Graphitic Carbon Nitride (g-C3N4)-Derived Bamboo-Like Carbon Nanotubes/Co Nanoparticles Hybrids for Highly Efficient Electrocatalytic Oxygen Reduction

Design of a new Ni@NCNT/graphene hybrid structured catalyst for high-performance electrochemical CO2 reduction: unravelling the roles of N-doping

Doping strategies have been recognized as effective approaches for developing cost-effective and durable catalysts with enhanced reactivity and selectivity in the electrochemical synthesis of value-added compounds directly from CO2. However, the reaction mechanism and the specific roles of heteroatom doping, such as N doping, in advancing the CO2 reduction reaction are still controversial due to the lack of precise control of catalyst surface microenvironments. In this study, we investigated the effects of N doping on the performances for electrochemically converting CO2 to CO over Ni@NCNT/graphene hybrid structured catalysts (Ni@NCNT/Gr). Ni nanoparticles (Ni NPs) were encapsulated in N-doped carbon nanotubes (NCNTs) which were in situ generated from g-C3N4 during the annealing process due to the thermal catalysis of the existing Ni NPs. Our results show that the optimized pyrrolic N doping level, coupled with stable NCNT/Gr hybrid structures, high electrochemically active surface area, rich active sites, and reduced Ni NP size, synergistically contribute to the distinguished electrocatalytic performances. The as-prepared Ni@NCNT/Gr-R catalyst demonstrated a high CO faradaic efficiency (>90%) with negligible differences in CO FE across a wide potential range (-0.71--0.91 V vs. RHE) in an H-cell while maintaining magnificent stability with negligible current density loss for 24 hours at -0.71 V (vs. RHE). Our findings provide evidence and insight into the optimization of pyrrolic N doping levels together with reducing NP size within the stable NCNT/Gr hybrid substrate for designing efficient CO2 reduction catalysts.

Non-metal cocatalyst CNT-modified emerging g-C3N4 for enhanced treatment of waste drilling fluid filtrate

Loading with non-metal cocatalysts to regulate interfacial charge transfer and separation has become a prominent focus in current research. In this study, g-C3N4/CNT composites loaded with non-metallic cocatalysts were prepared through in situ pyrolysis using urea and CNTs. Various characterization techniques, including transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), photoelectrochemical (PEC) analysis, fluorescence lifetime spectroscopy (TRPL), electron paramagnetic resonance spectroscopy (ESR), and photoluminescence (PL) spectroscopy, were employed to analyze the sample's microstructure, phase composition, elemental chemical states, and photoelectronic properties. The photocatalytic performance of the g-C3N4/CNT composite in the degradation of actual drilling hydraulic filtrate was evaluated under simulated sunlight irradiation, with the degradation results assessed through COD and chroma measurements. The findings indicate that in g-C3N4/CNT composites loaded with non-metal cocatalysts, the photocatalytic performance improves significantly as the CNT content increases. At a CNT mass fraction of 6.0%, the composite achieves optimal performance, with a COD degradation rate of 0.3742 h-1 and a chroma degradation rate of 81%. These results offer valuable insights into enhancing photocatalytic treatment of waste drilling hydraulic filtrate using g-C3N4-based non-metallic cocatalysts.

Exploring the synergistic effect of palladium nanoparticles and highly dispersed transition metals on carbon nitride/super-activated carbon composites for boosting electrocatalytic activity

In the present work, multifunctional electrocatalysts formed by palladium nanoparticles (Pd NPs) loaded on Fe or Cu-containing composite supports, based on carbon nitride (C3N4) and super-activated carbon with a high porosity development (SBET 3180 m2/g, VDR 1.57 cm3/g, and VT 1.65 cm3/g), were synthesised. The presence of Fe or Cu sites favoured the formation of Pd NPs with small average particle size and a very narrow size distribution, which agreed with Density Functional Theory (DFT) calculations showing that the interaction of Pd clusters with C3N4 flakes is weaker than with Cu- or Fe-C3N4 sites. The electroactivity was also dependent on the composition and, as suggested by preliminary DFT calculations, the Pd-Cu catalyst showed lower overpotential for hydrogen evolution reaction (HER) while bifunctional oxygen reduction reaction/ oxygen evolution reaction (ORR/OER) behaviour was superior in Pd-Fe sample. The Pd-Fe electrocatalyst was studied in a zinc-air battery (ZAB) for 10 h, showing a performance similar to a commercial Pt/C + RuO2 catalyst with a high content of precious metal. This study demonstrates the synergistic effect between Pd species and transition metals and shows that transition metals anchored on C3N4-based composite materials promote the electroactivity of Pd NPs in HER, ORR and OER due to the interaction between both species.

