Electrocatalytic Activity of Nitrogen-Doped Carbon Nanotube Cups

Fabrication of nitrogen-carbon mediated γ-Mo2N nanocomposite based electrochemical sensor for rapid and sensitive determination of antioxidant 6-PPD in the environment

The rapid and sensitive determination of antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-henylenediamine (6-PPD) in the environment is crucial for early intervention to prevent its adverse effects. Here, a reliable electrochemical sensor based on a N-C mediated γ-Mo2N nanocomposite (γ-Mo2N@N-C) modified carbon paste electrode (CPE) was developed and applied for selective and sensitive determination of 6-PPD. Benefiting from the superior stability and faster electron diffusion coefficient, the peak current responded to 6-PPD on the sensor linearly over a concentration range from 5 × 10-8 mol L-1 to 1.0 × 10-5 mol L-1 with a detection limit of 1.67 × 10-8 mol L-1 (4.48 ng mL-1). Moreover, the sensor maintained good anti-interference ability in the determination of 6-PPD in soil samples from different regions in Zhengzhou City. Furthermore, the density functional theory (DFT) calculations combined with kinetics analysis proved that the enhanced basicity of the γ-Mo2N@N-C facilitated the deprotonation of 6-PPD, with the preferred orientation facet of (200) in γ-Mo2N playing a vital role in inducing the dissociation of 6-PPD, thereby improving the sensor's response. Such an electrochemical sensor, with its good stability and superior sensitivity, has the potential to be applied for real-time evaluation and monitoring of environmental pollutants.

Nitrogen doped carbonaceous materials as platinum free cathode electrocatalysts for oxygen reduction reaction (ORR)

Comparison of physicochemical properties and electrocatalytic behavior of different N-doped carbonaceous materials as potential catalysts for oxygen reduction reaction (ORR) was attended. Ball-milling of graphite with melamine and solvothermal treatment of graphite oxide, graphene nanoplatelets (GNP) with ammonia were used as preparation methods. Elemental analysis and N2 physisorption measurements revealed the synthesis of N-doped materials with strongly different morphological parameters. Contact angle measurements proved that all three samples had good wettability properties. According to analysis of XRD data and Raman spectra a higher nitrogen concentration corresponded to a smaller size of crystallites of the N-doped carbonaceous material. Surface total N content determined by XPS and bulk N content assessed by elemental analysis were close, indicating homogenous inclusion of N in all samples. Rotating disc electrode tests showed that these N-doped materials weremuch less active in acidic medium than in an alkaline environment. Although the presence of in-plane N species is regarded to be advantageous for the ORR activity, no particular correlation was found in these systems with any type of N species. According to Koutecky–Levich analysis, both the N-containing carbonaceous materials and the reference Pt/C catalyst displayed a typical one-step, four-electron ORR route. Both ball-milled sample with high N-content but with low SSA and solvothermally synthesized N-GNP with high SSA but low N content showed significant ORR activity. It could be concluded that beside the total N content other parameters such as SSA, pore structure, structural defects, wettability were also essential for achieving high ORR activity.

Sensing of mercury ion using light induced aqueous leaf extract mediated green synthesized silver nanoparticles of Cestrum nocturnum L

In this study, a simple, one-pot, and eco-friendly biosynthesis of silver nanoparticles (AgNPs) was accomplished with the use of aqueous leaves extract of Cestrum nocturnum L.(AECN). Different techniques like ultraviolet-visible (UV-Vis) spectrophotometry, Fourier transform infrared (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning area electron diffraction were used to investigate the optical, operational, and physical properties of the green synthesized AECN-AgNPs.The AECN-AgNPs were further used for the detection of Hg²⁺ by UV-Vis and electrochemical methods. The disintegration of the AECN-AgNPs solution caused the formation of an Ag-Hg amalgam, which caused discoloration of the solution. Sensing performance for a variety of metals such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Ni²⁺, Cu ²⁺, Fe³⁺, Zn²⁺, Co²⁺, Cd²⁺, Pb²⁺, As³⁺, and Mn²⁺ at 10-mM concentrations was measured in order to determine the selectivity of the sensor towards the Hg²⁺. For the electrochemical determination of 2 + Hg²⁺ , AECN-AgNPs were immobilized on a glassy carbon (GC) electrode, and the resulting modified electrode (GC/AECN-AgNPs) was characterized by cyclic voltammetry. This phenomenon is advantageously used for the sensitive determination of trace level Hg²⁺. GC/AECN-AgNPs demonstrated a linear calibration range of 100 nM to 10 μM and a limit of detection of 21 nM for Hg²⁺ determination.

