Construction of a sp3 /sp2 Carbon Interface in 3D N-Doped Nanocarbons for the Oxygen Reduction Reaction

Se-functionalized metal-free catalysts rich in sp3-hybridized carbon enable efficient oxygen electroreduction

Carbon-based metal-free materials are emerging as leading candidates to replace noble-metal catalysts in the oxygen reduction reaction (ORR). Herein, we introduce a facile secondary carbonation technique for fabricating Se and N co-doped metal-free catalysts using a zeolite imidazole framework (ZIF-8) as the precursor. The optimal electrocatalyst, designated SeNC-900, exhibited good ORR performance under both alkaline and acidic conditions, with half-wave potentials of 0.864 V and 0.731 V (vs. RHE), respectively. Density functional theory (DFT) calculations reveal that the enhanced activity of SeNC-900 originates from Se doping, which triggers an increase in the intrinsic defects of sp3-hybridized C. Concurrently, the sp3-hybridized C, in concert with Se dopant, modulates the electronic structure of the active C atoms. This work not only underscores the significance of tuning the electronic structure to boost catalytic performance by enriching intrinsic defects but also presents a fresh insight into the effect of heteroatom doping on carbon-based materials for electrocatalysis.

Onion-Like Carbon Nanozyme: Controlling Peroxidase-Like Activity by Carbon Hybridization Patterns for Antibacterial Therapy

Since the inception of the concept of nanozymes, there has been a growing interest in the rational design and controllable synthesis of nanozymes with adjustable activities. In this study, onion-liked carbon (OLC) with remarkable peroxidase-like (POD) activity are developed through delicately controlling the sp2/sp3 configuration. The investigation reveals that enzymatic activity of OLC increases first and then decreases with the increased graphitic degree, with the highest activity observed at a moderate sp2/sp3 ratio of 17.17%. A series of experiments and theoretical calculations are conducted to elucidate the catalytic mechanism, and the structure-dependent activity is attributed to a synergistic effect of surface adsorption and electron transfer processes. The POD activity enables the OLC to catalyze the decomposition of H2O2, producing reactive oxygen species for eradicating Gram-positive and Gram-negative bacteria. Additionally, toxicity tests based on nematode and mouse models confirmed the excellent biocompatibility of OLC. Furthermore, the OLC exhibited antibacterial ability and promoted bacterial-infected wound healing in a mouse model. This work not only gives a deeper understanding of the structure-activity relationship and catalytic mechanism of carbon-based nanozymes, but also unveils a novel avenue for antibacterial therapy and wound healing applications.

Coordinately unsaturated single Fe-atoms with N vacancies and enhanced sp3 carbon defects in Fe-N(sp2)-C structural units for suppression of cancer cell metabolism and electrochemical oxygen evolution

Installing coordinately unsaturated Fe-N-C structural units on polymer-composite-derived N-doped carbon offers highly active Fe-Nx sites for the electrochemical oxygen evolution reaction (OER) and reactive oxygen species (ROS) generation in tumor cells. An NH4Cl-driven high-temperature etching method was employed for the formation of FeSA950NC with coordinately unsaturated single Fe-atoms in an Fe-N(sp2)-C structural unit together with N vacancies (VN) and sp3 defects. The carbonization of Fe-phen@ZIF-8 at 800 °C for 30 min under argon, followed by grinding Fe-ZIF-8@RF-urea with NH4Cl at 950 °C for 2 hours, resulted in sp3 carbon defects and VN sites with coordination unsaturation in Fe-Nx due to NH4Cl decomposition to NH3 and HCl, which produced substantial internal stress for etching the carbon matrix. FeSA950NC was used to treat both A549 lung cancer cells and NIH3T3 mouse fibroblast cells to determine its potential as an efficient tumor therapeutic strategy using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and ROS assays. Additionally, FeSA950NC provided high stability and excellent OER activity through the Fe-N(sp2)-C structural unit on pyridinic nitrogen by delivering at a minimum overpotential of 300 mV, which is much lower than that of structurally similar Fe-atom sites. The significantly stronger ROS and OER activities of FeSA950NC suggested the role of VN and sp3-carbon defects with coordinately unsaturated Fe-N2 sites in improving its catalytic performance.

Assessing the Effect of a Schwarz P Surface on the Oxygen Electroreduction Performance of Porous Single-Atom Catalysts

The surface curvature of catalysts has a decisive impact on their catalytic performance. However, the influence of a negative-Gaussian-curvature surface on the catalytic performance of porous catalysts has remained unexplored due to the lack of suitable samples. Bicontinuous-structured porous structures can serve as ideal models, but they are known as "Plumber's nightmare" due to their highly difficult preparation. Here, using metal-organic frameworks as the precursor and polymer cubosomes as the template, a bicontinuous mesoporous Fe single-atom catalyst (named bmFeSAC) with a Schwarz P surface is synthesized. The bmFeSAC catalyst has a large specific surface area of 916 m2 g-1 and uniformly distributed Fe-N4 active sites with a 1.80 wt.% Fe content. The continuous channels enabled high utilization efficiency of the Fe-N4 catalytic sites, while the negative-Gaussian-curvature surface enabled low reaction energy barrier. As an electrocatalyst of the oxygen reduction reaction, bmFeSAC delivered a high half-wave potential of 0.931 V versus. RHE in alkaline electrolyte, reaching the leading level among those of the reported state-of-the-art electrocatalysts. Furthermore, the bmFeSAC-based Zn-air batteries exhibited excellent performance, demonstrating the potential application of bmFeSAC. This study revealed that a bicontinuous-structured porous structure can improve catalytic activity by increasing the utilization ratio of catalytic sites and, more importantly, by regulating the electronic structure of catalyst surfaces through the negative-Gaussian-curvature.

Revealing the Effect of Curvature Structure in Hard Carbon Anodes for Lithium/Sodium Ion Batteries

Heteroatom doping is the most common means to enhance the Li+/Na+ ions storage of hard carbon (HC). The explanation of the storage mechanism of heteroatom-doped HC is to increase the active site or widen the layer spacing while ignoring the effect of local bending structure induced by it. Meanwhile, the storage mechanism by the localized bending structure also lacks in-depth study. Herein, a locally curved configuration and an amorphous structure are designed by introducing different heteroatoms, respectively, and the mechanism of the two types of structures on the Li+/Na+ ions storage is explored. The density functional theory (DFT) calculation shows that the adsorption energy of Li+/Na+ ions is optimal at the appropriate curvature of 27.72 m-1. Serving as anode for lithium/sodium ion batteries in ester electrolytes, the optimized HCs demonstrate satisfied specific capacity and high-rate capability, respectively. Furthermore, the charging capacity below 1.0 V of HC with suitable curvature microstructure reaches 84.8% and 90.1% of the total charge capacity, confirming that the curvature defects can better control the delithiation/desodiation process, and provide a higher energy density. This study enlightens new insights into the storage mechanisms of Li+/Na+ ions and provides guidance for better design of heteroatom-doped carbon anodes with superior performance.

