Electrocatalysts for Glucose Electrooxidation Reaction: A Review

Insights in Pt-based electrocatalysts on carbon supports for electro-oxidation of carbohydrates: an EIS-DEMS analysis

In this work, the electrochemical oxidation of carbohydrates (glucose, fructose, and sucrose) was induced at the interface of Pt-nanoparticles supported on different carbon-based materials as carbon vulcan (C) and carbon black (CB). It was found that the support plays an important role during carbohydrates electro-oxidation as demonstrated by electrochemical techniques. In this context, current-concentration profiles of the redox peaks show the behavior of the pathways at carbohydrates-based solutions. Herein, the trend of current measured was glucose > sucrose > fructose, attributed to differences in the organic functional groups and chain-structure. Raman, XRD, SEM-EDS and XPS put in clear important structural, morphological, and electronic differences linked with the intrinsic nature of the obtained material. Differential Electrochemical Mass Spectroscopy (DEMS) indicated that the selectivity and the conversion of the formed reaction products during oxidation is linked with the catalyst nature (distribution, particle size) and the interaction with the carbon-based support.

A highly sensitive and long-term stable wearable patch for continuous analysis of biomarkers in sweat

Although increasing efforts have been devoted to the development of non-invasive wearable or stretchable electrochemical sweat sensors for monitoring physiological and metabolic information, most of them still suffer from poor stability and specificity over time and fluctuating temperatures. This study reports the design and fabrication of a long-term stable and highly sensitive flexible electrochemical sensor based on nanocomposite-modified porous graphene by simple and facile laser treatment for detecting biomarkers such as glucose in sweat. The laser-reduced and patterned stable conductive nanocomposite on the porous graphene electrode provides the resulting glucose sensor with an excellent sensitivity of 1317.69 μAmM-1cm-2 with an ultra-low limit of detection (LOD) of 0.079 μM. The sensor can also detect pH and exhibit extraordinary stability to maintain more than 91% sensitivity over 21 days in ambient conditions. Taken together with a temperature sensor based on the same material system, the dual glucose and pH sensor integrated with a flexible microfluidic sweat sampling network further results in accurate continuous on-body glucose detection calibrated by the simultaneously measured pH and temperature. The low-cost, highly sensitive, and long-term stable platform could facilitate and pave the way for the early identification and continuous monitoring of different biomarkers for non-invasive disease diagnosis and treatment evaluation.

Theoretical study on the adsorption and oxidation of glucose on Au(111) surface

CONTEXT

While Au-based catalysts recently have shown tremendous potential in glucose oxidation to gluconic acid, the detailed reaction mechanism is still unclear, which impedes the development of direct glucose fuel cell (DGFC).

METHODS

Using density functional theory (DFT), we exhibit some new adsorption configurations and oxidation mechanisms by considering both the open chain form and the ring form of glucose on Au(111) surface in the presence of OH. The strong interactions between glucose and the OH adsorbed surface are obtained. Moreover, form the calculated energy pathways, the oxidation of glucose in the open chain involves the dissociation of the formyl C - H bond by the adsorbed OH, while the ring form glucose oxidation is initiated by O - H bond rupture rather than C - H bond scission and preferentially undergoes the ring-open process to generate the open chain form glucose. Meanwhile, the results demonstrate that the adsorbed OH assists in reducing the activation energy of reaction process.

Diboronic-Acid-Based Electrochemical Sensor for Enzyme-Free Selective and Sensitive Glucose Detection