Doping of the Mn vacancy of Mn2B2 with a single different transition metal atom as the dual-function electrocatalyst

The design of efficient electrocatalysts is essential to enhance the performance of rechargeable metal-air cells, renewable fuel cells and overall water splitting. Based on this, how to improve the catalytic activity of oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) becomes self-evident. Currently, single atom catalysts (SACs) are widely used as structural design models for the OER, ORR and HER because of the single active site and maximum metal atom utilization, but significant challenges remain. Herein, the catalytic properties of the OER, ORR and HER with a single metal atom as the active site are discussed through first-principles calculations by introducing a single metal atom in the Mn vacancy of Mn₂B₂ (TM@Mn₂B₂, TM = Au, Ag, Co, Cd, Cu, Ir, Pd, Ni, Rh, Ru and Pt). The results show that Ni@Mn₂B₂ is suitable as a dual-function electrocatalyst for the OER/ORR with overpotentials of 0.38 V and 0.37 V, which are lower than those of the OER overpotential of RuO₂/IrO₂ (0.42 V/0.56 V) and the ORR overpotential of Pt (0.45 V). Meanwhile, Pt@Mn₂B₂ is available as an OER/HER dual-function electrocatalyst for overall water splitting with a lower overpotential of OER (0.45 V) and lower |ΔG_H| (-0.15eV) under 1/4 hydrogen coverage for the HER. This work proposes a practical strategy for developing single metal atom doped MBene as a dual-function electrocatalyst.

Efficient Hydrogen Evolution Reaction with Bulk and Nanostructured Mitrofanovite Pt3Te4

Here, we discuss the key features of electrocatalysis with mitrofanovite (Pt₃Te₄), a recently discovered mineral with superb performances in hydrogen evolution reaction. Mitrofanovite is a layered topological metal with spin-polarized topological surface states with potential applications for spintronics. However, mitrofanovite is also an exceptional platform for electrocatalysis, with costs of the electrodes suppressed by 47% owing to the partial replacement of Pt with Te. Remarkably, the Tafel slope in nanostructured mitrofanovite is just 33 mV/dec, while reduced mitrofanovite has the same Tafel slope (36 mV/dec) as state-of-the-art electrodes of pure Pt. Mitrofanovite also affords surface stability and robustness to CO poisoning. Accordingly, these findings pave the way for the advent of mitrofanovite for large-scale hydrogen production.

Nitrogen-doped carbon dots/Ni-MnFe-layered double hydroxides (N-CDs/Ni-MnFe-LDHs) hybrid nanomaterials as immunoassay label for low-density lipoprotein detection

Nitrogen-doped carbon dots/Ni-MnFe-layered double hydroxides (N-CDs/Ni-MnFe-LDHs) are demonstrated as superior peroxidase mimic antibody labels alternative to horseradish peroxidase (HRP) in an immunoassay, potentially overcoming some of the inherent disadvantages of HRP and other enzyme mimicking nanomaterials. They revealed efficient peroxidase-like activity and catalyzed the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to form the intense blue product (at 620 nm) in the presence of hydrogen peroxide (H₂O₂). Using low-density lipoprotein (LDL) as a model target, an ultra-low limit of detection (0.0051 mg/dL) and a linear range of 0.0625-0.750 mg/dL were achieved, exhibiting higher sensitivity than the HRP-based immunoassay. Thus, the proposed N-CDs/Ni-MnFe-LDHs can be used as HRP mimicking analogs for developing highly sensitive colorimetric immunosensors for detection of biomarkers, as well as trace chemical analysis.

Nanostructured Carbon Electrocatalysts for Energy Conversions

The growing energy demand worldwide has led to increased use of fossil fuels. This, in turn, is making fossil fuels dwindle faster and cause more negative environmental impacts. Thus, alternative, environmentally friendly energy sources such as fuel cells and electrolyzers are being developed. While significant progress has already been made in this area, such energy systems are still hard to scale up because of their noble metal catalysts. In this concept paper, first, various scalable nanocarbon-based electrocatalysts that are being synthesized for energy conversions in these energy systems are introduced. Next, notable heteroatom-doping and nanostructuring strategies that are applied to produce different nanostructured carbon materials with high electrocatalytic activities for energy conversions are discussed. The concepts used to develop such materials with different structures and large density of dopant-based catalytic functional groups in a sustainable way, and the challenges therein, are emphasized in the discussions. The discussions also include the importance of various analytical, theoretical, and computational methods to probe the relationships between the compositions, structures, dopants, and active catalytic sites in such materials. These studies, coupled with experimental studies, can further guide innovative synthetic routes to efficient nanostructured carbon electrocatalysts for practical, large-scale energy conversion applications.

