N-doped Graphitic Carbon Research Articles

Fe3O4 encapsulated in hierarchically porous nitrogen-doped graphitic carbon layers for efficient oxygen reduction reaction: Enhanced intrinsic activity via directional interfacial charge transfer

Constructing efficient electrocatalysts for the oxygen reduction reaction (ORR) is crucial for the commercialization of metal-air batteries. Iron oxide-based catalysts exhibit promising potential for ORR. However, addressing the issue of inferior catalytic performance is essential, and a comprehensive understanding of the catalytic mechanism of iron oxide-based catalysts is also lacking. In this study, we present Fe3O4 nanoparticles encapsulated in N-doped graphitic carbon layers (NGC) hosted by hierarchically porous carbon (Fe3O4@NGC), achieved through a facile dual melt-salt template strategy. The encapsulation of Fe3O4 nanoparticles protects them from corrosion and exfoliation, endowing the catalysts with superior stability. Density functional theory (DFT) calculations discover that the electronic interaction between Fe3O4 nanoparticles and N-doped graphitic carbon layers induces directional interfacial electron transfer, which effectively modulates the surface electronic structure to improve the binding ability to O2, weaken the OO bond, and optimize the adsorption of intermediates, thus boosting the intrinsic activity. DFT unveils that the C atoms nearest to graphitic-N in NGC are active sites. Finally, the synergistic effects of Fe3O4 nanoparticles and NGC result in outstanding ORR performance and superior stability and methanol tolerance of Fe3O4@NGC, with a half-wave potential of 0.89 V, surpassing that of Pt/C by 50 mV. Fe3O4@NGC also shows better performance than Pt/C when used as the air-electrode catalyst in zinc-air battery.

Iron nanoparticle engineered N-doped graphitic carbon composite as a binary electrocatalyst for overall water splitting and supercapacitor

In this study, we report on the tailored synthesis of nitrogen-(N)-doped carbon and iron-(Fe)-loaded N-doped carbon composites and their use for the oxygen evolution reaction (OER), hydrogen evolution reaction (HER), overall electrochemical water splitting, and supercapacitors. FE-SEM and HR-TEM analyses reveal that the developed composite material exhibits a core-shell structure with enhanced porosity upon Fe incorporation. By adjusting the ratio of Fe to N-doped carbon in the composites, it was identified that the catalyst 5Fe@NC demonstrates outstanding electrochemical activity alongside commendable stability. Specifically, the 5Fe@NC electrocatalyst achieves current densities of +10 mAcm−2 and -10 mAcm−2 in alkaline electrolyte with minimal overpotentials of 376 mV and 520 mV, respectively. Notably, impressive Tafel slopes of 84 mV/dec and 212 mV/dec for the OER and HER were obtained, indicating superior kinetic activity of the developed composite materials. As a supercapacitor, 5Fe@NC electrode material exhibits a measurable specific capacitance of 294 F/g at 0.5 A/g current density with excellent durability (78 % retention after 1000 charge-discharge cycles). Furthermore, we conducted assessments on stability, charge transfer resistance, and ECSA, yielding excellent outcomes. This work successfully demonstrates a highly effective dual-purpose electrocatalyst prepared from indole and furfural (heterocycles abundant in biomass), exhibiting excellent electrochemical activity and stability in facilitating HER and OER within alkaline electrolytes.

Vertically-stacked W/W2C heterojunctions with high electrocatalytic capability for the hydrogen evolution reaction in a wide pH range

