Vertically Aligned Carbon Nanotube Arrays Co-doped with Phosphorus and Nitrogen as Efficient Metal-Free Electrocatalysts for Oxygen Reduction

Revisiting the phosphonium salt chemistry for P-doped carbon synthesis: toward high phosphorus contents and beyond the phosphate environment

The introduction of phosphorus and nitrogen atoms in carbo-catalysts is a common way to tune the electronic density, and thereby the reactivity, of the material, as well as to introduce surface reactive sites. Numerous environments are reported for the N atoms, but the P-doping chemistry is less explored and focuses on surface POx groups. A one-step synthesis of P/N-doped carbonaceous materials is presented here, using affordable and industrially available urea and tetrakis(hydroxymethyl)phosphonium chloride (THPC) as the N and P sources, respectively. In contrast to most of the synthetic pathways toward P-doped carbonaceous materials, the THPC precursor only displays P-C bonds along the carbon backbone. This resulted in unusual phosphorus environments for the materials obtained from direct thermal treatment of THPC-urea, presumably of type C-P-N according to 31P NMR and XPS. Alternatively, the in situ polymerization and calcination of the precursors were run in calcium chloride hydrate, used as a combined reaction medium and porogen agent. Following this salt-templating strategy led to particularly high phosphorus contents (up to 18 wt%), associated with porosities up to 600 m2 g-1. The so-formed P/N-doped porous materials were employed as metal-free catalysts for the mild oxidative dehydrogenation of N-heterocycles to N-heteroarenes at room temperature and in air.

Defects in Carbon-Based Materials for Electrocatalysis: Synthesis, Recognition, and Advances

ConspectusOwing to climate change and over-reliance on fossil fuels, the study and development of sustainable energy is of essential importance in the next few decades. In recent years, rapid advances have been witnessed in various power to gas electrocatalysis technologies including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) for realizing the target of blue planet with carbon neutrality. Nevertheless, practical applications with superior performance and affordable cost are largely limited by the electrode materials because the reactions are regularly driven by precious metals such as platinum (Pt) or iridium (Ir) based catalysts. Therefore, it is of significance to develop novel electrocatalysts with high electroactivity and limited cost for boosting the commercialization of green hydrogen technology.Since nitrogen-doped carbon nanotubes were first reported for enhanced ORR performance in 2009, the exploitation of carbon-based metal-free catalysts (CMFCs) as potential replacements for the precious metal electrocatalysts has become an attractive research field. To date, great progress has been made in developing new dopant strategies for CMFCs; however, the details of the catalytic mechanism and identification of active sites remain unclear, owing to the complexity in controlling the dopants and their homogeneity in carbon-based materials. To tackle this issue, our group has presented a series of works on defects catalyzing electrochemical reactions and proposed a defect catalysis mechanism since 2015. This theory is now widely accepted by the research community and has become a very important area in electrocatalysis worldwide.In this Account, we first present the defect theory for the reasonable design of defective carbon-based materials (DCMs) and subsequently summarize our previous works on the state-of-the-art defect engineering strategies to design DCMs possessing high activity, with the particular emphasis on the conjunction between defect structures and electrochemical performances. We also categorize recent defect modulation approaches on active sites in DCMs as well as showcase the advanced characterization techniques to confirm the types and densities of defects in DCMs. Finally, several perspectives on the challenges and future research opportunities of this exciting field are proposed. Remarkably, rapid advances of DCMs possessing both high electrochemical activities and low cost as a new generation of electrode materials may greatly facilitate the deployment of sustainable energy infrastructures.

