Nitrogen-doped Graphitic Carbon Research Articles

Mechanically and Electrically Stable Hybrid Aerogels as Free‐Standing Anodes for High‐Capacity Lithium‐Ion Battery

Molybdenum disulfide (MoS2) is a promising alternative to graphite anodes in battery materials. Therefore, it is critical to scrutinize their structural stability and charge storage capacity during battery operation. Herein, freestanding electrodes consisting of MoS2‐incorporated carbon nanotube aerogels are fabricated using a simple yet scalable hydrothermal method, as used in lithium‐ion batteries. The outer nitrogen‐doped graphitic carbon (NGr) layers support efficient charge transport, even under a substantial compressive environment, and improve the structural integrity, showing significant improvements in battery performance, such as a high rate capacity of 820 mAh g−1 at the current density of 5 A g−1 and 94% capacity retention after 170 cycles (1170 mAh g−1 at 1 A g−1 after 170 cycles), even in the absence of polymer binders and conductive additives. The resulting NGr/MoS2/single‐walled carbon nanotubes freestanding electrodes have great potential to increase the volumetric and gravimetric energy density of batteries.

Bifunctional nitrogen-doped carbon quantum dot-modified graphitic carbon nitride/cadmium sulfide nanomaterials for antibiotic selective detection and photocatalytic degradation

In this paper, an S-type NCN/CdS heterojunction was formed by anchoring cadmium sulfide on nitrogen-doped carbon quantum dot-modified g-C3N4 (abbreviated as NCN) via hydrothermal and calcination methods. The bifunctional properties of NCN/CdS for the detection and degradation of antibiotics [tetracycline (TC) and chlortetracycline (CTC)] were demonstrated. The S-type heterojunction has a strong redox capacity and effectively separates photogenerated e−-h+ pairs, which improves photocatalytic performance. NCDs is located between cadmium sulfide and g-C3N4, which forms a charge-transport channel that accelerates the carrier transport between the interfaces of the S-type heterojunction. Good photocatalytic performance (TC: 98.0 % for 45 min; CTC: 100 % for 70 min) and excellent cycling stability were obtained. This study provides a new strategy for designing efficient, stable and bifunctional materials for environmental pollution treatment.

Polyoxometalate coupled polymers induced molybdenum phosphide with large surface area for efficient hydrogen evolution

Developing highly active hydrogen evolution reaction (HER) electrocatalysts possesses great significance for the green renewable energy conversion and storage. Here, through the electrostatic attraction between polyoxometalate (PMo12) and ammonium polyphosphate (APP) and the coordination with polyallylamine hydrochloride (PAH), the precursor was constructed, and then nitrogen-doped graphite carbon layer-coated MoP active particles (MoP@NC) were successfully prepared by high temperature carbonization. For HER, the overpotential of η10 for MoP@NC is 119 and 126 mV in acidic and alkaline electrolyte. Furthermore, in alkaline solution, when the current density reaches a certain degree (≥110 mA cm−2), the hydrogen production activity of the catalysts are the same as that of the industrial Pt/C catalysts, or even have a slight advantage. The synergistic interaction of active particles (MoP) and graphitic carbon layers and high specific surface area ensure the excellent activity of HER. N-doped porous carbon layers also protect MoP@NC working for 24 h. Moreover, the catalysts prepared in the same experimental environment with ammonium molybdate as metal source also showed good HER performance in acidic and alkaline environments. This study opens a general way to develop earth-rich Mo-based phosphide electrocatalysts with high activity for hydrolysis applications.