Polyphenol-Based Bicontinuous Porous Spheres Via Amine-Mediated Polymerization-Induced Fusion Assembly

Bicontinuous porous materials, which possess 3D interconnected network and pore channels facilitating the mass diffusion to the interior of materials, have demonstrated their promising potentials in a large variety of research fields. However, facile construction of such complex and delicate structures is still challenging. Here, an amine-mediated polymerization-induced fusion assembly strategy is reported for synthesizing polyphenol-based bicontinuous porous spheres with various pore structures. Specifically, the fusion of pore-generating template observed by TEM promotes the development of bicontinuous porous networks that are confirmed by 3D reconstruction. Furthermore, the resultant bicontinuous porous carbon particles after pyrolysis, with a diameter of ≈600 nm, a high accessible surface area of 359 m2 g-1, and a large pore size of 40-150 nm manifest enhanced performance toward the catalytic degradation of sulfamethazine in water decontamination. The present study expands the toolbox of interfacial tension-solvent-dependent porous spheres while providing new insight into their structure-property relationships.

Enabling the Transport Dynamics and Interfacial Stability of Porous Si Anode Via Rigid and Flexible Carbon Encapsulation for High-Energy Lithium Storage

The stable electrode/electrolyte interface and fast electron/ion transport channel play important roles in boosting the rate performance and cycling life of lithium-ion batteries. Herein, a porous silicon/carbon composite (pSi@PC@MC) is presented by integrating hollow porous silicon (pSi) with pitch-derived carbon (PC) and dopamine-derived mesoporous carbon (MC), employing microporous zeolite as the silicon source. The finite element simulation first reveals the stress release effect of rigid and flexible carbon encapsulation on the hollow Si anode for lithium-ion storage. In situ and ex situ characterization results further elucidate that hybrid sp2/sp3 carbon coating greatly enhances the liquid/solid interface stability and the compatibility with the electrolyte, as well as facilitates the electron/ion transmission dynamics, achieving a uniform, stable, and LiF-rich SEI film, ultimately improving the lithium storage performance. As expected, the as-designed pSi@PC@MC anode delivers an impressive rate capability (756.6 mAh g-1 at 6 A g-1) and excellent cycling stability with a capacity of 1650 mAh g-1 after 300 cycles at 0.2 A g-1. Meanwhile, the pSi@PC@MC//NCM811 full-cell exhibits an outstanding cycling stability (75.8% capacity retention after 100 cycles). This study highlights the significance of rational porous design and effective hybrid carbon encapsulation for the development of fast-charging Si/carbon anodes.

Polymerizable Ionic Liquid-Derived N, S co-Doped sp3/sp2 Carbon as Electrocatalyst for H2O2 Generation

The H2O2 generation via the green electrochemical process is of high interest. For the H2O2 electrochemical generation, the oxygen reduction reaction (ORR) is important. Unfortunately, the ORR is kinetically sluggish and catalysts are needed. However, noble metal ORR catalysts are pricy and scarcely applicable in applications. Therefore, non-precious metal catalysts are desired. Heteroatom-doped carbons show promise as metal-free ORR catalysts. The ORR catalytic activity will be enhanced by the carbon's sp2 and/or sp3 engineering. For N, S co-Cdoped and sp2/sp3 modulated carbon, a polymerizable ionic liquid of hydrolyzed vinyl imidazolium was studied. The carbon is studied as a metal-free catalyst for the ORR via the 2e- process. It is possible to get an onset potential of 0.88 V vs. RHE with approximately 50 % selectivity for the H2O2. The current study offers a simple technique for synthesizing heteroatom-doped sp2/sp3 designed carbon as catalysts for the electroreduction of O2 to produce H2O2, and a new way of tunning the sp3/sp2 carbon catalytic activity by modulating the ionic liquid.

High Capacitance Performance N, O Codoped Carbon Foams Synthesized via an All-In-One Step Carbonization of Molecular Salt Strategy

The preparation of porous carbon is constrained by the extensive use and detrimental impact of activators and dopants. Therefore, developing green and efficient strategies that leverage the intrinsic properties and pretreatment of the materials to achieve self-activation and self-doping is particularly crucial for porous carbon materials. Herein, potassium histidine was utilized as the molecular salt precursor, attaining the efficient and streamlined preparation of porous carbon through a one-step carbonization process that enables self-activation, self-doping, and self-templating. More interestingly, the carbonization temperature significantly impacts the porous structure of the molecular salt precursors, the properties of the heteroatoms, and electrochemical performance. The designed electrodes exhibit high accessibility to electrolyte ions and effective ion-electron transport channels. Therefore, the optimal carbon material (KHis800) has an excellent mass-specific capacitance of 305.2 F g-1 at 0.2 A g-1, and a high capacitance retention rate of 115.6% (50,000 cycles at 5 A g-1). Notably, KHis800 also shows a maximum energy density of 19.6 Wh kg-1. This research is dedicated to exploring a more efficient preparation method for porous carbon material via molecular salts, offering insights for the sustainable development of carbon materials.

Unveiling the Role of Hydrophobicity on Multilayer Carbon Nanosheets Enriched in sp2-Carbon for Toluene Adsorption under Humid Conditions

Carbon materials are regarded as a promising adsorbent for the adsorption of volatile organic compounds (VOCs). However, their adsorption behaviors are usually compromised at ambient conditions, attributed to the competitive VOCs adsorption with water vapor. In this study, we demonstrated that the selectivity for toluene than water of carbon can be effectively enhanced by introducing more sp2-carbon with two-dimensional nanosheets stacked. The multilayer carbon nanosheets enriched with sp2-carbon (CNS-MCA) exhibit a 151° H2O-contact angle, indicating hydrophobicity. Dynamic adsorption behaviors revealed that CNS-MCA retain 71% of their toluene adsorption capacity (91 mg/g) even at 60% relative humidity. Density functional theory (DFT) calculations, static adsorption studies, in situ Raman spectroscopy, and time-resolved in situ nuclear magnetic resonance (NMR) spectroscopy collectively indicate that toluene exhibits enhanced adsorption and selectivity due to π-π* interactions between its aromatic rings and the sp2-carbon. Conversely, water adsorption is attenuated, attributed to the reduced availability of surface-exposed hydrogen bonds associated with sp2-carbon and the inherent hydrophobic nature of multilayer graphene. This study extends a novel solution for the enhancement of VOCs adsorption under humid conditions.