The hydrogen evolution reaction (HER) in water splitting is among the foremost methods to produce clean and green hydrogen from renewable sources. The practical use of the HER technology is however hindered by the high price and/or the relatively low efficiency of the currently used catalysts. Herein, we report a heterostructured W/W2C electrocatalyst featuring vertically stacked interfaces and embedded in N-doped porous graphitic carbon (denoted as W/W2C@N-PGC) as a high-performance electrocatalyst for the HER in a wide pH range. The catalyst synthesis, accomplished through a straightforward one-pot method, is both facile and highly efficient, involving freeze-drying a suspension of the starting materials followed by pyrolyzing the obtained dry gel. Density functional theory calculations revealed the crucial role of the W/W2C heterojunction in promoting the two key steps of the HER, viz. HOH bond scission and H2 emission. Electrochemical data confirmed the excellent electrocatalytic capability of W/W2C@N-PGC toward the HER process in a wide pH range including alkaline, acidic, and neutral electrolytes. In 1.0 M KOH, we measured a low overpotential of 102 mV to drive a current density of 10 mA cm−2; a long-term stability (up to 24 h) was also realized. The data presented in this work highlight the importance of electrocatalysts with heterojunctions for the HER and the methodology presented in this work may be extended to other contemporary energy-related technologies such as CO2 reduction, oxygen evolution, and oxygen reduction reactions.

A Dual-Carbon Potassium-Ion Capacitor Enabled by Hollow Carbon Fibrous Electrodes with Reduced Graphitization.

The large size of K+ ions (1.38 Å) sets a challenge in achieving high kinetics and long lifespan of potassium storage devices. Here, a fibrous ZrO2 membrane is utilized as a reactive template to construct a dual-carbon K-ion capacitor. Unlike graphite, ZrO2-catalyzed graphitic carbon presents a relatively disordered layer arrangement with an expanded interlayer spacing of 0.378nm to accommodate K+ insertion/extraction. Pyridine-derived nitrogen sites can locally store K-ions without disrupting the formation of stage-1 graphite intercalation compounds (GICs). Consequently, N-doped hollow graphitic carbon fiber achieves a K+-storage capacity (primarily below 1V), which is 1.5 time that of commercial graphite. Potassium-ion hybrid capacitors are assembled using the hollow carbon fiber electrodes and the ZrO2 nanofiber membrane as the separator. The capacitor exhibits a high power of 40 000 W kg-1, full charge in 8.5 s, 93% capacity retention after 5000 cycles at 2 A g-1, and a low self-discharge rate of 8.6mV h-1. The scalability and high performance of the lattice-expanded tubular carbon electrodes underscores may advance the practical potassium-ion capacitors.

Ni-incorporated N-doped graphitic carbon derived from pomegranate peel biowaste as an efficient OER and HER electrocatalyst for sustainable water splitting

The electrochemical energy conversion process must develop effective, long-lasting, and reasonably priced bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this work, we present a simple, sustainable, economical, and scalable method for the preparation of stable and useful nickel nanoparticles on highly porous graphitic carbon doped with nitrogen. Direct pyrolysis followed by carbonization was used to create robust catalysts at different temperatures in an environment containing nitrogen (N2). The carbon material generated at 600 °C (Ni@NPC-600) shows greater electrochemical efficiency when compared to other catalysts. The synthesized electroactive catalyst Ni@NPC-600 requires a less overpotential 280 mV (114 mV dec−1) for OER and 151 mV (98 mV dec−1) to conduct a HER at 10 mA cm−2 in 1 M KOH. The active catalyst Ni@NPC-600 shows long-lasting robustness over 90 h with a current loss of <3.33 % and <4.9 % for OER and HER respectively. In addition, the overall water disintegration of Ni@NPC-600/NF//Ni@NPC-600/NF was achieved at 1.51 V with a continuous evolution of H2 and O2 at the cathode and anode respectively for approximately 150 h of prolonged robustness with a current reduction of < 4.6 %.