CoFe Alloys Dispersed on Se, N Co-Doped Graphitic Carbon as Efficient Bifunctional Catalysts for Zn-Air Batteries

The development of a stable and efficient non-noble metal catalyst with both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is paramount to achieving the widespread application of Zn-air batteries (ZABs) but remains a great challenge. Herein, a novel Co3 Fe7 alloy nanoparticle dispersed on Se, N co-doped graphitic carbon (denoted as CoFe/Se@CN) was prepared through a facile hydrothermal and pyrolysis process. The synthesized CoFe/Se@CN exhibits outstanding ORR and OER properties with an ultralow potential gap of 0.625 V, which is mainly attributed to the abundant porous structure, the rich structural defects formed by doping Se atoms, and the strong synergistic effects between the CoFe alloys and graphitic carbon nanosheet. Furthermore, the ZAB fabricated by CoFe/Se@CN shows a high peak power density of 160 mW cm-2 and a large specific capacity of 802 mA h g-1 with favorable cycling stability, outperforming that of Pt/C+RuO2 . Our study offers a plausible strategy to explore bifunctional carbon-based materials with efficient electrocatalytic properties for rechargeable ZABs.

Integrating PtCo nanoparticles on N, S doped pore carbon nanosheets as high-performance bifunctional catalysts for oxygen reduction and hydrogen evolution reactions

The development of low-Pt bifunctional electrocatalysts with excellent performance for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is critical for the advancement of the hydrogen economy. Here, we have integrated low-loading Pt and Co metals into N, S doped porous carbon nanosheets to obtain composite catalysts encapsulating PtCo alloy nanoparticles (PtCo2@Co9S8/N-CNS and PtCo2@N-CNS). The acquired PtCo nanoparticles, with dimensions of about 2.5 nm, are uniformly distributed and firmly anchored in N, S doped carbon nanosheets with large specific surface areas and rich pore structure, forming multiple active centers and effectively preventing the aggregation of metal nanoparticles. The PtCo2@Co9S8/N-CNS and PtCo2@N-CNS display high ORR catalytic mass activity of 1.65 A mgPt-1 and 1.01 A mgPt-1 in 0.1 M HClO4. The PtCo2@N-CNS catalyst exhibits excellent HER performance in 0.5 M H2SO4, with a mass activity (at 50 mV) 4.3 times higher than that of Pt/C. The PtCo2@Co9S8/N-CNS and PtCo2@N-CNS also exhibit stronger ORR and HER stability than Pt/C after accelerated durability tests. The superior catalytic activity performance of catalysts can be attributed to the synergistic effect of multiple active centers of PtCo, Co9S8 and Co-N in the catalysts. The confinement of PtCo nanoparticles by Co metal and N, S doped porous nanosheets derived from graphitic carbon nitride (g-C3N4) as the template, which can effectively prevent the corrosion and migration of the catalysts under acidic conditions, enhances the catalytic stability of the materials. This study provides a new perspective for the development of economical and efficient bifunctional low-Pt catalysts.