A diboronic acid anthracene-based fluorescent system for detecting blood glucose could be used for 180 days. However, there has not yet been a boronic acid immobilized electrode to selectively detect glucose in a signal-increased way. Considering malfunctions of sensors at high sugar levels, the electrochemical signal should be increased proportionally to the glucose concentration. Therefore, we synthesized a new diboronic acid derivative and fabricated the derivative-immobilized electrodes for the selective detection of glucose. We performed cyclic voltammetry and electrochemical impedance spectroscopy with an Fe(CN)₆^3-/4- redox pair for detecting glucose in the range of 0-500 mg/dL. The analysis revealed increased electron-transfer kinetics such as increased peak current and decreased semicircle radius of Nyquist plots as the glucose concentration increased. The cyclic voltammetry and impedance spectroscopy showed that the linear detection range of glucose was 40 to 500 mg/dL with limits of detection of 31.2 mg/dL and 21.5 mg/dL, respectively. We applied the fabricated electrode to detect glucose in artificial sweat and obtained 90% of the performance of the electrodes in PBS. Cyclic voltammetry measurements of other sugars such as galactose, fructose, and mannitol also showed linear increased peak currents proportional to the concentrations of the tested sugars. However, the slopes of the sugars were lower than that of glucose, indicating selectivity for glucose. These results proved the newly synthesized diboronic acid is a promising synthetic receptor for developing a long-term usable electrochemical sensor system.

Investigation of glucose electrooxidation mechanism over N‐modified metal‐doped graphene electrode by density functional theory approach

In this work, various precious and non‐precious metals reported in the literature as the most effective catalysts for glucose electrooxidation reaction were investigated by the density functional theory (DFT) approach in order to reveal the mechanisms taking place over the catalysts in the fuel cell. The use of a single‐atom catalyst model was adopted by insertion of one Au, Cu, Ni, Pd, Pt, and Zn metal atom on the pyridinic N atoms doped graphene surface (NG). β form of d‐glucose in alkaline solution was used to determine the reaction mechanism and intermediates that formed during the reaction. DFT results showed that the desired glucono‐lactone was formed on the Cu‐3NG electrode in a single‐step reaction pathway whereas it was produced via different two‐step pathways on the Au and Pt‐3NG electrodes. Although the interaction of glucose with Ni, Pd, and Zn‐doped surfaces resulted in the deprotonation of the molecule, lactone product formation did not occur on these electrode surfaces. When the calculation results are evaluated in terms of energy content and product formation, it can be concluded that Cu, Pt, and especially Au doped graphene catalysts are effective for direct glucose oxidation in fuel cells reactor.

3D-Structured Au(NiMo)/Ti Catalysts for the Electrooxidation of Glucose

In this study, 3D-structured NiMo coatings have been constructed via the widely used electrodeposition method on a Ti surface and decorated with very small Au crystallites by galvanic displacement (Au(NiMo)/Ti). The catalysts have been characterized using scanning electron microscopy, energy dispersive X-ray analysis, and inductively coupled plasma optical emission spectroscopy. Different Au(NiMo)/Ti catalysts, which had Au loadings of 1.8, 2.3, and 3.9 µgAu cm−2, were prepared. The electrocatalytic activity of the Au(NiMo)/Ti catalysts was examined with respect to the oxidation of glucose in alkaline media by cyclic voltammetry. It was found that the Au(NiMo)/Ti catalysts with Au loadings in the range of 1.8 up to 3.9 µgAu cm−2 had a higher activity compared to that of NiMo/Ti. A direct glucose-hydrogen peroxide (C6H12O6-H2O2) single fuel cell was constructed with the different Au-loading-containing Au(NiMo)/Ti catalysts as the anode and Pt as the cathode. The fuel cells exhibited an open circuit voltage of ca. 1.0 V and peak power densities up to 8.75 mW cm−2 at 25 °C. The highest specific peak power densities of 2.24 mW µgAu−1 at 25 °C were attained using the Au(NiMo)/Ti catalyst with the Au loading of 3.9 µg cm−2 as the anode.

Cellulose-acetate coating of carbon cloth diffusion layer for liquid-fed fuel cell applications

Direct glucose fuel cells (DGFCs) and direct methanol fuel cells (DMFCs) commonly supply the reducing agent in liquid (aq.) form. In this work, we present key characteristics of implementing cellulose acetate (CA) coatings, which can subsequently be deacetylated toward cellulose, on carbon cloth used as a fuel diffusion layer in aqueous fuel-fed cells. Specifically, we illustrate functionality with an abiotic glucose fuel cell. Carbon cloth with and without a CA coating (with varying deacetylation) was characterized in terms of liquid permeation rate, electronic conductivity, and roll-off angle wetting characteristics. Additionally, fuel cell power production was measured over a variety of fuel concentrations and alkalinities by generating polarization curve data. These coatings facilitated a significant increase in aqueous solution permeation and adhesion properties, as well as providing up to two-fold increases in maximum power generation in an alkaline DGFC, despite experiencing some decreased conductivity of the carbon cloth diffusion layer.