Highly Curved Defect Sites: How Curvature Effect Influences Metal-Free Defective Carbon Electrocatalysts

Topological defects are widely recognized as effective active sites toward a variety of electrochemical reactions. However, the role of defect curvature is still not fully understood. Herein, carbon nanomaterials with rich topological defect sites of tunable curvature is reported. The curved defective surface is realized by controlling the high-temperature pyrolytic shrinkage process of precursors. Theoretical calculations demonstrate bending the defect sites can change the local electronic structure, promote the charge transfer to key intermediates, and lower the energy barrier for oxygen reduction reaction (ORR). Experimental results convince structural superiority of highly-curved defective sites, with a high kinetic current density of 22.5 mA cm-2 at 0.8 V versus RHE for high-curvature defective carbon (HCDC), ≈18 times that of low-curvature defective carbon (LCDC). Further raising the defect densities in HCDC leads to the dual-regulated products (HCHDC), which exhibit exceptionally outstanding ORR activity in both alkaline and acidic media (half-wave potentials: 0.88 and 0.74 V), outperforming most of the reported metal-free carbon catalysts. This work uncovers the curvature-activity relationship in carbon defect for ORR and provides new guidance to design advanced catalysts via curvature-engineering.

Precisely Designed Morphology and Surface Chemical Structure of Fe-N-C Electrocatalysts for Enhanced Oxygen Reaction Reduction Activity

Fe-N-C materials have been regarded as one of the potential candidates to replace traditional noble-metal-based electrocatalysts for the oxygen reduction reaction (ORR). It is believed that the structure of carbon support in Fe-N-C materials plays an essential role in highly efficient ORR. However, precisely designing the morphology and surface chemical structure of carbon support remains a challenge. Herein, we present a novel synthetic strategy for the preparation of porous carbon spheres (PCSs) with high specific surface area, well-defined pore structure, tunable morphology and controllable heteroatom doping. The synthesis involves Schiff-based polymerization utilizing octaaminophenyl polyhedral oligomeric silsesquioxane (POSS-NH2) and heteroatom-containing aldehydes, followed by pyrolysis and HF etching. The well-defined pore structure of PCS can provide the confinement field for ferroin and transform into Fe-N-C sites after carbonization. The tunable morphology of PCS can be easily achieved by changing the solvents. The surface chemical structure of PCS can be tailored by utilizing different heteroatom-containing aldehydes. After optimizing the structure of PCS, Fe-N-C loading on N,S-codoped porous carbon sphere (NSPCS-Fe) displays outstanding ORR activity in alkaline solution. This work paves a new path for fabrication of Fe-N-C materials with the desired morphology and well-designed surface chemical structure, demonstrating significant potential for energy-related applications.

Multifunctional Film Assembled from N-Doped Carbon Nanofiber with Co-N4-O Single Atoms for Highly Efficient Electromagnetic Energy Attenuation

Single-atom materials have demonstrated attractive physicochemical characteristics. However, understanding the relationships between the coordination environment of single atoms and their properties at the atomic level remains a considerable challenge. Herein, a facile water-assisted carbonization approach is developed to fabricate well-defined asymmetrically coordinated Co-N4-O sites on biomass-derived carbon nanofiber (Co-N4-O/NCF) for electromagnetic wave (EMW) absorption. In such nanofiber, one atomically dispersed Co site is coordinated with four N atoms in the graphene basal plane and one oxygen atom in the axial direction. In-depth experimental and theoretical studies reveal that the axial Co-O coordination breaks the charge distribution symmetry in the planar porphyrin-like Co-N4 structure, leading to significantly enhanced dielectric polarization loss relevant to the planar Co-N4 sites. Importantly, the film based on Co-N4-O/NCF exhibits light weight, flexibility, excellent mechanical properties, great thermal insulating feature, and excellent EMW absorption with a reflection loss of - 45.82 dB along with an effective absorption bandwidth of 4.8 GHz. The findings of this work offer insight into the relationships between the single-atom coordination environment and the dielectric performance, and the proposed strategy can be extended toward the engineering of asymmetrically coordinated single atoms for various applications.

Cobalt-Copper-Embedded Nitrogen-Doped Carbon Nanostructures Derived from Zeolite Imidazolate Frameworks as Electrocatalysts for the Oxygen Reduction Reaction

In recent years, researchers have focused on developing zeolite imidazolate frameworks (ZIFs) as an alternative to Pt electrocatalysts for various applications, including water splitting, lithium-air batteries, zinc-air batteries, and fuel cells. In this study, we synthesized CoCu-ZIF to be used as a precursor in the development of cathode catalysts for the oxygen reduction reaction (ORR) in fuel cells. Hydrazine played a crucial role in maintaining uniformity in the development and particle size of the ZIF-67 structures. Moreover, it facilitated the rapid formation of the ZIF-67 structures at higher temperatures. A unique pseudorhombic dodecahedral morphology was obtained at a Co/Cu molar ratio of 7:3. Among all the synthesized N-doped carbon nanostructures embedded with Co and Cu nanoparticles, CoCu@NC-750, pyrolyzed at 750 °C, showed superior ORR catalytic performance. This catalyst exhibited a notably higher half-wave potential of 0.816 V and demonstrated a clear 4-electron transfer mechanism. The overpotential of CoCu@NC-750 shifted by only 11 mV over 10,000 cyclic voltammetry cycles, whereas a 55 mV shift was observed for Pt/C. CoCu@NC-750 exhibited a ∼0.8% decrease in current density during a 12-h ORR, in contrast to the 8.3% decline shown by Pt/C. This superior catalytic activity and stability can be attributed to factors such as higher oxygen adsorption induced by the N-doped carbon layer due to the localized changes in electron density and the enhanced stability of the bimetallic core. Our findings suggest that CoCu@NC-750 is a promising alternative to Pt/C in fuel cell cathodes.

Shear Field-Controlled Synthesis of Nitrogen-Doped Carbon Nanochains Forest with High-Density sp3 Defects for Efficient CO2 Electroreduction Reaction

Defect engineering and nitrogen doping being effective strategies for modulating the surface chemical state of the carbon matrix have been widely explored to promote the catalytic activity in the territory of electrochemical energy storage and conversion devices. However, the controllable synthesis of carbon material with high-density specific defects and high nitrogen doping is still full of challenges. Here, we first synthesize one-dimensional necklace-like nitrogen-doped carbon nanochains (N-CNCs) with abundant defects on carbon fiber paper (CFP) by chemical vapor deposition (CVD) method. The resultant nanostructures are a bunch of interconnected carbon spheres with a hollow structure at the internode and present the complete one-dimensional nanochain configuration. Specifically, the N-CNCs with a corrugated surface possesses high content of sp3 defects (31.2%) and nitrogen (23.6 at %). Combining finite element analysis and experimental results, it reveals that the robust shear field generated by etching gas releasing from thermal decomposition of melamine in situ modulates the CVD process via changing the size and force environment of the metal catalyst droplets for formation of N-CNCs. Benefiting from the high ratio of sp3/sp2 and nitrogen doped on the surface, the N-CNCs@CFP displays a superior electrocatalytic performance for CO2RR, delivering CO Faradaic efficiency of 95.9% and a current density of 23.2 mA cm-2 at -0.86 V vs RHE. This work provides promising synthesis strategy and some inspirations for construction of ultradense and specific defects coupling with nitrogen doping sites into carbon materials to achieve high-efficiency electrocatalysis applications.