Multifunctional Catalyst CuS for Nonaqueous Rechargeable Lithium-Oxygen Batteries

Copper sulfide with flower-like (f-CuS) and carambola-like (c-CuS) morphologies was successfully synthesized by a facile one-step solvothermal route with different surfactants. When employed as cathode catalysts for lithium-oxygen batteries (LOBs), f-CuS outperforms c-CuS in terms of oxygen electrochemistry, judging from the faster kinetics and the higher reversibility of oxygen reduction/oxidation reactions, as well as the better LOB performance. Moreover, an abnormal high-potential discharge plateau was observed in the discharge profile of the LOB. To understand the different performances of f-CuS and c-CuS and the abnormal high-potential plateau, theoretical calculations were conducted, based on which a mechanism was proposed and verified with experiments. On the whole, CuS can work as a multifunctional catalyst for promoting LOB performance, which means that the dissolved CuS in LiTFSI/TEGDME electrolyte can serve as a liquid catalyst by the redox couples of Cu(TFSI)₂/Cu(TFSI)₂^-/Cu(TFSI)₂^2-, in addition to the function as a traditional solid catalyst in the cathode.

Boron containing metal-organic framework for highly selective photocatalytic production of H2O2 by promoting two-electron O2 reduction

A zirconium-based metal-organic framework containing boron (UiO-66-B) is prepared, which displays efficient photocatalytic H₂O₂ production. The H₂O₂ evolution rate is about 1002 μmol g^-1 h^-1, much higher than that of most known photocatalysts. Pristine UiO-66 displays a much lower activity (314 μmol g^-1 h^-1) under the same conditions, suggesting the significant role of boron. Both theoretical calculations and the combined experimental results verify the above conclusion, and the role of boron is ascribed to the following aspects: (1) enhanced O₂ adsorption, (2) highly selective proton-coupled two-electron transfer, (3) faster carrier separation and surface charge transfer, and (4) faster generation but slower decomposition rates of H₂O₂. This work highlights key factors in the two-electron O₂ reduction reaction (ORR), presents a deeper understanding of the role of boron in enhancing H₂O₂ production, and provides a new strategy for designing photocatalysts with excellent H₂O₂ evolution efficiency.

Fabrication of defective graphene oxide for efficient hydrogen production and enhanced 4-nitro-phenol reduction

Hydrogen has been considered as one of the most promising alternative energy source to solve the future energy demands due to its high energy capacity and emission-free character. The generation of hydrogen from non-fossil sources is necessary for the sustainable development of human life on this planet. The hydrolysis of sodium borohydride can quickly produce a large amount of hydrogenin situand on-demand in the presence of the catalyst, which can be used as an alternative energy source. So, it is crucial to fabricate the highly efficient, robust, and economical catalyst for the production of hydrogen via hydrolysis of sodium borohydride. Herein, a facile and efficient approach for the synthesis of metal-functionalized reduced graphene oxide for the production of hydrogen at room temperature was used. Moreover, the synthesized catalyst has also been tested in the field of environmental catalysis for the reduction of toxic 4-nitrophenol to valuable 4-aminophenol in the presence of sodium borohydride. The enhanced activity of prepared metal-functionalized reduced graphene oxide is ascribed to a strong affinity between Fe-N_Xand reduced graphene oxide which facilitates electron transfer as well as synergistic effect. Overall, this work presents a crucial procedure for green chemistry reactions when a carbonaceous material is selected as a catalyst.