A membrane-less Glucose/O2 non-enzymatic fuel cell based on bimetallic Pd-Au nanostructure anode and air-breathing cathode: Towards micro-power applications at neutral pH

Herein, the authors propose a miniaturized glucose/O₂ n-EFC based on a new direct electron transfer. The anode is a screen-printed carbon electrode (SPCE) modified with functionalized carbon nanotubes (f-CNTs) and cauliflower-like PdAu nanostructures (PdAuNS). The PdAuNS/f-CNT biomimetic nanocatalyst was prepared using a cost-effective and straightforward method, which consisted of drop-casting well-dispersed f-CNTs over the SPCE surface before PdAuNS electrodeposition. This enzyme-free interface was used for glucose electrooxidation at neutral medium (pH 7.4). The electrochemical behaviour of the PdAuNS/f-CNT/SPCE was investigated using cyclic voltammetry, linear sweep voltammetry, and amperometry. Several parameters were optimized and discussed, including the metal precursor concentration (HAuCl₄, PdCl₂) and the electrodeposition conditions. The cathode for oxygen electroreduction is an air-cathode which is composed of Pt-coated carbon cloth. The electrochemical performances of the anode and the cathode were evaluated separately for glucose oxidation and oxygen reduction, respectively. Both electrodes were then assembled in a membrane-less single chamber n-EFC with an innovative architecture. Electrical characterization of the n-EFC supplied with a neutral buffered solution containing 20 mM glucose showed a maximal power output of 129 ± 11 μW cm^-2, a current density of 600 ± 39 μA cm^-2 with a cell voltage of 0.35 V, and an open circuit potential of 0.56 V. The proposed electrocatalyst possesses several advantages such as fast response, low cost, reusability, poison-free characteristics, and good stability. Hence, glucose/O₂ n-EFC could be of great interest in direct glucose fuel cell applications (e.g., powering mountable/implantable biomedical micro-devices running at low electrical power supply) or in self-powered biosensing.

Nanoporous Cauliflower-like Pd-Loaded Functionalized Carbon Nanotubes as an Enzyme-Free Electrocatalyst for Glucose Sensing at Neutral pH: Mechanism Study

In this work, we propose a novel functionalized carbon nanotube (f-CNT) supporting nanoporous cauliflower-like Pd nanostructures (PdNS) as an enzyme-free interface for glucose electrooxidation reaction (GOR) in a neutral medium (pH 7.4). The novelty resides in preparing the PdNS/f-CNT biomimetic nanocatalyst using a cost-effective and straightforward method, which consists of drop-casting well-dispersed f-CNTs over the Screen-printed carbon electrode (SPCE) surface, followed by the electrodeposition of PdNS. Several parameters affecting the morphology, structure, and catalytic properties toward the GOR of the PdNS catalyst, such as the PdCl₂ precursor concentration and electrodeposition conditions, were investigated during this work. The electrochemical behavior of the PdNS/f-CNT/SPCE toward GOR was investigated through Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV), and amperometry. There was also a good correlation between the morphology, structure, and electrocatalytic activity of the PdNS electrocatalyst. Furthermore, the LSV response and potential-pH diagram for the palladium–water system have enabled the proposal for a mechanism of this GOR. The proposed mechanism would be beneficial, as the basis, to achieve the highest catalytic activity by selecting the suitable potential range. Under the optimal conditions, the PdNS/f-CNT/SPCE-based biomimetic sensor presented a wide linear range (1–41 mM) with a sensitivity of 9.3 µA cm⁻² mM⁻¹ and a detection limit of 95 µM (S/N = 3) toward glucose at a detection potential of +300 mV vs. a saturated calomel electrode. Furthermore, because of the fascinating features such as fast response, low cost, reusability, and poison-free characteristics, the as-proposed electrocatalyst could be of great interest in both detection systems (glucose sensors) and direct glucose fuel cells.

