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The published version of this article, unfortunately, contains error. The authors regret that one typo was present in the first author name "Cuxing Xu" when it should be "Cuixing Xu". [ABSTRACT FROM AUTHOR]

Mesoporous carbon nanorods (MCNRs) were prepared from honey as the carbon source and by using crab (Brachyuran) shells as the hard template. The unique nanostructure of the MCNRs with their uniform mesoporous size, abundant defective sites and numerous oxygen-functional groups was characterized by nitrogen adsorption-desorption isotherms, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Cyclic voltammograms of a glassy carbon electrode (GCE) modified with MCNRs revel a higher peak current density and lower peak potential (−0.03 V vs. Ag/AgCl) for ascorbic acid (AA) electrooxidation compared to a conventional GCE and a carbon nanotube-modified GCE. Figures of merit for this sensor include (a) a wide linear range (10-2770 μM), (b) high electrochemical sensitivity (216.91 μA mM−1 cm−2) and (c) a low detection limit (2.3 μM). These compare favorably to the respective data for a CNT-modified GCE (50-2150 μM, 5.20 μA mM−1 cm−2 and 26.8 μM) and a plain GCE (100-2000 μM, 0.58 μA mM−1 cm−2 and 54.6 μM). The modified GCE was successfully applied to the determination of AA in (spiked) real samples including an injection, soft drinks and fresh lemon juice. Therefore, the new sensor can be considered as an affordable tool for electrochemical sensing of AA in real samples.Mesoporous carbon nanorods (MCNRs) were prepared by using honey as the carbon source and crab shells as the hard template. The MCNRs modified a glassy carbon electrode (MCNRs/GCE) was used for the ascorbic acid (AA) detection by amperometry. [ABSTRACT FROM AUTHOR]

The authors describe a method for synthesis of a three-dimensional (3D) interconnected carbon nanorod aerogel (3D-ICNA) starting from wax gourd (Benincasa hispida) which is a low-cost biomass. The 3D-ICNA possesses unique 3D interconnected and porous nanostructure, with abundant edge-plane-like defective sites, a large specific surface area (823 m2 g−1) and a large pore volume (0.12 cm3 g−1). This makes the material attractive in terms of electrochemical sensing. To validate the feasibility, the voltammetric response towards ferricyanide, hydrogen peroxide (H2O2), acetaminophen, ascorbic acid (AA), dopamine, uric acid and epinephrine was investigated by using a glassy carbon electrode (GCE) modified with 3D-ICNA. The modified GCE shows higher electron-transfer capacity than a conventional GCE. In addition, as an electrochemical sensor for AA or H2O2, the electrode exhibits better analytical performance with lower detection limit [3.5 μM for AA or 0.68 μM for H2O2 based on 3σ/m criterion (where σ is the standard deviation of the blank and m is the slope of the calibration plot)], wider linear range and higher sensitivity (0.14, 0.11 and 0.080 μA μM−1 cm−2 for AA or 0.24 and 0.20 μA μM−1 cm−2 for H2O2) compared to a plain GCE or a carbon nanotube-modified GCE. The modified GCE exhibits a large potential for the amperometric determination of AA or H2O2 in real samples.By employing the biomass of wax gourd (Benincasa hispida) as the precursor, a three-dimensional interconnected carbon nanorod aerogel was prepared. It is shown to be a viable material for the construction of an advanced electrochemical sensor for H2O2 and ascorbic acid. [ABSTRACT FROM AUTHOR]

[Display omitted] Designing two-dimensional (2D) porous carbon nanosheets is expected to boost the water splitting efficiency of low-cost iron (Fe) and cobalt (Co)-based catalysts. Nevertheless, the aggregations, tedious preparation procedures, and expensive precursors for synthesizing 2D porous carbon nanosheets have hindered their widespread application. Herein, for the first time, we developed a low-cost method for large-scale and rapid synthesis of the three-dimensional (3D) hierarchically porous architectures self-assembled by the ultrafine FeCo nanoparticles embedded and boron/nitrogen-codoped 2D porous carbon nanosheets (denoted as FeCo@BNPCNS). The optimal FeCo@BNPCNS-900 exhibited abundant porous channels, a large surface area, and vast carbon edges/defects. Therefore, 8.10 at% electrochemically active boron (B)/nitrogen (N) centers were doped into the porous carbon nanosheets. In an alkaline solution, the optimal FeCo@BNPCNS-900 nanosheets revealed excellent hydrogen evolution reaction (HER) electrocatalytic activity, surpassing commercial 20 wt% Pt/C. For instance, the HER potential at 10 mA cm−2 [-50.6 mV vs. reversible hydrogen electrode (RHE)] of FeCo@BNPCNS-900 was even 19.3 mV more positive than that of commercial 20 wt% Pt/C (-69.9 mV vs. RHE). Meanwhile, its oxygen evolution reaction (OER) catalytic activity was just a little worse than ruthenium oxide (RuO 2). The water electrolysis cell of FeCo@BNPCNS-900 nanosheets just required a small voltage of 1.589 V for full water splitting to achieve 10 mA cm−2, even 70.3 mV more negative than that of the state-of-the-art 20 wt% Pt/C||RuO 2 benchmark (1.660 V) with outstanding stability. The perfect 3D hierarchically porous and honeycomb-like architecture, abundant porous channels/mesopores, and uniformly dispersed electrocatalytically active sites on FeCo@BNPCNS-900 nanosheets were responsible for the outstanding water splitting performance. Finally, this study provides an efficient strategy for the large-scale, rapid, and low-cost synthesis of 2D porous carbon nanosheets without using any template, surfactant, or expensive precursors. [ABSTRACT FROM AUTHOR]

Non-precious transition metal electrocatalysts with high catalytic performance and low cost enable the scalable and sustainable production of hydrogen energy through water splitting. In this work, based on the polymerization of CoMoO 4 nanorods and pyrrole monomer, a heterointerface of carbon-wrapped and Co/Mo 2 C composites are obtained by thermal pyrolysis method. Co/Mo 2 C composites show considerable performance for both hydrogen and oxygen evolution in alkaline media. In alkaline media, Co/Mo 2 C composites show a small overpotential, low Tafel slope, and excellent stability for water splitting. Co/Mo 2 C exhibits a small overpotential of 157 mV for hydrogen evolution reaction and 366 mV for oxygen evolution reaction at current density of 10 mA cm−2, as well as a low Tafel slope of 109.2 mV dec−1 and 59.1 mV dec−1 for hydrogen evolution reaction and oxygen evolution reaction, respectively. Co/Mo 2 C composites also exhibit an excellent stability, retaining 94% and 93% of initial current value for hydrogen evolution reaction and oxygen evolution reaction after 45,000 s, respectively. Overall water splitting via two-electrode water indicates Co/Mo 2 C can hold 91% of its initial current after 40,000 s in 1 M KOH. Image 1 • Co/Mo 2 C composites were synthesized by polymerization and pyrolysis. • The dependence of activity on the ratio and pyrolysis temperature of precursors. • High activity and stability for Co/Mo 2 C. [ABSTRACT FROM AUTHOR]

Development of electrocatalysts composed of low cost and abundant elements that exhibit catalytic activity comparable to noble metals is important for water splitting. As such, in this study, a catalyst material with a ginger-like morphology consisting of Co 6 W 6 C is synthesized via a hydrothermal reaction and pyrolysis treatment. The Co 6 W 6 C catalyst exhibits satisfactory electrochemical properties towards both hydrogen and oxygen evolution reactions in an alkaline electrolyte, with a low overpotential, low Tafel slope, and durable stability. Co 6 W 6 C possesses a high activity for the hydrogen evolution reaction in alkaline conditions, with an onset potential and overpotential of −0.024 V and 101 mV, respectively, and low Tafel slope of 80.5 mV dec−1 at a current density of 10 mA cm−2. In addition, Co 6 W 6 C achieves a current density of 10 mA cm−2 for the oxygen evolution reaction at an overpotential of only 343 mV. Furthermore, electrochemical stability tests indicate that the Co 6 W 6 C catalyst maintains 91% of the original current after 60,000 s for the hydrogen evolution reaction and 95% of the original current after 45,000 s for the oxygen evolution reaction. Moreover, electrochemical splitting of water via a two-electrode system employing this catalyst can hold 89% of the initial current after 40,000 s in 1 M KOH. Image 1 • A simple hydrothermal and pyrolysis method for preparation of Co 6 W 6 C. • The different pyrolysis atmosphere leads to different activity and composition. • High electrocatalytic activity and stability for Co 6 W 6 C toward the water splitting reaction. [ABSTRACT FROM AUTHOR]

Wearable sweat sensors have the potential to provide continuous measurements of useful biomarkers. However, current sensors cannot accurately detect low analyte concentrations, lack multimodal sensing or are difficult to fabricate at large scale. We report an entirely laser-engraved sensor for simultaneous sweat sampling, chemical sensing and vital-sign monitoring. We demonstrate continuous detection of temperature, respiration rate and low concentrations of uric acid and tyrosine, analytes associated with diseases such as gout and metabolic disorders. We test the performance of the device in both physically trained and untrained subjects under exercise and after a protein-rich diet. We also evaluate its utility for gout monitoring in patients and healthy controls through a purine-rich meal challenge. Levels of uric acid in sweat were higher in patients with gout than in healthy individuals, and a similar trend was observed in serum. Low levels of uric acid and tyrosine in sweat are detected in patients with gout and healthy individuals with an entirely laser-engraved wearable sensor. [ABSTRACT FROM AUTHOR]