Bagasse derived N-doped graphitic carbon encapsulated cobalt nanoparticles as an efficient bifunctional catalyst for water splitting reactions

The utilization of non-precious metal-based electrodes to unlock cost-effective and scalable processes for the production of clean energy is highly desirable. Herein, we reported a straightforward hydrothermal carbonization method for the synthesize of nitrogen-doped graphitic carbons integrated with cobalt (Co@NGC-600, Co@NGC-700, and Co@NGC-800) from sugarcane bagasse and their electrocatalytic applications in oxygen and hydrogen evolution reactions. The graphitic nature of the Co integrated N-doped carbon materials was confirmed by Raman and XPS analysis. FESEM and HRTEM analysis confirms the dispersion of Co on N-doped carbon nanosheets. The Co@NGC-800 catalyst shows low overpotential and Tafel slope, requiring only 304 mV (84.1 mV dec−1) for oxygen electrode and 234 mV (118 mV dec−1) for HER at a current density of 10 mA cm−2. Moreover, Co@NGC-800 materials showed better activity than Co@NGC-700, Co Co@NGC-600, and Co@NC. The active Co@NGC-800 bifunctional electrocatalysts pair contributes to the fabrication of a water electrolyser with a 10 mA/cm2 current density at 1.68 V. The Co@NGC-800 // Co@NGC-800 electrocatalyst exhibits good stability over a period of 24 h with negligible potential aberration during the process of water splitting. The electrocatalytic performance of the prepared catalyst in a 1.0 M KOH solution exhibits admirable bifunctional activity and remarkable stability. In fact, it outperforms cobalt-based and carbon-supported electrocatalysts, including highly valued commercial catalysts like IrO2 and Pt@C. The solar cell configuration, utilizing the energetic bifunctional Co@NGC-800 electrocatalyst, can continuously generate hydrogen and oxygen. The overall water-splitting process of Co@NGC-800 catalyst delivered at a cell voltage of 1.68 V, enabling sustained and efficient oxygen and hydrogen evolution at a large scale.

Degradation of atrazine by N-doped graphitic carbon encapsulated Nickel-iron alloy via heterogeneous activation of peroxymonosulfate

Heterogeneous magnetic catalysts for peroxymonosulfate (PMS) activation that are used to degrade pollutants have attracted growing attention, and bimetallic alloy catalysts have excellent catalytic performance. In this study, nitrogen-doped graphite carbon encapsulated NiFe (NiFe@NC) alloy catalysts were synthesized using nickel-iron Prussian blue analog precursors to remove atrazine (ATZ) via the activation of PMS. The effects of various operating parameters (NiFe@NC dosage, PMS concentration, initial solution pH, and reaction temperature), and the effects of co-existing components were investigated. The synergistic catalysis of Ni and Fe gives NiFe@NC good catalytic properties. The NiFe@NC/PMS system achieved 100% removal of 10 mg L−1 ATZ was achieved in 30 min with an initial pH of 5.9; the TOF was 4.33 min−1, and the system exhibited resistance to interference from many co-existing substances. The graphite-carbon core-shell structure of NiFe@NC slowed down the leaching rate of metal ions and had good stability. Redox cycles in the system were achieved by facilitating the interaction between the transition metal and HSO5-, ensuring the continuous generation of reactive oxygen species. Ecotoxicity assessment showed that the toxicity level was significantly reduced after treatment. The total treatment cost of treating 1 m3 wastewater was lower than that of Fenton sludge catalyst. A continuous flow reactor was constructed to achieve continuous degradation of ATZ for long periods. This study expanded the application of PMS advanced oxidation technology by synthesizing an economical and recyclable magnetic catalyst and provided new insights for the removal of refractory organic matter.

Crystallinity and interfacial Mo–N–C bond engineered MoS2 embedded graphitic nitrogen doped carbon hollow sphere for enhanced HER activity

To restrain fossil fuel depletion, the need of the hour is the development of efficient, durable, and non-precious electrocatalysts for the hydrogen evolution reaction (HER). The hierarchical nanostructure consisting of transition metal dichalcogenides and graphitic heteroatom-doped carbon with an abundant interfacial M–N–C catalytic site is highly demanding for electrolytic applications. Herein, we report crystallinity-engineered ultrathin MoS2 nanosheets hierarchy over nitrogen-doped graphitic carbon (NC) hollow spheres as a promising material for HER. The well optimized NC@MoS2 demonstrates superior HER activity with a low onset overpotential of 9 mV and an overpotential of 145 mV at a current density of −10 mA cm−2. It exhibits low Tafel slope of 39 mV dec−1 and excellent chronoamperometric stability. Superior HER activity originates from interfacial Mo–N–C bonds. Density functional theory (DFT) calculations unveil that Mo–N–C bonds between MoS2 and NC matrix ease electronic transportation and further diminish Gibbs free energy for HER.

