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Cationic (Zn) vacancies were introduced into ZnCo2O4 microspheres via solvothermal synthesis method. These vacancies improved the electrochemical performance of ZnCo2O4 when utilized as electrode material in battery-type supercapacitors.

Reduced graphene oxide (RGO)-supported Pd–CeO2 nanoparticles prepared by a chemical reduction method were shown to exhibit superior electrocatalytic activity towards formic acid compared to the commercial Pd/C catalyst.

Bimetallic nanoparticles with extremely uniform dispersion on conductive-carbon supports are very much in need to improve the kinetics of sluggish electrochemical reactions relevant to fuel cell applications. Here, bimetallic platinum-cobalt (26.7 wt% Pt + 2.8 wt% Co on reduced graphene oxide with atomic composition of platinum-to-cobalt as 3:1) and platinum-nickel (26.8 wt% Pt + 2.8 wt% Ni on reduced graphene oxide support with atomic composition of platinum-to-nickel as 3:1) nanoparticles with high degree of uniform dispersion (average particle sizes of about 1–2.25 nm) on graphene oxide in its partially reduced form (‘rGO’) were fabricated by a simple one-pot chemical-based reduction method. A pomegranate peel extract was utilized to neutralize the high acidic graphene oxide (GO) formed during the chemical exfoliation of natural graphite and used along with metal precursors during the chemical reduction to achieve well-dispersed Pt3Ni/rGO and Pt3Co/rGO nanoparticles. The efficiencies towards electrocatalytic oxygen reduction reaction (ORR) of the synthesized catalysts were tested in different media (acidic and basic). In acidic medium, the ORR activity descriptors like mass-specific and area-specific current density as well potential at half-wave (E1/2) are considerably higher for Pt3Ni/rGO nanocatalysts than Pt3Co/rGO, Pt/rGO and Pt/C electrocatalysts. Interestingly, in basic medium the Pt3Co/rGO exhibit higher ORR activity among the other catalysts tested. The general facile fabrication strategy shown in this work is promising to extend to prepare other mono, bi and ternary metallic nanoparticles with high uniformity on carbon-based substrates to utilize as highly advanced electrocatalysts.

Direct methanol fuel cells (DMFCs) offers promising possibilities in meeting future energy needs in a most sustainable way. To electro oxidize methanol at anode of DMFCs, till date Pt and Pt-based materials were widely employed. To improve the utilization of precious metals it is highly desirable to disperse them on conductive carbon structures. Here, we synthesized ultra-range bimetallic platinum–palladium (Pt–Pd) nanospheres (NSs) with uniform dispersion on reduced graphene oxide (RGO) sheets by a simple hydrothermal method and studied their efficacies towards methanol oxidation reaction (MOR). From HR-TEM analysis, it was found that the synthesized bimetallic Pt–Pd NSs possess an average particles size of about 5 to 7 nm consistent with XRD data. The MOR electro catalytic activity of bimetallic PtPd-RGO NSs was higher compared to homemade mono metallic Pt-RGO, Pd-RGO catalysts and commercial E-tekPt/C.

Oxygen reduction reaction (ORR) is a very important reaction that occurs at the cathodic side in proton exchange membrane fuel cells (PEMFCs). The high cost associated with frequently used Pt-based electrocatalysts for ORR limits the commercialization of PEMFCs. Through bifunctional and electronic effects, theoretical calculations have proved that alloying Pt with a suitable transition metal is likely to improve ORR mass activity when compared to Pt-alone systems. Herein, we demonstrate the preparation of bimetallic Pt–Fe nanoparticles supported on reduced graphene oxide sheets (RGOs) via a simple surfactant-free chemical reduction method. The present method produces PtFe/RGO catalyst particles with a 3.2 nm diameter without agglomeration. PtFe/RGO showed a noticeable positive half-wave potential (0.503 V vs. Ag/AgCl) compared with a commercial Pt/C catalyst (0.352 V vs. Ag/AgCl) with minimal Pt-loading on a glassy carbon electrode. Further, PtFe/RGO showed a higher ORR mass activity of 4.85 mA/cm2-geo compared to the commercial Pt/C (3.60 mA/cm2-geo). This work paves the way for designing noble−transition metal alloy electrocatalysts on RGO supports as high-performance electrocatalysts for ORR application.

