Cost Effective Synthesis of Graphene Nanomaterials for Non-Enzymatic Electrochemical Sensors for Glucose: A Comprehensive Review

The high conductivity of graphene material (or its derivatives) and its very large surface area enhance the direct electron transfer, improving non-enzymatic electrochemical sensors sensitivity and its other characteristics. The offered large pores facilitate analyte transport enabling glucose detection even at very low concentration values. In the current review paper we classified the enzymeless graphene-based glucose electrocatalysts’ synthesis methods that have been followed into the last few years into four main categories: (i) direct growth of graphene (or oxides) on metallic substrates, (ii) in-situ growth of metallic nanoparticles into graphene (or oxides) matrix, (iii) laser-induced graphene electrodes and (iv) polymer functionalized graphene (or oxides) electrodes. The increment of the specific surface area and the high degree reduction of the electrode internal resistance were recognized as their common targets. Analyzing glucose electrooxidation mechanism over Cu-Co-and Ni-(oxide)/graphene (or derivative) electrocatalysts, we deduced that glucose electrochemical sensing properties, such as sensitivity, detection limit and linear detection limit, totally depend on the route of the mass and charge transport between metal(II)/metal(III); and so both (specific area and internal resistance) should have the optimum values. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.Asst. Prof. Brouzgou, A., thankfully acknowledges the Research, Innovation and Excellence Structure (DEKA) of the University of Thessaly for the funding of the research program entitled: ‘Electrochemical (bio)sensors: synthesis of novel carbon monolayer-based nanoelectrodes for biomolecules detection’ and Ms Balkourani, G. (PhD student) thankfully acknowledges the Hellenic Foundation for Research and Innovation (HFRI), the PhD Fellowship grant. 25, 6816

Emerging materials for the electrochemical detection of COVID-19

The SARS-CoV-2 virus is still causing a dramatic loss of human lives worldwide, constituting an unprecedented challenge for the society, public health and economy, to overcome. The up-to-date diagnostic tests, PCR, antibody ELISA and Rapid Antigen, require special equipment, hours of analysis and special staff. For this reason, many research groups have focused recently on the design and development of electrochemical biosensors for the SARS-CoV-2 detection, indicating that they can play a significant role in controlling COVID disease. In this review we thoroughly discuss the transducer electrode nanomaterials investigated in order to improve the sensitivity, specificity and response time of the as-developed SARS-CoV-2 electrochemical biosensors. Particularly, we mainly focus on the results appeard on Au-based and carbon or graphene-based electrodes, which are the main material groups recently investigated worldwidely. Additionally, the adopted electrochemical detection techniques are also discussed, highlighting their pros and cos. The nanomaterial-based electrochemical biosensors could enable a fast, accurate and without special cost, virus detection. However, further research is required in terms of new nanomaterials and synthesis strategies in order the SARS-CoV-2 electrochemical biosensors to be commercialized. © 2021 Elsevier B.V

Nanostructure Engineering of Metal–Organic Derived Frameworks: Cobalt Phosphide Embedded in Carbon Nanotubes as an Efficient Orr Catalyst

Heteroatom doping is considered an efficient strategy when tuning the electronic and structural modulation of catalysts to achieve improved performance towards renewable energy applications. Herein, we synthesized a series of carbon-based hierarchical nanostructures through the controlled pyrolysis of Co-MOF (metal organic framework) precursors followed by in situ phosphidation. Two kinds of catalysts were prepared: metal nanoparticles embedded in carbon nanotubes, and metal nanoparticles dispersed on the carbon surface. The results proved that the metal nanoparticles embedded in carbon nanotubes exhibit enhanced ORR electrocatalytic performance, owed to the enriched catalytic sites and the mass transfer facilitating channels provided by the hierarchical porous structure of the carbon nanotubes. Furthermore, the phosphidation of the metal nanoparticles embedded in carbon nanotubes (P-Co-CNTs) increases the surface area and porosity, resulting in faster electron transfer, greater conductivity, and lower charge transfer resistance towards ORR pathways. The P-Co-CNT catalyst shows a half-wave potential of 0.887 V, a Tafel slope of 67 mV dec−1, and robust stability, which are comparatively better than the precious metal catalyst (Pt/C). Conclusively, this study delivers a novel path for designing multiple crystal phases with improved catalytic performance for energy devices. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Acknowledgments: S.S.A. Shah is grateful to the higher education commission (HEC) of Pakistan for IPFP funding at the Institute of Chemistry, The Islamia University of Bahawalpur, Pakistan. Furthermore, P. Tsiakaras, A. Brouzgou and C. Molochas thankfully acknowledge the co-financing by the European Union & Greek National funds through the Operational Program Competitiveness, Entrepreneurship, and Innovation, under the call RESEARCH–CREATE–INNOVATE (T1EDK-02442)

