Optimization of glassy carbon electrode based graphene/ferritin/glucose oxidase bioanode for biofuel cell applications

A glassy carbon (GC)/graphene/ferritin/glucose oxidase (GOx) anode was developed by using graphene/ferritin biocomposite as an electron transfer enhancer and mediator, respectively. The electrode exhibited good electrocatalytic activity towards the oxidation of glucose. The electrocatalytic oxidation of glucose using GOx modified electrode increased with increasing the concentration of glucose upto 45 mM. The results showed that the graphene/ferritin biocomposite mediator provides enhancement in electron transfer generated at the active cites of GOx to the electrode. All electrochemical measurements were carried out by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). A saturation current density of 66.5 ± 2 mA cm⁻² at scan rate 100 mV s⁻¹ for the oxidation of 45 mM glucose was achieved.     

Preparation and characterization of a bioanode (GC/MnO2/PSS/Gph/Frt/GOx) for biofuel cell application

In this study, a bioanode (GC/MnO₂-PSS-Gph/Frt/GOx) was developed by depositing a manganese dioxide-polystyrene sulfonate-graphene (MnO₂-PSS-Gph) composite containing ferritin (Frt) as mediator and glucose oxidase (GOx) as a catalytic enzyme on a glassy carbon (GC) electrode. The GOx oxidize the glucose to gluconolactone with the release of electrons. The composite was prepared by extending the Hummers method and characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared (FTIR) spectroscopy. The electrochemical functioning of the fabricated bioanode was investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge techniques. A maximum current density of 2.7 ± 0.2 mAcm⁻² associated with the bioanode was observed at the scan rate of 100 mVs⁻¹ in a potential range from −0.2 to 0.8 V having a glucose concentration of 40 mM. The surface concentration of GOx on the prepared bioelectrode was found to be 2.3 × 10⁻¹⁰ mol cm⁻² and rate constant for the electron transfer was calculated to be 3.89 s⁻¹.     

Hydrothermally synthesized defective NiMoSe2 nanoplates decorated on the surface of functionalized SWCNTs doped polypyrrole scaffold for enzymatic biofuel cell applications

The prospective of this work is to synthesize a new nanocomposite that serves as an electrode material for the immobilization of biomolecules. In this work surface-functionalized single-walled carbon nanotubes (f–COOH–SWCNTs), and hydrothermally synthesized surface defected 2D nanoplates wrapped by polpyrrole matrix was developed. The developed nanocomposite was utilized as the anode material for the immobilization of enzymes. Nanocomposite f-SWCNTs@Ppy@NiMoSe₂ was characterized by X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the electrochemical methods including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV). The electrochemically controlled bioanode reached to the open circuit potential (OCV) of 0.35 V and delivered the maximum current density of 9.01 mA cm^?2 in 50 mM glucose concentration prepared in phosphate buffer solution (PBS) (pH 7.0) as the testing solution at 100 mVs^?1 scan rates.     

Optimization of MnO2-Graphene/polythioaniline (MnO2-G/PTA) hybrid nanocomposite for the application of biofuel cell bioanode

This study reports the synthesis of a nanocomposite comprised of graphene (G) supported manganese dioxide (MnO₂) incorporated into the network of polythioaniline (MnO₂-G/PTA). The hybrid composite was applied as an electrode material for the development of a bioanode. The bioanode was fabricated by the electrochemical entrapment of ferritin (Frt) as mediator and glucose oxidase (GOx) enzyme in the matrix of the as-synthesized MnO₂-G/PTA deposited on glassy carbon electrode (GCE) surface. The structural features and electrochemical behaviour of the modified electrodes were investigated by Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The results unfolded that the hybrid electroactive support (MnO₂-G/PTA) employed for the immobilization of the enzyme (GOx) established an appropriate electrical cabling between the redox enzyme (GOx) and the electrode surface with the assistance provided by the biocompatible mediator (Frt) working to enhance the electrical signals. The developed GCE/MnO₂-G/PTA/Frt/GOx bioanode attained a maximum current density of 3.68 mAcm^?2 at 35 mM glucose concentration at a scan rate of 100 mVs^?1. Thus, the MnO₂-G/PTA/Frt/GOx modified electrode possesses high potential and good biocompatibility for bio-electricity production from glucose.     

