchical pores, oriented mesochannels and high conductivity, the optimized Fe_SA‐N‐C exhibits excellent oxygen reduction activity and stability, surpassing almost all non‐noble‐metal catalysts and state‐of‐the‐art Pt/C, in both alkaline and more challenging acidic media. More far‐reaching, this MOF‐based mixed‐ligand strategy opens a novel avenue to the precise fabrication of efficient single‐atom catalysts.     

Ordered Porous Nitrogen‐Doped Carbon Matrix with Atomically Dispersed Cobalt Sites as an Efficient Catalyst for Dehydrogenation and Transfer Hydrogenation of N‐Heterocycles

Single‐atom catalysts (SACs) have been explored widely as potential substitutes for homogeneous catalysts. Isolated cobalt single‐atom sites were stabilized on an ordered porous nitrogen‐doped carbon matrix (ISAS‐Co/OPNC). ISAS‐Co/OPNC is a highly efficient catalyst for acceptorless dehydrogenation of N‐heterocycles to release H₂. ISAS‐Co/OPNC also exhibits excellent catalytic activity for the reverse transfer hydrogenation (or hydrogenation) of N‐heterocycles to store H₂, using formic acid or external hydrogen as a hydrogen source. The catalytic performance of ISAS‐Co/OPNC in both reactions surpasses previously reported homogeneous and heterogeneous precious‐metal catalysts. The reaction mechanisms are systematically investigated using first‐principles calculations and it is suggested that the Eley–Rideal mechanism is dominant.     

Electrocatalytically Active Fe‐(O‐C2)4 Single‐Atom Sites for Efficient Reduction of Nitrogen to Ammonia

Single‐atom catalysts have demonstrated their superiority over other types of catalysts for various reactions. However, the reported nitrogen reduction reaction single‐atom electrocatalysts for the nitrogen reduction reaction exclusively utilize metal–nitrogen or metal–carbon coordination configurations as catalytic active sites. Here, we report a Fe single‐atom electrocatalyst supported on low‐cost, nitrogen‐free lignocellulose‐derived carbon. The extended X‐ray absorption fine structure spectra confirm that Fe atoms are anchored to the support via the Fe‐(O‐C₂)₄ coordination configuration. Density functional theory calculations identify Fe‐(O‐C₂)₄ as the active site for the nitrogen reduction reaction. An electrode consisting of the electrocatalyst loaded on carbon cloth can afford a NH₃ yield rate and faradaic efficiency of 32.1 μg h^?1 mg_cat.^?1 (5350 μg h^?1 mg_Fe^?1) and 29.3 %, respectively. An exceptional NH₃ yield rate of 307.7 μg h^?1 mg_cat.^?1 (51 283 μg h^?1 mg_Fe^?1) with a near record faradaic efficiency of 51.0 % can be achieved with the electrocatalyst immobilized on a glassy carbon electrode.     

Understanding the Origin of Highly Selective CO2 Electroreduction to CO on Ni,N‐doped Carbon Catalysts

Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO₂ electroreduction (CO₂R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni?N bonding and correlating CO₂ reduction (CO₂R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO₂R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts.     

Minimalistic Ditopic Ligands: An α‐S,N‐Donor‐Substituted Alkyne as Effective Intermetallic Conjugation Linker

The capability of donor‐substituted alkynes to link different metal ions in a side‐on carbon donor‐chelate coordination mode is extended from the donor centers S and P to the second period element N. The complex [Tp′W(CO)₂{η²‐C₂(S)(NHBn)}] (Tp′=hydrido‐tris(3,5‐dimethylpyrazolyl)borate, Bn=benzyl) bearing a terminal sulfur atom and a secondary amine substituent is accessible by a metal‐template synthesis. Subsequent deprotonation allowed the formation of remarkably stable heterobimetallic complexes with the [(η⁵‐C₅H₅)Ru(PPh₃)] and the [Ir(ppy)₂] moiety. Electrochemical and spectroscopic investigations (cyclic voltammetry, IR, UV/Vis, luminescence, EPR), as well as DFT calculations, and X‐ray structure determinations of the W–Ru complex in two oxidation states reveal a strong metal–metal coupling but also a limited delocalization of excited states.     

