Two different kinds of carbon-based amorphous molybdenum sulfide composite catalysts (activated carbon supported amorphous molybdenum sulfide and acetylene black supported amorphous molybdenum sulfide) had been prepared in a facile and scalable one-step liquid phase chemical method. The morphological and structural information of catalysts was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and it’s electro-catalytic HER activity were evaluated by linear sweep voltammetry(LSV), amperometric i-t technology and AC impedance technology. The as-prepared carbon-based amorphous molybdenum sulfides showed greatly enhanced electro-catalytic activity for HER compared with pure amorphous molybdenum sulfides. Especially, the nano-sized acetylene black supported molybdenum sulfide exhibited excellent electro-catalytic HER performances with a low onset potential of −116 mV versus reverse hydrogen electrode (RHE) and a small Tafel slope of 51 mV per decade.

Surface-nitrogen enriched carbon spheres with core–shell structure were prepared by a facile and general strategy with dopamine and melamine as the precursors. This strategy includes three steps: the polymerization of dopamine to form polydopamine (PDA) spheres, the soaking of spheres in melamine (MA) and the pyrolysis of PDA spheres/MA. The resulting carbon spheres as electrode materials for supercapacitors display better performances than common N-doped carbon spheres (NCS) with a high specific capacitance (203 F/g at 0.5 A/g), acceptable rate capability (66% retention at 5 A/g) and good long-term stability (94.6% retention after 5000 cycles at 2 A/g). This formation of polymer spheres-soaking in inflating agent-pyrolysis strategy makes it easy to produce surface-nitrogen-rich and hierarchically porous carbon spheres on a large scale with different sources. These carbon spheres hold great potential applications in energy storage and conversion devices such as supercapacitors and fuel cells due to their unique structure and hierarchical composition.

•MoS2 nanosheets were in-situ grown on the commercial carbon nanofibers (MoS2@CNFs).•The MoS2@CNFs for HER was investigated in detail.•The resulting MoS2@CNFs hybrid exhibited high electrocatalytic activity in HER.•The method is a simple but effective strategy for preparation of HER catalysts.Developing an effective and facile method to achieve mass production of MoS2 nanostructures with abundant of edges may be the feasible way to meet the increasing demand for hydrogen evolution electrocatalysts. We developed a facile glucose-assisted hydrothermal method to in-situ grow MoS2 nanosheets on the commercial carbon nanofibers (CNFs). The controlled growth of MoS2 on CNFs (MoS2@CNFs) is leveraged to reveal mass ratio- and structure-dependent catalytic activity in the hydrogen evolution reaction (HER). Due to the unique shell structure, abundant edges of the MoS2 layer are exposed as active site, as well as the underlying CNFs effectively improves the conductivity, the resulting MoS2@CNFs hybrid exhibited high electrocatalytic activity in HER. The catalyst demonstrated the lowest overpotential of 52 mV, the highest current density of 101.49 mA cm−2 at ∼200 mV overpotential and the smallest Tafel slope of 49 mV/decade, suggesting the Volmer–Heyrovsky mechanism for the MoS2-catalyzed HER.

•CoAl-LDHs were synthesized on the surface of graphene oxide in situ.•The oxygen reduction reaction activity of the catalyst was investigated.•The synergistic effect between CoAl-LDHs and rGO is discussed in detail.•The roles of Co2+ in the LDHs were clarified.Precious metal-free electrocatalysts with high efficiency and durability for the oxygen reduction reaction (ORR) are strongly desired in the field of energy technology. Herein, the CoAl layered double hydroxides (CoAl-LDHs)/reduced graphene oxide (rGO) composites were successfully prepared by growing CoAl-LDHs on the surface of GO in situ via coprecipitation and subsequently hydrothermal treatment. The structure, composition, morphology and ORR catalytic activity of the CoAl-LDHs/rGO composites were investigated as a function of mass ratios of CoAl-LDHs and GO. The results show that there is an optimum mass ratio of CoAl-LDHs and GO (wCoAl-LDHs:wGO = 1:5) for the ORR catalytic activity, where the electron transfer number for ORR at the CoAl-LDHs/rGO composites reaches to 3.5, closing to the full four-electron process. The synergistic effect between CoAl-LDHs and rGO is discussed in detail and the discussion is instructive for the construction of the better transition metal oxides/carbon composite-based ORR catalysts.