In this work, porphyrin-based 2D MOF CuTCPP/platelet ordered mesoporous carbon (pOMC) composites were successfully synthesized by conventional solvothermal reaction. The introduction of pOMC increases conductivity of CuTCPP/pOMC composites, weakens accumulation of the CuTCPP layers, and exposes active sites of CuTCPP. CuTCPP/pOMC composites show high electro-catalytic activity to the oxidation of hydroxylamine and the redox of chlorogenic acid. An electrochemical sensor based on CuTCPP/pOMC was constructed for quantitative determination of hydroxylamine and chlorogenic acid, and relevant mechanisms were discussed. Under optimized conditions, the fabricated sensor displays two wide linear responses in the ranges of 5.8–733.8 μM and 733.8–2933.8 μM for hydroxylamine, with a rapid response time about 1 s. For chlorogenic acid, the sensor presents linear responses in the ranges of 0.1–2 μM and 2–15 μM, with a high sensitivity of 10.18 μA/μM. The sensor was used to detect hydroxylamine and chlorogenic acid in real samples, and satisfactory results were obtained. The synthesis of CuTCPP/pOMC composites provides new strategy for designing electrochemical sensors based on 2D MOFs. Image 1 • 2D CuTCPP nanosheets and platelet OMC composites were synthesized for the first time. • CuTCPP/pOMC sensor shows enhanced electro-catalytic activity compared to CuTCPP. • The linear range is wide and the response time is fast for hydroxylamine. • The sensitivity of chlorogenic acid is the highest in non-noble metal materials. • CuTCPP/pOMC composites provide new strategy for electrochemical sensors based on 2D MOFs. [ABSTRACT FROM AUTHOR]

[Display omitted] Designing two-dimensional (2D) porous carbon nanosheets is a promising strategy for enhancing the water-splitting activities of non-noble metal catalysts. In this study, we developed a novel method for synthesizing the novel three-dimensional (3D) hierarchically porous iron–nickel (FeNi) nanoparticles encapsulated in boron (B) and nitrogen (N)-codoped porous carbon nanosheets (denoted as FeNi@BNPCNS). Owing to the advantages of morphology and structure of B and N, 10.31 atom % of B/N active centers were successfully doped into the optimal FeNi@BNPCNS-800 nanosheets. FeNi@BNPCNS-800 exhibited better hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalytic activities than control catalysts in an alkaline solution. However, the HER and OER electrocatalytic activities of FeNi@BNPCNS-800 were slightly lower than 20 wt% Pt/C and RuO 2. The FeNi@BNPCNS-800||FeNi@BNPCNS-800 electrolyzer achieved 10 mA cm−2 at 1.514 V, which was 73 mV lower than that of 20 wt% Pt/C||RuO 2 electrolyzer (1.587 V). The perfect 3D honeycomb-like architectures, abundant mesopores/defects, and abundant electrocatalytic active sites were attributed to the outstanding water-splitting performances of FeNi@BNPCNS-800 nanosheets. This study provides an efficient strategy for the large-scale, rapid, and low-cost fabrication of 2D porous carbon nanosheets without using any template, surfactant, or expensive raw material, thus presenting a simple approach to design advanced non-noble metal electrocatalysts for water splitting. [ABSTRACT FROM AUTHOR]

Carbon nitride (C 3 N 4) is doped with cobalt species and supported on ordered mesoporous carbon (Co C 3 N 4 /OMC), to design macrocyclic metal-nitrogen catalyst in alkaline fuel cells for oxygen reduction reaction (ORR). The structural characterization proves Co N bond in Co C 3 N 4. The ORR activity of Co C 3 N 4 /OMC is improved by rich approachable Co-N x active sites and rapid transfer in the pores of Co C 3 N 4 /OMC. The electrocatalytic properties reveal that reduction of oxygen is catalyzed by Co C 3 N 4 in a four electron pathway. Additionally, Co C 3 N 4 /OMC unveils equivalent ORR performance, maximum methanol tolerance ability and improved durability in contrast to Pt/C and bodes well for designing of favorable non-precious cathode catalyst in fuel cells. The chemical doping approach in this work provides insights to advance other related catalyst in fuel cells. Image 1 • Doping of Co with C 3 N 4 for the formation Co-N x active sites. • Enhanced mass transport in an ordered porous medium with high surface area. • Approachable Co-N x active sites for oxygen reduction reaction. • High oxygen reduction reaction activity and good stability at Co C 3 N 4 /OMC. [ABSTRACT FROM AUTHOR]

Graphical abstract The B N bond contents calculated from either N or B XPS spectra are less than 8.2% of total N or B atoms for 3D porous Fe 3 C@B 1.0 NPCFs-900 networks as the electrostatic repulsion effect between precursors. Abstract In this paper, polyvinylpyrrolidone (PVP) and 4-hydroxybenzeneboronic acid (o-HPBA) are polarized in alkaline solution and then employed as boron (B) and nitrogen (N) sources. Fe(AC) 2 /o-HPBA/PVP/DMF(N,N-Dimethylformamide) slurries are first electrospunned into three-dimensional (3D) networks. Due to the electrostatic repulsion between negatively charged O− groups surrounding N and B atoms, N and B atoms can be kept far away from each other. Upon optimizing o-HPBA dosages, the maximum amount of isolated B and N atoms are successfully doped into the 3D porous iron carbide (Fe 3 C) embedded B and N co-doped carbon fibers (Fe 3 C@B 1.0 NPCFs) networks with tiny B N clusters. Electrochemical measure results demonstrate that Fe 3 C@B 1.0 NPCFs exhibit much better oxygen reduction reaction (ORR) activity than 20 wt% Pt/C in alkaline electrolyte. In acidic electrolyte, Fe 3 C@B 1.0 NPCFs also displays ORR activity comparable to Pt/C (its onset and half-wave potentials are just 40 and 50 mV more negative than those of Pt/C). Moreover, Fe 3 C@B 1.0 NPCFs show better stability and methanol tolerance ability than Pt/C for ORR in both alkaline and acidic solutions. This work opens new avenues for intentionally preventing the malignant combination of B and N atoms and boosting the electrocatalytic activity of B and N co-doped and Fe 3 C embedded carbon catalysts. [ABSTRACT FROM AUTHOR]

Active, low-cost and abundant electrocatalysts for water splitting (i.e. both hydrogen evolution reaction and oxygen evolution reaction) with high efficiency is highly desired. In this work, Co x Ni 1-x -nitrilotriacetic acid complexes are supported on commercial nickel foam by a simple hydrothermal method. Followed by phosphorization, Co x Ni 1-x P nanoparticles embedded into by nitrogen-doped carbon layer are synthesized on nickel foam, serving as bifunctional alkaline electrocatalysts for both hydrogen evolution reaction and oxygen evolution reaction. For the cathodic hydrogen evolution reaction catalytic performance, Co 0.5 Ni 0.5 P nanoparticles embedded in carbon layers on nickel foam (NF) (Co 0.5 Ni 0.5 P/NC/NF) requires an overpotential of 90.0 mV to deliver current density of 10 mA cm −2 , approaching that of commercial Pt/C which was fabricated on NF (Pt/C/NF) catalyst. As an anodic oxygen evolution reaction electrocatalyst, with a potential as low as 1.56 V, the current density response is 50 mA cm −2 , showing superior performance close to RuO 2 /NF. Moreover, in the alkaline electrolyzer, Co x Ni 1-x P nanoparticles require a low potential of 1.49 V to achieve a current density of 20 mA cm −2 for full water splitting. [ABSTRACT FROM AUTHOR]

In this study, porphyrin-based zirconium MOF (MOF-525)/macroporous carbon (MPC) composites were successfully prepared by conventional solvothermal reaction for the first time. Structural characteristics and experimental studies show that MOF-525/MPC composites combine the advantages of MOF-525 and MPC, which possess high BET surface area, large pore size, excellent conductivity and high catalytic activity of porphyrin. A novel electrochemical sensor based on MOF-525/MPC was fabricated, which presents superior electrocatalytic activity to the oxidation of luteolin. Meanwhile, the reaction mechanism of luteolin on MOF-525/MPC modified glassy carbon electrode (GCE) was researched. Electrochemical detection indicates that the luteolin sensor displays two linear responses in the ranges of 5 nM-0.1 μM and 0.1–5 μM, with a low detection limit of 0.35 nM. The proposed sensor was also used for the determination of luteolin in actual samples, and the results are satisfactory, revealing great potential of the sensor in practical applications. [ABSTRACT FROM AUTHOR]

The zirconium-based MOF (UiO-66)/mesoporous carbon (MC) composite was synthesized using conventional hydrothermal method for the first time. The surface morphology and structure of UiO-66/MC composite were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). A novel electrochemical sensor based on UiO-66/MC was constructed for simultaneous and sensitive determination of dihydroxybenzene isomers (DBIs) of hydroquinone (HQ), catechol (CT) and resorcinol (RS). The proposed sensor displays excellent electrocatalytic activity toward the oxidation of HQ, CT and RS. The peak-to-peak potential separations between CT and HQ, and RS and CT are 0.130 V and 0.345 V, respectively. Under the optimized conditions, the electrochemical sensor shows a wide linear response in the concentration range of 0.5–100 μM, 0.4–100 μM and 30–400 μM with a detection limit of 0.056 μM, 0.072 μM and 3.51 μM (S/N = 3) for HQ, CT and RS, respectively. In addition, the sensor has superior sensitivity and electrochemical stability along with good reproducibility and anti-interference properties. The fabricated sensor was also applied for the determination of DBIs in the real water samples with satisfying results. [ABSTRACT FROM AUTHOR]