Novel and Highly Sensitive Electrochemical Sensor for the Determination of Oxytetracycline Based on Fluorine-Doped Activated Carbon and Hydrophobic Deep Eutectic Solvents

Residues of oxytetracycline (OTC), a veterinary antibiotic and growth promoter, can be present in animal-derived foods; their consumption is harmful to human health and their presence must therefore be detected and regulated. However, the maximum residue limit is low, and consequently highly sensitive and accurate detectors are required to detect the residues. In this study, a novel highly sensitive electrochemical sensor for the detection of OTC was developed using a screen-printed electrode modified with fluorine-doped activated carbon (F-AC/SPE) combined with a novel deep eutectic solvent (DES). The modification of activated carbon by doping with fluorine atoms (F-AC) enhanced the adsorption and electrical activity of the activated carbon. The novel hydrophobic DES was prepared from tetrabutylammonium bromide (TBABr) and a fatty acid (malonic acid) using a green synthesis method. The addition of the DES increased the electrochemical response of F-AC for OTC detection; furthermore, it induced preconcentration of OTC, which increased its detectability. The electrostatic interactions between DES and OTC as well as the adsorption of OTC on the surface of the modified electrode through H-bonding and π-π interactions helped in OTC detection, which was quantified based on the decrease in the anodic peak potential (E _pa = 0.3 V) of AC. The electrochemical behavior of the modified electrode was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. Under optimum conditions, the calibration plot of OTC exhibited a linear response in the range 5-1500 μg L^-1, with a detection limit of 1.74 μg L^-1. The fabricated electrochemical sensor was successfully applied to determine the OTC in shrimp pond and shrimp samples with recoveries of 83.8-100.5% and 93.3-104.5%, respectively. In addition to the high sensitivity of OTC detection, the proposed electrochemical sensor is simple, cost-effective, and environmentally friendly.

A Simple Method for Preparation of Highly Conductive Nitrogen/Phosphorus-Doped Carbon Nanofiber Films

Heteroatom-doped conductive carbon nanomaterials are promising for energy and catalysis applications, but there are few reports on increasing their heteroatom doping content and conductivity simultaneously. In this manuscript, we use 2-(4-aminophenyl)-5-aminobenzimidazole as the diamine monomer to prepare polyamic acid with asymmetric structural units doped with phosphoric acid (PA) and polyacrylonitrile (PAN) as innovative composite precursors, which are then electrospun into nanofiber films. After stabilization and carbonization, the electrospun fibers are converted into N/P co-doped electrospun carbon nanofiber films (ECNFs) with high heteroatom content, including 4.33% N and 0.98% P. The morphology, structure, and conductivity of ECNFs were systematically characterized. The ECNFs doped with 15 wt.% PA exhibited conductivity that was 47.3% higher than that of the ECNFs undoped with PA, but the BET surface area decreased by 23%. The doped PA in the precursor nanofibers participated in the cyclization of PAN during thermal stabilization, as indicated by infrared spectroscopy and thermogravimetric analysis results. X-ray diffraction and Raman results indicate that a moderate amount of PA doping facilitated the formation of ordered graphitic crystallite structures during carbonization and improved the conductivity of ECNFs.

Improving the air quality with Functionalized Carbon Nanotubes: Sensing and remediation applications in the real world

With the world developing exponentially every day, the collateral damage to air is incessant. There are many methods to purify the air but using carbon nanotubes (CNTs) as adsorbents remains one of the most efficient and reliable methods, due to their high maximum adsorption capacity which renders them extremely useful for removing pollutants from the air. The different types of CNTs, their synthesis, functionalization, purification, functioning, and advantages over conventional filters are deliberated along with diverse types of CNTs like single-walled (SWCNTs), multiwalled (MWCNTs), and others, which can be functionalized and deployed for the removal of harmful gases like oxides of nitrogen and sulphur, and ozone, and volatile organic compounds (VOCs), among others. A comprehensive description of CNTs is provided in this overview with illustrative examples from the past five years. The fabrication methods and target gases of many CNTs-based gas sensors are highlighted, in addition to the comparison of their properties, mainly sensitivity. The effect of functionalization on sensors has been discussed in detail for various composites targeting specific gases, including the future outlook of functionalized CNTs in assorted practical applications.