Electrochemical properties of enzyme electrode covalently immobilized on a graphite oxide/cobalt hydroxide/chitosan composite mediator for biofuel cells

A critical factor for the performance of a biofuel cell is an immobilization of the redox enzyme for continuous catalytic reaction and efficient electron transfer. However, the main obstacle associated with enzyme electrode is the reduced surface area for the accommodation of enzymes, leading to poor power output. This study aimed to optimize the efficient electrical communication for glucose oxidase (GOx) on the surface of a graphite oxide/cobalt hydroxide/chitosan composite as mediator, thereby enhancing the generation of power output. Immobilization efficiency was affected by the different concentrations of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC)/N-hydroxysuccinimide (NHS). Also, the surface of enzyme electrode was observed by XPS, Raman, and AFM, respectively. The electrochemical characterization showed that the immobilized GOx possesses the highest activity at EDC:NHS(40:80 mM) concentration. The power output under the optimal condition was found to be 2.24 mWcm^?2 of power density using the three-electrode cell in 0.1 M PBS solution at room temperature.     

Preparation and characterization of copper oxide particles/polypyrrole (Cu2O/PPy) via electrochemical method: Application in direct ethanol fuel cell

The electrocatalytic performance of Polypyrrole-Copper oxide particles modified carbon paste electrode (Cu₂O/PPy/CPE) for electrocatalytic oxidation of ethanol was reported for the first time in alkaline media. The composite Cu₂O/PPy was prepared using a facile approach consisting on the deposition of Polypyrrole film on CPE using galvanostatic mode then followed by the deposition of Copper particles at a constant potential. Scanning electron spectroscopy (SEM), infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the structural and electrochemical properties of the Cu₂O/PPy/CPE and to explain the mechanism of electrooxidation of ethanol. The experimental parameters that influence the electrooxidation of ethanol were investigated and optimized. Our findings suggest that the electrodeposition of Copper particles on Polypyrrole film enhanced the catalytic activity towards the ethanol oxidation with a peak current density of 2.25 mA cm⁻² at 0.8 V vs Ag/AgCl, which is 2.6 times higher than the peak current density obtained by PPy/CPE electrode. It important to note that the saturation limit reaches a value of 5 M. To summarize, the good catalytic activity, stability and easy preparation make the Cu₂O/PPy composite as an excellent electrocatalyst for ethanol oxidation.     

Au nanoparticles decorated on magnetic nanocomposite (GO-Fe3O4/Dop/Au) as a recoverable catalyst for degradation of methylene blue and methyl orange in water

In the present research, magnetically recyclable graphene oxide (GO)/dopamine hydrochloride/AuNPs nanocatalyst are prepared by a green path with Acorus calamus seeds extract as a stabilizing and reducing agent and its catalytic efficiency was used for the reduction of methylene blue (MB) and methyl orange (MO) in the presence of NaBH₄ as a reducing agent in the aqueous medium in the ambient conditions. The prepared nanocatalyst was characterized by X-ray diffraction (XRD), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), Fourier transformed infrared (FT-IR) spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and UV–Vis spectroscopy. The prepared nanocatalyst has good catalytic activity and can be regain by an external magnet and recycled several times without considerable loss of its catalytic activity in the process of reduction of organic dyes.     

Development of NiO/Co3O4 nanohybrids catalyst with oxygen vacancy for oxygen evolution reaction enhancement in alkaline solution

The oxygen evolution reaction (OER) is a significant reaction in water splitting and energy conversion. However, high price and sluggish kinetics catalysts prevent commercial applications. Generally, noble metals (e.g., iridium and ruthenium), which are expensive and unstable, have been used as catalysts for OER because of their high electrocatalytic activity. In this study, we report a high-performance OER catalyst with oxygen vacancies comprising NiO/Co₃O₄ nanohybrids. For OER, the NiO/Co₃O₄ heterostructure show good electrocatalytic performance with a low overpotential of 330 mV. This is higher than those of NiO, Co₃O₄, and benchmark IrO₂ candidates at current density of 10 mA cm^?2. Furthermore, the NiO/Co₃O₄ nanohybrids show long-term electrochemical stability for 10 h. The present research results show that NiO/Co₃O₄ heterostructure is an excellent electrocatalyst for OER.     