A fluorimetric and colorimetric dual-signal sensor for hydrogen peroxide and glucose based on the intrinsic peroxidase-like activity of cobalt and nitrogen co-doped carbon dots and inner filter effect

Herein, cobalt and nitrogen co-doped carbon dots (Co-N-CDs) were fabricated via a one-pot hydrothermal approach. The obtained Co-N-CDs displayed peroxidase-like activity and fluorescence properties. It could catalyze the oxidization of guaiacol (GA) in the presence of hydrogen peroxide (H₂O₂), and thus, resulted in color change, accompanied by a new absorption peak in 470 nm. Owing to the inner filter effect, the oxidized product of GA (known as 2-PQ) largely absorbed the Co-N-CD fluorescence which was excited at 380 nm. Such changes in absorbance and fluorescence intensity were H₂O₂ concentration-dependent. Specifically, H₂O₂ could be generated by glucose oxidase to catalyze the oxidation of glucose, and thus, a colorimetric and fluorimetric sensor for glucose was established with high selectivity and excellent sensitivity. After the optimization of experimental conditions, this colorimetric sensor has a good linear range from 2 to 100 μM for glucose and the detection limit was 1.16 μM. Besides, the linear relationship between the fluorescence quenching value (ΔF) and the glucose concentration (0.4-40 μM) was obtained with a detection limit of 0.18 μM. Meanwhile, the proposed sensor has also been successfully applied for glucose detection in human serum samples, and the results were consistent with those of the standard method.

Nitrogen doped graphene quantum dots based on host guest interaction for selective dual readout of dopamine

Herein, yellow emissive nitrogen doped graphene quantum dots (N@GQDs) were prepared by a novel advanced thermal driven oxidation. The N@GQDs was functionalized with β-cyclodextrin (β-CD) to improve its catalytic performance towards dopamine (DA) detection. The β-CD/N@GQDs exhibited strong fluorescence at λ_em. = 550 nm after excitation at 460 nm with a quantum yield of 38.6%. The β-CD/N@GQDs showed good peroxidase like activity via catalyzing the oxidation of tetramethylbenzidine (TMB) in presence of H₂O₂ to form blue colored product at λ_max = 652 nm. In the colorimetric assay of DA, the detection based on the oxidation of TMB by H₂O₂ in presence of β-CD/N@GQDs as a catalyst. Then, the color of the blue oxidized TMB (oxTMB) product was reduced by addition of DA. While the fluorometric detection of DA based on the "inner filter effect" of the overlapped emission spectrum of β-CD/N@GQDs with the absorption spectrum of oxTMB, where, addition of DA reduces oxTMB to TMB and restores the fluorescence intensity of β-CD/N@GQDs. Under the optimized conditions, the colorimetric method achieved linearity range of 0.12-7.5 µM and LOD (S/N = 3) of 0.04 µM, while the fluorometric method achieved linearity range of 0.028-1.5 µM and LOD (S/N = 3) of 0.009 µM. The peroxidase like activity of β-CD/N@GQDs was used to detect DA in human plasma and serum samples with good % recoveries. The colorimetric and fluorometric methods exhibited good sensitivity and selectivity toward DA detection.

Mimicking Peroxidase-Like Activity of Nitrogen-Doped Carbon Dots (N-CDs) Coupled with a Laminated Three-Dimensional Microfluidic Paper-Based Analytical Device (Laminated 3D-μPAD) for Smart Sensing of Total Cholesterol from Whole Blood

This work presents a simple hydrothermal synthesis of nitrogen-doped carbon dots (N-CDs), fabrication of microfluidic paper-based analytical device (μPAD), and their joint application for colorimetric determination of total cholesterol (TC) in human blood. The N-CDs were characterized by various techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD), and the optical and electronic properties of computational models were studied using the time-dependent density functional theory (TD-DFT). The characterization results confirmed the successful doping of nitrogen on the surface of carbon dots. The N-CDs exhibited high affinity toward 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)-diammonium salt (ABTS) with the Michaelis-Menten constant (K_M) of 0.018 mM in a test for their peroxidase-like activity. Particularly, since hydrogen peroxide (H₂O₂) is the oxidative product of cholesterol in the presence of cholesterol oxidase, a sensitive and selective method of cholesterol detection was developed. Overall, the obtained results from TD-DFT confirm the strong adsorption of H₂O₂ on the graphitic N positions of the N-CDs. The laminated three-dimensional (3D)-μPAD featuring a 6 mm circular detection zone was fabricated using a simple wax screen printing technique. Classification of TC according to the clinically relevant criteria (healthy, <5.2 mM; borderline, 5.2-6.2 mM; and high risk, >6.2 mM) could be determined by the naked eye within 10 min by simple comparison using a color chart. Overall, the proposed colorimetric device serves as a low-cost, rapid, simple, sensitive, and selective alternative for TC detection in whole blood samples that is friendly to unskilled end users.

Electrochemical sensor for rutin detection based on N-doped mesoporous carbon nanospheres and graphene

A new electrochemical sensor shows great sensing performance to rutin and high selectivity towards even 13 interfering species and realizes detection of rutin in real samples such as human serum.