The development of non−Pt or carbon−based catalysts for anion exchange membrane fuel cells (AEMFCs) requires identification of the active sites of the catalyst. Since not only metals but also carbon materials exhibit oxygen reduction reaction (ORR) activity in alkaline conditions, the contribution of carbon-based materials to ORR performance should also be thoroughly analyzed. However, the conventional CN− poisoning experiments, which are mainly used to explain the main active site of M−N−C catalysts, are limited to only qualitative discussions, having the potential to make fundamental errors. Here, we report a modified electrochemical analysis to quantitatively investigate the contribution of the metal and carbon active sites to ORR currents at a fixed potential by sequentially performing chronoamperometry with two reaction inhibitors, CN− and benzyl trimethylammonium (BTMA+). As a result, we discover how to quantify the individual contributions of two active sites (Pt nanoparticles and carbon support) of carbon−supported Pt (Pt/C) nanoparticles as a model catalyst. This study is expected to provide important clues for the active site analysis of carbon-supported non−Pt catalysts, such as M−N−C catalysts composed of heterogeneous elements.

Graphene is an intriguing two-dimensional honeycomb-like carbon material with a unique basal plane structure, charge carrier mobility, thermal conductivity, wide electrochemical spectrum, and unusual physicochemical properties. Therefore, it has attracted considerable scientific interest in the field of nanoscience and bionanotechnology. The high specific surface area of graphene allows it to support high biomolecule loading for good detection sensitivity. As such, graphene, graphene oxide (GO), and reduced GO are excellent materials for the fabrication of new nanocomposites and electrochemical sensors. Graphene has been widely used as a chemical building block and/or scaffold with various materials to create highly sensitive and selective electrochemical sensing microdevices. Over the past decade, significant advancements have been made by utilizing graphene and graphene-based nanocomposites to design electrochemical sensors with enhanced analytical performance. This review focus on the synthetic strategies, as well as the structure-to-function studies of graphene, electrochemistry, novel multi nanocomposites combining graphene, limit of detection, stability, sensitivity, assay time. Finally, the review describes the challenges, strategies and outlook on the future development of graphene sensors technology that would be usable for the internet of things are also highlighted.

Bimetallic nanomaterials have potential catalytic behaviour in hydrogenation, clean- energy production, catalysis and sensors due to their great stability, loftier activity unique electrical and chemical properties. Herein, we prepared Pd Ag bimetallic nanoparticles synthesized by using fungal extracted aqueous method, which is environmentally friendly cost-effective and simple procedure. The fabricated Pd Ag bimetallic nanoparticles were investigated by small area electron diffraction (SAED), transmission electron microscopy (TEM) X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) analysis. The electrochemical response of uric acid (UA) at Pd-Ag/CPE was studied in 0.1 M phosphate buffer solution at various pH, concentration and scan rate was investigated. Compare to Bare CPE, the Pd Ag nanocomposite modified electrode displayed the highest electrocatalytic activity for the detection of UA A linear response in the range of 4.69–273 nM with remarkable detection limit of 5.543 nM (CDL = 3ϭ/M) and quantification limit of 16.64 nM (CQL = 10ϭ/M) was obtained. The established nanoparticles (Pd Ag) embedded with carbon paste electrode (Pd-Ag/CPE) makes a good analytical tool for the sensing of UA in the biological and pharmaceutical samples.

A nanocomposite of SiO2@Fe3O4 were synthesized and characterized by Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy. The poly(dipicolinic acid)/SiO2@Fe3O4 based electrochemical based sensor was fabricated by the electropolymerization of dipicolinic acid (DPA) on the surface of SiO2@Fe3O4 nanocomposite immobilizing the carbon paste electrode (CPE). The developed electrochemical sensor was abbreviated as poly(DPA)SiO2@Fe3O4/CPE. This electrochemical sensor shows an excellent electrochemical activity towards the detection of uric acid. Under the optimized experimental conditions the linear dynamic range (LDR) for the sensing of uric acid was calculated to be 1.2 to 1.8 μM with a good limit of detection (LOD) and limit of quantification (LOQ) of 0.4 μM and 1.2 μM, respectively. The poly(DPA)SiO2@Fe3O4/CPE has also shown the significant sensitivity and selectivity towards the sensing of uric acid in the presence of ascorbic acid and dopamine without any interference. The developed sensor was also successfully applied for the determination of uric acid in real sample analysis.