Influence of electronic transport on electrochemical performance of (Cu,Mn)3O4 solid oxide fuel cell cathodes

Alkaline Earth free spinel oxides provide a potential benefit over Sr-doped perovskite-based materials commonly used as electrodes in high-temperature electrochemical energy conversion devices, e.g., solid oxide fuel cells (SOFCs). Sr-segregation is a known issue leading to performance degradation. In this study, Cu_xMn_3-xO₄ (x = 1, 1.2, and 1.5) porous electrodes were examined as SOFC cathodes using electrochemical impedance spectroscopy to investigate the oxygen reduction reaction (ORR) kinetics in relation to the material's intrinsic conductivity, the extrinsic electrode structure, and the cell test design. Similar to the electronic conducting (La,Sr)MnO₃ SOFC cathodes, the ORR kinetics of Cu_xMn_3-xO₄ spinel electrodes was governed by the oxygen adsorption and diffusion at the particle surface as well as the charge transfer at the triple phase boundaries. The overall electrode polarization resistance was highly dependent on contact density with the metallic current collector, active material particle connectivity, electrode thickness, and the intrinsic electronic materials conductivity. We describe the importance of effective electronic charge transport parallel to the electrode surface in maximizing the electrochemically active electrode volume and enhancing electrode performance. We discuss an approach to optimize cell and electrode design with respect to active materials properties. This aspect is critical to ensure reliable evaluation of new materials, since laboratory-scale button-cells typically exhibit a high degree of electrode microstructure (e.g. porosity, thickness) and electrical contact density variation from sample to sample.     

Fabrication and transport mechanisms of 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl)acetonitrile/p-silicon hybrid solar cell

2-(2,3-Dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl) acetonitrile (DOPNA) is an organic compound; it has been synthesized and examined as a photovoltaic material in thin-film form grown on single crystal of p-type silicon wafer substrate (p-Si). A polycrystalline structure has been formed in as-synthesized powder. Nano-crystallite grains are formed in the as-deposited film. The dark current-voltage (I-V) characteristics of Au/p-DOPNA/p-Si/Al heterojunction diode measured at different temperatures ranging from 298 to 423 K have been investigated. The operating conduction mechanisms, series and shunt resistances, rectification ratio, ideality factor and potential barrier height were determined. The capacitance-voltage (C-V) measurements of the device were performed in dark condition and analyzed to determine carrier concentration and built-in potential. Solar cell parameters were also evaluated and the power conversion efficiency was estimated as 5.74%.     

MoO3 nanorods/Fe2(MoO4)3 nanoparticles composite anode for solid oxide fuel cells

MoO₃ nanorods/Fe₂(MoO₄)₃ nanoparticles composite has been prepared by a hydrothermal method combined with an in situ diffusion growth process. Single cells based on 300 μm LSGM electrolyte have been fabricated with the MoO₃ nanorods/Fe₂(MoO₄)₃ nanoparticles composite anode and a composite cathode consisting of Sr_0.9Ce_0.1CoO_3−δ and Sm-doped ceria (SDC). The peak power densities reach 225, 50, 75 mW cm⁻² at 900 °C in H₂, CH₄ and C₃H₈, respectively. The cell shows excellent long-term stability at 850 °C. The preliminary results demonstrate that the MoO₃ nanorods/Fe₂(MoO₄)₃ nanoparticles composite is a promising alternative anode for solid oxide fuel cells.     

Performance of a novel La(Sr)MnO3-Pd composite current collector for solid oxide fuel cell cathode

The electrochemical performance of LSM-Pd composite material as current collector of SOFC cathode is studied on (La_0.8Sr_0.2)_0.9MnO₃ (LSM90) cathode. The influence of Pd content on contact resistance is investigated. The investigation shows that the contact resistance of LSM-Pd is about 20 mΩ cm² at 750 °C when the composite contains 8 wt% Pd, and it could be comparable to pure Pt. The ohmic resistance of a single cell using LSM-Pd composite is about 255 mΩ cm² that contains 4 wt% Pd as current collector, this value is close to that of a cell using expensive Pt paste as current collector.     

The charge transfer pathway of g-C3N4 decorated Au/Bi(VO4) composites for highly efficient photocatalytic hydrogen evolution