Calf thymus ds-DNA intercalation with pendimethalin herbicide at the surface of ZIF-8/Co/rGO/C3N4/ds-DNA/SPCE; A bio-sensing approach for pendimethalin quantification confirmed by molecular docking study

Pendimethalin (PND) is a herbicide that is regarded to be possibly carcinogenic to humans and toxic to the environment. Herein, we fabricated a highly sensitive DNA biosensor based on ZIF-8/Co/rGO/C₃N₄ nanohybrid modification of a screen-printed carbon electrode (SPCE) to monitor PND in real samples. The layer-by-layer fabrication pathway was conducted to construct ZIF-8/Co/rGO/C₃N₄/ds-DNA/SPCE biosensor. The physicochemical characterization techniques confirmed the successful synthesis of ZIF-8/Co/rGO/C₃N₄ hybrid nanocomposite, as well as the appropriate modification of the SPCE surface. The utilization of ZIF-8/Co/rGO/C₃N₄ nanohybrid as a modifier was analyzed using. The electrochemical impedance spectroscopy results showed that the modified SPCE exhibited significantly lowered charge transfer resistance due to the enhancement of its electrical conductivity and facilitation of the transfer of charged particles. The proposed biosensor successfully quantified PND in a wide concentration range of 0.01-35 μM, with a limit of detection (LOD) value of 8.0 nM. The PND monitoring capability of the fabricated biosensor in real samples including rice, wheat, tap, and river water samples was verified with a recovery range of 98.2-105.6%. Moreover, to predict the interaction sites of PND herbicide with DNA, the molecular docking study was performed between the PND molecule and two sequence DNA fragments and confirmed the experimental findings. This research sets the stage for developing highly sensitive DNA biosensors that will be used to monitor and quantify toxic herbicides in real samples by fusing the advantages of nanohybrid structures with crucial knowledge from a molecular docking investigation.

Engineering the electronic structure of high performance FeCo bimetallic cathode catalysts for microbial fuel cell application in treating wastewater

The development of high-performance, strong-durability and low-cost cathode catalysts toward oxygen reduction reaction (ORR) is of great significance for microbial fuel cells (MFCs). In this study, a series of bimetallic catalysts were synthesized by pyrolyzing a mixture of g-C₃N₄ and Fe, Co-tannic complex with various Fe/Co atomic ratios. The initial Fe/Co atomic ratio (3.5:0.5, 3:1, 2:2, 1:3) could regulate the electronic state, which effectively promoted the intrinsic electrocatalytic ORR activity. The alloy metal particles and metal-N_x sites presented on the catalyst surface. In addition, N-doped carbon interconnected network consisting of graphene-like and bamboo-like carbon nanotube structure derived from g-C₃N₄ provided more accessible active sites. The resultant Fe₃Co₁ catalyst calcined at 700 °C (Fe₃Co₁-700) exhibited high catalytic performance in neutral electrolyte with a half-wave potential of 0.661 V, exceeding that of the commercial Pt/C (0.6 V). As expected, the single chamber microbial fuel cell (SCMFC) with 1 mg/cm² loading of Fe₃Co₁-700 catalyst as the cathode catalyst afforded a maximum power density of 1425 mW/m², which was 10.5% higher than commercial Pt/C catalyst with the same loading (1290 mW/m²) and comparable to the Pt/C catalyst with 2.5 times higher loading ( 1430 mW/m²). Additionally, the Fe₃Co₁-700 also displayed better long-term stability over 1100 h than the Pt/C. This work provides an effective strategy for regulating the surface electronic state in the bimetallic electro-catalyst.

Convex Cube-Shaped Pt34 Fe5 Ni20 Cu31 Mo9 Ru High Entropy Alloy Catalysts toward High-Performance Multifunctional Electrocatalysis

High entropy alloy (HEA) catalysts exhibit excellent multifunctional catalytic performance due to the synergistic effect of multi-metal components. However, shape-controlled synthesis of such kinds of HEA catalysts, especially those with high index facets, still faces great challenges, limiting further enhancement of their catalytic performance. Herein, one-pot synthesis of convex cube-shaped Pt₃₄ Fe₅ Ni₂₀ Cu₃₁ Mo₉ Ru HEA catalysts which possess rich (310) facets and a diagonal crystalline size of 38.5 nm is reported. Transmission electron microscopy measurements indicate cube-shaped nanocrystals are obtained first and further selective growth of pyramid on each facet of the cube-shaped nanocrystal results in a convex cube shape. Pt₃₄ Fe₅ Ni₂₀ Cu₃₁ Mo₉ Ru HEA catalysts show excellent electrocatalytic performance toward the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and oxygen evolution reaction (OER), which exhibit a half-wave potential of 0.87 V for ORR in 0.1 m HClO₄ , and overpotential of 20 and 259 mV for HER and OER at a current density of 10 mA cm^-2 in an alkaline medium. A control experiment and density functional theory calculation indicate that the Ru element plays a decisive role in both the formation of the convex cube shape and also the high catalytic performance.