Transition metal nitrides embedded in N-doped porous graphitic Carbon: Applications as electrocatalytic sulfur host materials

While transition metal nitrides (TMNs) are promising electrocatalysts, their widespread use is challenged by the complex synthetic methodology and a limited understanding of the underlying electrocatalytic mechanisms. Herein, we describe a novel synthesis of TMNs (including Mo2N, NbN, and ZrN) and explore their potential as electrocatalysts to affect sulfur cathode reactions. The TMNs were prepared in-situ using a process that simultaneously infuses nitrogen-doped porous graphitic carbon (designated as TMN@N-PGC). The methodology avoids the use of ammonia, which poses safety risks due to its flammability and toxicity. Analysis of the d-p hybridized orbitals formed between the transition metal ions and sulfur species revealed that the antibonding orbitals are empty. Thus, TMNs with more negative d-band centers exhibit stronger affinities towards polysulfides. NbN facilitated polysulfide conversion as well as Li2S detachment, and thus featured a high electrocatalytic capability for promoting cathode kinetics. Lithium−sulfur (Li–S) batteries containing NbN@N-PGC exhibited the highest performance metrics in terms of specific capacity (1488 mA h g−1 at 0.1 C), rate capacity (521 mA h g−1 at 6 C), and cycling stability (603 mA h g−1 at 0.5 C after 1300 cycles, corresponding a capacity decay of 0.030% per cycle). Li−S cells with high sulfur loadings also exhibit outstanding performance.

Effects of peroxide types on the removal performance and mechanism of sulfonamide antibiotics using graphene-based catalytic membranes

This study reports in situ catalytic oxidation processes using graphene-based catalytic membranes to activate peroxydisulfate (PDS), peroxymonosulfate (PMS), and hydrogen peroxide (H2O2). Sulfonamide antibiotics in water, including sulfamethoxazole (SMX), sulfadiazine (SDZ), sulfamerazine (SMR), and sulfamethazine (SM2), were used as target pollutants. The composites of reduced graphene oxide and nitrogen-doped carbon nanotubes were loaded onto nylon microfiltration membranes at 8 g·m–2 mass dosage. The PDS-based systems exhibited the highest efficiency in removing SDZ (≥ 98%) and SMX (> 93%) during continuous 10 h filtration. In contrast, PMS was more suitable for oxidizing SMR (≥ 99%) and SM2 (≥ 90%) in a single pass. Based on functional group characterization and density functional theory calculations, structural defects and pyridinic/graphitic nitrogen species in carbon mats were identified as the main active centers for peroxide activation. Moreover, PDS, PMS and H2O2 exhibited distinct adsorption behaviors on defective and nitrogen-doped graphitic carbon, influencing the cleavage of peroxide bonds to generate reactive oxygen species. The reaction mechanism was investigated through electron paramagnetic resonance and chemical quenching tests. Surface-active species and singlet oxygen dominated in the PDS- and PMS-based systems, representing non-radical pathways, that selectively oxidize sulfonamides in real water matrices more effectively than the hydroxyl radicals involved in H2O2-based systems. PDS activating exhibited significant performance in organic fouling polishing, lowering the transmembrane pressure during continuous filtration. These findings offer valuable insights into implementing in situ catalytic oxidation processes in actual water purification.

Cobalt/Nitrogen Co-Doped Carbon Materials Enhance the Reaction Rate of Sodium-Potassium Alloy Electrodes.