Polyoxometalate and Resin‐Derived P‐Doped Mo2C@N‐Doped Carbon as a Highly Efficient Hydrogen‐Evolution Reaction Catalyst at All pH Values

A new type of P‐doped Mo₂C coated by N‐doped carbon (P‐Mo₂C@NC) has been successfully prepared by calcining a mixture of H₃[PMo₁₂O₄₀] polyoxometalates (POMs) and urea‐formaldehyde resin under an N₂ atmosphere. Urea‐formaldehyde resin not only serves as the carbon source to ensure carbonization but also facilitates the uniform distribution of POM precursors, which efficiently avoid the aggregation of Mo₂C particles at high temperatures. TEM analysis revealed that the average diameter of the Mo₂C particles was about 10 nm, which is coated by a few‐layer N‐doped carbon sheet. The as‐prepared P‐Mo₂C@NC displayed excellent hydrogen‐evolution reaction (HER) performance and long‐term stability in all pH environments. To reach a current density of 10 mA cm^?2, only 109, 159, and 83 mV were needed for P‐Mo₂C@NC in 0.5 m H₂SO₄ (pH 0), 0.1 m phosphate buffer (pH 7), and 1 m KOH (pH 14), respectively. This could provide a high‐yield and low‐cost method to prepare uniform nanosized molybdenum carbides with highly efficient and stable HER performance.     

RuP2‐Based Catalysts with Platinum‐like Activity and Higher Durability for the Hydrogen Evolution Reaction at All pH Values

Highly active, stable, and cheap Pt‐free catalysts for the hydrogen evolution reaction (HER) are under increasing demand for future energy conversion systems. However, developing HER electrocatalysts with Pt‐like activity that can function at all pH values still remains as a great challenge. Herein, based on our theoretical predictions, we design and synthesize a novel N,P dual‐doped carbon‐encapsulated ruthenium diphosphide (RuP₂@NPC) nanoparticle electrocatalyst for HER. Electrochemical tests reveal that, compared with the Pt/C catalyst, RuP₂@NPC not only has Pt‐like HER activity with small overpotentials at 10 mA cm⁻² (38 mV in 0.5 m H₂SO₄, 57 mV in 1.0 m PBS and 52 mV in 1.0 m KOH), but demonstrates superior stability at all pH values, as well as 100 % Faradaic yields. Therefore, this work adds to the growing family of transition‐metal phosphides/heteroatom‐doped carbon heterostructures with advanced performance in HER.     

Supramolecular hydrogen‐bonding patterns in the organic–inorganic hybrid compound bis(4‐amino‐5‐chloro‐2,6‐dimethylpyrimidinium) tetrathiocyanatozinc(II)–4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–water (1/2/2)

Zinc thiocyanate complexes have been found to be biologically active compounds. Zinc is also an essential element for the normal function of most organisms and is the main constituent in a number of metalloenzyme proteins. Pyrimidine and aminopyrimidine derivatives are biologically very important as they are components of nucleic acids. Thiocyanate ions can bridge metal ions by employing both their N and S atoms for coordination. They can play an important role in assembling different coordination structures and yield an interesting variety of one‐, two‐ and three‐dimensional polymeric metal–thiocyanate supramolecular frameworks. The structure of a new zinc thiocyanate–aminopyrimidine organic–inorganic compound, (C₆H₉ClN₃)₂[Zn(NCS)₄]·2C₆H₈ClN₃·2H₂O, is reported. The asymmetric unit consist of half a tetrathiocyanatozinc(II) dianion, an uncoordinated 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidinium cation, a 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine molecule and a water molecule. The Zn^II atom adopts a distorted tetrahedral coordination geometry and is coordinated by four N atoms from the thiocyanate anions. The Zn^II atom is located on a special position (twofold axis of symmetry). The pyrimidinium cation and the pyrimidine molecule are not coordinated to the Zn^II atom, but are hydrogen bonded to the uncoordinated water molecules and the metal‐coordinated thiocyanate ligands. The pyrimidine molecules and pyrimidinium cations also form base‐pair‐like structures with an R₂²(8) ring motif via N—H…N hydrogen bonds. The crystal structure is further stabilized by intermolecular N—H…O, O—H…S, N—H…S and O—H…N hydrogen bonds, by intramolecular N—H…Cl and C—H…Cl hydrogen bonds, and also by π–π stacking interactions.     

