Iron sulfides/oxides/fluorides have been profoundly investigated as electrodes for rechargeable batteries recently in view of their high-theory capacities, low cost, and environmentally benign nature. Here, Fe3S4 nanoparticles (NPs) wrapped in reduced graphene oxide (Fe3S4 NPs@rGO) have been obtained using a simple one-pot hydrothermal approach, which is characterized using various techniques. As the anode for Li-ion batteries, Fe3S4 NPs@rGO displays a reversible discharge capacity of 950 mA h/g after 100 cycles at 0.1 A/g, and 720 mA h/g capacity can be achieved after 800 cycles even at 1 A/g. Even at 10 A/g, 462 mA h/g capacity can be maintained. The excellent electrochemical properties for Fe3S4 NPs@rGO can be ascribed to a collaborative effect between Fe3S4 NPs and an rGO matrix, which possess high Li-ion storage ability and excellent conductivity, respectively.Keywords: anode; electrochemical properties; Fe3S4 NPs@rGO; LIBs; one-pot hydrothermal approach;

Starting from the renewable biomass material palm kernel shell (PKS), nitrogen, sulfur and phosphorus co-doped high specific surface area porous activated carbon materials were prepared through carbonization and KOH chemical activation and applied to the supercapacitor electrode materials. PKS is a low-cost carbon source byproduct of biomass, which is rich in cellulose, lignin, and moisture, and its other components also provide nitrogen, sulfur, phosphorus and other heteroatoms for the final product. After further activation with different ratios of alkali and carbon, porous activated carbon (PAC) with different pore sizes could be obtained. The presence of heteroatoms not only provides redox pseudocapacitance, but doping heteroatoms is also beneficial to suppress irreversible changes of the oxygen-containing functional groups on the carbon material surface during the charging and discharging process. In 3 mol L−1 KOH electrolyte solution, PAC showed an excellent electrochemical performance with good cycling stability, and its maximum specific capacity could reach 380 F g−l.

Ferrous sulfide (FeS) particles dispersed in the pores of carbon (FeS/PC) from the polyacrylonitrile carbonization were prepared via a facile one-pot solid-state method, which was extensively characterized by XRD, SEM, TEM, Raman spectrum, and XPS techniques. As an anode material for lithium-ion batteries, this FeS/PC composite can achieve a high initial discharge capacity of 1428.8 mAh/g at 0.1 C, and can maintain 624.9 mAh/g capacity after 150 cycles. The porous carbon accommodates the volume change during the cycling, and the special structure of the FeS/PC composite results in its advanced electrochemical performance by enhancing the structure stability.

In this study, we use N, P co-doped activated carbon prepared from honeycomb as an electrode material for supercapacitors. The texture characteristics of the materials are determined by using nitrogen adsorption analysis. Thermal properties, the crystal structure/phase composition and surface element composition are observed by TGA, XRD and XPS, respectively. The morphologies of the samples have been characterized via FESEM and HRTEM. In order to further study the surface functional groups and degree of graphitization (conductivity) of the samples, we have conducted FTIR and Raman spectra tests. The electrochemical performance is investigated using an electrochemical workstation. In 3 M KOH electrolyte solution, N, P co-doped activated carbon shows an excellent electrochemical performance with good high specific capacitance (375.0 F g−1 at 0.5 A g−1) and remarkable rate capability (315.1 F g−1 at even 10 A g−1). It also shows excellent cycle performance, after 10 000 charge and discharge cycles the specific capacitance was still maintained as the original 98.7%. In addition, we fabricate a symmetric supercapacitor device to further to study the electrochemical performance of N, P co-doped activated carbons. At a current density of 1.0 A g−1, the symmetric supercapacitor exhibits an excellent cycle performance in that the specific capacitance was maintained as the original 98.1% after 10 000 charge–discharge cycles. The symmetric supercapacitor gives a maximum energy density of 27.6 W h kg−1 at a power density of 398.4 W kg−1.