A novel methodology for promoting the topological carbon defects and B/N doping amounts of B/ N -enriched porous Co@BN-PCFs catalysts, which discloses a new direction for further boosting ORR catalytic efficiencies and stabilities of Co N C catalysts in both acids and bases. [Display omitted] • Carboxyl induced abundant mesopores and ultrahigh carbon topological defects in Co@BN-PCNFs. • Ultrahigh B and N doping amounts of 5.87 and 5.91 at.% with 8.70 at.% of B/N based electrocatalytic active centers. • The ORR E onset and E 1/2 values of Co@BN-PCNFs-900 are ∼ 64 and ∼ 63 mV more positive than 20 wt% Pt/C in 0.1 M KOH. • The ORR E onset and E 1/2 values of Co@BN-PCNFs-900 just ∼ 11 and ∼ 7 mV more negative than 20 wt% Pt/C in 0.1 M H 2 SO 4. • The comparatively stable topological edges, BC 3 and partial N C/Co N C induced excellent stability toward ORR. Transition metal-nitrogen-carbon (M N C) type catalysts have been considered a promising alternative to noble metals for oxygen reduction reaction (ORR) electrocatalysis. Nevertheless, poor stabilities of M N C catalysts in acidic solutions limit their commercialization. In this study, we design and synthesize novel three-dimensional (3D) cobalt (Co) nanoparticles encapsulated in ultrahigh content of boron (B) and nitrogen (N) -doped hierarchically porous carbon nanofibers (denoted as Co@BN-PCNFs) by carbonizing the 3D acetic acid/cobalt nitrate/4-hydroxybenzeneboronic acid/polyvinylpyrrolidone precursor networks woven using electrospinning method under a nitrogen atmosphere. The optimal Co@BN-PCNFs-900 catalyst has abundant micro/mesopores and numerous topological defects and exhibits the largest surface area. Under the synergistic effect of oxygen-containing acetic acid molecules and the electrospinning technology, 5.87 at.% of B and 5.91 at.% of N atoms were doped into carbon nanofibers. Specifically, B/N electrocatalytic active centers (including BC 3 , pyridinic-N/Co N C, pyrrolic-N, and graphitic-N) of approximately 8.70 at.% were successfully introduced into the skeletons of Co@BN-PCNFs-900. In 0.1 M KOH, the ORR onset potential (E onset) and half-wave potential (E 1/2) of Co@BN-PCNFs-900 were ∼ 64 and ∼ 63 mV, respectively, more positive than those of 20 wt% Pt/C. Additionally, in 0.5 M H 2 SO 4 , the ORR E onset and E 1/2 values of Co@BN-PCNFs-900 were only ∼ 11 and ∼ 7 mV, respectively, more negative than those of 20 wt% Pt/C. As the 3D hierarchically porous architectures, topological carbon edges, BC 3 , and partial N C/Co N C are relatively stable, the Co@BN-PCNFs-900 exhibits excellent stability toward ORR catalysis in both acidic and basic media. These favorable properties of Co@BN-PCNFs-900 nanofibers make them the best non-noble metal-based carbonaceous electrocatalysts for ORR in acidic electrolytes. [ABSTRACT FROM AUTHOR]

An iron-based MOF (MIL-100 (Fe)) was synthesized and combined with large mesoporous carbon (LMC) by a solvothermal method. The composite was characterized in detail by a variety of characterization methods. The incorporation of large mesoporous carbon (LMC) significantly improves the electrocatalytic performance and electrochemical stability of MIL-100 (Fe)@LMC as compared to pure MIL-100 (Fe). The composite modified electrode exhibits superb electrocatalytic ability for the reduction of hydrogen peroxide and the oxidation of hydrazine. The smaller overpotential and larger peak current justify the excellent electrocatalytic ability of the composite. For hydrogen peroxide, the overpotential decreased by 0.205 V. And for hydrazine, it reduced by 0.415 V. The peak currents were increased by 21 times and 2.5 times respectively. [ABSTRACT FROM AUTHOR]

In this work, a novel porphyrinic metal-organic framework-based composite has been successfully synthesized by a simple one-step solvothermal method through growing Zr-PorMOF on macroporous carbon (MPC). Porphyrin-base MOFs combining the structural adjustable of MOFs and the specific catalytic activity of biomimetic catalysts play an important role in electrocatalysis. A series of characterization show that the roles of MPC as follow: (1) MPC could avoid the agglomeration of Zr-PorMOF particles and increase the specific surface area; (2) MPC could improve the electrochemical stability of Zr-PorMOF particles; (3) MPC could reduce the electron transfer resistance. Therefore, MPC plays the role of the conductive bridges to provide facile charge transport. The obtained Zr-PorMOF/MPC composites exhibit much better electrocatalytic activity for the reduction of hydrogen peroxide (H 2 O 2 ) than the pristine Zr-PorMOF due to the synergy of Zr-PorMOF and MPC. This enzyme-free H 2 O 2 sensor shows two linear relationships in the ranges 0.5–137 μM (R 2 = 0.991, sensitivity = 66 μA mM −1 ) and 137–3587 μM (R 2 = 0.993, sensitivity = 16 μA mM −1 ), with a low over-potential at −0.2 V, a fast response time within 1 s and a low limit of detection (LOD) of 0.18 μM. Moreover, Zr-PorMOF/MPC composites were used to simultaneously detect uric acid (UA), xanthine (XA) and hypoxanthine (HX). These three substances are degradation products of purine metabolism. In addition, Zr-PorMOF/MPC composites can be used to develop multifunctional biosensors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Designing Mn 3 (BO 3) 2 and Fe 3 C@BNC functionalized boron and nitrogen codoped Fe 1 Mn 1 @BN-PCFs networks. • Mesopores and carbon defects/edges boosted ultrahigh B and N doping amounts of 11.12 and 6.53 atom %. • The HER E onset and E 10 values of Fe 1 Mn 1 @BN-PCFs just 70.3 and 121.9 mV more negative than 20 wt% Pt/C. • The OER E onset and E 10 values of FeMn@BN-PCFs just 11 and 4 mV more positive than RuO 2. • A low voltage of 1.6217 V at 10 mA cm−2 for Fe 1 Mn 1 @BN-PCFs||Fe 1 Mn 1 @BN-PCFs just 14.2 mV larger than Pt/C||RuO 2. With high prices of precious metals (such as platinum, iridium, and ruthenium) and transition metals (such as cobalt and nickel), the design of high-efficiency and low-cost non-precious-metal-based catalysts using iron (Fe) and manganese (Mn) metals for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are critical for commercial applications of water splitting devices. In the study, without using any template or surfactant, we successfully designed novel cross-linked manganese borate (Mn 3 (BO 3) 2) and iron carbide (Fe 3 C) embedded into boron (B) and nitrogen (N) co-doped three-dimensional (3D) hierarchically meso /macroporous carbon nanowires (denoted as Fe x Mn y @BN-PCFs). Electrochemical test results showed that the HER and OER catalytic activities of Fe 1 Mn 1 @BN-PCFs were close to those of 20 wt% Pt/C and RuO 2. For full water splitting, (-) Fe 1 Mn 1 @BN-PCFs||Fe 1 Mn 1 @BN-PCF (+) cell achieved a current density of 10 mA cm−2 at a cell voltage of 1.622 V, which was 14.2 mV larger than that of (-) 20 wt% Pt/C||RuO 2 (+) benchmark. The synergistic effect of 3D hierarchically meso /macroporous architectures, excellent charge transport capacity, and abundant active centers (cross-linked Mn 3 (BO 3) 2 /Fe 3 C@BNC, BC 3 , pyridinic-N, M N C, and graphitic-N) enhanced the water splitting catalytic activity of Fe 1 Mn 1 @BN-PCFs. The (-) Fe 1 Mn 1 @BN-PCFs||Fe 1 Mn 1 @BN-PCF (+) cell exhibited excellent stability owing to the superior structural and chemical stabilities of 3D hierarchically porous Fe 1 Mn 1 @BN-PCFs. [ABSTRACT FROM AUTHOR]

In the present work, we described a green and facile fabrication of mixed manganese-iron oxide loaded carbon fibers (Mn 2 O 3 -Fe 2 O 3 /CFs) through electrospinning and subsequent heat treatment processes. For optimal performance, a series of samples were synthesized by the same way with varying Mn/Fe molar ratios (1:0, 3:1, 1:1, 1:3, 0:1) in precursors. The composition, morphology and catalytic property of as-prepared samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), X-ray photo-electron spectroscopy (XPS) and electrochemical methods. Mn 2 O 3 -Fe 2 O 3 /CFs (3:1) exhibits the highest catalytic ability towards hydrogen peroxide (H 2 O 2 ) reduction and hydrazine (N 2 H 4 ) oxidation. Furthermore, Mn 2 O 3 -Fe 2 O 3 /CFs/GCE (3:1) displays remarkable analytical performances for the detection of H 2 O 2 and N 2 H 4 in terms of wide linear range, low limit of detection, short current response time, excellent anti-interference ability, good repeatability and long-time stability. In addition, it can be applied to the analysis of real samples with satisfactory results. [ABSTRACT FROM AUTHOR]