Sodium-potassium (NaK) alloy electrodes are ideal for next-generation dendrite-free alkali metal electrodes due to their dendrite-free nature. However, issues such as slow diffusion kinetics due to the large K+ radius and the loss of active potassium during the reaction severely limit its application. Here a novel cobalt/nitrogen-doped carbon material is designed and it is applied to the construction of a NaK alloy electrode. The experimental and theoretical results indicate that the confining effect of the nitrogen-doped graphitic carbon layer can protect the cobalt nanoparticles from corrosion leaching, while the presence of Co─Nx bonds and cobalt nanoparticles provides more active sites for the reaction, realizing the synergistic effect of adsorption-catalytic modulation, lowering the K+ diffusion energy barrier and promoting charge transfer and ion diffusion. The application of this electrode to a symmetrical battery can achieve more than 1800 stable cycles under a current density of 0.4mA cm-2 and a charge/discharge specific capacity of 122.64 mAh g-1 under a current of 0.5C in a full battery. This finding provides a new idea to realize a fast, stable, and efficient application of NaK alloy electrodes.

Advanced Analytical Electron Microscopy Techniques for Probing Individual PGM-Free Catalyst Sites

Hydrogen fuel cells currently utilize expensive platinum group metal nanoparticles as catalysts [1]. To reduce the cost of catalyst materials, large efforts to develop viable platinum group metal-free (PGM-free) catalyst materials, which often consist of single transition metal atoms embedded in nitrogen-doped graphitic carbon structures, are being undertaken [2]. Given the atomic-scale nature of the metal sites in these materials, their performance and stability are highly dependent on the local coordination environment and consequently electronic structure of the sites [3]. A detailed understanding of the local elemental composition and lattice structure of individual sites, and how these properties vary between sites, is therefore needed to further develop improved PGM-free catalyst materials. While many bulk techniques are available that can provide average properties of these sites, such as Mössbauer and X-ray absorption spectroscopies, techniques with high spatial resolution are needed to measure the properties of individual sites. As a result, scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDS) has proven an invaluable tool for characterization of these materials due to its ability to probe structural and electronic properties at the atomic scale [4]. However, combined with the instability of many metal sites under the electron probe, the quantity and type of information accessible by conventional STEM instrumentation and acquisition methods is limited. To better understand the local coordination environment and electronic structure of individual sites, as well as how these properties vary site to site, new techniques and hardware are therefore needed.Here, we demonstrate advancements in STEM-EELS and -EDS that allow the quality and quantity of spectroscopic information obtained from individual sites to be significantly improved over conventional method. First, we demonstrate direct real-space mapping of metal sites by using a direct electron detector in the EELS spectrometer. This increases the data acquisition rate and signal-to-noise ratio sufficiently to map metal atom positions at the atomic scale. In addition, we show how automated metal atom position identification and subsequent probe positioning allow the rate at which metal sites are probed to be increased by another order of magnitude while simultaneously increasing the quantity of data obtained from each site. Using EELS and EDS signals acquired in parallel, this automated acquisition method enables a wide range of metal site elements to be identified, as well as the local coordination environment around the sites to be determined. Combined with electronic structure measurements of the metal atoms themselves, this technique provides significantly more information about individual sites than conventional methods. The techniques presented here are therefore poised to significantly improve our understanding of the local coordination environment and electronic structure of individual PGM-free metal sites, as well how these properties vary site to site, accelerating development of these low-cost hydrogen fuel cell catalyst materials [5].