•Recent progress on polyanion-type cathode materials for sodium-ion batteries is overviewed.•Ortho-, pyro- and fluoro-phosphates are the main candidates.•Mixed anions-type cathode materials are receiving increasing attention.In the past several years, many efforts have been made to develop polyanion-type cathode materials for sodium ion batteries by chemists and material scientists. These materials are one of the main types of promising cathodes though the studies are still in their infancy. This paper reviews almost all the important advances of polyanion-type cathodes on their syntheses, crystal structures, morphologies, electrochemical performance and Na redox mechanisms. It specifically focuses on their crystal chemistry and electrochemical behaviors. The contents are divided into several categories according to their chemical compositions. After introduction of the synthetic methods, phosphates (ortho-, pyro- and fluoro-), silicates, sulfates, and mixed anions type cathodes are summarized and discussed successively.Download high-res image (345KB)Download full-size image

Ordered porous Co3O4 materials with pore sizes of 5 nm (Co3O4–5), 20 nm (Co3O4–20), and 70 nm (Co3O4–70) have been synthesized via a hard-template method and were studied as catalysts to bring insight into non-enzymatic electrochemical sensing of glucose. A glassy carbon electrode modified with Co3O4–70 responds more quickly and sensitively to glucose than those modified with Co3O4–5 or Co3O4–20. The sensor based on the use of Co3O4–70 and operated at a working voltage of 0.6 V (vs. Ag/AgCl) in 0.1 M NaOH solution shows a lower detection limit of 0.025 μM, good repeatability and high selectivity over ascorbic acid, uric acid, dopamine, and KCl. These results suggest that ordered porous Co3O4 is a promising material for quantitative electrochemical determination of glucose, and that the pore size has a strong effect on performance.

Noble metal-based materials have been intensively investigated as good additives of electrode materials for supercapacitors, since they can improve the specific capacitance, conductivity, and chemical and thermal stabilities of the electrode materials. This review carefully summarizes noble metal-based materials for high-performance supercapacitor electrodes. The advances of hybrid electrodes are then assessed to include hybrid systems of noble metal-based materials with compounds such as carbonaceous materials, metals and transition metal oxides or hydroxides. A variety of synthetic methods such as hydrothermal/solvothermal methods, polymerization, and electrodeposition methods are also discussed to prepare noble metal-based materials. This review comprehensively summarizes and evaluates the recent progress in the research on noble metal-based electrode materials for supercapacitors, including synthesis methods, electrochemical performances, and related devices.

•Vanadium based materials for high performance supercapacitor were reviewed.•The advantages and disadvantages were discussed in details.•Perspectives as to the future directions of vanadium based materials were provided.As a kind of supercapacitors, pseudocapacitors have attracted wide attention in recent years. The capacitance of the electrochemical capacitors based on pseudocapacitance arises mainly from redox reactions between electrolytes and active materials. These materials usually have several oxidation states for oxidation and reduction. Many research teams have focused on the development of an alternative material for electrochemical capacitors. Many transition metal oxides have been shown to be suitable as electrode materials of electrochemical capacitors. Among them, vanadium based materials are being developed for this purpose. Vanadium based materials are known as one of the best active materials for high power/energy density electrochemical capacitors due to its outstanding specific capacitance and long cycle life, high conductivity and good electrochemical reversibility. There are different kinds of synthetic methods such as sol-gel hydrothermal/solvothermal method, template method, electrospinning method, atomic layer deposition, and electrodeposition method that have been successfully applied to prepare vanadium based electrode materials. In our review, we give an overall summary and evaluation of the recent progress in the research of vanadium based materials for electrochemical capacitors that include synthesis methods, the electrochemical performances of the electrode materials and the devices.