Carbon-Supported Noble-Metal Nanoparticles for Catalytic Applications—A Review

Noble-metal nanoparticles (NMNPs), with their outstanding properties, have been arousing the interest of scientists for centuries. Although our knowledge of them is much more significant today, and we can obtain NMNPs in various sizes, shapes, and compositions, our interest in them has not waned. When talking about noble metals, gold, silver, and platinum come to mind first. Still, we cannot forget about elements belonging to the so-called platinum group, such as ruthenium, rhodium, palladium, osmium, and iridium, whose physical and chemical properties are very similar to those of platinum. It makes them highly demanded and widely used in various applications. This review presents current knowledge on the preparation of all noble metals in the form of nanoparticles and their assembling with carbon supports. We focused on the catalytic applications of these materials in the fuel-cell field. Furthermore, the influence of supporting materials on the electrocatalytic activity, stability, and selectivity of noble-metal-based catalysts is discussed.

Heteroatom-Doped Metal-Free Carbon Nanomaterials as Potential Electrocatalysts

In recent years, heteroatom-incorporated specially structured metal-free carbon nanomaterials have drawn huge attention among researchers. In comparison to the undoped carbon nanomaterials, heteroatoms such as nitrogen-, sulphur-, boron-, phosphorous-, etc., incorporated nanomaterials have become well-accepted as potential electrocatalysts in water splitting, supercapacitors and dye-sensitized solar cells. This review puts special emphasis on the most popular synthetic strategies of heteroatom-doped and co-doped metal-free carbon nanomaterials, viz., chemical vapor deposition, pyrolysis, solvothermal process, etc., utilized in last two decades. These specially structured nanomaterials' extensive applications as potential electrocatalysts are taken into consideration in this article. Their comparative enhancement of electrocatalytic performance with incorporation of heteroatoms has also been discussed.

Proposal of a Facile Method to Fabricate a Multi-Dope Multiwall Carbon Nanotube as a Metal-Free Electrocatalyst for the Oxygen Reduction Reaction

In this study, a one-pot, low-temperature synthesis method is considered for the fabrication of heteroatom dope multiwall carbon nanotubes (MWCNT). Doped MWCNT is utilized as an effective electrocatalyst for oxygen reduction reaction (ORR). Single, double, and triple doping of boron, nitrogen and sulfur elements are utilized as the dopants. A reflux system with temperature of 180 °C is implemented in the doping procedure. Actually, unlike the previous studies in which doping on the carbon structures was performed using a furnace at temperatures above 700 °C, in this green and sustainable method, the triple doping on MWCNT is conducted at atmospheric pressure and low temperature. The morphology and structure of the fabricated catalysts were evaluated by Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Raman spectroscopy. According to the results, the nanoparticles were encapsulated in the carbon nanotubes. Aggregated clusters of the sulfur in the case of S-MWCNT are considerable. Cyclic voltammetry (CV), rotating disk electrode, linear sweep voltammetry (LSV), and chronoamperometry electrochemical tests are employed for assessing the oxygen reduction activity of the catalysts. The results illustrate that by using this doping method, the onset potential shifts to positive values towards the oxidized MWCNT. It can be deduced that by doping the N, B, and S atoms on MWCNTs, the defects in the CNT structure, which serve as active sites for ORR application, increase. The N/S/B-doped graphitic layers have a more rapid electron transfer rate at the electrode/electrolyte interface. Thus, this can improve the electrochemistry performance and electron transfer of the MWCNTs. The best performance and electrochemical activity belonged to the NB-MWCNT catalyst (−0.122 V vs. Ag/AgCl). Also, based on the results gained from the Koutecky–Levich (KL) plot, it can be said that the ORR takes place through the 4 e− pathway.