Due to the π–π interaction of graphene (GR) layers, GR sheets tend to aggregate irreversibly to graphite during the application process. In addition, nanoparticles supported on GR layers are easily sandwiched or secluded inside the stacked layers and therefore not efficient exposure for catalysis. To address the irreversible aggregation of GR and increase the utilization efficiency of supported nanoparticles, in this work, porous GR (PGR) was prepared using SiO 2 as a template and used as support for the NiCo 2 O 4 . The porous structure provided larger surface area and more opportunity for the exposure of supported NiCo 2 O 4 . Due to the porous structure of PGR, the NiCo 2 O 4 supported on PGR were not hidden by aggregated GR layers and were highly exposed to target molecules. Compared with NiCo 2 O 4 /GR, the electrocatalytic activity of NiCo 2 O 4 supported on PGR is effectively increased accompanied with the high utilization efficiency of NiCo 2 O 4 supported on PGR. By combination of the catalytic properties of highly exposed NiCo 2 O 4 and structural properties of PGR, the NiCo 2 O 4 /PGR is highly active, cheap and selective noble-metal free catalysts for oxygen reduction reaction (ORR) in alkaline solution. In addition, the ORR activity of NiCo 2 O 4 /PGR is increased accompanied with the decrease of pore size of PGR. NiCo 2 O 4 /PGR is potential efficient and inexpensive noble metal-free ORR catalysts with good long term stability in alkaline solution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Designing MnO functionalized Fe 3 C@nitrogen doped mesoporous Fe x Mn y @NC materials. • Mn boosts the formation of mesoporous structures along surfaces of Fe x Mn y @NC. • The HER E onset and E 10 values of Fe 3 Mn 1 @NC just 84.8 and 156 mV more negative than Pt/C. • The OER E onset and E 10 values of Fe 3 Mn 1 @NC just 8 and 18.7 mV more positive than RuO 2. • A low voltage of 1.6287 V at 10 mA cm−2 for Fe 3 Mn 1 @NC||Fe 3 Mn 1 @NC just 24.9 mV larger than 1.6038 V of Pt/C||RuO 2. In the development of water splitting, the sluggish electrocatalytic kinetics of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have restricted their energy conversion efficiencies. Along with the continuous rise in the prices of noble metals and transition metals (such as cobalt and nickel), constructing high-efficiency HER/OER catalysts based on low cost transition metals, such as iron and manganese, is becoming more meaningful in developing industrialized water splitting devices. In this paper, in the absence of a template or active agent, three-dimensional, hierarchically porous Fe x Mn y nanoparticles (NPs) were embedded and nitrogen-doped carbon materials (denoted as Fe x Mn y @NC; x:y, representing the molar ratio of Fe:Mn) were successfully prepared via pyrolysis of corresponding precursors containing different metallic salt components. Various morphological, structural, and chemical characterization analysis demonstrate that at an Fe:Mn molar ratio of 3:1, the optimal Fe 3 Mn 1 @NC material shows high graphitization degree, rich mesoporous structures, a large surface area, and abundant carbon defects/edges, which promote the uniform dispersion of pyridinic-N (pyridinic- N -metal), graphitic-N, carbon oxygen bonds (C O), manganese oxide (MnO) nanocrystals, and Fe 3 C NPs-embedded, N -doped carbon sheet (Fe 3 C@NC) active sites. In alkaline conditions, the HER onset potentials (E onset) and potentials recorded at 10 mA cm−2 (E 10) of the optimal Fe 3 Mn 1 @NC are just 84.8 and 156 mV more negative than those of 20 wt% platinum carbon (Pt/C). Meanwhile, the OER E onset and E 10 values of the optimal Fe 3 Mn 1 @NC are just 8 and 18.7 mV more positive than those of RuO 2. Furthermore, optimized Fe 3 Mn 1 @NC catalysts were assembled into a water splitting cell, where the catalytic current density achieves 10 mA cm−2 at a low voltage of 1.6287 V (with superior catalytic stability), which is just 24.9 mV higher than that of the (-) 20 wt% Pt/C||RuO 2 (+) benchmark (1.6038 V) under the same conditions. This work describes the regulating efficiency of Mn toward growing mesopores and opens new possibilities for the development of novel carbonaceous catalysts with excellent hydroxide catalytic efficiencies based on low cost Mn/Fe elements. [ABSTRACT FROM AUTHOR]

Highlights: [•] P-doped ordered mesoporous carbons (POMCs) as support for Pt nanoparticles. [•] The addition of P promote the formation of oxygen-containing functional groups. [•] The P-doped OMCs demonstrate excellent CO-tolerance towards MOR. [•] Pt/P7OMCs shows much enhanced electrochemical activity and long-term stability. [ABSTRACT FROM AUTHOR]

• CoRu nanoalloy@N-doped graphene was prepared by laser in air at room temperature for the first time. • The synthesis was finished in 2 min. • CoRu@NG-3 (Ru 0.18%) shows a good electrocatalytic performance and high stability for HER at all-pH values. High temperature pyrolysis needs complicated and harsh preparative condition, such as inert gas protection, long reaction time and high pyrolysis temperature. This work reported that a cobalt-ruthenium nanoalloy coated with nitrogen- doped graphene (CoRu@NG-x) was rapidly prepared from Ru-ZIF-67 as precursors by laser engraving in air environment and at room temperature for the first time. The addition of a small amount of ruthenium in cobalt can further improve the hydrogen catalytic performance. CoRu@NG-3 (Ru, 0.18wt%) is an efficient HER electrocatalyst in a wide pH range. Compared with the reported ruthenium alloys, the content of ruthenium in CoRu@NG-3 is the lowest. It's worth noting that the optimal CoRu@NG-3 shows overpotentials of 62, 52 and 88 mV at the current density of 10 mA cm−2 in 1.0 M KOH, 0.5 M H 2 SO 4 and 1.0 M PBS solution for HER catalysis. CoRu@NG-3 also has a good stability under all pH conditions. This study may offer a novel strategy to rapidly prepare electrode materials at room temperature and in the air. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Integrated electrochemical platform for determining food colorants was proposed. • Sensing chip and electrochemical miniaturized workstation were integrated. • Pt nanoparticles/laser-engraved graphene was synthesized as the sensing material. • Sensing chip showed excellent colorant sensing performance. • Integrated electrochemical platform exhibited practicability in real samples. This study presents the first integrated electrochemical platform (IEP) with point-of-use and portable features for on-site determination of ponceau 4R (RP), amaranth (AM), and tartrazine (TZ) in food by integrating a mass-producible Pt nanoparticles/laser-engraved graphene (Pt NPs/LEG)-based sensing chip and a reusable electrochemical miniaturized workstation. The sensing chip utilizes Pt NPs/LEG with unique architectures as electrode material and exhibits desirable analytical performance towards RP, AM, or TZ with satisfied linear range (0.25–50 μM for RP, AM, and TZ), high sensitivity (7.29 μA μM−1 cm−2, 7.18 μA μM−1 cm−2, and 2.02 μA μM−1 cm−2 for RP, AM, and TZ, respectively) and low limit of detection (50 nM, 58 nM, and 204 nM for RP, AM, and TZ, respectively). The sensing chip shows excellent selectivity, high stability, outstanding reproducibility, and acceptable mechanical stability. IEP can be implemented to test RP, AM, or TZ in real samples with satisfactory accuracy and recoveries. [ABSTRACT FROM AUTHOR]

Herein, we report a novel composite fabricated via embedding rod-like Co based metal-organic framework (Co-MOF-74) crystals into MC matrix for the first time. The introduction of MC astricts the size of Co-MOF-74 crystals, enlarges the pore size and improves the electrical conductivity, which lead to the good electrochemical properties of the composite. The fabricated sensor based on Co-MOF-74@MC exhibits superior electrocatalytic activity toward the reduction of pyrazinamide (PZA) and the oxidation of isonicotinyl hydrazide (INZ). Under optimized conditions, the sensor shows two linear ranges from 0.3 to 46.5 μM and 46.5–166.5 μM with a high sensitivity of 7.2 μA μM−1 cm−2 and a detection limit of 0.21 μM for the determination of PZA. The electroanalytical sensing of INZ also gives two linear ranges of 0.15–1.55 μM and 1.55–592.55 μM with a detection limit of 0.094 μM. The mechanism involved was also discussed, briefly. The sensor is assessed toward the detection of PZA and INZ in human serum and urine samples. Recovery values varied from 97.08 to 103.20% for PZA sensing and 96.67–102.90% for INZ sensing, revealing the promising practicality of sensor for PZA and INZ detection. Image 1 • Synthesizing Co-MOF-74@MC composite via embedding rod-like Co-MOF-74 crystals into MC for the first time. • Co-MOF-74@MC/GCE shows improved electrocatalytic activity to INZ oxidation and PZA reduction. • Satisfactory results are achieved for INZ and PZA in real samples. [ABSTRACT FROM AUTHOR]