Disclosing the intrinsic nature of efficient removal of antibiotics in N/S dual-doped porous carbon-based materials: The manipulation of internal electric field

N/S co-doping has emerged as a prevailing strategy for carbon-based adsorbents to facilitate the antibiotic removal efficiency. Nevertheless, the underlying interplay among N, S, and their adjacent vacancy defects remains overlooked. Herein, we present a novel in situ strategy for fabricating pyridinic-N dominated and S dual-doped porous carbon adsorbent with rich vacancy defects (VNSC). The experimental results revealed that N (acting as the electron donor) and S (acting as the electron acceptor) form an internal electric field (IEF), with a stronger IEF generated between pyridinic-N and S, while their adjacent vacancy defects activate carbon π electrons, thus enhancing the charge transfer of the IEF. Density functional theory (DFT) calculations further demonstrated that the rich charge transfer in the IEF facilitated the π-π electron donor-acceptor (EDA) interaction between VNSC and tetracycline (TC) as well as norfloxacin (NOR), and thus is the key to adsorption performance of VNSC. Consequently, VNSC exhibited high adsorption capacities toward TC (573.1 mg g-1) and NOR (517.0 mg g-1), and its potential for environmental applications was demonstrated by interference, environmentally relevant concentrations, fixed-bed column, and regeneration tests. This work discloses the natures of adsorption capacity for N/S dual-doped carbon-based materials for antibiotics.

Second-Shell N Dopants Regulate Acidic O2 Reduction Pathways on Isolated Pt Sites

Pt is a well-known benchmark catalyst in the acidic oxygen reduction reaction (ORR) that drives electrochemical O2-to-H2O conversion with maximum chemical energy-to-electricity efficiency. Once dispersing bulk Pt into isolated single atoms, however, the preferential ORR pathway remains a long-standing controversy due to their complex local coordination environment and diverse site density over substrates. Herein, using a set of carbon nanotube supported Pt-N-C single-atom catalysts, we demonstrate how the neighboring N dopants regulate the electronic structure of the Pt central atom and thus steer the ORR selectivity; that is, the O2-to-H2O2 conversion selectivity can be tailored from 10% to 85% at 0.3 V versus reversible hydrogen electrode. Moreover, via a comprehensive X-ray-radiated spectroscopy and shell-isolated nanoparticle-enhanced Raman spectroscopy analysis coupled with theoretical modeling, we reveal that a dominant pyridinic- and pyrrolic-N coordination within the first shell of Pt-N-C motifs favors the 4e- ORR, whereas the introduction of a second-shell graphitic-N dopant weakens *OOH binding on neighboring Pt sites and gives rise to a dominant 2e- ORR. These findings underscore the importance of the chemical environment effect for steering the electrochemical performance of single-atom catalysts.

Generation of a specific aptamer for accurate detection of sarafloxacin based on fluorescent/colorimetric/SERS triple-readout sensor

Sarafloxacin (SAR), one of the most widely used fluoroquinolone antibiotics, is a serious threat to aquatic environments and human health due to its illegal abuse. Herein, we first screened an aptamer (SAR-1) that specifically binds to SAR using capture-SELEX technology. Based on molecular docking technology, SAR-1 was gradually truncated, and a short SAR-1a with better affinity and specificity was obtained. The optimal SAR-1a was further combined with a Pt nanoparticle (Pt NP)- decorated bimetallic Fe/Co-MOF to fabricate a multimode sensing platform for SAR determination. The Fe/Co-MOF@Pt NPs exhibited excellent peroxidase-like activity, which catalyzed the H2O2-mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), thereby enabling visual detection of SAR. Meanwhile, the generated oxTMB can also produce SERS responses and be used for the SERS detection of SAR. Moreover, the inherent fluorescence property of Fe/Co-MOF@Pt NPs enabled fluorescence detection of SAR. The designed triple-readout aptasensor showed good sensitivity for SAR detection with limits of detection of 0.125 ng/mL (fluorescent mode) and 0.05 ng/mL (colorimetric and SERS mode). The aptamer-based triple-mode sensing platform provided mutual verification of detection results in different output modes, effectively improving the assay accuracy and providing a promising tool for highly sensitive, selective, and accurate determination of SAR in daily life.

Oxygen-enriched pitch-derived hierarchically porous carbon toward boosted zinc-ion storage performance

The lack of cathode materials with satisfactory Zn2+ storage capability substantially hinders the realization of high-performance aqueous zinc-ion hybrid capacitors (ZHCs). Herein, we propose a facile KMnO4 template-assisted KOH activation strategy to prepare a novel oxygen-enriched hierarchically porous carbon (HPC-1-4). This strategy efficiently converts coal tar pitch (CTP) into a well-tuned carbon material with a large specific surface area of 3019 m2 g-1 and a high oxygen content of 9.20 at%, which is conducive to providing rich active sites, rapid charge transport, and appreciable pseudocapacitance for Zn-ion storage. Thus, the as-fabricated HPC-1-4-based aqueous ZHC exhibits prominent performance, including a high gravimetric capacity (206.7 mAh g-1 at 0.25 A g-1), a remarkable energy density (153.4 Wh kg-1 at 184.2 W kg-1), and an impressive power output (15240 W kg-1 at 63.5 Wh kg-1). In-depth ex-situ characterizations indicate that the excellent electrochemical properties of ZHCs are due to the synergistic effect of the Zn2+ adsorption mechanism and reversible chemisorption. In addition, the assembled quasi-solid-state device demonstrates excellent electrochemical stability of up to 100% capacity retention over 50000 cycles, accompanied with a desirable energy density of 115.6 Wh kg-1. The facile preparation method of converting CTP into carbonaceous functional materials has advanced the development of efficient and eco-friendly energy storage technologies.

Corrosion Dynamics of Carbon-Supported Platinum Electrocatalysts with Metal-Carbon Interactions Revealed by In Situ Liquid Transmission Electron Microscopy

Carbon support is essential for electrocatalysis, but limitations remain, as carbon corrosion can lead to electrocatalyst degradation and affect the long-term durability of electrocatalysts. Here, we studied the corrosion dynamics of carbon nanotubes (CNTs) and Vulcan carbon (VC) together with platinum (Pt) nanoparticles in real time by liquid cell (LC) transmission electron microscopy (TEM). The results showed that CNTs with a high degree of graphitization exhibited higher corrosion resistance compared to VC. Furthermore, we observed that the main degradation path of Pt nanoparticles in Pt/CNTs was ripening, while in Pt/VC, it was aggregation and coalescence, which was dominated by the interactions between Pt nanoparticles and different hybridization of carbon supports. Finally, we performed an ex situ CV stability test to confirm the conclusions obtained from in situ experiments. This work provides deep insights into the corrosion mechanism of carbon-supported electrocatalysts to optimize the design of electrocatalysts with a higher durability.