Fullerene-Derived Carbon Nanotubes and Their Electrocatalytic Properties in Oxygen Reduction and Zn-Air Batteries

Carbon-based materials with superior electrochemical performances have been prepared from fullerenes by releasing their intrinsic advantages such as pentagon defects and π-electron carbons. To the best of our knowledge, fullerene-derived carbon nanotubes (CNTs) and their electrochemical behavior have not been experimentally investigated. In this work, in situ growth of CNT composites from fullerene is realized via a self-catalyzed process by employing an Fe-decorated fullerene (ferrocenylpyrrolidine C₆₀) as the precursor and NH₃ as the pyrolysis atmosphere. The results show that the in situ Fe doping in fullerene, the self-assembly of fullerene molecules, the pyrolysis temperature, and the NH₃ flow play essential roles in the generation of CNTs. The as-prepared MN7-10/3 CNT composite exhibits efficient oxygen reduction performance with E_1/2 = 0.82 V and E_on = 1.02 V vs the RHE. The flexible solid-state Zn-air battery constructed based on MN7-10/3 exhibits a superior power density (109.3 mW cm^-2 at 180.9 mA cm^-2) and long-term durability (the voltage remains at 95.6% of the initial value after discharging for 5000 s) compared with the benchmark Pt/C catalyst. The transformation of the Fe-decorated fullerene to CNTs reveals a new function of fullerenes and demonstrates a new solid-state synthetic method for CNTs.

Cobalt phosphide nanoparticles encapsulated in manganese, nitrogen co-doped porous carbon nanosheets with rich nanoholes for high-efficiency oxygen reduction reaction

It is a challenging task to research oxygen reduction electrocatalysts with cost-effectiveness, high-performance and ultra-stability to replace traditional noble metal catalysts in renewable energy conversion/storage devices. Herein, cobalt phosphide (Co₂P) nanoparticles encapsulated in Mn, N co-doped porous carbon nanosheets with abundant nanoholes (Co₂P/Mn,N-PCNS) were prepared by a alizarin complexone coordination regulated pyrolysis at 800 °C. In the controlled experiments, the pyrolysis temperature and metal types were investigated in details. The resultant catalyst exhibited rapid mass/charge transfer and superior oxygen reduction reaction (ORR) performance (E_onset = 0.96 V; E_1/2 = 0.86 V vs RHE), surpassing commercial Pt/C. This work presents some constructive guidelines for synthesis of appealing ORR electrocatalysts in renewable energy technology.

Highly Dispersed Co-, N-, S-Doped Topological Defect-Rich Hollow Carbon Nanoboxes as Superior Bifunctional Oxygen Electrocatalysts for Rechargeable Zn-Air Batteries

Rechargeable Zn-air batteries have received extensive attention due to their use of nontoxic materials, safety, and high energy density. However, the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air electrode of Zn-air batteries both suffer from slow kinetics, limiting their commercialization development. Herein, we prepared Co, N, and S co-doped hollow carbon nanoboxes (Co-N/S-CNBs) rich in topological defects using polyphenylene sulfide (PPS) as a sulfur-rich carbon source. Critically, by utilizing the self-propagating high-temperature synthesis (SHS), PPS can avoid melting, while simultaneously enabling the catalyst to take on a unique hollow structure. Additional post-treatment to introduce Co and N atoms as active centers further increases the defect sites and microporous structures of the catalyst. Under alkaline electrolytes, the Co-N/S-CNBs enabled Zn-air batteries to exhibit excellent bifunctional catalytic activity for both ORR and OER, surpassing commercial catalysts. Chemical analysis showed that the cracking loss of small molecules from PPS during pyrolysis is the main reason for the formation of topological defects, where the defect sites act as active centers to enhance the catalytic performance. Overall, this work provides new insights into the mechanism of how defects are formed in such a catalyst, as well as shows how a high-performance bifunctional electrocatalyst can be utilized for practical Zn-air batteries.