Transition metal (e.g., Fe, Co, Ni)-based layered double hydroxides (LDHs) and their exfoliated nanosheets have great potential applications due to their redox and magnetic properties. Here we report a facile approach for the preparation of Co–Fe LDHs with good crystallinity and high purity. The proposed approach includes two steps: (1) The mixed divalent metal (e.g., Co2+, Fe2+) hydroxides were first synthesized using a homogeneous precipitation without piping N2 into the system; hexamethylenetetramine (HMT) was the hydrolysis agent providing OH−, and hydroxylamine hydrochloride (HAH) was used as both a reducing and a complexing reagent. (2) Then the as-prepared hydroxides were slowly oxidated by air and simultaneously intercalated by CO32− to form CO3-intercalated LDHs. The Co–Fe LDHs were roundly characterized by XRD, SEM, EDX and FT-IR. The effect of HAH on the morphology and structure of the Co–Fe LDHs was also studied. The magnetism of Co–Fe LDHs at room temperature was investigated and the results showed that the LDHs displayed a low saturation magnetization value of 6.3 emu g−1, suggesting that the purity of the products was very high. In addition, the intercalated CO32− in the Co–Fe LDHs could be successfully exchanged with other anions such as Cl− and ClO4−. Furthermore, the exchanged-LDHs could be exfoliated in formamide. This work establishes a new method for the synthesis of Fe-based LDHs with good crystallinity and high purity under mild conditions, and can accelerate the development of applications using these layered materials.A facile approach has been developed for synthesis of Co–Fe LDH with high crystallinity, using hydroxylamine hydrochloride as reducing and complexing reagent without piping N2 to the system.

An intumescent flame retardant (IFR), including melamine (MA), ammonium polyphosphate (APP), and polydopamine (PDA), was utilized as the precursor to prepare P,N co-doped hierarchically porous carbon which exhibited high electrocatalytic activity and durability for the oxygen reduction reaction (ORR). This finding indicates that an ingenious design of the precursor can lead to functional carbon materials using a simple process.

•Carbon nanodots and CoFe LDHs composites were prepared via simply mixing C-Dots and CoFe-LDHs.•Direct electrochemistry of several horseradish peroxidase (HRP) was achieved at C-Dots/LDHs modified electrode.•The biosensor based on immobilized HRP displayed an enhanced electrocatalytic reduction towards H2O2.•The excellent analytical performance of biosensor can be attributed to the synergistic effect of HRP, C-Dots and CoFe-LDHs.Carbon nanodots and CoFe layered double hydroxide composites (C-Dots/LDHs) were prepared via simply mixing C-Dots and CoFe-LDHs. The as-prepared composites were used for the immobilization of horseradish peroxidase (HRP) on the glass carbon (GC) electrode. The electrochemical behavior of the HRP/C-Dots/LDHs/GC electrode and its application as a H2O2 biosensor were investigated. The results indicated that HRP immobilized by C-Dots/LDHs retained the activity of enzyme and displayed quasi-reversible redox behavior and fast electron transfer with an electron transfer rate constant ks of 8.46 s−1. Under optimum experimental conditions, the HRP/C-Dots/LDHs/GC electrode displayed good electrocatalytic reduction activity and excellent analytic performance toward H2O2. The H2O2 biosensor showed a linear range of 0.1–23.1 μM (R2=0.9942) with a calculated detection limit of 0.04 μM (S/N=3). In addition, the biosensor exhibited high sensitivity, good selectivity, acceptable reproducibility and stability. The superior properties of this biosensor are attributed to the synergistic effect of HRP, C-Dots and CoFe-LDHs, which has been proved by investigating their electrochemical response to H2O2. Thus the C-Dots and LDHs composites provide a promising platform for the immobilization of redox enzymes and construction of sensitive biosensors.

