One-pot synthesis of ternary polypyrrole⿿Prussian-blue⿿graphene-oxide hybrid composite as electrode material for high-performance supercapacitors

An ultrasensitive electrochemical sensor for detecting porcine epidemic diarrhea virus based on a Prussian blue-reduced graphene oxide modified glassy carbon electrode

This study developed a novel, ultrasensitive sandwich-type electrochemical immunosensor for detecting the porcine epidemic diarrhea virus (PEDV). By electrochemical co-deposition of graphene and Prussian blue, a Prussian blue-reduced graphene oxide-modified glassy carbon electrode was made, further modified with PEDV-monoclonal antibodies (mAbs) to create a new PEDV immunosensor using the double antibody sandwich technique. The electrochemical characteristics of several modified electrodes were investigated using cyclic voltammetry (CV). We optimized the pH levels and scan rate. Additionally, we examined specificity, reproducibility, repeatability, accuracy, and stability. The study indicates that the immunosensor has good performance in the concentration range of 1 × 10^1.88 to 1 × 10^5.38 TCID₅₀/mL of PEDV, with a detection limit of 1 × 10^1.93 TCID₅₀/mL at a signal-to-noise ratio of 3σ. The composite membranes produced via co-deposition of graphene and Prussian blue effectively increased electron transport to the glassy carbon electrode, boosted response signals, and increased the sensitivity, specificity, and stability of the immunosensor. The immunosensor could accurately detect PEDV, with results comparable to real-time quantitative PCR. This technique was applied to PEDV detection and served as a model for developing additional immunosensors for detecting hazardous chemicals and pathogenic microbes.

EDTA derived graphene supported porous cobalt hexacyanoferrate nanospheres as a highly electroactive nanocomposite for hydrogen peroxide sensing

Developed a highly electroactive graphene and porous cobalt hexacyanoferrate nanosphere (Gr/P-CoHCF-NSPs) composite for H2O2 sensing by using EDTA chelation strategy.

Selective fluoride removal in capacitive deionization by reduced graphene oxide/hydroxyapatite composite electrode

Capacitive deionization (CDI) is an emerging desalination technology with an environmental-friendly operation and energy-efficient properties. However, activated carbon (AC) used for CDI electrode does not have a significant preference toward anions, leading to unnecessary energy consumption for treating fluoridated water. Hence, we achieved selective fluoride removal in CDI system using a reduced graphene oxide/hydroxyapatite composite (rGO/HA), a novel fluoride selective electrode material. The results showed that the rGO/HA electrode has 4.9 times higher fluoride removal capacity than the AC electrode from a ternary solution consisting of fluoride, chloride, and nitrate ions. The fluoride removal capacity increased when the adequate voltage was applied. Furthermore, the rGO/HA electrode exhibited stability and reusability without significant capacity loss even after 50-cycle operation, maintaining about 0.21 mmol g^-1 of fluoride removal capacity and approximately 96% of regeneration efficiency. Thus, this study suggests a novel electrode material for effective and selective fluoride removal in the CDI system.

Prussian blue-doped nanosized polyaniline for electrochemical detection of benzenediol isomers

Simultaneous speciation of benzenediol isomers (BDIs), 1,2-benzenediol (catechol, CC), 1,3-benzenediol (resorcinol, RS), and 1,4-benzenediol (hydroquinone, HQ), was investigated by differential pulse voltammetry (DPV) using a graphite paste electrode (GPE) modified with Prussian blue-polyaniline nanocomposite. The modified GPE showed good stability, sensitivity, and selectivity properties for all the three BDIs. Prussian blue-doped nanosized polyaniline (PBNS-PANI) was synthesized first by using mechanochemical reactions between aniline and ferric chloride hexahydrate as the oxidants and then followed by the addition of potassium hexacyanoferrate(II) in a solid-state and template-free technique. The material was characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The DPV measurements are performed in phosphate electrolyte solution with pH 4.0 at a potential range of - 0.1 to 1.0 V. The proposed modified electrode displayed a strong, stable, and continuous three well-separated oxidation peaks towards electrooxidation at potentials 0.20, 0.31, and 0.76 V for HQ, CC, and RS, respectively. The calibration curves were linear from 1 to 350.5 μM for both HQ and CC, while for RS, it was from 2 to 350.5 μM. The limit of detection was determined to be 0.18, 0.01, and 0.02 μM for HQ, CC, and RS, respectively. The analytical performance of the PBNS-PANI/GPE has been evaluated for simultaneous determination of HQ, CC, and RS in creek water, commercial hair dye, and skin whitening cream samples with satisfactory recoveries between 90 and 106%. Overall, we demonstrated that the presence of NS-PANI and PB resulted in a large redox-active surface area that enabled a promising analytical platform for simultaneous detection of BDIs. Graphical abstract.