Incorporating a built-in electric field into a NiFe LDH heterojunction for enhanced oxygen evolution and urea oxidation

Herein, a N-doped carbon-supported Co and NiFe LDH (Co-NC@NiFe LDH) array was developed, which demonstrated superior catalytic activities for both the OER and UOR in an alkaline medium. The intrinsic electron transfer is effectively regulated by the construction of a built-in electric field, which reduces the reaction energy barrier and consequently leads to a significant enhancement in electrocatalytic activity.

Controllable Electrochemical Liberation of Hydrogen from Sodium Borohydride

Sodium borohydride (NaBH4 ) has earned recognition as a promising hydrogen carrier, attributed to its exceptional hydrogen storage capacity, boasting a high theoretical storage capacity of 10.8 wt %. Nonetheless, the utilization of traditional pyrolysis and hydrolysis methods still presents a formidable challenge in achieving controlled hydrogen generation especially under ambient conditions. In this work, we report an innovative electrochemical strategy for production H2 by coupling NaBH4 electrooxidation reaction (BOR) at anode in alkaline media with hydrogen evolution reaction (HER) at cathode in acidic media. To implement this, we have developed a bifunctional electrocatalyst denoted as Pd-Mo2 C@CNTs, wherein Pd nanoparticles are grown in situ on Mo2 C embedded within N-doped carbon nanotubes. This electrocatalyst demonstrates exceptional performance in catalyzing both alkaline BOR and acidic HER. We have developed a hybrid acid/alkali cell, utilizing Pd/Mo2 C@CNTs as the anode and cathode electrocatalysts. This configuration showcases remarkable capabilities for self-sustained, precise, and uninterrupted indirect release of H2 stored in NaBH4 , even at high current densities of 100 mA cm-2 with a Faraday efficiency approaching 100 %. Additionally, this electrochemical device exhibits significant promise as a fuel cell, with the ability to deliver a maximum power density of 20 mW cm-2 .

Highly dispersed Fe7S8 anchored on sp2/sp3 hybridized carbon boosting peroxymonosulfate activation for enhanced EOCs elimination though singlet oxygen-dominated nonradical pathway

The synergistic effect of carbon materials with high sp2/sp3 hybridized carbon ratio and metal materials can enhance the efficiency of peroxymonosulfate (PMS) based advanced oxidation processes. In this study, a composite of highly dispersed Fe7S8 anchored on sp2/sp3 hybridized carbon (Fe7S8@HC) was developed by a facile synthesis for PMS activation. Within 10 min, the removal efficiency of the target pollutant doxycycline (DOX) could reach ca. 96 % in optimal Fe7S8@HC/PMS system through a 1O2-dominated non-radical pathway. Correlation mechanism analysis revealed that thiophene S, sp2/sp3 ratio and Fe(II) were critical factors for elongating of the O-O bond of PMS. Moreover, the Fe7S8@HC/PMS system exhibited favorable adaptability to interference such as common inorganic anions, humic acid and pH changes and could effectively remove various organic pollutants with low ionization potential. Moreover, the system maintained high DOX removal efficiency by running 30 cycles in a continuous flow reactor. Finally, susceptible sites of DOX and four degradation pathways were proposed by density functional theory calculation and LC-MS detection. This work not only offered new insights into the design of high-performance catalysts combining metal and biomass-based carbon materials, but also provided technical support for the remediation of water bodies containing emerging organic contaminants.

Engineering Electronic Structure of Nitrogen-Carbon Sites by sp3 -Hybridized Carbon and Incorporating Chlorine to Boost Oxygen Reduction Activity

Development of efficient and easy-to-prepare low-cost oxygen reaction electrocatalysts is essential for widespread application of rechargeable Zn-air batteries (ZABs). Herein, we mixed NaCl and ZIF-8 by simple physical milling and pyrolysis to obtain a metal-free porous electrocatalyst doped with Cl (mf-pClNC). The mf-pClNC electrocatalyst exhibits a good oxygen reduction reaction (ORR) activity (E1/2 =0.91 V vs. RHE) and high stability in alkaline electrolyte, exceeding most of the reported transition metal carbon-based electrocatalysts and being comparable to commercial Pt/C electrocatalysts. Likewise, the mf-pClNC electrocatalyst also shows state-of-the-art ORR activity and stability in acidic electrolyte. From experimental and theoretical calculations, the better ORR activity is most likely originated from the fact that the introduced Cl promotes the increase of sp3 -hybridized carbon, while the sp3 -hybridized carbon and Cl together modify the electronic structure of the N-adjacent carbons, as the active sites, while NaCl molten-salt etching provides abundant paths for the transport of electrons/protons. Furthermore, the liquid rechargeable ZAB using the mf-pClNC electrocatalyst as the cathode shows a fulfilling performance with a peak power density of 276.88 mW cm-2 . Flexible quasi-solid-state rechargeable ZAB constructed with the mf-pClNC electrocatalyst as the cathode exhibits an exciting performance both at low, high and room temperatures.

Unveiling the sp2 ─sp3 C─C Polar Bond Induced Electromagnetic Responding Behaviors by a 2D N-doped Carbon Nanosheet Absorber

The infertile electromagnetic (EM) attenuating behavior of carbon material makes the improvement of its performance remain a significant challenge. Herein, a facile and low-cost strategy radically distinct from the prevalent approaches by constructing polar covalent bonds between sp2 -hybridized and sp3 -hybridized carbon atoms to introduce strong dipolar polarization is proposed. Through customizing and selectively engineering the N moieties conjugated with carbon rings, the microstructure of the as-synthesized 2D nanosheet is gradually converted with the partial transition from sp3 carbons to sp2 carbons, where the electric dipoles between them are also tuned. Supported by the DFT calculations, a progressively enhanced sp2 ─sp3 C─C dipolar polarization is caused by this controllable structure evolution, which is demonstrated to contribute dominantly to the total dielectric loss. By virtue of this unduplicated loss behavior, a remarkable effective absorption bandwidth (EAB) beyond -10 dB of 8.28 GHz (2.33 mm) and an ultrawide EAB beyond -5 dB of 13.72 GHz (4.93 mm) are delivered, which upgrade the EM performance of carbon material to a higher level. This study not only demonstrates the huge perspective of sp2 ─sp3 -hybridized carbon in EM elimination but also gives pioneering insights into the carbon-carbon polarization mechanism for guiding the development of advanced EM absorption materials.