Herein, we describe a high-performance electrochemical sensor for the detection of regorafenib (REG) using bimetallic Pd–Ru nanoparticles anchored on pomegranate peel extract (PPE) derived reduced graphene oxide (Pd–Ru/rGO). PPE was employed to neutralize the extremely acidic graphene then cast-off along with the metal precursor for the duration of the chemical reduction to accomplish well dispersed Pd–Ru nanoparticles. Bimetallic Pd–Ru/rGO nanocomposites were synthesized using a facile chemical reduction method. Under optimal conditions, based on the differential pulse voltammetric studies it has been confirmed that the fabricated sensors has good electrocatalytic activity toward the detection of REG, spanning over the linear dynamic range of 0.5–300 nM. Moreover, the sensor exhibited a low limit of detection of 1.6 nM and a limit of quantification of 4.8 nM. The electrochemical sensor unveiled admirable selectivity and sensitivity, reproducibility, and repeatability. The fabricated sensor was suitable for real sample analysis (pharmaceutical tablet, human blood plasm, wastewater) with satisfactory recovery. The strategy presented herein can be employed in the development of electrochemical sensors for other target analytes.

Pt–Ni bimetallic nanoparticles on the surface of reduced graphene oxide (rGO) nanosheets were prepared by using a wet–reflux strategy and characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), Xray diffraction (XRD) and Raman spectroscopy. The glassy carbon electrode modified with Pt–Ni/rGO demonstrated excellent electrochemical activity towards dopamine (DA) in the presence of acetaminophen (APAP) and etilefrine hydrochloride (ET). From the differential pulse voltammetry (DPV) results obtained for the ternary mixture of DA, APAP and ET, the limit of detection (LOD) and limit of quantification (LOQ) of DA were calculated to be 0.0026 μM and 0.00876 μM, respectively. The proposed sensor was successfully employed for the sensing of DA in aqueous solution, pharmaceutical drugs and human serum samples in a mixture with APAP and ET.

Use of Pt-based electro-catalysts for the oxygen reduction reaction (ORR) is a major hindrance in large-scale application of proton exchange membrane fuel cells (PEMFCs). Hence, new, cost-effective and high performance electro-catalysts are required for the commercial success of PEMFCs. In this work, a Pt-free magnesium oxide (MgO) decorated multi-layered reduced graphene oxide (MLGO) composite is tested as an electro-catalyst for the ORR. The ORR activity of MgO/MLGO in terms of diffusion-controlled current density is found to be superior (6.63 mA per cm2-geo) than that of in-house prepared Pt/rGO (5.96 mA per cm2-geo) and commercial Pt/C (5.02 mA per cm2-geo). The applicability of less expensive MgO/MLGO not only provides a new electro-catalyst but also provides a new direction in exploring metal oxide-based electro-catalysts for the ORR.

TiO2 nanoparticles anchored on the reduced graphene oxide (rGO) nanocomposites were prepared by hydrothermal method and characterized by the X- ray diffraction (XRD) and transmission electron microscopy (TEM). An effective electrochemical sensing platform for the detection of Rifampicin based upon TiO2 nanoparticles anchored graphene oxide sheets modified glassy carbon electrode (TiO2/rGO/GCE) is reported. Moreover, the TiO2/rGO modified glassy carbon electrode showed an excellent selectivity towards the detection of an anti-tuberculosis drug (Rifampicin). The TiO2/rGO/GCE electrochemical sensing platform is found to exhibit linear range from 0.01 – 0.1 nM with a low limit of detection 0.03 μM. The fabricated TiO2/rGO/GCE sensor is explored high sensitivity, high stable and good reproducible towards the sensing of RIF and has the potential to be utilized as a clinical assay and pharmaceuticals.

To exploit the full advantages of electrocatalysts for fuel cell reactions, a promising support is essential to disperse electrocatalytically active metal nanoparticles. Here, at first a graphene oxide-titanium dioxide composite support (GO-TiO2) is fabricated by a sol–gel method. Later, a facile chemical reduction method is demonstrated to simultaneously reduce Pt4+, Cu2+ and GO-TiO2 to form bimetallic PtCu nanoparticles (15 wt% Pt + 5 wt% Cu) on a reduced graphene oxide-titanium dioxide (RGO-TiO2) composite support. A combined action of ethylene glycol and ascorbic acid play a positive role in attaining well dispersed PtCu with a size of 7 nm particles on RGO-TiO2 sheets. The resulting PtCu/RGO-TiO2 nanocomposite exhibits superior electrode-area normalized ORR limiting current density (6.14 mA/cm2-geo) when compared to commercial Pt/C (3.61 mA/cm2-geo) and in-house synthesized PtCu/RGO (4.68 mA/cm2-geo) and Pt/RGO (3.95 mA/cm2-geo) catalysts. The synthesized catalysts are characterized for structural, morphological and surface elemental features by using a combination of diffraction, spectroscopy and electron microscopy techniques. The positive role played by PtCu and RGO-TiO2 composite support assists the improved ORR activity. The versatile synthesis methodology presented here is convenient to fabricate other similar electrocatalytic nanostructures for fuel cell reactions.