In this work, FeCo nanoparticles encapsulated in graphitic carbon layers are derived by direct pyrolysis of Prussian blue/ZIF-67. First, the Prussian blue nanocubes with size of 100–150 nm are selected as cores for growth of ZIF-67 metal organic frameworks. Subsequent direct pyrolysis of Prussian blue/ZIF-67 in nitrogen atmosphere enables the formation of carbon nanospheres with FeCo nanoparticles embedded into the nitrogen-doped graphitic carbon layers. The encapsulation of FeCo nanoparticles into the nitrogen-doped carbon layers favors the electron penetration from the underlying FeCo nanoparticles to the nitrogen-doped graphitic carbon layers, tuning the electron density and the electronic properties at the carbon overlayers and then promoting the both hydrogen and oxygen evolution reaction activity. By optimizing the ratio between the Prussian blue and ZIF-67, the active and inexpensive carbon layers-encapsulated FeCo nanoparticles achieve high activity towards the hydrogen evolution reaction, exhibiting a low overpotential of 106 mV at 10 mA cm−2 as well as a low Tafel slope of 90.0 mV dec−1. As oxygen evolution reaction electrocatalysts, the carbon layers-encapsulated FeCo nanoparticles deliver an overpotential of 312 mV at 10 mA cm−2 and a low Tafel slope of 40.6 mV dec−1. Severing as both anode and cathode, the carbon layers-encapsulated FeCo nanoparticles show a potential of 1.495 V at 10 mA cm−2 for water splitting, which is close to the noble metal benchmarks of Pt/C and RuO 2 counterparts. The carbon layers-encapsulated FeCo nanoparticles can be used as an attractive replacement for electrocatalytic water splitting. Image 1 • Preparation of carbon layer-coated FeCo by direct pyrolysis of Prussian blue/MOFs. • Promotion of activity by alloying the Fe and Co elements. • High stability and activity of carbon layer-encapsulated FeCo nanoparticles. [ABSTRACT FROM AUTHOR]

Ultrafine Co 7 Fe 3 nanoparticles embedded in nitrogen-doped porous carbon nanosheets (denoted as Co 7 Fe 3 /NPCSs) are successfully synthesized by utilizing porous plant tissue as a precursor. The morphological, structural, and chemical contents of the Co 7 Fe 3 /NPCSs and other control samples are analyzed by X-ray (powder) diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N 2 adsorption–desorption, Raman spectroscopy, inductively coupled plasma (ICP), and X-ray photoelectron spectroscopy (XPS) techniques. The glucose oxidation and detection performances of each catalyst are evaluated by using cyclic voltammetry and chronoamperometry. The experimental results demonstrate that the electrocatalytic abilities of the resultant catalysts toward glucose oxidation decrease in the order of Co 7 Fe 3 /NPCSs > Co/NPCSs > CoFe/NPCSs > Fe 2 C-Co 3 Fe 7 /NPCSs > Fe 2 C/NPCSs. The experimental results prove that a small number of Fe atoms in Co 7 Fe 3 can increase the number of active Co4+ sites. Meanwhile, the ultrafine Co 7 Fe 3 nanoparticles uniformly dispersed along the porous carbon nanosheets' surfaces, which further improved the dispersion of the abundant electrochemically available active sites. Due to the synergistic effect of the hierarchical porous structures, high-density active sites and excellent electron conductivity, the optimal Co 7 Fe 3 /NPCSs display the best glucose detection efficiency of all the catalysts examined. For instance, the Co 7 Fe 3 /NPCSs exhibit large sensitivity values (795.28 µA cm−2 mM−1 between 0.001 and 2.20 mM and 401.98 μA cm−2 mM−1 between 2.20 and 14.00 mM), a rapid response time (2.2 s), a low detection limit (1.0 µM), excellent anti-interference toward electroactive molecules, a perfect reproducibility and a superior long-term stability. The Co 7 Fe 3 /NPCSs also exhibit a satisfying efficiency for glucose detection in human serum samples. Finally, our low-cost synthetic strategy can advance research used for designing 3D hierarchical meso/macroporous noble-metal-free catalysts without any tedious steps or templates. [ABSTRACT FROM AUTHOR]

The zirconium fumarate metal-organic framework (MOF-801) and mesoporous carbon (MC) composite was prepared by a conventional method. Compared with MOF-801, MOF-801/MC has a larger specific surface area, pore volume, improved conductivity, and better electrocatalytic performance. The new electrochemical sensor based on MOF-801/MC exhibits significant electrocatalytic activity for the oxidation of GA and the redox of luteolin. And the mechanisms of these two substances are discussed. Under the optimum test conditions, the detection of GA displays a wider linear range, consisted of two linear segments (0.2–5 and 5–100 μM) and the limit of detection (LOD) is 0.15 μM (S/N = 3). At the same time, the detection of luteolin also exhibits two linear relationships, 0.02–0.2 and 0.2–10 μM with LOD of 2.90 nM (S/N = 3). In addition, the MOF-801/MC sensor has good stability, selectivity and reproducibility. MOF-801/MC/GCE sensor was also used for detection of GA and luteolin in green tea and urine with satisfactory results. Unlabelled Image • Mesoporous carbon and Zr-MOF-801 were combined for the first time. • MOF-801/MC shows larger specific surface area, pore volume and improved conductivity. • MOF-801/MC has wider linear range and comparable sensitivity for the oxidation of GA. • MOF-801/MC exhibits higher sensitive to the oxidation of luteolin. • Satisfactory results for the detection of actual samples. [ABSTRACT FROM AUTHOR]

A facile, low cost and effective method was used to synthesize porous holey nitrogen-doped graphene (PHNG) with three-dimensional (3D) structure via direct pyrolysis of a mixture of urea and magnesium acetate tetrahydrate, followed by treating with hydrochloric acid to remove magnesium cations. The unique structure of PHNG significantly decreases the irreversible stacking of graphene nanosheet, favors the exposure of active edge sites, and enables more accessibility for reactants/electrolytes. The PHNG shows porous structure with a large surface area and can serve as support for nanoparticles. PtPd nanoparticles with different ratios were deposited on PHNG surface to synthesize PtPd/PHNG. The PtPd/PHNG-2 shows high direct oxidation activity towards the glucose, achieving a high sensitivity (52.526 μA mM−1 cm−2), wide linear range (100–4000 μM), fast response time (<3 s), low limit of detection (1.82 μM), as well as high selectivity. Image 1 • High surface area and porous structure of porous holey nitrogen-doped graphene. • High dispersion of PtPd nanoparticles supported on porous holey nitrogen-doped graphene. • A sensitive nonenzymatic sensor based on PtPd/porous holey nitrogen-doped graphene. [ABSTRACT FROM AUTHOR]

Abstract In this work, the low-cost carbon nanorods assembled hierarchical meso-macroporous carbons networks aerogels (CNs-HMCNAs) was environment-friendly synthesized from a cheap and abundant biomass of apples (Malus pumila Mill) for the first time. The biomass of apples derived CNs-HMCNAs exhibited the unique hierarchical meso-macroporous structure with large specific surface area and high density of edge defective sites. At the CNs-HMCNAs modified GCE (CNs-HMCNAs/GCE), the electron transfer between the glassy carbon electrode (GCE) and the ascorbic acid (AA) (or hydrogen peroxide (H 2 O 2)) was effectively enhanced, and thus induced a low overvoltage for AA electrooxidation (or H 2 O 2 electroreduction). As an electrochemical AA (or H 2 O 2) sensor, the CNs-HMCNAs/GCE exhibited wider linear range, lower detection limit, higher sensitivity and stability than GCE and the carbon nanotubes modified GCE (CNTs/GCE). In particular, the CNs-HMCNAs/GCE showed great potential feasibility in the practical determination of AA (in AA injection, Vitamin C tablet and kiwi juice) or H 2 O 2 (in human urine, milk and beer). Graphical abstract Image 1 Highlights • Apples derived hierarchical meso-macroporous carbons networks aerogels for electrochemical sensing. • Improved electrocatalytic performance towards AA electrooxidation and H 2 O 2 electroreduction. • Sensitive and selective detection of AA and H 2 O 2. • Great potential feasibility in the practical determination of AA and H 2 O 2. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, kelp ( Laminaria japonica ), as a kind of abundant biomass, is used as the precursor for the preparation of kelp-derived hierarchical meso-macroporous carbons (K-dHMMCs) through the carbonization under nitrogen (N 2 ) atmosphere at high temperature. The K-dHMMCs exhibits the unique structure with high specific surface area of 416.02 m 2  g −1 , large pore volume of 0.24 cm 3  g −1 , the hierarchical meso-macroporous size distribution centered at 2, 12 and 82 nm and high density of defective sites, enabling K-dHMMCs attractive for the electrocatalysis. Drop-casting K-dHMMCs on the glassy carbon (GC) surface allows the construction of K-dHMMCs based electrochemical sensing platform, which shows electrocatalytic activities towards many electroactive molecules, such as potassium ferricyanide, nicotinamide adenine dinucleotide (NADH), hydrogen peroxide (H 2 O 2 ), dopamine (DA), uric acid (UA), ascorbic acid (AA), epinephrine (EP), l -tyrosine (Tyr) and acetaminophen (APAP). Especially, the K-dHMMCs modified GC (K-dHMMCs/GC) electrode exhibits higher sensitivity, wider linear range, and lower detection limit than both carbon nanotubes modified GC (CNTs/GC) and GC electrodes for H 2 O 2 detection, which makes the K-dHMMCs/GC electrode to be able to determine the H 2 O 2 levels in human urine sample and monitor the H 2 O 2 released from human cancer cells. These results demonstrate that K-dHMMCs/GC possesses a great potential for conventional electrochemical sensing applications. [ABSTRACT FROM AUTHOR]