•A one-pot in-situ solid state method to prepare active material.•SeS0.1 particles on the surface or in the pores of 3D NCPAN.•SeS0.1/NCPAN has initial capacity of 1387 mAh/g.•Around 600 mAh/g maintained in 20 cycles for SeS0.1/NCPAN.•SeS0.1/NCPAN has much better electrochemical behaviors than Se/NCPAN.Novel 3-D network SeSx/NCPAN (nitrogen-doped carbonized polyacrylonitrile) (x = 0.1 and 0) composites were prepared by one-step in situ solid-state method, directly heated the mixture of Se, S and PAN sealed in a quartz tube under vacuum, which was characterized by powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectrum and X-ray photoelectron spectroscopy (XPS) techniques. It is discovered that SeS0.1 is dispersed in the 3-D network of NCPAN. The reversible electrode operation of SeS0.1 at ca. 1.1 V vs Li was identified with the capacity of 1387 mAh/g and around 600 mAh/g maintained after 20 cycles, demonstrating much better electrochemical performance than Se/NCPAN. This is the first study on one-step in-situ preparation of SeSx/NCPAN composites as the active cathode material for lithium–ion battery.

We present an efficient Pb2+ electrosorption by nitrogen-doped graphene aerogels (NGAs) prepared by one-pot hydrothermal synthesis of nitrogen-doped graphene hydrogels (NGHs) followed by freeze-drying treatment. Pb2+ can be effectively removed by the as-prepared NGAs at an applied negative potential, and the removal mechanisms include (1) electrostatic attraction derived from external electric field, (2) electrostatic attraction caused by intrinsic charges on NGAs and Pb2+, (3) large specific surface area (SBET) of NGAs, and (4) coordination between doped nitrogen atoms and Pb2+. More importantly, after a simple and convenient electrodesorption treatment, the NGAs exhibit promising performance in recyclable electrosorption, and the removal ratio (%R) of Pb2+ decreases only ∼5% after successive 100 cycles, which is significantly superior to conducting polymer and conducting polymer/reduced graphene oxide (rGO) composites-based electrosorption.

This study demonstrated a facile method to form a porous polymeric membrane, immobilizing a biocatalyst. A polyelectrolyte-based amphiphilic diblock copolymer, i.e., polystyrene-block-poly(acrylic acid) (PS-b-PAA), self-assembled with hemoglobin (Hb) dually driven by charge and amphiphilicity during solution-casting and evaporation. XPS and contact angle measurements suggested that the PS block enriched on the membrane surface. The PAA block pointed toward the internal membrane as well as ordered the Hb arrangement at the interface of the polymer and electrode. The obtained PS-b-PAA/Hb electrode showed a remarkably enhanced direct electron transfer (ET), which was revealed to be a surface-controlled process accompanied by single-proton transfer. The membrane was tested to catalyze the reduction of hydrogen peroxide, and exhibited an excellent reproducibility and stability. This method with a charge and amphiphilicity dually driven (CADD) self-assembly opened up a new way to construct a third-generation electrochemical biosensor.Keywords: amphiphilic diblock copolymer; direct electron transfer; dually driven self-assembly; electrocatalysis; porous membrane;

An unprecedented quaternary sulfide borate, Sm3S3BO3 (1), was obtained via a high-temperature solid-state synthesis method. It crystallizes in the triclinic space group P1̅, and its 3D structure features a 2D (Sm2S2)∞ wrinkled layer and a 1D (SmS)∞ ladderlike chain bridged by trigonal-planar (BO3)3– through Sm–O bonds, demonstrating the first sulfide borate without S–O and B–S bonds. Its optical energy gap is measured to be around 2.5 eV and verified by electronic structure calculation.

MnO2 was doped into a conducting copolymer, poly(aniline-co-o-aminophenol) (PANOA), via a one-step process during the chemical oxidative polymerization. The doping of MnO2 could enhance the electrochemical activity and reversibility of the copolymer. When used as the electrode materials of a supercapacitor, the capacitive behaviors of the as-prepared PANOA–MnO2 were superior to those of pure PANOA, especially at high potential scan rate and high charge–discharge current density. The MnO2 doped copolymer also had an excellent cyclic performance.MnO2 doped conducting copolymer (PANOA) is synthesized facilely via a one-step process, in which the doping of MnO2 and the chemical oxidative copolymerization of aniline and o-aminophenol is achieved simultaneously. Due to the introduction of MnO2, the as-prepared PANOA–MnO2 exhibits better capacitive behaviors compared to PANOA, especially at high potential scan rate and high charge/discharge current density.