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.

Stabilizer-free bismuth nanoparticles for selective polyol electrooxidation

Bismuth is the least toxic element among heavy metals, an outstanding advantage for environmental and health considerations. Yet, utilizing bismuth as anodic electrocatalyst is hindered by the formation of a spreading Bi(OH)₃ inhibitor layer during the anodic process. Herein, we report that bismuth nanoparticles, produced using laser ablation, can avoid such drawbacks. The production of Bi(V) species assists polyol electrooxidation. For glucose, instead of the commonly reported gluconic acid as the product, the Bi(V) species enables highly selective oxidation and C–C bond cleavage to produce arabinonic acid, erythronic acid, and eventually glyceric acid. We not only generate high-valent Bi(V) species for catalytic applications, especially for bioelectrocatalysis where the less toxic bismuth is highly appreciated, but also present Bi nanoparticle as a highly selective electrocatalyst that can break C–C bond. We believe that Bi electrocatalyst can find broader applications in electrochemical biomass conversion and electrosynthesis.

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Stabilizer-free bismuth nanoparticles (Bi NPs) are synthesized by laser ablation

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Bi NPs show activity toward polyol electrooxidation, breaking C-C bond

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The in situ generated Bi(V) is essential for the electrocatalytic oxidation

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Unlike Bi polycrystal, surface oxide layers do not inhibit the activity of Bi NPs

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.

Simple Yeast-Direct Catalytic Fuel Cell Bio-Device: Analytical Results and Energetic Properties

This paper reports the analytical detection and energetic properties of a glucose-fed Direct Catalytic Fuel Cell (DCFC) operated in association with yeast cells (Saccharomyces Cerevisiae). The cell was tested in a potentiostatic mode, and the operating conditions were optimized to maximize the current produced by a given concentration of glucose. Results indicate that the DCFC is characterized by a glucose detection limit of the order to 21 mmol L⁻¹. The cell was used to estimate the “pool” of carbohydrate content in commercial soft drinks. Furthermore, the use of different carbohydrates, such as fructose and sucrose, has been shown to result in a good current yield.

The effect of reaction layer composition on Pt/NiO function for glucose oxidation reaction in neutral media

This study shows the application of carbon supported electrodes containing Pt/NiO nanoparticles to catalyze the electrochemical oxidation of glucose in neutral media. In particular, this study describes the effect of the Pt content and type of carbon (carbon black, expanded graphite, or charcoal active) in the reaction layer on this oxidation process in neutral media. Pt/NiO nanoparticles were synthesized by a simple hydrothermal method, and further characterized by scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), and cyclic voltammetry. These nanoparticles were used to modify carbon electrodes. The effectiveness of these electrodes for electrochemical glucose oxidation was evaluated. The results revealed that the catalytic activity of the electrodes depends on the content of Pt/NiO nanoparticles and the type of carbon. The 10% Pt/NiO with 90% loading (use of activated charcoal in the reaction layer) as optimum electrode indicated good stability after 1200 voltammetry cycles. This modified electrode was highly active for glucose oxidation in neutral media, which could be attributed to the presence of Pt/NiO nanoparticles as catalyst and high surface area of activated charcoal on the electrode surface.

Development of a Ratiometric Fluorescent Glucose Sensor Using an Oxygen-Sensing Membrane Immobilized with Glucose Oxidase for the Detection of Glucose in Tears

