The shuttling effect of the polysulfide (PS) is the most detrimental factor that causes capacity fading of Li- S batteries. By substituting carbon atoms with heteroatoms, the host materials can provide a chemical interaction with PS to trap it within the electrochemically active range of the cathode. In this study, first-principles-based calculations identify the most stable nitrogen (N) and phosphorus (P) codoped atomic structures and their corresponding adsorption energy toward different PS species. Based on the simulated predictions, we introduce a glucosamine-derived carbon nanotube aerogel (CNA) with a secondary dopant of P during the synergetic polymerization and carbonization process. The N-P codoped CNA and S composite (NPCNA-S) renders a highly stable performance even at a sulfur loading of 3.5 mg cm(-2). The specific capacity is >900 mAh g(-1) and the stabilized capacity retention is >70% over 450 cycles at 0.2 C rate (1 C = 1675 mA g(-1)).

An overview and insights toward the advancement and intrinsic mechanisms of MOF-based OER electrocatalysts.

Due to robustness, easy large-scale preparation and low cost, nanomaterials with enzyme-like characteristics (defined as ‘nanozymes’) are attracting increasing interest for various applications. However, most of currently developed nanozymes show much lower activity in comparison with natural enzymes, and the deficiency greatly hinders their use in sensing and biomedicine. Single-atom catalysts (SACs) offer the unique feature of maximum atomic utilization, providing a potential pathway to improve the catalytic activity of nanozymes. Herein, we propose a Fe-N-C single-atom nanozyme (SAN) that exhibits unprecedented peroxidase-mimicking activity. The SAN consists of atomically dispersed Fe─Nx moieties hosted by metal–organic frameworks (MOF) derived porous carbon. Thanks to the 100% single-atom active Fe dispersion and the large surface area of the porous support, the Fe-N-C SAN provided a specific activity of 57.76 U mg-1, which was almost at the same level as natural horseradish peroxidase (HRP). Attractively, the SAN presented much better storage stability and robustness against harsh environments. As a proof-of-concept application, highly sensitive biosensing of butyrylcholinesterase (BChE) activity using the Fe-N-C SAN as a substitute for natural HRP was further verified.

Core–shell PdPb@Pd aerogels with multiply-twinned grains and an ordered intermetallic phase was synthesized, which exhibited good electrocatalytic activity towards ethanol oxidation.

Graphitic carbon nitride/bismuth ferrite nanocomposites (g-C3N4/BiFeO3 NCs) were synthesized by a facile one step sol-gel combustion method and employed as a peroxidase-like catalyst. Based on the catalytical activity on the luminol-H2O2 reaction, the nanocomposites were utilized as a colorimetric/chemiluminescent dual-readout immunochromatographic assay (ICA) for the multiplexed detection of pesticide residues by utilizing chlorpyrifos and carbaryl as the model analytes. In the proposed protocol, chlorpyrifos antibody and carbaryl antibody were tagged to g-C3N4/BiFeO3 NCs for developing the spatially-resolved multianalyte ICA. After two competitive immunoreactions completed on the ICA test strip, the tracer antibodies were captured by the immobilized antigens on two test lines. The accumulation of g-C3N4/BiFeO3 NCs led to the appearance of brown color, which were observed as a colorimetric and semi-quantitative signal. Furthermore, the g-C3N4/BiFeO3 NCs-driven generation of CL signal was collected as a sensitively quantitative signal after initiating the luminol-H2O2 reaction on the test lines. Under the optimal conditions, the limits of detection of chlorpyrifos and carbaryl were both 0.033 ng/mL. The dual-readout ICA was successfully used to detect chlorpyrifos and carbaryl spiked in environmental water and traditional Chinese medicine samples with acceptable recovery values of 80-119% and 90-118%. Due to many advantages including low cost, time efficiency, high sensitivity and good portability, the novel ICA showed great potential in many areas such as drug safety, environmental monitoring and clinical diagnosis.

As one of the alternatives to replace precious metal catalysts, transition-metal-nitrogen-carbon (M-N-C) electrocatalysts have attracted great research interest due to their low cost and good catalytic activities. Despite nanostructured M-N-C catalysts can achieve good electrochemical performances, they are vulnerable to aggregation and insufficient catalytic sites upon continuous catalytic reaction. In this work, metal-organic frameworks derived porous single-atom electrocatalysts (SAEs) were successfully prepared by simple pyrolysis procedure without any further posttreatment. Combining the X-ray absorption near-edge spectroscopy and electrochemical measurements, the SAEs have been identified with superior oxygen reduction reaction (ORR) activity and stability compared with Pt/C catalysts in alkaline condition. More impressively, the SAEs also show excellent ORR electrocatalytic performance in both acid and neutral media. This study of nonprecious catalysts provides new insights on nanoengineering catalytically active sites and porous structures for nonprecious metal ORR catalysis in a wide range of pH.