For the first time, the carbon nanoplates with high density of defective sites derived from the biomass of ground cherry ( Physalis peruviana ) husks was synthesized for the construction of an advanced electrochemical sensing platform. Electrochemical responses of different molecules (potassium ferricyanide, β-nicotinamide adenine dinucleotide, hydrogen peroxide, epinephrine and dopamine, the mixture of four free DNA bases (guanine, thymine, cytosine and adenine), cysteine, ascorbic acid, L-tryptophan, uric acid and acetaminophen) were studied at the biomass derived ground cherry husks derived carbon nanoplates (BG-CNPs) modified glassy carbon (GC) (BG-CNPs/GC) electrode, which shows higher electrocatalytic activities than GC electrode. Especially, the BG-CNPs/GC electrode exhibits remarkably strong electrocatalytic response toward hydrogen peroxide (H 2 O 2 ) compared with carbon nanotubes modified GC (CNTs/GC) and GC electrodes, indicating the great potential feasibility in the detection of H 2 O 2 in human urine as well as the monitoring of H 2 O 2 released from the living cells. All the results indicate that BG-CNPs is a promising carbon material which could be utilized to develop an advanced electrochemical sensing platform with multifunctional applications ranging from voltammetric sensing to amperometric sensing and DNA sensing. [ABSTRACT FROM AUTHOR]

The fast, low-cost, and efficient design of zeolite imidazolate frameworks (ZIF) based derivatives with perfect hollow channels is an effective method for enhancing their full water-splitting catalytic activities and achieving their commercial use. In this study, the novel cobalt nanoparticles embedded in nitrogen-doped porous carbon nanocages uniformly dispersed over two curved surfaces of biomass-derived hollow carbon fibers (Co@NC nanocage/HCF) were synthesized via the carbonization of the ZIF-67/hollow biomass fiber precursors. After the usage amounts of biomass fibers were optimized, the optimal Co@NC nanocage/HCF 200 exhibited a larger surface area and higher dispersion states of Co@NC nanocages than the tightly packed pure Co@NC nanocages. Particularly, owing to the hollow and porous structures of Co@NC nanocages, more electrocatalytic active centers (i.e. the pyridinic-N, Co-N x -C, pyrrolic-N, graphitic-N, high-valence Co, and other oxygen-containing functional groups) were exposed along surfaces of the Co@NC nanocage/HCF 200 catalyst. In an alkaline solution, the hydrogen evolution reaction potential at 10 mA cm−2 for Co@NC nanocage/HCF 200 was 165 mV more negative than that of 20 wt% Pt/C. Particularly, the oxygen evolution reaction potential at 10 mA cm−2 for Co@NC nanocage/HCF 200 was 17 mV more negative than that of RuO 2. For overall water splitting, the bifunctional Co@NC nanocage/HCF 200 catalyst-based electrolysis cell achieved a current density of 10 mA cm−2 at a cell voltage of 1.618 V, which is 4 mV smaller than that of the state-of-the-art 20 wt% Pt/C||RuO 2 cell (1.614 V). The perfect hollow and porous structures, uniformly dispersed Co@NC nanocages (locked by vast in situ formed carbon nanotubes), and abundant electrocatalytic active sites along the inner and outer surfaces of Co@NC nanocage/HCF 200 contributed to the excellent water splitting catalysis. Particularly, owing to the excellent stabilities of hollow structures and uniformly dispersed porous Co@NC nanocages, the Co@NC nanocage/HCF 200 exhibited higher stability toward water electrolysis. [Display omitted] • Co@NC nanocages uniformly dispersed hollow carbon fibers. • The large surface area and various active sites of Co@NC nanocages/HCF 200. • HER E 10 value of optimal catalyst is 165 mV more negative than 20 wt% Pt/C. • OER E 10 value of optimal catalyst is 17 mV more negative than that of RuO 2. • Cell voltage at 10 mA cm−2 for optimal catalyst is 4 mV smaller than 20 wt% Pt/C||RuO 2. [ABSTRACT FROM AUTHOR]

In this study, novel ZIF-67@carbon fiber composites were fabricated by a simple and facile approach. In order to explore the influence of carbon fiber structure on enhancing the electrocatalytic efficiency of the ZIF-67, different structural carbon fibers (hollow porous carbon fiber (PCF) and solid carbon fiber (SCF)) were used for preparing ZIF-67/carbon fiber catalysts. ZIF-67/carbon fiber composites were characterized via X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and electrochemical methods. Thanks to excellent hollow structural characteristic of PCF, ZIF-67/PCF possesses more exposed active sites, smaller particle size of ZIF-67, better conductivity, electrochemical stability, more mass transport channels as well as superior electrocatalytic abilities than ZIF-67/SCF. Furthermore, ZIF-67/PCF(1:1) sample-modified glassy carbon electrode presents a linear range to nitrobenzene that is composed by two line segments, i.e. from 0.3 to 50 μM with a sensitivity of 454.7 μA mM −1 and from 50 to 390 μM with a sensitivity of 132.0 μA mM −1 , and a low detection limit of 0.16 μM. It also exhibits a wide linear response to l -cysteine in the range of 5–160 μM and 160–1580 μM with a rapidly response within 1.0 s as well as high catalytic rate constant, good stability and anti-interference ability. Our work provides useful information for searching and choosing carbon materials with excellent structure benefit to electrochemical applications. [ABSTRACT FROM AUTHOR]

Nitrogen-doped graphene (N/GR) has been considered as active metal-free electrocatalysts for oxygen reduction reaction (ORR). However, the nitrogen (N) doping efficiency is very low and only few N atoms are doped into the framework of GR. To boost the N doping efficiency, in this work, a confined pyrolysis method with high N doping efficiency is used for the preparation of cobalt nanoparticles/nitrogen-doped GR (Co/N/GR). Under the protection of SiO 2 , the inorganic ligand NH 3 in cobalt amine complex ([Co(NH 3 ) 6 ] 3+ ) is trapped in the confined space and then can be effectively doped into the framework of GR without the introduction of any carbon residues. Meanwhile, due to the redox reaction between the cobalt ions and carbon atoms of GR, Co nanoparticles are supported into the framework of N/GR. Due to prevention of GR layer aggregation with SiO 2 , the Co/N/GR with high dispersion provides sufficient surface area and maximum opportunity for the exposure of Co nanoparticles and active sites of N dopant. By combination of enhanced N doping efficiency, Co nanoparticles and high dispersion of GR sheets, the Co/N/GR is remarkably active, cheap and selective noble-metal free catalysts for ORR. [ABSTRACT FROM AUTHOR]

Exploring highly efficient bi-functional electro-catalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are critical for developing energy conversion and storage systems. Herein, for the first time, without any template or surfactant, a family of Fe/Co N-doped three-dimensional (3D) hierarchical meso/macroporous carbon encapsulated FeCo nanoparticles (denoted as FexCo(1−x)-N/PC) have been successfully synthesized through pyrolyzing the low-cost biomass-based precursors in the NH 3 atmosphere. After optimizing the molar ratio of Fe/Co, benefiting from the collaborative advantages of the Fe/Co N C species, cobalt-based electro-active phases, and unique 3D electrode configuration, the resultant Fe0.5Co0.5-N/PC amazingly shows considerable ORR activity comparable with commercial Pt/C catalyst via a 4e − pathway in alkaline electrolyte. When used for OER catalysis in an alkaline medium, Fe0.5Co0.5-N/PC achieves an extremely negative potential of 1.625 V vs. RHE at a current density of 10 mA cm −2 and a low Tafel slope of 68.3 mV dec −1 . Furthermore, the overpotential (Δ E ) between ORR and OER is just 0.813 V, which is nearly the minimum value for the non-precious metal catalysts. We believe that our present synthetic strategy can be further extended to develop other 3D hierarchical meso/macroporous carbonaceous catalysts for various applications, such as sensors, batteries, and supercapacitors. [ABSTRACT FROM AUTHOR]