Glucose concentration is an important parameter in biomedicine since glucose is involved in many metabolic pathways in organisms. Many methods for glucose detection have been developed for use in various applications, particularly in the field of healthcare in diabetics. In this study, ratiometric fluorescent glucose-sensing membranes were fabricated based on the oxygen levels consumed in the glucose oxidation reaction under the catalysis of glucose oxidase (GOD). The oxygen concentration was measured through the fluorescence quenching effect of an oxygen-sensitive fluorescent dye like platinum meso-tetra (pentafluorophenyl) porphyrin (PtP) by oxygen molecules. Coumarin 6 (C6) was used as a reference dye in the ratiometric fluorescence measurements. The glucose-sensing membrane consisted of two layers: The first layer was the oxygen-sensing membrane containing polystyrene particles (PS) doped with PtP and C6 (e.g., PS@C6^PtP) in a sol–gel matrix of aminopropyltrimethoxysilane and glycidoxypropyltrimethoxysilane (GA). The second layer was made by immobilizing GOD onto one of three supporting polymers over the first layer. These glucose-sensing membranes were characterized in terms of their response, reversibility, interferences, and stability. They showed a wide detection range to glucose concentration in the range of 0.1 to 10 mM, but high sensitivity with a linear detection range of 0.1 to 2 mM glucose. This stable and sensitive ratiometric fluorescent glucose biosensor provides a reliable way to determine low glucose concentrations in blood serum by measuring tear glucose.

Electrocatalytic Glucose Oxidation at Coral-Like Pd/C3N4-C Nanocomposites in Alkaline Media

Porous coral-like Pd/C3N4-C nanocomposites are fabricated by a simple one-pot chemical reduction method. Their electrocatalytic performance is ~50% higher than a carbon-loaded palladium electrocatalyst (Pd/C) in alkaline media. This confirms that the glucose electrooxidation and sensing performance of a Pd/C can be improved by the synergy of graphitic carbon nitride (C3N4), though C3N4 exhibits poor electrical conductivity. Compared to Pd/C, the size of Pd nanoparticles in Pd/C3N4-C decreases. As a result, the activity of Pd/C3N4-C is enhanced due to the higher dispersion and the synergistic effect. Pd/C3N4-C presents a rapid response and high sensitivity to glucose. The sensitivity for glucose sensing at Pd/C3N4-C is 3.3 times that of at Pd/C in the range of 0.001–10 mM. In the lower range of 0.001–1 mM, the sensitivity at Pd/C3N4-C is ~10 times greater than Pd/C.

One-Pot Aqueous Synthesis of Icosahedral Au as Bifunctional Candidates for Enhanced Glucose Electrooxidation and Surface-Enhanced Raman Scattering

Bifunctional candidates, which could provide catalytic and plasmonic properties simultaneously, could activate a promising development for biomedicine. Here, we kinetically controlled and synthesized a penta-twinned icosahedral Au (Ih Au) by a facile wet-chemical protocol without assistance of stabilizers. Benefiting from icosahedral morphology and kinetic synthesis process, the Ih Au nanoparticles (NPs) incorporate three key advantages: (i) ample active sites/"hot spots" and surface strain, (ii) good stability/chemical inertness and easy functionalization, and (iii) biological compatibility and a clean surface, which could promote their electrocatalysis and photonic capacity. Ih Au NPs, as bifunctional nanomaterials, exert excellent electrocatalytic and surface-enhanced Raman scattering (SERS) performances. Ih Au delivers the highest glucose electrooxidation (GEO) peak current density with 6.87 mA cm^-2, which is 14 times larger than that of Turkevich Au (0.49 mA cm^-2) under the same condition. Moreover, the SERS signals of rhodamine 6G (R6G) on Ih Au are much stronger than that on the other corresponding Au counterparts. Particularly, the SERS intensity of R6G on Ih Au increases by about four times compared to that on Au NPs. This study motivates the great prospect for combining Ih Au's bifunctionalities and indicates the potential of bifunctional nanomaterials in biologically implanted devices.