Herein, a ratiometric fluorescence (RF) enzyme-linked immunosorbent assay (RF-ELISA) for sensitive detection of ethyl carbamate (EC) was developed by introducing fluorescent silicon nanoparticles (Si NPs) into the chromogenic substrate system (o-phenylenediamine (OPD)/H2O2) of a conventional horseradish peroxidase (HRP)-based ELISA platform to assemble a RF-based signal output system. For this system, the fluorescence of Si NPs at 440 nm (I-440) was acted as the reference signal which could be efficiently quenched by 2,3-diaminophenazine (DAP), the HRP-catalyzed oxidation product of OPD; Meanwhile, the fluorescence of DAP at 570 nm (I-570) was served as response signal. Therefore, variation in the amount of HRP labeled secondary antibody bound on the microplate which is associated with antibody-antigen recognition events in conventional HRP-based ELISA could be transferred into a more sensitive RF signal (I-520/I-440). On the basis of monoclonal antibody (mAb) which could specifically recognize EC derivative, xanthyl ethyl carbamate (XEC), a Si NPs-based RF-ELISA for EC via a simple pre-analysis derivatization was developed. When detecting the EC content in red wine, this method exhibits a working range from 3.9 to 105.0 mu g/L and a limit of detection (LOD) of 2.6 mu g/L with excellent specificity, accuracy and reproducibility. The sensitivity is approximately 33-fold higher than that of traditional colorimetric ELISA. The proposed Si NPs-based RF-ELISA is not only highly suitable for screening EC in a large number of samples, but also provides a potential platform for high-throughput and sensitive determination of other analytes for food safety monitoring. (C) 2017 Elsevier B.V. All rights reserved.

Increasing energy demands and environment awareness have promoted extensive research on the development of alternative energy conversion and storage technologies with high efficiency and environmental friendliness. Among them, electrochemical water splitting is very appealing, and is receiving more and more attention. Essential to the water splitting is the kinetically sluggish oxygen evolution reaction (OER), which demands efficient electrocatalysts. To make the water splitting process more energy-efficient and economical, developing high-performance noble metal-free catalysts, i.e., transition-metal-based nanomaterials, has aroused great attention due to their distinct advantages, such as relatively low cost, low toxicity, great flexibility in terms of structure and morphology, and satisfying electrochemical performance. We focus on the rational design of porous nanostructures with tunable composition and other favorable synergistic factors, aiming at increasing the number of the active sites and enhancing the reactivity of the active sites. Taking advantage of these favorable structural and compositional parameters, the resultant nanostructures exhibited excellent OER activity and stability, holding great promise in water splitting. References: Song, C. Zhu, B. Xu, S. Fu, M. Engelhard, R. Ye, D. Du, S. Beckman, Y. Lin. Bimetallic Cobalt-Based Phosphide Zeolitic Imidazolate Framework: CoPx Phase-Dependent Electrical Conductivity and Hydrogen Atom Adsorption Energy for Efficient Overall Water Splitting. Advanced Energy Materials 7, 2017, 1601555 S Fu, C Zhu, J Song, M Engelhard, X Li, D Du, Y Lin. Highly Ordered Mesoporous Bimetallic Phosphides as Efficient Oxygen Evolution Electrocatalysts. 2016, 1, 792-796 Zhu, S. Fu, D. Du, Y. Lin. Facilely tuning porous NiCo2O4 nanosheets with metal valence states alteration and abundant oxygen vacancies as robust electrocatalysts towards water splitting. Chemistry European J. 2016, 22, 4000-4007 Fu, J. Song, C. Zhu, G. Xu, K. Amine, C. Sun, X. Li; M. H Engelhard, D. Du, Y. Lin. Ultrafine and highly disordered Ni2Fe1 Nanofoams Enabled Highly Efficient Oxygen Evolution Reaction in Alkaline Electrolyte. Nano Energy. Submitted

The great interest in fuel cells inspires a substantial amount of research on nonprecious metal catalysts as alternatives to Pt‐based oxygen reduction reaction (ORR) electrocatalysts. In this work, bimodal template‐based synthesis strategies are proposed for the scalable preparation of hierarchically porous M–N–C (M = Fe or Co) single‐atom electrocatalysts featured with active and robust MN 2 active moieties. Multiscale tuning of M–N–C catalysts regarding increasing the number of active sites and boosting the intrinsic activity of each active site is realized simultaneously at a single‐atom scale. In addition to the antipoisoning power and high affinity for O 2 , the optimized Fe–N–C catalysts with FeN 2 active site presents a superior electrocatalytic activity for ORR with a half‐wave potential of 0.927 V (vs reversible hydrogen electrode (RHE)) in an alkaline medium, which is 49 and 55 mV higher than those of the Co–N–C counterpart and commercial Pt/C, respectively. Density functional theory calculations reveal that the FeN 2 site is more active than the CoN 2 site for ORR due to the lower energy barriers of the intermediates and products involved. The present work may help rational design of more robust ORR electrocatalysts at the atomic level, realizing the significant advances in electrochemical conversion and storage devices.