Direct Conversion of Solid g-C3N4 into Metal-ended N-doped Carbon Nanotubes for Rechargeable Zn-Air Batteries

Developing low-cost and bifunctional electrocatalysts with activity for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is great desirable for metal-air battery. Herein, we demonstrate an approach to realize...

Atomic and nanosized Co species functionalized N-doped porous carbon hybrids for boosting electrocatalytic oxygen reduction

Co@NRPC electrocatalysts with excellent ORR performance were synthesized by pyrolyzing the hybrid precursors. Atomic CoNx and nanosized metallic Co species were active sites. Porous carbon hybrids ensured efficient charge and mass transport.

High-Level Oxygen Reduction Catalysts Derived from the Compounds of High-Specific-Surface-Area Pine Peel Activated Carbon and Phthalocyanine Cobalt

Non-platinum carbon-based catalysts have attracted much more attention in recent years because of their low cost and outstanding performance, and are regarded as one of the most promising alternatives to precious metal catalysts. Activated carbon (AC), which has a large specific surface area (SSA), can be used as a carrier or carbon source at the same time. In this work, stable pine peel bio-based materials were used to prepare large-surface-area activated carbon and then compound with cobalt phthalocyanine (CoPc) to obtain a high-performance cobalt/nitrogen/carbon (Co-N-C) catalyst. High catalytic activity is related to increasing the number of Co particles on the large-specific-area activated carbon, which are related with the immersing effect of CoPc into the AC and the rational decomposed temperature of the CoPc ring. The synergy with N promoting the exposure of CoNx active sites is also important. The Eonset of the catalyst treated with a composite proportion of AC and CoPc of 1 to 2 at 800 °C (AC@CoPc-800-1-2) is 1.006 V, higher than the Pt/C (20 wt%) catalyst. Apart from this, compared with other AC/CoPc series catalysts and Pt/C (20 wt%) catalyst, the stability of AC/CoPc-800-1-2 is 87.8% in 0.1 M KOH after 20,000 s testing. Considering the performance and price of the catalyst in a practical application, these composite catalysts combining biomass carbon materials with phthalocyanine series could be widely used in the area of catalysts and energy storage.

CoFe alloy embedded in N-doped carbon nanotubes derived from triamterene as a highly efficient and durable electrocatalyst beyond commercial Pt/C for oxygen reduction

For development of green and sustainable energy, it is of importance to search highly efficient and low-cost electrocatalysts of oxygen reduction reaction (ORR) in energy conversion devices. Herein, CoFe alloyed nanocrystals embedded in N-doped bamboo-like carbon nanotubes (CoFe@NCNTs) were facilely synthetized by one-step co-pyrolysis with the mixture of triamterene, metal chlorides and graphitic carbon nitride (g-C₃N₄). The resultant CoFe@NCNTs exhibited excellent ORR activity with the positive shifts in the onset potential (E_onset = 0.97 V) and half-wave potential (E_1/2 = 0.88 V), outperforming commercial Pt/C (E_onset = 0.96 V; E_1/2 = 0.84 V). Compared to metal organic frameworks (MOFs)-based strategy for synthesis of low-cost carbon-based ORR catalysts, this method is simple and convenient, coupled by avoiding the complicated synthesis of MOFs and its ligands. This work provides a promising route to fabricate advanced transition-metal-based carbon catalysts in the researches correlated with energy conversion devices.