Heteroatom-doped carbon-based oxygen reduction electrocatalysts with tailored four-electron and two-electron selectivity

Oxygen reduction reaction (ORR) plays a pivotal role in electrochemical energy conversion and commodity chemical production. Oxygen reduction involving a complete four-electron (4e-) transfer is important for the efficient operation of polymer electrolyte fuel cells, whereas the ORR with a partial 2e- transfer can serve as a versatile method for producing industrially important hydrogen peroxide (H2O2). For both the 4e- and 2e- pathway ORR, platinum-group metals (PGMs) have been materials of prevalent choice owing to their high intrinsic activity, but they are costly and scarce. Hence, the development of highly active and selective non-precious metal catalysts is of crucial importance for advancing electrocatalysis of the ORR. Heteroatom-doped carbon-based electrocatalysts have emerged as promising alternatives to PGM catalysts owing to their appreciable activity, tunable selectivity, and facile preparation. This review provides an overview of the design of heteroatom-doped carbon ORR catalysts with tailored 4e- or 2e- selectivities. We highlight catalyst design strategies that promote 4e- or 2e- ORR activity. We also summarise the major active sites and activity descriptors of the respective ORR pathways and describe the catalyst properties controlling the ORR mechanisms. We conclude the review with a summary and suggestions for future research.

Carbon Nanohorn-Based Electrocatalysts for Energy Conversion

In the context of even more growing energy demands, the investigation of alternative environmentally friendly solutions, like fuel cells, is essential. Given their outstanding properties, carbon nanohorns (CNHs) have come forth as promising electrocatalysts within the nanocarbon family. Carbon nanohorns are conical nanostructures made of sp2 carbon sheets that form aggregated superstructures during their synthesis. They require no metal catalyst during their preparation and they are inexpensively produced in industrial quantities, affording a favorable candidate for electrocatalytic reactions. The aim of this article is to provide a comprehensive overview regarding CNHs in the field of electrocatalysis and especially, in oxygen reduction, methanol oxidation, and hydrogen evolution, as well as oxygen evolution from water splitting, underlining the progress made so far, and pointing out the areas where significant improvement can be achieved.

A review of recent progress on electrocatalysts toward efficient glycerol electrooxidation

Glycerol electrooxidation has attracted immense attention due to the economic advantage it could add to biodiesel production. One of the significant challenges for the industrial development of glycerol electrooxidation process is the search for a suitable electrocatalyst that is sustainable, cost effective, and tolerant to carbonaceous species, results in high performance, and is capable of replacing the conventional Pt/C catalyst. We review suitable, sustainable, and inexpensive alternative electrocatalysts with enhanced activity, selectivity, and durability, ensuring the economic viability of the glycerol electrooxidation process. The alternatives discussed here include Pd-based, Au-based, Ni-based, and Ag-based catalysts, as well as the combination of two or three of these metals. Also discussed here are the prospective materials that are yet to be explored for glycerol oxidation but are reported to be bifunctional (being capable of both anodic and cathodic reaction). These include heteroatom-doped metal-free electrocatalysts, which are carbon materials doped with one or two heteroatoms (N, B, S, P, F, I, Br, Cl), and heteroatom-doped nonprecious transition metals. Rational design of these materials can produce electrocatalysts with activity comparable to that of Pt/C catalysts. The takeaway from this review is that it provides an insight into further study and engineering applications on the efficient and cost-effective conversion of glycerol to value-added chemicals.

Three-dimensional ordered macroporous ZIF-8 nanoparticle-derived nitrogen-doped hierarchical porous carbons for high-performance lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries have attracted considerable attention due to their ultra-high specific capacity and energy density.

Recent Progresses in Oxygen Reduction Reaction Electrocatalysts for Electrochemical Energy Applications

Abstract

Electrochemical energy storage systems such as fuel cells and metal–air batteries can be used as clean power sources for electric vehicles. In these systems, one necessary reaction at the cathode is the catalysis of oxygen reduction reaction (ORR), which is the rate-determining factor affecting overall system performance. Therefore, to increase the rate of ORR for enhanced system performances, efficient electrocatalysts are essential. And although ORR electrocatalysts have been intensively explored and developed, significant breakthroughs have yet been achieved in terms of catalytic activity, stability, cost and associated electrochemical system performance. Based on this, this review will comprehensively present the recent progresses of ORR electrocatalysts, including precious metal catalysts, non-precious metal catalysts, single-atom catalysts and metal-free catalysts. In addition, major technical challenges are analyzed and possible future research directions to overcome these challenges are proposed to facilitate further research and development toward practical application.