Novel joint catalytic properties of Fe and N co-doped graphene for CO oxidation

Using density functional theory, we have performed detailed calculations of the joint catalytic activity of graphene co-doped with Fe and N atoms. The Fe atom can be located on single vacancy graphene and acts as the active site. Due to the strong attraction of the Fe ion, the O-O bond length of the O2 molecule is elongated, which decreases the bonding energy between the O atoms. The energy barrier of CO oxidization is 0.84 eV. When N atoms are doped into the graphene, the interactions between the Fe ions and O2 molecules are stronger, and the O-O bond lengths are elongated further, which makes the desorption of the quasi-CO2 molecule easier. The energy barriers are reduced to 0.62 eV, 0.49 eV, and 0.33 eV for graphene doped with one, two and three N atoms, respectively. The O atom remaining on the Fe ion can form a CO2 molecule with an additional CO molecule. The produced CO2 molecule can be released with a small or even zero energy barrier by adsorbing an O2 molecule. The adsorbed O2 molecule is then involved in the next reaction process, and the material can be used as a recycled catalyst.

Reactive Plasma N-Doping of Amorphous Carbon Electrodes: Decoupling Disorder and Chemical Effects on Capacitive and Electrocatalytic Performance

Nitrogen-free amorphous carbon thin films prepared via sputtering followed by graphitization, were used as precursor materials for the creation of N-doped carbon electrodes with varying degrees of amorphization. Incorporation of N-sites was achieved via nitrogen plasma treatments which resulted in both surface functionalization and amorphization of the carbon electrode materials. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to monitor composition and carbon organization: results indicate incorporation of predominantly pyrrolic-N sites after relatively short treatment cycles (5 min or less), accompanied by an initial etching of amorphous regions followed by a slower process of amorphization of graphitized clusters. By leveraging the difference in the rate of these two processes it was possible to investigate the effects of chemical N-sites and C-defect sites on their electrochemical response. The materials were tested as metal-free electrocatalysts in the oxygen reduction reaction (ORR) in alkaline conditions. We find that the introduction of predominantly pyrrolic-N sites via plasma modification results in improvements in selectivity in the ORR, relative to the nitrogen-free precursor material. Introduction of defects through prolonged plasma exposure has a more pronounced and beneficial effect on ORR descriptors than introduction of N-sites alone, leading to both increased onset potentials, and reduced hydroperoxide yields relative to the nitrogen-free carbon material. Our results suggest that increased structural disorder/heterogeneity results in the introduction of carbon sites that might either serve as main activity sites, or that enhance the effects of N-functionalities in the ORR via synergistic effects.

Metal-Free Colorimetric Detection of Pyrophosphate Ions by Inhibitive Nanozymatic Carbon Dots

The pyrophosphate ion (P₂O₇^4-, PPi) plays a critical role in various biological processes and acts as an essential indicator for physiological mechanism investigations and disease control monitoring. However, most of the currently available approaches for PPi species detection for practical usage still lack appropriate indicator generation, straightforward detection requirements, and operation convenience. In this study, a highly sensitive and selective PPi detection approach via the use of nanozymatic carbon dots (CDs) is introduced. This strategy eliminates the common need for metal ions in the detection process, where a direct indicator-PPi interaction is adopted to provide straightforward signal reports, and importantly, through a green indicator preparation. The preparation of this nanozymatic CDs' indicator utilizes an aqueous solution refluxing, employing galactose and histidine as the precursor materials. The mild conditions of the solution refluxing produce fluorescent CDs exhibiting peroxidase-mimic properties, which can catalyze the o-phenylenediamine oxidation under the presence of H₂O₂. The introduction of PPi species, interestingly, inhibits this process very efficiently, the extent of which can be colorimetrically monitored by the generated yellow product 2,3-diaminophenazine. Spectroscopic results point to CD surface functional groups' selective binding toward PPi species, which severely interferes with the electron transfer process in the enzymatic catalysis. Relying on this CD peroxidase-mimetic property inhibition, sensitive and selective recognition of PPi reaches a detection limit of 4.29 nM, enabling practical usage in complex matrixes. Owing to the superior compatibility and high stability of nanozymatic CDs, they can also be inkjet-printed on paper-based devices to create a portable and convenient platform for PPi detection. Both the solution and the paper-device-based selective recognitions confirm this unique and robust metal-free inhibitive PPi detection, which is supported by a convenient green preparation of nanozymatic CDs.