A facile, effective, and environmentally friendly method has been adopted for the first time to prepare tiny Co 3 O 4 nanocrystals embedded carbon matrices without using surfactants, harmful organic reagents or extreme conditions. Structural characterizations reveal that the size-controlled Co 3 O 4 nanocrystals are uniformly dispersed on carbon matrices. Electrochemical measurements reveal that Co 3 O 4 -ordered mesoporous carbon (OMC) can more efficiently catalyze glucose oxidation and acquire better detection parameters compared with those for the Co 3 O 4 -macroporous carbon, Co 3 O 4 -reduced graphene oxide, and free Co 3 O 4 nanoparticles (NPs) (such as: the large sensitivity (2597.5 μA cm −2 mM −1 between 0 and 0.8 mM and 955.9 μA cm −2 mM −1 between 0.9 and 7.0 mM), fast response time, wide linear range, good stability, and surpassingly selective capability to electroactive molecules or Cl − ). Such excellent performances are attributed to the synergistic effect of the following three factors: (1) the high catalytic sites provided by the uniformly dispersed and size-controlled Co 3 O 4 nanocrystals embedded on OMC; (2) the excellent reactant transport efficiency caused by the abundant mesoporous structures of OMC matrix: (3) the improved electron transport in high electron transfer rate (confinement of the Co 3 O 4 NPs in nanoscale spaces ensured intimate contact between Co 3 O 4 nanocrystals and the conducting OMC matrix). The superior catalytic activity and selectivity make Co 3 O 4 -OMC very promising for application in direct detection of glucose. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a comparative study on the electrocatalytic activities of ordered mesoporous carbons (OMCs) and graphene (GR) is presented. Using voltammetry and amperometry as detection methods, four DNA bases, double-stranded DNA (dsDNA), six important electroactive compounds and various biomolecules were employed to investigate their electrochemical responses on OMC and GR modified glassy carbon electrodes (OMC/GCE and GR/GCE). The results show that OMC/GCE enhances the electron transfer kinetics of these compounds compared to GR/GCE. The discrepancy in electrochemical activities can be attributed to the different microstructures of OMC and GR, which were examined by transmission electron microscopy, X-ray photoelectron spectra, X-ray diffraction, Raman spectra and nitrogen adsorption–desorption. [Copyright &y& Elsevier]

Designing low-cost, high-efficiency and non-noble metal-based electrocatalysts is fairly essential for the commercial utilization of electrochemical sensors and energy conversion devices. Low-cost CuFe 2 O 4 spinel has been widely researched as an electrocatalyst in electrochemical sensors and catalysis. Nevertheless, the low utilization of active sites in bulk CuFe 2 O 4 and the poor electro conductivity of CuFe 2 O 4 invariably restrict its upgrade in catalytic efficiency. Herein, by utilizing the facile electrospinning technique and without involving any template or surfactant, we successfully design three-dimensional (3D) hierarchically porous architecture woven by abundant ultrafine CuFe 2 O 4 crystal-coupled porous carbon nanowires (denoted as CuFe 2 O 4 /PCFs). Characterization results verify the 3D net-like textural structures of CuFe 2 O 4 /PCFs. Especially, the hierarchically porous structure, high surface area, and abundant carbon edges boost the uniform dispersion of tiny CuFe 2 O 4 crystals; these obviously promote the amounts of electrochemically available CuFe 2 O 4 active sites while decreasing the mass transport resistance of CuFe 2 O 4 /PCFs in electrocatalytic processes. Meanwhile, introducing carbon matrices can drastically enhance the electrical conductivity of CuFe 2 O 4 /PCF nanowires. All these advances in structural and physical performances truly make tremendous progress for CuFe 2 O 4 /PCFs for H 2 O 2 reduction and oxygen evolution reaction (OER) catalysis compared with bulk CuFe 2 O 4. For instance, the CuFe 2 O 4 /PCF catalyst exhibits a high sensitivity of 69.18 μA mM−1 cm−2, low detection limit of 1.20 μM and wide linear range of 0.11–22.0 mM for H 2 O 2 sensing. Meanwhile, the CuFe 2 O 4 /PCF catalyst just needs a potential value of 1.589 V (vs. reversible hydrogen electrode) to achieve the OER catalysis current density of 10 mA cm−2 in 1.0 M KOH, it only shows a small Tafel slope of 89.34 mV dec−1 for the OER as well. Our catalyst design strategy of CuFe 2 O 4 /PCF nanowires not only demonstrates the successful design of a novel high-efficiency non-noble-metal catalyst for both OER and H 2 O 2 reduction catalysis but also affords a new methodology for boosting the electrocatalytic abilities of spinel-type hybrid materials by designing a 3D structure and improving conductivity. Image 1 • Ultrafine CuFe 2 O 4 nanocrystallines coupled porous carbon nanowires. • The 3D hierarchical porous net-like architecture consist of CuFe 2 O 4 /PCFs nanowires. • Riched catalytic active sites and excellent electroconductibility for electrocatalysis. • Wide linear range (0.11–22.0 mM) and high sensitivity (69.18 μA mM−1 cm−2) toward H 2 O 2 sensing. • A negative OER E 10 value of 1.589 V vs. RHE and a low Tafel slope of 89.34 mV dec−1. [ABSTRACT FROM AUTHOR]

Highly efficient electrocatalysts for oxygen evolution reaction play key roles in various energy storage/conversion devices. Promoting the reaction rates and decreasing the overpotentials of the electrocatalysts for oxygen evolution reaction are critical for their practical application. Herein, we realize the first successful synthesis of Co 2 N 0.67 with three-dimensional architecture of hierarchical meso-macroporous nanoflowers stacked by the nanoplates with polystyrene spheres as the template. The Co 2 N 0.67 nanoflowers exhibit both low overpotential (258 mV at 10 mA cm−2) and low Tafel slope (52.22 mV dec−1) as well as superior stability for oxygen evolution reaction in alkaline medium, which makes Co 2 N 0.67 nanoflowers to be one of best earth-abundant elements based electrocatalysts toward oxygen evolution reaction to date. Importantly, being different from the previous observation that the cobalt nitrides with higher nitrogen content possess lower oxygen evolution reaction electrocatalytic abilities, we find Co 2 N 0.67 exhibits higher oxygen evolution reaction activity than Co 5.47 N. The density functional theory calculations reveal that during the oxygen evolution reaction, the oxidation step from O* to OOH* on Co 2 N 0.67 and Co 5.47 N is considered as the rate-determining step, making oxygen evolution reaction to be more thermodynamically favorable on Co 2 N 0.67 than that on Co 5.47 N. Image 1 • Co 2 N 0.67 possesses 3D architecture of hierarchical meso-macroporous nanoflowers (NFWs). • Co 2 N 0.67 NFWs needs a low potential of 1.488 V vs. RHE to drive 10 mA cm−2 for OER in 1.0 M KOH. • Co 2 N 0.67 exhibits higher OER electrocatalytic activity than Co 5.47 N in alkaline solution. • DFT calculations confirm the higher thermodynamical favorability on Co 2 N 0.67 than that on Co 5.47 N. [ABSTRACT FROM AUTHOR]

Fully integrated wearable sensors are capable of dynamically, directly, and independently tracking biomarkers in raw noninvasive biofluids without any other equipment or accessories by integrating the unique on-body monitoring feature with the special complete functional implementation attribute. Sweat, saliva, and urine are three important noninvasive biofluids, and changes in their biomarkers hold great potential for revealing physiological conditions. However, it is still a challenge to design single fully integrated wearable sensor arrays (FIWSAs) that are universally able to concurrently measure electrolytes and metabolites in three of the most common noninvasive biofluids including sweat, saliva, and urine. Here, we propose the first single universal FIWSAs for wirelessly, noninvasively, and simultaneously measuring various metabolites (i.e., uric acid) and electrolytes (i.e., Na + and H + ) in raw sweat, saliva, or urine under subjects' exercise by integrating the specifically designed microfluidic, sensing, and electronic modules in a seamless manner. We evaluate its utility for noninvasive gout management in healthy subjects and in gout patients through a purine-rich meal challenge and with a medicine-treatment control, respectively. Noninvasive monitoring of multiple electrolytes and metabolites in a variety of raw noninvasive biofluids via such single universal FIWSAs may enrich the understanding of the biomarkers' levels in the body and would also facilitate self-health management.

Fully integrated wearable electronics that combine the extraordinary feature of incessant and on-body operation with the distinctive external equipment-free trait are the ultimate goal of modern wearables. Epidermal sweat and wound exudate, as two noninvasively accessible biofluids on/surrounding the skin, reflect underlying health conditions. However, the design of universal wearable sensors with the bifunctional capability to monitor both epidermal secretions is still a challenge. Here, a single bifunctional fully integrated wearable tracker for wirelessly, simultaneously, and dynamically in situ measuring multiple epidermal sweat or wound exudate biomarkers is propos. Considering the electrolytes (e.g., Na + , K + , and H + ) and metabolites (e.g., uric acid (UA)) levels in sweat or wound exudate may correlate with health or wound conditions, the dynamic and skin-on tracking of the biomarkers of Na + , K + , pH, and UA levels in sweat under subjects' exercise and in wound exudate during subjects' wound healing are performed through the seamless integration of microfluidic, sensing, and electronic modules. Its applicability is evaluated for noninvasive hyperuricemia management in hyperuricemia/healthy subjects through a purine-rich intake test and for wound management in subjects' infected wounds through a control medical treatment., (© 2022 Wiley-VCH GmbH.)