Graphic Abstract

Synthesis of P- and N-doped carbon catalysts for the oxygen reduction reaction via controlled phosphoric acid treatment of folic acid

Herein, we synthesized P- and N-doped carbon materials (PN-doped carbon materials) through controlled phosphoric acid treatment (CPAT) of folic acid (FA) and probed their ability to catalyze the oxygen reduction reaction (ORR) at the cathode of a fuel cell. Precursors obtained by heating FA in the presence of phosphoric acid at temperatures of 400-1000 °C were further annealed at 1000 °C to afford PN-doped carbon materials. The extent of precursor P doping was maximized at 700 °C, and the use of higher temperatures resulted in activation and increased porosity rather than in increased P content. The P/C atomic ratios of PN-doped carbon materials correlated well with those of the precursors, which indicated that CPAT is well suited for the preparation of PN-doped carbon materials. The carbon material prepared using a CPAT temperature of 700 °C exhibited the highest ORR activity and was shown to contain -C-PO₂ and -C-PO₃ moieties as the major P species and pyridinic N as the major N species. Moreover, no N-P bonds were detected. It was concluded that the presence of -C-PO₂ and -C-PO₃ units decreases the work function and thus raises the Fermi level above the standard O₂/H₂O reduction potential, which resulted in enhanced ORR activity. Finally, CPAT was concluded to be applicable to the synthesis of PN-doped carbon materials from N-containing organic compounds other than FA.

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.

Carbon-Based Metal-Free ORR Electrocatalysts for Fuel Cells: Past, Present, and Future

Replacing precious platinum with earth-abundant materials for the oxygen reduction reaction (ORR) in fuel cells has been the objective worldwide for several decades. In the last 10 years, the fastest-growing branch in this area has been carbon-based metal-free ORR electrocatalysts. Great progress has been made in promoting the performance and understanding the underlying fundamentals. Here, a comprehensive review of this field is presented by emphasizing the emerging issues including the predictive design and controllable construction of porous structures and doping configurations, mechanistic understanding from the model catalysts, integrated experimental and theoretical studies, and performance evaluation in full cells. Centering on these topics, the most up-to-date results are presented, along with remarks and perspectives for the future development of carbon-based metal-free ORR electrocatalysts.

Chemical Approaches to Carbon-Based Metal-Free Catalysts

Highly active and durable catalysts play a key role in clean energy technologies. However, the high cost, low reserves, and poor stability of noble-metal-based catalysts have hindered the large-scale development of renewable energy. Owing to their low cost, earth abundance, high activity, and excellent stability, carbon-based metal-free catalysts (CMFCs) are promising alternatives to precious-metal-based catalysts. Although many synthetic methods based on solution, surface/interface, solid state, and noncovalent chemistries have been developed for producing numerous CMFCs with diverse structures and functionalities, there is still a lack of effective approaches to precisely control the structures of active sites. Therefore, novel chemical approaches are needed for the development of highly active and durable CMFCs that are capable of replacing precious-metal catalysts for large-scale applications. Herein, a comprehensive and critical review on chemical approaches to CMFCs is given by summarizing important advancements, current challenges, and future perspectives in this emerging field. Through such a critical review, our understanding of CMFCs and the associated synthetic processes will be significantly increased.

Doping of Carbon Materials for Metal-Free Electrocatalysis

Carbon atoms in the graphitic carbon skeleton can be replaced by heteroatoms with different electronegative from that of the carbon atom (i.e., heteroatom doping) to modulate the charge distribution over the carbon network. The charge modulation can be achieved via direct charge transfer with an electron acceptor/donor (i.e., charge transfer doping) or through introduction of defects (i.e., defective doping). Various doping strategies, including heteroatom doping, charge-transfer doping, and defective doping, have now been devised for modulating the charge distribution of numerous graphite carbon materials to impart new properties to carbon materials. Consequently, carbon nanomaterials with defined doping have recently become prominent members in the carbon family, promising for a variety of applications, including catalysis, energy conversion and storage, environmental remediation, and important chemical production and industrial processes. The purpose of this review is to present an overview on the doping of carbon materials for metal-free electrocatalysis, especially the development of doping strategies and doping-induced structure and property changes for potential catalytic applications. Current challenges and future perspectives in the doped carbon-based metal-free catalyst field are also discussed.