Hierarchical Hollow MOF-Derived Bamboo-like N-doped Carbon Nanotube-Encapsulated Co0.25Ni0.75 Alloy: An Efficient Bifunctional Oxygen Electrocatalyst for Zinc-Air Battery

The synthesis of nonprecious electrocatalysts for oxygen electrocatalysis is of considerable interest for the development of electrochemical energy devices. Herein, we demonstrate a facile approach for the synthesis of bamboo-like nitrogen-doped carbon nanotube-encapsulated Co_0.25Ni_0.75 alloy electrocatalyst (Co_0.25Ni_0.75@NCNT) and its bifunctional oxygen electrocatalytic performance toward oxygen reduction and oxygen evolution reactions. The Co_0.25Ni_0.75 alloy wrapped with NCNT is obtained by a one-step carbothermal reduction approach using dicyandiamide and NiCo-MOF precursors. Dicyandiamide acts as a nitrogen source, and the in situ generated Co_0.25Ni_0.75 alloy nanoparticles catalyze the growth of bamboo-like NCNTs. The hollow NiCo-MOF plays a sacrificial role in providing a suitable environment for the controlled growth of Co_0.25Ni_0.75 alloy and NCNT. Co_0.25Ni_0.75@NCNT efficiently catalyzes both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) at a favorable overpotential. It shows a low potential gap (ΔE) of ∼0.8 V between the two reactions, and it qualifies for the development of air cathode in metal-air batteries. The enhanced bifunctional activity and excellent durability stem from the chemical composition and the synergistic effect between Co_0.25Ni_0.75 alloy and encapsulating NCNT. The original phase and morphology of the catalyst is preserved after an extensive durability test. Aqueous rechargeable Zn-air battery (ZAB) is fabricated using a Co_0.25Ni_0.75@NCNT-based air cathode. The battery has high open-circuit voltage (1.53 V) and a maximum peak power density of 167 mW cm^-2 with only 1.6% loss in the voltaic efficiency after 36 h charge-discharge cycles. As a proof-of-concept demonstration, the as-fabricated ZAB is successfully used for the electrochemical water splitting in alkaline solution.

Carbon nitride/positive carbon black anchoring PtNPs assembled byγ-rays as ORR catalyst with excellent stability

Electrocatalytic performance of low-cost graphitic carbon nitride (CN) is greatly limited by its limited conductivity and small specific surface area. Herein, a simple and cost-effective idea to produce novel nanocomposite is constructed by the CN and cetyl trimethyl ammonium bromide functionalized carbon black (CB) anchored platinum nanoparticles as highly efficient oxygen reduction catalysts based on gamma irradiation. The assembled carbon nitride/positive carbon black anchoring PtNPs (Pt/CN₂-CB⁺₁) catalyst exhibits significantly improved specific surface area, high graphitization, and uniformly dispersed ultra-small platinum nanoparticles. For the oxygen reduction reaction (ORR) performance, the catalyst shows more positive onset-potential (0.93 V versus RHE) and larger diffusion limiting current density (5.65 mA cm^-2) compared with benchmark Pt/C catalysts in alkaline medium. Moreover, the Pt/CN₂-CB⁺₁catalyst exhibits a small Tafel slope (92 mV dec^-1). Besides, the catalyst was demonstrated the remarkable methanol tolerance and good long-term stability under working conditions. This work provides a new and effectiveγ-rays irradiation for synthesizing the carbon nitride catalysts for energy conversion and storage applications.

A g-C3N4 self-templated preparation of N-doped carbon nanosheets@Co-Co3O4/Carbon nanotubes as high-rate lithium-ion batteries' anode materials