MoC nanoparticles embedded in superior thin g-C3N4 nanosheets for efficient photocatalytic activity

Photogenerated charge carrier transfer efficiency in graphitic carbon nitride (g-C3N4) based heterostructures depended strongly on the interface nature. In this paper, MoC nanoparticles less than 5 nm were implanted in superior thin g-C3N4 nanosheets to create high charge carrier separation and transfer efficiency. Cubic MoC in N-doped graphitic carbon was first fabricated using dicyandiamide and ammonium molybdate tetrahydrate at 800 °C. The MoC nanoparticles were homogeneously implanted in g-C3N4 nanosheets by further thermal polymerization of bulk g-C3N4 prepared using melamine and MoC/C composites to create a Schottky junction which was confirmed by band gap analysis and free radical capture test. Melamine and dicyandiamide also play important role to create highly efficient catalysts. The MoC nanoparticles revealed fine crystallinity. A well-developed interface between MoC and g-C3N4 was observed. Because of high conductivity of MoC, well-developed interface, and co-catalyst role of MoC, the MoC/g-C3N4 junction exhibited ideal photocatalytic activity for dye degradation and water splitting. The kinetic constant rate of Rhodamine B degradation using a MoC/g-C3N4 sample created by optimized conditions was 0.061 min−1 which was 8.7 times of that of pristine g-C3N4 nanosheets. In the case of without co-catalyst addition, the photocatalytic hydrogen generation rate using this composite sample was 233.0 μmol g−1 h−1 which was 15.2 times of that of initial g-C3N4 nanosheets. These results supply an efficient approach for the first time to homogeneously distribute small cubic MoC nanoparticles in superior thin g-C3N4 nanosheets to construct heterostructures and greatly reduce photogenerated charge carrier recombination.

Boosting the electrocatalytic overall water splitting performance by synergistically coupling N-doped delaminated niobium carbide MXene and N-doped graphitic carbon

A robust trifunctional electrocatalyst based on N-doped delaminated niobium carbide (N-Nb4C3Tx) nanosheets encapsulated by N-doped graphitic carbon (NGC) (abbreviated as N-Nb4C3Tx/NGC) is synthesized, which exhibits a low overpotentials of 96 and 291 mV at 10 mA cm−2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. The superior electrocatalytic performance can be attributed to the synergetic effect of the highly conductive N-Nb4C3Tx and doping of the high-content NGC. The introduction of N species plays an important roles of generating graphitic N-doped carbon species and anchoring N in the carbon matrix, which further boost the electrocatalytic activity. The structure properties and nitrogen content of MXene were regulated by the mass ratio of Nb4C3Tx to hexamethylenetetramine (HMTA). These results indicate that the method of synergistically coupling N-Nb4C3Tx and NGC can boost the HER, OER, and overall water splitting performance, providing a new strategy for the development of economical and efficient MXene based electrocatalysts.

One single-atom Mn doping strategy enabling two functions of oxygen reduction reaction and pseudocapacitive performance

Single-atom metal species as highly effective active sites are crucial for enhancing energy storage and conversion properties. However, achieving the simultaneous construction of single-atom sites and the regulation of matrix structures to enable their application in both energy storage and conversion remains a challenge. Here, we have successfully developed unique MnN2C2 active sites, atomically dispersed on N-doped mesoporous graphitic carbon sheets (MnSAs/NMC). This is accomplished through the strategic utilization of MnCl2 salt, which serves dual roles of a pore-forming agent and a template. The MnSAs/NMC catalyst demonstrates compelling electrocatalytic activity for the oxygen reduction reaction (ORR), with an impressive half-wave potential (E1/2 = 0.90 V), alongside superior capacitance reaching 444 F g-1 at 0.5 A g-1 for supercapacitors. Crucially, both experimental and theoretical simulations validate that the single-atom dispersed MnN2C2 optimizes the adsorption energy of reactants and intermediates in the ORR process and pseudocapacitive behavior, leading to excellent ORR activity and capacitive performance. Interestingly, MnSAs/NMC-based Zn-air batteries exhibit concurrently high-power density derived from capacitive property and high energy density enhanced by ORR process. This study presents a novel preparation method for single-atom catalysts, which paves the way for the commercial application of super energy storage and conversion devices.