Nickel iron hydroxides are the most promising non-noble electrocatalysts for oxygen evolution reaction (OER) in alkaline media. By in situ reduction of metal precursors, compositionally controlled three-dimensional NixFey nanofoams (NFs) are synthesized with high surface area and uniformly distributed bimetallic networks. The resultant ultrafine and highly disordered amorphous Ni2Fe1 NFs exhibit extraordinary electrocatalytic performance toward OER and overall water splitting in alkaline media. At a potential as low as 1.42V (vs. RHE), Ni2Fe1 NFs can deliver a current density of 10mA/cm2 and show negligible activity loss after 12h stability test. Even at large current flux of 100mA/cm2, an ultralow overpotential of 0.27V is achieved, which is about 0.18V more negative than benchmark RuO2. Both ex-situ Mӧssbauer spectroscopy and X-ray Absorption Spectroscopy reveal a phase separation and transformation for the Ni2Fe1 catalyst during OER process. The evolution of oxidation state and disordered structure of Ni2Fe1 might be a key to the high catalytic performance for OER.

Lithium-sulfur (Li-S) batteries have been attractive alternatives to lithium-ion (Li-ion) batteries due to the high theoretical capacity of sulfur cathode. However, the polysulfide shuttling effect is detrimental to the long-term cycling stability. Chemically absorptive host materials provide an effective way to mitigate the dissolution of lithium polysulfide. Carbon nitride (C3N4) is one of the effective host materials with strong interaction with polysulfide species. The low electronic conductivity, however, is unfavorable for high sulfur utilization. In this work, we report the controlled synthesis of porous, well-interconnected C3N4/reduced graphene oxide (rGO) aerogels as hybrid sulfur host using a simple hydrothermal reaction followed by freeze-drying, which combines the structural merits of both highly conductive rGO networks and chemically active C3N4. By further tuning the structure/morphology and the ratio between C3N4 and rGO, we have demonstrated the C3N4/rGO composites with optimized 1: 2 ratio of C3N4: rGO (termed as CG12) exhibits not only very high sulfur utilization but also excellent rate capability compared to other C3N4/rGO composites, pure rGO, and C3N4. The compositionally and structurally tailored CG12 also shows stable cycling performance over 400 cycles with a low decay rate of 0.09% per cycle. (C) 2017 Elsevier Ltd. All rights reserved.

Cobalt‐based bimetallic phosphide encapsulated in carbonized zeolitic imadazolate frameworks has been successfully synthesized and showed excellent activities toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Density functional theory calculation and electrochemical measurements reveal that the electrical conductivity and electrochemical activity are closely associated with the Co2P/CoP mixed phase behaviors upon Cu metal doping. This relationship is found to be the decisive factor for enhanced electrocatalytic performance. Moreover, the precise control of Cu content in Co‐host lattice effectively alters the Gibbs free energy for H* adsorption, which is favorable for facilitating reaction kinetics. Impressively, an optimized performance has been achieved with mild Cu doping in Cu0.3Co2.7P/nitrogen‐doped carbon (NC) which exhibits an ultralow overpotential of 0.19 V at 10 mA cm–2 and satisfying stability for OER. Cu0.3Co2.7P/NC also shows excellent HER activity, affording a current density of 10 mA cm–2 at a low overpotential of 0.22 V. In addition, a homemade electrolyzer with Cu0.3Co2.7P/NC paired electrodes shows 60% larger current density than Pt/RuO2 couple at 1.74 V, along with negligible catalytic deactivation after 50 h operation. The manipulation of electronic structure by controlled incorporation of second metal sheds light on understanding and synthesizing bimetallic transition metal phosphides for electrolysis‐based energy conversion.