A Universal Cross-Synthetic Strategy for Sub-10 nm Metal-Based Composites with Excellent Ion Storage Kinetics

The sub-10 nm metal-based nanomaterials (SMNs) show great potential for the electrochemical energy storage field. However, their ion storage capacity and stability suffer from severe agglomeration and interface problems. Herein, a universal strategy is reported to synthesize a wide range of SMNs (e.g., metal, nitride, oxide, and sulfides) embedded in free-standing carbon foam (SMN/FC-F) composite electrodes by crossing the interfacial confinement of NaCl self-assembly with the thermal-mechanical coupling of powder metallurgy. The pressure-enhanced NaCl self-assembly interfacial confinement is greatly beneficial to preventing SMN agglomeration and promoting SMNs embedded in FC-F which originate from the welding of carbon nanosheets. They are confirmed via a series of advanced characterizations including X-ray photoelectron spectroscopy, and spherical aberration-corrected scanning transmission electron microscopy, with theoretical computations. Benefiting from the unique structure, SMNs/FC-F delivers ultrafast and stable ion-storage kinetics. As a proof-of-concept demonstration, the MoS2 /FC-F shows excellent ion storage kinetics and superior long-term cycling performance for ion storage (e.g., Na3 V2 (PO4 )2 O2 F/C//MoS2 /FC-F sodium-ion batteries exhibit a high reversible capacity of 185 mAh g-1 at 0.5 A g-1 with a decay rate of 0.05% per cycle.). This work provides a new opportunity to design and fabricate promising SMN-based free-standing working electrodes for electrochemical energy storage and conversion applications.

Boosting Oxygen Reduction Reaction Kinetics by Designing Rich Vacancy Coupling Pentagons in the Defective Carbon

In the energy conversion context, the design and synthesis of high-performance metal-free carbon nanomaterials with topological defects for the oxygen reduction reaction (ORR) are essential. Herein, we first report a template-assisted strategy to fabricate carbon defect electrocatalysts with rich vacancy coupling pentagons (VP) as active sites in two-dimensional (2D) carbon nanosheets (VP/CNs). Experimental characterizations verify the presence of abundant VP active sites in the VP/CNs electrocatalyst, and the ORR activity is linearly related to the amounts of VP active sites. In situ spectroscopic results identify that the VP/CNs can catalyze direct O-O bond cleavage, bypassing the formation of traditional *OOH intermediates, resulting in the fast kinetics of ORR via a dissociative pathway. The as-prepared VP/CNs show outstanding intrinsic activity for alkaline ORR (half-wave potential of 0.86 V vs reversible hydrogen electrode) with an almost 99% efficiency for four-electron selectivity, outperforming that using the benchmark of Pt/C. Density functional theory calculations further reveal that the cooperative effect between carbon vacancy and adjacent pentagons significantly increases the charge transfer and achieves a lower ORR reaction energy barrier compared with the counterpart of adjacent pentagons or single pentagon. The well-designed carbon defects pave a new avenue for the rational design of metal-free electrocatalysts with high efficiency.

N, S codoped carbon matrix-encapsulated CoFe/Co0.2Fe0.8S heterostructure as a highly efficient and durable bifunctional oxygen electrocatalyst for rechargeable zinc-air batteries

The realization of durable and efficient oxygen evolution reactions (OER) at large current densities and low overpotentials is of significant importance but remains a great challenge. In this study, a CoFe/Co_0.2Fe_0.8S@NS-CNTs/CC (CF/CFS@NS-CNTs/CC) heterogeneous structure was fabricated by isolating CoFe/Co_0.2Fe_0.8S (CF/CFS) particles locked in nitrogen/sulfur codoped carbon nanotubes (NS-CNTs). Appreciable oxygen evolution reaction activity and durability was achieved with an ultralow overpotential of 110 mV at 10 mA•cm^-2. The operation was stable for 300 h at a current density of 500 mA•cm^-2. The structure was then assembled into a zinc-air battery (ZAB), which delivered a high power density of 194 mW•cm^-2, a specific capacity of 837.3 mAh•g_Zn^-1, and stable operation for 788 h without obvious voltage attenuation and altered morphology. The electronic interactions were studied by X-ray photoelectron spectroscopy (XPS), which revealed that both the bimetal components and the synergistic effect at the interface stimulated the transfer of Co and Fe sites to higher chemical valence states. Theoretical calculations indicated that the synergistic effect of the bimetal components, build-in interfacial potential, and surface chemical reconstruction adjusted the Fermi level to optimize the thermodynamic formation of O* to OOH*, thus enhancing the intrinsic activity.

N-Doped Carbon Nanotubes Supported Fe-Mn Dual-Single-Atoms Nanozyme with Synergistically Enhanced Peroxidase Activity for Sensitive Colorimetric Detection of Acetylcholinesterase and Its Inhibitor

Monitoring acetylcholinesterase (AChE) and its inhibitors is of importance for early diagnosis and therapy of neurological diseases. Herein, N-doped carbon nanotubes supported Fe-Mn dual-single-atoms (FeMn DSAs/N-CNTs) were fabricated by a simple pyrolysis, as thoroughly figured out by a series of the characterization techniques. The peroxidase-like activity of FeMn DSAs/N-CNTs was investigated by catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate rich hydroxyl radicals (·OH) in the H₂O₂ system, which effectively catalyzed colorless TMB oxidation to blue oxidized TMB (ox-TMB). Besides, the peroxidase-like activity was greatly weakened by thiocholine (derived from AChE), accompanied by making blue ox-TMB fade. Impressively, the highly improved peroxidase-like property is further evidenced by density functional theory (DFT) calculations, where the dual-single atoms show a lower energy barrier (0.079 eV) and their interactions with the N-CNTs played critical roles for producing the oxygen radicals. By virtue of the nanozyme, a low-cost, specific, and sensitive colorimetric sensor was built for detection of AChE with a broader linear range of 0.1-30 U L^-1 and a lower limit of detection (LOD, 0.066 U L^-1), combined with its feasible analysis in human serum samples. Also, this platform was applied for measuring huperzine A inhibitor with a wide linear scope of 5-500 nM and a LOD down to 4.17 nM. This strategy provides a low-cost and convenient approach for early clinical diagnosis and drug development.

Molecular Design of Porous Organic Polymer-Derived Carbonaceous Electrocatalysts for Pinpointing Active Sites in Oxygen Reduction Reaction

The widespread application of fuel cells is hampered by the sluggish kinetics of the oxygen reduction reaction (ORR), which traditionally necessitates the use of high-cost platinum group metal catalysts. The indispensability of these metal catalysts stems from their ability to overcome kinetic barriers, but their high cost and scarcity necessitate alternative strategies. In this context, porous organic polymers (POPs), which are built up from the molecular level, are emerging as promising precursors to produce carbonaceous catalysts owning to their cost-effectiveness, high electrical conductivity, abundant active sites and extensive surface area accessibility. To enhance the intrinsic ORR activity and optimize the performance of these electrocatalysts, recognizing, designing, and increasing the density of active sites are identified as three crucial steps. These steps, which form the core of our review, serve to elucidate the link between the material structure design and ORR performance evaluation, thereby providing valuable insights for ongoing research in the field. Leveraging the precision of polymer skeletons based on molecular units, POP-derived carbonaceous catalysts provide an excellent platform for in-depth exploration of the role and working mechanism for the specific active site during the ORR process. In this review, the recent advances pertaining to the synthesis techniques and electrochemical functions of various types of active sites, pinpointed from POPs, are systematically summarized, including heteroatoms, surficial substituents and edge/defects. Notably, the structure-property relationship, between these active sites and ORR performance, are discussed and emphasized, which creates guidelines to shed light on the design of high-performance ORR electrocatalysts.