Pyrolysis of folic acid: Identification of gaseous/volatile products and structural evolution of N-doped graphitic carbon

Folic acid (FA) is a low-cost and suitable source for producing different N-doped carbon materials by pyrolysis. However, the pyrolytic steps of FA are not entirely understood, particularly above 350 °C, which hampers the intelligent design of tailor-made carbon materials by a one-pot route. In this work, the pyrolytic decomposition steps of FA were investigated by simultaneous thermogravimetric analysis (TGA) and differential scanning calorimetry (TGA-DSC). The released gaseous/volatile products were probed by coupling TGA to infrared spectroscopy and mass spectrometry (TGA-FTIR-MS). Considering the thermal analysis data, FA was pyrolysed in a furnace at 350, 430, 570, 800, and 1000 °C, and the products were analysed by X-ray diffractometry (XRD), vibrational spectroscopy, and X-ray photoelectron spectroscopy. In situ high-temperature X-ray diffractometry (HT-XRD) experiments were also conducted under the nitrogen atmosphere. According to the data set, insights about FA decomposition steps could be proposed, including gaseous/volatile products released during the process and the structural evolution of N-doped graphitic carbon. The formation of carbonaceous material initiated between 200 and 350 °C through polymerisation/condensation reactions, and this step was marked by the release of 2-pyrrolidone and aniline. The graphitisation was enhanced above 350 °C, increasing graphitic nitrogen while the amide groups vanished. The process was accompanied by deoxygenation (i.e., CO and CO2 release) and denitrogenation (e.g., NH3, HNCO, and HCN) reactions. In the 570–800 °C range, the N-enrichment of carbon material (N-pyridine, N-pyrrole/Csp2-N in 5,7-membered rings, and nitrile) could occur by the reaction of released NH3 over the char surface. Graphitic-like structures containing mainly N-graphite and N-pyridine were obtained above 800 °C. The original data about the thermal decomposition steps of FA allow for optimising the synthesis of N-doped carbon materials suitable for applications in adsorption, sensing, catalysis, and energy storage.

Pyrolytic conversion of nylon-6 and red mud into N-doped carbon composite and its application into azo-dye degradation

The continuous growth of the global population and industries has led to the mass generation of plastic and industrial waste, posing significant environmental challenges due to their incompatibility with conventional waste management practices. This study investigates the thermochemical conversion of plastic (nylon-6) and industrial waste (red mud) into value-added products, presenting a waste-to-resource conversion strategy. Nylon-6 and red mud were co-pyrolyzed, resulting in a metal-carbon composite characterized as porous N-doped graphitic carbon with embedded Fe0 particles. Application of the composite to an amaranth solution demonstrated its ability to activate persulfate, facilitating amaranth oxidation at a rate (kobs = 1.78 min−1) significantly higher than other Fe-based catalysts. Quenching experiments verified the generation of OH· and SO4·- radicals during activation, with the latter playing a dominant role in amaranth degradation. The composite exhibited robust reusability, maintaining an amaranth removal efficiency of >80 % after five reaction cycles. Additionally, red mud significantly enhanced syngas (H2 and CO) generation from nylon-6, suggesting a catalytic effect. In conclusion, the proposed thermochemical approach offers a viable method for converting waste materials into valuable products, including environmental catalysts and gas fuels.

Size tuning of vanadium nitride particles from atomic to micron level as efficient catalysts for zinc-air battery

Transition metal nitrides present superior electrocatalytic activities on the air electrode for fuel cells or metal-air batteries. Despite that, the weak intrinsic activity and ease of aggregation have hampered their catalytic kinetic properties and practical application. Herein, vanadium nitride (VN) particles of different sizes, micron to molecular level, have been fabricated using a facile, in-situ urea-nitridation method, and embedded in an N-doped graphitic carbon aerogel electrocatalyst (VN@CA), the doped material serving as an oxidation catalyst. Having a balance of atomic-level dispersed VN clusters and a high active site density, the obtained VN@CA catalytic material exhibits enhanced catalytic efficiency for the oxygen reduction reaction (ORR), the values of onset and half-wave voltages were measured to be 0.97 V and 0.90 V, respectively, compared to Pt/C (which had voltages of 0.95 V and 0.87 V). Furthermore, the assembled Zn-air battery using VN@CA as catalyst exhibits a high-power density of 176 mW cm−2, a substantial specific discharge capacity of 851 mAh gZn−1 at 20 mA cm−2, a narrow gap between charging and discharging voltages (0.73 V at 50 mA cm−2), and an excellent charge-discharge cycling stability, exceeding 270 cycles with a 66 % round-trip efficiency. This work confirms that the particle size and the density both are responsible for the enhanced electrochemical activity.