Rational design of high active and robust nonprecious metal catalysts with excellent catalytic efficiency in oxygen evolution reaction (OER) is extremely vital for making the water splitting process more energy efficient and economical. Among these noble metal-free catalysts, transition-metal-based nanomaterials are considered as one of the most promising OER catalysts due to their relatively low-cost intrinsic activities, high abundance, and diversity in terms of structure and morphology. Herein, a facile sugar-blowing technique and low-temperature phosphorization are reported to generate 3D self-supported metal involved carbon nanostructures, which are termed as Co2 P@Co/nitrogen-doped carbon (Co2 P@Co/N-C). By capitalizing on the 3D porous nanostructures with high surface area, homogeneously dispersed active sites, the intimate interaction between active sites, and 3D N-doped carbon, the resultant Co2 P@Co/N-C exhibits satisfying OER performance superior to CoO@Co/N-C, delivering 10 mA cm-2 at overpotential of 0.32 V. It is worth noting that in contrast to the substantial current density loss of RuO2 , Co2 P@Co/N-C shows much enhanced catalytic activity during the stability test and a 1.8-fold increase in current density is observed after stability test. Furthermore, the obtained Co2 P@Co/N-C can also be served as an excellent nonprecious metal catalyst for methanol and glucose electrooxidation in alkaline media, further extending their potential applications.

SnO2 is a promising material for both Li-ion and Na-ion batteries owing to its high theoretical capacities. Unfortunately, the electrochemical performance of SnO2 is unsatisfactory because of the large volume change that occurs during cycling, low electronic conductivity of inactive oxide matrix, and poor kinetics, which are particularly severe in Na-ion batteries. Herein, ultra-fine SnO2 nanocrystals anchored on a unique three-dimensional (3D) porous reduced graphene oxide (rGO) matrix are described as promising bifunctional electrodes for Li-ion and Na-ion batteries with excellent rate capability and long cycle life. Ultra-fine SnO2 nanocrystals of size ∼6 nm are well-coordinated to the graphene sheets that comprise the 3D macro-porous structure. Notably, superior rate capability was obtained up to 3 C (1/n C is a measure of the rate that allows the cell to be charged/discharged in n h) for both batteries. In situ X-ray diffractometry measurements during lithiation (or sodiation) and delithiation (or desodiation) were combined with various electrochemical techniques to reveal the real-time phase evolution. This critical information was linked with the internal resistance, ion diffusivity (\({D_{L{i^ + }}}\) and \({D_{N{a^ + }}}\)), and the unique structure of the composite electrode materials to explain their excellent electrochemical performance. The improved capacity and superior rate capabilities demonstrated in this work can be ascribed to the enhanced transport kinetics of both electrons and ions within the electrode structure because of the well-interconnected, 3D macro-porous rGO matrix. The porous rGO matrix appears to play a more important role in sodium-ion batteries (SIBs), where the larger mass/radius of Na-ions are marked concerns.

Dendritic nanostructures are capturing increasing attention in electrocatalysis owing to their unique structural features and low density. Herein, we report for the first time, bromide ion mediated synthesis of low Pt-content PdCuPt ternary nanodendrites via galvanic replacement reaction between a Pt precursor and a PdCu template in aqueous solution. The experimental results show that the ternary PdCuPt nanodendrites present enhanced electrocatalytic performance for oxygen reduction reaction in acid solution compared with commercial Pt/C as well as some state-of-the-art catalysts. In detail, the mass activity of the PdCuPt catalyst with optimized composition is 1.73 A mgPt-1 at 0.85 V vs. RHE, which is 14 times higher than that of a commercial Pt/C catalyst. Moreover, the long-term stability test demonstrates its better durability in acid solution. After 5k cycles, there is still 70% electrochemical surface area maintained. This method provides an efficient method to synthesize trimetallic alloys with controllable composition and specific structure for oxygen reduction reaction.

The electrochemically controlled ion-exchange properties of multi-wall carbon nanotube (MWNT)/electronically conductive polypyrrole (PPy) polymer composite in the various electrolyte solutions have been investigated. The ion-exchange behavior, rate and capacity of the electrochemically deposited polypyrrole with and without carbon nanotube (CNT) were compared and characterized using cyclic voltammetry (CV), chronoamperometry (CA), electrochemical quartz crystal microbalance (EQCM), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It has been found that the presence of carbon nanotube backbone resulted in improvement in ion-exchange rate, stability of polypyrrole, and higher anion loading capacity per PPy due to higher surface area, electronic conductivity, porous structure of thin film, and thinner film thickness providing shorter diffusion path. Chronoamperometric studies show that electrically switched anion exchange could be completed more than 10 times faster than pure PPy thin film. The anion selectivity of CNT/PPy film is demonstrated using X-ray photoelectron spectroscopy (XPS).

Self-assembled M-N-doped carbon nano-tube aerogels with single-atom catalyst feature are for the first time reported through one-step hydrothermal route and subsequent facile annealing treatment. By taking advantage of the porous nanostructures, 1D nanotubes as well as single-atom catalyst feature, the resultant Fe-N-doped carbon nanotube aerogels exhibit excellent oxygen reduction reaction electrocatalytic performance even better than commercial Pt/C in alkaline solution.