The direct electron transfer (DET) between glucose oxidase (GOD) and the underlying glassy carbon electrode (GCE) can be readily achieved via colloidal laponite nanoparticles as immobilization matrix. Cyclic voltammetry of laponite/GOD/GCE, in anaerobic phosphate buffer solution (PBS, 0.1 M, pH 5.0), showed a pair of stable and quasi-reversible peaks at potentials Epa = −0.372 V and Epc = −0.391 V vs. SCE, provoked by the prosthetic FAD group linked to the protein. The electrochemical reaction of laponite/GOD/GCE exhibited a surface-controlled process with the apparent heterogeneous electron transfer rate constant (ks) of 6.52 s−1 and charge-transfer coefficient (α) of 0.5. The experiments of FTIR and UV–vis spectroscopy demonstrate that the immobilized GOD on colloidal laponite nanoparticles retained its native structure and its biocatalytic ability to its substrates. Based on the decrease of oxygen electrocatalytic signal, the proposed laponite/GOD/GCE was successfully applied in the reagentless glucose sensing at −0.45 V. The proposed electrode exhibited fast amperometric response (8 s), broad linear range (2.0 × 10−5–1.9 × 10−3 M), good sensitivity (4.8 ± 0.5 mA M−1 cm−2), low detection limit (1.0 × 10−5 M) at a signal-to-noise ratio of 3, and excellent selectivity.

The determination of xanthine has considerable importance in clinical and food quality control. Therefore, in this present work, we developed a novel xanthine biosensor based on immobilization of xanthine oxidase (XnOx) by attractive materials layered double hydroxides (LDHs). Amperometric detection of xanthine was evaluated by holding the modified electrode at 0.55 V (versus saturated calomel electrode (SCE)). Due to the special properties of LDHs, such as chemical inertia, mechanical and thermal stability, anionic exchange ability, high porosity and swelling properties, XnOx/LDHs-modified electrode exhibited a developed analytical performance. The biosensor provided a linear response to xanthine over a concentration range of 1 × 10−6 M to 2 × 10−4 M with a sensitivity of 220 mA M−1 cm−2 and a detection limit of 1 × 10−7 M based on S/N = 3. In addition, the immobilized XnOx layers have been characterized using atomic force microscopy under both air atmosphere and liquid environment, which exhibited the interesting swelling phenomenon of LDHs. The investigation of inhibition of XnOx by allopurinol was carried out using this XnOx/LDHs-modified electrode. The experimental results indicated that inhibitory effect could be achieved by allopurinol with a quasi-reversible competitive type.

An attractive biocomposite based on polycrystalline bismuth oxide (BiOx) film and polyphenol oxidase (PPO) was proposed for the construction of a mediator-free amperometric biosensor for phenolic compounds in environmental water samples. The phenolic biosensor could be easily achieved by casting the biocomposite on the surface of glassy carbon electrode (GCE) via the cross-linking step by glutaraldehyde. The laboratory-prepared bismuth oxide semiconductor was polymorphism. Its hydrophilicity provided a favorable microenvironment for retaining the biological activity of the immobilized protein. The parameters of the fabrication process and the various experimental variables for the enzyme electrode were optimized. The proposed PPO/BiOx biosensor provided a linear response to catechol over a concentration range of 4 × 10−9 M to 1.5 × 10−5 M with a dramatically developed sensitivity of 11.3 A M−1 cm−2 and a detection limit of 1 × 10−9 M based on S/N = 3. In addition, the PPO/BiOx biocomposite was characterized by scanning electron microscope (SEM), Fourier transform infrared spectra (FTIR) and rotating disk electrode voltammetry.