Fabrication of N-doped graphitic carbon nanosheets via reaction between CaC2 and g-C3N4 as promising Li-ions battery anode

Nitrogen-doped carbon materials have attracted much attention for energy storage. Herein, we synthesize nitrogen-doped graphitic carbon nanosheets (NGCN) via a simple reaction between g-C3N4 and CaC2. The NGCN product integrates various features including high nitrogen content (3.98 at.%), large surface area (72.96 m2 g−1) and high graphitization degree (interplanar spacing, 0.335 nm). When served as anode material in Li-ions batteries, the NGCN exhibits a quite encouraging reversible capacity of 475 mAh g−1 at a current density of 500 mA g−1, with a capacity retention of 98.5 % after 1000 cycles. It also has an acceptable rate capability (238 mAh g−1 at 5000 mA g−1). This work promises an efficient route to convert sustainable carbon sources into nitrogen-doped graphitic carbon nanosheets with excellent electrochemical performances for energy storage.

Enhanced interfacial evaporation and desalination by solar heat localisation using nitrogenated graphitic carbon and Co3O4 nanorods

The problem of worldwide scarcity of clean water can be resolved efficiently by utilizing the significant heat localizing capability of the solar-driven interfacial evaporator with a nominal impact on the environment. A novel flexible, recyclable, hydrophilic photothermal composite membrane containing a blend of mesoporous Co3O4 nanorod and nanoporous nitrogen-doped graphitic carbon hollow spheres has been proposed. The composite membrane exhibits an enhanced broadband optical absorption which leads to a high interfacial evaporation rate (2.28 kg m−2 h−1) and a notable solar-to-steam generation efficiency (93%) under sunlight (900 W/m2) at 3.5 wt% NaCl salinity. The lower salt accumulation on the evaporation surface and the remarkable recyclability of the photothermal membrane under sunlight prove its practical usability in the desalination of seawater, water purification, salt production, and solar energy harvesting.

Fe-Co/Fe3C dual active sites catalysts supported on nitrogen-doped graphitic carbon for ultrafast degradation of high concentration Rhodamine B

Iron-based catalysts have garnered great attention as alternatives for Fenton-like catalysts in the degradation of organic compounds. However, there is a demand for the synthesis of highly efficient iron-based catalysts that can solve the problems of iron dissolution and poor stability. Herein, nitrogen-doped graphitic carbon-supported Fe-Co/Fe3C dual active sites catalyst (Fe-Co/Fe3C-NC) is successfully prepared by ball milling method combined with subsequent high-temperature self-reduction. 0.5 wt%-Fe-Co/Fe3C-NC shows high efficiency in the activation of peroxymonosulfate (PMS) for the ultrafast degradation of high concentration Rhodamine B (200 mg/L of RhB is completely degraded within 8 min and the degradation rate constant is as high as 0.5066 min−1), as well as high stability and good reproducibility, attributing to the synergistic mechanism between the dual active sites (Fe-Co and Fe3C) and the adsorption sites (Fe3C and pyrrolic-N). Chemical quenching experiments and electron paramagnetic resonance indicate that the prepared 0.5 wt%-Fe-Co/Fe3C-NC exhibits outstanding activation for PMS by generating reactive oxygen species (SO4•−, •OH, 1O2) and high-valent FeCo=O species. This work shows useful insights into the synthesis of iron-based dual active sites catalysts, providing exciting chances for the highly efficient degradation of high concentration organic wastewater.

3D Porous Oxygen-Doped and Nitrogen-Doped Graphitic Carbons Derived from Metal Azolate Frameworks as Cathode and Anode Materials for High-Performance Dual-Carbon Sodium-Ion Hybrid Capacitors.