In this report, a novel g-C₃N₄/Au/BiVO₄ photocatalyst has been prepared successfully by assembling gold nanoparticles on the interface of super-thin porous g-C₃N₄ and BiVO₄, which exhibits outstanding photocatalytic performance toward hydrogen evolution and durable stability in the absence of cocatalyst. FESEM micrograph analysis suggested that the intimate contact between Au, BiVO₄, and g-C₃N₄ in the as-developed photocatalyst allows a smooth migration and separation of photogenerated charge carriers. In addition, the XRD, EDX and XPS analysis further confirmed the successful formation of the as-prepared g-C₃N₄/Au/BiVO₄ photocatalyst. The photocatalytic hydrogen production activity of the developed photocatalyst was evaluated under visible-light irradiation (λ > 420 nm) using methanol as a sacrificial reagent. By optimizing the 5-CN/Au/BiVO₄ composite shows the highest H₂ evolution rate (2986 μmolg⁻¹h⁻¹), which is 15 times higher than that of g-C₃N₄ (199 μmolg⁻¹h⁻¹) and 10 time better than bare BiVO₄ (297 μmolg⁻¹h⁻¹). The enhancement in photocatalytic activity is attributed to efficient separation of the photoexcited charges due to the anisotropic junction in the g-C₃N₄/Au/BiVO₄ system. The enhancement in photocatalytic activity is attributed to efficient separation of the photoexcited charges due to the anisotropic junction in the g-C₃N₄/Au/BiVO₄ system.     

Study on electrochemical performances of composite carbon (FeO/C) materials fabricated by coal tar pitch and Fe3O4 particles

The new functional FeO/C composite carbon materials are successfully fabricated by controlling the adding amounts of Fe₃O₄ particles in mixtures of coal tar pitch and Fe₃O₄ particles. The structures of prepared FeO/C composite carbon materials were verified by XRD measurements. The excellent electrochemical performances of FeO/C composite carbon materials were evaluated in detail. For instance, the prepared materials show the high cycling performances at 679 mAh/g after carrying out charge-discharge 100 cycles. Meanwhile, the high rate performances and long cycle life characteristics of FeO/C composite materials were also observed. As a result, it is palpable that the carbon contents and specific area are the vital factors to improve the electrochemical performances of FeO/C composite materials, which effectively provides the reference to design the transition metal oxide/carbon composite materials as Li⁺ ion storage materials.     

Impedance spectroscopy studies of Gd-CeO2-(LiNa)CO3 nano composite electrolytes for low temperature SOFC applications

Electrical properties of 20 mol % Gd doped CeO₂ with varying amounts of (LiNa)CO₃ have been investigated by employing AC-impedance spectroscopic technique. The impedance spectra show a high frequency depressed arc, represents the bulk composite and low frequency incomplete semicircle representing electrode contribution. The bulk resistance of the composites decreases with increasing carbonate content up to 30 wt% (LiNa)CO_3, thereafter the resistance increases, whereas all the compositions show a decrease in resistance with increasing temperature. The typical nature of the impedance spectra of the composite shows the possibility of coexistence of multi ionic transport or existence of space charge effect at the interface of Gd-CeO₂ and carbonate phase. The composite containing 25 wt% (LiNa)CO₃ shows the highest ionic conductivity of 0.1757 S cm⁻¹ at 550 °C and lowest activation energy of 0.127 eV in the temperature range 550-800 °C. A symmetric cell is fabricated with GDC-25 wt% (LiNa)CO₃ electrolyte, NiO-GDC(LiNa)CO₃ anode and lithiated NiO-GDC(LiNa)CO₃ cathode. Pure H₂ and air are used as fuel and oxidant. The cell delivers a maximum power density of 45 mW/cm², 58 mW/cm² and 92 mW/cm² at 450, 500 and 550 °C, respectively.     

Performance of stainless steel interconnects with (Mn,Co)3O4-Based coating for solid oxide electrolysis

Mixed transition-metal oxide coatings are commonly applied to stainless steel interconnects for solid oxide cell stacks. Such coatings reduce oxidation and Cr evaporation rates, leading to improved degradation rate and stack lifetime. Here, the ChromLok? MCO-based composition (Mn,Co)₃O₄ is applied to Crofer 22 APU stainless steel and evaluated specifically for application in solid oxide electrolyzer stacks operating around 800 °C and utilizing oxygen-ion-conducting solid oxide cells. The MCO coating is found to decrease the stainless steel oxidation rate by about one order of magnitude, and decrease the Cr evaporation rate by fourfold. The coating also dramatically lowers the rate of area-specific resistance increase for stainless steel coupons oxidized for 500 h with constant current applied, from 33 mΩ1cm² kh^?1 for an uncoated coupon to less than 4 mΩ1cm² kh^?1 for coated coupons. The coating is demonstrated on full-scale interconnects for single-cells, where the coating dramatically reduces degradation rate, and for a stack, which displays stable operation for 700 h.     