Hemoglobin (Hb) was successfully immobilized in poly(acrylonitrile-co-acrylic acid) (PAN-co-PAA) film modified glassy carbon electrode (GCE). The Hb-PAN-co-PAA film exhibited a pair of well-defined and quasi-reversible cyclic voltammetric peaks for Hb Fe(III)/Fe(II) redox couple in a pH 7.0 phosphate buffer. The formal potential of Hb heme Fe(III)/Fe(II) couple varied linearly with the increase of pH in the range of 4.0–8.0 with a slope of −53.5 mV pH−1, implying that one proton was accompanied with one electron transferred in the electrochemical reaction. Position of Soret absorption band of Hb-PAN-co-PAA film suggested that the Hb kept its secondary structure similar to its native state in the PAN-co-PAA matrix. The protein in PAN-co-PAA matrix acted as a biologic catalyst to catalyze reduction of hydrogen peroxide. The electrocatalytic response showed a linear dependence on the H2O2 concentration ranging from 9.2 × 10−6 to 2 × 10−3 M with a detection limit of 4.5 × 10−6 M at 3σ.

In this work, colloidal laponite nanoparticles were further expanded into the design of the third-generation biosensor. Direct electrochemistry of the complex molybdoenzyme xanthine oxidase (XnOx) immobilized on glassy carbon electrode (GCE) by laponite nanoparticles was investigated for the first time. XnOx/laponite thin film modified electrode showed only one pair of well defined and reversible cyclic voltammetric peaks attributed to XnOx–FAD cofactor at about −0.370 V vs. SCE (pH 5). The formal potential of XnOx–FAD/FADH2 couple varied linearly with the increase of pH in the range of 4.0–8.0 with a slope of −54.3 mV pH−1, which indicated that two-proton transfer was accompanied with two-electron transfer in the electrochemical reaction. More interestingly, the immobilized XnOx retained its biological activity well and displayed an excellent electrocatalytic performance to both the oxidation of xanthine and the reduction of nitrate. The electrocatalytic response showed a linear dependence on the xanthine concentration ranging from 3.9 × 10−8 to 2.1 × 10−5 M with a detection limit of 1.0 × 10−8 M based on S/N = 3.

This paper aimed at showing the interest of the composite material based on layered double hydroxides (LDHs) and chitosan (CHT) as suitable host matrix likely to immobilize enzyme onto electrode surface for amperometric biosensing application. This hybrid material combined the advantages of inorganic LDHs and organic biopolymer, CHT. Glucose oxidase (GOD) immobilized in the composite material maintained its activity well as the usage of glutaraldehyde was avoided. The process parameters for the fabrication of the enzyme electrode and various experimental variables such as pH, applied potential and temperature, were explored for optimum analytical performance of the enzyme electrode. The enzyme electrode provided a linear response to glucose over a concentration range of 1 × 10−6 to 3 × 10−3 M with a high sensitivity of 62.6 mA M−1 cm−2 and a detection limit of 0.1 μM based on the signal-to-noise ratio of 3.

The direct electron transfer between hemoglobin (Hb) and the underlying glassy carbon electrode (GCE) can be readily achieved via a high biocompatible composite system based on biopolymer chitosan (CHT) and inorganic CaCO3 nanoparticles (nano-CaCO3). Cyclic voltammetry of Hb-CHT/nano-CaCO3/GCE showed a pair of stable and quasi-reversible peaks for HbFe(III)/Fe(II) redox couple in pH 7.0 buffer. The electrochemical reaction of Hb immobilized in CHT/nano-CaCO3 composite matrix exhibited a surface-controlled process accompanied by electron and proton transfer. The electron transfer rate constant was estimated to be 1.8 s−1. This modified electrode showed a high thermal stability up to 60 °C. The apparent Michaelis–Menten constant was calculated to be 7.5 × 10−4 M, indicating a high catalytic activity of the immobilized Hb toward H2O2. The interaction between Hb and this nano-hybrid material was also investigated using FT-IR and UV–vis spectroscopy, indicating that Hb retained its native structure in this hybrid matrix.