Prussian blue analogue derived porous hollow nanocages comprising polydopamine-derived N-doped C coated CoSe2/FeSe2 nanoparticles composited with N-doped graphitic C as an anode for high-rate Na-ion batteries

CoFe-Prussian blue analogue (CoFe-PBA) templated N-doped graphitic carbon (NGC) and polydopamine-derived carbon (PDA-20) double-coated CoSe2/FeSe2 nanoparticles are introduced as anodes for highly efficient sodium-ion batteries (SIBs). These nanoparticles are encapsulated within porous hollow nanocages, which exhibit remarkable stability in cyclic performance. The synthesis method involved co-precipitation, followed by PDA coating at varying concentrations and a subsequent selenization process. This resulted in the creation of (Co,Fe)Se-NGC nanocages, (Co,Fe)Se-NGC@PDA-20 hollow nanocages, and (Co,Fe)Se-NGC@PDA-100 filled nanocages. This strategic preparation approach leverages the synergistic effects of dual carbon coating, resulting in highly conductive and porous nanostructures. These structures facilitate rapid charge species diffusion, efficient electrolyte infiltration, and effective management of volumetric changes. When used as anodes for SIBs, the (Co,Fe)Se-NGC@PDA-20 hollow nanocages demonstrate impressive structural robustness and high-rate performance. They exhibit remarkable structural integrity, maintaining stable cycling performance for up to 200 cycles at 0.5 and 1.0 A g−1. In terms of rate capability, the hollow nanocages exhibit a high discharge capacity of 126 mA h g−1 at 10 A g−1. This clearly highlights the structural advantages of the prepared hollow nanocages.

Active Sites of Mixed-Metal Core-Shell Oxygen Evolution Reaction Catalysts: FeO4 Sites on Ni Cores or NiN4 Sites in C Shells?

Water electrolysis for clean hydrogen production requires high-activity, high-stability, and low-cost catalysts for its particularly sluggish half-reaction, the oxygen evolution reaction (OER). Currently, the most promising of such catalysts working in alkaline conditions is a core-shell nanostructure, NiFe@NC, whose Fe-doped Ni (NiFe) nanoparticles are encapsulated and interconnected by N-doped graphitic carbon (NC) layers, but the exact OER mechanism of these catalysts is still unclear, and even the location of the OER active site, either on the core side or on the shell side, is still debated. Therefore, we herein derive a plausible active-site model for each side based on various experimental evidence and density functional theory calculations and then build OER free-energy diagrams on both sides to determine the active-site location. The core-side model is an FeO4-type (rather than NiO4-type) active site where an Fe atom sits on Ni oxide layers grown on top of the core surface during catalyst activation, whose facile dissolution provides an explanation for the activity loss of such catalysts directly exposed to the electrolyte. The shell-side model is a NiN4-type (rather than FeN4-type) active site where a Ni atom is intercalated into the porphyrin-like N4C site of the NC shell during catalyst synthesis. Their OER free-energy diagrams indicate that both sites require similar amounts of overpotentials, despite a complete shift in their potential-determining steps, i.e., the final O2 evolution from the oxophilic Fe on the core and the initial OH adsorption to the hydrophobic shell. We conclude that the major active sites are located on the core, but the NC shell not only protects the vulnerable FeO4 active sites on the core from the electrolyte but also provides independent active sites, owing to the N doping.