Single-atom Pt on non-metal modified graphene sheets as efficient catalysts for CO oxidation

By the density functional theory (DFT) calculations, the formation geometries, electronic structures and catalytic properties of metal Pt and nonmetal (NM) atom-co-modified graphene (Pt–3NM–graphene, NM = N, Si, P) as reactive substrates were investigated.

Enhancement mechanism of sulfur dopants on the catalytic activity of N and P co-doped three-dimensional hierarchically porous carbon as a metal-free oxygen reduction electrocatalyst

A sulfur, nitrogen and phosphorus ternary-doped cattle-bone-derived hierarchically porous carbon metal-free electrocatalyst was synthesized, exhibiting superior oxygen reduction performance compared to Pt/C.

Oxygen reduction reaction mechanism on a phosporus-doped pyrolyzed graphitic Fe/N/C catalyst

The interaction between neighbouring FeN₄ and P_subs sites of a P-doped pyrolyzed Fe/N/C catalyst promotes four-electron reduction through associative and dissociative mechanisms.

Defects on carbons for electrocatalytic oxygen reduction

The exploration of highly active and durable cathodic oxygen reduction reaction (ORR) catalysts with economical production costs is still the bottleneck to realize the large-scale commercialization of fuel cells. In recent years, remarkable progress has been achieved in fabricating effective non-precious metal based ORR catalysts. In particular, modified carbon materials have aroused extensive research interest because of their excellent performance and low cost. In this review, we present an overview on recent advancements in developing defective carbon based materials for catalyzing the ORR. In particular, three general kinds of defective carbon electrocatalysts will be summarized. They are non-metal induced defective carbons (modified by heteroatoms), intrinsic defective carbons (defects created by a physical or chemical method), and atomic metal species induced/coordinated defective carbons (metal-macrocycle complexes with different coordination environments). The common configurations of various defective carbons will be discussed, with typical examples on recently developed both metal-free and precious/non-precious metal species coordinated carbons. Finally, the future research directions of the defective carbon materials are proposed. The newly established defect promoted catalysis mechanism will be beneficial for the design and fabrication of highly effective electrocatalysts for practical energy storage and conversion applications.

Three-Dimensional Heteroatom-Doped Nanocarbon for Metal-Free Oxygen Reduction Electrocatalysis: A Review

The oxygen reduction reaction (ORR) at the cathode is a fundamental process and functions a pivotal role in fuel cells and metal–air batteries. However, the electrochemical performance of these technologies has been still challenged by the high cost, scarcity, and insufficient durability of the traditional Pt-based ORR electrocatalysts. Heteroatom-doped nanocarbon electrocatalysts with competitive activity, enhanced durability, and acceptable cost, have recently attracted increasing interest and hold great promise as substitute for precious-metal catalysts (e.g., Pt and Pt-based materials). More importantly, three-dimensional (3D) porous architecture appears to be necessary for achieving high catalytic ORR activity by providing high specific surface areas with more exposed active sites and large pore volumes for efficient mass transport of reactants to the electrocatalysts. In this review, recent progress on the design, fabrication, and performance of 3D heteroatom-doped nanocarbon catalysts is summarized, aiming to elucidate the effects of heteroatom doping and 3D structure on the ORR performance of nanocarbon catalysts, thus promoting the design of highly active nanocarbon-based ORR electrocatalysts.

Size effect of oxygen reduction reaction on nitrogen-doped graphene quantum dots

The adsorption strength of ORR intermediates, the reaction free energy of rate-determining step, and the overpotential increase with the increase of the size of N-doped graphene quantum dots.