Coordination Engineering of Defective Cobalt-Nitrogen-Carbon Electrocatalysts with Graphene Quantum Dots for Boosting Oxygen Reduction Reaction

Developing efficient and robust metal-nitrogen-carbon electrocatalysts for oxygen reduction reaction (ORR) is of great significance for the application of hydrogen-oxygen fuel cells and metal-air batteries. Herein, a coordination engineering strategy is developed to improve the ORR kinetics and stability of cobalt-nitrogen-carbon (Co-N-C) electrocatalysts by grafting the oxygen-rich graphene quantum dots (GQDs) onto the zeolite imidazole frameworks (ZIFs) precursors. The optimized oxygen-rich GQDs-functionalized Co-N-C (G-CoNOC) electrocatalyst demonstrates an increased mass activity, nearly two times higher than that of pristine defective Co-N-C electrocatalyst, and retains a stability of 90.0% after 200 h, even superior to the commercial Pt/C. Comprehensive investigations demonstrate that the GQDs coordination can not only decrease carbon defects of Co-N-C electrocatalysts, improving the electron transfer efficiency and resistance to the destructive free radicals from H₂ O₂ , but also optimize the electronic structure of atomic Co active site to achieve a desired adsorption energy of OOH^- , leading to enhanced ORR kinetics and stability by promoting further H₂ O₂ reduction, as confirmed by theoretical calculations and experimental results. Such a coordination engineering strategy provides a new perspective for the development of highly active noble-metal-free electrocatalysts for ORR.

Revealing the Mechanism of sp-N Doping in Graphdiyne for Developing Site-Defined Metal-Free Catalysts

Due to the limited reserves of metals, scientists are devoted to exploring high-performance metal-free catalysts based on carbon materials to solve environment-related issues. Doping would build up inhomogeneous charge distribution on surface, which is an efficient approach for boosting the catalytic performance. However, doping sites are difficult to control in traditional carbon materials, thus hindering their development. Taking the advantage of unique sp-C in graphdiyne (GDY), a new N doping configuration of sp-hybridized nitrogen (sp-N), bringing a Pt-comparable catalytic activity in oxygen reduction reaction is site-defined introduced. However, the reaction intermediate of this process is never captured, hindering the understanding of the mechanism and the precise synthesis of metal-free catalysts. After the four-year study, the fabrication of intermediate-like molecule is realized, and finally sp-N doped GDY via the pericyclic reaction is obtained. Compared with GDY doped with other N configurations, the designed sp-N GDY shows much higher catalytic activity in electroreduction of CO₂ toward CH₄ production, owing to the unique electronic structure introduced by sp-N, which is more favorable in stabilizing the intermediate. Thus, besides opening the black-box for the site-defined doping, this work reveals the relationship between doping configuration and products of CO₂ reduction.

N-Doped sp2 /sp3 Carbon Derived from Carbon Dots to Boost the Performance of Ruthenium for Efficient Hydrogen Evolution Reaction

The structure and properties of the carrier significantly affect the catalytic activity of the active centers for supported electrocatalysts. Therefore, elaborate design and regulation of the physicochemical properties of carbon carriers are essential to improve the activity and stability of the carbon-supported ruthenium-based catalysts. Herein, enlightened by the unique characteristics of coexisting sp² and sp³ carbon nuclei in N-doped carbon dots (NCDs), a hybrid structure of N-doped carbon substrates featuring N-doped sp² /sp³ carbon interfaces loaded with Ru nanoparticles (Ru/NCDs) is obtained. Spectroscopic analysis and density functional theory calculations illustrate that the interaction between Ru and NCDs effectively modulates the electronic structure of the active center Ru, and the formed N-doped sp² /sp³ carbon interface lowers the energy barrier of the intermediates in hydrogen evolution reaction (HER) and balances the hydrogen adsorption and desorption and, thereby, greatly improves the activity of Ru/NCDs. Remarkably, Ru/NCDs exhibit excellent HER activity and stability in comparison to Pt/C, which merely requires overpotentials as low as 37 and 14 mV at 10 mA cm^-2 in alkaline and acidic electrolytes, respectively. This finding will provide more thoughts about the influence of substrate properties on the catalytic activity and rational design of carbon-loaded electrocatalysts.

Coordinated single-molecule micelles: a self-template approach for preparing mesoporous doped carbons

Porous carbons prepared using a self-template approach inherit the pore features of template, but they exhibit almost no evenly dispersed mesopores, which is significant for diffusion-limited applications. Herein, N-doped hierarchically porous carbons (NHPCs) with uniform mesopores are prepared using a self-template method. The spherical single-molecule micelle of polystyrene-b-poly(4-vinyl pyridine) (PS-b-P4VP) is turned into a Zn²⁺-coordinated PS-b-P4VP micelle (CPM) by coordination of Zn²⁺ with the P4VP shell. Then, the self-template of the CPM is carbonized into a hollow carbon nanosphere. During carbonization, the PS core is decomposed to generate the central mesopore, whereas the Zn²⁺-coordinated P4VP shell is transformed into a carbonaceous shell. These even hollow carbon nanospheres aggregate to form uniformly mesoporous carbon lumps. Simultaneously, the coordinated Zn²⁺ of the CPM is reduced to metal zinc at high temperatures and then it is evaporated, thus creating numerous micropores in the carbonaceous shell. These NHPCs with uniform mesopores display a high specific surface area. As a demonstration in diffusion-limited applications, their catalytic performances for the oxygen reduction reaction (ORR) are investigated. Strikingly, NHPCs exhibit outstanding catalytic performances for the ORR. This self-template method paves a facile approach for preparing mesoporous carbons with high performances.