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.     

Nanosized Metal Phosphides Embedded in Nitrogen‐Doped Porous Carbon Nanofibers for Enhanced Hydrogen Evolution at All pH Values

Transition‐metal phosphides (TMPs) have emerged as promising catalyst candidates for the hydrogen evolution reaction (HER). Although numerous methods have been investigated to obtain TMPs, most rely on traditional synthetic methods that produce materials that are inherently deficient with respect to electrical conductivity. An electrospinning‐based reduction approach is presented, which generates nickel phosphide nanoparticles in N‐doped porous carbon nanofibers (Ni₂P@NPCNFs) in situ. Ni₂P nanoparticles are protected from irreversible fusion and aggregation in subsequent high‐temperature pyrolysis. The resistivity of Ni₂P@NPCNFs (5.34 Ω cm) is greatly decreased by 10⁴ times compared to Ni₂P (>10⁴ Ω cm) because N‐doped carbon NFs are incorporated. As an electrocatalyst for HER, Ni₂P@NPCNFs reveal remarkable performance compared to other previously reported catalysts in acidic media. Additionally, it offers excellent catalytic ability and durability in both neutral and basic media. Encouraged by the excellent electrocatalytic performance of Ni₂P@NPCNFs, a series of pea‐like M_xP@NPCNFs, including Fe₂P@NPCNFs, Co₂P@NPCNFs, and Cu₃P@NPCNFs, were synthesized by the same method. Detailed characterization suggests that the newly developed method could render combinations of ultrafine metal phosphides with porous carbon accessible; thereby, extending opportunities in electrocatalytic applications.     

Boosting CO2 Electroreduction on N,P‐Co‐doped Carbon Aerogels

Electroreduction of CO₂ to CO powered by renewable electricity is a possible alternative to synthesizing CO from fossil fuel. However, it is very hard to achieve high current density at high faradaic efficiency (FE). Here, the first use of N,P‐co‐doped carbon aerogels (NPCA) to boost CO₂ reduction to CO is presented. The FE of CO could reach 99.1 % with a partial current density of ?143.6 mA cm^?2, which is one of the highest current densities to date. NPCA has higher electrochemical active area and overall electronic conductivity than that of N‐ or P‐doped carbon aerogels, which favors electron transfer from CO₂ to its radical anion or other key intermediates. By control experiments and theoretical calculations, it is found that the pyridinic N was very active for CO₂ reduction to CO, and co‐doping of P with N hinder the hydrogen evolution reaction (HER) significantly, and thus the both current density and FE are very high.     

Nitrogen‐Doped Mesoporous Carbon‐Encapsulated MoO2 Nanobelts as a High‐Capacity and Stable Host for Lithium‐Ion Storage

N‐doped mesoporous carbon‐capped MoO₂ nanobelts (designated as MoO₂@NC) were synthesized and applied to lithium‐ion storage. Owing to the stable core–shell structural framework and conductive mesoporous carbon matrix, the as‐prepared MoO₂@NC shows a high specific capacity of around 700 mA h g⁻¹ at a current of 0.5 A g⁻¹, excellent cycling stability up to 100 cycles, and superior rate performance. The N‐doped mesoporous carbon can greatly improve the conductivity and provide uninhibited conducting pathways for fast charge transfer and transport. Moreover, the core–shell structure improved the structural integrity, leading to a high stability during the cycling process. All of these merits make the MoO₂@NC to be a suitable and promising material for lithium ion battery.