•The bifunctional nanocomposites were synthesized.•A modified magnetic glassy carbon electrode was fabricated.•The electrode was used for the selective detection of Pb2+ and Cd2+ ions.•The proposed sensor features a wider linear range and higher sensitivity.The present paper has focused on the potential application of the bifunctional polydopamine@Fe3O4 core–shell nanoparticles for development of a simple, stable and highly selective electrochemical method for metal ions monitoring in real samples. The electrochemical method is based on electrochemical preconcentration/reduction of metal ions onto a polydopamine@Fe3O4 modified magnetic glassy carbon electrode at −1.1 V (versus SCE) in 0.1 M pH 5.0 acetate solution containing Pb2+ and Cd2+ during 160 s, followed by subsequent anodic stripping. The proposed method has been demonstrated highly selective and sensitive detection of Pb2+ and Cd2+, with the calculated detection limits of 1.4 × 10−11 M and 9.2 × 10−11 M. Under the optimized conditions, the square wave anodic stripping voltammetry response of the modified electrode to Pb2+ (or Cd2+) shows a linear concentration range of 5.0–600 nM (or 20–590 nM) with a correlation coefficient of 0.997 (or 0.994). Further, the proposed method has been performed to successfully detect Pb2+ and Cd2+ in aqueous effluent.Graphical abstract

Graphene-supported PdPt nanocomposite films can be deposited on the glassy carbon electrodes through two-step electrochemical method. The as-prepared catalyst, which exhibits high electrocatalytic ability in methanol oxidation and good tolerance to the intermediates generated during methanol oxidation, is very pure as a result of the surfactant-, reductant- and fixative-free formation process. This simple, straightforward, and effective method is of significance for the facile preparation of Pd-based catalysts on underlying electrodes directly.Highlights► Graphene‐supported PdPt nanocomposite was prepared by two-step electrodeposition. ► The electrocatalyst on glassy carbon electrode is surfactant-, reductant- and fixative-free. ► This composite exhibits high electrocatalytic ability and stability for methanol oxidation. ► The method is of significance for the preparation of Pd-based catalysts on electrodes directly.

We report a facile electrochemical strategy for the synthesis of Ni/Al layered double hydroxides (LDHs) and gold nanoparticle (AuNPs)-coated glassy carbon electrode (GCE). The new electrode is named LDH/AuNPs/GCE. The new electrode is named LDH/AuNPs/GCE. The electrocatalytic activity of LDH/AuNPs toward methanol electro-oxidation was studied by cyclic voltammetry and chronoamperometry. Compared to the Ni/Al-LDH modified GCE without AuNPs film (LDH/GCE), the LDH/AuNPs/GCE exhibits remarkably higher catalytic activity for methanol electro-oxidation, e.g. the lower oxidation potential (0.57 V vs. SCE) and the higher current density (6-fold). The enhancement may be attributed to the higher electrocatalytic activity of Ni/Al-LDHs in the presence of AuNPs, the synergy effect between them, or both. The results presented here may be of broad interest not only for developing fuel cells but also for understanding of OH− electro-generated on noble metal surfaces.Highlights► Ni/Al-LDHs and AuNPs film exhibits high catalytic activity for methanol oxidation. ► The catalytic oxidation can be attributed to the synergy effect of them. ► The low-cost LDH/AuNPs films may be used as potential anode materials for DMFCs.

In this study, the Fe-based layered double hydroxides (Mg3Fe LDH) were used to immobilize heme proteins including hemoglobin (Hb), myoglobin (Mb) and horseradish peroxidase (HRP) for fabrication of heme/Mg3Fe LDH film on glassy carbon electrode (Mg3Fe-heme/GCE). The possible role of iron in framework of LDH to promote direct electron transfer (DET) of heme proteins was investigated using an LDH containing non-iron as a reference. Hb was selected as a model protein for studying the electrocatalytic activity of immobilized heme in LDH film. The Mg3Fe-Hb/GCE displayed an enhanced electrocatalytic reduction towards H2O2. The biosensor showed a very low detection limit (0.036 μM) and apparent Michaelis–Menten constant (7.98 μM). This work outlines that Fe-based LDH modified electrode provides a promising platform for immobilization of heme proteins and development of sensitive biosensors.Highlights► Low-cost Fe-based LDHs were facilely synthesized by the coprecipitation method. ► Direct electron transfer of heme were achieved at the heme-LDH modified electrodes. ► The biosensor displayed an enhanced electrocatalytic reduction towards H2O2. ► The biosensor showed a low detection limit and apparent Michaelis–Menten constant.