Supramolecular gel assisted synthesis of Co2P nanosheets as an efficient and stable catalyst for oxygen reduction reaction

Co₂P/C, with nanosheet morphology, is prepared through a facile supramolecular-gel assisted strategy which presents excellent electrocatalytic performance for ORR.

Self-template synthesis of biomass-derived 3D hierarchical N-doped porous carbon for simultaneous determination of dihydroxybenzene isomers

Nitrogen doped hierarchical porous carbon materials (HPCs) was achieved by the successful carbonization, using pig lung as biomass precursor. Three-dimensional HPCs constituted with sheets and lines were synergistically inherited from original pig lung. Such structure provided a large specific surface area (958.5 g-1 m2) and rich porous, effectively supported a large number of electro-active species, and greatly enhanced the mass and electron transfer. High graphitization degree of HPCs resulted in good electrical conductivity. Furthermore, the different electronegativity between nitrogen and carbon atoms in HPCs could affect the electron cloud distribution, polarity and then the electrochemical oxidation kinetics of dihydroxybenzene isomers. Based on these characteristics of HPCs, the electrochemical sensor for dihydroxybenzene isomers exhibited high sensitivity, excellent specificity and stability. Quantitative analysis assays by differential pulse voltammetry (DPV) technology showed that the sensor has wide linear ranges (0.5-320, 0.5-340 and 1-360 μmol L-1) and low detection limits (0.078, 0.057 and 0.371 μmol L-1) for the catechol, resorcinol and hydroquinone, respectively. This proposed method was successfully applied for simultaneous detection of dihydroxybenzene isomers in river water.

Robust Fe3 Mo3 C Supported IrMn Clusters as Highly Efficient Bifunctional Air Electrode for Metal-Air Battery

Catalysts at the air cathode for oxygen reduction and evolution reactions are central to the stability of rechargeable metal-air batteries, an issue that is gaining increasing interest in recent years. Herein, a highly durable and efficient carbide-based bifunctional catalyst consisting of iron-molybdenum carbide (Fe₃ Mo₃ C) and IrMn nanoalloys is demonstratred. This carbide is chemically stable in alkaline media and over the potential range of an air cathode. More importantly, Fe₃ Mo₃ C is very active for oxygen reduction reaction (ORR) in alkaline media. Fe₃ Mo₃ C supported IrMn as a bifunictional catalysts exhibits superior catalytic performance than the state of the art ORR catalyst (Pt/C) and the oxygen evolution reaction catalyst (Ir/C). IrMn/Fe₃ Mo₃ C enables Zn-air batteries to achieve long-term cycling performance over 200 h with high efficiency. The extraordinarily high performance of IrMn/Fe₃ Mo₃ C bifunictional catalyst provides a very promising alternative to the conventional Pt/C and Ir/C catalyst for an air cathode in alkaline electrolyte.

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocatalysis, batteries, supercapacitors, solar cells, photocatalysis, and sensing platforms. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.

S, N Dual-Doped Graphene-like Carbon Nanosheets as Efficient Oxygen Reduction Reaction Electrocatalysts

Replacement of rare and precious metal catalysts with low-cost and earth-abundant ones is currently among the major goals of sustainable chemistry. Herein, we report the synthesis of S, N dual-doped graphene-like carbon nanosheets via a simple pyrolysis of a mixture of melamine and dibenzyl sulfide as efficient metal-free electrocatalysts for oxygen reduction reaction (ORR). The S, N dual-doped graphene-like carbon nanosheets show enhanced activity toward ORR as compared with mono-doped counterparts, and excellent durability in contrast to the conventional Pt/C electrocatalyst in both alkaline and acidic media. A high content of graphitic-N and pyridinic-N is necessary for ORR electrocatalysis in the graphene-like carbon nanosheets, but an appropriate amount of S atoms further contributes to the improvement of ORR activity. Superior ORR performance from the as-prepared S, N dual-doped graphene-like carbon nanosheets implies great promises in practical applications in energy devices.