Plastering Sponge with Nanocarbon-Containing Slurry to Construct Mechanically Robust Macroporous Monolithic Catalysts for Direct Dehydrogenation of Ethylbenzene

Nanocarbons have shown great potential as a sustainable alternative to metal catalysts, but their powder form limits their industrial applications. The preparation of nanocarbon-based monolithic catalysts is a practical approach for overcoming the resulting pressure drop associated with their powder form. In our previous work, a ploycation-mediated approach was used to successfully prepare nanocarbon-containing monoliths. Unfortunately, because there are no macropores in the monolith, it needs to be crashed into millimeter-sized particles before application. Therefore, developing a facile method for preparing mechanically robust nanocarbon-based macroporous monolithic catalysts is vital but still challenging. Herein, evoked by swallows building their nests, we report an approach for successfully preparing a mechanically robust nanodiamond-based macroporous monolith catalyst by plastering melamine sponge (MS) with a slurry composed of nanodiamonds (NDs) and poly(imidazolium-methylene) chloride (PImM) followed by an annealing process. The macroporous monolith catalyst (ND/NC_MS-NC_PImM) containing NDs well dispersed in N-doped carbon is mechanically robust with enriched macroscopic pores. It exhibits outstanding catalysis toward ethylbenzene to styrene through a direct dehydrogenation reaction with a high styrene rate in a steady state (5.50 mmol g^-1 h^-1) and high styrene selectivity (99.5%). ND/NC_MS-NC_PImM shows much higher activity than powder ND by 1.9 fold. In addition, this work solves the significant problem of large pressure drop encountered with conventional powdered nanocarbon catalysts in the flow reactor. This work not only creates an excellent nanodiamond-based macroporous monolithic ethylbenzene direct dehydrogenation catalyst but also presents a promising avenue for preparing other macroporous monolithic catalysts for diverse transformations.

A Self-Reconstructed Bifunctional Electrocatalyst of Pseudo-Amorphous Nickel Carbide @ Iron Oxide Network for Seawater Splitting

Here, a sol-gel method is used to prepare a Prussian blue analogue (NiFe-PBA) precursor with a 2D network, which is further annealed to an Fe3 O4 /NiCx composite (NiFe-PBA-gel-cal), inheriting the ultrahigh specific surface area of the parent structure. When the composite is used as both anode and cathode catalyst for overall water splitting, it requires low voltages of 1.57 and 1.66 V to provide a current density of 100 mA cm-2 in alkaline freshwater and simulated seawater, respectively, exhibiting no obvious attenuation over a 50 h test. Operando Raman spectroscopy and X-ray photoelectron spectroscopy indicate that NiOOH2-x active species containing high-valence Ni3+ /Ni4+ are in situ generated from NiCx during the water oxidation. Density functional theory calculations combined with ligand field theory reveal that the role of high valence states of Ni is to trigger the production of localized O 2p electron holes, acting as electrophilic centers for the activation of redox reactions for oxygen evolution reaction. After hydrogen evolution reaction, a series of ex situ and in situ investigations indicate the reduction from Fe3+ to Fe2+ and the evolution of Ni(OH)2 are the origin of the high activity.

Electronic Regulation of ZnCo Dual-Atomic Active Sites Entrapped in 1D@2D Hierarchical N-Doped Carbon for Efficient Synergistic Catalysis of Oxygen Reduction in Zn-Air Battery

Transition metal-based nitrogen-doped carbon (M-N_x -C) is considered as a promising catalyst for the oxygen reduction reaction (ORR) in clean energy storage and conversion devices. Herein, ZnCo dual-atomic sites are incorporated in hierarchical N-doped carbon (HNC), with 1D nanotubes wrapped in 2D nanosheets structure (termed as 1D@2D ZnCo-HNC), via a one-step bio-inspired pyrolysis. The feeding ratio of Zn to Co precursor and pyrolytic temperature are critically modulated to achieve well-defined morphologies of the products, endowing them with the integrated merits of nanotubes and nanosheets as efficient ORR catalysts. Benefiting from the particular structure and electronic regulation of Zn on Co, the ZnCo-N_x dual-atomic system exhibits excellent ORR catalytic characteristics with an onset potential of 1.05 V and a half-wave potential of 0.82 V. Density functional theory calculations further explain the regulating role of Zn, such that the adjusted Co in ZnCo-N_x sites significantly reduces the energy cost to ultimately facilitate the ORR. Moreover, the Zn-air battery assembled with ZnCo-HNC is capable of delivering the maximum power density of 123.7 mW cm^-2 and robust stability for 110 h (330 cycles). This method provides a promising strategy for fabricating efficient transition metal-based carbon catalysts for green energy devices.

Coupling of N-Doped Mesoporous Carbon and N-Ti3 C2 in 2D Sandwiched Heterostructure for Enhanced Oxygen Electroreduction

2D heterostructures provide a competitive platform to tailor electrical property through control of layer structure and constituents. However, despite the diverse integration of 2D materials and their application flexibility, tailoring synergistic interlayer interactions between 2D materials that form electronically coupled heterostructures remains a grand challenge. Here, the rational design and optimized synthesis of electronically coupled N-doped mesoporous defective carbon and nitrogen modified titanium carbide (Ti₃ C₂ ) in a 2D sandwiched heterostructure, is reported. First, a F127-polydopamine single-micelle-directed interfacial assembly strategy guarantees the construction of two surrounding mesoporous N-doped carbon monolayers assembled on both sides of Ti₃ C₂ nanosheets. Second, the followed ammonia post-treatment successfully introduces N elements into Ti₃ C₂ structure and more defective sites in N-doped mesoporous carbon. Finally, the oxygen reduction reaction (ORR) and theoretical calculation prove the synergistic coupled electronic effect between N-Ti₃ C₂ and defective N-doped carbon active sites in the 2D sandwiched heterostructure. Compared with the control 2D samples (0.87-0.88 V, 4.90-5.15 mA cm^-2 ), the coupled 2D heterostructure possesses the best onset potential of 0.90 V and limited density current of 5.50 mA cm^-2 . Meanwhile, this catalyst exhibits superior methanol tolerance and cyclic durability. This design philosophy opens up a new thought for tailoring synergistic interlayer interactions between 2D materials.

Deciphering the Precursor-Performance Relationship of Single-Atom Iron Oxygen Electroreduction Catalysts via Isomer Engineering

Single atom Fe-nitrogen-carbon (Fe-N-C) catalysts have high catalytic activity and selectivity for the oxygen reduction reaction (ORR), and are possible alternatives for Pt-based materials. However, the reasonable design and selection of precursors to establish their relationship with Fe-N-C catalyst performance is still a formidable task. Herein, precursors with controllable structures are easily achieved through isomer engineering, with the purpose of regulating the active site density and microscopic morphology of the final electrocatalyst. As-proof-of-concept, phenylenediamine isomers-based polymers are used as precursors to fabricate Fe-N-C catalysts. The Fe-PpPD-800 derived from p-phenylenediamine shows that the best ORR activity with a half-wave potential (E_1/2 ) reaches 0.892 V vs reversible hydrogen electrode (RHE), which is better than the counterparts derived from o-phenylenediamine (Fe-PoPD-800) and m-phenylenediamine (Fe-PmPD-800), even surpassing commercial Pt/C (E_1/2  = 0.881 V vs RHE). Furthermore, the self-made zinc-air battery based on Fe-PpPD-800 achieves high power density and specific capacity up to 242 mW cm^-2 and 873 mA h g_Zn ^-1 respectively, a stable open circuit voltage of 1.45 V, and excellent cycling stability. This work not only proves the practicability of adjusting the catalytic activity of single-atom catalysts through isomer engineering, but also provides an approach to understand the relationship between precursors and target catalysts performance.