Iron carbide anchored on N-doped hierarchically porous carbon core/shell architecture for highly efficient OER water splitting

Metal-nitrogen-carbon complexes are emerging as efficient electrocatalysts for the oxygen evolution reaction (OER) owing to the excellent activity, stability, natural abundance, and cost-effectiveness of these complexes. This study introduces an innovative approach to synthesizing an N-doped porous graphitic carbon with a Fe3C core-shell structure (N-PGC@Fe3C) using biomass-derived carbon. Characterized by a large specific surface area of 3169 m2/g and hierarchical mesoporosity, the synthesized N-PGC@Fe3C catalysts demonstrate superior OER activity, achieving low overpotentials of 143.8 and 312.2 mV at current densities of 20 and 50 mA/cm2, respectively, in a 1 M KOH electrolyte. Notably, the N-PGC@Fe3C-3 exhibits outstanding cycle performance after 2000 cycles. Density functional theory calculations confirm that the core-shell-structured N-PGC@Fe3C provides the primary active site for the OER. The observed efficiency is attributed to the synergistic action of the Fe–N–C active sites, ultrafine Fe3C encapsulation, and the hierarchical porous nanosheet structure that facilitates mass diffusion and increases the exposure of active sites. Furthermore, when employed as an anode during overall water splitting, N-PGC@Fe3C achieves a cell voltage of 1.49 V at a current density of 10 mA/cm2 under alkaline conditions. This study can facilitate the development of high-performance Fe–N–C-based catalysts and clarify the underlying OER mechanisms, thereby advancing the field of electrocatalytic water splitting and energy storage systems.

Bimetallic Ni–Fe nanoparticles encapsulated with biomass-derived N-doped graphitic carbon core-shell nanostructures an efficient bifunctional electrocatalyst for enhanced overall seawater splitting and human urine electrolysis

Producing green hydrogen from abundant natural resources such as seawater and human urine is a viable solution for energy and industrial applications. However, the field of electrocatalysis faces challenges in developing cost-effective metal catalysts for efficient electrolysis of seawater and urea sewage. Here, we reported bimetallic NiFe nanoparticles encapsulated in a biomass derived N-doped graphitic carbon core shell structure (NiFe@BNGC-700) as a stable and effective catalyst for seawater and human urine electrolysis. NiFe@BNGC-700 exhibits remarkable electrocatalytic performance, with a low overpotential requiring 300 mV for OER and 297 mV for HER in alkaline 1.0 M KOH + seawater and 1.36 V for UOR in alkaline 1.0 M KOH + human urine at 50 mA cm−2 current density, respectively. The active bifunctional NiFe@BNGC-700 electrocatalyst symmetry pair facilitates the construction of a seawater electrolyser, achieving a cell voltage of 1.74 V at 50 mA cm−2 current density. Furthermore, the human urine-mediated electrolyser employing NiFe@BNGC-700//NiFe@BNGC-700 achieves a cell voltage of 1.64 V at the same current density, maintaining stability over 12 h with negligible potential deviation. Continual evolution of hydrogen and oxygen is feasible in a solar seawater a cell assembled with NiFe@BNGC-700 electrocatalyst, delivering at cell voltage of 1.74 V, enabling sustained and effective green hydrogen delivery on a large scale. This study proposes a sustainable strategy for fabricating electrodes consisting of non-precious metals, thereby permitting the economical and extensive generation of green hydrogen on a large scale.

Prussian Blue Analogue Derived N-Doped Graphitic Carbon Wrapped Iron-Cobalt Nanoparticles as Recyclable Heterogeneous Catalysts for Friedel-Crafts Acylation

Prussian Blue Analogue Derived N-Doped Graphitic Carbon Wrapped Iron-Cobalt Nanoparticles as Recyclable Heterogeneous Catalysts for Friedel-Crafts Acylation

Fabrication of N-doped graphitic carbon encapsulated Fe3C/Fe nanoparticles with dual-reaction centers for highly effective Fenton-like degradation of organic pollutants