Synthesis and characterization of Pt/ZnO@SWCNT/Fe3O4 as a powerful catalyst for anodic part of direct methanol fuel cell reaction

Platinum is a preferred metal in fuel cell applications owing to its superior catalytic activity; Platinum's high cost and CO poisoning in oxidation processes, limit its usage as a standalone catalyst. At this point, it is important to develop new intermediate tolerant electrocatalysts. In this study, Zinc Oxide/Single Wall Carbon Nanotube/Iron oxide (ZnO@SWCNT/Fe₃O₄₎ catalyst was obtained by using ZnO, SWCNT/Fe₃O₄ support material, and Zinc Oxide/Single Platinum/Wall Carbon Nanotube/Iron oxide (Pt/ZnO@SWCNT/Fe₃O₄₎ catalyst was obtained by chemical synthesis method by adding Pt metal. With these catalysts, the efficiency of the use of Pt was examined within the scope of the study, and reducing limiting factors by using a low amount of Pt, at the same time, it is aimed to prepare a high electrocatalyst. The morphological structure of the obtained catalysts was characterized by scanning electron microscope (SEM), and X-ray diffraction (XRD). Methanol oxidation reactions (MOR) were conducted to determine the electrochemical performance of the catalysts. In the results obtained, it was observed that the current value obtained as a result of the Cyclic Voltammetry (CV) of the ZnO@SWCNT/Fe₃O₄ catalyst was 103.36 mA/cm², and the current value obtained as a result of the CV of the Pt/ZnO@SWCNT/Fe₃O₄ catalyst was 362.46 mA/cm². The results showed high stability for both catalysts, and it was seen that Pt increased the conductivity, methanol oxidation performance, and stability in the catalyst. The obtained catalysts showed high potential for methanol oxidation and are promising for fuel cell applications.     

Facile synthesis of M-CuFe2O4 (M= Al2O3, CeO2, La2O3, ZrO2, Mn2O3) catalysts using a one-pot method and their applications in high-temperature water gas shift reaction

Water gas shift reaction is an essential process of hydrogen production and carbon monoxide removal from syngas. In this study, the promotional effect of ZrO₂, CeO₂, La₂O₃, Al₂O₃, and Mn₂O₃ was investigated on the CO conversion and thermal stability of the copper ferrite in high-temperature water gas shift reaction (HTSR) and hydrogen purification. The powders were synthesized by a simple solid-state route and characterized by XRD, H2-TPR, SEM, FT-IR, TG-DTA, and BET analyses. Promoters (ZrO₂, CeO₂, La₂O₃, Al₂O3, and Mn₂O₃) could affect the WGSR performance in activity and stability. In the M-CuFe2O4 catalyst, alumina acts as a texture promoter and aids in the fine dispersion of copper ferrite. The results indicated that the surface area of the Al₂O₃–CuFe₂O₄ (210 m²/g) catalyst was higher than the other samples. This catalyst presented higher CO conversion in HTSR and had higher stability at 1000 min on stream. It was found that the incorporation of different contents of alumina had a significant influence on the textural and catalytic properties of the CuFe₂O₄-based catalysts. The 30%Al₂O₃–70%CuFe₂O₄ catalyst exhibited the highest CO conversion of 65% at 350 °C, uniform pore size distribution, and intense interaction between copper ferrite and alumina, causing the effective stabilization of the active phase in the catalyst structure. The findings of this study represent that the solid-state method, due to its simplicity and creation of a mesoporous structure, can also be applied for the preparation of many heterogeneous metal oxide catalysts.     

Effect of O2 and temperature on the catalytic performance of Ni/Al2O3 and Ni/MgAl2O4 for the dry reforming of methane (DRM)

Al₂O₃ and MgAl₂O₄ supported 10% (w/w) Ni catalysts having a dispersion of 1.5 and 2.0% are active for DRM at 600 and 750 °C. High temperature reduction of both the calcined catalysts resulted in metallic Ni being formed, suggesting strong support metal interactions. The CH₄ and CO₂ conversion during DRM are relatively constant with time-on-stream, and are higher for Ni/MgAl₂O₄ than Ni/Al₂O₃. Carbon-whiskers are also detected on both catalysts. O₂ co-feed of 2.6% (v/v) and increasing reaction temperature to 750 °C helped in decreasing the amount of carbon deposited, except for Ni/MgAl₂O₄ at 600 °C. Furthermore, higher conversions and H₂/CO ratios are achieved. It appears that on spent Ni/MgAl₂O₄ a different type of carbon species was formed, and this carbon species was difficult to remove by oxygen at 600 °C. Thus, co-feeding O₂, using an appropriate temperature, and choosing a suitable support can reduce the carbon present on the nickel catalysts during DRM.