A novel strategy to fabricate an amperometric biosensor for phenol determination based on chitosan/laponite nanocomposite matrix was described. The composite film was used to immobilize PPO on the surface of a glassy carbon electrode. Chitosan was utilized to improve the analytical performance of the pure clay-modified bioelectrode. The biosensor exhibited a series of properties: good affinity to its substrate (the apparent Michaelis–Menten constant for the sensor was found to be 0.16 mM), high sensitivity (674 mA M−1 cm−2 for catechol) and remarkable long-term stability in storage (it retains 88% of the original activity after 60 days). In addition, optimization of the biosensor construction as well as effects of experimental variables such as pH, operating potential and temperature on the amperometric response of the sensor were discussed.

A novel sensitive and stable phenols amperometric biosensor, based on polyaniline–polyacrylonitrile composite matrix, was applied for determination of benzoic acid. The electrochemical biosensor functioning was based on the inhibition effect of benzoic acid on the biocatalytic activity of the polyphenol oxidase (PPO) to its substrate (catechol) in 0.1 M phosphate buffer solution (pH 6.5). A potential value of −50 mV versus SCE, and a constant catechol concentration of 20 μM were selective to carry out the amperometric inhibition measurement. The kinetic parameters Michaelis-Menten constant (KMapp) and maximum current (Imax) in the absence and in the presence of benzoic acid were also evaluated and the possible inhibition mechanism was deduced. The inhibiting action of benzoic acid on the polyphenol oxidase electrode was reversible and of the typical competitive type, with an apparent inhibition constant of 38 μM. This proposed biosensor detected levels of benzoic acid as low as 2 × 10−7 M in solution. In addition, the effects of temperature, pH value of solution on the inhibition and the interferences were investigated and discussed herein. Inhibition studies revealed that the proposed electrochemical biosensor was applicable for monitoring benzoic acid in real sample such as milk, yoghurt, sprite and cola.

Calcium carbonate nanoparticles (nano-CaCO3) may be a promising material for enzyme immobilization owing to their high biocompatibility, large specific surface area and their aggregation properties. This attractive material was exploited for the mild immobilization of glucose oxidase (GOD) in order to develop glucose amperometric biosensor. The GOD/nano-CaCO3-based sensor exhibited a marked improvement in thermal stability compared to other glucose biosensors based on inorganic host matrixes. Amperometric detection of glucose was evaluated by holding the modified electrode at 0.60 V (versus SCE) in order to oxidize the hydrogen peroxide generated by the enzymatic reaction. The biosensor exhibited a rapid response (6 s), a low detection limit (0.1 μM), a wide linear range of 0.001–12 mM, a high sensitivity (58.1 mA cm−2 M−1), as well as a good operational and storage stability. In addition, optimization of the biosensor construction, the effects of the applied potential as well as common interfering compounds on the amperometric response of the sensor were investigated and discussed herein.

We reported on the utilization of a novel attractive nanoscaled calcium carbonate (nano-CaCO3)-polyphenol oxidase (PPO) biocomposite to create a highly responsive phenol biosensor. The phenol sensor could be easily achieved by casting the biocomposite on the surface of glassy carbon electrode (GCE) via the cross-linking step by glutaraldehyde. The special three-dimensional structure, porous morphology, hydrophilic and biocompatible properties of the nano-CaCO3 matrix resulted in high enzyme loading, and the enzyme entrapped in this matrix retained its activity to a large extent. The proposed PPO/nano-CaCO3 exhibited dramatically developed analytical performance such as such as a broad determination range (6 × 10−9–2 × 10−5 M), a short response time (less than 12 s), high sensitivity (474 mA M−1), subnanomolar detection limit (0.44 nM at a signal to noise ratio of 3) and good long-term stability (70% remained after 56 days). In addition, effects of pH value, applied potential, temperature and electrode construction were investigated and discussed.