Preparation of a NiAl-Oxide@Polypyrrole Composite for High-Performance Supercapacitors

A core-shell NiAlO@polypyrrole composite (NiAlO@PPy) with a 3D "sand rose"-like morphology was prepared via a facile in situ oxidative polymerization of pyrrole monomer, where the role of PPy coating thickness was investigated for high-performance supercapacitors. Microstructure analyses indicated that the PPy was successfully coated onto the NiAlO surface to form a core-shell structure. The NiAlO@PPy exhibited a better electrochemical performance than pure NiAlO, and the moderate thickness of the PPy shell layer was beneficial for expediting the electron transfer in the redox reaction. It was found that the NiAlO@PPy₅ prepared at 5.0 mL L^-1 addition amount of pyrrole monomer demonstrated the best electrochemical performance with a high specific capacitance of 883.2 F g^-1 at a current density of 1 A g^-1 and excellent capacitance retention of 91.82 % of its initial capacitance after 1000 cycles at 3 A g^-1 . The outstanding electrochemical performance of NiAlO@PPy₅ were due to the synergistic effect of NiAlO and PPy, where the uniform network-like PPy shell with the optimal thickness made electrolyte ions more easily accessible for faradic reactions. This work provided a simple approach for designing organic-inorganic core-shell materials as high-performance electrode materials for electrochemical supercapacitors.

Current Innovations of Metal Hexacyanoferrates-Based Nanocomposites toward Electrochemical Sensing: Materials Selection and Synthesis Methods

Mixed valence transition metal hexacyanoferrates (MeHCF)-Prussian blue and its analogs receive enormous research interest in the electrochemical sensing field. In recent years, conducting materials such as conducting polymer, carbon nanomaterial, and noble metals have been used to form nanocomposites with MeHCF. The scope of this review offers the reasons behind the preparation of various MeHCF based nanocomposite toward electrochemical detection. We primarily focus on the current progress of the development of MEHCF-based nanocomposites. The synthesis methods for these nanocomposites are also reviewed and discussed.

Ionic Liquids as Environmentally Benign Electrolytes for High-Performance Supercapacitors

Electrochemical capacitors (ECs) are a vital class of electrical energy storage (EES) devices that display the capacity of rapid charging and provide high power density. In the current era, interest in using ionic liquids (ILs) in high-performance EES devices has grown exponentially, as this novel versatile electrolyte media is associated with high thermal stability, excellent ionic conductivity, and the capability to withstand high voltages without undergoing decomposition. ILs are therefore potentially useful materials for improving the energy/power performances of ECs without compromising on safety, cyclic stability, and power density. The current review article underscores the importance of ILs as sustainable and high-performance electrolytes for electrochemical capacitors.

Design and fabrication of polypyrrole/expanded graphite 3D interlayer nanohybrids towards high capacitive performance

Polypyrrole/expanded graphite (PPy/EG) nanohybrids, with a hierarchical structure of a three dimensional EG framework with a thick PPy coating layer, have been synthesized via a vacuum-assisted intercalation in situ oxidation polymerization method. In the synthesis, pyrrole monomers were intercalated into the irregular pores of EG with the assistance of a vacuum pump. Subsequently, the intercalated pyrrole monomers assembled on both sides of the EG nanosheets and formed PPy by an in situ polymerization method. As electrode materials, the typical PPy/EG10 sample with an EG content of 10% had a high specific capacitance of 454.3 F g⁻¹ and 442.7 F g⁻¹ (1.0 A g⁻¹), and specific capacitance retention rate of 75.9% and 73.3% (15.0 A g⁻¹) in 1 M H₂SO₄ and 1 M KCl electrolytes, respectively. The two-electrode symmetric supercapacitor showed a high energy density of 47.5 W h kg⁻¹ at a power density of 1 kW kg⁻¹, and could retain superb stability after 2000 cycles. The unique self-supporting structure feature and homogeneous PPy nanosphere coating combined the contributions of electrochemical double layer capacitance and pseudo-capacitance, which made the nanohybrids an excellent electrode material for high performance energy storage devices.

Polypyrrole/expanded graphite nanohybrids with a hierarchical structure were synthesized as electrode materials, and showed outstanding energy storage performance.