A novel N-doped graphene-like carbon nanosheets (CNs) and carbon nanotubes (CNTs)-encapsulated Co-Co₃O₄ nanoparticles (NPs) (CN@Co-Co₃O₄/CNTs) were synthesized successfully by a simple hydrothermal and annealing method with graphite carbon nitride (g-C₃N₄) as self-template. By annealing Co²⁺/g-C₃N₄ under N₂ atmosphere, g-C₃N₄ was transformed into CN/CNTs, and Co²⁺ was reduced into CoNPs which were embedded in CNs. Further annealing in air, a shell of Co₃O₄ was formed around CoNPs. The amount of CNs, CNTs, and CoNPs can be adjusted by changing the ratio of Co²⁺ in Co²⁺/g-C₃N₄. The graphene-like CNs provided a large number of active sites and a large specific surface area for loading lots of small CoNPs uniformly. The CNTs with a diameter of 100 nm could not only improve the conductivity but also provide a buffer space for the aggregation and volume expansion of Co₃O₄. CNTs also enlarged the interlayer distance of CNs, which prevented the re-stacking of CNs and provided great convince for the intercalation and de-intercalation of Li⁺. When applied for anode material of lithium-ion batteries, CN@Co-Co₃O₄/CNTs exhibited a high discharge capacity of 460.0 mAh g^-1 at 5000 mA g^-1 after 300 cycles with a Coulombic efficiency of 98% and excellent higher-rate capacity (401.0 mAh g^-1 at 2000 mA g^-1 and 329.0 mAh g^-1 at 5000 mA g^-1).

Exfoliated Boron Nitride (e-BN) Tailored Exfoliated Graphitic Carbon Nitride (e-CN): An Improved Visible Light Mediated Photocatalytic Approach towards TCH Degradation and H2 Evolution

A series of 2D/2D exfoliated boron nitride/exfoliated g-C₃N₄ nanocomposites denoted as e-BN/e-CN have been successfully prepared using a simple in situ technique. The successful deposition of e-BN on e-CN was confirmed from high-resolution transmission electron microscopy analysis. According to electrochemical measurements, 1.5 wt % e-BN/e-CN nanocomposites showed 1.5 times more photocurrent than e-CN, which indicates the successful formation of an e-BN/e-CN heterostructure. The photocatalytic activities of the e-CN and e-BN/e-CN composites were investigated through photocatalytic tetracycline hydrochloride (TCH) degradation and H₂ evolution under visible light illumination. The 1.5 wt % e-BN/e-CN composite demonstrated the highest photocatalytic activities, which are about 21 and 1.5 fold greater than e-CN towards H₂ generation with an apparent conversion efficiency of 2.34% and TCH degradation, respectively. The improved photocatalytic activities of e-BN/e-CN photocatalysts were ascribed to the augmented light-harvesting ability and enhanced separation efficiency of charge carriers. Lower photoluminescence intensity and a smaller arc value in the impedance spectra again proved the reduced recombination of the e^--h⁺ pairs in the e-BN/e-CN nanocomposites. Trapping experiments show that ^•O₂^-, h⁺, and ^•OH radicals are the predominant reactive species that accelerated the photocatalytic activities of e-BN/e-CN composites. This study opens up a new window towards the fabrication of such 2D/2D nanocomposites in the field of photocatalysis.

Co0.7Fe0.3 NPs confined in yolk-shell N-doped carbon: engineering multi-beaded fibers as an efficient bifunctional electrocatalyst for Zn-air batteries

The development of bifunctional catalysts with a delicate structure, high efficiency, and good durability for the oxygen evolution reaction (ORR) and oxygen evolution reaction (OER) is crucial to renewable Zn-air batteries. In this work, Co_0.7Fe_0.3 alloy nanoparticles (NPs) confined in N-doped carbon with a yolk-shell structure in multi-beaded fibers were prepared as a bifunctional electrocatalyst. The confinement structure was composed of an N-doped graphitized carbon shell and a core formed by numerous Co_0.7Fe_0.3 NPs, and was evenly threaded into a one-dimensional fiber. Moreover, this distinctive hierarchical structure featured abundant mesopores, a high BET surface area of 743.8 m² g^-1, good electronic conductivity, and uniformly distributed Co_0.7Fe_0.3/Co(Fe)-N_x coupling active sites. Therefore, the experimentally optimized Co_0.7Fe_0.3@NC_2:1-800 showed excellent OER performance (overpotential reached 314 mV at 10 mA cm^-2) that far exceeded RuO₂ (353 mV), and good ORR catalytic performance (half-wave potential of 0.827 V) comparable to Pt/C (0.818 V). Impressively, the Co_0.7Fe_0.3@NC_2:1-800 Zn-air battery delivered a higher open circuit voltage of 1.449 V, large power density of 85.7 mW cm^-2, and outstanding charge-discharge cycling stability compared with the commercial RuO₂ + 20 wt% Pt/C catalyst. This work provides new ideas for the structural design of electrocatalysts and energy conversion systems.