Electrooxidation of glucose by binder-free bimetallic Pd1Ptx/graphene aerogel/nickel foam composite electrodes with low metal loading in basic medium

Many 2D graphene-based catalysts for electrooxidation of glucose involved the use of binders and toxic reducing agents in the preparation of the electrodes, which potentially causes the masking of original activity of the electrocatalysts. In this study, a green method was developed to prepare binder-free 3D graphene aerogel/nickel foam electrodes in which bimetallic Pd-Pt NP alloy with different at% ratios were loaded on 3D graphene aerogel. The influence of Pd/Pt ratio (at%: 1:2.9, 1:1.31, 1:1.03), glucose concentration (30 mM, 75 mM, 300 mM, 500 mM) and NaOH concentration (0.1 M, 1 M) on electrooxidation of glucose were investigated. The catalytic activity of the electrodes was enhanced with increasing the Pd/Pt ratio from 1:2.9 to 1:1.03, and changing the NaOH/glucose concentration from 75 mM glucose/0.1 M NaOH to 300 mM glucose/1 M NaOH. The Pd1Pt1.03/GA/NF electrode achieved a high current density of 388.59 A g−1 under the 300 mM glucose/1 M NaOH condition. The stability of the electrodes was also evaluated over 1000 cycles. This study demonstrated that the Pd1Pt1.03/GA/NF electrode could be used as an anodic electrode in glucose-based fuel cells

High-Utilisation Nanoplatinum Catalyst (Pt@cPIM) Obtained via Vacuum Carbonisation in a Molecularly Rigid Polymer of Intrinsic Microporosity

Polymers of intrinsic microporosity (PIM or here PIM-EA-TB) offer a highly rigid host environment into which hexachloroplatinate(IV) anions are readily adsorbed and vacuum carbonised (at 500 °C) to form active embedded platinum nanoparticles. This process is characterised by electron and optical microscopy, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and electrochemical methods, which reveal that the PIM microporosity facilitates the assembly of nanoparticles of typically 1.0 to 2.5-nm diameter. It is demonstrated that the resulting carbonised “Pt@cPIM” from drop-cast films of ca. 550-nm average thickness, when prepared on tin-doped indium oxide (ITO), contain not only fully encapsulated but also fully active platinum nanoparticles in an electrically conducting hetero-carbon host. Alternatively, for thinner films (50–250 nm) prepared by spin coating, the particles become more exposed due to additional loss of the carbon host. In contrast to catalyst materials prepared by vacuum-thermolysed hexachloroplatinate(IV) precursor, the platinum nanoparticles within Pt@cPIM retain high surface area, electrochemical activity and high catalyst efficiency due to the molecular rigidity of the host. Data are presented for oxygen reduction, methanol oxidation and glucose oxidation, and in all cases, the high catalyst surface area is linked to excellent catalyst utilisation. Robust transparent platinum-coated electrodes are obtained with reactivity equivalent to bare platinum but with only 1 μg Pt cm−2 (i.e. ~100% active Pt nanoparticle surface is maintained in the carbonised microporous host). [Figure not available: see fulltext.