It is highly desirable to develop durable and advanced electrocatalysts for pH-universal hydrogen evolution reaction (HER). While it makes much progress so far, the development of an environmental-friendly and cost-effective method to upgrade earth-abundant biomass into high value-added products still remains a major challenge. Thermal pyrolysis method which requires high pyrolysis temperature and long synthesis period is considered as a general method for preparation of carbon-based electrocatalysts. In view of this, ruthenium, nitrogen co-doped porous carbon (Ru@CN) is synthesized by laser conversion method at room temperature using cheap and renewable biomass honey as green carbon source. By controlling the loading of Ru and laser power, the electrocatalytic activities of as-prepared electrocatalysts can be adjusted effectively. Because of the advantage of rich Ru 0 and Ru-N sites, the synthesized 0.04-Ru@CN-6 with Ru loading amount of 2.66 wt% exhibits a preferable electrocatalytic activity toward HER under all-pH conditions. Especially in alkaline solution, the optimal 0.04-Ru@CN-6 exhibits a small overpotential (11 mV) at 10 mA cm -2 current density, which is even much better than commercial 20 wt% Pt/C (37 mV). This strategy reported here may be a feasible and unique approach to synthesis and design of high-performance as well as cost-effective all-pH HER electrocatalyst., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Rational design and synthesis of multifunctional electrocatalysts with high-efficient activity and robust stability toward the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are highly desirable, but remain a challenging step. Herein, a novel hollow bimetallic carbide/nitrogen-doped carbon nanotube (Co 6 Mo 6 C 2 @NCNT) is successfully synthesized through the simple pyrolysis of polypyrrole (PPy)-supported metal-organic framework (MOF) composite. Remarkable characteristics of the large surface area, hollow and porous structure, rich active sites and synergistic effect between Co 6 Mo 6 C 2 and NCNT arouse high catalytic efficiency. Notably, the Co 6 Mo 6 C 2 @NCNT presents excellent ORR catalytic activity (a high half-wave potential of 0.875 V vs. reversible hydrogen electrode (RHE) and diffusion-limited current density of 6.22 mA cm -2 ) via a four-electron pathway, together with outstanding stability and methanol tolerance over commercial Pt/C in 0.1 M KOH solution. The composite also exhibits superior HER performance, delivering a low overpotential of 122.14 mV at current density of 10 mA cm -2 , as well as good catalytic performance for OER in 1.0 M KOH solution. This work may provide some insight in design multifunctional electrocatalysts derived from MOF with advanced performance for sustainable energy technologies., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

In this paper, a novel Fe 3 O 4 /N/C@MWCNTs composite derived from iron-based metal-organic frameworks (H 2 N-Fe-MIL-88B) with multi-walled carbon nanotubes (MWCNTs) was prepared successfully through a simple calcination process. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and electrochemical measurements were employed to comprehensive characterize the composites. Compare with the physical mixture, in-situ insertion of MWCNTs in the Fe 3 O 4 /N/C formed Fe 3 O 4 /N/C@MWCNTs composite has the higher conductivity, larger BET surface area and more satisfying electrocatalytic properties. Meanwhile, this composite with the reasonable combinations exhibits remarkable electrocatalytic activities for acetaminophen (AP) and metronidazole (MNZ) due to the synergistic interaction between the components. Thus, the Fe 3 O 4 /N/C@MWCNTs-2-600-based electrochemical sensor was established to effectively detect these two medicine molecules, respectively. In the optimized test conditions, the proposed sensor exhibits a wide linear response (0.5-5.0 μM and 5.0-1355.0 μM) for AP and the limit of detection (LOD) was achieved to be 0.14 μM (S/N = 3). Meanwhile, this sensor also shows two linear relationships with the concentration of MNZ in the range of 1.0 μM to 10.0 μM and 10.0 μM to 725.0 μM with the LOD of 0.19 μM (S/N = 3). Moreover, the satisfactory results were also acquired when the proposed sensor was used for the determination of AP and MNZ in the human serum and urine, demonstrating great promising of this electrochemical sensor for clinical applications., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In this work, a novel enzyme-free glucose and hydrogen peroxide (H 2 O 2 ) sensor based on Ni 3 N nanoparticles on conductive 3D graphene aerogels (Ni 3 N/GA) has been successfully synthesized by using hydrothermal reaction, freeze-dried and then calcined under NH 3 atmosphere. The obtained Ni 3 N/GA composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption isotherms and electrochemical methods. The results show the obtained 3D Ni 3 N/GA composites exhibit excellent electrochemical performance toward glucose oxidation and H 2 O 2 reduction with larger catalytic rate constant K cat value of 3.75 × 10 3  M -1  s -1 and 1.24 × 10 3  M -1  s -1 , respectively. As a glucose sensor, the obtained electrode provides a wide detection range of 0.1-7645.3 μM, fast response time within 3 s, high sensitivity of 905.6 μA mM -1  cm -2 and low detection limit of 0.04 μM. For detection of H 2 O 2 , this prepared sensor offers a wide detection range (5 μM-75.13 mM), fast response time (within 5 s), sensitivity (101.9 μA mM -1  cm -2 ) and low detection limit (1.80 μM). This enzyme-free glucose and H 2 O 2 sensor display satisfactory selectivity, reproducibility and long-term storage stability. Additionally, the sensor can also be used for glucose and H 2 O 2 detection in human blood serum. The results demonstrate that 3D GA nanostructures provide an enviable conductive network for efficient charge transfer and avoid Ni 3 N nanoparticles aggregation, which is advantageous for electrocatalytic applications., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In this paper, H 2 N-Fe-MIL-88B@OMC composites were fabricated by the simple hydrothermal method through in-situ growth iron-based metal-organic frameworks (H 2 N-Fe-MIL-88B) on ordered mesoporous carbon (OMC). Compared with pure H 2 N-Fe-MIL-88B crystals, the introduction of OMC can shrink the size of H 2 N-Fe-MIL-88B, increase the specific surface area, decrease the electron transfer resistance and drastically improve the electrochemical performance of H 2 N-Fe-MIL-88B@OMC. The composite exhibits remarkable electrocatalytic activity for p-nitrotoluene (p-NT) reduction and hydrazine (N 2 H 4 ) oxidation. Therefore, a novel electrochemical sensor based on H 2 N-Fe-MIL-88B@OMC was constructed for the efficient detection of these two environmental pollutants, respectively. Under the optimal experimental conditions, the proposed sensor displays a wide linearity range for p-NT that is composed by two line segments (20-225 μM and 225-2600 μM) and the limit of detection (LOD) is 8 μM (S/N = 3). Meanwhile, the sensor also shows a linear response to N 2 H 4 in the range of 0.006-0.061 μM and 0.061-611.111 μM with a high sensitivity of 20.1 μA/μM·cm 2 in low concentration range as well as a very low LOD as 5.3 nM (S/N = 3). And the response time of the sensor for N 2 H 4 detection is about 1 s. In addition, the proposed sensor shows satisfactory electrochemical stability, reproducibility, selectivity and practicability. H 2 N-Fe-MIL-88B@OMC may be a splendid candidate for developing electrochemical sensors to detect environmental pollutants., (Copyright © 2018 Elsevier B.V. All rights reserved.)

As a novel single-atom-thick sheet of sp 2 hybridized carbon atoms, graphene (GR) has attracted extensive attention in recent years because of its unique and remarkable properties, such as excellent electrical conductivity, large theoretical specific surface area, and strong mechanical strength. However, due to the π-π interaction, GR sheets are inclined to stack together, which may seriously degrade the performance of GR with the unique single-atom layer. In recent years, an increasing number of GR-based electrochemical sensors and biosensors are reported, which may reflect that GR has been considered as a kind of hot and promising electrode material for electrochemical sensor and biosensor construction. However, the active sites on GR surface induced by the irreversible GR aggregations would be deeply secluded inside the stacked GR sheets and therefore are not available for the electrocatalysis. So the alleviation or the minimization of the aggregation level for GR sheets would facilitate the exposure of active sites on GR and effectively upgrade the performance of GR-based electrochemical sensors and biosensors. Less aggregated GR with low aggregation and high dispersed structure can be used in improving the electrochemical activity of GR-based electrochemical sensors or biosensors. In this review, we summarize recent advances and new progress for the development of electrochemical sensors based on less aggregated GR. To achieve such goal, many strategies (such as the intercalation of carbon materials, surface modification, and structural engineering) have been applied to alleviate the aggregation level of GR in order to enhance the performance of GR-based electrochemical sensors and biosensors. Finally, the challenges associated with less aggregated GR-based electrochemical sensors and biosensors as well as related future research directions are discussed., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Designing and preparing porous transition metal ferrites without using any template, shape-directing agent, and surfactant is a challenge. Herein, heterojunction MFe2O4 (M = Co, Ni, Cu, Mn) nanofiber (NF) based films with three-dimensional configurations were synthesized by electrospinning and the subsequent thermal treatment processes. Characterization results indeed show the 3D net-like textural structures of the electrospun spinel-type MFe2O4 NFs. In particular, the resulting MFe2O4 NFs have lengths up to several dozens of micrometers with an average diameter size of about 150 nm and possess abundant micro/meso/macropores on both the surface and within the films. The hierarchically porous structures and high surface areas of these MFe2O4 NFs (for example, the CoFe2O4 NFs possess a larger BET specific surface area (61.48 m(2) g(-1)) than those of the CoFe2O4 NPs (5.93 m(2) g(-1))) can afford accessible transport channels for effectively decreasing the mass transport resistances, enhancing the electrical conductivity, and increasing the density and reactivity of the exposed catalytic active sites. All these advantages will be responsible for the better electrocatalytic performances of these MFe2O4 NFs compared with their structural isomers (i.e. the MFe2O4 NPs) for the oxygen evolution reaction (OER) and H2O2 reduction in alkaline solution. Meanwhile, both the OER and H2O2 reduction catalytic activities for these MFe2O4 NFs obey the order of CoFe2O4 NFs > CuFe2O4 NFs > NiFe2O4 NFs > MnFe2O4 NFs > Fe2O3 NFs. The CoFe2O4 NFs represent a new class of highly efficient non-noble-metal catalysts for both OER and H2O2 reduction/detection in alkaline media.