Sodium-ion hybrid capacitors (SIHCs) in principle can utilize the advantages of batteries and supercapacitors and satisfy the cost demand of large-scale energy storage systems, but the sluggish kinetics and low capacities of its anode and cathode are yet to be overcome. Here, a strategy is reported to realize high-performance dual-carbon SIHCs using 3D porous graphitic carbon cathode and anode materials derived from metal-azolate framework-6s (MAF-6s). First, MAF-6s, with or without urea loading, are pyrolyzed to synthesize MAF-derived carbons (MDCs). Then, cathode materials are synthesized via the controlled KOH-assisted pyrolysis of MDCs (K-MDCs). K-MDCs, 3D graphitic carbons, resulting in a record-high surface area (5214m2 g-1 ) being ≈four-fold higher than pristine MAF-6, oxygen-doped sites for high capacity, rich mesopores affording fast ion transport, and high capacity retention over 5000 charge/discharge cycles. Moreover, 3D porous MDC anode materials are synthesized from N-containing MAF-6 and exhibited to allow cycle stability over 5000 cycles. Furthermore, dual-carbon MDC//K-MDC SIHCs with different loadings (3 to 6mgcm-2 ) are demonstrated to achieve high energy densities exceeding those of sodium-ion batteries and supercapacitors. Additionally, it allows an ultrafast-chargeable high power density of 20000Wkg-1 and robust cycle stability overcoming those of a typical battery.

Three-dimensional hierarchically porous micro sponge-ball comprising anatase TiO2 nanodots and nitrogen-doped graphitic carbon as anodes for ultra-stable lithium-ion batteries

Hierarchically porous three-dimensional micro sponge-balls comprising highly conductive nitrogen-doped graphitic carbon (NGC) and anatase-type TiO2 nanodots (TiO2@NGC MSB) are synthesized using spray pyrolysis technique followed by heat treatment. The as-sprayed powders obtained after spray pyrolysis consist of polystyrene (PS) nanobeads-derived macropores and anatase TiO2 nanodots embedded in an amorphous carbon (AC)-NGC carbon matrix (TiO2@NGC-AC MSB). The subsequent heat treatment of the as-sprayed powders at 300 °C resulted in the formation of additional micropores by selective removal of the AC into gaseous products to form TiO2@NGC MSB. The obtained hierarchically porous and highly conductive architecture guarantees effective electrolyte infiltration inside the electrode, enhanced Li-ion diffusion, and faster charge transfer during the redox reactions. Benefited from the structural merits, the TiO2@NGC MSB anode exhibits remarkable electrochemical performance compared to those of TiO2@NGC-AC MSB and filled-type TiO2 anodes. A reasonable discharge capacity of 105 mA h g−1 at a high current density of 10.0 A g−1 and exceptional cycling performance (219 mA h g−1 with 0.0006 % decay rate after 2000 cycles at 2.0 A g−1 and 160 mA h g−1 with 0.003 % decay rate after 5000 cycles at 3.0 A g−1) are obtained.

Photocatalytic hydrogen under visible light by nitrogen-doped rutile titania graphitic carbon nitride composites: an experimental and theoretical study

Photocatalytic hydrogen under visible light by nitrogen-doped rutile titania graphitic carbon nitride composites: an experimental and theoretical study

Fabrication of Naturally Derived Chitosan and Ilmenite Sand-Based TiO2/Fe2O3/Fe-N-Doped Graphitic Carbon Composite for Photocatalytic Degradation of Methylene Blue under Sunlight

Fabrication of chitosan and ilmenite sand-based novel photocatalysts through the catalytic graphitization of chitosan is reported. Nanocomposites consisted of TiO2, Fe2O3 and Fe nanoparticles dispersed on a nitrogen-doped graphitic carbon framework. The surface area, pore volume and macropore structure of the carbon matrix is disturbed by the heterogeneously distributed nanoparticles. The extent of graphitization expanded with increasing metal loading as indicated by variation in the ID/IG ratio. The nanomaterial's surface consists of Fe3+ and Ti4+, and graphitic, pyridinic and pyrrolic nitrogen were found in the carbon matrix. The band gap values of the composites varied in the 2.06-2.26 eV range. The photocatalytic activity of the synthesized nanomaterials was determined, and the highest rate constant for the photodegradation of methylene blue under sunlight was 4.4 × 10-3 min-1, which resulted with 10 mg/L MB and 25 mg of the best-performing catalyst. The rate constant rose with increasing concentrations of persulfate added to the medium. The rate constant greatly diminished with the addition of isopropyl alcohol as it scavenged hydroxyl radicals. The presence of co-pollutants including Pb2+, rhodamine B, PO43- and Cl- curtailed the rate of reaction. The activity reduced with an increasing number of uses of the catalyst.