Functional nanoarrays for investigating stem cell fate and function

Stem cells show excellent potential in the field of tissue engineering and regenerative medicine based on their excellent capability to not only self-renew but also differentiate into a specialized cell type of interest. However, the lack of a non-destructive monitoring system makes it challenging to identify and characterize differentiated cells before their transplantation without compromising cell viability. Thus, the development of a non-destructive monitoring method for analyzing cell function is highly desired and can significantly benefit stem cell-based therapies. Recently, nanomaterial-based scaffolds (e.g., nanoarrays) have made possible considerable advances in controlling the differentiation of stem cells and characterization of the differentiation status sensitively in real time. This review provides a selective overview of the recent progress in the synthesis methods of nanoarrays and their applications in controlling stem cell fate and monitoring live cell functions electrochemically. We believe that the topics discussed in this review can provide brief and concise guidelines for the development of novel nanoarrays and promote the interest in live cell study applications. A method which can not only control but also monitor stem cell fate and function will be a promising technology that can accelerate stem cell therapies.

Plasma-Assisted Controllable Doping of Nitrogen into MoS2 Nanosheets as Efficient Nanozymes with Enhanced Peroxidase-Like Catalysis Activity

Heteroatom doping is one of the effective ways to improve the catalytic performances of nanozymes. In the present work, the plasma-assisted controllable doping of nitrogen (N) into MoS₂ nanosheets has been initially proposed, resulting in efficient nanozymes. The so-obtained nanozymes were characterized separately by TEM, XRD, XPS, and FTIR. It was discovered that the resulting N-doped MoS₂ nanosheets could present dramatically enhanced peroxidase-like catalytic activities depending on the plasma treatment time. Particularly, that with the 2-min treatment could display the highest catalytic activity, which is over 3-fold higher than that of pristine MoS₂, that was also demonstrated by the kinetics studies. Herein, the N₂ plasma treatment could facilitate the N elements to be doped covalently into MoS₂ nanosheets to achieve the increased surface wettability and affinity of nanozymes for the improved access of the electrons and substrates of catalytic reactions. More importantly, the covalent doping of N elements into MoS₂ nanosheets with a lower Fermi level, as evidenced by the DFT analysis, could facilitate the promoted electron transferring, resulting in the enhanced catalysis of N-doped MoS₂ nanozymes, in addition to the high catalytic stability in water. Such a controllable plasma treatment strategy may open a new door toward the large-scale applications for doping heteroatoms into various nanozymes with improved catalysis performances.

Theoretical study of the strain effect on the oxygen reduction reaction activity and stability of FeNC catalyst

The oxygen reduction performance of Cu@FeNC (1.9%-FeNC) is different from the corresponding 2%-FeNC, mainly due to the coordination between the Cu substrate and Fe atom.

γ-Graphyne nanotubes as defect-free catalysts of the oxygen reduction reaction: a DFT investigation

γGyNTs as excellent metal-free ORR catalysts without any defects.

Carbon-Based Nanomaterials as Sustainable Noble-Metal-Free Electrocatalysts

Nowadays, due to the worldwide growth demand of energy, over consumption of fossil fuel as well as their accompanying increased negative environmental impacts, the development of renewable energy systems, such as fuel cells and water electrolyzers, is becoming one of the "holy grail" for researchers. However, their large-scale applications have been severely limited by precious and unsustainable noble-metal electrocatalysts. Hence, it is highly desirable to develop robust electrocatalysts composed exclusively of low-cost and earth-abundant elements, to reduce or replace expensive and scarce noble-metals. Carbon-based nanomaterials, including heteroatoms-doped carbons and carbon-encapsulated metal materials, have recently attracted great interests because they show remarkable electrocatalytic performance and long-term stability for energy-related reactions, such as oxygen reduction reaction (ORR), hydrogen and oxygen evolution reactions (OER), hydrazine oxidation reaction (HzOR), etc. This review summarizes the recent progress in heteroatoms-doped carbon and carbon-encapsulated metal materials, highlighting the promise as cost-efficient electrocatalysts. Finally, a prospective on the future development of these promising materials is offered.