Gold nanoparticles-based multifunctional nanoconjugates for highly sensitive and enzyme-free detection of E.coli K12

Immobilization of proteins on a biocompatible conductive interface is highly desirable for the fabrication of biosensors. In this study, a nanocomposite has been prepared by assembling well-distributed gold nanoparticles (AuNPs) on the surface of a polypyrrole-reduced graphene oxide (PPy-rGO) composite through electrostatic adsorption. This serves as a platform for immobilization of a capture antibody, which was conjugated onto the ferrocene doped polypyrrole-gold nanoparticles (PPy@Fc/AuNPs) composite. The design and performance of the biosensor was tested against detection of a whole-cell bacteria E. coli K12. This nanocomposite has a high surface area, good conductivity and biocompatibility, which is shown to be very suitable for enzyme-free detection of this bacteria. Results show excellent analytical performance with a linear range from 1.0 × 10¹ to 1.0 × 10⁷ CFU mL^-1 and a low detection limit of 10 CFU mL^-1. The sensor has high selectivity, excellent reproducibility, and good stability.

Carbon Quantum Dot-Induced MnO2 Nanowire Formation and Construction of a Binder-Free Flexible Membrane with Excellent Superhydrophilicity and Enhanced Supercapacitor Performance

Manganese oxides (MnO₂) are regarded as typical and promising electrode materials for supercapacitors. However, the practical electrochemical performance of MnO₂ is far from its theoretical value. Nowadays, numerous efforts are being devoted to the design and preparation of nanostructured MnO₂ with the aim of improving its electrochemical properties. In this work, ultralong MnO₂ nanowires were fabricated in a process induced by carbon quantum dots (CQDs); subsequently, a binder-free flexible electrode membrane was easily obtained by vacuum filtration of the MnO₂ nanowires. The effects of the CQDs not only induced the formation of one-dimensional nanostructured MnO₂, but also significantly improved the wettability between electrode and electrolyte. In other words, the MnO₂ membrane demonstrated a superhydrophilic character in aqueous solution, indicating the sufficient and abundant contact probability between electrode and electrolyte. The binder-free flexible MnO₂ electrode exhibited a preeminent specific capacitance of 340 F g^-1 at 1 A g^-1; even when the current density reached 20 A g^-1, it still maintained 260 F g^-1 (76% retention rate compared to that at 1 A g^-1). Moreover, it also showed good cycling stability with 80.1% capacity retention over 10 000 cycles at 1 A g^-1. Furthermore, an asymmetric supercapacitor was constructed using the MnO₂ membrane and active carbon as the positive and negative electrodes, respectively, which exhibited a high energy density of 33.6 Wh kg^-1 at 1.0 kW kg^-1, and a high power density of 10 kW kg^-1 at 12.5 Wh kg^-1.

Facile synthesis of Mesoporouscobalt Hexacyanoferrate Nanocubes for High-Performance Supercapacitors

Mesoporous cobalt hexacyanoferrate nanocubes (meso–CoHCF) were prepared for the first time through a facile sacrificial template method. The CoHCF mesostructures possess a high specific surface area of 548.5 m²·g⁻¹ and a large amount of mesopores, which enable fast mass transport of electrolyte and abundant energy storage sites. When evaluated as supercapacitor materials, the meso–CoHCF materials exhibit a high specific capacitance of 285 F·g⁻¹, good rate capability and long cycle life with capacitance retention of 92.9% after 3000 cycles in Na₂SO₄ aqueous electrolyte. The excellent electrochemical properties demonstrate the rational preparation of mesoporous prussian blue and its analogues for energy storage applications.

Graphene oxide directed in-situ synthesis of Prussian blue for non-enzymatic sensing of hydrogen peroxide released from macrophages

A novel electrochemical non-enzymatic hydrogen peroxide (H₂O₂) sensor has been developed based on Prussian blue (PB) and electrochemically reduced graphene oxide (ERGO). The GO was covalently modified on glassy carbon electrode (GCE), and utilized as a directing platform for in-situ synthesis of electroactive PB. Then the GO was electrochemically treated to reduction form to improve the effective surface area and electroactivity of the sensing interface. The fabrication process was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). The results showed that the rich oxygen containing groups play a crucial role for the successful synthesis of PB, and the obtained PB layer on the covalently immobilized GO has good stability. Electrochemical sensing assay showed that the modified electrode had tremendous electrocatalytic property for the reduction of H₂O₂. The steady-state current response increased linearly with H₂O₂ concentrations from 5μM to 1mM with a fast response time (less than 3s). The detection limit was estimated to be 0.8μM. When the sensor was applied for determination of H₂O₂ released from living cells of macrophages, satisfactory results were achieved.