3D Hydrogen Titanate Nanotubes on Ti Foil: A Carrier for Enzymatic Glucose Biosensor

Glucose oxidase (GOx) based biosensors are commercialized and marketed for the high selectivity of GOx. Incorporation nanomaterials with GOx can increase the sensitivity performance. In this work, an enzyme glucose biosensor based on nanotubes was fabricated. By using Ti foil as a carrier, hydrogen titanate nanotubes (HTNTs), which present fine 3D structure with vast pores, were fabricated in-situ by the hydrothermal treatment. The multilayer nanotubes are open-ended with a diameter of 10 nm. Then glucose oxidase (GOx) was loaded on the nanotubes by cross-linking to form an electrode of the amperometric glucose biosensor (GOx/HTNTs/Ti electrode). The fabricated GOx/HTNTs/Ti electrode had a linear response to 1-10 mM glucose, and the response time was 1.5 s. The sensitivity of the biosensor was 1.541 μA·mM-1·cm-2, and the detection limit (S/N = 3) was 59 μM. Obtained results indicate that the in-situ fabrication and unique 3D structure of GOx/HTNTs/Ti electrode are beneficial for its sensitivity.

Organic thin film photofaradaic pixels for on-demand electrochemistry in physiological conditions

Organic photofaradaic pixels operate in physiological conditions transducing deep red irradiation into O₂ reduction to H₂O₂, with simultaneous oxidation of glucose as an electron donor.

Mucilage-capped silver nanoparticles for glucose electrochemical sensing and fuel cell applications

A simple, cost-effective and green mucilage-capped silver nanoparticles (Mucilage-AgNPs) modified glassy carbon electrode (GC) composite was constructed for efficient and facile electrochemical oxidation of glucose for the first time. Mucilage-AgNPs were synthesized through the direct chemical reduction of Ag⁺ by mucilage extracted from Opuntia ficus-indica. Mucilage-AgNPs were identified and characterized using ultraviolet-visible spectroscopy, transmission electron microscopy and square wave voltammetry. Modification of the GC with AgNPs was carried out via a transfer-sticking technique with an immobilization time of 1 h. The Mucilage-AgNPs/GC composite was studied as a possible anode for glucose oxidation in a biofuel cell. The composite resulted in glucose oxidation with a current density and power density of 85.7 μA cm⁻² and 25.7 μW cm⁻², respectively. Glucose sensing using the Mucilage-AgNPs/GC composite was achieved successfully via two pathways: glucose oxidation and AgNP inhibition. The glucose oxidation-based sensor showed a lower detection limit of 0.01 mM and a linear range of 0.01 to 2.2 mM. The AgNPs inhibition-based sensor provides an indirect determination pathway of glucose with a detection limit of 0.1 mM and a linear range of 0.1 to 1.9 mM. AgNP inhibition is a novel pathway that could be used for determining a large number of organic and inorganic molecules. Overall, the Mucilage-AgNPs/GC is considered a pioneering composite for glucose sensing and fuel cell applications.

A simple, cost-effective and green mucilage-capped silver nanoparticles (Mucilage-AgNPs) modified glassy carbon electrode (GC) composite was constructed for efficient and facile electrochemical oxidation of glucose for the first time.

Pd-Shaped Nanoparticles Modified by Gold ad-Atoms: Effects on Surface Structure and Activity Toward Glucose Electrooxidation

Palladium nanoparticles (Pd-NPs) with controlled distributions of sizes and shapes (nanospheres-Pd-NS-, nanocubes -Pd-NC-, and nanooctahedrons -Pd-NO-) are synthesized by wet chemistry methods and characterized by TEM/HRTEM. The surfaces of Pd-NPs are modified by spontaneous adsorption of gold and characterized by cyclic voltammetry in acidic medium. It is shown that the modification of Pd-NPs by dipping in HAuCl4 solutions of different concentrations allows controlling the surface coverage by gold. It is also shown that the modification of Pd-NPs surfaces involves first the formation of PdAu surface alloys. For higher coverages, both PdAu surface alloys and pure Au structures are formed. The activity toward the glucose electrooxidation reaction is determined by linear scan voltammetry (LSV). Higher activity is observed on pure Pd-NC presenting extended (100) surfaces than on Pd-NO with mainly (111) surface orientation and on Pd-NS without preferential surface orientation, both these latter Pd-NPs displaying almost the same activity. The modification of the surface by spontaneous adsorption of gold greatly improves the activity of all Pd-NPs. However, Au-modified Pd-NC materials remain the most active catalysts. PdAu surface alloys seem to be involved in the improvement of the catalytic activity at low potentials, although the role of pure gold structures on Pd-NPs toward the enhancement of the catalytic activity cannot be excluded for high gold coverage. The study allows a better understanding of the material structure/electrocatalytic behavior relationship.

