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

Transition metal-nitrogen-carbon catalysts for oxygen reduction reaction in neutral electrolyte

© 2016 The Authors Platinum group metal-free (PGM-free) catalysts based on M-N-C types of materials with M as Mn, Fe, Co and Ni and aminoantipyrine (AAPyr) as N-C precursors were synthesized using sacrificial support method. Catalysts kinetics of oxygen reduction reaction (ORR) was studied using rotating ring disk electrode (RRDE) in neutral pH. Results showed that performances were distributed among the catalysts as: Fe-AAPyr>Co-AAPyr>Mn-AAPyr>Ni-AAPyr. Fe-AAPyr had the highest onset potential and half-wave potential. All the materials showed similar limiting current. Fe-AAPyr had an electron transfer involving 4e− with peroxide formed lower than 5%. Considering H2O2 produced, it seems that Co-AAPyr, Mn-AAPyr and Ni-AAPyr follow a 2×2e− mechanism with peroxide formed during the intermediate step. Durability test was done on Fe-AAPyr for 10,000cycles. Decrease of activity was observed only after 10,000cycles

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.

Non-Precious Electrocatalysts for Oxygen Reduction Reaction in Alkaline Media: Latest Achievements on Novel Carbon Materials

Low temperature fuel cells (LTFCs) are considered as clean energy conversion systems and expected to help address our society energy and environmental problems. Up-to-date, oxygen reduction reaction (ORR) is one of the main hindering factors for the commercialization of LTFCs, because of its slow kinetics and high overpotential, causing major voltage loss and short-term stability. To provide enhanced activity and minimize loss, precious metal catalysts (containing expensive and scarcely available platinum) are used in abundance as cathode materials. Moreover, research is devoted to reduce the cost associated with Pt based cathode catalysts, by identifying and developing Pt-free alternatives. However, so far none of them has provided acceptable performance and durability with respect to Pt electrocatalysts. By adopting new preparation strategies and by enhancing and exploiting synergetic and multifunctional effects, some elements such as transition metals supported on highly porous carbons have exhibited reasonable electrocatalytic activity. This review mainly focuses on the very recent progress of novel carbon based materials for ORR, including: (i) development of three-dimensional structures; (ii) synthesis of novel hybrid (metal oxide-nitrogen-carbon) electrocatalysts; (iii) use of alternative raw precursors characterized from three-dimensional structure; and (iv) the co-doping methods adoption for novel metal-nitrogen-doped-carbon electrocatalysts. Among the examined materials, reduced graphene oxide-based hybrid electrocatalysts exhibit both excellent activity and long term stability

Σχεδιασμός και ανάπτυξη κυψελίδων καυσίμου γλυκόζης

The development of direct glucose fuel cells or glucose sensors in-vivo or in-vitro for the measurement of glucose concentration in the human blood is desirable for medical applications. An implantable, miniature, accurate and reliable sensor to monitor the glucose concentration in the body is desirable for treatment of diabetes mellitus. An implantable glucose-oxygen fuel cell has been proposed for artificial hearts using glucose and oxygen in the blood as the reactant. A practical fuel cell system has not yet been developed for this application, however. The electrocatalytic glucose sensor and glucose fuel cell are based on the catalytic glucose oxidation on an electrode surface which produces a current related to the concentration of glucose. Different electrodes have been investigated for glucose electrooxidation, e.g. platinum [1-6], gold [7-11], glassy carbon [12, 13], cobalt, rhodium and iridium [12-15], nickel and palladium [12, 13, 15], copper and silver [12, 13], phthalocyanines and porphyrins complexes of cobalt, manganese and iron [12]. Moreover, glucose oxidation has been studied in acid [16], neutral [16, 17] and alkaline [18] solutions. In literature there are few works [3, 19] concerning the study of glucose electrooxidation on Pd-based/C electrocatalysts, in alkaline environment. In the present Ph.D thesis, firstly literature review was conducted in order to identify the most efficient and studied electrocatalysts for direct-liquid proton exchange membrane fuel cells. In sequence, the literature review was continued including also the novel type of direct liquid anion exchange membrane fuel cells. According to the above reviews platinum was recognized as the best electrocatalyst for direct liquid-fed proton exchange membrane fuel cells, while palladium was identified as the best one for direct liquid-fed anion exchange membrane fuel cells. The first step of design and development of fuel cells is the recognition of the most active electrocatalysts towards anode and cathode reaction. To this purpose, in the present work binary Pd-based electrocatalysts were prepared and were investigated as anode electrocatalysts for glucose electrooxidation in half direct glucose alkaline fuel cells. More precisely, PdxRuy (20 wt%)/C, PdxRhy (20 wt%)/C and PdxSny (20 wt%)/C are studied as anode direct glucose alkaline fuel cells’ materials, while PdxAuy (20 wt%)/C is investigated as glucose sensors’ material. The above-mentioned electrocatalysts and the respective results are reported for first time in literature, indicating the novelty of the present PhD thesis. For the preparation of the examined electrocatalysts a modified-microwave assisted polyol method was used. The physicochemical characterization of electrocatalysts was conducted by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy-Energy Dispersive X-RaySpectroscopy and Thermogravimetric Analysis (TG). The electrochemical characterization was carried out with the Cyclic Voltammetry (CV-half direct glucose alkaline fuel cell), Rotating Disk Electrode Technique (RDE) and Chronoamperometry techniques (CA). At room temperature Pd3Sn2/C and PdRh/C presented almost the same activity towards glucose electrooxidation; however the first one presented higher poisonous rate. Considering the activity (good activity) and poisonous-tolerance together (the highest among the examined electrocatalysts), Pd30Au70/C was chosen for being studied as glucose sensor. Moreover, the effect of glucose’s, electrolyte’s concentration and temperature were studied, extracting important kinetic parameters for glucose’s electrooxidation reaction. Increasing glucose’s and electrolyte’s concentration, current density was enhanced for all the examined electrocatalysts, except for PdxRhy/C ones over which for electrolyte’s concentration higher than 1 M KOH current density was suppressed. Finally, glucose electrooxidation reaction current density was increased increasing temperature until 40oC. For higher temperature values glucose’s alkaline solution was observed to degrade forming a dark yellow caramel line smell liquid, decreasing current density values. For T>30oC, PdRh/C is suggested as anode material for glucose electrooxidation reaction, while Pd30Au70/C as glucose sensors’ material. Future outlooks are the optimization of the electrocatalysts’ preparation method as well as of the PdRh/C and Pd30Au70/C electrocatalysts and the development of a single direct glucose alkaline fuel cell