We have developed a simple and efficient method for the enhanced loading of silver nanoparticles onto carbon nanospheres, and how this method can be used to design an electrochemical sensor for hydrogen peroxide (HP). A glassy carbon electrode was modified with hemoglobin, carbon nanospheres, and by enhanced loading of silver nanoparticles onto the carbon nanospheres via spontaneous polymerization of dopamine. The hemoglobin exhibits a remarkable electrocatalytic activity for the reduction of HP. The electrochemical response to HP is linear range in the 1.0–147.0 μM concentration range, with a detection limit of 0.3 μM at a signal-to-noise ratio of 3.

Graphene was synthesized by a chemical method to reduce graphite oxide and well characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD) and Fourier transform infrared (FTIR) spectra. Horseradish peroxidase (HRP) immobilized on a graphene film glassy carbon electrode was found to undergo direct electron transfer and exhibited a fast electron transfer rate constant of 4.63 s−1. The HRP-immobilized electrode was investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The CV results showed that the modified electrode gave rise to well-defined peaks in phosphate buffer, corresponding to the electrochemical redox reaction between HRP–Fe(III) and HRP–Fe(II). The obtained electrode also displayed an electrocatalytic reduction behavior towards H2O2. The new H2O2 sensor shows a linear range of 0.33–14.0 μM (R2 = 0.9987) with a calculated detection limit of 0.11 μM (S/N = 3). Furthermore, the biosensor exhibits both good operational storage and storage stability.

This letter reports on a new method for immobilization of electroactive species on a solid electrode surface based on the composite film of naphthol green B (NGB) and Co–Al layered double hydroxides (LDHs). After the oxidation potential of Co(III)/(II) couple was dramatically enhanced by NGB, the functionalized LDHs exhibited a remarkable electrocatalytic activity toward the oxidation of hydrazine in a weak acidic medium. The amperometric response to hydrazine showed a linear range of 0.17 μM–400 mM, with the calculated detection limit of 0.1 μM at a signal-to-noise ratio of three and the sensitivity of the amperometric hydrazine sensor was found to be 35.26 μA μM−1. The modified electrode displayed an acceptable reproducibility and good stability. The new strategy is expected to have wide applications for changing of the potential of redox couple in metal oxides, hydroxides, double hydroxides, and so on.

Layers of Ni-Al-NO3 layered double hydroxides were deposited on a gold electrode by electrosynthesis and applied in a low-cost non-enzymatic glucose sensor possessing high sensitivity and long-term stability. The amperometric current of the electrode is proportional to the concentration of glucose over the range of 0.0007–1.2 mM, the detection limit being 0.5 μM (at an S/N = 3). The electrode has been applied to determine glucose in glucose injection solutions, wine and urine.

Dithiocarbamate and gold nanoparticles have been successfully assembled onto the surface of the gold electrode and a novel ultrastable chemical modified electrode (CME) was fabricated conveniently. The as-prepared CME was investigated by electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM) and quartz crystal microbalance (QCM), and its electrochemical behaviors for catalytic oxidation of dopamine (DA) was also observed by cyclic voltammetry (CV) and amperometric i–t curve. The results indicated that the novel surface has endowed the electrode with not only ultrastability but also the advantages of organic ligands and gold nanoparticles, which open up a new way to design high efficient and utility electrochemical sensors for biomolecule detection.

An intumescent flame retardant (IFR), including melamine (MA), ammonium polyphosphate (APP), and polydopamine (PDA), was utilized as the precursor to prepare P,N co-doped hierarchically porous carbon which exhibited high electrocatalytic activity and durability for the oxygen reduction reaction (ORR). This finding indicates that an ingenious design of the precursor can lead to functional carbon materials using a simple process.