Templated Synthesis of Exfoliated Porous Carbon with Dominant Graphitic Nitrogen

We present here a new approach for the synthesis of nitrogen-doped porous graphitic carbon (g-NC) with a stoichiometry of C6.3H3.6N1.0O1.2, using layered silicate as a hard sacrificial template. Autogenous exfoliation is achieved due to the heterostacking of 2D silicate and nitrogen-doped carbon layers. Micro- and meso-porosity is induced by melamine and cetyltrimethylammonium (C16TMA). Our density functional calculations and X-ray photoelectron spectroscopy (XPS) observations confirm that the most dominant nitrogen configuration in g-CN is graphitic, while pyridinic and pyrrolic nitrogens are thermodynamically less favored. Our large-scale lattice dynamics calculations show that surface termination with H and OH groups at pores accounts for the observed H and O in the composition of the synthesized g-NC. We further evaluate the electrocatalytic and the supercapacitance activities of g-NC. Interestingly, this material exhibits a specific capacitance of ca. 202 F g–1 at 1 A g–1, retaining 90% of its initial capacitance after 10,000 cycles.

Nitrogen-Doped Graphitic Carbon Dots Embedded in Carbon Nitride Scaffolds for Water Decontamination

Functionalized carbon dots (CDs) exhibit intriguing photo-exciton dynamics. CDs can donate or accept electrons depending on their functional groups and electrostatic characteristics. We exploited the electron-accepting capability of nitrogen-doped graphitic carbon dots (N-g-CDs) to improve the charge-carrier separation of the polymeric carbon nitride (PCN) photocatalyst. l-Aspartic acid pyrolyzed at 320 °C yielded ∼25 nm size N-g-CDs that were embedded with PCN. The in-plane infiltration of nanosized N-g-CDs increased the surface area of PCN from 11.5 to 104.9 m2 g–1. The N-g-CDs/PCN hybrid catalyst tested for photocatalytic chromium reduction evidenced about a 3-fold higher rate than PCN. Also, the antibiotic tetracycline and rhodamine B dye rapidly degraded with faster degradation kinetics. The carrier dynamic analysis and computational investigations suggest that the electron acceptor feature of N-g-CDs governs the effective separation of photo-excitons and the high surface area of N-g-CDs/PCN contributes to photoactivity enhancement. This study offers insights into designing high-performance metal-free photocatalysts for water treatment applications.

Boosting Oxygen Electrocatalytic Activity of Fe-N-C Catalysts by Phosphorus Incorporation.

Nitrogen-doped graphitic carbon materials hosting single-atom iron (Fe-N-C) are major non-precious metal catalysts for the oxygen reduction reaction (ORR). The nitrogen-coordinated Fe sites are described as the first coordination sphere. As opposed to the good performance in ORR, that in the oxygen evolution reaction (OER) is extremely poor due to the sluggish O-O coupling process, thus hampering the practical applications of rechargeable zinc (Zn)-air batteries. Herein, we succeed in boosting the OER activity of Fe-N-C by additionally incorporating phosphorus atoms into the second coordination sphere, here denoted as P/Fe-N-C. The resulting material exhibits excellent OER activity in 0.1 M KOH with an overpotential as low as 304 mV at a current density of 10 mA cm-2. Even more importantly, they exhibit a remarkably small ORR/OER potential gap of 0.63 V. Theoretical calculations using first-principles density functional theory suggest that the phosphorus enhances the electrocatalytic activity by balancing the *OOH/*O adsorption at the FeN4 sites. When used as an air cathode in a rechargeable Zn-air battery, P/Fe-N-C delivers a charge-discharge performance with a high peak power density of 269 mW cm-2, highlighting its role as the state-of-the-art bifunctional oxygen electrocatalyst.