The highly active and durable design of heterogeneous catalysts holds vital importance in the popularization of Fenton-like process for wastewater remediation. In this study, we successfully fabricated magnetic N-doped graphitic carbon (NC) encapsulated Fe3C/Fe nanoparticles, designated as Fe3C/Fe@NC-2.8, with a two-step pyrolysis method. We employed chitosan as a green precursor of NC, which is used as a heterogeneous Fenton-like catalyst to degrade refractory organic pollutants. Density functional theory (DFT) calculations revealed that the built-in electric field from the shell to core promoted electron transfer from NC to Fe3C/Fe, and thereby improved regeneration of Fe(II) and H2O2 activation. Because of the strong synergistic effects of the dual-reaction regions of Fe and Fe3C, as well as the core-shell structure advantages, the optimized Fe3C/Fe@NC rapidly degraded the typical refractory organic pollutants, and showed a much higher activity than the reference Fe2O3 and Fe3O4 samples. The total organic carbon removal efficiency of bisphenol A reached 70 % after reaction for 60 min. In addition, Fe3C/Fe@NC-2.8 possessed trace Fe leaching and satisfactory magnetically separable ability. This work provides mechanistic and practical perspectives for the development of advanced catalysts for recalcitrant pollutant treatment.

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.

Hierarchical porous nanofibers comprising N-doped graphitic C and ZIF-8 derived hollow N-doped C nanocages for long-life K-ion battery anodes

Hierarchical porous carbon nanofibers (NFs) are designed via electrospinning, followed by simple carbonization, and applied as the anode for K-ion batteries (KIBs). The carbonization process is optimized to simultaneously satisfy sufficient graphitization of polyacrylonitrile (PAN)-derived soft carbon and complete conversion of zeolitic imidazolate framework-8 (ZIF-8) to hollow N-doped C nanocages. The prepared NFs through an optimized carbonization consists of porous and hollow N-doped C nanocages, which are encapsulated within the conductive graphitic carbon (GC) matrix, that acts as an efficient electron transport pathway. Moreover, the interconnected porous and hollow nanocages ensure a high contact area between the electrode and electrolyte and reduces the K-ion diffusion length. The N-doped GC with high electrical conductivity in the structure demonstrates reinforcing structural integrity as well as providing additional transport pathways for the unique electron transport. Therefore, the hierarchical porous carbon NFs show outstanding energy storage properties, such as stable cycle performance up to 10,000 cycles at the high current density of 1.0 A g-1 with high areal loading mass (1.8–1.9 mg cm−2) of the active material, which clearly suggests the structural advantages of the nanostructure introduced in this study.

Nanometric Cu-ZnO Particles Supported on N-Doped Graphitic Carbon as Catalysts for the Selective CO2 Hydrogenation to Methanol.

The quest for efficient catalysts based on abundant elements that can promote the selective CO2 hydrogenation to green methanol still continues. Most of the reported catalysts are based on Cu/ZnO supported in inorganic oxides, with not much progress with respect to the benchmark Cu/ZnO/Al2O3 catalyst. The use of carbon supports for Cu/ZnO particles is much less explored in spite of the favorable strong metal support interaction that these doped carbons can establish. This manuscript reports the preparation of a series of Cu-ZnO@(N)C samples consisting of Cu/ZnO particles embedded within a N-doped graphitic carbon with a wide range of Cu/Zn atomic ratio. The preparation procedure relies on the transformation of chitosan, a biomass waste, into N-doped graphitic carbon by pyrolysis, which establishes a strong interaction with Cu nanoparticles (NPs) formed simultaneously by Cu2+ salt reduction during the graphitization. Zn2+ ions are subsequently added to the Cu-graphene material by impregnation. All the Cu/ZnO@(N)C samples promote methanol formation in the CO2 hydrogenation at temperatures from 200 to 300 °C, with the temperature increasing CO2 conversion and decreasing methanol selectivity. The best performing Cu-ZnO@(N)C sample achieves at 300 °C a CO2 conversion of 23% and a methanol selectivity of 21% that is among the highest reported, particularly for a carbon-based support. DFT calculations indicate the role of pyridinic N doping atoms stabilizing the Cu/ZnO NPs and supporting the formate pathway as the most likely reaction mechanism.