Co-Zn-MOFs Derived N-Doped Carbon Nanotubes with Crystalline Co Nanoparticles Embedded as Effective Oxygen Electrocatalysts

The oxygen reduction reaction (ORR) is a crucial step in fuel cells and metal-air batteries. It is necessary to expand the range of efficient non-precious ORR electrocatalysts on account of the low abundance and high cost of Pt/C catalysts. Herein, we synthesized crystalline cobalt-embedded N-doped carbon nanotubes (Co@CNTs-T) via facile carbonization of Co/Zn metal-organic frameworks (MOFs) with dicyandiamide at different temperatures (t = 600, 700, 800, 900 °C). Co@CNTs- 800 possessed excellent ORR activities in alkaline electrolytes with a half wave potential of 0.846 V vs. RHE (Reversible Hydrogen Electrode), which was comparable to Pt/C. This three-dimensional network, formed by Co@CNTs-T, facilitated electron migration and ion diffusion during the ORR process. The carbon shell surrounding the Co nanoparticles resulted in Co@CNTs-800 being stable as an electrocatalyst. This work provides a new strategy to design efficient and low-cost oxygen catalysts.

Morphological and reactive optimization of g-C3N4-derived Co,N-codoped carbon nanotubes for hydrogen evolution reaction

Scheme for the synthesis of bamboo-like N-doped carbon nanotubes.

Micelles of Mesoporous Silica with Inserted Iron Complexes as a Platform for Constructing Efficient Electrocatalysts for Oxygen Reduction

Iron, N-codoped carbon materials (Fe-N-C) are promising electrocatalysts toward oxygen reduction reactions due to their high atom utilization efficiency and intrinsic activity. Nanostructuring of the Fe-N-C materials, such as introducing porosity into the carbon structure, would be conducive to further increasing the exposure of active sites as well as improving the mass transfer. Herein, we explore the potential of iron complex-functionalized micelles of mesoporous SiO₂ as a platform for constructing porous Fe-N-C materials. The classical three-dimensional MCM-48 was selected as a proof-of-concept example, which was utilized as the hard template, and cetyltrimethylammonium bromide micelles inside it played the role of the main carbon source. Fe-N_x sites were derived from Fe-1,10-phenanthroline complexes in the micelles introduced by in situ incorporation of 1,10-phenanthroline and post Fe²⁺ insertion in an aqueous solution. After thermal annealing in a nitrogen atmosphere and subsequent removal of the MCM-48 framework, a carbon material that possesses porous structural features with uniformly dispersed Fe-N_x sites (MPC@PhFe) was obtained, which shows superior ORR activity in a 0.1 M KOH solution and great potential for Zn-air battery applications as well. This work demonstrates the feasibility as well as the effectiveness of turning micelles of mesoporous SiO₂ into porous carbon structures and might offer a universal strategy for manufacturing carbon materials for future application in energy storage and conversion.

From polymeric carbon nitride to carbon materials: extended application to electrochemical energy conversion and storage

As an emerging photocatalyst, polymeric carbon nitride (PCN) currently has drawn ever-increasing attention for electrochemical energy conversion and storage due to its graphite-like structure, metal-free characteristic and excellent structural tunability. Nonetheless, its practical applications are still hindered by the poor electrical conductivity induced irreversible capacity loss. Recently, PCN-derived carbon materials with improved conductivity have received increasing interest and made tremendous progress for advanced electrochemical energy conversion and storage. This review highlights the latest research advancements regarding the electrochemical energy conversion (hydrogen evolution reaction, oxygen reduction/evolution reaction, nitrogen reduction reaction, carbon dioxide reduction reaction, etc.) and storage (Li-ion batteries, Li-S batteries, supercapacitors, etc.) application from PCN to PCN-derived carbon materials. A perspective about the challenges and trends in the electrochemical application of PCN and PCN-derived carbon materials is also provided at the end of the review.