A three-dimensional nickel–cobalt oxide nanomaterial as an enzyme-mimetic electrocatalyst for the glucose and lactic acid oxidation reaction

Here we demonstrate a highly porous three-dimensional nickel–cobalt oxide (NiCo₂O₄) nanomaterial as a potential glucose oxidase (GOx) enzyme-mimicking catalyst for the electrochemical oxidation of glucose and lactic acid in alkaline medium.

High-Power Abiotic Direct Glucose Fuel Cell Using a Gold-Platinum Bimetallic Anode Catalyst

We developed a high-power abiotic direct glucose fuel cell system using a Au-Pt bimetallic anode catalyst. The high power generation (95.7 mW cm^-2) was attained by optimizing operating conditions such as the composition of a bimetallic anode catalyst, loading amount of the metal catalyst on a carbon support, ionomer/carbon weight ratio when the catalyst was applied to the anode, glucose and KOH concentrations in the fuel solution, and operating temperature and flow rate of the fuel solution. It was found that poly(N-vinyl-2-pyrrolidone)-stabilized Au₈₀Pt₂₀ nanoparticles (mean diameter 1.5 nm) on a carbon (Ketjen Black 600) support function as a highly active anode catalyst for the glucose electrooxidation. The ionomer/carbon weight ratio also greatly affects the cell properties, which was found to be optimal at 0.2. As for the glucose concentration, a maximum cell power was derived at 0.4-0.6 mol dm^-3. A high KOH concentration (4.0 mol dm^-3) was preferable for deriving the maximum power. The cell power increased with the increasing flow rate of the glucose solution up to 50 cm³ min^-1 and leveled off thereafter. At the optimal condition, the maximum power density and corresponding cell voltage of 58.2 mW cm^-2 (0.36 V) and 95.7 mW cm^-2 (0.34 V) were recorded at 298 and 328 K, respectively.

Efficient Biomass Fuel Cell Powered by Sugar with Photo- and Thermal-Catalysis by Solar Irradiation

The utilization of biomass sugars has received great interesting recently. Herein, we present a highly efficient hybrid solar biomass fuel cell that utilizes thermal- and photocatalysis of solar irradiation and converts biomass sugars into electricity with high power output. The fuel cell uses polyoxometalates (POMs) as photocatalyst to decompose sugars and capture their electrons. The reduced POMs have strong visible and near-infrared light adsorption, which can significantly increase the temperature of the reaction system and largely promotes the thermal oxidation of sugars by the POM. In addition, the reduced POM functions as charge carrier that can release electrons at the anode in the fuel cell to generate electricity. The electron-transfer rates from glucose to POM under thermal and light-irradiation conditions were investigated in detail. The power outputs of this solar biomass fuel cell are investigated by using different types of sugars as fuels, with the highest power density reaching 45 mW cm^-2 .

3D Copper Foam-Supported CuCo₂O₄ Nanosheet Arrays as Electrode for Enhanced Non-Enzymatic Glucose Sensing

CuCo₂O₄ anchored on Cu foam (CuCo₂O₄/CF) with polycrystalline features was fabricated by a mild process based on solvothermal reaction and subsequent calcination in this work. The structure and morphology of the obtained materials were thoroughly characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy. According to the above analysis, the morphology of the CuCo₂O₄ was nanosheet arrays. Meanwhile, the CuCo₂O₄ was grown on Cu foam successfully. The CuCo₂O₄/CF displayed good electrochemical properties for glucose detection at a linear range from 0 mM to 1.0 mM. Meanwhile, the detection limit was as low as 1 μM (S/N = 3), and the sensitivity was 20,981 μA·mM⁻¹·cm⁻². Moreover, the selectivity and the stability were tested with excellent results. This nanomaterial could show great potential application in electrochemical sensors.