Synergy of sp-N and sp2-N codoping endows graphdiyne with comparable oxygen reduction reaction performance to Pt

Nitrogen doped graphdiyne (NGDY) has been reported to have comparable oxygen reduction reaction (ORR) performance to Pt-based catalysts. However, the source of this enhanced ORR performance is not clearly understood. Herein, density functional theory calculations were performed to study the detailed ORR process on NGDY. The theoretically predicted overpotential (η) of GDY materials was 0.442 V, which is comparable to that of Pt-based catalysts, suggesting that GDY is a candidate for non-expensive metal-free ORR catalyst. Our results revealed that the good ORR performance of NGDY originates from the synergy of sp-N and sp²-N, which rules out the experimental proposal that sp-N doping is the dominating factor. Our results further suggest that local positive charge is not a definite descriptor to predict the ORR performance of GDY; instead ΔG_O shows a better correlation with performance. Furthermore, it was revealed that the adsorption site is crucial for determining ORR performance, which should not be ignored to fully understand the catalytic activity of GDY-based materials.

Cooperative Pollutant Adsorption and Persulfate-Driven Oxidation on Hierarchically Ordered Porous Carbon

This study presents a 3D hierarchically ordered porous carbon material (HOPC) that simultaneously achieves efficient adsorption of a range of water pollutants as well as catalytic oxidation of adsorbed pollutants. High adsorption capacity and rapid adsorption kinetics are attributed to the hydrophobic nature of the carbon substrate, the large surface area due to high porosity, and the relatively uniform size of pores that comprise the structure. The oxidative degradation is achieved by efficient mediation of electron transfer from pollutants to persulfate through the sp²-hybridized carbon and nitrogen network. As the persulfate activation and pollutant oxidation do not involve reactive radicals, oxidative degradation of the adsorbent is prevented, which has been a primary concern when adsorption and oxidation are combined either to regenerate adsorbate or to enhance oxidation performance. Batch tests showed that near complete removal of various recalcitrant micropollutants can be achieved within a short time (less than 1 min) even when treating a complex water matrix, as pollutants are concentrated on the surface of HOPC, where their oxidation is catalyzed.

Progress in Nonmetal-Doped Graphene Electrocatalysts for the Oxygen Reduction Reaction

Owing to energy shortages and environmental pollution, green energy sources such as polymer electrolyte fuel cells and metal-air batteries play a more and more important role, whereby the oxygen reduction reaction (ORR) is the rate-determining step. Development of high-efficiency and stable catalysts to facilitate the ORR is of importance. Graphene is a new type of material with two-dimensional structure and high surface area, which has wide-ranging applications in many fields. However, graphene with zero band gap shows low electrocatalytic activity toward the ORR. Introduction of nonmetal atoms can change the electronic arrangement, generate active sites, and further improve the catalytic activity of graphene. Some nonmetal-doping strategies (e.g., N, S, and P doping) can promote ORR activity. Herein, the recent development of nonmetal-doped graphene catalysts for ORR is reviewed. Some common synthetic methods for nonmetal-doped graphene materials are summarized, and the active sites and possible reaction mechanisms for ORR on various nonmetal-doped graphene catalysts are discussed.

Controllable Sulfur, Nitrogen Co-doped Porous Carbon for Ethylbenzene Oxidation: The Role of Nano-CaCO3

Heteroatom-doped porous carbon materials have exhibited promising applications in various fields. In this work, sulfur, nitrogen co-doped carbon materials (SNCs) with abundant pore structure were prepared by pyrolysis of sulfur, nitrogen-containing porous organic polymers (POPs) mixed with nano-CaCO₃ at high temperature. Among the resultant materials, SNC-Ca-850 possesses a relatively high level of doped heteroatoms and exhibits an excellent catalytic performance for the selective oxidation of benzylic C-H bonds. It is noteworthy that nano-CaCO₃ increases the doped sulfur content in the synthesized carbon materials to a large extent and impacts the existence modes of sulfur. In addition, it enhances the porous structure and specific surface area of the resultant SNCs significantly. This work provides a viable strategy to promote the doping of sulfur into carbon materials during the pyrolysis process.

Stepwise Fabrication of Co-Embedded Porous Multichannel Carbon Nanofibers for High-Efficiency Oxygen Reduction

A novel nonprecious metal material consisting of Co-embedded porous interconnected multichannel carbon nanofibers (Co/IMCCNFs) was rationally designed for oxygen reduction reaction (ORR) electrocatalysis. In the synthesis, ZnCo2O4 was employed to form interconnected mesoporous channels and provide highly active Co3O4/Co core-shell nanoparticle-based sites for the ORR. The IMC structure with a large synergistic effect of the N and Co active sites provided fast ORR electrocatalysis kinetics. The Co/IMCCNFs exhibited a high half-wave potential of 0.82 V (vs. reversible hydrogen electrode) and excellent stability with a current retention up to 88% after 12,000 cycles in a current-time test, which is only 55% for 30 wt% Pt/C.