A Thermodynamic approach of the aqueous-phase glucose reforming reaction for hydrogen production: A comparative study with glycerol and ethylene glycol

In the present work is reported for the first time the thermodynamic analysis of aqueous-phase glucose reforming. The reaction has been studied at low temperature values (298-338K) and at atmospheric pressure with the reactants to be in liquid phase and the products in gas phase. For the calculations it is considered the Van't Hoff's equation and the case that the two phases (liquid and vapor) are in equilibrium. According to the results temperature increase affects positively the conversion of glucose to hydrogen. Comparable with glycerol and ethylene glycol which are also considered being among the most promising sources for hydrogen production, glucose gives the highest conversion

Electrocatalysts for Glucose Electrooxidation Reaction: A Review

The up-to-date research as far as it concerns the abiotic direct glucose fuel cells (DGFCs) is summarized and discussed in the present review. Platinum and gold-based as well as Raney-type electrocatalysts are among the most studied ones. In abiotically (non-implantable) DGFCs, unsupported Pt and PtRuO2, exhibited good activity (power density ∼20 mW cm-2), at room temperature and at atmospheric pressure. On the other hand, Au-based electrocatalysts adopted in a DGFC resulted in power densities up to ca. 5 mW cm-2, exhibiting however high poisoning tolerance. Recently, after the introduction of alkaline membranes into the market, Pd-based electrocatalysts have attracted the attention of the research community because of their enhanced activity in alkaline media. However, there are still very few investigations where membrane electrode assemblies with palladium electrocatalysts have been applied. Moreover, Raney-type electrocatalysts, not yet examined for other fuels in direct polymer electrolyte fuel cells, are considered to be the most appropriate for implantable abiotic DGFCs. A novel implantable fuel cell in a human brain performed with 3.4 × 10-3 μW power for 10 h adopting Raney-type electrocatalysts. © 2015 Springer Science+Business Media New York

Performance modeling of an alkaline anion exchange membrane-based direct glucose fuel cell

An AEM-based DGFC performance model is developed and compared against literature experimental results. Performance predictions for different anode and PtAg/C cathode catalysts, using the 1-D flux-based model, are reported. Copyright © 2013 Delta Energy and Environment

Interconnects for solid oxide fuel cells

Interconnect materials serve an important role in solid oxide fuel cell (SOFC) technology, connecting the current collectors of each cell to either the next one or the electrical load. Up to date, two types of interconnects have been developed: (i) the ceramic and (ii) the metallic ones. The ceramic interconnects are oxides, which are very stable in oxidizing atmosphere, but their cost is high and they exhibit lower electrical conductivity in comparison with the metallic ones at the operating temperatures. The most studied ceramic interconnects are lanthanum and yttrium chromites, and perovskite p-type semiconductors. Currently, ceramic conductive materials are widely used as thin protective layers deposited on metallic interconnects. The metallic interconnects are cheaper than the ceramic ones, and they are used at lower operating temperatures. Compared with ceramics, they exhibit higher electronic conductivity, but they are not stable in oxidizing atmospheres. During the last decade, several solutions have been approached, predominating the surface modification of the metallic interconnects via protective oxide layers (ceramic one) deposition on them. This alternative approach increases the lifetime of metallic interconnects, especially under cathode conditions. Reactive element oxides, perovskites, spinels, and dual layers are the kind of coatings that have also been developed. © 2017, CISM International Centre for Mechanical Sciences

Electrocatalytic activity of Vulcan-XC-72 supported Pd, Rh and PdxRhy toward HOR and ORR

Carbon-supported (Vulcan XC-72) Pd, Rh, and PdxRhy (20 wt%, x:y = 1:1, 3:1, 1:3) electrocatalysts are prepared according a modified pulse-microwave assisted polyol synthesis method and their electrocatalytic activity toward hydrogen electrooxidation (HOR) and oxygen reduction (ORR) reactions is investigated. The as-prepared electrocatalysts are physicochemically characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Their electrochemical characterization is carried out by the aid of cyclic voltammetry (CV), rotating disk electrode (ROE) and chronoamperometry (CA) techniques. It is found that among the as-prepared catalysts, PdRh3 exhibits the highest HOR (i(k) = 7.6 mA cm(-2)) and ORR (i(k) = 5.20 mA cm(-2)) electrocatalytic activity. It is also found that the addition even of small amount of Rh (Pd3Rh-2.7 mu g cm(-2)) enhances both Pd's HOR and ORR electrocatalytic activity by 33% and by 53%, respectively. For the as prepared electrocatalysts, the HOR activity order, in terms of kinetic current density, is found to be as follows: PdRh3 approximate to PdRh > Rh > Pd3Rh > Pd, while a similar trend was found for ORR activity: PdRh3 > PdRh > Rh > Pd3Rh > Pd. (C) 2015 Elsevier B.V. All rights reserved