A novel glucose biosensor was constructed by electrochemical entrapment of glucose oxidase (GOD) into porous poly(acrylonitrile-co-acrylic acid), which was synthesized via radical polymerization of acrylonitrile and acrylic acid. The obtained biosensor showed a better stability and higher sensitivity than the biosensor prepared by simple physical adsorption. Effects of some experimental variables such as immobilization time, enzyme concentration, pH, applied potential, and temperature on the amperometric response of the sensor were investigated. The biosensor exhibited a rapid response to glucose (<30 s) with a linear range of 5 × 10−6 to 3 × 10−3 M and a sensitivity of 6.82 mA M−1 cm−2. The apparent Michaelis–Menten constant (KMapp) was 7.3 mM.

A new type of in situ electropolymerization method was used for electrochemical biosensor design. The biologic film was prepared by in situ electropolymerization of aniline into microporous polyacrylonitrile-coated platinum electrode in the presence of glucose oxidase. The novel glucose biosensor exhibited good selectivity, sensitivity and stability, which showed no apparent loss of activity after 100 consecutive measurements and intermittent usage for 100 days with storage in a phosphate buffer at 4 °C. Blood glucose determinations agreed well with standard hospital laboratory analysis. The construction and operational parameters of the biosensor were also optimized.

Hemoglobin (Hb) was successfully immobilized in poly(acrylonitrile-co-acrylic acid) (PAN-co-PAA) film modified glassy carbon electrode (GCE). The Hb-PAN-co-PAA film exhibited a pair of well-defined and quasi-reversible cyclic voltammetric peaks for Hb Fe(III)/Fe(II) redox couple in a pH 7.0 phosphate buffer. The formal potential of Hb heme Fe(III)/Fe(II) couple varied linearly with the increase of pH in the range of 4.0–8.0 with a slope of −53.5 mV pH−1, implying that one proton was accompanied with one electron transferred in the electrochemical reaction. Position of Soret absorption band of Hb-PAN-co-PAA film suggested that the Hb kept its secondary structure similar to its native state in the PAN-co-PAA matrix. The protein in PAN-co-PAA matrix acted as a biologic catalyst to catalyze reduction of hydrogen peroxide. The electrocatalytic response showed a linear dependence on the H2O2 concentration ranging from 9.2 × 10−6 to 2 × 10−3 M with a detection limit of 4.5 × 10−6 M at 3σ.

Using calcium carbonate nanoparticles as enzyme immobilization matrix, the developments of xanthine biosensor were achieved by both electrooxidation and electroreduction of the enzymatic-generated hydrogen peroxide based on xanthine oxidase (XnOx) and horseradish peroxidase (HRP). Amperometric detection of xanthine was evaluated by holding the modified electrode at 0.55 and −0.05 V (versus SCE), for XnOx/Nano-CaCO3 and XnOx/HRP/Nano-CaCO3, respectively. The linear dynamic ranges of anodic and cathodic detections of xanthine were between 2 × 10−6 to 2.5 × 10−4 M and 4 × 10−7 to 5 × 10−5 M, respectively. The detection limits were determined to be of 2 × 10−6 and 1 × 10−7 M with anodic and cathodic processes, respectively. At lower working potential, XnOx/HRP/Nano-CaCO3/GCE bienzymatic system exhibited excellent selectivity; the bienzyme electrode was inert towards ascorbic and uric acid present. Moreover, the permeability of enzyme/Nano-CaCO3 was evaluated by the use of rotating disk electrode voltammetry.

Noble metal-based materials have been intensively investigated as good additives of electrode materials for supercapacitors, since they can improve the specific capacitance, conductivity, and chemical and thermal stabilities of the electrode materials. This review carefully summarizes noble metal-based materials for high-performance supercapacitor electrodes. The advances of hybrid electrodes are then assessed to include hybrid systems of noble metal-based materials with compounds such as carbonaceous materials, metals and transition metal oxides or hydroxides. A variety of synthetic methods such as hydrothermal/solvothermal methods, polymerization, and electrodeposition methods are also discussed to prepare noble metal-based materials. This review comprehensively summarizes and evaluates the recent progress in the research on noble metal-based electrode materials for supercapacitors, including synthesis methods, electrochemical performances, and related devices.