N,P-Doped carbon with encapsulated Co nanoparticles as efficient electrocatalysts for oxygen reduction reactions

Exploring efficient non-noble ORR catalysts as alternatives to Pt-based catalysts are highly demanded for their possible application in fuel cells and rechargeable metal-air batteries. Herein, we demonstrate a rational design and synthesis of a N, P-doped carbon with encapsulated Co nanoparticles as efficient electrocatalysts for ORR. The catalyst is derived from a mixture of Co-MOF and triphenylphosphine with a mass ratio of 3 : 1 by pyrolysis in N2 atmosphere at 700 °C. The catalyst exhibited a superior ORR catalytic performance among its counterparts in 0.1 M KOH with onset and half-wave potentials of 0.88 V and 0.80 V, a much larger limiting current density of -5.93 mA cm-2 that surpassed commercial 20% Pt/C, in addition to its durability and resistance to methanol. This enhanced ORR activity of the catalyst can be attributed to the synergistic effect between Co NPs and N, P atoms, the relatively large contact surface, more exposed active sites and good electrical conductivity. This study would provide some new ideas for the design and construction of promising carbon-based non-precious metal electrocatalysts for future practical fuel cell applications.

Noble metal supported hexagonal boron nitride for the oxygen reduction reaction: a DFT study

Discovering active, stable and cost-effective catalysts for the oxygen reduction reaction (ORR) is of utmost interest for commercialization of fuel cells. Scarce and expensive noble metals such as Pt and Pd are the state-of-the-art active ORR catalysts but suffer from low stability against CO poisoning. Hexagonal boron nitride (h-BN) is a particularly attractive material due to its low cost and stability; however, it suffers from intrinsic low activity toward the ORR in the pristine form as a result of its inherently low conductivity with a large band gap of ∼5.5 electron volts. During the past few years, several strategies such as using metal supports, metal doping and atomic vacancies have been reported to significantly increase the conductivity, thereby promoting the ORR activity. Herein we use density functional theory calculations to systematically study these strategies for activating inert h-BN and further examine the stability against CO poisoning. We show that noble metals, such as Ag, Pd, and Pt, require boron (B) or nitrogen (N) vacancies to reasonably activate h-BN toward the ORR. For example, Pd supported h-BN with B-vacancies exhibits significantly high ORR activity. All three examined metal supported h-BNs are predicted to be stable against CO poisoning. These results demonstrate that supporting h-BN on noble metals is a promising strategy to increase the stability against CO poisoning while maintaining high ORR activity.

Electrospun cobalt-ZIF micro-fibers for efficient water oxidation under unique pH conditions

A unique electrospinning methodology to fabricate Co based ZIF microfibers has been developed which showed superior electrocatalytic water oxidation both in acidic and alkaline electrolytes.

Cost-effective synthesis of three-dimensional nitrogen-doped nanostructured carbons with hierarchical architectures from the biomass of sea-tangle for the amperometric determination of ascorbic acid

In this work, the three-dimensional nitrogen-doped nanostructured carbons with hierarchical architectures (3D-NNCsHAs) with high density of defective sites, high surface area and pluralities of pore size distributions was prepared through the pyrolysis of sea-tangle (Laminaria japonica), an inexpensive, eco-friendly and abundant precursor. Benefitting from their structural uniqueness, a selective and sensitive ascorbic acid (AA) sensor based on 3D-NNCsHAs was developed. Compared to the glassy carbon electrode (GCE) and the carbon nanotubes modified GCE (CNTs/GCE), the 3D-NNCsHAs modified GCE (3D-NNCsHAs/GCE) presents higher performance towards the electrocatalysis and detection of AA, such as lower detection limit (1 μM), wider linear range (10-4410 μM) and lower electrooxidation peak potential (-0.02 V vs. Ag/AgCl). In addition, 3D-NNCsHAs/GCE also exhibits high anti-interference and anti-fouling abilities for AA detection. Particularly, the fabricated 3D-NNCsHAs/GCE is able to determine AA in real samples and the results acquired are satisfactory. Therefore, the 3D-NNCsHAs can be considered as a kind of novel electrode nanomaterial for the fabrication of selective and sensitive AA sensor for the extensive practical applications ranging from food analysis, to pharmaceutical industry and clinical test.